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- Title
川中北部地区茅口组白云岩成因分析 ——来自岩石学、原位地球化学及年代学证据.
- Authors
肖钦仁; 袁海锋; 谌 辰; 李跃杰; 陈 聪; 张玺华; 匡明志; 徐 婷; 叶子旭; 王 涛; 王炳森; 李正勇
- Abstract
Recently, significant breakthroughs have been made in the exploration of dolomite reservoirs in the Maokou Formation in the northern slope area of central Sichuan. In order to explore the genesis of dolomite reservoirs, the author used techniques such as core observation, thin section microscopy, cathodoluminescence, laser in-situ analysis of major and trace elements, and U⁃Pb isotope dating to systematically study the geochemical characteristics of the Maokou Formation dolomite reservoirs in the northern slope area of central Sichuan, and established the diagenetic sequence of the Maokou Formation dolomite in the study area. And the diagenetic fluid characteristics of various types of dolomite were determined, ultimately establishing a dolomitization model for the Maokou Formation in the study area. The main understanding includes: (1) Three types of dolomite are mainly developed in the study area, namely, biotite dolomite, crystalline dolomite and saddle dolomite, and the diagenetic sequence based on petrological and geochemical characteristics is as follows: the first generation of D1-1 → the second generation of D2-1 → the third generation of SD1 → the fourth generation of SD2 → the fifth generation of D2-2. The D1-2 was successively formed by the influence of the second-generation D2-1 and the third-generation SD1. (2) The geochemical characteristics of the dolomites show obvious Ce-negative and Y-positive anomalies, indicating that each type of dolomite has been affected by the sea-derived fluids and their derivatives to different degrees. At the same time, the positive δEu anomalies in some samples of each type of dolomite and even clastic tuffs indicate the existence of late tectonic-hydrothermal effects. (3) Five phases of dolomitization were developed successively in the syn- and medium-deep burial periods, and the first and second phases occurred successively in the syn- and quasi-syncline periods, resulting in the formation of the dolomite matrix, such as clastic dolomite and its fine-crystal dolomite, etc.; the tectonic effects were influenced by the tectonic effect in the quasi- and shallow burial periods; and the dolomites in the quasi-and shallow burial periods were influenced by the tectonic effect. In the quasi-symbiotic period, two phases of tectonic-hydrothermal dolomitization occurred under the influence of tectonics, forming saddle-shaped dolomite and accounting for part of the matrix dolomite; the fifth phase of dolomitization in the middle-deep burial period accounted for the formation of a large number of trachyte dolomite and other fine-crystalline dolomite. (4) Phase I dolomitization and Phase II dolomitization are beneficial to the preservation of primary pore space because of their early occurrence. Phase III dolomitization and Phase IV dolomitization are typical tectonic-hydrothermal dolomitization, which have both constructive and destructive effects on the pore space of dolomite reservoirs, and Phase V dolomitization of the buried period occurs in a closed system, which is the most important diagenesis for the formation of the dolomite reservoirs in the study area.
- Publication
Natural Gas Geoscience, 2024, Vol 35, Issue 7, p1160
- ISSN
1672-1926
- Publication type
Article
- DOI
10.11764/j.issn.1672-1926.2023.12.004