"GUTTER CAST" TEXTURE AS POSSIBLE CORRELATIVE MARKER - EXAMPLE OF LOWER TRIASSIC SEDIMENTARY SEQUENCE PLAVNO AND STRMICA (CROATIA AND BOSNIA AND HERZEGOVINA)

Lower Triassic (Scythian) sedimentary sequence developed in similar lithofacies were studied at two sections in vicinity of Knin - Plavno (in Croatia) and Strmica (in Bosnia and Herzegovina). Characteristics of the Siliciclastic lithofacies, which corresponds to the Lower Scythian, Seis beds, and of the Mudstone and Siltstone - mudstone lithofacies of Upper Scythian, Campil beds, reflect the storm influence at the shallower and deeper parts of shelf, as well as the sea-level oscilations resulting in a presumed 5th, 4th and 3rd order cycles. Appearance of gutter casts exposed on lower bedding planes of sedimentary rocks in Mudstone and Siltstone-mudstone lithofacies has been considered as a consequence of bottom current flow component in the outer shelf area. This unidirectional current flow has a helicoidal component with horizontal axis parallel to the sediment surface. The flow generates characteristic storm imprint on the broad shelf area. Lacking any other types of either the biostratigraphic or litostratigraphic marker horizons, this structure, having only one way of formation, allows the improvement of chronostratigraphic correlation of the vertical sequence on both explored locations. The firs appearance of this structure in sediment successions of Plavno and Strmica, may serve as possible correlative marker. Using such a correlative principle gutter casts are in vertical succession grouped in interval, which signifies approximately penecontemporaneous events. Should the correlation be based on the gutter cast structure, the differences in thickness at both location can be explained by their more proximal or more distal position within the sedimentary basin. If this is true, the inveterate principle of correlating the contact between of Lower Scythian and Upper Scythian sediments as a contact between the red, dominantly clastic Seis beds and grey, dominantly calcareous Campil beds, is therefore found to be chronostratigraphically inadequate and can be excluded.