The stratigraphy of the Penarth Group (Late Triassic) of the East Devon coast

The stratigraphy of the Penarth Group (Late Triassic) of the East Devon coast
复制标题

东德文郡海岸珀纳斯群（晚三叠世）的地层

DOI：
--
复制
发表时间：
2008
期刊：
影响因子：
--
通讯作者：
R. Gallois
R. Gallois
中科院分区：
--
文献类型：
--
作者：
R. Gallois

文献摘要

被引文献

相似文献

多塞特郡和东德文郡郡海岸世界遗产地德文郡郡部分的悬崖和前滨暴露出一个完整的 晚三叠世-早侏罗世层序从三叠纪麦西亚泥岩群的陆相红层相到 侏罗纪Lias群的完全海洋条件发生在Penarth群，一系列泥岩，粉砂岩和 沉积在泻湖和受保护的不同盐度的浅海环境中的石灰岩。Penarth集团作为 根据塞文的典型剖面，目前定义为韦斯特伯里组，上覆于利尔斯托克组 河口地区。德文郡东海岸出露的韦斯特伯里组地层的岩性和沉积学与 与模式区可比，但与Lilstock组不可比。因此，建议在岩性和 根据历史，这个地层应该被覆盖在白色Lias地层上的Cotham地层所取代。这将 在不改变其原始定义的情况下，恢复英国两个最古老的正式定义的地层名称 中生代的。所有三个地层在岩性上都是不同的，并被侵蚀面与相邻地层隔开， 表示非序列。那些在韦斯特伯里和科瑟姆地层底部的地层被富含 脊椎动物遗骸（“骨床”）。Cotham组是一个高度浓缩的系列，由薄互层组成， 泥岩和石灰岩与涟漪列车，叠层石，干燥的表面和滑塌床，其中最后一个已经 地震或火流星撞击造成的德文郡东海岸出露的白色Lias地层的石灰岩 沉积学上复杂，有水道、滑塌和干燥的表面。三叠纪-侏罗纪界线的位置是 目前正在审查中。可能的位置包括科瑟姆组的底部，组内的层位， 白色Lias，上覆的蓝色Lias地层的底部或蓝色Lias地层内的层位。
The cliff and foreshore exposures in the Devon part of the Dorset and East Devon Coast World Heritage Site expose an unbroken late Triassic to early Jurassic succession. The change from the terrestrial, red-bed facies of the Triassic Mercia Mudstone Group to the fully marine conditions of the Jurassic Lias Group takes place via the Penarth Group, a succession of mudstones, siltstones and limestones deposited in lagoonal and sheltered shallow-marine environments of varying salinities. The Penarth Group as currently defined is divided into the Westbury Formation overlain by the Lilstock Formation, based on type sections in the Severn Estuary area. The lithology and sedimentology of the Westbury Formation strata exposed on the east Devon coast are closely comparable with those of the type area, but those of the Lilstock Formation are not. It is therefore proposed on lithological and historical grounds that this formation should be replaced by a Cotham Formation overlain by a White Lias Formation. This would reinstate, without any change in their original definitions, two of the oldest formally defined stratigraphical names in the British Phanerozoic. All three formations are lithologically distinctive, and are separated from their neighbours by erosion surfaces that represent non-sequences. Those at the bases of the Westbury and Cotham formations are overlain by pebble beds rich in vertebrate remains (‘bone beds’). The Cotham Formation is a highly condensed succession comprised of thinly interbedded mudstones and limestones with ripple trains, stromatolites, desiccated surfaces and slumped beds, the last of which have been attributed to earthquakes or a bolide impact. The limestones of the White Lias Formation exposed on the east Devon coast are sedimentologically complex with channels, slumps and desiccated surfaces. The position of the Triassic-Jurassic boundary is currently under review. Possible positions include the base of the Cotham Formation, a horizon within the formation, the base of the White Lias, the base of the overlying Blue Lias Formation or a horizon within the Blue Lias Formation.