SEDIMENTOLOGIC AND PALEOCLIMATE EVALUATION OF END-PERMIAN EXTINCTION AND MIXED SILICICLASTIC CARBONATE DEPOSITION WITHIN THE KHUFF FORMATION IN CENTRAL SAUDI ARABIA

Paleotemperature proxy data indicates substantial climate warming across the Permian/Triassic boundary (PTB), but the extent to which this change induced regional changes in weathering regimes remains poorly constrained. We use data from two sections of the Khartam Member of the Khuff Formation to reconstruct the intensity of continental weathering during the end-Permian mass extinction. The sections are located 10 km northeast of Buraydah. Both show an upward transgressive shift across the PTB from mudrock, siltstone, and sandstone intercalated with green and dark gray shales, and anhydrite nodules of the lower Khartam Member to oolitic, peloidal lime grainstone with thin-shelled bivalves and microgastropods intercalated with lime mudstone and bright-red mudrock in the upper Khartam Member.

Lower Khartam Member facies indicate evaporative, sabkha-type conditions changing to shallow-marine environments, with widespread oolitic shoals in the upper member. Lime mudstone with restricted biota pass upward to oolitic-skeletal and peloidal packstone to grainstones and microbialites with open marine biota. The bright-red mudrock at the PTB contains root casts. Diagenetic phases include marine isopachous bladed cements in intergranular porosity, dissolution of ooids, bladed cement and equant spar filling oomolds, compaction, and dolomitization.

δ¹³C shifts by -2.66‰ across the PTB, from 1.19‰ to -1.47‰. Elevated elemental proxies for siliciclastic and nutrient input in the mudrock of the Upper Permian and PTB interval are consistent with siliciclastic and nutrient flux from land. A drop in uranium concentration across the PTB is consistent with sequestration of U in anoxic regions of the global ocean. Chemical index of alteration (CIA) increases across the PTB and remains high (~85-90) in the Lower Triassic. Siliciclastics across the PTB are characterized by a decrease in feldspar content (28 to 0.2%), an increase in total clay (23 to 84%), and a higher proportion of kaolinite (0 to 33%).

Root casts, elevated CIA and mineralogical shift in mudrock at the PTB are consistent with a scenario of extreme global warming featuring a pulse of increased humidity and acid rain leading to intense chemical weathering in the region during the global perturbation generated by Siberian traps volcanism at the end of the Permian.