ALBERT

Description: The modern, over 250-m-deep basin of Lake Constance represents the underfilled northern part of an over 400-m-deep, glacially overdeepened trough, which reaches well into the Alps at its southern end. The overdeepening was formed by repeated glacial advance-retreat cycles of the Rhine Glacier throughout the Middle to Late Pleistocene. A seismic survey of Lake Constance revealed a Quaternary sediment fill of more than 150 m thickness representing at least the last glacial cycle. The stratified sedimentary fill consists at the base of ice-contact deposits on top of the molasse bedrock, overlain by glaciolacustrine to lacustrine sediments. During the successful field test of a newly developed, mid-size coring system ("HIPERCORIG"), the longest core (HIBO19) ever taken in Lake Constance was retrieved with an overall length of 24 m. The sediments recovered consist of a nearly continuous succession of lacustrine silts and sands including more than 12 m of Late Glacial sediment at the base. 14 lithotypes were identified through petrophysical and geochemical analyses. In combination with a 14C- and OSL-based age-depth model, the core was divided into three main chronostratigraphic units. The basal age of ~ 13.7 ka BP dates the base of the succession back to the Bølling-Allerød interstadial, with overlying strata representing a complete and thick Younger-Dryas to Holocene succession. The sediments offer a high-resolution insight into the evolution of paleo-Lake Constance from a cold, postglacial to a more productive and warmer Holocene lake. The Late Glacial succession is dominated by massive, m-thick sand beds reflecting episodic sedimentation pulses. They are most likely linked to a subaquatic channel system originating in the river Seefelder Aach, which is, despite the Holocene drape, still apparent in today’s lake bathymetry. The overlying Holocene succession reveals a prominent, several cm-thick, double-turbiditic event layer representing the most distal impact of the Flimser Bergsturz, the largest known rockslide of the Alps that occurred over 100 km upstream the river Rhine at ~ 9.5 ka BP. Furthermore, lithologic variations in the Holocene succession document the varying sediment loads of the river Rhine and the endogenic production representing a multitude of environmental changes.

Description: The basin sediments of Lake Constance encompass superior records of glacial to late glacial and Holocene environmental conditions but were hitherto not recovered from greater depths due to the lack of high-quality but inexpensive coring instruments. In a test and commissioning campaign in 2019, a new scientific coring device, called Hipercorig, was deployed and recovered from two parallel boreholes a 20 and a 24 m long drillcore and one two-m-long surface core (Harms et al. 2020, Schaller et al. 2022). The drill site is in 200 m deep waters close to the northwestern lake shoreline near the town of Hagnau and was selected based on new seismic surveys. They revealed an up to 150 m thick sediment fill of the overdeepened Lake Constance basin created by several advance and retreat cycles of the Rhine Glacier during the mid to late Quaternary. The deposits comprise proglacial sediments overlain by glaciolacustrine and finally lake strata. The latter make up the top 12 m of the core recovered while below sandy intercalations indicate downward increasing influence of dynamic sedimentation pulses that were deposited through subaquatic channel systems fed by declining glaciers and meltwater pulses from the north. The cores retrieved were sampled for microbiology and pore fluids at University of Constance (Germany). They were opened at Bern University (Switzerland) in fall 2019, sedimentologically described, instrumentally logged, and sampled for further studies including age dating. These data served to identify 14 lithotypes that were differentiated into three chronostratigraphic units based on a 14C- and OSL-based age model. The cores section base with the proglacial unit is about 13.7 ka BP old while the lacustrine strata cover Bølling-Alerød and Holocene ages. A prominent turbiditic event layer could be dated at 9.5 ka BP, coeval with the largest Holocene Alpine rock slide, the Flimser Bergsturz, that caused damming of the river Rhine and finally an outburst reaching as turbidite even northern Lake Constance. These initially gained data sets and the instruments utilized are described in the data description.