Environmental parameters of a coral assemblage from the Akerchi Formation (Carboniferous), Adarouch Area, central Morocco
Environmental parameters of a coral assemblage from the Akerchi Formation (Carboniferous), Adarouch Area, central Morocco
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DOI：
10.5209/jige.33865
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发表时间：
2010-09
影响因子：
1.3
通讯作者：
I. Said;S. Rodríguez;Mostafa Berkhli;P. Cózar;Alberto Gómez-herguedas
中科院分区：
文献类型：
--
作者：
I. Said;S. Rodríguez;Mostafa Berkhli;P. Cózar;Alberto Gómez-herguedas
在El-Hajeb市附近的Tizra， Akerchi和Idmarrach地层（密西西比）中出现了丰富的红珊瑚组合。约140米厚的Akerchi组分为两段。下段上部为2 ~ 5米厚的生物层，主要由嵌于灰岩中的绢珊瑚和巨型腕足类组成。其局部厚度从西南向东北增加，露头延伸超过一公里。Akerchi生物层主要由红珊瑚组成。腕足动物、苔藓虫、多孔动物（毛囊动物、海绵动物）和软体动物是生物层的显著组成部分，但它们都不是重要的组成部分。其他常见的薄片化石分类是有孔虫、藻类和蓝藻、介形虫、三叶虫和棘皮动物。生物层中的珊瑚组合被认为是一个古群落，因为生物层不是由不同时间片上的不同珊瑚层组成的，而是一群珊瑚，在许多情况下显示出它们的原始关系和连续的殖民地生长。该群落种类繁多，包括12属20种。珊瑚和周围岩石的微观和宏观相分析允许一些环境推断：束状群落中分支的破碎程度和岩石的其他特征表明能量水平很高。然而，能量不足以破坏菌落，并且大量泥晶的存在表明能量水平是不连续的。根据古生态和地貌学证据推断的其他环境因素是浅水，海水盐度正常，鲕粒坝的快速胶结和丰富的生物碎屑提供了坚硬的基质。巨大的珊瑚群落和巨大的产物直接附着在鲕粒上，而鲕粒又为在生物层中占主导地位的束状珊瑚的附着提供了坚硬的基质。
Rich assemblages of rugose corals occur in the Tizra, Akerchi and Idmarrach formations (Mississippian) near El-Hajeb City. The Akerchi Formation, approximately 140 m thick, is divided into two members. The upper part of the lower member contains a biostrome 2 to 5 m thick, composed mainly of rugose corals and gigantoproductid brachiopods embedded in marly limestone. Its local thickness increases from southwest to northeast in an outcrop extending for more than one kilometre. The Akerchi biostrome is mostly composed of rugose corals. Brachiopods, bryozoans, porifera (chaetetids, sponges), and molluscs are conspicuous elements of the biostrome, but none of them constitutes a significant component. Other common fossil taxa in thin sections are foraminifers, algae and cyanobacteria, ostracods, trilobites and echinoderms. The coral assemblage in the biostrome is regarded as a paleocommunity, because the biostrome is not composed of distinct coral bearing beds in different time slices, but rather, it is a mass of corals which in many instances show their original relationships and continuous colonial growth. The assemblage is diverse, including 12 genera and 20 species. Micro- and macrofacies analyses of corals and surrounding rock allowed some environmental inferences: a high level of energy is suggested by the degree of fragmentation of branches in fasciculate colonies and other features of the rocks. However, the energy was not high enough to destroy the colonies, and the presence of abundant micrite indicates that the energy level was discontinuous. Other environmental factors inferred from paleoecological and taphonomical evidences are shallow water with normal marine salinity and a hard substrate provided by quick cementation of oolite bar and by abundant bioclasts. Massive coral colonies and gigantoproductids are attached directly to the oolite bar which in turn provided a hard susbstrate for attachment of fasciculate corals that are dominant in the biostrome.