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 the widespread establishment of deep-water anoxic and dysoxic conditions. The extinction event was thus caused by habitat loss due to the extensive development of inhospitable conditions. The initial Griesbachian transgression in Pakistan produced extensive shallow, normal marine conditions in which Permian holdover taxa were able to survive until the development of dysaerobic facies in the late Griesbachian. The exceptionally complete sections of China show a three-phased deepening and extinction event beginning in the latest Permian. By the late Griesbachian a variety of dysaerobic and anaerobic facies were developed in all the regions studied. Several of these contain evidence for minimal sulphate reducing activity suggesting that marine productivity and thus organic matter flux to the sediments was very low in early Triassic seas.