2004 - 2006
|Sedimentary dynamics and
paleogeography of Middle Pleistocene (Saalian) glacial lakes in the
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).
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.
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
early Saalian glacial lake deposits (NW Germany): evidence of local ice
margin retreat and associated calving processes. Sedimentary Geology,
Winsemann, J., Hornung
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.