Abstract
The average thickness of Paleogene sandstones reaches about 3000–4000 m at the northern margin of the Qaidam Basin. However, the provenance and sedimentary environment of these sandstones are uncertain; thus, more comprehensive research is needed. Integrated research is conducted on the provenance and weathering process based on petrographic characteristics, clay minerals, and geochemical compositions of sandstones in the center of the northern Qaidam Basin. The results of lithofacies analysis show that the Paleogene sandstones were mainly derived from an active continental magmatic arc, subduction accretion, or a fold-thrust belt. The average illite content in the Paleogene clay minerals is more than 50%, followed by chlorite and smectite, which reflect climatic and environmental characteristics that were arid to semi-arid, whereas the characteristics of carbon–oxygen isotopes reveal a mainly freshwater sedimentary environment. The corrected chemical index of alteration (CIAcorr) is between 56.3 and 75.7, with an average value of 66.5. These results indicate that the provenance of the Paleogene sandstones in the center of the northern Qaidam Basin mainly formed under cold and dry climatic conditions and experienced limited chemical weathering with a small amount that underwent intermediate chemical weathering under warm and humid conditions.
Highlights
Since the Cenozoic era, the collision between the Indian and Eurasian plates has caused the Qinghai–Tibet plateau to substantially rise [1]
Previous studies on the sedimentary system, reservoir genesis, androcks diagenetic evolution the characteristics of clay mineral assemblages and contents of major and trace elements and their have investigated the central region of the northern margin of the Qaidam Basin [9]
Regardless of the complexity of the tectonic evolution prior to the Mesozoic, the subduction of Regardless of the complexity of the tectonic evolution prior to the Mesozoic, the subduction of oceanic crust and collision between continental lithospheric plates completed in northwestern China oceanic crust and collision between continental lithospheric plates completed in northwestern China by the end of the Triassic [16]
Summary
Since the Cenozoic era, the collision between the Indian and Eurasian plates has caused the Qinghai–Tibet plateau to substantially rise [1]. The complex intra-continental deformation process has had a profound impact on environmental climate change, sedimentary tectonic evolution, and the source-sink system in the inland region of Asia, which has considerably affected environmental resources, especially the accumulation, migration, and transformation of oil and gas in the inner basins of the Qinghai–Tibet plateau [2,3,4]. The study of clay mineral contents and their combination provides important information for understanding the provenance, paleoclimate, sedimentary environment, and diagenetic characteristics for reproducing depositional and diagenetic processes [12]. Previous studies on the sedimentary system, reservoir genesis, androcks diagenetic evolution the characteristics of clay mineral assemblages and contents of major and trace elements and their have investigated the central region of the northern margin of the Qaidam Basin [9]. EBL II—Eboliang II; EBL III—Eboliang III; HLS—Hulushan; LH VI—Lenghu VI; LH VII—Lenghu VII; NBX—Nanbaxian; MB—Mabei; YKYWR—Yikeyawuru; YH—Yahu; TJNR—Taijinaier
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