In this paper, we present the detailed microfacies study and geochemical characteristics of carbonate exotics (olistoliths) associated with the Eocene Disang group of Assam–Arakan Basin, Northeast India to deduct their relative age, and depositional environment. The studied carbonate rocks contain diverse fauna with the dominance of foraminiferal assemblages (planktonic and benthic). The well-preserved planktonic foraminifera, especially Globotruncana spp. and Heterohelix spp. are recorded in carbonates and age has been assigned as late Cretaceous (Maastrichtian in age). Rare earth element (REE) contents (~ 56 ppm average value) in these carbonates are high compared with the average value of typical marine carbonate (~ 28 ppm). The Post-Archean Australian Shale (PAAS)-normalized REE patterns of these carbonates exhibit seawater-like REE patterns with light rare earth elements (LREE) depletion and relatively heavy rare earth elements (HREE) enrichment with negative Ce anomalies and positive Eu anomalies. The geochemical data along with microfacies suggest that the investigated carbonate rocks might have been formed in low energy environments deposited in neritic to bathyal palaeoenvironment during Campanian–Maastrichtian age. Our study also confirmed that the investigated Disang group carbonates are similar to the adjoining carbonates exposed in the ophiolitic mélange zone of Manipur ophiolites, NE India. It is likely that the carbonate rocks were influenced by diagenetic activities at different tectonic processes during the evolution of MOC and later emplaced with the Disang group flysch-like sediments during subduction and obduction processes of the Indian plate and Myanmar plate collision.

在本文中，我们详细介绍了与印度东北部阿萨姆-若开盆地始新世迪桑群相关的碳酸盐外来矿物（石质岩）的详细微相研究和地球化学特征，以推断它们的相对年龄和沉积环境。所研究的碳酸盐岩包含以有孔虫组合（浮游和底栖）为主的多种动物群。保存完好的浮游有孔虫，尤其是Globotruncana spp。和异螺旋属 记录在碳酸盐岩中，年龄被指定为晚白垩世（年龄为马斯特里赫特）。与典型海洋碳酸盐的平均值 (~ 28 ppm) 相比，这些碳酸盐中的稀土元素 (REE) 含量（~ 56 ppm 的平均值）较高。这些碳酸盐的后太古代澳大利亚页岩 (PAAS) 归一化的 REE 模式表现出类似海水的 REE 模式，具有轻稀土元素 (LREE) 耗尽和相对重稀土元素 (HREE) 富集，具有负 Ce 异常和正 Eu 异常。地球化学数据和微相表明，所研究的碳酸盐岩可能是在坎帕阶-马斯特里赫特时代沉积在浅海至深海古环境的低能量环境中形成的。我们的研究还证实，所研究的迪桑组碳酸盐与印度东北部曼尼普尔蛇绿岩蛇绿混杂岩带中暴露的相邻碳酸盐相似。碳酸盐岩很可能在 MOC 演化过程中受到不同构造过程的成岩活动的影响，后来在印度板块和缅甸板块碰撞的俯冲和俯冲过程中被迪桑群复理石类沉积物侵位。