Bio-chronostratigraphy and sequence stratigraphic interpretation of the Triassic succession of Socotra Island, Yemen

Along the eastern coast of Socotra Island (Yemen) a 220-m-thick marine Triassic succession is rather well exposed. The succession rests on a crystalline basement of Proterozoic age and is truncated by Jurassic sediments with slight angular unconformity. The Triassic of Socotra was deposited on an epicontinental setting and sedimentation was mostly controlled by sea-level changes. Its peculiar feature is the unusually rich paleontologic record consisting of conodonts, ammonoids, brachiopods and megalodontid bivalves. Three stratigraphic sections were studied at Ras Momi and Ras Falanj. The lithology is dominated by marls and limestones, often organized into shoaling upward cycles. Dolomitization occurs in the upper part of the succession. From the lithostratigraphic point of view the succession is attributed to one formation, divided into two members. The lower member is mostly calcareous, while the upper member mainly consists of dolostones. The detection of sequence boundaries, transgressive and highstand systems tracts (TST and HST) allow the identification of five depositional sequences from Olenekian to Late Carnian age. The age of the first three cycles is especially wellconstrained with conodonts and ammonoids. The five depositional sequences can be well correlated with the Sharland et al. (2001, 2004) peri-Arabian sequences Tr30, Tr40, Tr50, Tr60, Tr70. However, the high-resolution conodont and ammonoid bio-chronostratigraphic data from Socotra allow the re-calibration of the age of sequences Tr40 and Tr50.