Palaeogeographic variation in the Permian-Triassic boundary microbialites： A discussion of microbial and ocean process esafter the end-Permian mass extinction

摘要

Shallow marine carbonate sediments that formed after the end-Permian mass extinction are richin a thin （maximum ca. 15 m） deposit of microbialites. Microbial communities that constructed the micro-biatites have geographic variability of composition, broadly divisible into two groups： 1） eastern Tethys sitesare catcimicrobe-dominated （appearing as thrombotites in the field）, with rare occurrence of sediment-constructed microbiatites and uncommon cements either within microbial structure or as inorganic pre-cipitates, 2） other Tethys sites are sediment-dominated structures forming stromatotites and thrombotites,composed of micrites and cements, with some inorganic precipitates. These other Tethys locations includewestern and central Tethys sites but their pataeogeographic positions depend on the accuracy of continentalreconstructions, of which there are several opinions. In contrast to geographic variation of microbialites, theconodont Hindeodus parvus, which appeared after the extinction and defines the base of the Triassic, iswidespread, indicating easy lateral migration throughout Tethys. Conodont animals were active nekton,although being sma{[ animals were presumably at least partly carried by water currents, imp[ying activeTethyan surface water circulation after the extinction event. Post-extinction ammonoid taxa, presumed activeswimmers, show poor evidence of a wide distribution in the Griesbachian beds immediately after theextinction, but are more cosmopolitan higher up, in the Dienerian strata in Tethys. Other shelly fossils alsohave poorly defined distributions after the extinction, but ostracods show some wider distribution suggestingmigration was possible after the extinction. Therefore there is a contrast between the geographic differencesof microbialites and some shelly fossils.