Distribution pattern of the Late Triassic Pergamidia (Bivalvia) and its significance

The large epibyssate bivalve Pergamidia, ranging from tne Carnian to the Norian (Late Triassic), is abundantly distributed in the areas between Turkey and the Timoralong Palaeotethys suture, inclunfing Balia of Kleinasien in Turkey, Tuotuto River of northern Tibet, Tuoba and Jiangda of Qamdo area of eastern Tibet, Changtai, Yidun and Litang areas of western Sichuan, Ninglang, Lijiang, Yongsheng and Heqing areas of western Yunnan in China and Timor. Pergamidia fossils have been found in slates and tuffaceous sandstones, and also in the sulfide deposits. Such a distribution pattern along the Palaeotethys suture its occurrence in various environments, particularly in the sulfide deposits, suggest that during Late Triassic from Turkey to Timor the Tethyan sea comprised rifts, fore-arc, and shallow to deep areas. Thus, Pergamidia is and index bivalve of the Late Triassci Tethys. Its occurrence was primarily controlled by physico-chemical rather than biological factors. Pergamidia was able to colonize various environments including tozic environments with sulfides.