Bedrock, Quaternary sediments and recent fault activity in central Lake Neuchâtel, as derived from high-resolution reflection seismics

Abstract

A high-resolution seismic reflection survey (ca. 65 km) was conducted in the central part of Lake Neuchâtel in order to trace the continuation of the major strike-slip fault of La Lance across the lake. On seismic data, this dextral fault appears at the top Molasse/Mesozoic bedrock as a ca. 1 km wide zone affecting the top Molasse and offsetting the Mesozoic. These seismic observations can be correlated with onshore data. Four seismic facies are distinguished and interpreted from bottom to top within the Quaternary: glacial, subglacio-lacustrine, glacio-lacustrine and lacustrine. They show similarities with other perialpine lakes (Lake Geneva, Lake Annecy, Lake Le Bourget). Slumps and faults affecting the upper part of the Quaternary may be associated with the recent activity of the La Lance fault zone. Moreover, glacial erosion of the Molasse bedrock seems to have been locally guided by active tectonics.Key wordsfaultglacial sedimentationhigh-resolution seismicMolasseneotectonicsQuaternary infillseismic facies