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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 northwe

deuqua special publications

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