Did an earthquake located off Jersey trigger a mudflow preserving the only loess outcrop known under the seas?
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- handle: 10670/1.s9gcny
- hal: hal-02958801
- doi: 10.1144/jgs2020-030
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info:eu-repo/semantics/altIdentifier/doi/10.1144/jgs2020-030
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Jean-Pierre Lefort et al., « Did an earthquake located off Jersey trigger a mudflow preserving the only loess outcrop known under the seas? », HAL-SHS : archéologie, ID : 10.1144/jgs2020-030
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A 5 m long core sample, retrieved from between Jersey and the Cotentin (France) has been studied using different techniques. Between the lower part and the top, the core is a yellowish loess, a black mud and a grey shelly formation. The basal formation, which displays a typical loess granulometry, is the only loess found anywhere in situ on the subtidal seabed worldwide. Elsewhere, this fragile sediment has always been washed out by the successive Quaternary transgressions. The overlying mud formation, which displays characteristics of a landslide, sealed the loess deposit. Because this core has been sampled on the rim of a submarine valley located in front of a major onshore geological disruption, clearly associated with an active seismic zone, it is possible that an earthquake triggered a slope failure causing a gravity collapse of materials that protected the loess deposit from subsequent erosion, although we cannot completely rule out the effects of a large flood.