Natural gamma data from the Permiam-Triassic boundary in Shangsi section, Sichuan，China

Rocks generally contain varying amounts of radioactive elements such as uranium (U) and thorium (Th) and continuously emit radiation. Natural gamma data can be obtained from instrumental measurements of the natural gamma-ray intensity of rocks. Owing to the strong adsorption capacity of clay minerals for radioactive elements, the natural gamma-ray intensity of rocks is directly proportional to the clay content. The clay content in sedimentary rocks is influenced by the depositional environment. For instance, in environments with rising sea levels and weak hydrodynamic conditions, the clay content is higher, and vice versa.The steps to obtain natural gamma data are as follows: 1) A fresh surface of the rock samples on the field outcrop was taken at equal intervals of 0.2 m using a geological hammer. Then, 2) a portable gamma energy spectrum detector (model GR135) was used to align the fresh surface of the rock for data acquisition, with a sampling time of not less than 60 s. Finally, the gamma value (measured in API units) was recorded after the data were stable. A total of 688 data points were collected from the top of the Upper Permian Wujiaping Formation to the bottom of the Upper Triassic Feixianguan Formation, spanning a stratigraphic thickness of 137.4 m.