Compositional variations during phases of progradation and retrogradation of a Triassic carbonate platform (Picco di Vallandro/Durrenstein, dolomites, Italy)

In this paper data are presented on the composition of sediments deposited at the toe of slope during progradation or retreat of Triassic carbonate pl atforms in the Dolomites (Italy). For this purpose a succession was studied from the toe of slope of a Triassic (Carnian) carbonate platform (Picco di Vallendro/Durrenstein. Dolomites, Italy). The microfacies analysis of sele cted calciturbidites sequences revealed a reduced input of oncolites and oo ids during progradation and an increase in clasts. The main input, however, was derived from the reefs on the platform. Retrogradation of the platform showed an increase of filaments and radiolarians (open ocean biota) as wel l as carbonate mud and a reduced input of grains that originated within the reefs on the platform. Both during progradation and retrogradation parts o f the platform were flooded and could produce excess sediment that could be exported to the surrounding basins. However, the absence of platform inter ior biota documents that progradation occurred from sediments of the reefal belt, probably during relative sea-level lowstands. Carbonate composition varies systematically with toe-of-slope progradation/retrogradation and, th us, argues for carbonate production as the main driver of the geometries ob served at the toe of slope.