The project was aimed to improve the reconstruction of Middle Pleistocene (Saalian) glacial lakes in the central Weser Valley and adjacent areas (Niedersachsen and Nordrhein-Westfalen, NW-Germany) and their associated coarse-grained sedimentary deposits.
Vast glacial lakes were formed during early Saalian glaciation in front of the Scandinavian ice-sheet in the region of the Weserbergland. Sediments of the basin center consists of varvites, mud and silt, whereas coarse-grained clastic sediment (gravel and sand) bodies became deposited along the basin margins, especially in the north (along the southern escarpments of the Weserkette and Wiehengebirge). These deposits, previously mostly interpreted as to be glaciofluvial in origin, can often be re-interpreted as glacilacustrine marginal deposits (subaqueous fans, deltas). Their sedimentation was controlled by the lake level and ice-margin dynamics. Local tectonics, isostasy or subsidence are not thought to substantially influence the sedimentation patterns (Winsemann et al. 2004).
Detailed logging and facies interpretation in outcrops near Veltheim led to the discovery of a large and complex subaqueous ice-contact fan system in front of the Porta Westfalica pass, which served as a major outlet for Saalian ice-sheet meltwater flow towards the south. The locally well preserved facies architecture reveals a highly dynamic system with strong changes in meltwater flow velocity, steadiness and sediment load, leading to the deposition of large-scaled, coarse-grained upper flow-regime bedforms under peak efflux conditions. The latter have been formed by supercritical jet-flows which were powerful enough to locate the hydraulic jump roller hundreds of meters downflow from the glacial tunnel outlet (Hornung et al. 2007). Sedimentation at the Porta Complex was further controlled by changes in lake-level, resulting in temporary transition into a proglacial deltaic system and local incision (Winsemann et al. 2009).
Coarse-grained subaqueous fan and delta deposits of the Middle Pleistocene Porta Fan/Delta Complex, Müller II open-pit near Veltheim, Porta Westfalica, NW
Germany. Outcrop height is about 10 m.
Hornung, J.J., Asprion, U. & Winsemann, J. (2007): Jet-efflux deposits of a subaqueous ice-contact fan, glacial Lake Rinteln, northwestern Germany. Sedimentary Geology, 193: 167-192.
Winsemann, J., Asprion, U. & Meyer, T. (2004): Sequence analysis of early Saalian glacial lake deposits (NW Germany): evidence of local ice margin retreat and associated calving processes. Sedimentary Geology, 165: 223-251.
Winsemann, J., Hornung J.J., Meinsen, J., Asprion, U., Polom, U., Brandes, C., Bußmann, M. & Weber, C. (2009): Anatomy of a subaqueous ice-contact fan and delta complex, Middle-Pleistocene, North-west Germany. Sedimentology, 56: 1041-1076.