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In this paper, the original nature of organic matters is introduced for the first time to reevaluate the lower Permian (P 1) source rocks. The carbonate rocks in Maokou Formation (P 1 m) whose high organic carbon values were caused by external asphalt have poor hydrocarbon generation ability, but the argillaceous rocks in P 1 m have some, especially the recent discovered black shale in Gufeng deep-water facies in the north have good hydrocarbon generation ability. The black shale is 5–20 m thick and the measured average value of organic carbon can reach up to 7.24 wt%, which can greatly increase the hydrocarbon generation capacity in the north; The studies of natural gas sources of the lower Permian in eastern Sichuan basin show that the contribution of gas source is mainly Silurian. In the north, the lower Permian source rock is supplemented, while in the south, it's greatly affected by the coal-measure source rocks of Longtan Formation (P 2 l); Take the Wutan-1 well in Tanmuchang as an example to dissect the reservoir in syncline area. The Wutan-1 well has a tested daily production of more than 80 × 104 m3, and the paleotectonic evolution history shows that it was in the high position of the structure during the generation and expulsion peak of hydrocarbon. The fracture-vuggy lithologic reservoir of Wutan-1 well is favorable for hydrocarbon capture and later preservation. According to the above, the Tanmuchang syncline has a good spatio-temporal matching relationship, which is the key to hydrocarbon accumulation and exploration. This knowledge has expanded the exploration area of the Lower Permian Maokou Formation in eastern Sichuan, and more importantly, it brings much enlightenment to the exploration of the syncline areas in Sichuan basin and other basins at home and abroad. • The original nature of organic matters is introduced for the first time to reevaluate the lower Permian source rocks. • The black shale in Gufeng deep-water facies has hydrocarbon generation capacity in the north of the eastern Sichuan Basin. • The sources of natural gas in Maokou Formation are different between the north and the south in the eastern Sichuan Basin. • The syncline area of the Lower Permian Maokou Formation in eastern Sichuan has the potential for gas accumulation. [ABSTRACT FROM AUTHOR]

Details of the Lower Cambrian succession of the newly-discovered intraplatfrom basin of the Yangtze Platform (South China), source rocks of the giant Ediacaran-Cambrian gasfields of the Sichuan Basin, including its stratigraphic framework, redox and organic matter accumulation histories, remain unresolved. This paper describes results of a petrological and geochemical investigation of Lower Cambrian strata near the center of the Sichuan Basin with the goal of elucidating those processes that controlled the sedimentary history of the succession. We recognize two intervals of organic-rich source rocks deposited in the intraplatfrom basin, including the Maidiping Formation and overlying Qiongzhusi Formation. The Maidiping accumulated in a carbonate platform setting during Fortunian-Early Stage 2 time (~541–526.5 Ma) and comprises a variety of rock types, including carbonate, chert, phosphorite, shale, and Mn-ore layers. Total organic carbon (TOC) value ranges from 0.47 to 5.06 wt.%; the highest quality source rocks are found in its lower member. The Qiongzhusi Formation was deposited as part of a clastic shelf during Middle Stage 2-Middle Stage 3 (~526.5–515 Ma) time. This unit is dominated by shale and argillaceous siltstone and displays TOC values varying from 0.30 to 4.28 wt.%. The most organic-rich deposits are found in its lower and upper members. Redox and hydrographic proxies suggest that the intraplatfrom basin was dominated by a strongly restricted environment and anoxic bottom water conditions that experienced intermittent episodes of euxinic or dysoxic-oxic conditions during the Fortunian-Middle Stage 3 time. However, bottom water conditions appear to have been oxic during Late Stage 2 time. Accumulation of Lower Cambrian source rocks across the Yangtze Platform appears to have been closely linked to depositional setting. Our findings suggest that organic matter accumulation in the intraplatfrom basin was fundamentally redox-controlled whereas productivity exerted the greatest control on deposition of organic matter near the slope-deep basin of the Yangtze Platform. In summary, Early Cambrian high-quality source rocks preferentially accumulated in topographic lows, including the intraplatfrom basin and slope-deep basin, an association useful to targeting conventional and unconventional hydrocarbons in the Sichuan Basin. • Stratigraphic framework of the Lower Cambrian deposits in an intraplatfrom basin on the Yangtze Platform were established. • The intraplatfrom basin was dominated by anoxic bottom water with intermittent episodes of euxinic/dysoxic-oxic conditions. • A model depicting controls on OM accumulation across the Yangtze Block during the Early Cambrian was proposed. [ABSTRACT FROM AUTHOR]