Natural gamma data from Permo-Triassic boundary strata 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.

岩石通常含有不同含量的铀（U）、钍（Th）等放射性元素，并持续释放辐射。天然伽马数据可通过仪器测量岩石的天然伽马射线强度获取。由于黏土矿物对放射性元素具有较强的吸附能力，岩石的天然伽马射线强度与黏土含量呈正相关。沉积岩中的黏土含量受沉积环境影响：例如，在海平面上升、水动力条件较弱的环境中，黏土含量更高，反之则更低。
获取天然伽马数据的步骤如下：1）使用地质锤在野外露头的岩样上按0.2米的等间距采集新鲜断面；2）采用便携式伽马能谱探测器（型号GR135）对准岩石新鲜断面进行数据采集，采样时长不低于60秒；最后，待数据稳定后记录伽马值（单位为API）。本次采集共获取688个数据点，采样层位为上二叠统吴家坪组顶部至上三叠统飞仙关组底部，地层厚度跨度为137.4米。