Arid
DOI10.1002/gj.1070
The Ridgeway Conglomerate Formation of SW Wales, and its implications. The end of the Lower Old Red Sandstone?
Hillier, Robert D.; Williams, Brian P. J.
通讯作者Hillier, Robert D.
来源期刊GEOLOGICAL JOURNAL
ISSN0072-1050
出版年2007
卷号42期号:1页码:55-83
英文摘要

The Devonian Old Red Sandstone Ridgeway Conglomerate Formation crops out in Pembrokeshire, SW Wales. It was deposited as part of a dryland alluvial fan, axial fluvial valley deposystem. It conformably overlies the mid Lochkovian Freshwater West Formation and probably predates deposition of the Lower Cosheston Group Mill Bay Formation indicating an Early Devonian (latest Lochkovian to earliest Pragian) age, rather than a Middle Devonian age as suggested by previous workers. It therefore represents the youngest preserved formation of the Milford Haven Group south of the Ritec Fault. The Formation thickens drastically into the Ritec Fault, indicating its control on sedimentation. The half-graben topography initiated deposition of a hangingwall alluvial fan that was sourced from a southerly Lower Palaeozoic/Precambrian provenance within the present-day Bristol Channel. The Formation is heterolithic in nature, with deposits on the fan reflecting a mixture of processes. Conglomerates were deposited primarily by laterally extensive sheetfloods, and as bars in low-relief, laterally accreted channels. Sandstones were also predominantly deposited by sheetfloods. Gritty mudrocks in comparison demonstrate deposition by cohesive debris flows.


The fan prograded northward and interfingered with a low-gradient, high-sinuosity fluvial channel system dominated by inclined and non-inclined heterolithic stratification. Thinly laminated mudstone and sandstone interbeds were deposited in ephemeral fan-toe and axial valley lakes that may have developed during sub-humid climatic episodes. The lacustrine heterolithic association has associated matgrounds and possible ’algal roll-up’ structures. Calcretized peetee structures and root traces comprise a lake margin calcrete association.


Fan gravels prograded into the axial fluvial valley during periods of increased sediment flux that may represent semi-arid conditions and/or episodes of tectonic activity. Calcretes of varying development were established in both the fan and axial valley zones. Calcretes with lower stages of development are more proximal to the Ritec Fault reflecting decreased soil residence times and high deposition rates within the axial valley. More strongly developed soil profiles on the fan may indicate sequence boundaries associated with low sediment flux, or increased soil residence time due to active fan-channel migration (the pedofacies concept). Groundwater calcretes have sharp-based and layer-bound calcrete profiles. Gully-bed cements are locally developed within the fan gravels. Copyright (C) 2007 John Wiley & Sons, Ltd.


英文关键词Devonian conglomerate alluvial fan Old Red Sandstone Anglo-Welsh Basin calcrete dryland rivers
类型Review
语种英语
国家Wales ; Scotland
收录类别SCI-E
WOS记录号WOS:000243912100004
WOS关键词CANYON ALLUVIAL-FAN ; KICKING-HORSE-RIVER ; RIO-GRANDE RIFT ; SOUTHWEST WALES ; DEATH-VALLEY ; DEBRIS-FLOW ; FLUVIATILE SEDIMENTATION ; STRUCTURAL CONTROLS ; SOUTHEAST SPAIN ; COSHESTON GROUP
WOS类目Geosciences, Multidisciplinary
WOS研究方向Geology
资源类型期刊论文
条目标识符http://119.78.100.177/qdio/handle/2XILL650/154300
作者单位(1)Natl Museum Wales, Dept Geol, Cardiff CF1 3NP, S Glam, Wales;(2)Univ Aberdeen, Dept Geol & Petr Geol, Aberdeen, Scotland
推荐引用方式
GB/T 7714
Hillier, Robert D.,Williams, Brian P. J.. The Ridgeway Conglomerate Formation of SW Wales, and its implications. The end of the Lower Old Red Sandstone?[J],2007,42(1):55-83.
APA Hillier, Robert D.,&Williams, Brian P. J..(2007).The Ridgeway Conglomerate Formation of SW Wales, and its implications. The end of the Lower Old Red Sandstone?.GEOLOGICAL JOURNAL,42(1),55-83.
MLA Hillier, Robert D.,et al."The Ridgeway Conglomerate Formation of SW Wales, and its implications. The end of the Lower Old Red Sandstone?".GEOLOGICAL JOURNAL 42.1(2007):55-83.
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