Preservation of trace fossils and molds of terrestrial biota by intense storms in mid-last interglacial (MIS 5c) dunes on Bermuda, with a model for development of hydrological conduits

摘要

We document massive deposition of carbonate sands along the south shore of Bermuda that were emplaced during one or two great storms during the last interglacial. As determined by their stratigraphic position and geochronological data, these deposits formed during marine isotope substage (MIS) 5c ca. 100 ka ago. Within a leeward set of eolian beds, evidence of a living landscape was preserved that includes delicate footprints of a shorebird (Scolopacidae, Catoptrophorus) preserved in frothy dune foreset beds. In the same stratigraphic unit, outlines of a standing forest of palm trees (Sabal bermudana), some evidently with fronds in place, were molded in the fine carbonate dune sand. All available evidence points to an MIS 5c sea level positioned several meters below the present datum, which would require great intensity of storms to transport such voluminous deposits well above present sea level. Waves and storm currents transported loose sediments from the shallow shelf onto the shore, where hurricane winds piled up sand sufficiently deep to bury established forests of 8-to 10-m-tall trees. Evidence of such powerful storms preserved in the rock record is a measure of the intensity of past hurricanes, and a possible bellwether of future storm events. Entombment of the trees involved rapid burial and cementation creating external molds in limestone, a process that is important in the development of vertical hydrological conduits commonly observed in eolianites.