Earth Science Frontiers ›› 2023, Vol. 30 ›› Issue (6): 14-31.DOI: 10.13745/j.esf.sf.2023.2.15

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The botryoidal-lace texture and its role in dolomite reservoir control in the 2nd member, Sinian Dengying Formation in Sichuan Basin

LU Pengda1,2(), LI Zeqi1,2, TIAN Tengzhen1,2, WU Juan1,2, SUN Wei1,2, QIAO Zhanfeng3, WANG Yongsheng3, LIU Shugen1,2,4, DENG Bin1,2,*()   

  1. 1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, China
    2. College of Energy, Chengdu University of Technology, Chengdu 610059, China
    3. PetroChina Hangzhou Research Institute of Petroleum Geology, Hangzhou 310023, China
    4. Xihua University, Chengdu 610039, China
  • Received:2023-01-05 Revised:2023-02-05 Online:2023-11-25 Published:2023-11-25

Abstract:

The genesis and depositional environment of the unique botryoidal-lace dolomite in the 2nd member of the Sinian Dengying Formation are widely debated. Through detailed petrological and geochemical analyses we show that (1) the botryoidal-lace texture is formed by karst activities under high-frequency sea-level fluctuations quasi-contemporaneous with Sinian “aragonite-dolomite seas”, while the spatial heterogeneity of microbialite across the karst zone ultimately controls the textural differentiation to result in various fibrous dolomite cement types. (2) There is an obvious correlation between the botryoidal-lace texture and microbiolite matrix (MM) abundances. The botryoidal texture is mainly composed of FSDs (fascicular slow dolomite) and FFDs (fascicular fast dolomite), usually developed in sections of granular dolomite at the top and thrombolites dolomite at the bottom of the fourth-order cycles. The lace texture is composed of fascicular slow dolomite and RFDs (radial fast dolomite), mainly developed in the middle of the fourth-order cycles, in sections of laminated-stromatolites dolomite. Therefore, the longitudinal multi-spinulite feature and intermittent dissolution of microbialite by atmospheric water, together form the multi-stage, three-dimensional architecture of the high-quality botryoidal-lace dolomite in the Dengying Formation.

Key words: Sichuan Basin, Dengying Formation, carbonate, microbilite, karst reservoir

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