| Hydrothermal Dolomite in the Upper Sinian (Upper Proterozoic) Dengying Formation, East Sichuan Basin, China |
| |
| 作者姓名： | LIU Shugen HUANG Wenming JANSA Luba F. WANG Guozhi SONG Guangyong ZHANG Changjun SUN Wei and MA Wenxin |
| |
| 作者单位： | 1 State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, Sichuan, China
2 Geological Exploration & Development Research Institute, CNPC Chuanqing Drilling Engineering Company Limited, Chengdu 610059, Sichuan, China
3 Geological Survey of Canada-Atlantic, Dartmouth. N.S. & Earth Science Department, Dalhousie University, Halifax, N. S. Canada
4 Petrochina Hangzhou Research Institute of Geology, Hangzhou 310023, Zhejiang, China |
| |
| 基金项目： | This work was funded by National Basic Research Program of China (Grant No. 2012CB214805). |
| |
| 摘 要： | Hydrothermal Dolomite （HTD） is present in the Upper Sinian （Upper Proterozoic） Dengying Formation, east Sichuan Basin, China. The strata are comprised by primary dolomite. The HTD has various textures, including zebra dolomite, subhorizontal sheet-like cavities filled by saddle dolomite and breccias cemented by saddle dolomites as well occur as a fill of veins and fractures. Also co-occur MVT type lead-zinc ores in the study area. The δ13C and δ18O isotopes of HTD in the Upper Sinian Dengying Formation are lighter than those of the host rocks, while STSr/86Sr is higher. The apparent difference in carbon, oxygen and strontium isotopes, especially the large difference in S7Sr/S6Sr isotopes ratio indicate crystallization from hot basinal and/or hydrothermal fluids. Saddle dolomite was precipitated at temperatures of 270-320℃. The diagenetic parasequences of mineral assemblage deposited in the Dengying Formation are： （1） dolomite host rock →sphalerite-galena-barite-fluorite; （2） dolomite host rock →saddle dolomite →quartz; （3） dolomite host rock →saddle dolomite→bitumen; （4） dolomite host rock →saddle dolomite →barite. The mean chemical composition of the host dolomite matrix and HTD didn＇t change much during hydrothermal process. The fluids forming the HTDs in the Dengying Formation were mixtures of freshwater from the unconformity at the top of Sinian, fluids from diagenetic compaction and hydrocarbon generation ＆ expulsion from the Lower Cambrian Niutitang Formation mudstones or the Doushantuo Formation silty mudstones, and hydrothermal fluids from the basement. The hydrocarbon reservoirs associated with the HTD were mostly controlled by the basement faults and fractures and karsting processes at the unconformity separating Sinian and Cambrian strata. The hydrocarbon storage spaces of HTD included dissolved cavities and intercrystalline pores. Dissolution cavities are extensive at the top of Dengying Formation, up to about 46m below the unconformity between Sinian an
|
| 关 键 词： | 上震旦统 四川盆地 热液蚀变 上元古界 灯影组 白云岩 中国 地层不整合 |
| 收稿时间： | 2014/2/27 0:00:00 |
| 修稿时间： | 2014/8/15 0:00:00 |
Hydrothermal Dolomite in the Upper Sinian (Upper Proterozoic) Dengying Formation,East Sichuan Basin,China |
| |
| Authors: | LIU Shugen HUANG Wenming JANSA Luba F WANG Guozhi SONG Guangyong ZHANG Changjun SUN Wei MA Wenxin |
| |
| Abstract: | Hydrothermal Dolomite (HTD) is present in the Upper Sinian (Upper Proterozoic) Dengying Formation, east Sichuan Basin, China. The strata are comprised by primary dolomite. The HTD has various textures, including zebra dolomite, subhorizontal sheet‐like cavities filled by saddle dolomite and breccias cemented by saddle dolomites as well occur as a fill of veins and fractures. Also co‐occur MVT type lead‐zinc ores in the study area. The δ13C and δ18O isotopes of HTD in the Upper Sinian Dengying Formation are lighter than those of the host rocks, while 87Sr/87Sr is higher. The apparent difference in carbon, oxygen and strontium isotopes, especially the large difference in 87Sr/86Sr isotopes ratio indicate crystallization from hot basinal and/or hydrothermal fluids. Saddle dolomite was precipitated at temperatures of 270–320° C. The diagenetic parasequences of mineral assemblage deposited in the Dengying Formation are: (1) dolomite host rock → sphalerite‐galena‐barite‐fluorite; (2) dolomite host rock → saddle dolomite → quartz; (3) dolomite host rock → saddle dolomite→ bitumen; (4) dolomite host rock → saddle dolomite → barite. The mean chemical composition of the host dolomite matrix and HTD didn't change much during hydrothermal process. The fluids forming the HTDs in the Dengying Formation were mixtures of freshwater from the unconformity at the top of Sinian, fluids from diagenetic compaction and hydrocarbon generation & expulsion from the Lower Cambrian Niutitang Formation mudstones or the Doushantuo Formation silty mudstones, and hydrothermal fluids from the basement The hydrocarbon reservoirs associated with the HTD were mostly controlled by the basement faults and fractures and karsting processes at the unconformity separating Sinian and Cambrian strata. The hydrocarbon storage spaces of HTD included dissolved cavities and intercrystalline pores. Dissolution cavities are extensive at the top of Dengying Formation, up to about 46m below the unconformity between Sinian and Cambrian and were generated mainly during karstification. Hydrothermal alteration enhanced the reservoir property of the Dengying Formation dolomites with 3%–5% increase in porosity. No agreement has been reached why zebra dolomite occurs only in the Upper Sinian strata, which would indicate that HTD mineralization occurred during two different periods, each of them related to major extensional tectonic event. The early one related to the Xingkai taphrogenesis (Z2?€1) and the later one to the Emei taphrogenesis (D2‐T2). But, all the data from saddle dolomite suggest that the predominant crystallization occurred during the latter event. |
| |
| Keywords: | Hydrothermal dolomite(HTD) Upper Sinian Series Dengying Formation Sichuan basin |
| 本文献已被 CNKI 维普 等数据库收录！ |
| 点击此处可从《Acta Geologica Sinica》浏览原始摘要信息 |
| 点击此处可从《Acta Geologica Sinica》下载免费的PDF全文 |
|
