Relations between paleoclimatological conditions and mineralogical characteristics of clays in Miocene sediments at Linxia basin, China

摘要

Linxia basin is a late Cenozoic fault-block basin along the border between the Tibet plateau and the Loess plateau in Northwestern China. Its formation and sediments' record may be directly affected by the structural dynamics and the uplift of the Tibet Plateau. For this reason, we studied the mineral characteristics of the Maogou formation of Miocene sediments using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that quartz, chlorite, illite, calcite, plagioclase, orthoclase, kaolinite, and trace palygorskite are present throughout the sequence of the cross-section in Linxia basin. In contrast, gypsum and ankerite occur occasionally in the upper portion of the Miocene deposits. The content of calcite varied with layers in the profile and was relatively concentrated in mudstone. Chlorite and illite were observed transforming into palygorskite under SEM observation. Based on the mineral characteristics and the change of mineral composition, especially the clay minerals, it could be inferred that an arid environment prevailed in the region with warm and cold intervals during Miocene time.