Response of a continental fault basin to the global OAE1a during the Aptian: Hongmiaozi Basin, Northeast China.

This paper presents new research on a lacustrine anoxic event (LAE). These data include stable carbon isotope (δ13Corg), pyrite sulfur isotope (δ34Spy), trace element and biomarker ratios from the Hongmiaozi Basin (North China) and unravel the response of continental lakes under the influence of early Aptian extreme climate conditions. According to the stratigraphic chronology (122-118 Ma) and carbon isotope correlations, terrestrial sediment was influenced by the early Aptian Oceanic Anoxic Event (OAE1a). The results show that the Xiahuapidianzi Group experienced a significant warming process under negative excursions in carbon isotopes due to the influence of increased carbon dioxide partial pressure (pCO2). The climate varied from warm and humid to hot and arid (high Sr/Cu, low Rb/Sr, calcareous mudstone), the evaporation and salinity increased (high Sr/Ba and B/Ga), and land input sources decreased (low Zr, Ti and Th). Moreover, high total organic carbon (TOC) content was source from bacteria, algae (n-alkanes), and euxinic depositional environments (Pr/Ph, Cu/Zn and U V Mo). In the stage of continuous carbon isotopes positive excursion, organic matter accumulated rapidly. A paleolake environment model has provided a better understanding of current global climate issues under global warming caused by increased carbon dioxide concentrations.

Sedimentology, petrography, and reservoir quality of the Zarga and Ghazal formations in the Keyi oilfield, Muglad Basin, Sudan.

The Zarga and Ghazal formations constitute important reservoirs across the Muglad Basin, Sudan. Nevertheless, the sedimentology and diagenesis of these reservoir intervals have hitherto received insignificant research attention. Detailed understanding of sedimentary facies and diagenesis could enhance geological and geophysical data for better exploration and production and minimize risks. In this study, subsurface reservoir cores representing the Zarga formation (1114.70-1118.50 m and 1118.50-1125.30 m), and the Ghazal formation (91,403.30-1406.83 m) were subjected to sedimentological (lithofacies and grain size), petrographic/mineralogic (thin section, XRD, SEM), and petrophysical (porosity and permeability) analyses to describe their reservoir quality, provenance, and depositional environments. Eight (8) different lithofacies, texturally characterized as moderately to well-sorted, and medium to coarse-grained, sub-feldspathic to feldspathic arenite were distinguished in the cored intervals. Mono-crystalline quartz (19.3-26.2%) predominated over polycrystalline quartz (2.6-13.8%), feldspar (6.6-10.3%), and mica (1.4-7.6%) being the most prominent constituent of the reservoir rocks. Provenance plot indicated the sediments were from a transitional continental provenance setting. The overall vertical sequence, composition, and internal sedimentary structures of the lithofacies suggest a fluvial-to-deltaic depositional environment for the Ghazal formation, while the Zarga formation indicated a dominant deltaic setting. Kaolinite occurs mainly as authigenic mineral, while carbonates quantitatively fluctuate with an insignificant amount of quartz overgrowths in most of the analyzed cores. Integration of XRD, SEM, and thin section analysis highlights that kaolinite, chlorite, illite, and smectite are present as authigenic minerals. Pore-destroying diagenetic processes (e.g. precipitation, cementation, and compaction etc.) generally prevailed over pore-enhancing processes (e.g. dissolution). Point-counted datasets indicate a better reservoir quality for the Ghazal formation (ɸ = 27.7% to 30.7%; K = 9.65 mD to 1196.71 mD) than the Zarga formation (17.9% to 24.5%; K = 1051.09 mD to 1090.45 mD).