| The Lower Cambrian Yuertusi Formation is an important source rock layer in Tarim Basin. The research on
the organic matter enrichment mechanism could provide valuable guidance for the exploration of ultra-deep marine oil
and gas reserves. Based on data of mineral petrology, inorganic geochemistry, and elemental analysis of Well A,
combined with data of Well LT1 cited from reference, this study explores the sedimentary paleoenvironment of the
Yuertusi Formation source rock in Tarim Basin and its control on organic matter enrichment, with integrated element
geochemical indicators such as paleoproductivity, redox conditions and others. The results show that: (1) Yuertusi
Formation in the Tahe area has high organic matter content, and the organic matter quality of the lower section, with an
average TOC of 6%, is superior to the upper section. (2) Paleoproductivity level (P/ Ti, Babio), water retention degree
(Mo/TOC, Co·Mn), terrigenous detrital input (Ti/Al) and anoxia degree (Ni/Co, U/Th, V/Sc) show a gradual decreasing
trend from early to late period of Yuertusi Formation. (3) Closely corresponded with variations in the sedimentary
paleoenvironment induced by sea level fluctuations, the organic matter enrichment in the Yuertusi Formation is jointly
influenced by preservation conditions, weak hydrothermal activity, and upwelling currents. In the early stage of Yuertusi,
under a sea level of relatively low, a medium-high water retention developed, and the weak hydrothermal activity made
the bottom seawater being in an anoxic state, and the long-term anoxic and sulfidation environment was conducive to the
preservation of organic matter, thus the lower section of Yuertusi Formation with high TOC formed. In the late stage of
Yuertusi, the sea level experienced fluctuating rise and gradual decline, the water retention degree reduced under the high
sea level, and when the sea level decreased significantly, the environment gradually changed from anoxic to oxygen-poor,
which may lead to the oxidation and decomposition of some organic matter, thus the upper section with low TOC formed. |
