Storm Influenced Shelf Sedimentation - An Example from the Lower Triassic (Scythian) Siliciclastic and Carbonate Succession near Knin (Southern Croatia and Western Bosnia and Herzegovina)

Abstract

Scythian sedimentary rocks exposed at Strmica and Plavno near Knin represent storm-generated deposits in inner (Lower Scythian) and outer (Upper Scythian) shelf settings. The Lower Scythian is represented by Siliciclastic facies which consists of two subfacies components - thin-bedded shale-siltstone-sandstone alternations attached to the distal part of the inner shelf, and a thick-bedded sandstone-oolite subfacies attached either to the proximal part of the inner shelf or to the shoreface. Repetitive alternation of these two subfacies which form the Siliciclastic facies is interpreted as high frequency sedimentary cycles possibly related to high-frequency sea-level changes which in turn induced wave-base oscillations. This is observed as a rapid introduction of high energy proximal inner shelf or shoreface deposits into a muddy, distal part of the inner shelf environment. Upper Scythian sedimentary rocks are lime mudstones with marls in the Mud facies, and with marls and calcarenaceous siltstones in the Siltstone-mudstone facies. No obvious cyclic periodicity was observed within these two facies except the random occurence of punctuated storm layers with basal skeletal lag (Mud facies) and silty material input in normally mud dominated outer shelf sedimentary rocks (Siltstone - mudstone facies). According to the facies characteristics the Lower Triassic succession near Knin is interpreted as a consequence of a low-term, possibly third-order sea level rise compared to the global sea level rise during the Scythian.