ABSTRACT

Despite belonging to an important time slice in the geological history, the Eocene shallow-marine beds of the Alborz region in Iran have received little attention from researchers. We selected two stratigraphic sections (Mojen and Kalateh) ascribed to the Ziarat Formation as suitable representatives for the current analysis, emphasising on their constituent microfacies and paleoenvironmental implications. The biotic communities are characterised by larger benthic foraminifera (LBF), coralline algae, corals, and bivalves as the major carbonate facies components. The microfacies gradients and paleoenvironmental analysis suggest deposition in a shallow-marine oligotrophic ramp environment within two platform stages. Both these stages indicate an increase in water depth from the inner to the middle ramp settings with spatial distribution of the LBF and other benthic components. Our data support the previous view that the early Eocene witnessed an increase in LBF taxa with near obliteration of the coral reefs in the sedimentary platforms across the Tethys. The corals reinitiated building reefal structures in the Middle Eocene, marking an important phase in the Tethyan paleoenvironmental evolution.

摘要

尽管属于地质历史上的一个重要时间片，伊朗阿尔伯兹地区始新世浅海床却很少受到研究人员的关注。我们选择了属于 Ziarat 组的两个地层剖面（Mojen 和 Kalateh）作为当前分析的合适代表，强调了它们的组成微相和古环境影响。生物群落的特征是较大的底栖有孔虫（LBF）、珊瑚藻、珊瑚和双壳类动物作为主要的碳酸盐相成分。微相梯度和古环境分析表明沉积在两个平台阶段内的浅海贫营养斜坡环境中。这两个阶段都表明水深从内部到中间斜坡设置增加，LBF 和其他底栖成分的空间分布。我们的数据支持先前的观点，即早始新世见证了 LBF 分类群的增加，特提斯海峡沉积平台中的珊瑚礁几乎消失。珊瑚在始新世中期重新开始建造珊瑚礁结构，标志着特提斯古环境演化的一个重要阶段。