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• Two types of homogenites are found in the Shulu Sag based on sedimentary characteristics. • Earthquakes are the most reasonable triggers of homogenite formation. • Seismic shaking and basin morphology control the formation of homogenites. Homogenites are homogeneous and structureless, fine-grained rocks. They have been studied extensively in marine settings and are typically interpreted as being related to catastrophic events such as earthquakes. However, studies on lacustrine homogenite-like rocks are limited. New core data from the Shulu Sag in China reveal that thick massive calcilutites exist in the lower Shahejie 3 Formation, which formed during the middle Eocene rifting stage. Based on petrographic, geochemical, and mineralogical data, these massive calcilutites are interpreted as homogenites and grouped into two types. Type A homogenite is composed of intrabasinal materials characterized by high calcite, total organic carbon (TOC) content, and δ13C value. Type A homogenite has two facies successions, the first of which is characterized by homogeneous appearance capped by an erosional interface and the second is characterized by repeated massive-laminated calcilutite successions. Type B homogenite contains abundant allochthonous materials displaying relatively high dolomite content and low calcite, TOC, and δ13C content. Type B homogenite represents the topmost finer portion of a graded megabed which includes, from base to top, grain supported carbonate conglomerates, slumped deformed portions, and debrites. The whole unit can be considered as a megaturbidite. Earthquakes are the most reasonable triggers of homogenite formation in the Shulu Sag. Type A homogenites are thought to be derived by fluidification, resuspension, and decantation of lacustrine fines due to shock waves generated by an earthquake. Type B homogenites might be deposits of distal turbidity currents and turbid clouds transformed from other gravity flows. The results of this study provide a better understanding of the formation of homogenites caused by earthquakes in a confined lacustrine basin. [ABSTRACT FROM AUTHOR]

In the Upper Ediacaran Dengying Formation of the Sichuan Basin, the presence of abundant, well-preserved microbial carbonates provides a unique opportunity to study Precambrian paleoceanography and microbial carbonate origins. Particularly, the underexplored coated grain dolostones of this formation, characterized by distinct microbially induced fabrics and intragranular dissolution, offer crucial insights for understanding late Ediacaran microbial mineralization and diagenetic sequences. Utilizing selected typical samples, we conducted detailed petrographic and geochemical analyses, revealing a dynamic interplay between microbial processes and sedimentary dynamics. We observe the coexistence of constructive micrite envelopes with microbially induced fabrics such as clots and laminations, highlighting microbial biomineralization's key role in fabric formation. The sedimentary dynamics critically determines the formation processes of the coated grains: low-energy settings foster grain agglomeration and consolidation through clot precipitation between grains, while high-energy settings favor smaller grains binding to microbial mats. Geochemically, micrite envelopes play an essential role in preserving distinct rare earth element (REE) signatures. The weak negative Ce anomalies and positive Eu anomalies within these envelopes point to a suboxic to anoxic depositional environment, directly indicative of the microenvironmental conditions conducive to microbial mineralization processes. Furthermore, our study sheds light on the structural evolution of coated grains with hollow nuclei, proposing that their internal pore formations are influenced by both mineral instability and selective dissolution by meteoric freshwater. These findings not only provide fresh insights into complex diagenetic processes in the Dengying Formation but also substantially advance our understanding of early microbial life and environmental adaptations during the Precambrian. • Revealed the relationship between micrite envelopes and microbially induced fabrics • Proposed a novel formation mechanism for coated grain dolostone in the Dengying Fm. • Investigated the diverse environmental responses of microbiolite fabrics • Established micrite envelopes as dependable records of seawater REE compositions [ABSTRACT FROM AUTHOR]