Palaeoclimate investigations on exposures of Permian- Triassic transitional strata are rare.The Erlongkou section, from the Fuling region in the eastern Sichuan Basin, is located in the Yangtze carbonate platform during the Late Permian. It exposed a set of relatively complete marine carbonate strata from the Late Permian to the Early Triassic, which were deposited in a backreef environment. The succession has been divided into layers 1 to 31 in an ascending order, with the boundary between Changxing Formation and Feixianguan Formation placed between layers 6 and 7, and the Permian- Triassic boundary placed between layers 19 and 20. The boundary between layers 6 and 7 is a subaerial exposure, and the overlying weathered layer 7 is a 3~10cm- thick (averaged 5cm thick). The layers 7~19 have less carbonate minerals, and more clay minerals than the layers 1~6, whereas the layers 20~31 are dominated by mudstones, with lesser thinly bedded claystones.The petrography and mineral compositions show that the weathering crust (layer 7) is largely composed of clay minerals, which are dominated by illite/smectite mixed- layers (I/S) with minor illite. Such assemblage of clay minerals can be stratigraphically correlated with many other sections in different sedimentary facies throughout the Yangtze platform. This indicates that regional geological processes, such as exogenous deposition caused by volcanic activity, may be the major factor controlling the involvement of clays in the weathering crust. As such, the accretion model instead of the alteration model must have formed the weathering crust. This suggestion can be further supported by the petrographic and stable isotopic evidences, which show that meteoric alterrations in the underlying host rock (layers 1~6) are absent. Additionally, the abundant illite/smectite mixed- layer (I/S) minerals and illite in the weathering crust indicates an alkaline, xerothermic and anoxic depositional environment probably initiated at the end of Permian. From layer 7 to layer 31, the abundance of illite/smectite mixed- layer minerals and their I/S ratios decrease, whereas the abundance of chlorite increases. Such a change in clay mineral is consistent with the notion that the alkaline, xerothermic and anoxic conditions were probably exacerbated during the Permian/Triassic transitional period. Therefore, clay minerals at the Permian- Triassic boundary intervals provide a robust archive for paleoenvironmental changes in the Yangtze platform.