Provenance of Middle Jurassic sandstones from the Yuqia depression in the northern Qiadam Basin (NW China): Implications for basin evolution and paleoclimatic conditions

The petrography of 106 clastic rock samples from the Middle Jurassic Dameigou and Shimengou Formations in the Qaidam Basin was analyzed to investigate their provenance and basin evolution. Five distinct sandstone units have been identified from the base of the Dameigou Formation to the top of the Shimengou Formation, hereafter termed as S-I, S-II, S-III, S-IV, and S-V. Petrographic analysis suggests that during the deposition of S-I (Aalenian stage), sediments were sourced from the Qaidam Main Block at the southern margin of the basin and the South Qilian Mountains at the northern margin. However, during the deposition of S-II, S-III, S-IV, and S-V (Bajocian to early Callovian stages), the basin received sediments from the East Kunlun Mountains to the south and the Qilian Mountains to the north. Mineralogical Index of Alteration (MIA) values, along with discrimination diagrams, indicate that the Middle Jurassic climate in the Qaidam Basin transitioned from semi-humid and warm (S-I) to humid and warm (S-II to S-IV), before returning to semi-humid and warm conditions (S-V). A basin evolution model was developed according to our findings, which provide a better understanding in the basin-forming processes and the principle of resource accumulation in the Middle Jurassic.