Trace fossil assemblages and their palaeoenvironmental significance in the Pliocene marginal marine deposits of the Baix Ebre (Catalonia, N.E. Spain)

Abstract

The Pliocene sedimentary filling of the Baix Ebre basin includes both a transgressive and a regressive sequence. During the transgressive period, buildups and bioerosion surfaces were developed on the most isolated areas of the paleorelief with low or no terrigenous sedimentation. Other nearshore areas were occupied by pebbly-sandy beaches including typically littoral trace fossils (Gastrochaenolites , Entobia, Skolithos) which change laterally and vertically to shallow bay sands and clays deposited in a rather restricted environment with low bioturbation dominated by J-burrows. The blue clays which underlie those deposits correspond to the maximum of the transgression, and they are fully bioturbated. During the regression, the marine deposits were sands and clays including different facies and ichnoas-semblages which correspond to bay deposits (Sinusichnus and Teichichnus-Fugichnia assemblages), sand bars (Skolithos assemblage) and restricted proximal environments (Teichichnus assemblage). The continental units, lacustrine and alluvial culminate the regressive sequence.