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首页> 外文期刊>Facies >Anatomy of carbonate mounds from the Middle Anisian of Nakhlak (Central Iran): Architecture and age of a subtidal microbial-bioclastic carbonate factory
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Anatomy of carbonate mounds from the Middle Anisian of Nakhlak (Central Iran): Architecture and age of a subtidal microbial-bioclastic carbonate factory

机译：Nakhlak中部阿尼西亚人（伊朗中部）的碳酸盐土丘的解剖：潮下带微生物-生物碎屑碳酸盐工厂的结构和年代

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The Anisian succession of Nakhlak (in Central Iran) is characterized by a siliciclastic succession with minor carbonate units, with massive carbonate mounds up to 50 m thick in its upper part. The mounds, constrained in age to the late Bithynian (Ismidicus Zone) by ammonoids and conodonts, are characterized by a flat top and a lateral pinch-out marked by clinostratified slopes (about 15° in dip). Stratigraphic and microfacies analyses document an inner part of the mound characterized by massive microbial carbonates with open-space structures (stromatactis) filled with fine-grained internal sediments and marine cements. Isolated sponges (up to 5 cm), serpulids and bryozoans are present, which grew on the calcimicrobial limestone. A narrow bioclastic margin (mainly with crinoids and brachiopods) produces most of the slope facies (consisting of bioclastic grainstone and packstone, with intraclasts from the inner part of the mounds) which interfinger basinward with volcaniclastic sandstones. The demise of carbonate productivity is marked on the top of the carbonate mounds by a condensed surface, rich in ammonoids, glaucony grains, and articulated crinoids, documenting a rapid drowning. Paleolatitude data support deposition in a tropical setting, and sedimentological constraints indicate deposition close to the fair-weather wave base, within the photic zone. The late Bithynian Nakhlak carbonate mounds developed before the appearance (documented since the Pelsonian in different parts of the world) of scleractinians which, despite the favorable environmental conditions, are absent at Nakhlak. The Nakhlak mounds thus represent one of the last occurrences of the microbial factories (which developed after the Permo-Triassic extinction event and persisted for most of the Middle Triassic, but with a gradually increasing role played by scleractinians) before the first appearance of the Mesozoic corals.
机译：Nakhlak（位于伊朗中部）的阿尼西斯演替的特征是硅质碎屑演替，其碳酸盐单元较小，上部的块状碳酸盐丘高达50 m。这些土墩的年龄受铵盐和牙形石限制在比西尼安晚期（伊斯密底丘斯带），其特征是顶部平坦，侧面呈斜向倾斜状（倾斜约15°）。地层学和微相分析记录了土丘的内部，其特征为块状微生物碳酸盐，其内部充满了细粒内部沉积物和海相水泥，这些碳酸盐具有开放空间结构（基质层）。存在孤立的海绵（最大5厘米），虫卵石和苔藓虫，它们生长在钙微微生物石灰石上。狭窄的生物碎屑边缘（主要是海百合和腕足类动物）产生了大多数斜坡相（由生物碎屑岩和堆积岩组成，丘间有内部碎屑），它们与火山碎屑岩向盆地间穿插。碳酸盐生产能力的消亡在碳酸盐丘的顶部以凝结的表面为标志，该表面富含氨水，青uc和铰接的海藻，表明溺水迅速。古纬度数据支持在热带环境中的沉积，沉积学约束表明沉积区靠近光合带内的公平天气波基。 Bithynian Nakhlak晚期碳酸盐土丘发育于Scleractinians出现之前（自世界Pelsonian以来有文献记载），尽管环境条件良好，但Sakhturk在Nakhlak中却没有。因此，Nakhlak土墩代表了中生代首次出现之前微生物工厂的最后一次出现（微生物工厂在二叠纪-三叠纪灭绝事件后发展，并在中三叠纪的大部分地区都持续存在，但由纤长动物扮演的角色逐渐增加）。珊瑚。

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