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首页> 外文期刊>Neues Jahrbuch fur Geologie und Palaontologie. Abhandlungen >Sequence stratigraphic significance of shell concentrations in the Mobarak Formation (Mississippian), Alborz Zone, Northern Iran
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Sequence stratigraphic significance of shell concentrations in the Mobarak Formation (Mississippian), Alborz Zone, Northern Iran

机译：北伊朗北部的Mobarak形成中壳体浓度的序列地层意义（密西西比人），伊朗北部

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摘要

The Lower Carboniferous carbonate shallow marine sediments of the Mobarak Formation (Alborz Zone, northern Iran) are interpreted as a deepening-shallowing cycle interpreted as recording changes in relative sea level which correspond to depositional sequences. The field observations and laboratory studies were used to identify nine facies, which can be grouped into four depositional zones: shallow open marine (shaly and marly (A1) and bioclastic mudstones/wackestones (A2) facies), shoal (crinoidal grainstone, rudstone (A3) and coral framestone (A4) facies), lagoon (bioclastic peloidal wackestone /packstone (A5), foraminiferal packstone (A6), gastropod bioclastic wacke-stone and packstone (A7) facies) and tidal flat (dolomitized lime mudstone (A8) and oncoidal pack-stone (A9) facies). Based on the absence of distinct palaeobathymetric changes, the wide lateral distribution of facies and the depositional system likely represent an eastward-deepening homoclinal ramp. Five 3rd-order depositional sequences were distinguished in the Mobarak Formation. In the Mobarak Formation, four types of shell concentrations can be identified based on sedimentologic, stratigraphic, taphonomic and palaeoecological characteristics. These four types of shell concentrations are found in distinct positions within depositional sequences which are transgressive lag (at the base of transgressive systems tract (TST), hiatal concentrations, event concentrations and multiple-event concentrations. The features of lag concentrations include distinct basal erosional surface, poor sorting, high fragmentation and abrasion, disarticulation and convex-up orientation which deposited above the fair-weather wave base in a high-energy inner ramp environment. Concentration at the end of the TST (which overlies by mfs sediments) is a hiatal concentration characterized by high percentages of articulated brachiopods in life position with high rates of bioerosion. This concentration was accumulated during high rates of production of biogenic hard parts and low sedimentation rates, below storm wave base in outer ramp environments. Concentrations occurring in the mfs are in situ event concentrations characterized by autochthonous and highly time-averaging. Besides, they were accumulated during times of the rapid sedimentation in middle ramp above SWB environment. This is approved by their high preservation quality (comparatively high percentage of articulated shells) that the biogenic alteration is the most important taphonomic feature. Multiple-event concentrations at the top of the HST have characteristics such as densely fossiliferous deposits with complete disarticulation, convex-up and high grades of bioerosion, low grades of abrasion in a lower middle to upper outer ramp environments with sporadic high-energy events.
机译：Mobarak形成的较低的石炭碳酸盐浅海洋沉积物（Alborz区，伊朗北部）被解释为一种深化的雌性循环，被解释为相对海平面的记录变化，这对应于沉积序列。现场观察和实验室研究用于鉴定九个相，可以将其分组为四个沉积区：浅滩海洋（Shaly和Marly（A1）和生物弹性泥岩/疣（A2）相），Shoal（Crinoidal Grainstone，Rudstone（ A3）和珊瑚蛙（A4）各方），泻湖（生物塑料Peloidal Wackestone / Packstone（A5），多孔碎石包装（A6），胃肠杆菌生物型骨灰石 - 石头和包装（A7）相）和潮汐平（二元石灰泥岩（A8）和尾状包 - 石头（A9）相）。基于没有明显的古食虫变化，相和沉积系统的宽侧横向分布可能代表了东方深化的同源坡道。在Mobarak的形成中区分了五次3阶沉积序列。在Mobarak形成中，可以基于沉积学，地层，术和古生学特征来鉴定四种类型的壳浓度。在沉积序​​列内的不同位置中发现这四种类型的壳浓度（在侵袭系统沟（TST），流离失所浓度，事件浓度和多次事件浓度的基础上。滞后浓度的特征包括不同的基础侵蚀表面，差的分类，高碎片和磨损，缺陷和凸起取向，其沉积在高能内斜坡环境中的公平天气波基底上方。TST末端的浓度（由MFS沉积物覆盖）是一个Hiatal浓度以高百分比的生物腐蚀速率在生物腐蚀速率高率的高百分比上表征。在生物固有的硬质零件和低沉降速率的高速率下积累了这种浓度，在外坡道环境中的风暴波基础下方。在MFS中发生的浓度是原位事件浓度，其特征是通过自动加载和高的Y时间平均。此外，它们在高于SWB环境的中坡道快速沉淀期间累积。这是通过它们的高保性质量（相对高的铰接壳比例）批准，即生物改变是最重要的撰写意识。 HST顶部的多次事件浓度具有诸如密集的化纤沉积物，具有完全吻合，凸起和高等级的生物渗透，低级中间的低级磨损，具有散发性高能量事件。

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