The distributions and variations of Quaternary Thames River Terrace deposits of Greater London

IF 1.3 4区 工程技术 Q3 ENGINEERING, GEOLOGICAL Quarterly Journal of Engineering Geology and Hydrogeology Pub Date : 2023-07-26 DOI:10.1144/qjegh2023-016
Elizabeth Aston, P. Mason
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Abstract

A database containing ca 27000 records of Quaternary lithostratigraphy extracted from ca 5800 individual boreholes drilled to a variety of depths, has been compiled from information contained in logs recorded and held by British Geological Survey (BGS) and from the Crossrail (CR) project. After ‘cleaning’ and quality assessment the raw borehole log data have been investigated for patterns in distribution, and variations in the Quaternary facies across Greater London. In particular, the analysis of Quaternary River Terrace Deposits has been focused on here and a summary of relevant published terminology and nomenclature is also included in this report, as an aid to understanding. The spatial distributions of each major Quaternary lithostratigraphic interval, as identified in the log descriptions, are also presented as point locations in map form, and in comparison with the corresponding BGS mapped outcrop patterns of the respective lithostratigraphic units. The presence of various specific clasts in the log descriptions, e.g. cobbles and chalk clasts, is also presented at stratigraphic member levels against their apparent source outcrops. For instance, cobbles recorded from the Boyne Hill Terrace intervals are concentrated in the eastern outcrops and reflect the Wealden source and former river system of the Darrent – Wid towards the Essex coast at Maldon. Similarly, the presence and distribution of shell and chalk clasts within river terrace sands and gravels reflect the geology of the underlying subcropping strata of Lower Shelly Clay and Chalk respectively. The Crossrail data also include some grain size information from sieve analysis and some engineering in situ test values, which require careful analysis beyond the scope of this work but are potentially useful. The grain size distributions for some of the samples from the river terrace sands and gravels show fining up and coarsening up sequences, and geographical grain size trends in various stratigraphic intervals. The recorded presence of faults, fractures and fissures, as identified by the drilling contractors or logging geologists, are also extracted and mapped. Supplementary evidence, from repeated stratigraphy or improbable spatial proximity changes in subcrop depths, suggest a cause other than deposition for such changes and on the presumption that their cause is natural, are interpreted as likely to be representative of faulting of some kind, including low angle thrust faults. Faulting is also considered to have controlled the distribution of several interglacial silt members and is the subject of considerable research in the deeper intervals of London stratigraphy, so is only briefly dealt with here. To define the period over which tectonic structures, now known to exist within the strata of the London Basin, were active requires an analysis of Quaternary deposits that overlie them. This Technical Note provides an initial review of the data available from boreholes for such work and for any other studies requiring knowledge of these deposits. Thematic collection: This article is part of the Geology of London and its implications for ground engineering collection available at: https://www.lyellcollection.org/topic/collections/geology-of-london-and-its-implications-for-ground-engineering Supplementary material: https://doi.org/10.6084/m9.figshare.c.6700313
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大伦敦地区第四纪泰晤士河阶地沉积的分布与变化
从英国地质调查局(BGS)和横贯铁路(CR)项目记录和保存的日志信息中收集了大约27000条第四纪岩石地层学记录,这些记录是从5800个不同深度的钻孔中提取的。经过“清洗”和质量评估,原始钻孔测井数据的分布模式和第四纪相在大伦敦地区的变化进行了研究。本报告特别着重分析了第四纪河流阶地沉积,并对已发表的相关术语和命名法进行了总结,以帮助理解。测井描述中确定的各主要第四纪岩石地层段的空间分布也以图的形式表示为点位,并与相应的BGS绘制的各岩石地层单元的露头格局进行比较。测井描述中各种特殊碎屑的存在,如鹅卵石和白垩碎屑,也在地层成员水平上与其明显的来源露头相比较。例如,从Boyne Hill Terrace区间记录下来的鹅卵石集中在东部露头,反映了威尔登的源头和达伦特-维德河在马尔登流向埃塞克斯海岸的前河流系统。同样,河阶地砂和砾石中贝壳碎屑和白垩碎屑的存在和分布,分别反映了下雪利粘土和白垩下垫地层的地质情况。Crossrail数据还包括筛分分析的一些粒度信息和一些工程现场测试值,这些数据需要仔细分析,超出了本工作的范围,但可能有用。部分阶地砂和砾石样品的粒度分布呈现出细化和粗化的序列,以及不同层段的地理粒度趋势。由钻井承包商或测井地质学家识别的断层、裂缝和裂缝的记录也被提取并绘制成地图。从重复的地层学或不可能的次层深度空间接近变化中获得的补充证据表明,这种变化是由沉积以外的原因造成的,并且假设它们的原因是自然的,这些证据被解释为可能是某种断裂的代表,包括低角度逆冲断层。断裂作用也被认为控制了几个间冰期粉砂体的分布,是伦敦地层学中较深层段大量研究的主题,因此这里只作简要讨论。要确定伦敦盆地地层中存在的构造构造的活动时期,需要对其上的第四纪沉积物进行分析。本技术说明对此类工作和任何其他需要了解这些矿床的研究所获得的钻孔数据进行了初步审查。专题合集:本文是伦敦地质及其对地面工程的影响合集的一部分,可在:https://www.lyellcollection.org/topic/collections/geology-of-london-and-its-implications-for-ground-engineering补充材料:https://doi.org/10.6084/m9.figshare.c.6700313
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来源期刊
CiteScore
3.40
自引率
14.30%
发文量
66
审稿时长
6 months
期刊介绍: Quarterly Journal of Engineering Geology and Hydrogeology is owned by the Geological Society of London and published by the Geological Society Publishing House. Quarterly Journal of Engineering Geology & Hydrogeology (QJEGH) is an established peer reviewed international journal featuring papers on geology as applied to civil engineering mining practice and water resources. Papers are invited from, and about, all areas of the world on engineering geology and hydrogeology topics. This includes but is not limited to: applied geophysics, engineering geomorphology, environmental geology, hydrogeology, groundwater quality, ground source heat, contaminated land, waste management, land use planning, geotechnics, rock mechanics, geomaterials and geological hazards. The journal publishes the prestigious Glossop and Ineson lectures, research papers, case studies, review articles, technical notes, photographic features, thematic sets, discussion papers, editorial opinion and book reviews.
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