The History of Transgressions during the Late Paleocene-Early Eocene in the Kuqa Depression, Tarim Basin: Constraints from C-O-S-Sr Isotopic Geochemistry

Abstract

The Tethys Sea extended into the Kuqa Depression from the Paleocene to the late Eocene and provided an abundant provenance for the deposition of evaporite sequences. Until now, detailed research on the history of transgressions during the late Paleocene-early Eocene in the Kuqa Depression has been limited. Therefore, in this study, we took the upper Paleocene Talak section and the lower Eocene Xiaokuzibai section in the western part of the Depression as the research objects and analyzed the petrology, the carbon and oxygen isotopes of carbonate rocks, and the sulfur and strontium isotopes of gypsum rocks to systematically study the above issues. The δ13C, δ18O and δ34S values of the upper Paleocene evaporite sequences were determined to be between 4.2‰ and 5.7‰, between −5.2‰ and 2.4‰, and between 16.5‰ and 17.9‰, respectively. The δ13C, δ18O, δ34S, and 87Sr/86Sr values of the lower Eocene evaporite sequences were determined to be between −6.9‰ and −2.0‰, between −9.0‰ and −4.5‰, between 10.5‰ and 17.0‰, and between 0.708642 and 0.709883, respectively. The analysis results show that the evaporite sequence of the upper Paleocene was formed by transgression. The deposition of the evaporite sequence changed from continental to marine deposition, and then gradually transitioned to continental during the Early Eocene. This paper is of great significance for reconstructing the history of transgressions in the Tethys tectonic realm during this period.

Geochemistry and Sr, S, and O stable isotopes of Miocene Abu Dhabi evaporites, United Arab Emirates

“…Due to the limited significance of isotope fractionation associated with the precipitation of sulfates, the δ 34 S values of evaporitic minerals should reflect the isotope composition of fluids from which they precipitate [ 53 , 55 , 56 ]. The sulfate isotope composition does not change during gypsum deposition and anhydrite hydration, owing to the negligible sulfur isotope fractionation [ 4 , 18 , 45 , 57 ]. In addition, the effect of bacterial sulfate reduction should increase the δ 34 S recorded values [ 21 , 23 ].…”

“…It can be used to objectively determine the age of the sulfate deposition (gypsum and anhydrite). Such minerals naturally incorporate substantial amounts of Sr into their lattices, replacing Ca [ 12 , 17 , 18 ]. Because Sr is extremely susceptible to alteration effects (fluid-rock interactions with fluids of meteoric, diagenetic, tectonic, and metamorphic origins), caution is necessary when testing the 87 Sr/ 86 Sr ratio.…”

The Sulfur Isotopic Characteristics of Evaporites in the Yarkand Basin of Xinjiang Province in the Paleocene and Its Paleoenvironmental Evolution

“…The contact between During the Early Cretaceous, seawater intruded into the Yarkand Basin from the southwestern Tarim Basin in a west-to-east direction. The transgression continued to increase during the Paleocene era [40]. The sediment sources in front of the South Tianshan Mountains and the West Kunlun Mountains controlled the deposition in the Yarkand Basin during the Early Cretaceous.…”

Whether the Middle Eocene Salt-Forming Brine in the Kuqa Basin Reached the Potash-Forming Stage: Quantitative Evidence from Halite Fluid Inclusions

“…The chemical compositions of halite fluid inclusions are characterized by high Ca 2+ and Sr 2+ concentrations, which may be due to the supply of terrestrial fresh water involved in the salinization process. Zhang et al [12] and Xu et al [59] systematically analyzed the carbon, oxygen, sulfur, and strontium isotope compositions of middle Eocene carbonate rocks and sulfate rocks and found that the provenance in the salt-forming environment was mostly a mixture of marine and continental sediments. The Br − data from that study are compared with the chemical analysis results for the rock salt from borehole DZK01 [60], and the Br − content in the latter is lower than the detection limit, whereas the Br − content in the former is higher than the detection limit.…”