Mesozoic calci turbidites in Deep Sea Drilling Project hole 416A, eastern North Atlantic - recognition of a drowned carbonate platform.

Abstract

This Tithonian-Hauterivian section contains c 10% limestone and marlstone interbedded with shale and sandstone. Depositional structures, grain composition, and diagenetic fabrics of the limestone beds as well as association with graded sandstone and brown shale suggest their deposition by turbidity currents below CCD. Carbonate material was initially shed from a shallow-water platform with ooid shoals and peloidal sands. Soft clasts of deep-water carbonate muds were ripped up during downslope sediment transport. Shallow-water mud of metastable aragonite and Mg calcite was deposited on top of the graded sands, forming the fine tail of the turbidite; it has been subsequently altered to tight micritic limestone. Drowning of the platform during the Valanginian is inferred from the disappearance of the micritic limestones, the increase in abundance of phosphorite, of ooids with quartz nuclei, and of the quartz content in the calciturbidites. In Hauterivian time, the carbonate supply disappeared completely. -from Author Rosenstiel School of Marine and Atmospheric Science, Division of Marine Geology and Geophysics, University of Miami, Miami, Florida.