Earth Science Frontiers ›› 2023, Vol. 30 ›› Issue (6): 181-198.DOI: 10.13745/j.esf.sf.2023.2.11

Previous Articles     Next Articles

Comparative study on the organic enrichment mechanisms between western Hubei and northeastern Guizhou during the Early Cambrian

ZHANG Liyu1,2(), CHEN Qianglu1,2, LI Maowen2,3, YUAN Kun1,2, MA Xiaoxiao3, XI Binbin1,2, YUE Yong4, HUANG Taiyu5   

  1. 1. Wuxi Research Institute of Petroleum Geology, Petroleum Exploration and Production Research Institute, SINOPEC, Wuxi 214126, China
    2. Key Laboratory of Petroleum Accumulation Mechanisms, SINOPEC, Wuxi 214126, China
    3. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 102206, China
    4. Wuhan Center of China Geological Survey, Wuhan 430223, China
    5. General Prospecting Institute, China National Administration of Coal Geology, Beijing 100039, China
  • Received:2023-01-04 Revised:2023-02-05 Online:2023-11-25 Published:2023-11-25

RichHTML

4

PDF (PC)

137

Abstract:

Early Cambrian petroleum source rocks are widely distributed in the middle and upper Yangtze region. Understanding the coupling relationship between source-rock deposition and paleogeography/paleoclimate/paleo-ocean and the mechanistic differences in organic enrichment under different depositional environments is critical for understanding the intrinsic relationship between environment and resources, so as to provide a geological basis for resource potential analysis. In this study, Early Cambrian source rocks from outcrops in western Hubei and wells in northeastern Guizhou are characterized to reveal the main controlling factors of organic accumulation in intrashelf/interplatform basins and slope facies, using petrological, organic geochemical (rock pyrolysis, kerogen carbon isotope, total organic carbon) and inorganic geochemical (whole-rock major and trace elements, X-ray diffraction) methods. The Early Cambrian source rocks in the study area are mainly composed of type I kerogen. Along the Yazikou basin cross-section the Al contents, nutrient elements (Ba, Cu, Zn, Ni) and clay contents remain nearly constant in the organic rich interval. The redox sensitive elements (Mo, U, V) and TOC are higher in the lower Lower Cambrian Shuijingtuo Formation and show an upward decreasing trend. The Th/U (< 2) and V/(V+Ni) (> 0.54) ratio data suggest continuous anoxia in the lower Shuijingtuo Formation. In contrast, in well ZK513 slope facies, there is no obvious increase of Al and clay contents in the organic rich interval but co-variation and slight increase of nutrient elements, redox-sensitive elements and TOC in the Lower Cambrian Niutitang Formation and upper Lower Cambrian Jiumenchong Formation, indicating an increase of primary productivity and marine euxinia; such euxinic condition is further conform by the Th/U and V/(V+Ni) ratio data. Based on the paleogeographic features and previous researches, we propose that the main controlling factors of organic enrichment in well ZK513 (slope facies) are high productivity and favorable preservation conditions, where high nutrient elements brought by upwelling promote the primary productivity and lead to organic accumulation and subsequent bacterial sulfate reduction (BSR) and seawater uxinia. Whereas in the Yazikou section of the intrashelf/interplatform basins with no significant primary productivity enhancement, organic enrichment is mainly controlled by the preservation conditions.

Key words: the early Cambrian, western Hubei-Northeastern Guizhou area, organic matter enrichment, upwelling, uxinia

CLC Number: