{"title":"中国西南部四川盆地西北部上泥盆统沙窝子组白云岩的特征和成因","authors":"Xiaoqin Liu, Fengjie Li, Weiwei Tang","doi":"10.1007/s13146-024-00956-3","DOIUrl":null,"url":null,"abstract":"<p>Devonian thick–layer dolostone is widely developed in the Shawozi Formation (SWZF) of the Sichuan Basin, however, the properties of the dolomitisation fluid and its genesis require clarification. This study adopted field observations, microscopic identification, and geochemical data analysis methods that major and trace elements, rare–earth element (REE) analyses, carbon and oxygen isotopes based on 31 samples. The results showed that dolomites were divided into crystalline dolomites and calcareous dolomites. Crystalline dolomite, which is the most widely distributed, can be further divided into fine crystalline dolomite (FCD), fine–medium crystalline dolomite (FMCD), medium crystalline dolomite (MCD), and coarse crystalline dolomites (CCD). Calcareous dolomite, fine crystalline dolomite (FCD), and fine–medium crystalline dolomite (FMCD) have higher Fe, higher Mn, and lower Sr, whereas medium crystalline dolomite (MCD) and coarse crystalline dolomite (CCD) have the opposite characteristics. The REE content was lower and weak negative anomalies of Ce and Eu were apparent, indicating that dolomite was formed in a fragile redox environment and at a relatively low temperature. The δ<sup>13</sup>C<sub>PDB</sub> value had a small variation range, with an average value of 0.04‰. Although the variation range of δ<sup>18</sup>O<sub>PDB</sub> value was more extensive, most samples were concentrated in the range of -6.53‰~-2.1‰, indicating that the overall effect of diagenetic alteration was more negligible. Two dolomitisation models were developed: reflux seepage and burial dolomitisation. The reflux seepage model mainly developed calcareous dolomite, whereas the burial model mainly developed crystalline dolomite. The degree of dolomitisation increased with increasing burial depth and formation pressure.</p>","PeriodicalId":9612,"journal":{"name":"Carbonates and Evaporites","volume":"77 1","pages":""},"PeriodicalIF":1.1000,"publicationDate":"2024-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Characteristics and genesis of dolomites in the Upper Devonian Shawozi formation of the northwestern Sichuan basin, southwestern China\",\"authors\":\"Xiaoqin Liu, Fengjie Li, Weiwei Tang\",\"doi\":\"10.1007/s13146-024-00956-3\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>Devonian thick–layer dolostone is widely developed in the Shawozi Formation (SWZF) of the Sichuan Basin, however, the properties of the dolomitisation fluid and its genesis require clarification. This study adopted field observations, microscopic identification, and geochemical data analysis methods that major and trace elements, rare–earth element (REE) analyses, carbon and oxygen isotopes based on 31 samples. The results showed that dolomites were divided into crystalline dolomites and calcareous dolomites. Crystalline dolomite, which is the most widely distributed, can be further divided into fine crystalline dolomite (FCD), fine–medium crystalline dolomite (FMCD), medium crystalline dolomite (MCD), and coarse crystalline dolomites (CCD). Calcareous dolomite, fine crystalline dolomite (FCD), and fine–medium crystalline dolomite (FMCD) have higher Fe, higher Mn, and lower Sr, whereas medium crystalline dolomite (MCD) and coarse crystalline dolomite (CCD) have the opposite characteristics. The REE content was lower and weak negative anomalies of Ce and Eu were apparent, indicating that dolomite was formed in a fragile redox environment and at a relatively low temperature. The δ<sup>13</sup>C<sub>PDB</sub> value had a small variation range, with an average value of 0.04‰. Although the variation range of δ<sup>18</sup>O<sub>PDB</sub> value was more extensive, most samples were concentrated in the range of -6.53‰~-2.1‰, indicating that the overall effect of diagenetic alteration was more negligible. Two dolomitisation models were developed: reflux seepage and burial dolomitisation. The reflux seepage model mainly developed calcareous dolomite, whereas the burial model mainly developed crystalline dolomite. 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引用次数: 0
摘要
泥盆纪厚层白云岩广泛发育于四川盆地沙窝子地层(SWZF),但白云岩化液的性质及其成因亟待澄清。本研究采用野外观察、显微鉴定和地球化学数据分析方法,即基于 31 个样品的主要元素和微量元素、稀土元素分析、碳和氧同位素分析。结果表明,白云岩分为结晶白云岩和钙质白云岩。结晶白云岩分布最广,可进一步分为细结晶白云岩(FCD)、细-中结晶白云岩(FMCD)、中结晶白云岩(MCD)和粗结晶白云岩(CCD)。钙质白云石、细晶白云石(FCD)和细-中晶白云石(FMCD)具有较高的铁、较高的锰和较低的锶,而中晶白云石(MCD)和粗晶白云石(CCD)则具有相反的特征。REE 含量较低,Ce 和 Eu 呈弱负异常,表明白云石是在脆弱的氧化还原环境和相对较低的温度下形成的。δ13CPDB值的变化范围较小,平均值为0.04‰。虽然δ18OPDB值的变化范围较大,但大多数样品都集中在-6.53‰~-2.1‰的范围内,表明成岩蚀变的总体影响较小。建立了两种白云化模型:回流渗流和埋藏白云化。回流渗流模型主要发育钙质白云岩,而埋藏模型主要发育结晶白云岩。白云岩化程度随着埋藏深度和地层压力的增加而增加。
Characteristics and genesis of dolomites in the Upper Devonian Shawozi formation of the northwestern Sichuan basin, southwestern China
Devonian thick–layer dolostone is widely developed in the Shawozi Formation (SWZF) of the Sichuan Basin, however, the properties of the dolomitisation fluid and its genesis require clarification. This study adopted field observations, microscopic identification, and geochemical data analysis methods that major and trace elements, rare–earth element (REE) analyses, carbon and oxygen isotopes based on 31 samples. The results showed that dolomites were divided into crystalline dolomites and calcareous dolomites. Crystalline dolomite, which is the most widely distributed, can be further divided into fine crystalline dolomite (FCD), fine–medium crystalline dolomite (FMCD), medium crystalline dolomite (MCD), and coarse crystalline dolomites (CCD). Calcareous dolomite, fine crystalline dolomite (FCD), and fine–medium crystalline dolomite (FMCD) have higher Fe, higher Mn, and lower Sr, whereas medium crystalline dolomite (MCD) and coarse crystalline dolomite (CCD) have the opposite characteristics. The REE content was lower and weak negative anomalies of Ce and Eu were apparent, indicating that dolomite was formed in a fragile redox environment and at a relatively low temperature. The δ13CPDB value had a small variation range, with an average value of 0.04‰. Although the variation range of δ18OPDB value was more extensive, most samples were concentrated in the range of -6.53‰~-2.1‰, indicating that the overall effect of diagenetic alteration was more negligible. Two dolomitisation models were developed: reflux seepage and burial dolomitisation. The reflux seepage model mainly developed calcareous dolomite, whereas the burial model mainly developed crystalline dolomite. The degree of dolomitisation increased with increasing burial depth and formation pressure.
期刊介绍:
Established in 1979, the international journal Carbonates and Evaporites provides a forum for the exchange of concepts, research and applications on all aspects of carbonate and evaporite geology. This includes the origin and stratigraphy of carbonate and evaporite rocks and issues unique to these rock types: weathering phenomena, notably karst; engineering and environmental issues; mining and minerals extraction; and caves and permeability.
The journal publishes current information in the form of original peer-reviewed articles, invited papers, and reports from meetings, editorials, and book and software reviews. The target audience includes professional geologists, hydrogeologists, engineers, geochemists, and other researchers, libraries, and educational centers.