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首页> 外文期刊>Facies >Tectonically driven carbonate ramp evolution at the southern Tethyan shelf: the Lower Eocene succession of the Galala Mountains, Egypt
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Tectonically driven carbonate ramp evolution at the southern Tethyan shelf: the Lower Eocene succession of the Galala Mountains, Egypt

机译：Tethyan陆架南部构造驱动的碳酸盐岩斜坡演化：埃及加拉拉山的始新世演替

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摘要

The succession of the Galala Mountains at the southern Tethyan margin (Eastern Desert, Egypt) provides new data for the evolution of an isolated carbonate platform in the Early Eocene. Since the Late Cretaceous emergence of the Galala platform, its evolution has been controlled strongly by eustatic sea-level fluctuations and the tectonic activity along the Syrian Arc-Fold-Belt. Previous studies introduced five platform stages to describe platform evolution from the Maastrichtian (stage A) to the latest Paleocene shift from a platform to ramp morphology (stage E). A first Early Eocene stage F was tentatively introduced but not described in detail. In this study, we continue the work at the Galala platform, focussing on Early Eocene platform evolution, microfacies analysis and the distribution of larger benthic foraminifera on a south-dipping inner ramp to basin transect. We redefine the tentative platform stage F and introduce two new platform stages (stage G and H) by means of the distribution of 13 facies types and syn-depositional tectonism. In the earliest Eocene (stage F, NP 9b-NP 11), facies patterns indicate mainly aggradation of the ramp system. The first occurrence of isolated sandstone beds at the mid ramp reflects a post-Paleocene-Eocene thermal maximum (PETM) reactivation of a Cretaceous fault system, yielding to the tectonic uplift of Mesozoic and Palaeozoic siliciclastics. As a consequence, the Paleocene ramp with pure carbonate deposition shifted to a mixed carbonate-siliciclastic system during stage F. The subsequent platform stage G (NP 11-NP 14a) is characterised by a deepening trend at the mid ramp, resulting in the retrogradation of the platform. The increasing deposition of quartz-rich sandstones at the mid ramp reflects the enhanced erosion of Mesozoic and Palaeozoic deposits. In contrast to the deepening trend at the mid ramp, the deposition of cyclic tidalites reflects a coeval shallowing and the temporarily subaerial exposure of inner ramp environments. This oppositional trend is related to the continuing uplift along the Syrian Arc-Fold-Belt in stage G. Platform stage H (NP 14a-?) demonstrates the termination of Syrian Arc uplift and the recovery from a mixed siliciclastic carbonate platform to pure carbonate deposition.
机译：特提斯南部边缘（埃及东部沙漠）的加拉拉山脉演替为始新世早期孤立的碳酸盐台地演化提供了新的数据。自从晚白垩世出现Galala平台以来，它的演化受到欣喜的海平面涨落和叙利亚弧形褶皱带沿岸的构造活动的强烈控制。先前的研究介绍了五个平台阶段来描述平台从Maastrichtian（阶段A）到最新的古新世从平台向斜坡形态转变（阶段E）的过程。暂定引入了始新世早期的第一阶段F，但没有详细描述。在这项研究中，我们继续在Galala平台上开展工作，侧重于始新世平台演化，微相分析以及盆地倾角南倾内斜坡上较大底栖有孔虫的分布。我们通过定义13种相类型和同沉积构造，重新定义了试验性平台阶段F，并引入了两个新的平台阶段（阶段G和阶段H）。在最早的始新世（阶段F，NP 9b-NP 11）中，相图模式主要表明斜坡系统的聚集。中斜坡上首次出现孤立的砂岩层，反映了白垩纪断层系统的古新世-始新世热最大值（PETM）重新活化，产生了中生代和古生代硅质碎屑岩的构造隆升。结果，具有纯碳酸盐沉积的古新世斜坡在阶段F转移到混合碳酸盐-硅质碎屑系统。随后的平台阶段G（NP 11-NP 14a）的特征是中斜坡的加深趋势，导致回生平台。中斜坡上富含石英的砂岩的沉积增加，反映了中生代和古生代沉积物的侵蚀增加。与中坡道的加深趋势相反，环状潮汐岩的沉积反映了同时期的变浅和内部坡道环境的暂时地下暴露。这种相反的趋势与沿阶段G的叙利亚弧-褶皱带继续隆升有关。平台阶段H（NP 14a-？）证明了叙利亚弧的隆起终止，并从混合硅质碳酸盐碳酸盐台地恢复为纯碳酸盐沉积。 。

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