张航，蒋东，曾令平，等. 盐间白云岩成因：以川东北金珠坪飞仙关组为例[J].河南理工大学学报(自然科学版), doi: 10.16186/j.cnki.1673-9787.2024070023.

ZHANG H，JIANG D，ZENG L P，et al. Genesis of inter-salt dolostone: A case of the Feixianguan Formation at Jinzhuping，NE Sichuan[J]. Journal of Henan Polytechnic University( Natural Science), doi: 10.16186/j.cnki.1673-9787.2024070023.

盐间白云岩成因：以川东北金珠坪飞仙关组为例(网络首发)

张航 ¹，蒋东 ¹，曾令平 ¹，杨恒 ¹，李亮 ²，高政基 ³，路志朋 ³，罗连超 ³，文华国 ³

（1.中国石油西南油气田公司 川东北气矿，四川 达州 635000；2.中海石油（中国）有限公司湛江分公司 南海西部石油研究院，广东 湛江524057；3.成都理工大学 油气藏地质及开发工程全国重点实验室和沉积地质研究院，四川 成都 610059）

摘要: 目的 白云岩-蒸发岩共生体系是咸化背景下白云岩成因研究的重要对象，但少有研究关注互层型白云岩-蒸发岩共生体系中白云岩（即盐间白云岩）的形成机制。 方法 本研究对川东北金珠坪飞仙关组旋回Ⅱ内的盐间白云岩组合开展了综合性岩石学和地球化学研究，以此来查明盐间白云岩的成因机制。 结果 结果显示，金珠坪盐间白云岩组合表现出盐间白云岩（即含膏-膏质泥晶白云岩）与硬石膏岩类（即硬石膏岩和含云-云质硬石膏岩）的互层，硬石膏岩类层厚可达近10 m，且缺乏暴露标志。盐间白云岩组合的δ³⁴S_anh为14.6‰~18.3‰ V-CDT，在下三叠统海相硫酸盐蒸发岩的δ³⁴S_anh范围内。较厚的硬石膏岩层、致密的岩性、暴露标志的缺失以及与典型海相蒸发岩相似的δ³⁴S_anh表明，盐间白云岩组合沉积于低能蒸发潟湖环境，而盐间白云岩的白云石化流体可能与蒸发潟湖环境的高咸水相关。盐间白云岩的δ¹³C_dol 为−1.5‰~2.2‰ V-PDB，δ¹⁸O_dol为−6.8‰~−2.5‰ V-PDB，稀土元素组成受硅质碎屑的污染，排除污染样品后总体表现出MREE富集和显著的Ce负异常。氧同位素温度计恢复的白云石化流体温度显示，旋回Ⅱ下部的白云石化流体计算温度仅略高于同期开阔海水，再次证明蒸发潟湖水可能对盐间白云岩的形成影响巨大。但是，旋回Ⅱ中上部的盐间白云岩显示出显著偏高的白云石化流体计算温度，这可能与δ¹⁸O较低的大气淡水和/或正常海水的输入有关。盐间白云岩的Ce负异常和MREE富集表明其白云石化流体与同生期海水相关，白云石化发生很早。 结论 综合分析表明，金珠坪盐间白云岩的形成与蒸发潟湖水联系密切，很可能是（准）同生期蒸发海水渗透白云石化的产物。本研究的相关发现将深化对白云岩-蒸发岩共生体系中白云岩成因机制的认识。

关键词: 白云岩-蒸发岩共生体系；泥晶白云岩；硬石膏岩；地球化学；飞仙关组；川东北

中图分类号：P618.13

doi: 10.16186/j.cnki.1673-9787.2024070023

基金项目: 国家自然科学基金资助项目（42272133）

收稿日期：2024-07-04

修回日期：2024-10-12

网络首发日期：2024-05-22

Genesis of inter-salt dolostone：A case of the Feixianguan Formation at Jinzhuping，NE Sichuan (Online)

ZHANG Hang¹，JIANG Dong¹，ZENG Lingping¹，YANG Heng¹，LI Liang²，GAO Zhengji³，LU Zhipeng³，LUO Lianchao³，WEN Huaguo³

（1.Northeastern Sichuan Oil and Gas District，PetroChina Southwest Oil and Gas Field Company，Dazhou 635000，Sichuan，China；2. Zhanjiang Branch of China National Off shore Oil Corporation Ltd.，Zhanjiang 524057，Guangdong，China；3.State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation & Institute of Sedimentary Geology，Chengdu University of Technology，Chengdu 610059，Sichuan，China）

Abstract: Objectives Dolostone-evaporite associations are good subjects for studying the genesis of dolostone in saline settings，but rare research focused on the dolostone within dolostone-evaporite associations formed of interbedded dolostone and evaporite （i.e.， inter-salt dolostone）. Methods In this study，the petrological and geochemical characteristics of the inter-salt dolostone association of the Cycle Ⅱ of the lower Feixianguang Fm. at Jinzhuping （NE Sichuan） was therefore investigated with the aim to deterring the genesis of inter-salt dolostone. Results The results show that the inter-salt dolostone is anhydrite-bearing dolo-mudstone，while the inter-salt dolostone was characterized by layers of inter-salt dolostone （i.e.，anhydrite-bearing dolo-mudstone） alternating with anhydrite evaporite or dolomite-bearing anhydrite evaporite. Each layer can reach near ten meters in thickness. No exposed structures were observed. The studied inter-salt dolostone association yields δ³⁴S of anhydrite between 14.6‰ and 18.3‰ V-CDT，falling into the δ³⁴S range of lower Triassic marine sulfate evaporites. The thick anhydrite evaporite layers，the low-porous rocks，the absence of exposed structures，and the similar δ³⁴S between the studied inter-salt dolostone association and lower Triassic marine sulfate evaporites suggest that the inter-salt dolostone association was largely deposited in low-energy evaporative lagoons and the dolomitizing fluids might be closely related to the hypersaline fluids within the lagoons. The inter-salt dolostone displays δ¹³C_dol from −1.5‰ to 2.2‰ V-PDB and δ¹⁸O_dol from −6.8‰ to −2.5‰ V-PDB. The REE patterns of the inter-salt dolostone were partially contaminated by the siliciclastic detritus. When excluding the samples with few or no detritus contamination，the inter-salt dolostone shows MREE-enrichment and significant negative Ce anomaly. The computed temperatures of the dolomitizing fluids based on traditional oxygen isotope thermometers show that the fluids dolomitizing the lower part of the Cycle Ⅱ have temperatures only slightly higher than those of normal open-marine seawaters. This indicates that the evaporative lagoon water is probably significantly linked with the formation of inter-salt dolostone. However，the inter-salt dolostone from the middle-upper part of the Cycle Ⅱ displays dolomitizing fluid temperatures significantly higher than those of the lower part. This is interpretated to be the result of the input meteoric water and/or normal seawater. The MREE-enrichment and significant negative Ce anomaly of the inter-salt dolostone reflect that the dolomitizing fluids might be closely linked to the （pene）contemporaneous seawater. Conclusions An integrated investigation disclosed that the inter-salt dolostone had a close relationship to the evaporative lagoon seawater and was largely originated from the seepage dolomitization of （pene）contemporaneous evaporative seawater. The findings of this study may help us better understanding the genesis of dolostone within dolostone-evaporite associations.

Key words：dolostone-evaporite association; dolo-mudstone; anhydrite evaporite; geochemistry; Feixianguang Fm; NE Sichuan

CLC: P618.13