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首页> 外文期刊>Geosciences >Methane Derived Authigenic Carbonate (MDAC) Aragonite Cemented Quaternary Hardground from a Methane Cold Seep, Rathlin Basin, Northern Ireland: δ 13 C and δ 18 O Isotopes, Environment, Porosity and Permeability
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Methane Derived Authigenic Carbonate (MDAC) Aragonite Cemented Quaternary Hardground from a Methane Cold Seep, Rathlin Basin, Northern Ireland: δ 13 C and δ 18 O Isotopes, Environment, Porosity and Permeability

机译：甲烷衍生的Aherigenic碳酸盐（MDAC）来自甲烷冷渗，Rathlin Basin，北爱尔兰的甲烷冷渗水泥土硬币：δ13c和δ18o同位素，环境，孔隙度和渗透率

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A block of sandstone retrieved by divers from near Rathlin Island, Co. Antrim, Northern Ireland, represents an aragonite cemented sand formed during the Quaternary. Strongly negative δ 13 C of the aragonite cement (?50 to ?60‰ δ 13 C) indicates that the hardground was formed by the anaerobic oxidation of methane (AOM), resulting in the formation of a methane-derived authigenic carbonate (MDAC) hardground. Such hardgrounds have previously been recorded as forming extensive pavements in deeper waters in the mid Irish Sea (e.g., Croker Carbonate Slabs), although the latter also contains high-magnesium calcite. Sand was initially deposited as part of a storm lag deposit, with a reworked bivalve and gastropod fauna. This sand was then colonised by a probable crustacean fauna, producing horizontal open dwelling burrows ( Thalassinoides ). After aragonite cementation, the hardground was colonised by boring bivalves, with slightly negatively elevated levels of δ 13 C. Finally, the hardground was colonised by an encrusting fauna (bryozoans, calcareous algae and serpulids), by then in warmer seas. Continued depleted levels of δ 13 C present within the encrusting fauna (?1 to ?5‰ δ 13 C) indicate continued methane generation and seepage, which may still be active to the present day, and to the possibility of shallow gas reserves. The δ 18 O values change between macro-infauna vs. encrusters, indicating a warming in water temperature, reflecting glacial and post-glacial environments. The aragonite cemented sandstone has a highly variable porosity, with large vugs (open burrows and borings), smaller mouldic porosity within gastropods and bivalves and complex micro-porosity associated with acicular aragonite cements. Overall permeability was recorded at the 2.5 to 23 Darcies level, reflecting the highly variable vuggy porosity, although matrix permeability was around 100 mD and controlled by the MDAC fabric. Actual permeability will likely be controlled by the extent to which larger pores are interconnected. The sea around the Rathlin Island area contains a diverse fauna, which is worthy of future study in the context of cold seep and MDAC pavement formation.
机译：由Rathlin Island附近的潜水员检出的一块砂岩块，北爱尔兰Antrim，代表了在第四纪期间形成的金属石粘液砂。金属石水泥（Δ50至60℃Δ13c）的强负δ13c表明硬盘由甲烷（AOM）的厌氧氧化形成，导致形成甲烷衍生的碳酸酯（MDAC）硬底。此前已经被记录成在中爱尔兰海洋中的深水中形成广泛的路面（例如，碳酸碳酸盐板），尽管后者还含有高镁方解石。砂最初作为风暴滞后矿床的一部分沉积，具有重新加工的双级和胃肠杆菌动物。然后通过可能的甲壳类动物的动物群地殖民地殖民，生产水平开放的居住挖洞（丘脑管骨）。在化妆品后，硬符被钻孔双向沉积的沉积，Δ13c水平略微升高。最后，通过封闭的动物群（盐酸盐，钙质藻类和锯齿）来殖民地殖民，然后在较温暖的海洋中。在结壳的动物区内（α1至5℃Δ13c）中存在的δ13c的延续水平表示持续的甲烷生成和渗流，这可能仍然活跃于现在的一天，以及浅气体储备的可能性。 Δ18O值在宏观 - infauna与封端之间的变化，表示在水温中变暖，反映冰川和冰川后环境。金属石粘液砂岩具有高度可变的孔隙率，具有大的Vug（开挖挖掘机和钻石），胃肠杆菌和纤维孔隙率较小，纤维孔隙率和与针状物质水泥相关的偏心和复杂的微孔隙率。在2.5至23级达布的水平上记录了整体渗透性，反映了高度可变的Vuggy孔隙率，尽管矩阵渗透率约为100 md并由MDAC织物控制。实际渗透性可能会通过互联孔的程度来控制。 Rathlin岛屿地区周围的海域包含一个不同的动物群，这是在冷渗透和MDAC路面形成的背景下的未来研究。

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