| 塔西北地区下寒武统碳酸盐岩地球化学特征及其古环境意义: 以舒探1井为例 |
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| 引用本文： | 张春宇,管树巍,吴林,任荣,熊连桥.塔西北地区下寒武统碳酸盐岩地球化学特征及其古环境意义: 以舒探1井为例[J].地质科技通报,2021,40(5):99-111. |
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| 作者姓名： | 张春宇 管树巍 吴林 任荣 熊连桥 |
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| 基金项目： | 国家自然科学基金项目41902158 |
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| 摘 要： | 近年来，塔里木盆地盐下已成为深层油气勘探最重要的领域之一。下寒武统肖尔布拉克组是最主要的勘探层位，目前该层段地球化学特征和古环境的分析主要集中在柯坪露头区，而盆内缺乏相关研究。以盆内巴楚隆起舒探1井为例，对下寒武统肖尔布拉克组岩石学和地球化学特征(主、微量元素，稀土元素及碳氧同位素)进行了高精度分析，重建了其沉积时期的古环境及其变化特征。研究表明:舒探1井肖尔布拉克组发育多种类型的白云岩。下部以厚层藻云岩为主，中部为薄层泥岩夹白云质灰岩，上部以细-粉晶白云岩为主。样品Lan/Ybn均值为1.09，下部和上部呈现出Eu的正异常，薄片中可见硅质胶结、硅质碎屑和溶蚀现象，表明研究区可能受到了热液作用的影响。该组中部沉积物粒度较细并富集氧化还原敏感元素，V/Cr和Ni/Co分别介于2~4.25和5~7之间，表明沉积水体为次氧化环境，而上部和下部沉积物粒度较粗，氧化-还原敏感元素含量及其比值均较低，表明沉积水体为氧化环境。肖尔布拉克组δ13C值在-1.3‰~2.7‰之间，由下自上先降低后升高，下部和中部存在2个显著的正异常及1个负异常。古环境恢复表明肖尔布拉克期古盐度先降低后升高，古温度显示出逐渐上升的特点；肖尔布拉克组顶部古盐度较高，藻云岩发育，伴随着后期的淋滤和改造作用，是优质白云岩储层发育的有利部位。研究成果可以为该区的油气勘探提供依据。
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| 关 键 词： | 早寒武世 肖尔布拉克组 地球化学 碳同位素 古环境 |
| 收稿时间： | 2020-12-24 |
Geochemical characteristics and its paleo-environmental significance of the Lower Cambrian carbonate in the northwestern Tarim Basin: A case study of Well Shutan-1 |
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| Abstract: | Recently, subsalt exploration in the Tarim Basin has been one of the most significant targets of the deep hydrocarbon exploration.The Lower Cambrian Xiaoerbulake Formation is the major reservoir in current exploration.However, the analysis of the detailed geochemical and paleoenvironmental characteristics are limited in Keping area in absence of studies in the interior of the basin.This paper focuses on the Well Shutan-1 in the Bachu Uplift of the northwestern Tarim Basin.Based on the analysis of petrology and the geochemical characteristics (major, trace, rare elements and carbon-oxygen isotope), depositional environment of the Lower Cambrian Xiaoerbulake Formation is explored.Our study indicates that the lower, middle and upper part of the Xiaoerbulake Formation in Well Shutan-1 comprise thick algal dolomite, mudstone interbedded with dolomitic limestone and fine to silty dolomite, respectively.The average value of Lan/Ybn is 1.09 in the Xiaoerbulake Formation, of which the lower and upper part show positive Eu anomaly.Silica cementation, silica fragment and dissolution can be seen in the thin section, indicative of hydrothermal influence.Redox-sensitive trace elements are enriched in the middle of the formation.V/Cr and Ni/Co range from 2 to 4.25 and 5 to 7.The grain size of the sediment is finer.These are indications of suboxic bottom-water condition.The RSTEs and their ratios are relatively low in the upper and lower Xiaoerbulake Formation.The grain size of sediment is coarser.These are indications of oxic bottom-water condition.The carbon isotope ranges from -1.3‰ to 2.7‰. It decreases firstly and then increase throughout the interval.Two positive and one negative isotope excursion are identified in the lower and middle part of the interval, respectively.Paleoenvironmental reconstructions indicate that paleo-salinity firstly increased and then decreased.Paleo-seawater temperature gradually increased.Dolomite reservoirs were well developed in the late stage due to moderate salinity, occurrence of algal dolomite along with later weathering and dissolution.The research results can provide a basis for oil and gas exploration in this area. |
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