23-25 September 2013
GEOMAR East shore
Europe/Berlin timezone
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Subaquatic landslides and fluid expulsion features within the sedimentary archive of Lake Neuchâtel, Switzerland

Presented by Anna REUSCH on 23 Sep 2013 from 17:15 to 19:15
Type: Poster presentation
Session: Poster session
Track: Poster presentations

Content

Subaquatic landslide deposits are important components of the sedimentary infill of lakes. Lakes offer the unique possibility to study subaqueous mass-wasting phenomena, similar to the processes in marine environments, under more accessible and spatially confined conditions. Lake sediments are highly sensitive archives of environmental changes and geological events, such as earthquakes. Previous studies linked subaquatic landslide deposits to historic earthquakes, in the marine, as well as in the lacustrine realm. Synchroneity of multiple mass-transport deposits at different locations within a basin is the main criterion to postulate seismic triggering. Additionally, subaquatic landslide events are often accompanied by fluid expulsion features. In this study, we investigate the sedimentary archive of sublacustrine mass-transport deposits in Lake Neuchâtel, Western Switzerland. We show that sublacustrine slopes failed several times since Late Glacial times and that these multiple landslide events were accompanied by expulsion phases of large-scale pockmarks on the lake floor. Eventually, this project aims to investigate the potential link between sediment remobilization, fluid flow and neotectonic activity. We present results from an extensive high-resolution reflection seismic and swath bathymetry survey, as well as newly acquired and published sediment-core data. Swath-bathymetry data (Kongsberg EM 2040 multibeam) provide precise high-resolution lake floor morphological data. Dense grids of high-resolution reflection seismic data (3.5 kHz pinger source) are used to image the sedimentary infill of the Lake Neuchâtel basin with decimeter-scale vertical resolution. Additionally, selected morphological features were investigated using ultra-high-resolution lake-floor surface and subsurface imaging tools (sub-bottom profiler [0.6 – 15 kHz Chirp System] and side scan sonar) mounted on an autonomous underwater vehicle (AUV “MARUM SEAL”). This allows for systematic mapping of mass-movement deposits, landslide scars and fluid-seepage structures. Results of the sediment cores, integrated with seismic data, indicate sequences of interbedded lacustrine background sediment and thin turbiditic deposits, which are intercalated with mass-transport units. Seismic-stratigraphic correlation is used to determine the chronostratigraphic relations between the mass-transport units assigned to seismic-stratigraphic event horizons. Our data reveal strong evidence for at least two distinct seismic-stratigraphic horizons with multiple, basin-wide subaquatic landslides in the sedimentary record of Lake Neuchâtel. These multiple landslide event horizons are interpreted as the fingerprint of past earthquakes. Furthermore, seismic reflection and swath-bathymetry data image large pockmarks of up to 160 m in diameter and 30 m depth. Geochemical and hydrological analyses on the pockmarks are ongoing, and further analysis will reveal whether these features indicate active fluid seepage structures, possibly related to karst features (e.g. sublacustrine karst springs) and/or migration pathways along possibly active fault zones. The edges of these pockmarks are characterized by several distinct overflow deposits, clearly showing multiple phases of outflow events at discrete periods in the past. Seismic-stratigraphic correlation reveals that two of the multiple landslide horizons correlate with pockmark overflow-events, suggesting that landslide and overflow deposits were emplaced simultaneously or within a very short time period. A causal link between multiple landsliding and fluid-expulsion activity, likely triggered by past earthquakes, is hypothesized. Future investigations, which include dating of the event horizons for correlation with independent paleoseismological archives, will reveal whether the observed event horizons relate to past seismic activity.

Place

Location: GEOMAR East shore
Address: Wischhofstr. 1-3 / D-24148 Kiel
Room: Lithothek

Primary authors

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Co-authors

  • Dr. Jasper MOERNAUT ETH Zürich, Geological Institute (Sediment Dynamics)
  • M. HILBE Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Surface Waters, CH-8600 Dübendorf
  • J. MOSAR University of Fribourg, Department of Geosciences, CH-1700 Fribourg
  • G. MEINECKE Marum, Center for Marine Environmental Sciences, D-28359 Bremen
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