Geochemistry characteristics and dolomitization mechanism of the Upper Cambrian dolomite, eastern Ordos Basin, China
Geochemistry characteristics and dolomitization mechanism of the Upper Cambrian dolomite, eastern Ordos Basin, China
复制标题
鄂尔多斯盆地东部上寒武统白云岩地球化学特征及白云石化机制
DOI：
10.1002/gj.3580
复制
发表时间：
2020-04
影响因子：
1.8
通讯作者：
Zhemin Hao
中科院分区：
文献类型：
--
作者：
Siyi Fu;Chenggong Zhang;Hongde Chen;Hairuo Qing;Anqing Chen;Junxing Zhao;Zhongtang Su;Zhemin Hao
鄂尔多斯盆地下古生界碳酸盐岩地层广泛发育。然而，以往的研究更多地关注了奥陶系，而忽略了同样具有更大沉积厚度的寒武系。近年来，随着奥陶系马家沟组白云岩气田的不断发现，更多的研究开始集中在寒武系三山子组深层白云岩上（Є3s）。通过岩石学分析、主微量元素分析、稳定同位素分析和稀土元素分析，探讨了白云岩的成因。结果表明：研究区白云岩主要类型为白云岩（1型）、泥晶-细晶白云岩（2型）和中晶白云岩（3型）。各组白云岩的δ13C值和δ18O值与海水源白云岩的δ13C值和δ18O值接近，Na2+浓度略高，表明白云岩的形成与海水密度较大密切相关。稀土元素组成以轻稀土富集、重稀土亏缺为特征，表现出明显的负Eu异常和轻微的负Ce异常，表明Є3s白云岩可能形成于弱还原-弱氧化环境。3型白云岩的总REE （ΣREE）浓度低于其他类型白云岩，说明3型白云岩可能在成岩作用过程中丢失了稀土元素。与其他两种白云岩相比，1型白云岩的MgO和CaO值较低，Mn2+浓度较高，说明1型白云岩受到了大气淡水的作用。2型白云岩的Mg、Ca值低于3型白云岩，说明3型白云岩的白云化程度较高。结合古地理背景进一步研究证实了研究区白云化模式：1型和2型白云化可能是在早期成岩作用中准同生或渗漏回流白云化形成的。随后，地层隆升导致1型白云岩受到大气淡水的作用，但没有发生严重的白云化。2型白云岩在这一时期以渗流-回流白云化作用成为主要的白云岩类型。2型白云岩在逐渐埋藏过程中转化为3型白云岩。
There are widely developed carbonate formations in the lower Palaeozoic, Ordos Basin, China. However, previous studies have paid more attention to the Ordovician formations and largely ignored the Cambrian formations, which also have a larger sediment thickness. Recently, with the continuous discovery of dolomite gas fields in the Ordovician Majiagou formation, more investigations have begun to focus on the deeper dolomite in the Cambrian Sanshanzi Formation (Є3s). This study looks into the origin of the dolomite through a combination of petrology, major–trace elements, and stable isotope and rare earth element (REE) analysis of samples from five outcrops. The results show that the main dolomite types in the study area are dolarenite (Type 1), micrite‐fine crystalline dolomite (Type 2), and medium crystalline dolomite (Type 3). The δ13C values and δ18O values of each dolomite formation are close to those of seawater‐derived dolomite and have slightly higher Na2+ concentrations, suggesting that dolomite formation is closely related to the denser seawater. The REE compositions are characterized by enrichment for light REEs and depletion for heavy REEs, exhibiting an apparent negative Eu anomaly and a slight negative Ce anomaly, indicating that the dolomites of the Є3s may form in a weak‐reduction to the weak‐oxidation environment. The total REE (ΣREE) concentrations of Type 3 dolomites are lower than other types, suggesting that those dolomites may mean that the REEs are lost during the diagenesis. Type 1 dolomite has lower MgO and CaO values and a higher Mn2+ concentration than the other two types of dolomites, indicating that Type 1 dolomite suffered the action of atmospheric fresh water. Type 2 dolomite has lower Mg and Ca values than Type 3 dolomite, suggesting that Type 3 dolomite has a higher dolomitization degree. Further study into the combined palaeogeographical background confirms the dolomitization model of the study area: Type 1 and Type 2 dolomites may have been formed by penecontemporaneous or seepage–reflux dolomitization during early‐stage diagenesis. Subsequently, stratigraphic uplift lead to the Type 1 dolomite suffering the action of atmospheric fresh water, but there was no dorag dolomitization. Type 2 dolomite became the main dolomite type by seepage–reflux dolomitization in this period. Later, Type 2 dolomite was converted into Type 3 dolomite during progressive burial.
登录
查看更多内容
影响因子：
1.8
作者：
Mahnaz Sabbagh Bajestani;A. Mahboubi;I. Al-Aasm;R. Moussavi-Harami;M. Nadjafi
通讯作者：
Mahnaz Sabbagh Bajestani;A. Mahboubi;I. Al-Aasm;R. Moussavi-Harami;M. Nadjafi
DOI：
--
发表时间：
2006
期刊：
Acta Geological Sinica
影响因子：
--
作者：
Wang Jianqiang
通讯作者：
Wang Jianqiang
影响因子：
1.7
作者：
Mingcai Hou;W. Jiang;F. Xing;S. Xu;X. C. Liu;C. Xiao
通讯作者：
Mingcai Hou;W. Jiang;F. Xing;S. Xu;X. C. Liu;C. Xiao
影响因子：
5.8
作者：
R. Larson
通讯作者：
R. Larson
影响因子：
3.5
作者：
Langhorne B. Smith
通讯作者：
Langhorne B. Smith