Facies variability in Lower Liassic carbonate successions of the Western Dinarides (Croatia)

摘要

In the Western Dinarides the Lower Liassic carbonates are underlain by Upper Triassic “Hauptdolomit”, whereas the first appearance of the foraminiferOrbitopsella praecursor (Gümbel) marks the beginning of the Middle Liassic. Their composition, observed at several localities in Western Croatia, shows a correlation of sedimentation events, which took place during Early Liassic on the Adriatic-Dinaridic carbonate platform. Facies variability is interpreted as result of autocyclic sedimentary processes on which the carbonate platform reacted by periodical oscillations of sea-bottom near the fair-weather wavebase. As a consequence, the Lower Liassic carbonate successions in the Dinarides is characterized by stacking of two main types of coarsening-upward parasequences: (1) the basal part of the Lower Liassic succession is represented by parasequences composed of mudstones or pelletal-bioclastic wackestones as their lower members, and peloidal-bioclastic wackestone/packstones to grain-stones as their upper members; and (2) the upper part of the Lower Liassic succession with parasequences consisting of mudstones or pelletal-bioclastic wackestones overlain by ooid grainstones. Judging from the composition of parasequences and thickness relations of their members, the first type is interpreted to comprise late transgressive system tract (ITST) and/or early highstand system tract (eHST), while the second type corresponds to a late highstand system tract (1HST) and/or early lowstand system tract (eLST) of a third-order sequence.