CHANGES IN ENVIRONMENTAL CONDITIONS, BIOTA, AND DEPOSITIONAL PATTERNS WITHIN LOWER TRIASSIC CLASTIC AND CARBONATE DEPOSITS, MUĆ-OGORJE, CENTRAL DALMATIA (CROATIA)

Abstract: The Lower Triassic of the Muć-Ogorje area in Central Dalmatia (southern Croatia) is characterized by clastic and carbonate deposits which are investigated through a 230 m thick succession. The fossil associations identified point to a Dienerian age for the lower, and a Spathian age for the upper part of the studied profile, while trace fossils suggest deposits of Smithian age in the middle part, enabling comparisons with other successions in the region. Changes in sedimentology and associated biota throughout the succession, and environmental conditions are reconstructed for seven facies associations, the distribution of which suggests multiple oscillations in relative sea level. Sedimentary structures point to the influence of high environmental energy, possible storms, with signs of tectonic influence in the studied area. The study deposits lack ooid limestone intervals, which are well represented in other Lower Triassic sections in Croatia, Slovenia, Italy, and Hungary. Moreover, the study section exhibits changes in biota abundance, presence of organic-rich laminae and pyrite, as well as changes in siliciclastic input and transgressive-regressive cycles, especially within the upper, Olenekian, part of the succession studied. The results confirm that environmental stress was persistent throughout the Early Triassic, and contribute to our better understanding of the aftermath of the end Permian extinction and the environmental conditions of the western Tethys epicontinental shelf area.