Permo-Triassic climate change and faunal turnover in the Salt and Surghar ranges, Northern Pakistan
Keywords:
Permian-Triassic mass extinction; Recovery; Salt Range; Surghar Range; Northern PakistanAbstract
One of the greatest biological crisis which happened at the Permian-Triassic boundary (250 million years (My) ago) is best documented in the well-exposed rocks of the Salt Range and the adjacent Surghar and Khisor Ranges in northern Pakistan which has been intensively studied since the pioneer work of Waagen in 1895. In these ranges the Upper Permian to Middle Triassic is represented by mixed siliciclastic carbonate sediments, named (in ascending order) the Chhidru, Mianwali, and Tredian formations. The present studies have brought in new insights to stratigraphy, faunal turn-over dynamics and environmental conditions of the Permo-Triassic (PT) sequence exposed in western Salt Range continuing in the adjoining Surghar Range.
The Permo-Triassic (PT) boundary is reportedly diachronous in the Salt and Surghar Ranges. The conodont fauna suggest that the PT boundary coincides with the disconformity at the Chhidru-Mianwali formations but the palynological assemblages from the upper-most Chhidru Formation have affinities with Permian as well as Griesbachian (basal Early Triassic). The Ammonite fauna from the Lower Triassic Mianwali Formation shows at least two episodes of radiation-extinction in the time interval from the Griesbachian to the early Spathian: within just three-to-four million years' time span. The palynological and the carbon isotope analysis of the Upper Chhidru-Mianwali-Lower Tredian sequence suggest series of reduced humidity events which coincides with positive shifts in global carbon isotopes record. The particulate organic matter record of the Mianwali Formation does not support the prolonged 'Early Triassic marine anoxia' but suggests rather oxygenated environmental conditions. In summary, the diversification patterns and environmental changes after the end-Permian extinction event are much more complex than previously thought, which are being highlighted in this paper.
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