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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]

Abstract Tight oil has been discovered in calcilutite and carbonate conglomerate reservoirs in the lower part of the third member of the Eocene Shahejie Formation of the Shulu Sag, Bohai Bay Basin, Northern China. Understanding the nature of lithofacies is essential to evaluating the quality of tight reservoirs. This study analyzed the sedimentary characteristics, geochemistry, and reservoir characteristics of each lithofacies based on thin-section and field-emission-scanning electron microscope observations combined with X-ray diffraction, geochemical parameter, and physical property analysis. Eight lithofacies were identified: (1) varve-like laminated calcilutite, (2) non-regular laminated calcilutite, (3) interlaminated calcisiltite-calcilutite, (4) massive calcilutite, (5) massive calcisiltite-calcarenite, (6) grain-supported carbonate nconglomerate, (7) matrix-supported carbonate conglomerate, and (8) mixed-source carbonate conglomerate. The varve-like laminated calcilutites have intrabasinal organic matter with a low Pr/Ph ratio (0.50–0.63) and high gammacerane/C 31 homohopane (0.13–0.29), indicating that they are normal sediments and have good hydrocarbon generation potential. The other lithofacies are event sediments containing a certain amount of terrestrial organic matter. Laminated, organic-rich lithofacies develop organic matter pores and other storage spaces modified by organic acid. Their reservoir quality is better than that of massive or organic matter-lean lithofacies. The conglomerates containing less matrices have better reservoir quality than conglomerates with high matrix contents. The hydrocarbon generation ability and reservoir quality of lithofacies as well as the fracture density are the key factors that control the formation of tight oil reservoirs in the Shulu Sag. Highlights • Using geochemical data to analysis hydrocarbon generation potential of lithofacies. • Evaluating the nature of tight calcilutite and conglomerate reservoirs. • Laminated, organic matter-rich calcilutite is the best self-sourced reservoir. • Grain-supported conglomerate has better reservoir quality than all lithofacies. [ABSTRACT FROM AUTHOR]

This paper presents the experimental characterisation of hydraulic and mechanical properties of two fine-grained materials from the Aigion Fault Zone, on the southern shore of the Gulf of Corinth, Greece. One is a calcilutite, which commonly caps the basal limestone units, and the other is siliceous active fault gouge from 760 m depth in the borehole. Oedometric compaction/consolidation tests of unconsolidated cylindrical samples at variable stresses were conducted under drained conditions, and then permeability measured by a constant flow technique. The axial strain measurements show consolidation curves with a decelerating strain rate that can be approximated by a power-law function. The permeability is negatively and linearly correlated to the stress, and ranges from 9 to 15×10−18 m2 for the calcilutite and 0.9 to 2×10−18 m2 for the fault gouge with varied vertical stresses. To cite this article: I. Song et al., C. R. Geoscience 336 (2004). [Copyright &y& Elsevier]