Abstract Lacustrine carbonates are widely distributed in the third member of the Eocene Shahejie Formation (Es3L) of the Shulu sag and other rift basins in the Bohai Bay Basin, which can act as reservoirs for hydrocarbon and provide insights into paleoenvironment. However, the origins of lacustrine carbonate deposition and their implications for porosity development and paleoenvironment are not well understood. Based on micropetrological characteristics, X-ray diffraction (XRD), stable carbon and oxygen isotope analyses, and organic geochemistry data, four types of calcite (calcite debris; calcareous biological detritus; micrite in fine-grained marlstone; fibrous sparry calcite) and two types of dolomite (dolomite debris; rhombic euhedral dolomite) with distinctly different characteristics and origins are identified. The δ13C and δ18O values of calcite and dolomite debris are consistent with that of the Cambrian-Ordovician carbonate rock in the provenance area, suggesting that the carbonate debris was sourced from the surrounding Cambrian-Ordovician carbonate bedrock. Microcrystalline calcites are commonly developed in organic-rich marlstones with a large number of algae. The δ13C values of the microcrystalline calcites are higher than that of carbonate debris and the positive excursion of the δ13C value is along with the increase of TOC content. These indicate that origin of the microcrystalline calcite was authigenic calcite and was formed by biochemical process. Bedding-parallel fibrous sparry calcite occurs in intervals with high TOC contents and within the thermally mature zone of hydrocarbon generation, indicating that oil generation should be responsible for the sparry calcite formation. Rhombic euhedral dolomite commonly occurs as isolated micro-crystals with euhedral to subhedral rhombs shape. Micro-sized spherule-like dolomite in the early stage of crystal growth were also present. Rhombic euhedral dolomite are commonly associated with organic matter and developed in organic-matter rich intervals with plenty of fossilized bacterial filaments and framboidal pyrite. These suggest that rhombic euhedral dolomite were probably microbially mediated dolomite. Mineral components can affect reservoirs quality. The porosities of samples show a positive correlation with dolomite content and the porosities of fibrous sparry calcite-bearing intervals are higher than non-parry calcite-bearing intervals. The increase in authigenic microcrystalline calcite content reflects a rise in lake level and an increase in water depth and primitive productivity.

中文翻译：

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渤海湾盆地束鹿凹陷源控湖相碳酸盐岩系列碳酸盐矿物成因对孔隙发育及古环境的意义

摘要 湖相碳酸盐岩广泛分布于渤海湾盆地束鹿凹陷始新世沙河街组三段（Es3L）及其他裂谷盆地，具有油气藏储层和古环境洞察的作用。然而，湖泊碳酸盐沉积的起源及其对孔隙发育和古环境的影响尚不清楚。基于微岩石学特征、X 射线衍射 (XRD)、稳定碳氧同位素分析和有机地球化学数据，四种类型的方解石（方解石碎片；钙质生物碎屑；细粒泥灰岩中的泥晶；纤维状方解石）和两种确定了具有明显不同特征和成因的白云岩类型（白云岩碎片；菱形自形白云岩）。方解石和白云石碎屑的δ13C和δ18O值与物源区寒武系-奥陶系碳酸盐岩一致，表明碳酸盐碎屑来源于周围寒武系-奥陶系碳酸盐岩基岩。微晶方解石通常发育在含有大量藻类的富含有机质的泥灰岩中。微晶方解石的δ13C值高于碳酸盐碎屑，δ13C值随着TOC含量的增加而正向偏移。这表明微晶方解石的来源是自生方解石，是通过生化过程形成的。层理平行的纤维状方解石出现在 TOC 含量高的层段和生烃热成熟带内，表明生油应该是形成火花方解石的原因。菱形自形白云岩通常以自形至半自形菱形的孤立微晶形式出现。还存在晶体生长早期的微球粒状白云岩。菱形自形白云岩通常与有机质伴生，发育于富含有机质的层段，含有大量化石细菌丝和枝状黄铁矿。这些表明菱形自形白云岩可能是微生物介导的白云岩。矿物成分会影响储层质量。样品孔隙度与白云石含量呈正相关，含纤维状方解石层段孔隙度高于非含层方解石层段。