Modeling the paleogeography of north-western Palaeotethys across the Permian-Triassic boundary: constraints and possible solutions.

We simulated for the first time the palaeogeographic evolution of three thin depositional sequences of the shallow marine western Palaeotethys, deposited in the Southern Alps (SA, ftaly) during the devastating end-Per mia n extinction. The iimulation is calibrated by a rich set of published field data measured in the uppermost Bellerophon Formation-Iowermost Werfen Fm. Data and palaeogeographic maps are located in the palinspastically restored SA area. The employed software is a lpreliminary version of SIMSAFADIM-CLASTIC that simulates: I) the spatial distribution of terrigenous and clastic carbonate, b) rbe fossil cootent, c) the microbial content. The models (maps) "'ere realized as a back-analysis, by calibration with the 3D .architecture of real sedimentary sequences, particularly on the patial distribution of terrigenous-clastic carbonate ratios. The 'mulation covers a peri od of about 70 kyr, whereas each sedimentary sequeoce corresponds to a time-span of 15-20 kyr; dJe low-stand tract spans 5-6 kyr. Models that best match reality t("ere achieved by using a curve of sea level changes obtained empirically. The maximum sea level change is about a dozen lIletres; the study area underwent local short periods of emersion, represented by soil or intertidal carbonates, followed by shallow marine, foreshore facies. The sea level change curve is likely to represent the global reference. We interpret results of the model ~. the hypothesis that the curve of sea level change presented _ re could have been produced by alternating global warming d cooling of the oceans. This curve, obtained by an • dependent method, would be utilized as an important ronstraint on the numerical global models of coupled tmosphere--ocean circulation. On the contrary, the . appearence of Permian-type tua (fusulinids, foraminifers, 'valves and algae) pre-dating tbe P-T bouodary does not match e field data because tbe software lacks a few specific functions; ese biologie carbonate components seem to have beeen bstituted by a still-unknown environmental cause producing lites and carbonates of microbialitic origin.