Depositional Facies of Lower Paleozoic Allen Bay Carbonate Rocks and Contiguous Shelf and Basin Strata, Cornwallis and Griffith Islands, Northwest Territories, Canada
Depositional Facies of Lower Paleozoic Allen Bay Carbonate Rocks and Contiguous Shelf and Basin Strata, Cornwallis and Griffith Islands, Northwest Territories, Canada
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加拿大西北地区康沃利斯和格里菲斯群岛下古生界艾伦湾碳酸盐岩及连续陆架和盆地地层沉积相
DOI：
10.1306/2f9184b9-16ce-11d7-8645000102c1865d
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发表时间：
1979
期刊：
影响因子：
3.5
通讯作者：
J. P. Hobson
中科院分区：
文献类型：
--
作者：
Dario E. Sodero;J. P. Hobson
阿伦湾和上覆的里德湾陆架碳酸盐岩及其向北向菲利普斯角海盆碎屑岩的侧向过渡在康沃利斯和格里菲斯群岛上得到了很好的暴露。康沃利斯志留纪陆架对盆地地层的暴露在这部分地层记录中可能是世界上任何地方都没有的。艾伦湾碳酸盐岩约6000英尺（1830米）厚，主要由白云岩组成。臂足类动物表明亚连湾中上段为志留纪（温洛克纪至勒德洛夫纪）。尽管白云化现象普遍存在，但通过详细的露头研究，确定了5个主要沉积相和15个较小沉积相。根据四个过渡沉积阶段描述了沉积相的纵向和横向变化。沉积发生在从受限制的内部藻滩和陆架边缘sabkha岛到不受限制的盆地等环境条件下。碳酸盐岩陆架和陆架边缘的正常海相沉积发生在各种高能和低能环境中。在陆架和盆地之间，斜坡非常低，特别是在下艾伦湾沉积时期，但在中艾伦湾沉积时期，陆架边缘的白云化礁群提供了相对有效的屏障，斜坡可能更加明显。总的来说，在整个艾伦湾和下里德湾沉积过程中，盆地和斜坡的沉积速率明显与碳酸盐陆架的沉积速率保持同步。艾伦湾和过渡型艾伦湾-菲利普斯角相有机质热蚀变的数量、类型和程度对油气的生成都是最有利的。在阿伦湾，孔隙度较高的现象在陆架边缘和陆架内部的白云化碳酸盐砂和斑块礁中尤为普遍。在大陆架方向，特别是在阿伦湾中部，孔隙度的降低主要与白云化碳酸盐砂向更细纹理的保护大陆架和藻坪相转变有关。艾伦湾碳酸盐岩的白云化作用主要与海相和高咸水与淡水的层内混合作用有关。
Allen Bay and overlying Read Bay shelf carbonate rocks and their lateral northward transition to basinal clastic rocks of the Cape Phillips are well exposed on Cornwallis and Griffith Islands. The exposures of Silurian shelf to basin strata on Cornwallis may be unexcelled anywhere in the world for this part of the stratigraphic record. Allen Bay carbonate rocks, approximately 6,000 ft (1,830 m) thick, consist largely of dolomite. Brachiopods suggest a Silurian (Wenlockian to Ludlovian) age for the middle and upper Allen Bay. Detailed outcrop studies led to the recognition of five main depositional facies and 15 lesser facies, despite pervasive dolomitization. Vertical and lateral changes of facies are described in terms of four transitional depositional stages. Deposition took place in environmental settings ranging from restricted interior algal flats and shelf-edge sabkha islands to unrestricted basins. Normal marine deposition on the carbonate shelf and shelf edge occurred in a variety of high- and low-energy environments. Between shelf and basin, slopes were very low, particularly during lower Allen Bay deposition, but may have been more pronounced through deposition of the middle Allen Bay when a dolomitized shelf-edge reef complex provided a relatively effective barrier. In general the sedimentation rate in the basin and slope apparently kept pace with that of the carbonate shelf throughout Allen Bay and lower Read Bay deposition. The amount, type, and degree of thermal alteration of organic matter in the Allen Bay and transitional Allen Bay-Cape Phillips facies appear to have been optimum for generation of both oil and gas. Greater values of porosity in the Allen Bay are particularly common at the shelf edge and in dolomitized carbonate sands and patch reefs of the interior shelf. Reduction in porosity in a shelfward direction, particularly for the middle Allen Bay, is interpreted as related primarily to change from dolomitized carbonate sand to finer textured protected-shelf and algal-flat facies. Dolomitization of Allen Bay carbonate rocks is related primarily to intrastratal mixing of marine and hypersaline water with fresh water.