Palaeoseismology from microfabric and geochemical analysis of lacustrine sediment, Windermere, UK

Abstract

Lake sediments commonly contain detrital layers that record events such as floods or earthquakes but these may be disturbed or partially destroyed by bioturbation. Here we use a novel combination of techniques to relate microscopic sediment fabric features to lake-basin scale processes. X-radiography and micro-XRF of cores are complemented by backscattered electron imagery and energy dispersive X-ray microanalysis of resinembedded
sediment. Together, the microfabric and geochemical methods enable the
identification of clay-layer mass transport deposits despite bioturbational mixing of the original end members. Two cores with robust radionuclide chronologies contain correlative clay layers dated to 1979 (1974 – 1982) and 1979-1980 (1973 – 1986) respectively. These clay layers likely represent the distal turbidite generated by a major mass flow deposit identified from multibeam swath bathymetry and sediment grab sampling. A likely trigger
for the mass flow and associated turbidity current is the 4.7 ML 1979 Carlisle earthquake. The lake basin slope was likely preconditioned for failure by increased sedimentary biogenic gas production and sediment in-wash as a result of anthropogenic activities, coupled with sediment disruption and dredging. This study highlights the effectiveness of microstratigraphic techniques in the recognition and characterisation of event layers in sediments where bioturbative disruption has occurred.

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Identifiers

ORCID for Jonathan M. Bull: orcid.org/0000-0003-3373-5807

ORCID for Rachael S. Avery: orcid.org/0000-0002-4439-4174

ORCID for Peter G. Langdon: orcid.org/0000-0003-2724-2643

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