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首页> 外文期刊>Facies >Biofacies, taphonomy, and paleobiogeography of the Kamar-e-Mehdi Formation of east-central Iran, a Middle to Upper Jurassic shelf lagoon deposit
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Biofacies, taphonomy, and paleobiogeography of the Kamar-e-Mehdi Formation of east-central Iran, a Middle to Upper Jurassic shelf lagoon deposit

机译：伊朗中东部，中侏罗统陆架泻湖沉积物的Kamar-e-Mehdi组的生物相，地形学和古生物地理

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The Callovian-Lower Kimmeridgian Kamar-e-Mehdi Formation of the western Tabas Block, part of the Central-East Iranian Microcontinent, represents the fill of an extensive carbonate shelf lagoon situated between a barrier carbonate platform in the east and the uplifted Yazd Block in the west. In the course of its development, the shelf lagoon experienced increasing isolation which, together with a climatic change to more arid conditions, led to deposition of evaporites and severe restriction of the benthic fauna. Sedimentation in the predominantly low-energy lagoon was controlled by an influx of fine-grained carbonate from the neighboring platform, biogenic carbonate production within the lagoon and episodic influx of siliciclastic material by high-density currents from the uplifted western margin. Much of the succession is composed of meter-scale asymmetric cycles that record decreasing terrigenous input as well as increasing shelliness and substrate firmness due to a decreasing sedimentation rate. They are interpreted as small-scale climatic cycles recording changes in humidity. Larger-scale cycles, comprising 250-400 m in thickness, document changes in terrigenous influx and may also be climate-controlled, although a tectonic origin cannot be excluded. The shelf lagoon was populated by several level-bottom communities and small patch reefs. The latter are of low diversity, composed of calcareous sponges, corals, or oysters, and are usually associated with thick microbial crusts. The level-bottom assemblages are dominated by bivalves, and rarely also by gastropods or brachiopods. Fossils occur scattered or concentrated in pavements and beds. Shell concentrations are autochthonous to allochthonous, most commonly parautochthonous. Concentrating agents were storm-induced flows and low sedimentation rates, less commonly also storm-waves. Within the small-scale cycles, infaunal assemblages prevail but are replaced by epifaunal assemblages at their top. The latter are commonly dominated by the bivalves Pseudopecten tipperi and Camptonectes (Grandinectes) teres, the two most characteristic faunal elements of the shelf lagoon. Diversity values of the benthic fauna were low to moderate. Environmental stress was mainly produced by elevated salinity values, at times possibly intensified by lowered oxygen values and soft substrate conditions. Paleobiogeographically, the benthic macrofauna exhibits a close relationship to that of European shelf seas but contains some immigrants from the southern shores of the Tethys and the northwestern Pacific. The degree of endemism was low (two taxa).
机译：塔巴斯区块西部的Callovian-Lower Kimmeridgian Kamar-e-Mehdi组，是伊朗中东部微洲的一部分，代表了一个庞大的碳酸盐岩架泻湖的填充物，该泻湖位于东部的屏障碳酸盐台地和隆起的Yazd区块之间。西部。在其发展过程中，陆架泻湖经历了越来越多的孤立，再加上气候变化至更干旱的条件，导致了蒸发岩的沉积和底栖动物的严重限制。主要来自低能泻湖的沉积受到以下因素的控制：邻近平台的细粒碳酸盐涌入，泻湖内生物碳酸盐的产生以及高密度洋流从西缘隆起引起的硅质碎屑物质的间歇性涌入。大部分的演替过程都由米级的不对称循环组成，这些循环记录了减少的陆源输入以及由于沉降速率降低而增加的壳性和基质硬度。它们被解释为记录湿度变化的小规模气候周期。尽管不能排除构造起源，但包括250-400 m的大尺度旋回记录了陆源涌入的变化，也可能受气候控制。陆架泻湖由数个水平底下的群落和小片礁组成。后者的多样性低，由钙质海绵，珊瑚或牡蛎组成，通常伴有厚厚的微生物外壳。底部组合由双壳类动物控制，很少由腹足类或腕足类动物组成。化石分散或集中在人行道和床上。壳的浓度是自体到异体，最常见的是自体。浓集剂是暴风雨引起的流量和低沉积速率，很少是暴风浪。在小规模的周期内，无真菌的组合盛行，但在其顶部被表皮的组合所代替。后者通常由双壳类假单齿tip和Camp形纲（Grandinectes）支配，这是架子泻湖的两个最典型的动物区系。底栖动物的多样性值低至中等。环境压力主要由盐度值升高而产生，有时可能因氧值降低和软质底物条件而加剧。在古生物地理学上，底栖大型动物区系与欧洲大陆架海洋区系密切相关，但其中包含一些来自特提斯南部海岸和西北太平洋的移民。地方病的程度很低（两个分类群）。

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