Preface: Quaternary and Tertiary landscapes and their sediments in Hesse, Germany – a guidebook to selected field trips on geology, geomorphology and geoarchaeology

This field trip is intended to present an introduction to the geological and geomorphological evolution of Giessen and its surrounding areas (Fig. 1). The conference location of Giessen is located at the intersection of three major geological and morphological units: the Rheinisches Schiefergebirge (Rhenish Massif) to the west, the Hessische Senke (Hessian Depression) to the north and south and the Vogelsberg volcanic field to the east (Fig. 2). The rocks of the Rheinisches Schiefergebirge (Rhenish Massif) were formed during Paleozoic times, in the context of the Variscan orogeny. Dominant rock types include graywacke, slate, quartzite, and limestone, as well as mafic and felsic volcanics and their related pyroclastics. The area north and south of Giessen is dominated by the Hessische Senke (Hessian Depression), a north–southtrending subsidence area with several individual deposit segments. Due to Cenozoic tectonic activity, the Hessian Depression can be regarded as a connecting segment between the prominent Upper Rhine Graben and the smaller graben structures of northern Germany, and this is also documented by less consolidated Tertiary and Quaternary sediments. Long-lasting subsidence of the Hessian Depression, however, is indicated by the presence of Permian and Mesozoic sedimentary rocks. Rotliegend rocks are present towards the southwest rim of the Vogelsberg volcanic field and the Hanau-Seligenstädter Senke. Minor occurrences of Zechstein rocks are exposed along the Lahn valley between Giessen and Marburg. Mesozoic strata are dominated by Buntsandstein and are widespread in the Marburg area, with Muschelkalk and Keuper rocks being restricted to small erosional remnants in tectonic graben structures. The area to the east of Giessen is dominated by the Miocene Vogelsberg volcanic field, where an estimated area of 2500 km2 is covered by volcanic rocks of varying thickness, the Vogelsberg thus being the largest volcanic field of central Europe. The field trip provides an introduction to the geology, earth history and geomorphological characteristics of Giessen and its surrounding areas. We will therefore encounter rocks that formed in distinct geodynamic environments and within a timespan of roughly 400 Ma (Devonian to present). Kurzfassung: Die Exkursion bietet mit ihrem Routenverlauf und den ausgewählten Aufschlüssen eine Einführung in die vielgestaltige geologische und geomorphologische Entwicklungsgeschichte des Tagungsortes Gießen und seiner näheren Umgebung. Die Stadt Gießen liegt am Schnittpunkt dreier bedeutender geologischer und geomorphologischer Einheiten: im Westen das jungkänozoisch gehobene Rheinische Published by Copernicus Publications on behalf of the Deutsche Quartärvereinigung (DEUQUA) e.V. 4 F. Volker and S. Menges: Field Trip A (23 September 2018) Schiefergebirge, im Osten das ausgedehnte miozäne Vulkanfeld des Vogelsberges und dazwischen die N-S verlaufende Hessische Senke mit ihren mesozoischen und känozoischen Sedimentfüllungen. Die Gesteine des Rheinischen Schiefergebirges wurden im Paläozoikum gebildet und ihre Entstehung steht im engen Zusammenhang mit der Variszischen Orogenese. Die dominierenden Gesteinsarten umfassen, je nach Ablagerungsraum und plattentektonischer Position, Grauwacken, Tonschiefer, Quarzite, biogene Kalksteine sowie mafische und felsische Vulkanite mit ihren korrelaten Pyroklastika. Die heutige morphologische Ausgestaltung des Rheinischen Schiefergebirges ist zu einem großen Teil auf die quartärzeitliche Hebung zurückzuführen. Die Gebiete nördlich und südlich von Gießen werden von der Hessischen Senke dominiert, einem N-S verlaufenden Subsidenzgebiet mit mehreren individuellen Ablagerungsräumen. Der lang anhaltende Subsidenzcharakter wird belegt durch die Anwesenheit permischer und mesozoischer Sedimente. Gesteine des Rotliegend finden sich vereinzelt am SW-Rand des Vogelsbergs und in der Hanau-Seligenstädter Senke. Relikte von Zechstein-zeitlichen Gesteinen sind vereinzelt an den Lahnhängen zwischen Marburg und Gießen aufgeschlossen. Bei den mesozoischen Gesteinen dominieren die klastischen Abfolgen des Buntsandstein, die große Gebiete im Raum Marburg in charakteristischer Weise prägen. Im Känozoikum kam es dann zur Ausbildung des Europäischen Grabensystems, das vom Rhonegraben bis weit in die Nordsee reicht. In Mittelhessen führte dies zu einer Wiederauflebung der Subsidenz-Tektonik und zur Anlage mehrerer individueller Ablagerungsräume mit gering verfestigten tertiären und quartären Sedimenten. Die Hessische Senke kann somit als Bindeglied zwischen dem großen Oberrheingraben im Süden und den kleineren Grabenstrukturen im nördlichen Deutschland angesehen werden. Das Gebiet östlich von Gießen wird durch die miozänen Vulkanite des Vogelsbergs eindrucksvoll dominiert. Trotz intensiver Erosion im Neogen und Quartär bedecken die Vulkanite heute noch eine Fläche von etwa 2500 km2 und machen damit den Vogelsberg zum größten zusammenhängenden Vulkanfeld Mitteleuropas. Die Exkursion vermittelt somit einen Einblick in den vielgestaltigen Aufbau und die geomorphologischen Charakteristika des Tagungsortes Gießen und seiner näheren Umgebung. Im Verlauf der Exkursion werden Gesteine angetroffen, die in ganz unterschiedlichen geodynamischen Situationen entstanden sind und einen erdgeschichtlichen Zeitraum von etwa 400 Ma (Devon bis Rezent) umfassen. 1 The Rheinische Schiefergebirge (Rhenish Massif) to the west of Giessen Rocks of the present-day Rhenish Massif (RM) were formed from Silurian times up to the upper Carboniferous/early Permian, in close connection with the Variscan orogeny. Plate tectonic processes related to this major orogenic event included opening and closing of oceanic basins, terrane accretion, volcanism, sedimentation, orogenic folding and metamorphism as well as nappe formation. Major players included the Old Red Continent in the north, the Avalonia terrane, the Rhenohercynian and Rheic oceans and Gondwana further south (Fig. 3). These processes led to a large number of sedimentary, magmatic and metamorphic rocks, each representing their depositional, facies and/or geodynamic characteristics and thus providing valuable information for the reconstruction of these geological processes in space and time. Not surprisingly, (para-)autochthonous and allochthonous units are found in close contact with each other. In addition to varying degrees of alteration and post-orogenic displacements, this may well explain the difficulties in reconstructing the Paleozoic geodynamic processes as well as some of the fierce discussions in the recent scientific literature (Eckelmann et al., 2014; Dörr and Zulauf, 2012; Franke, 2012) and references therein). At the end of the Variscan orogenic processes, the RM suffered massive erosion of elevated regions and coeval filling of basin structures, resulting in a widespread peneplain during Permian times. During the Mesozoic, most parts of the RM were situated above sea level and acted as source regions for clastic sediments in adjacent basins. It is worth mentioning that the region of the RM west of Giessen lacks Mesozoic cover. Intensive chemical weathering during early Tertiary times is documented by thick clay-rich saprolite layers, locally capped/covered by intraplate volcanics (Eifel, Siebengebirge, Westerwald). These kaolinite-rich soils and saprolites, with locally preserved thicknesses of more than 150 m, reflect the humid tropical climate conditions during their time of formation. Climate conditions subsequently changed towards semi-arid characteristics, resulting in areal denudation of unprotected land surfaces. During the Quaternary, the RM was severely affected by periglacial processes as well as intense uplift (Fig. 4), with an accumulated maximum uplift of more than 250 m during the last 800 000 years in the uplift center (Eifel area). These led to the present-day morphologic characteristics of the RM, DEUQUA Spec. Pub., 1, 3–13, 2018 www.deuqua-spec-pub.net/1/3/2018/ F. Volker and S. Menges: Field Trip A (23 September 2018) 5 Figure 1. Topographic map with excursion route and major locations. Stop 1: Gleiberg and Vetzberg volcanoes, Stop 2: Herbstlabyrinth limestone cave, Stop 3: quarry south of Philippstein, Stop 4: abandoned quarry east of Langd. i.e., a large uplifted block with plateau-like regions, maximum heights of around 900 m and deeply incised river valleys (e.g., Middle Rhine, lower Mosel and lower Lahn rivers). Thus, morphologic processes during the Cenozoic are dominated by the following: 1. a phase of intense weathering and denudation during humid tropical and semi-arid climate conditions with peneplain formation 2. a phase of pronounced uplift and linear erosion during the Quaternary. 2 Stop 1: Gleiberg – Tertiary volcanism and overview The old castle of Gleiberg (12th century) was built on a small hill (308 m a.s.l. and 70–80 m above the surrounding area). The hill is made up of Miocene columnar basaltic rocks that penetrate graywacke of lower Carboniferous age that are part of the Giessen nappe (Fig. 5). Depending on weather conditions, this location and especially the castle keep offers a nice outlook and a panoramic view. Towards the southeast, we look into the small depression of the Giessener Becken, with the foothills of the Vogelsberg in the distance. To the east, we see the valley of the Lahn river, the corresponding main terrace and a prominent basalt hill (Lollarer Kopf). In the far distance, though morphologically not very prominent, the forested slopes of the main Vogelsberg can be seen. To the northeast, the Miocene basalt hill of Amöneburg and the Lahnberge of Marburg (early Mesozoic sandstone ridge) are visible. To the north, behind the village of Krofdorf, there is a large forest area on comparatively infertile graywacke. To the west, the plateau of Königsberg-Hohensolms, consisting of lower Carboniferous basaltic rocks that are locally known as “Diabas”, can be seen. To the northwest, a short distance from the prominent Dünsberg (498 m a.s.l.) is visible, a monadnock dominated by allochthonous lower Carboniferous lydite. In the foreground, Vetzberg and Köppel (Fig. 6), both volcanic edifices similar to Gleiberg (Weyl and Stibane, 1980) can be seen. It is worth noting that Gleiberg, Köppel and Vetzberg are aligned along a north–west-running fault line. Based on detailed geochemical and radiometric age studies by Turk et al. (1984), the location of Gleiberg, together with nearby Vetzberg and the small edifice of Köppel, comprise the westernmost eruption centers of the Vogelsberg volcanic field (VB). Columnar jointing is well developed at Vetzberg castle (Fig. 7). Along the road from Gleiberg to Breitscheid (Stop 2), paleozoic rocks (dominantly graywacke, slate, diabase, limestone and also lydite) are exposed in numerous small quarries and roadside outcrops. Occasionally, a transformation of the www.deuqua-spec-pub.net/1/3/2018/ DEUQUA Spec. Pub., 1, 3–13, 2018 6 F. Volker and S. Menges: Field Trip A (23 September 2018) Figure 2. Simplified geological sketch map of Giessen and surrounding areas (modified from Weyl and Stibane, 1980). Stop numbers as in Fig. 1. Four principal units can be distinguished: (1) Paleozoic rocks of the Rhenish Massif, (2) Permian to Triassic sedimentary rocks, confirming long-lasting subsidence of the Hessian Depression, (3) less consolidated Tertiary and Quaternary sediments in north–southrunning subsidence segments (Amöneburger Becken, Horloff-Graben), thus connecting the prominent Upper Rhine Graben with the smaller graben structures of northern Germany and (4) Miocene Vogelsberg volcanic rocks, with numerous erosional remnants of various sizes along the present-day rim of the volcanic field. silicate rocks into clay minerals is clearly visible. The formation of these clay minerals (kaolinite, illite) is attributed to intense chemical weathering during lower Tertiary and Miocene times (Felix-Henningsen, 1994). In adjacent areas of the Westerwald volcanic field, these clay-rich lithologies were covered by upper Tertiary volcanic rocks, resulting in an effective protection blanket against further weathering and especially erosion. Therefore, these clay deposits were to become the primary commodity for the famous ceramic industry in the Westerwald area, known as the “Kannenbäckerland”. 3 Stop 2: Breitscheid – Devonian limestone and recent karst 3.1 Mid-Devonian limestone Large limestone areas within the Rhenish Massif are genetically related to reef-building organisms, which include stromatoporoids, brachiopods, crinoids, bryozoa, echinoderms and others. Distribution of Devonian limestone within the Rhenish Massif clearly reflects two different paleomorphologic situations: shallow waters close to the northern shoreline, and submarine swells within the deeper parts of the ocean, created by volcanic edifices (Figs. 8, 9). Reef growth was further supported by the low-latitude position of the area during Devonian times (Fig. 3). Volcanic activity, especially pronounced towards the end of the Mid-Devonian, created volcanic swells of different sizes, which occasionally reached the water surface, thus creating small ocean islands and related atoll-like structures. During the subsequent upper Devonian, most reef-building organisms died, in relation to the Kellwasser event, a period of worldwide mass extinction. Ancient karst phenomena in this limestone indicate uplift events some time after the end of the reef-building phases, and examination of sedimentary input in karst cavities revealed both upper Devonian and lower Carboniferous ages (Flick, 2010). Recent carbonate solution and calcite precipitation is indicated by several characteristic features, including ponors, dolines and speleothems in limestone caves. DEUQUA Spec. Pub., 1, 3–13, 2018 www.deuqua-spec-pub.net/1/3/2018/ F. Volker and S. Menges: Field Trip A (23 September 2018) 7 Figure 3. Plate tectonic reconstruction for the Late Devonian to early Carboniferous (Eckelmann et al., 2014). Red star: position of the autochthonous Rhenish Massif. Blue star: source area of the nappe units in the southeast of the Rhenish Massif. Figure 4. Sketch map showing the uplift of the Rhenish Massif during the last 800 000 years (from Meyer and Stets, 2002). Small dots: observation points along rivers. Dashed line: the outer rim of the Rhenish Massif. 3.2 The limestone caves Herbstlabyrinth and


The Rheinische Schiefergebirge (Rhenish Massif) to the west of Giessen
Rocks of the present-day Rhenish Massif (RM) were formed from Silurian times up to the upper Carboniferous/early Permian, in close connection with the Variscan orogeny. Plate tectonic processes related to this major orogenic event included opening and closing of oceanic basins, terrane accretion, volcanism, sedimentation, orogenic folding and metamorphism as well as nappe formation. Major players included the Old Red Continent in the north, the Avalonia terrane, the Rhenohercynian and Rheic oceans and Gondwana further south (Fig. 3). These processes led to a large number of sedimentary, magmatic and metamorphic rocks, each representing their depositional, facies and/or geodynamic characteristics and thus providing valuable information for the reconstruction of these geological processes in space and time. Not surprisingly, (para-)autochthonous and allochthonous units are found in close contact with each other. In addition to varying degrees of alteration and post-orogenic displacements, this may well explain the difficulties in reconstructing the Paleozoic geodynamic processes as well as some of the fierce discussions in the recent scientific literature (Eckelmann et al., 2014;Dörr and Zulauf, 2012;Franke, 2012) and references therein). At the end of the Variscan orogenic processes, the RM suffered massive erosion of elevated regions and coeval filling of basin structures, resulting in a widespread peneplain during Permian times.
During the Mesozoic, most parts of the RM were situated above sea level and acted as source regions for clastic sediments in adjacent basins. It is worth mentioning that the region of the RM west of Giessen lacks Mesozoic cover.
Intensive chemical weathering during early Tertiary times is documented by thick clay-rich saprolite layers, locally capped/covered by intraplate volcanics (Eifel, Siebengebirge, Westerwald). These kaolinite-rich soils and saprolites, with locally preserved thicknesses of more than 150 m, reflect the humid tropical climate conditions during their time of formation. Climate conditions subsequently changed towards semi-arid characteristics, resulting in areal denudation of unprotected land surfaces.
During the Quaternary, the RM was severely affected by periglacial processes as well as intense uplift (Fig. 4), with an accumulated maximum uplift of more than 250 m during the last 800 000 years in the uplift center (Eifel area). These led to the present-day morphologic characteristics of the RM, i.e., a large uplifted block with plateau-like regions, maximum heights of around 900 m and deeply incised river valleys (e.g., Middle Rhine, lower Mosel and lower Lahn rivers).
Thus, morphologic processes during the Cenozoic are dominated by the following: 1. a phase of intense weathering and denudation during humid tropical and semi-arid climate conditions with peneplain formation 2. a phase of pronounced uplift and linear erosion during the Quaternary.

Stop 1: Gleiberg -Tertiary volcanism and overview
The old castle of Gleiberg (12th century) was built on a small hill (308 m a.s.l. and 70-80 m above the surrounding area). The hill is made up of Miocene columnar basaltic rocks that penetrate graywacke of lower Carboniferous age that are part of the Giessen nappe (Fig. 5).
Depending on weather conditions, this location and especially the castle keep offers a nice outlook and a panoramic view.
Towards the southeast, we look into the small depression of the Giessener Becken, with the foothills of the Vogelsberg in the distance.
To the east, we see the valley of the Lahn river, the corresponding main terrace and a prominent basalt hill (Lollarer Kopf). In the far distance, though morphologically not very prominent, the forested slopes of the main Vogelsberg can be seen.
To the northeast, the Miocene basalt hill of Amöneburg and the Lahnberge of Marburg (early Mesozoic sandstone ridge) are visible.
To the north, behind the village of Krofdorf, there is a large forest area on comparatively infertile graywacke.
To the west, the plateau of Königsberg-Hohensolms, consisting of lower Carboniferous basaltic rocks that are locally known as "Diabas", can be seen.
To the northwest, a short distance from the prominent Dünsberg (498 m a.s.l.) is visible, a monadnock dominated by allochthonous lower Carboniferous lydite. In the foreground, Vetzberg and Köppel (Fig. 6), both volcanic edifices similar to Gleiberg (Weyl and Stibane, 1980) can be seen. It is worth noting that Gleiberg, Köppel and Vetzberg are aligned along a north-west-running fault line. Based on detailed geochemical and radiometric age studies by Turk et al. (1984), the location of Gleiberg, together with nearby Vetzberg and the small edifice of Köppel, comprise the westernmost eruption centers of the Vogelsberg volcanic field (VB). Columnar jointing is well developed at Vetzberg castle (Fig. 7).
Along the road from Gleiberg to Breitscheid (Stop 2), paleozoic rocks (dominantly graywacke, slate, diabase, limestone and also lydite) are exposed in numerous small quarries and roadside outcrops. Occasionally, a transformation of the silicate rocks into clay minerals is clearly visible. The formation of these clay minerals (kaolinite, illite) is attributed to intense chemical weathering during lower Tertiary and Miocene times (Felix-Henningsen, 1994). In adjacent areas of the Westerwald volcanic field, these clay-rich lithologies were covered by upper Tertiary volcanic rocks, resulting in an effective protection blanket against further weathering and especially erosion. Therefore, these clay deposits were to become the primary commodity for the famous ceramic industry in the Westerwald area, known as the "Kannenbäckerland".

Mid-Devonian limestone
Large limestone areas within the Rhenish Massif are genetically related to reef-building organisms, which include stromatoporoids, brachiopods, crinoids, bryozoa, echinoderms and others. Distribution of Devonian limestone within the Rhenish Massif clearly reflects two different paleomorphologic situations: shallow waters close to the northern shoreline, and submarine swells within the deeper parts of the ocean, created by volcanic edifices (Figs. 8,9). Reef growth was further supported by the low-latitude position of the area during Devonian times (Fig. 3). Volcanic activity, especially pronounced towards the end of the Mid-Devonian, created volcanic swells of different sizes, which occasionally reached the water surface, thus creating small ocean islands and related atoll-like structures.
During the subsequent upper Devonian, most reef-building organisms died, in relation to the Kellwasser event, a period of worldwide mass extinction.
Ancient karst phenomena in this limestone indicate uplift events some time after the end of the reef-building phases, and examination of sedimentary input in karst cavities revealed both upper Devonian and lower Carboniferous ages (Flick, 2010).
Recent carbonate solution and calcite precipitation is indicated by several characteristic features, including ponors, dolines and speleothems in limestone caves.

The limestone caves Herbstlabyrinth and Adventhöhle
Both limestone caves are situated between the villages of Breitscheid and Erdbach, within the eastern part of the Rhenish Massif, about 40 km northwest of Giessen. The cave system as it is currently known has a total length of more than 11 km, documented by intensive speleological studies during the last decade (Dorsten et al., 2016). It is by far the largest cave system in Hesse. This segment of the Rhenish Massif is characterized by two belts of the Mid-Devonian massive limestone occurrences, both showing an alignment of southwest-northeast, as shown in Fig. 9. In the northern belt, the former reefs reflect shallow water conditions on the shelf segment of the Old Red Continent. In the region of the Lahn-Dill synclines, submarine volcanoes formed shallow ridges and shoals that allowed atoll-like reefs to grow surrounded by deep-water conditions (Flick, 2010). The Herbstlabyrinth and Adventhöhle cave system is located in the Dill syncline (Fig. 8).
The landscape between Breitscheid and Erdbach shows characteristic features of limestone karst areas, e.g., dolines, sinkholes, karst springs and dry valleys. The limestone has been quarried for several decades, and it was on 11 December 1993 in the limestone quarry Medenbach (Holcim GmbH) that members of the local Speläologische Arbeitsgemeinschaft Hessen (SAH) discovered the entrance to a cave that was named "Advent cave". In the following year, and close to the Advent cave, the access to another cave system was discovered by SAH, which was to become the Herbstlabyrinth. Recent speleological studies focus on the exploration and survey of newly discovered cave segments (currently known extension ca. 11.5 km; Dorsten, 2017). These field studies are accompanied by detailed work on the age determination of dripstone with the Th-U technique (Mischel et al., 2017), the correlation of cave-forming processes with neotectonic events and dated river terraces and geochemical and stabile isotope studies on drip water and cryogenic calcite. For details of these ongoing studies see Mischel et al. (2017).
Since 2009, parts of the cave have been open to the public, within the framework of guided tours (Fig. 10).

Stop 3: quarry south of Philippstein
The quarry is located about 1 km south of the village of Philippstein. Exposed rocks are mafic volcanics of Givetium/Adorfium age (Middle to Early Upper Devonian; Deutsche Stratigraphische Gesellschaft, 2016) as well as red iron ore deposits (Fig. 11). At the eastern wall of the quarry, several galleries of the abandoned mine "Maria" have been cut off by quarry activities. All rock units were deformed during the Variscan orogeny.
In the lower parts of the quarry, columnar jointing is clearly visible. These flow units were then covered by vol-  caniclastic lithologies (Nesbor, 2007). On top, the volcanics are present as pillow lavas, tubes and pillow fragments, indicating a submarine environment. Obviously, the lava split up into several lava tubes. Contact with seawater caused glassy rims, with the basaltic melt that is still hot flowing inside. Depending on the eruption rates, these lava tubes may have piled up to impressive volcanic masses.
The reddish iron ores belong to Lahn-Dill-type deposits, e.g., exhalative iron oxide mineralization associated with basaltic volcanic centers during Middle to Upper Devonian times (Von Raumer et al., 2017). In a first step, mobilization of Fe and associated Ca and Si was caused by hydrothermal alteration and leaching of subjacent submarine basaltic volcanics (Flick, 2010). Subsequently, the rising Fe-bearing hot fluids encountered cool oxidizing water, resulting in the precipitation of iron oxides and hydroxides. For a more detailed discussion of ore genesis in the RM, please see Von Raumer et al. (2017).
Iron ore mining in the Lahn-Dill ore district has been documented since the Celtic area, about 2000 years ago. Numerous Fe ore mines were operating during the 19th and   20th century. The last mine (Grube Fortuna north of Solms-Oberbiel) was closed down in 1983.

The Horloff-Graben (route from Philippstein (Stop 3) to Hungen-Langd (Stop 4))
Several small basins and graben structures connect the morphologic end of the Upper Rhine Graben with the graben structures of northern Germany. These include the Hanau-Seligenstädter Senke, the Wetterau, the Horloff-Graben, the Giessener Becken and the Amöneburger Becken. Thus, unconsolidated sediments of Cenozoic age are widespread in the regions north and south of Giessen (Fig. 2). Pleistocene loess cover is most pronounced in the basin areas, e.g., Amöneburger Becken, Wetterau and Horloff-Graben (see Field Trip B for details). It should be mentioned that, amongst these small subsidence structures, only the Horloff-Graben is of post-volcanic age. The morphologically well-defined Horloff-Graben incises into the southwestern section of the Vogelsberg, forming a north-south-running graben structure, 20 km long and 5 km wide (Figs. 2,12). Graben sediments are of Pliocene and Pleistocene age, with several brown coal seams being developed within the Pliocene pile. Despite their very young age, those brown coal seams were extensively exploited underground and later on in open-pit mines. Mining activities ended in 1991. Subsequent flooding of the open pit gave rise to the so-called "Wetterauer Seenplatte", now widely used for local recreation, water sports and nature protection.

The Vogelsberg volcanic field and internal structure
VB, located to the east of Giessen, was active during the Miocene. With an area of 2500 km 2 and a total volume of at least 500 km 3 , it is considered the largest volcanic field by volume in central Europe (Reischmann and Schraft, 2009;Fig. 12). Landscape structure of this huge volcanic field comprises four distinct units. The central parts are known as "Oberwald" above 600 m a.s.l. and "Hoher Vogelsberg" between 600 and 500 m (Leßmann et al., 2000). The "Unterer Vogelsberg" forms a zone of up to 20 km wide around the Hoher Vogelsberg. The volcanic layers extending to the northwest are known as the "Vorderer Vogelsberg". The Taufstein (774 m a.s.l.) and the Hoherodskopf (764 m) close by have the highest elevations.
Several boreholes provide important information on the minimum size and volume of VB volcanic rocks as well as the internal structures of the volcanic masses (Reischmann and Schraft, 2009). It should be emphasized, however, that the borehole "Forschungsbohrung Vogelsberg 1996", that penetrated the Central Part of the VB (Oberwald), did not reach the pre-volcanic basis, despite a total coring of 656 m of volcanic rocks. Thus the estimated volume of 500 km 3 must be regarded as a minimum mass.
Those boreholes, in conjunction with detailed field and radiometric studies, reveal new insights into the genesis of this huge volcanic edifice. Vogelsberg volcanism comprised a main activity phase at 19-16 Ma and, separated by a period of magmatic quiescence, a final phase at around 14 Ma (Nesbor, 2014;Abratis et al., 2015). Volcanism of the main phase started with basanitic to alkali basaltic magmas and pyroclastics, followed by dominantly trachytic rocks. Phreatomagmatic eruptions and maar structures occurred quite frequently (Nesbor, 2014). After a period of magmatic quies- Figure 11. Schematic sketch map of a Devonian submarine volcanic edifice in the Lahn-Dill area (from Nesbor, 2007). White rectangle: segment exposed at the Philippstein quarry (Stop 3). cence, volcanic activity recommenced at about 14 Ma with the eruption of alkali basaltic and basanitic lava flows, with eruption centers being essentially confined to the Oberwald region.
During the magmatic rest period, erosive and pedogenic processes dominated, causing leveling of volcanic edifices and a strong pedogenic overprint due to tropical-subtropical and humid climate conditions. These processes gave rise to a widespread erosional surface, which is still visible as a morphological step (Abratis et al., 2015).
Final volcanic activity was essentially concentrated in the central Oberwald region and dominated by low-viscosity mafic lava flows. Although volumetrically subordinate, these younger lava flows covered older volcanic sequences and erosional features. Due to a well-established climate change during the Langhian towards moderate and rather dry conditions, the final lava flows are much better preserved, thus giving the Vogelsberg volcanic field the appearance of a huge basaltic shield volcano (Nesbor, 2014).
The only rocks that are locally preserved are remnants of intense weathering of Vogelsberg volcanic rocks during Burgidalian times, e.g., Fe-rich crests and saprolite, the latter with thicknesses of more than 50 m (Schwarz, 1997) and most likely related to the mid-Miocene Climate Optimum.
Taking into account the field evidence from the Rhenish Massif to the west, we can emphasize two Cenozoic periods of intense chemical weathering, e.g., a lower Tertiary period, documented in widespread kaolinization of Paleozoic rocks, and a mid-Miocene period, which created Fe crests and saprolite on Vogelsberg volcanics that are 19-16 Ma old.

Stop 4: abandoned small quarry, close to Hungen-Langd
The old quarry is located about 500 m east of Hungen-Langd and provides an excellent view into the internal structure of   the Vogelsberg volcanic edifice (Ebhardt et al., 2001;Nesbor, 2014;Reischmann and Schraft, 2009). In the western segment of the quarry, four lava flows of basanitic to alkali-basaltic composition are exposed, each between 5 and 8 m thick, with well-developed breccia zones at their basis and upper regions (Fig. 13). Intercalated between the lava flows are tuff layers, which are dominated by mafic ash and fragments of country rock (e.g., Buntsandstein). Thus, volcanic activity included both effusive and explosive characteristics.
In the eastern part of the quarry, the lava flows were blown away by a younger explosive event which created a crater wall with a dip of ca. 45 • towards southeast. Pyroclastic rocks closest to the crater wall are dominated by tuff breccia that contain basanitic blocks, up to 1 m in size. Lapilli-size particles of the tuff breccia show very few vesicles. Thus the crater-forming event is most likely due to the interaction of rising hot mafic magma with groundwater at shallow depth, causing a phreatomagmatic explosion that destroyed the lava flows and created a maar-type conical crater.
The initial maar deposits are overlain by ca. 1 to 4 m of pyroclastics with different properties. This sequence is characterized by highly vesicular scoria, embedded in a lapilli and ash matrix. Obviously there was a change in eruptive behavior towards lava fountains and effective degassing, most probably related to a lack of groundwater supply.
The volcanic rocks that rest on this layer of highly vesicular scoria occupy the entire eastern section of the quarry. They consist of massive alkali basalts with clearly visible platy and columnar jointing due to comparatively slow cooling and shrinking (Fig. 14). This is best explained by further magma supply from below, ongoing degassing and prohibited groundwater influx, resulting in a slowly cooling lava lake that completely filled the conical crater structure.
Data availability. No data sets were used in this article.

Introduction
Our 1-day field trip will first lead us to an area south of Marburg in the middle reach of the Lahn valley. After an introduction to the natural settings of the area, we will visit the gravel quarry of Niederweimar, one of the largest of its kind in Hesse. The gravel quarry exposes three units of gravel which possibly represent the remains of different Quaternary glacial periods. The gravels are covered by late glacial and Holocene floodplain fines, showing a high-resolution stratigraphy. The floodplain fines include tephra of the Laacher See eruption that took place during the Allerød, and alternating layers of sands and silts, which may reflect climatic fluctuations of the late glacial. Above the tephra, a dark soil horizon marks the beginning of Holocene conditions. Furthermore, the area around Niederweimar is rich in archaeological finds of different periods. They indicate continuous settlement in the area over the last 11 000 years. Details will be presented at our coffee break at the so-called Zeiteninsel (island of times), an open-air museum showing settlements of different archaeological periods. Our next stop will be the abandoned gravel quarry Niederwalgern, which exposes gravels of the Lahn at the base and a thick sequence of floodplain fines, in-cluding a dark palaeosol. The sediments indicate massive deposition during the Holocene, probably due to anthropogenic forest clearing in the surrounding area. At our third stop, we will visit a loess palaeosol section south of Gießen, near a small village called Münzenberg. Our luminescence ages indicate that this profile comprises Middle Pleistocene loess, and possibly also a pre-Eemian palaeosol. The last glacial loess includes the Eltville tephra, another important tephra of the area, serving as a chronological marker for the Last Glacial Maximum. Establishing a secure chronostratigraphy at the site is however challenging, due to the position on a steep slope, which triggers erosional events.

Physiogeographic setting of the area
The geomorphological and geological setting of the area comprises a complex pattern of different geological units ranging from the Palaeozoic to the Holocene. An overview of the topography and geological units is shown in Figs. 1 and 2. The current annual rainfall in the area approximates 700 mm, and the average annual temperature is 8.8 • C. The main unit in the western part of the excursion route is represented by the Rhenish Massif (Rheinisches Schiefer- gebirge). Marine sands, silts and clays were deposited during the Devonian era, and were later metamorphized to quartzites and slates during the Variscian orogeny (Carboniferous). Locally, limestone, greywacke and radiolarite are also present, the last two especially in an area west of Gießen and Marburg. The Variscian orogen was eroded to its shield during the Permian era. During the Tertiary, the shield was fragmented into several fault blocks, of which some were uplifted during the Tertiary and the Quaternary. Examples of these uplifted blocks are, e.g. the Rhenish Massif or the Harz further to the northeast. Many of the gravels in the gravel quarry at Niederweimar (Stop 1) originate from the Rhenish Massif to the west, like quartzite, radiolarites and greywacke. Locally, this part of the Rhenish Massif is also called the Gladenbach Uplands (Gladenbacher Bergland). It has an average elevation of around 500 m a.s.l.
To the north and north-east of the excursion route, we mainly find red sandstones of the lower Triassic (Buntsandstein) and basalts which originate from the Vogelsberg eruption during the Tertiary (peak activity ca. 15 Ma ago). The Vogelsberg is the largest contiguous volcanic region in central Europe. The highest elevation of the Vogelsberg area is the Taufstein (773 m a.s.l.). The river Lahn intersects the Buntsandstein in an area north and south of Marburg, forming a relatively steep valley. At Niederweimar (Stop 1), the valley opens into a wider basin, which is filled with Pleistocene gravels and Holocene floodplain fines of the river Lahn. Buntsandstein and basalts are further important components of the gravel spectrum in the gravel pit at Niederweimar.
Further geomorphological-tectonic units near Gießen and Marburg are depressions which are filled with Tertiary fines and/or Pleistocene loess. The latter will be the focus of Stop 4. Like the uplifted Rhenish Massif, these basins represent tectonic blocks, which formed and subsided during the Tertiary and Quaternary.

Geology and geomorphology
The gravel quarry at Niederweimar is situated south of Marburg in the central Lahn valley. It is one of the largest gravel quarries in Hesse. The middle reach of the Lahn cuts through a wide range of geological units such as the Rhenisch Massif and sandstones of Permian and lower Triassic age. Tributaries coming in from the east pass the basaltic Vogelsberg massif. This leads to a rather diverse gravel spectrum, dominated by greywacke, associated with radiolarites, sandstones, basalts and quartzites. The hard rock base of the gravel pit is formed by red to purple sandstones and claystones of upper Permian age (Zechstein). Sediments within the gravel pit have not only been deposited by the river Lahn, but also by the river Allna, a tributary flowing in from the west, sourced in the Rhenish Massif. More detailed information on the fluvial history of the Lahn valley near Marburg can be found in Heine (1970). From a geomorphological point of view, the gravel pit is situated on the lower terrace of the Lahn. It is currently not inundated by floods, and its cover sediments are of Late Pleistocene and early Holocene age, as evidenced by the Laacher See tephra (LST; 12 900 ka, van den Boogard, 1995). Chronostratigraphically, the lower terrace would be assigned to the last glacial period. However, it appears that three gravel units are exposed in the pit, of which the lower ones seem to be much older than the last glacial. Elevation differences in the past and current floodplain of the Lahn are minimal (see Fig. 3); thus it is nearly impossible to distinguish different terrace levels from a geomorphological point of view. It therefore appears that at this location of the Lahn River, we are not dealing with a classical staircase of terraces, but with vertical stacking of terrace units, possibly due to (relative) tectonic subsidence in this part of the Lahn valley. So far, several radiocarbon ages, pollen and macrofossil assignments of the cover sediments as well as the gravel units have existed (e.g. Huckriede, 1982;Schirmer, 1999;Freund and Urz, 2000;Bos and Urz, 2003). But since large parts of the gravel units are older than 40 ka, numerical ages in particular of the older gravel units have been missing so far. New optically stimulated luminescence (OSL) and 14 C ages for the gravels as well as the floodplain loams are presented on this field trip.

Archaeology
During more than 20 years of excavation by the State Archaeological Service of Hesse on ca. 70 ha of river floodplains and adjacent alluvial terraces, a large area of settlements has been detected, spanning from the Mesolithic (11.7 to 7.5 ka) and different periods of the Neolithic (7.5 to 4.2 ka), Bronze (4.2 to 2.8 ka) and Iron Age (2.8 to 2.0 ka) to the Middle Ages. Such an extensive colonization of a local river landscape is, as yet, unique. The possibility to settle on the drier terraces near the water, as well as the species-rich flora and fauna, made the river landscape of the central Lahn valley attractive to humans (Bos and Urz, 2003).
Already in 1994, two early Mesolithic sites were found during a gravel excavation. They were dated to around 10.5 ka cal BP (Bos and Urz, 2003). Pollen and macrofossil analyses, which were part of two research projects during the DFG (German Research Foundation) priority programme "Changes of the Geo-Biosphere during the last 15 000 years, continental sediments as evidence for changing environmental conditions", suggest that forest-clearing due to deliberate burning by Mesolithic people occurred in the area (Bos and Urz, 2003). A reconstruction of the Mesolithic landscape in the central Lahn valley is shown in Fig. 4.
Since 2017, a DFG-funded research project has focused on plant remains from archaeological records as a source of information on the changing environmental conditions and agricultural systems within the prehistoric settlements near Niederweimar (Ralf Urz, Department of Geography, Philipps University of Marburg). Further details on the archaeology of Niederweimar can be found on the homepage of the archaeological survey of Hesse (https://lfd.hessen.de, last access: 11 July 2018).

Gravel unit
The gravel unit can be divided into three subunits (Fig. 5). The oldest unit (Unit I) forms the base of the gravel pit. It is not present and/or visible in all parts of the pit and is of dark grey to dark reddish colour. Unit II consists of brown gravels with trough and horizontal bedding and with a strong overprint caused by precipitation of iron oxides. This unit can be further divided into two subunits, separated by a discontinuous layer of larger blocks. Unit III is formed by greyish gravels with marked horizontal and trough bedding and a block layer at its base. Unit II and III are separated by an erosional disconformity. Further information on the gravel units is given in Freund and Urz (2000) and . They assign the lower part of the gravels (our Unit II) to the early Weichselian, based on pollen and macrorest analyses, and the upper part of the gravels (our Unit III) to the last Pleniglacial. The latter is supported by one 14 C age at Niederweimar of around 32 ka, and two further 14 C ages between 30 and 40 ka at the gravel quarry Niederwalgern . showing the Mesolithic camp sites, the differences in relief between the floodplain and the terraces and accompanying differences in forest vegetation (Bos and Urz, 2003).

Luminescence dating
Different luminescence methods were applied in order to date the gravel units. Unfortunately, OSL dating of quartz has an upper age limit of around 100 ka for the sediments in question (quartz dose rate 1.5 to 2.3 Gy ka −1 ). The lower gravel units were thus too old for conventional OSL dating. For this reason, TT-OSL and post-IR IRSL 225 dating were tested as additional methods. However, both methods suffered from incomplete bleaching. Thus the ages need to be treated with care. Results are shown in Table 1 and Fig. 5.

Heavy mineral analyses
Sodium polytungstate with a density of 2.85 g cm −3 was used as heavy liquid to separate the heavy from the light fraction in a centrifuge. The samples were boiled with concentrated HCl before centrifugation in order to remove iron and manganese hydroxide crusts, which would complicate the identification. The disadvantage of this method is the dissolution of carbonate, apatite and parts of monazite and olivine (Boenigk, 1983). Nevertheless, this was deemed acceptable because of the benefit of being able to make comparisons with our own and other previous analyses.
The lowermost gravel units (Unit I and II) show a very low content of heavy minerals, with 0.02-0.09 % in the fine sand fraction, while the other profile sections reveal heavy mineral contents ranging from 0.13 to 1.6 %. One of the key questions of this investigation was in which depth levels heavy minerals of volcanic origin, i.e. of the Laacher See tephra (LST) occur. The LST is characterized specifically by the volcanic heavy minerals pyroxene (augite), brown hornblende and titanite (e.g. Henningsen, 1980;Semmel, 2003), which comprise up to more than 75 % of the overall heavy mineral fraction.
Samples from gravel Unit I and II show high amounts of extremely stable heavy minerals, especially zircon and tourmaline. The sample from the overlying gravel unit (Unit III), just below the floodplain fines, shows a significant increase of the heavy mineral content as well as high amounts of volcanic heavy minerals (pyroxene 75 %, brown hornblende 15 % and titanite 3 %). It is thus assumed that at least parts of this gravel unit post-date the Laacher See event.

Stratigraphic interpretation
Due to the high sedimentation age of the lower gravel units, it is difficult to provide a numerical chronology of them. So far, only the following conclusions can be tentatively drawn.
The lowest gravel unit (Unit I) is probably older than the overlying unit. An assignment to a certain marine isotope stage (MIS) is impossible, but most likely the sample is older than 300 ka.  Table 1. Note that in the uppermost sample, heavy minerals typical of the Laacher See tephra were found. The intermediate gravel layer (Unit II) seems to have formed during one single glacial period, because the luminescence ages are of similar age (except for one outlier), independent of the method used. However, the ages are too imprecise and too unreliable for a clear assignment to a certain MIS. According to the luminescence ages, Unit II most likely formed during MIS 8 or MIS 10. This age strongly contradicts previous findings of Huckriede (1972,1982) as well as  and Freund and Urz (2000), who place the base of the unit in the Eemian and early Weichselian, based on pollen and macrofossil analyses.
The uppermost gravel unit (Unit III) showed a surprisingly young age. So far, we have assigned this unit to the middle Weichselian because earlier, preliminary OSL ages clustered around 30 ka. Also, several 14 C ages between 30 and 40 ka at Niederweimar and the nearby site of Niederwalgern Freund and Urz, 2000) indicate an older age of this unit. It is possible that during the Younger Dryas, the gravels of the middle Weichselian were partially incised by the braided river that shaped the riverbed at that time. The channels were then filled with Younger Dryas gravels and sands shortly before the onset of the Holocene. In many parts of the upper gravel layer, these former channels are visible. This Figure 6. Sketch of section NW-6 in the floodplain loams of Niederweimar, together with results from 14 C and OSL dating, grain size and heavy mineral analyses. Please note that the lowermost sample for OSL dating is derived from one of the neighbouring sections NW-3, from the same stratigraphic unit. young sedimentation age of the uppermost part of gravel Unit III is supported by the heavy mineral spectrum, which shows a signature characteristic of the LST.
Although the older luminescence ages have been unreliable so far, they allow the following overall interpretation: terrace units of different ages are vertically stacked onto each other, possibly indicating (relative) tectonic subsidence of the area. MIS 6 is not represented by a gravel unit in the studied section; thus it seems to have been completely removed by a later erosional period. Very large blocks in the lower part of Unit III testify to an extremely dynamic fluvial event, which may have caused this erosion. However, it cannot be ruled out that MIS 6 gravels are found in other parts of the gravel pit.

Floodplain loams
Floodplain loams overlie the Pleistocene gravels and show a very detailed stratigraphy, with alternating sand and silt layers in the lower part, one or several light grey layers of varying thickness in the middle and upper part, and a further dark palaeosol horizon in the uppermost part. From field observations, it is tempting to assign the greyish layers to the (relocated) Laacher See tephra, which would place the lower part of the floodplain loams in the late glacial and the upper part of the section mainly in the Holocene. This stratigraphy is supported by detailed pollen and macrofossil studies as well as radiocarbon dating carried out by, e.g. , Bos and Urz (2003) and Schirmer (1999). However, this stratigraphic interpretation contradicts the findings on the gravel unit investigated in the current study. Here, one OSL age places the uppermost part of the gravels in the Younger Dryas. Heavy mineral analyses also confirm that their deposition took place after the Laacher See event. In order to gain further insight into the chronostratigraphy of the site, further 14 C and OSL dating and palynological, granulometric and heavy mineral analyses on the floodplain loams were carried out.

Methods and results
Particle size distributions were determined by classical pipette and sieve procedures without decarbonation accord- ing to Köhn (ISO 11277). The chronology of the upper unit of floodplain fines is mainly based on calibrated 14 C age analyses (CalPal online; Weninger and Jöris, 2004), carried out on wooden macrofossils, obtained from the silt-rich sediment layers. Additionally, three luminescence ages were determined, using OSL on the coarse grain quartz fraction. Results are shown in Fig. 6 and Table 2.
Palynological analyses were carried out mainly on the silty layers in the bottom part of the section (Unit I to Unit III). They reveal vegetation changes over a short period of only 1000 years according to the 14 C ages (Fig. 7).
The layers II.1a and II.1c have similar pollen spectra with a dominance of Poaceae, Thalictrum, Artemisia and other herbs, such as the Helianthemum nummularium group, Ranunculus acris type, Apiaceae and Matricaria type, indicating a dominance of meadows. An open landscape is suggested by a low abundance of arboreal pollen (7 %), represented by Pinus and Betula. Presence of Myriophyllum and remains of Gleotrichia type and Spirogyra indicate stagnant or slowly flowing water. Pollen concentration is rather high and varies between 15 000 and 27 000 grains cm −3 , indicating a low sedimentation rate. A low abundance of mycorrhizal spores of Glomus type indicates low soil erosion rates. Charcoal concentration of up to 6000 particles cm −3 reveals the presence of fires.
The next four clay layers (Units II.3, II.5, II.7, and II.9) differ from the first ones by very low pollen concentrations of 2000-3000 grains cm −3 . This can possibly be explained by increased sedimentation rates due to enhanced soil erosion in the catchment. The latter is confirmed by a high abundance of Glomus type (87-302 %). Pollen spectra of all four layers are characterized by a significant increase of arboreal pollen like Picea (Bittmann, 2007), possibly partly reworked. Non-arboreal pollen (NAP) is still dominant in the spectrum with Cyperaceae, Poaceae and Artemisia, also suggesting wetter conditions and possible spread of tundra vegetation. Spores of coprophilous fungi (Arnium, Bombardioidea, Po-dospora, Sordaria and Sporormiella) indicate the presence of the herbivores in the area, but their increased abundance can possibly be explained by an increased soil erosion in the catchment. Pollen of Myriophyllum and algal remains indicates similar aquatic conditions to before. Interestingly, there are abundant sheaths of Gleotrichia-type, which is known as having been an aquatic pioneer during the early part of a late glacial due to its ability to fix nitrogen and make conditions suitable for other aquatic plants ( van Geel et al., 1989).
Layer II.11 has an increased pollen concentration (6000 grains cm −3 ), indicating a lower sedimentation rate during this period. The pollen concentration increases up to 64 000 grains cm −3 in the peat layer, indicating a slow peat growth rate. An abundance of arboreal pollen (AP) in layer 11 exceeds 50 % and it is dominated by Pinus and Betula, indicating further spread of birch-pine forests under milder conditions.
The heavy mineral samples from this section reveal a spectrum which is typical of the LST throughout the whole section of floodplain loams. Since especially pyroxene and brown hornblende are not very resistant to weathering, nearsurface samples are affected by a higher grade of mineral alteration, which causes a relative enrichment of the stable heavy mineral titanite.

Stratigraphic interpretation
The 14 C ages place the lower part of the floodplain loams in the Meiendorf and Bölling interstadials, as well as in the Older Dryas period. They coincide with 14 C ages presented by Schirmer (1999) for the same stratigraphic unit and predate the Laacher See eruption. Based on our investigations in the field, we placed the first layers containing LST in Unit III, supporting the 14 C ages. Furthermore, comparison of the preliminary pollen data with pollen diagrams presented in Schirmer (1999) allows a stratigraphical correlation of the lower part of our section to the late glacial. This is evidenced J. Lomax et al.: Field Trip B (27 September 2018)  However, the heavy minerals suggest that layers from Unit II also contain significant amounts of LST, as well as the underlying gravel unit. This finding is consistent with two of the OSL dates from the floodplain loams, which yield ages of 12.6 ± 1.2 and 10.8 ± 0.9 ka, thus post-dating the Laacher See event. Another OSL age from the underlying gravel (12.8 ± 1.2 ka) agrees with the Laacher See event and is consistent with another sample dated to 12.5 ± 0.8 ka investigated in the gravel section (see Sect. 3.3.1). However, the OSL chronology shows an age inversion in the uppermost sample. This is most likely due to methodological problems, namely OSL curves in this sample that decay slower than usual. The three lower samples showed typical OSL curves; they thus appear more reliable. On the other hand, the pollen data rule out a Holocene age of the middle OSL sample in the floodplain loams. The beginning of the Holocene in the area is well defined stratigraphically by a strong increase of pine pollen up to 80 % (Bos and Urz, 2003), and this signature is absent in our investigated pollen samples.
In summary, on the one hand it seems that the OSL data and the heavy mineral analyses support each other, with the uppermost gravel unit and the overlying floodplain loams post-dating the Laacher See event. On the other hand, the 14 C chronology is more consistent with the pollen data and the field observations, i.e. the onset of tephra deposition within Unit III. This stratigraphic inconsistency will be further investigated in the near future.
The 14 C chronology furthermore reveals that the lower part of the section, comprising a sequence of intercalated coarser and finer layers (Unit II), was deposited within a relatively short time, resembling an alluvial channel facies (Aurinnenfazies) sensu Schirmer (1983).

Abandoned gravel quarry of Niederwalgern
The site Niederwalgern is a former gravel quarry, which has now been turned into a lake that serves as a natural reserve for birds and other wildlife, and is also the habitat of a small herd of water buffalos. Geomorphologically, the former gravel quarry rests on the lower terrace of the Lahn, which in turn is covered by Holocene alluvial fines. The fines include a thick unit of sediments that contains abundant fragments of ceramics and charcoal, indicating anthropogenic alluvium which originates from hillslopes further to the west (Fig. 3). Detailed litho-, bio-and chronostratigraphic investigations at the site (during active quarrying) were carried out by .

Methods and results
Particle size distribution was determined by classical pipette and sieve procedures without decarbonation according to Köhn (ISO 11277). In order to provide a first chronology of the section, OSL dating was applied to the underlying gravels of the lower terrace and to the upper part of the overlying fine sediments. For this purpose, the coarse grain quartz fraction was analysed. Due to incomplete bleaching, the D e values of the floodplain fines are based on a minimum age model. In contrast, material from a sand lens within the underlying gravel was well bleached. Thus, the Central Age Model was applied for deriving the mean D e . Results are summarized in Table 3 and Fig. 8.

Stratigraphic interpretation
The investigated section comprises three units: the gravel unit (I) at the base of this site yields an OSL age of 8.5 ± 0.6 ka. In comparison to a 14 C age obtained by , which places this unit in the Younger Dryas, our OSL age appears to be too young. Further investigations on this issue will be undertaken in the near future. The intermediate layer (II) is composed of floodplain loams with a dominant sand fraction. The unit terminates with a dark soil complex, in which the clay content increases to around 40 % in the uppermost sample. This soil can possibly be correlated with the so-called black floodplain soil which is widespread in the area. The formation of this floodplain soil in middle Hesse is assigned to the early Holocene (Mäckel, 1969;Houben, 2002;Urz, 2003) or to the early to mid-Holocene (Rittweger et al., 2000). So far, precise numerical ages of this horizon have been sparse, and the site at Niederwalgern offers the potential for improving the chronology by undertaking further OSL analyses.
The sediments of the uppermost unit (III) are dominated by silt. Charcoal pieces and fragmented ceramics are also abundant, indicating strong anthropogenic impact. At the current stage of research, it is however not clear whether this sediment layer is a colluvium from the small slopes further to the west or an alluvial sediment. Five OSL ages assign the unit to the Early Medieval Period in the lower part and the High Medieval Period in the upper part. As in many other parts of Germany, the High Medieval Period was characterized by deforestation and intensive farming, not only in the lowlands, but also on the hillslopes of low mountain ranges. This led to intense soil erosion and deposition of material at toe slopes and floodplains as colluvial and alluvial deposits.

Study area
The section is situated on a slope within a former brickyard on the east side of the Wetter River (50 • 26 N, 08 • 46 E; 198 m a.s.l.), in the northern part of the Wetterau basin within the Hessian Depression (Fig. 9). The basin's topography is characterized by a gently rolling landscape, flanked by the northern Taunus mountains to the west and the basaltic Vogelsberg massif to the east. During the Tertiary, tectonic sub- sidence created a mosaic of small-scale depressions, accompanied by the deposition of marine, fluvial, limnic and aeolian sediments (Bibus, 1974(Bibus, , 1976. Therefore, the lithology of the study area is dominated by unconsolidated Miocene sediments consisting of sands, gravels and clays. Additionally, Miocene basalts and intensively saprolized rock form the subsurface of the northern part of the Wetterau, characterizing the lithology of the study area (Kümmerle, 1981;Sabel, 1982).
Under periglacial conditions during the Pleistocene, the river Wetter formed terraces above the present-day river bed. These terraces were later covered by calcareous aeolian sands and reworked loess-derived clayey silts. On northeastfacing slopes and geomorphologically sheltered positions, loess was deposited and has been preserved to thicknesses of up to 10 m (Schönhals, 1996). Farming in the area already started in the early Neolithic, ca. 7500 years ago, favoured by a moderate climate and fertile soils. Because of this longterm cultivation, the present-day soilscape of the area is char-acterized by truncated soil profiles and anthropogenic colluvium, e.g. truncated Luvisols, Cambisols and Regosols (Houben, 2012;Lang and Nolte, 1999;Schrader, 1978).

Methods
According to Bibus (1974), the investigated loess section can be subdivided into 17 units, including several palaeosols showing different intensity of pedogenesis, reaching a thickness of up to 10 m. However, the chronostratigraphic interpretation by Bibus (1976) was based solely on palaeopedological criteria, whereas there has been no numerical age control so far. Therefore, the existing loess profile has been extended, described and sampled in several field campaigns since summer 2013. Magnetic susceptibility measurements were conducted in the field with a SatisGeo Kappameter KM-7 at a 10 cm depth interval, recording five measurements per depth interval. Samples for sedimentological analyses were collected at high resolution (5 cm), yielding 180 bulk samples, based on the continuous column sampling method described in Antoine et al. (2009). Sedimentological analyses included determination of particle size distribution by classical pipette and sieve procedures without decarbonation according to Köhn and gas-volumetric determination of carbonate using the Scheibler method. Additionally, spectrophotometric analysis for determination of colour and lightness was conducted using a Konica Minolta CM-5 spectrophotometer at the laboratory for Physical Geography of RWTH Aachen. Based on the colour values, the Redness Index (RI) was calculated as a proxy for soil rubification and changes in hematite content (Barron and Torrent, 1986). For luminescence dating, 16 samples ( Fig. 10; red circles) were taken at night-time by direct sampling into opaque plastic bags, after removing the light-exposed outer sediment layer of the profile wall. Samples for dosimetry measurements were collected within a 30 cm radius of each luminescence sample. Sample preparation and post-IR IRSL measurements, following a modified post-IR IRSL 225 protocol originally proposed by Buylaert et al. (2009), were carried out at the Luminescence Laboratory of Giessen University. Further information can be found in Steup and Fuchs (2017). A total of 15 undisturbed samples were collected from the profile for micromorphological analyses ( Fig. 10; red boxes).
For the interpretation of relative variations in the geochemical composition along the loess section, XRF analyses were performed on a ITRAX XRF core scanner at Bremen University. The results are presented as element log ratios ( Fig. 12) to characterize weathering intensity and dust provenance.

Profile description and results
The division of the loess section into 14 pedostratigraphic units ( Fig. 10) is based on field observations including identification of major discontinuities and variations in colour, grain size distribution, magnetic susceptibility and carbonate content, as well as quantitative analyses of grain size distribution, carbonate content, spectrophotometric colour measurements and age estimates obtained from luminescence dating. The lowermost subsequence (Unit 1) of the section consists of Fe / Mn nodules of reddish brown compacted clayey silt ∼ 2 m thick, characterized by complete decarbonatization. It shows the highest content of illuvial and neoformed clay (< 2 µm; Fig. 11a, b), with almost 40 % clay at a depth of 10 m. Four subunits can be distinguished within the basal soil complex, based on grain size variability and changes in soil colour and elemental composition (based on XRF). The luminescence age estimates (Table 4) calculated from the pIRIR 225 signal in subunits a and b range from 177.6 ± 26.8 ka (GI 142) to 204.7 ± 21.8 ka (GI 143), indicating a time of deposition prior to the last interglacial (MIS 5e) and therefore soil formation during MIS 5 or 7.
Unit 2 marks a transitional stage between subsequence I and II, showing several indices for translocation, e.g. coarsening substrate, only partial decalcification and diffuse boundaries (Fig. 11c,d). It is superimposed by 1 m of homogeneous yellow-grey, calcareous (11-12 % CaCO 3 ) and silty loess (Unit 3) with incorporated CaCO 3 concretions (Ø 5-6 cm). Unit 4 differs clearly from the underlying and overlying typical calcareous loess layers (Units 3 and 5) in the occurrence of reworked yellowish brown to grey silt loams and sandy layers, both containing Fe / Mn concretions and erosive and translocated structures. The uppermost laminated calcareous loess (Unit 5) of subsequence II is infiltrated with large calcareous nodules up to 15 cm in diameter and marks the boundary towards the overlying light brown reddish silt loam (Unit 6), with a tabular structure and a lower carbonate content compared to the loess sediments. Luminescence ages of the under-and overlying sediments confirm a gap of ∼ 100 ka between subsequence II and IV, implying deposition of SS II during MIS 6 (GI 146: 167.5 ± 21.9 ka). The overlying subsequence IV represents MIS 2 and is characterized by the alternation of yellow sandy loess sediments with   Figure 12. Grain size data, weathering and provenance indices at Münzenberg as derived from XRF data. intercalated coarser brownish sand layers (Units 8, 10, 12) and greyish yellow horizons with higher silt and lower sand contents, reflecting incipient pedogenesis (Units 7,9,11,13). Transitions between sandy loess and bleached tongue horizons are represented by disturbed boundaries accompanied by redepositional features, such as rounded Fe / Mn nodules and the highest coarse sand contents of the entire sequence.
In the uppermost loess (Unit 12) a greyish-black layer of volcanic material 1-2 mm thin is observed, showing deformation features through solifluction processes. Based on the post-IR IRSL ages (GI 154 and GI 155), the volcanic ash layer can be attributed to the Eltville tephra, which serves as an important marker horizon and thus enables us to correlate the Münzenberg loess section with other sequences from central Germany containing this ash layer. The superimposed Unit 14 of subsequence V corresponds to the modern surface soil.
Author contributions. JL wrote the major part of the article, led the fieldwork and sampling and carried out luminescence dating for the research areas Niederweimar and Niederwalgern. RS wrote the part on Münzenberg, led fieldwork and sampling and carried out all analyses at Münzenberg. LS carried out the palynology and CH carried out the heavy mineral analyses. DS co-led fieldwork, carried out pedological investigations and organized radiocarbon dating. VvD carried out grain size analyses and prepared profile drawings. MF is the main organiser of the research team and research content.

Abstract:
The Devonian slates and sandstones of the Rhenish Massif were subject to deep and intensive weathering under (sub)tropical climate conditions during the Cretaceous, the Paleogene and the Neogene, which caused the development of a weathering mantle (regolith) > 100 m thick, consisting of kaolinitic saprolite and paleosols as well as correlated sediments. Especially the tectonic uplift of the Rhenish Massif and climate change during the Neogene and the Pleistocene led to a vast denudation of the weathering mantle. Only in less uplifted areas of the mountainous region did thick remnants of saprolites remain, and they were covered by Neogene sediments as well as Quaternary periglacial slope deposits. As the kaolinitic weathering products serve as raw materials for the clay industry, unique exposures are available in the Hintertaunus which offer impressive insights into the landscape development of the past ∼ 80 million years: the excursion proceeds from Giessen to Limburg and further south and southwest to the eastern and western Hintertaunus area. At site 1 near the village of Langhecke, characteristics and properties of the fresh, unweathered slates will be demonstrated. Excursion sites 2 and 3 are situated near the village of Eisenbach. In two open-cast clay mines, both a terrestrial and a semi-terrestrial saprolite from silt slate, covered by periglacial layers, are exposed. Properties and genesis will be discussed on the basis of morphological characteristics and mineralogical and geochemical analyses, as well as isovolumetric elemental mass balances. At site 4 a former basalt quarry near the village of Biebrich exposes a Paleogene Plinthosol above saprolite. The autochthonous paleosol was preserved below Upper Oligocene basalt tuff and periglacial layers. Site 5 is situated within a huge pit for mining of Upper Oligocene to Miocene quartz gravel near the village of Wasenbach. A Miocene Plinthosol developed from alluvial sediments on top of the gravel beds and was covered by periglacial slope deposits. At nearly all sites the basal layers of the periglacial cover beds consist of kaolinitic paleosol/saprolite material, which has an important influence on the site properties of the Holocene soils.  Die Exkursion führt von Gießen nach Limburg und von dort nach S und SW in den östlichen und westlichen Hintertaunus. Am Exkursionspunkt 1, bei der Ortschaft Langhecke, werden die Merkmale und Eigenschaften der frischen, unverwitterten Schiefer demonstriert. Die Exkursionspunkte 2 und 3 befinden sich nahe der Ortschaft Eisenbach. In zwei Tongruben sind ein terrestrischer und ein semiterrestrischer Saprolit aus Schluffschiefer aufgeschlossen, die von periglaziären Deckschichten überlagert werden. Auf Basis der morphologischen Merkmale, der mineralogischen und geochemischen Analysendaten sowie den Ergebnissen isovolumetrischer Massenbilanzen werden die Eigenschaften und Genese der Verwitterungsdecke und ihre Überprägung im Pleistozän diskutiert. Am Standort 4, nahe der Ortschaft Biebrich, ist in einem ehemaligen Steinbruch ein autochthoner Plinthosol aus dem Paläogen aufgeschlossen, der unter oberoligozänem Basalttuff konserviert und von gegliederten periglaziären Deckschichten überlagert wurde. Exkursionspunkt 5 befindet sich in einem großen Kiesabbau nahe der Ortschaft Wasenbach, in dem oberoligozäne -untermiozäne Quarzschotter und -sande des Vallendar-Flusssystems abgebaut werden. Ein miozäner Plinthosol entstand aus Hochflutsedimenten oberhalb der fluviatilen Kiese und wurde von periglaziären Deckschichten überlagert. Deren Basislage besteht hier, wie an den anderen Standorten, aus dem kaolinitischen Substrat des unterlagernden Saprolits/Paläobodens und hat damit einen bedeutenden Einfluss auf die Standorteigenschaften der holozänen Böden.

Introduction
The bedrock areas in mountainous regions of Middle Europe, which was a continent during the Mesozoic and Tertiary, were subject to deep weathering under (sub)tropical humid climate conditions, which caused the formation of a kaolinitic weathering mantle tens to hundreds of metres thick, consisting of a paleosol above saprolite (Fig. 1). Details about distribution and genesis as well as comprehensive references are published in Felix- Henningsen (1990Henningsen ( , 1994Henningsen ( , 2015. Due to tectonic uplift of the former planation plains and climate changes during the Neogene and the Quaternary, the Mesozoic-Tertiary weathering mantle (MTV) was in part or completely subject to erosion. Especially the strong uplift during the Quaternary and periglacial conditions during the cold periods strongly supported the removal of the weathering mantle and led to the expansion of a sequence of periglacial layers above the truncated weathering mantle (Felix-Henningsen et al., 1991;Sauer and Felix-Henningsen, 2006, Fig. 2). Only in areas with weaker tectonic uplift did more or less thick remnants of the weathering mantle remain.   Autochthonous kaolinitic paleosols of Cretaceous to Neogene age show characteristics of soils of the modern tropical regions (e.g. Ferralsols, Plinthosols). They developed at the former land surface by processes of soil formation, such as chemical and physical weathering and bioturbation. Remnants of such paleosols occur in small areas, protected against erosion by a cover of Tertiary sediments or volcanic rocks (Fig. 4).
Saprolites developed below the paleosols when the weathering front exceeded the depth of the soil. They are exclu- sively chemically weathered bedrock and show the preserved rock structure because with increasing depth of the weathering front the physical forces (swelling and shrinkage, rooting, bioturbation, frost pressure) intermitted, while dissolution of minerals and leaching of elements under sufficient precipitation proceeded unhampered (Fig. 1).
The excursion aims to present unique sections of the thick weathering mantle in the Hintertaunus (literal: back of the Taunus) region, which is a part of the eastern Rhenish Massif (Fig. 6), in order to discuss properties and genesis, as well as the Quaternary superimposition and the consequence for the site properties of Holocene soils. Due to a lesser tectonic uplift and weak denudation of the Cretaceous to Paleogene planation areas, more or less thicker remnants of the weathering mantle are well preserved. The excursion presents fresh slates as parent rock as well as unique exposures of terrestrial and semi-terrestrial saprolites and autochthonous paleosols of Paleogene and Miocene age. Furthermore, periglacial superficial layers above saprolite and paleosols, exposed in deep profiles, allow insight into the processes of periglacial overprinting of the MTV. In detail, the following topics will be presented and discussed: morphological characteristics as well as geochemical and mineralogical properties of different saprolite zones and their genesis; characteristics, properties, genesis and classification of autochthonous kaolinitic paleosols of Paleogene and Miocene age; organization, stratigraphy and properties of periglacial layers; demonstration and discussion of methodological approaches of clay mineral analyses and isovolumetric element mass balances.  Henningsen and Requadt, 1985). In the western Hintertaunus alternating layers of quarzitic Paleogene sandstones, silt slates and marine tuffs represent the Lower Devonian rocks, locally mounted by Eocene to Lower Miocene volcanoes (Müller, 1973). In a paleo-river system, which existed from the middle Eocene to the Upper Oligocene, fluvial milky quartz gravels (Vallendar gravel) were deposited in valleys and basins, where they reached a thickness of up to several tens of me- Bj-Gj is terrestrial or semi-terrestrial fersiallitic soil horizons, mCewj is bleached saprolite, mCoj is oxidized saprolite, mCrj is reduced saprolite and R is fresh rock; K is kaolinite, I is illite, M is muscovite, Chl-V-WL is chlorite-vermiculite mixed layer minerals, Sm is smectite and Chl is chlorite.

Geomorphology of the Hintertaunus region
tres (Ahlburg, 1915;Löhnertz, 1978;Andres et al., 1974;Semmel, 1984). In the western Rhenish Massif the paleoriver course can be traced parallel to the Mosel river down to the tectonical basin of Neuwied (Semmel, 1984). Requadt (1990) concludes that the Vallendar gravels were originally deposited as sediments of a Middle to Upper Oligocene (33-30 Ma) marine transgression advancing from the Mainz basin in the south of the Rhenish Massif towards the north. In this period, a connection existed between the northern alpine Molasse basin through the Upper Rhine fault trough and the Hessian basin to the North Atlantic (Walter, 1995). In a second phase, during tectonic uplift of the area, the eroded material of the weathering mantle was repeatedly redistributed and finally deposited in river valleys. Requadt and Buhr (1989) identified five terraces with deposits of milky quartz gravel in different altitudes adjacent to the lower Lahn valley. The tectonic uplift during the Pliocene favoured the fluvial dissection of the excursion area, which led to erosion of a great part of the Vallendar gravel and the underlying weathering mantle (Andres et al., 1974). Periglacial solifluction during the Upper Pleistocene caused extensive redistribution of the exposed paleosols, saprolites and Vallendar gravel and the formation of the basal layer. On flat slopes and in plain areas, loess, deposited during the glacial and afterwards partly redistributed by solifluction, remained as the middle layer. Area-wide, an upper layer of redistributed loess, mixed with pumice of the Laacher See volcano eruption, was deposited by eolian sedimentation and solifluction during the Younger Dryas period (Felix-Henningsen et al., 1991). Thick loess deposits within the basins of Limburg and Idstein were the parent material of fertile Holocene Luvisols, intensively used by agriculture.
The rivers Aar, Wörsbach and Emsbach (from west to east) are tributaries of the lower Lahn river, which drain the excursion area. The average annual temperatures are 8.5 to 9 • C in lower altitudes and about 7 • C above 500 m a.s.l. Annual precipitation amounts to 650-750 mm.

The Mesozoic-Tertiary weathering mantle
The bedrock of the Rhenish Massif consists of Devonian slates and sandstones, which are exposed to continental conditions at least since the Jurassic. During this period of about 200 Ma in total, discrete phases, each of Ma duration with (sub)tropical humid (Cretaceous and Paleogene, middle Miocene), semi-arid (Upper Oligocene, Lower Miocene), subtropical to moderate (Neogene) and moderate to arctic climate (Quaternary), influenced the development of the weathering mantle, paleosols and relief forms. In periods of millions of years with a humid (sub)tropical climate during the Upper Cretaceous and Tertiary, a saprolite more than 150 m thick (Spies, 1986) developed below a kaolinitic paleosol (Figs. 1 and 4), when the weathering front advanced with a higher rate to greater depths than the lowering of the land surface by erosion. The progression of the weathering front to greater depths on crystalline rocks shows rates of 1 to 5 cm in 1000 years under recent humid tropical climate conditions (references in Felix- Henningsen, 2015). Therefore, saprolites testify to periods lasting millions of years with warm humid climatic conditions, high weathering intensity and an extremely stable land surface due to a dense vegetation cover.
The occurrence of the MTV is bound to planation plains, which developed by extensive denudation during the Cretaceous until the Paleogene. Their remnants are preserved in weaker uplifted areas of the Rhenish Massif, mainly at the edges and within tectonic basins of the mountainous region. Also in the flat upland area of the Hintertaunus, which during the Neogene was already affected by tectonic subsidence, leading over to the downthrown fault blocks of the basins of Idstein, Limburg and the Westerwald, thick sections of the saprolite remained.
Saprolites from Lower Devonian slates are characterized by their preserved rock structure, a lower mechanical stability than the fresh slates and a change of colour due to weathering of silicates and oxidation. Morphological characteristics as well as chemical and mineralogical properties of saprolites, which in a similar way are distributed in weathering mantles of the recent tropics, change with depth, because the age and intensity of weathering decrease from the basis of the paleosol towards the weathering front at the basis of the saprolite. Thus, a vertical sequence of upper, middle and lower saprolite zones can be defined by their morphological characteristics as well as mineralogical, geochemical and physical properties (Felix-Henningsen, 1994, Fig. 5). Due to weathering of silicates and leaching of the dissolved ions, which do not contribute to the neo-formation of clay minerals, the bulk density (volume weight, vol-wt) and mechanical stability decrease from the weathering front towards the surface as a consequence of increasing mass loss (Table 2), porosity and permeability. In the lowest saprolite zone the primary Fe-Mg chlorites, which are the minerals with the lowest stability, changed to smectite under reducing conditions and chlorite-vermiculite mixed layer (m.l.) minerals under oxidizing conditions as intermediate products. With increasing intensity of weathering and leaching in the upper saprolite zones, these secondary minerals were dissolved and kaolinites precipitated (Fig. 5), while bases and silica were leached (e.g. Tables 3-7). For mapping of the weathering mantle and identification of tectonic faults, a subdivision of the saprolite in two mineralogical zones is useful (Spies,   1986): an upper zone with complete transformation of chlorite into kaolinite and a lower zone with incomplete transformation (Fig. 6). The mass loss of Al indicates that chlorite was not quantitatively transformed into kaolinite. Acid conditions in the weathering zone and presumably high contents of dissolved organic carbon in the pore solution, which derived from the decomposition of organic matter in the soil, supported the solubility and leaching of Al ions.
The morphological and geochemical characteristics of saprolites also depend on Cretaceous and Paleogene relief conditions. Red-or brown-coloured terrestrial saprolites, with high contents of pedogenic Fe and Mn oxides, weathered under oxidizing conditions and the influence of percolating water. In lower areas of the undulating planation surface, a high groundwater table caused the formation of semiterrestrial saprolites. As a consequence of weathering under groundwater saturation and leaching of dissolved metal ions under reducing conditions, these saprolites display a white colour due to bleaching (Felix-Henningsen, 1994). The known autochthonous paleosols on saprolite from Lower Devonian slates are Plinthosols of Cretaceous to Paleogene age with a bright pattern of red and white mottles. They occur locally, preserved below layers of Upper Oligocene basalt, tuffs and fluvial river sediments (Felix- Henningsen and Wiechmann, 1985) and show a high content (> 60 mass %) of kaolinitic clay. The sequence of a concretionary upper horizon and a mottled middle horizon, which fades with depth to a bleached, semi-terrestrial saprolite, indicates a soil development under a high groundwater table.
The paleosol of the MTV can be younger than the uppermost saprolite. In the case that a former paleosol was eroded during a climatically or tectonically induced period of denudation, the saprolite was the parent rock of a younger soil, which developed in a following phase of geomorphic stability. Paleogene and Neogene sediments of the Rhenish Massif testify to such periods of denudation of the MTV.
In the area of the Hintertaunus and the adjacent Westerwald, saprolites of the MTV are frequently exposed in opencast mines of the clay industry, which exploits them for ceramic products, bricks and roof tiles or green house substrates, depending on the mineralogy of the exposed zones. Correlated clay sediments, which were deposited during Paleogene and Neogene erosion phases in subsiding basins of the Westerwald, are valuable kaolinitic clay deposits used for the ceramic industry.
During periglacial periods of the Pleistocene, combined processes of congelifraction, cryoturbation and solifluction as well as deposition of loess and pumice formed a sequence of superficial layers (Fig. 2). The basal layer derived from the underlying saprolite or kaolinitic paleosol. A low potential for the formation of soil structure results from the low shrinkage and swelling capacity of the kaolinitic material. Thus, the basal layer causes very unfavourable soil properties due to high bulk density, water logging, low cation exchange capacity and lack of nutrients. Therefore, the recent potentials of the soils for land use are narrowly linked to the landscape development during the past deca-million years.

Excursion route
The excursion proceeds from Giessen via Limburg to the Hintertaunus region. The first three sites are situated in the eastern Hintertaunus (Fig. 7): 1. A slate quarry near the village of Langhecke demonstrates characteristics and properties of fresh slates (Fig. 9).
2. The saprolite open-cast mine "Töpferkaute" at the margin of the village of Eisenbach shows exposed terrestrial saprolite with periglacial superficial layers.
3. The saprolite open-cast mine "Ölkaute" near the village of Eisenbach shows exposed semi-terrestrial saprolite with periglacial superficial layers.
Two further sites are situated in the western Hintertaunus: 4. An autochthonous pre-Upper Oligocene Plinthosol above saprolite from Lower Devonian slates and covered by Upper Oligocene volcanic tuff, basalt and a sequence of periglacial superficial layers will be presented near the village of Biebrich.
5. An autochthonous Miocene Plinthosol, developed from alluvial sediments above quartz gravels and covered by a sequence of periglacial superficial layers, is exposed in a gravel pit near the village of Wasenbach.

Methods of investigation
In the following section, the procedures of physical, chemical and mineralogical soil analyses are briefly cited. They are described in detail in the method book of Blume et al. (2011). The procedure of isovolumetric balance of element masses in saprolites, which explains the mass losses and provides important information about the genesis of saprolites, is explained in detail Sect. 4.2.

Soil analytical procedures
The following analytical procedures were employed: -Texture of fine soil < 2 mm. After extraction of humus (H 2 O 2 ), carbonates (HCl) and iron oxides (Na dithionite, citrate and bicarbonate) and dispersion with Na 4 P 2 O 7 , the fractions were separated by wet sieving (2-0.02 mm) and a pipette method (20 to < 2 µm).
-Pedogenic oxides. Amorphous Fe (Fe o ) and Mn oxides (Mn o ) were extracted with NH 4 oxalate while the total amounts of pedogenic Fe (Fe d ) and Mn oxides (Mn d ) were extracted after dissolution with Na dithionite, citrate and bicarbonate; amorphous Al (Al l ) and Si oxides (Si l ) were extracted after dissolution in 0.5 M NaOH. The concentrations of all metal ions were measured with an atomic adsorption spectrometer (AAS).
-Total amounts of main and trace elements. Melt tablets were analysed using XFA (X-ray fluorescence analysis; Philips PW 1480).

Isovolumetric mass balance of saprolites
Saprolites are characterized by mass losses due to dissolution of weatherable minerals, mainly silicates, followed by the export of dissolved elements with percolating pore solution or migrating groundwater. Mass losses increase with age and intensity of weathering and, thus, from the weathering front at the saprolite-rock boundary with decreasing depth towards the land surface, until all weatherable minerals are dissolved (e.g. Table 2). The increasing porosity of saprolites and the potential of the self-energizing of weathering processes result from increasing mass losses, as well as the decreasing mechanic stability of the saprolite, which makes it breakable, friable, soft and easy to erode. Therefore, bulk mass losses are an indicator for the degree of weathering, porosity and mechanic stability of a saprolite. A calculation of element mass losses (Sect. 4.2.3) indicates which elements were exported to which degree. Their geochemical behaviour allows the reconstruction of chemical processes and factors in the different saprolite zones.

Test on homogeneity of parent rock and saprolite with Ti / Zr ratios
The quantification of the mineralogical and geochemical differences between saprolite and parent rock requires an extensive petrological investigation of the unweathered and weathered samples. An increasing proportion of quartz sand is indicated by decreasing Ti / Zr ratios, while the opposite is the case with decreasing sand content. The contents of Ti in fresh weathered slates is 0.6 mass % (n = 10, SD = 0.1 %), mainly bound in rutile, which is associated with mica (Mosebach, 1954) and therefore narrowly correlated with K t (r = 0.92 +++ , n = 10). Zr with average concentrations of 213 mg kg −1 (n = 10, s = 39 mg kg −1 ) in unweathered slates is bound in the heavy mineral zircon. With increasing contents of quartz sand, the Zr contents also increases, which causes the narrow correlation between Si t and Zr (r = 0.97 +++ , n = 10). On the other hand the contents of muscovite illite and the associated contents of rutile decrease with increasing contents of quartz (Si t / K t : r = −0.93 +++ , n = 10; Si t / Ti: r = −0.91 +++ , n = 10). Therefore, the concentrations of Ti and Zr change oppositely with a change of texture of the slates and the ratios can be used as a marker of parent material homogeneity. From the Ti / Zr ratios of 150 samples of fresh slates and saprolites and determination of textural composition, a classification of textural units was possible (Felix-Henningsen, 1994): Ti/Zr > 5 silty clay slate, Ti/Zr 5-4 clayey silt slate, Ti/Zr 4-2.8 sandy silt slate, Ti/Zr < 2.8 silty sandstone and greywacke.

Total mass losses of saprolites
Mass losses of saprolites compared to the fresh rock result from the export of elements, released from dissolving minerals, due to leaching with percolation or groundwater. Also, mass gains are possible, which result from precipitation of dissolved elements within a saprolite zone. The determination of volume of fragments of rock and saprolite is performed by weighing fragments, saturated with penetrating oil       Till and Spears, 1969). Of the horizons, R is fresh slate, Cv is weathered slate and Cj is saprolite. Of the neo-formed minerals, Sm is smectite, Chl-V is chlorite-vermiculite mixed layer minerals and K is kaolinite. (e.g. WD 40), under submersion in water. The bulk density in g cm −3 results from the ratio of the weight of the dried fragment (105 • C) and its volume. The total mass loss is indicated by the difference of bulk densities (volume weights) of fresh rock and saprolite: where b.m.l. is mass loss (g 100 cm −3 ) and b.d. is bulk density (g cm −3 ).

Element mass losses of saprolites
A 100 % mass of rock or saprolite is geochemically defined by the sum of main element oxides (determined by XRF, Xray fluorescence) plus the loss of ignition in mass % (Table 3). As weathering of saprolites did not change the volume of rock, the comparison of volume-related element masses of fresh rock and saprolites is the best and only way to identify the real extent of element losses and gains in saprolites. Therefore, the masses of individual element oxides per volume (Table 4) have to be calculated as follows: where mE c is the contents of main element oxide (g 100 g −1 = mass %, Table 3), mE m is the volume mass of the main element oxide (g 100 cm −3 = vol %, Table 4), LOI c is the loss of ignition (mass %), LOI m is the volume mass of loss of ignition (g 100 cm −3 ) and b.d. is bulk density.
Correspondingly, the masses of trace elements can be calculated and balanced.
The summarized volume masses of main elements and LOI account for the bulk density (g 100 cm −3 , Table 4 The differences between the volume masses of main element oxides and LOI, respectively, in rock and saprolite show the individual mass losses and gains of element oxides (and LOI) ( Table 5): where mE m is the mass loss or gain of element oxides (g 100 −1 cm −3 ). The total mass loss as well as individual mass losses of element oxides and LOI of saprolites (Table 5) in relation to the volume weight of element oxides and LOI, respectively, in the fresh rock (Table 4) shows the relative mass loss of element oxides (and LOI) in % (Table 6): The individual mass loss of element oxides and LOI in relation to the bulk mass loss (Table 5) results in the relative element oxide composition of the bulk mass loss in % ( Table where b.m.l. is bulk mass loss (= 100 %) and mE m is the mass loss of main elements and LOI (g 100 −1 cm −3 ).

Contents and losses of quartz
Silica makes the main contribution to the bulk mass losses of elements in saprolites due to desilication, which is also an indicator for a warm humid (sub)tropical climate. Potential sources of Si are silicates and quartz. The silicate mineral in slates with the lowest weathering stability is Fe-Mg chlorite, which shows a SiO 2 : Al 2 O 3 molar ratio of 1.99 (n = 11, after selective extraction with 2 N HCl, 80 • C), while kaolinite, which was newly formed from chlorite, shows a ratio of 2. Therefore, a quantitative neo-formation of kaolinite from chlorite did not lead to desilication. Furthermore, near the basis of saprolites, the neo-formation of smectites with a SiO 2 : Al 2 O 3 molar ratio of 5.12 (Weaver and Pollard, 1973:67) after weathered chlorites indicates that the dissolution of fine grained quartz must have mainly provided the high concentration of dissolved silica. The contents of quartz was determined by XDA (X-ray diffraction and absorption) according to the procedure described in Till and Spears (1969). The contents of quartz (mass %) is converted into mass per volume (g 100 −1 cm −3 ) and is isovolumetrically balanced (Table 8). The results show that dissolution and leaching of up to 18 % of the original quartz content in the fresh slate largely contributed to the loss of silica and the bulk mass loss of saprolites.

Contents of clay minerals and crystallinity of kaolinite
The contents of kaolinite as the neo-formed mineral after Fe-Mg chlorite (and in part smectite) was determined according to Islam and Lotse (1986). The contents of kaolinite were calculated from the amount of extracted Al after dissolution of the clay fraction in 0.5 N NaOH (80 • C, 3 min). All clay minerals were determined by X-ray diffraction (XRD) of oriented specimen of the natural clay fraction < 2 µm, dispersed in water, before and after saturation with ethylene glycol, K + , fumigation with DMSO (dimethyl sulfoxide) and heating (1 h 450 and 550 • C).
Well-ordered kaolinites can be identified by a peak-triplet at 20-25 • 2θ in X-ray diffraction diagrams (Cu radiation). Such kaolinites occur as white monomineralic precipitates and filling of veins in semi-terrestrial saprolites. Kaolinites of paleosols and saprolites (references in Felix- Henningsen, 1990Henningsen, , 2015, which mainly developed topotactically during the alteration of primary silicates, belong to the less ordered type of b-axis disordered kaolinites and fireclay minerals. These fractions can be distinguished by the expansion after intercalation with DMSO. As a result of fumigation of an oriented XRD clay specimen (70 • C for 72 h) with DMSO, wellcrystalline and b-axis disordered kaolinites, which are abundant (> 90 %) in saprolites, expand from 0.72 to 1.12 nm (Fig. 8).
On the contrary, the clay fraction (> 60 mass %) of the paleosol shows an increasing proportion (up to 90 %) of fireclay from the saprolite to the former topsoil. Fireclay does not expand after treatment with DMSO (Fig. 8). Therefore, DMSO intercalation allows the sources of kaolinites (from saprolites) and fireclay (from paleosol) in sediments to be Figure 9. Fresh slate of the Rhenish Massif with nearly vertical cleavage planes, covered by a layer of rock fragments due to periglacial congelifraction, exposed at the bottom of a valley in the eastern Hunsrück. In such deeply incised valleys the MTV has been completely eroded.
identified, and the results support the geomorphological reconstruction of landscape development.

Village of Langhecke: fresh slates
Clastic sedimentary rocks developed from shallow marine sediments of the Lower Devonian and have the largest extension in the Rhenish Massif. As a consequence of diagenesis and anchi-metamorphosis during the Variscian orogenesis, the pelitic sediments, 5-10 km thick, were transformed to folded clay and silt slates, while intercalated banks of greywacke sandstones originated from sand sediments (Fig. 9). Due to the diagenetic transformation of silicate minerals during the Variscian orogenesis, released silica was concentrated in milky quartz veins. Detritic organic matter of the marine sediments changed to coaly bituminous substances, which cover the surfaces of phyllosilicates and cause the black colour of the slates. Also in the Hintertaunus re- gion, Lower and Middle Devonian clay and silt slates, intercalated with banks of greywacke and greenstone, served as parent rock of the MTV.
The occurrence of fresh slates near the recent land surface is bound to the extent of Tertiary and Quaternary denudation of the MTV, which is up to 150 m thick. In the central and most uplifted areas (∼ 450-900 m a.s.l.) of the Rhenish Massif the weathering mantle was largely removed. Because of congelifraction of the exposed slate and solifluction, a basal layer of slate fragments developed during Quaternary periglacial periods, covered by a thin Late Pleistocene main layer of redistributed loess and pumice (Fig. 10).
In the less tectonically uplifted (∼< 450 m a.s.l.) lower and marginal zones of the mountainous region with thick remnants of the MTV, fresh slates only occur at the bottom of deeply incised erosion valleys (Fig. 11). As the clay slates of the Rhenish Massif have been used since Roman times as cover for roofs and walls of houses, they have been mined in open-cast and subsurface mines until today.
The excursion site at village of Langhecke shows an example of the occurrence of fresh slates, exposed in a former slate mine at the bottom of such an erosion valley. They display characteristics as described in the following points.
-Bulk densities are measured to be 2.50-2.58 g cm −3 for clay slates and 2.67-2.69 g cm −3 for silt slates.

Eisenbach Töpferkaute: terrestrial saprolite from slates
The open-cast clay mine Töpferkaute at the margin of the village of Eisenbach is situated at the north-west-exposed middle slope of the River Eisenbach valley (Fig. 6), which already started to incise during the Tertiary, and about 60 m below the remnant of a planation plain on which the Eisenbach Ölkaute excursion site is situated (see Sect. 5.3).

Saprolite
The profile, 25 m deep, exposes a terrestrial saprolite from fresh and nearly fresh slate to the upper, strongly weathered   zones. The individual zones are interfingered over distances of many metres. Interfingering is a typical phenomenon in deep weathered slates because the more or less steep inclined to vertical cleavage planes and tectonic joints cause differences in permeability and weathering intensity between jointed and massive parts of the slate. In the lowermost saprolite zone (Cj5 , Table 9), the blackgrey colour of the slate changes to an olive colour along cleavage plains and joints as a consequence of oxidation, which increases to the upper saprolite zones (Cj4, Table 9). The loss of primary coaly bituminous organic matter follows the penetration of air into the rock matrix and indicates an increase of porosity in the wake of dissolution of minerals and export of dissolved elements. This is confirmed by mass losses (Fig. 14) as well as the loss of mechanical stability. Within the olive-coloured parts, inner crystalline oxidation transformed the primary chlorites to chlorite-vermiculite mixed layer (m.l.) minerals, which occur beside kaolinite. The Stephan Schmidt KG mines this saprolite zone for use as a greenhouse substrate. The colour of the higher saprolite zones (Cj1-Cj3, Table 9) changes to brown, light and dark red and purple-red, as all iron-bearing silicates weath- Figure 13. Eisenbach Töpferkaute, terrestrial saprolite: volumetric masses of iron fractions (mineralogically bound Fe III min and Fe II min , as well as free iron oxides Fe d ) and trace elements of fresh slate and saprolite. ered completely, and free iron oxides, which precipitated as goethite and hematite, were formed.
Leaching of elements by percolation water under oxidizing conditions caused mass losses of 25-30 % of the original rock mass (Fig. 12) and a loss of stability of the saprolite, which changed to a soft, friable material. Especially Si, Al, bases and to a minor extent also Fe contributed to the mass loss. The loss of dissolved SiO 2 and bases was a consequence of weathering of silicates and leaching of dissolved elements under warm (sub)tropical climatic conditions, as the mobility of silica depends only on the temperature of the weathering solution. Because of the desilication the amorphous Si fraction of the saprolite is impoverished relatively to the contents of amorphous Al compounds (Table 11). The losses of total Al 2 O 3 (Fig. 12), dependent on acid conditions (pH < 4.5) and complexation by dissolved organic matter, increased above the lowermost saprolite zone, as the buffer capacity decreased after the leaching of bases. This also shows that Al, released from the primary silicates, was not quantitatively captured in neo-formed kaolinite. Restricted to the lowermost saprolite (Cj5, Fig. 12), Fe 2 O 3 contributes to the mass loss as intermittent waterlogging above the massive fresh slate supported the mobilization of iron under reducing conditions. In the upper saprolite zones (Cj1-4, Fig. 12) the mass loss of iron does not increase any more as the oxidizing conditions caused the formation of immobile oxides. ued under terrestrial conditions during the middle Miocene warm humid period.

Periglacial layers and Holocene soil
The saprolite is covered with periglacial layers up to several metres thick, which are the parent material of the Holocene Stagnic Luvisol. The analytical data are displayed in Tables 10-12. The basal layer consists of material from the uppermost saprolite zone, redistributed by solifluction, covered by a middle layer of loess and an uppermost main layer of loess mixed with pumice of the Late Pleistocene Laacher See eruption (Table 9). Therefore, the texture of the middle and upper layer is rich in coarse silt, typical of the large proportion of loess. The basal layer shows high clay contents as a consequence of intensive periglacial congelifraction of redistributed saprolite material and the admixture of substrate of a periglacially reworked paleosol rich in kaolinitic clay, which is indicated by the high total amounts of kaolinite in the clay fraction (Table 12). They also contain weakly weathered three-layer silicates, which in the main and middle layers derive from loess. In the basal layer, they originate from redistributed material of less weathered, lower saprolite zones, which were exposed by denudation in upslope areas. Due to congelifraction, cryoturbation and lateral transport the material was admixed to solifluction layers.

Saprolite
Since 1866, white, bleached saprolite has been mined in the Ölkaute quarry, near the village of Eisenbach, as raw material for the ceramic industry. The exposed saprolite from silt slate (Table 13) presents the transition of the bleached horizon (mCewj), up to 10 m thick, to a grey saprolite (mCorj) and further down a black-coloured saprolite (mCrj). In both zones the undisturbed rock structure of the slates is preserved, although the saprolite is strongly weathered, friable and can be disintegrated manually. According to the pedogenic iron forms (Table 15) and clay mineralogical composition (Table 16) differences between the saprolite zones exist. The white colour of the mCewj zone (Figs. 15 and 16) proves that the dissolution of all iron-bearing silicates and the formation of kaolinite, as well as the leaching of bases, silica and metal ions must have occurred under reducing conditions as a result of saturation with migrating ground water. Therefore, Fe and Mn ions, released from silicates, remained mobile and were completely leached with a lateral groundwater flow. The decay of the primary organic matter in the bleached horizon, which until today is still present in the lower saprolite zone with sustainable reducing conditions, is a consequence of oxidation after the lowering of the groundwater table. This went along with the tectonic uplift of the Hintertaunus area and regression of the nearby sea since the Figure 14. Eisenbach Ölkaute, semi-terrestrial saprolite: main element composition (vol-wt in g 100 −1 cm −3 ) of fresh slate and saprolite, isovolumetric bulk mass losses (ML) and relative elemental composition of mass losses (in % of the bulk mass loss).   Table 14. Eisenbach Ölkaute -texture of the fine earth (< 2 mm), free of humus and carbonates (texture analyses of saprolite were performed with ground material; therefore the data present the relative disintegration but not the real particle size of the original slate texture). Fractions: g, m and f are coarse, middle and fine; S is sand, U is silt and T is clay. Depth refers to the lower boundary.  Bulk mass losses are clearly higher within the bleached and reduced zones (Fig. 14) than in the terrestrial saprolite of Eisenbach Töpferkaute (Fig. 12). Because of leaching under reducing conditions, iron and other metal ions are strongly depleted (Fig. 17). Therefore, iron oxide contributes more than 25 % to the bulk mass loss. The relative proportion of SiO 2 in the bulk mass loss increases from the lower to the uppermost saprolite zone and indicates the increase of desilication. As only the illite minerals weathered to kaolinite while muscovite remained stable, the losses of K 2 O are rather low.

Soil sediment
A former erosion gully, several metres deep (Fig. 16), which extended from the former plantation plain downwards to a valley, cut through the bleached saprolite and was filled with soil material of a red-white mottled Plinthosol after the soil has been undercut by linear erosion of the soft saprolite. It broke down and was mixed with fragments of the bleached saprolite. The paleosol material has a clay content around  (Table 14), typical of Cretaceous-Paleogene fersiallitic paleosols. The reason for such a high clay content is the weathering of muscovite remaining stable within the saprolite and the transformation to kaolinite (65-70 mass %) and illite (30-35 mass %). Up to 50 % of the kaolinite fraction consists of fireclay. The negligible contents of fireclay within the saprolite shows that the formation of fireclay is typically bound to fersiallitic and ferrallitic paleosol horizons, which were subject to strong desilication.
From the characteristics of the soil sediment and the analytical data the processes of soil formation, such as acidification, weathering of silicates and desilication and neoformation of kaolinite, can be concluded. The isovolumetric balance shows that the volumetric contents of Fe 2 O 3 in the soil sediments match those of the fresh slate (Fig. 14). Iron obviously was not leached from the paleosol. This could be a consequence of permanent oxidizing conditions within the soil zone, which did not allow an enhanced mobility of iron. The fact that the underlying saprolite is nearly free of mineralogically bound iron and completely depleted in free iron oxides leads to two hypotheses: a. If bleached saprolite became the parent material of the soil after phases of erosion of previous soils (e.g. due to  (Tributh and Lagaly, 1989).
Paleogene climate changes or tectonic uplift), the contents of iron oxides must have been supplied by precipitation of iron in the capillary seam of the groundwater. This seems to be less possible, as the saprolite below is completely depleted in iron, which means that the iron concentration of the groundwater was extremely low.
b. The high iron content of the paleosol results from the weathering of the fresh slate under terrestrial conditions at the beginning of the formation of the weathering mantle and before the saprolite with the groundwater body was formed. According to this, during the whole period of formation of the weathering mantle, the soil surface was stable and little erosion took place. In the case of erosion, the primarily formed soil horizon was removed with time and the bleached saprolite became the parent material. This remains to be an unresolved question.

Silicified fluvial sediment
The western wall of the saprolite open-cast mine cuts a bank of fluvial sediments, superimposing the soil sediment fill of the former erosion gully and the adjacent bleached saprolite. The sediments consist of partly silicified and cemented pure quartz sand with gravel of well-rounded milky quartz, which derived from erosion of less weathered primary quartz veins within the saprolite. Less rounded boulders of Taunus quartzite, up to 40 cm in diameter, indicate a long distance transport of the fluvial sediments because the next sources of Taunus quartzite are located more than 3 km away in a south-south-east direction. They must have been sedimented in the Upper Oligocene Vallendar river system on the Pale-ogene planation plain, before the tectonic subsidence of the fault blocks and the incision of the Late Tertiary and Quaternary valleys, separating the planation plane around Ölkaute from the High Taunus. The isovolumetric balance of elements (Fig. 14) shows a strong absolute accumulation of silica, indicating silification as a consequence of (semi-)arid climate conditions, which existed throughout Middle Europe in the transition from the Upper Oligocene to the Lower Miocene.

Periglacial layers and Holocene soil
The uppermost layers, 2 m thick, above the Tertiary fluvial sediments consist of periglacial layers, organized in basal, middle and main layers (Table 13). The basal layer is free of loess but rich in clay (Table 14) and consists of a more or less brown to white loam, which derived from congelifraction of the saprolite. During thaw periods the porous saprolite was saturated with water, which caused rapid congelifraction during the frost periods. The disintegration of kaolinite aggregates (booklets), which tend to develop as pseudomorphoses of weathered silicates, severely enhanced the clay content. Admixture of saprolite zones and paleosol material increased the contents of pedogenic iron. The contents of amorphous silica and aluminum correlate with the contents of clay (Table 15). The middle layer is dominated by loess but contains also a proportion of material of the basal layer, rich in clay. The pedogenic SBt horizon characterizes a Stagnic Luvisol. Micromorphological analyses show that the majority of the clay cutans were destroyed by periglacial frost pressure and therefore occur as fragments and coatings as zones within the loess matrix, apart from recent voids. Thus, a pre-Holocene formation of a relic Bt horizon is probable. The main layer consists of loess mixed with pumice of the Laacher See eruption and shows clay accumulation in its basal part and impoverishment of clay in the upper part as a consequence of Holocene weathering and clay migration.

Burgkopf basalt quarry: autochthonous pre-Upper Oligocene Plinthosol
Near the village of Biebrich, the flat basalt dome, Burgkopf, rises above the Tertiary planation plain, covered by loessial periglacial layers with a strong admixture of Vallendar gravel, which intermits with the rise of the dome. The wall of a former quarry, in which basalt columns of the Upper Oligocene basalt duct were mined, exposes the profile of an autochthonous Plinthosol, about 4-6 m thick, above bleached saprolite from Devonian slates and sandstones (Table 17, Fig. 18). The volcanic basalt duct cuts through the paleosol which was preserved below a layer of laminated basalt tuff. This confirms a pre-Upper Oligocene age of the paleosol. High contents of clay above 50 mass % (Table 18) and pedogenic oxides (Table 19) indicate an intensive weathering
The contents of pedogenic oxides are high and decrease with depth following the decreasing intensity of weathering. During the eruption of the volcano, heat and moisture caused auto-hydrothermal processes that overprinted the layer of basalt tuff and led to silification and induration, as well as the formation of pure smectite concretions and veins. The basalt of the duct as well as a zone of the adjacent Plinthosol, 50 cm thick, also show a neo-formation of smectite.
Kaolinitization continued after the volcanic activity and caused the neo-formation of kaolinite from mafic minerals of the basalt tuff (Table 20).
The deposition of periglacial layers above the basalt tuff started with the accumulation of coarse fragments of basalt columns and boulders as a basal layer. The subsequently deposited loess of the middle layer invaded the hollows of the loosely packed rock fragments of the basal layer. The middle layer was subject to weathering and formation of a Luvisol during a pre-Holocene interglacial period. Micromorpholog-ical investigations of the Bt horizons show that clay cutans of former pores are disturbed and squeezed by frost pressure or cryoturbation, while recent pores show no signs of accumulation of fine clay. The main layer, which consists of a mixture of loess and pumice of the Late Pleistocene Laacher See eruption, shows a clear clay enrichment near the basis as a consequence of Holocene soil formation.
ering mantle. The abrupt changes in particle size, intercalated channel structures and banks of ferrous silcrete indicate the activity of a shallow river with intermittent rates of streamflow. Such sediments are typical of semi-arid climatic conditions with alternating rain and dry seasons. The fluvial sediments change from gravel to sand up to the surface and the contents of fine material progressively increases. The uppermost layer was deposited as flood plain sediments, rich in silt and clay, from which an autochthonous Plinthosol with intensive red, white and yellow mottles developed under the influence of an intermittent depth of the groundwater table (Fig. 20, Table 21). Soil development occurred probably during the Miocene. The contents of silt and clay (Table 22) and pedogenic oxides (Table 23), as well as total amounts of Al, Fe and heavy metals, bound in silicates, increase from the lowermost horizon to the surface of the Plinthosol. The clay fraction consists of illite and kaolinite in similar proportions (∼ 40 % kaolinite and ∼ 60 % illite) in all horizons (Table 24). Kaolinites of the Vallendar gravel mainly derive from reworked saprolite. The proportion of kaolinite increases from the gravel to the upper Plinthosol horizons and indicates that erosion of terrestrial kaolinitic soils (e.g. Ferralsols, Plinthosols) may have delivered the fines of the flood plain sediment rather than the weathering of primary silicates in situ. With increasing inclination of the land surface in the direction of the former Tertiary trough valley the paleosol during Pleistocene cold phases was affected by soil creep and slope downwards, increasingly incorporated into basal solifluction layers. The basal layer of the periglacial slope deposits consists of horizontally laminated, redistributed Plinthosol material. The middle layer, rich in loess with quartz gravel, and the main layer, consisting of a mixture of loess with Laacher See pumice, superimpose the basal layer. Both layers served as parent material for the Holocene Stagnic Luvisol.

M. Fuchs
Preface: Quaternary and Tertiary landscapes and their sediments in Hesse, Germany -a guidebook to selected field trips on geology, geomorphology and geoarchaeology 1

F. Volker and
Field