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The Permian Junggar Basin was the site of deposition of a large set of organic-rich sediments, among which the Lucaogou Formation is considered an excellent petroleum source bed. High-frequency variation in lithology is a typical feature of the Lucaogou Formation, reflecting the fluctuation of the paleoclimate and depositional environment. The relationship between climate fluctuation and organic matter enrichment still needs to be elucidated for the Lucaogou Formation. High-resolution sampling was applied to an 86.2 cm long core from the Lucaogou Formation from the Jimsar Sag in the Junggar Basin to examine the effects of climate fluctuation on organic carbon burial. Petrographic, mineralogical, and elemental analyses of the core indicated that the paleoclimate for the core went through a relatively wet-dry-wet sequence, with changes occurring on timescales of thousands of years. The influence of climate fluctuation on organic matter accumulation is multilevel and multifactorial, involving chemical weathering, sediment supply, lake level, paleosalinity, redox, and primary productivity. High-resolution geochemistry portrays the evolution of these factors and how they collectively determine the burial of sedimentary organic carbon. The Lucaogou epoch was generally characterized by dry/cold climatic conditions, low weathering intensity, and limited detrital input. Moreover, low temperatures and scanty nutrient input resulted in low to moderate productivity. The enrichment of organic matter in the Lucaogou Formation was primarily controlled by preservation. • Paleoclimate mediated organic matter enrichment through a complex multilevel and multifactorial process. • Chemical weathering, sediment supply, salinity, redox, and primary productivity changed along with fluctuating climates. • Organic matter accumulation was mainly controlled by preservation rather than primary productivity and mineral dilution. [ABSTRACT FROM AUTHOR]

β -Carotene, the precursor of β -carotane, is commonly rich in brackish sediments and would become unstable theoretically under the exposure to high temperatures, bright light conditions, and acidic or oxdizing environments. However, the specific process and mechanism of the absence of such compounds are still not clear sufficiently. To fill the knowledge gap, in this study we explore the origin of the absence of β -carotane in a 50-m-thick section of the Middle Permian Lucaogou Formation in the Jimusar Sag, Junggar Basin, northwest China, based on a combined mineralogical, petrographic, organic and inorganic geochemical study. Biomarker analyses indicate that the β -carotane-free section was deposited in a brackish, reducing, and semi-deep lacustrine environment. Hydrothermal fluid effects during sediment deposition are inferred to have caused the breakdown of β -carotene. The hydrothermal (<100 °C) effects are evidenced by mineralogy and geochemistry, e.g., the hydrothermal-indicative minerals (reedmergnerit, tuff and pyrite), high Fe/Ti and low Al/(Al + Fe) ratios, rare earth elements (REEs) distribution. Associated biomarker variations were found, e.g., low i -alkanes/ n -alkanes, high C 24 Tetracyclic/C 26 Tricyclic terpanes, high (C 19 + C 20)/(C 21 + C 23) tricyclic terpanes, high C 29 /C 30 hopanes, and very low gammacerane/C 30 hopane ratios. Our data suggest that hydrothermal fluids can prevent the preservation of β -carotene, and the absence of β -carotane indicates a period of hydrothermal activity during deposition of the Lucaogou Formation in a 50-meter-thick sequence. • β -Carotanes were found to be absent in a brackish lacustrine sequence. • Hydrothermal fluids have caused the breakdown of β -carotene. • Anomalously low abundance of isomerization alkanes and high C 24 Tet/C 26 TT ratios were also found. • Hydrothermal activity was present in the Permian Lucaogou Formation, Junggar Basin. • Absence of β -carotane can be used as a proxy for hydrothermal activity. [ABSTRACT FROM AUTHOR]