Depositional environment of the late Triassic-Early Jurassic Abu Shaybah formation along the southern Neotethys

Abstract EN

The Late Triassic/Early Jurassic Abu Shaybah Formation at Gharyan in northern Libya consists of 96m thick succession of clastic and subordinate carbonate sediments that can be divided into two members; a lower tidal member and an upper fluvial member.

The tidal member comprises sandstone, siltstone, claystone and dolomites, and is characterised by the presence of rhythmic bedding, flaser bedding, symmetrical ripple marks, desiccation cracks, burrows and fossils.

These characteristics suggest that this member was deposited within a tidal environment.

The fluvial member is characterised by an erosive base nonfossiliferous, fining-upward sequences, trough cross-bedded sandstone, overlain and laterally intertonguing with varicoloured siltstone and silty-shale.

The dominance of unidirectional palaeocurrents and the silicified wood fragments indicate deposition in a fluviatile environment.

The fluvial system drained basinwards into a shallow-marine setting of the Tethyan ocean existed to the north.