Primary and secondary synsedimentary structures in the lagoonal Almere member (Groningen Formation, Holocene, The Netherlands)

Abstract

Two main types of synsedimentary structures are distinguished: those produced by the action of a transporting agent and those that have another origin. They are classified as primary synsedimentary and secondary synsedimentary, respectively. This distinction is thought to be useful, since only the first group may give information about the process of sedimentation itself and about paleocurrent directions. The second group might be indicative of sedimentation velocity and predominant grain size. In the sediments described here, the first group comprises parallel and irregular lamination, wave ripples, current ripples and orientated particles. These latter two structures allow the reconstruction of paleocurrent directions, which are compared with those found by the analysis of channel elongation and grain-size distribution. This leads to the conclusion that weak tidal currents towards the north and the south prevailed. The secondary synsedimentary structures are represented by graded bedding and shallow depressions. These latter were synsedimentarily deepened by the burden of the accumulating sediment. Their sizes vary from a few centimetres to several metres.