GRIESBACHIAN (EARLIEST TRIASSIC) PALEOENVIRONMENTAL CHANGES IN THE SALT RANGE, PAKISTAN AND SOUTHEAST CHINA AND THEIR BEARING ON THE PERMO-TRIASSIC MASS EXTINCTION

Facies and faunal analysis from Pakistan and China show that the Permo -Triassic mass extinction of marine invertebrate faunas was associated with a spectacularly rapid Griesbachian transgression which lead to t he widespread establishment of deep-water anoxic and dysoxic condition s. The extinction event was thus caused by habitat loss due to the ext ensive development of inhospitable conditions. The initial Griesbachia n transgression in Pakistan produced extensive shallow, normal marine conditions in which Permian holdover taxa were able to survive until t he development of dysaerobic facies in the late Griesbachian. The exce ptionally complete sections of China show a three-phased deepening and extinction event beginning in the latest Permian. By the late Griesba chian a variety of dysaerobic and anaerobic facies were developed in a ll the regions studied. Several of these contain evidence for minimal sulphate reducing activity suggesting that marine productivity and thu s organic matter flux to the sediments was very low in early Triassic seas.