The structural setting and geometry of the Faringdon Trough defined by subsurface mapping

IF 1.2 4区地球科学 Q2 Earth and Planetary Sciences

Proceedings of the Geologists Association Pub Date : 2024-10-01 DOI:10.1016/j.pgeola.2024.09.001

Nigel Banks

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Abstract

Data from over 80 boreholes have been used together with the surface geology to interpret the subsurface structure and stratigraphy of the Corallian to Gault (Upper Jurassic to Lower Cretaceous) sediments in the Vale of the White Horse, between Faringdon and Wantage in West Oxfordshire. The gentle regional dip to the SSE of the sediments in this area is interrupted by two major features. The first is the Faringdon Fault, first defined at outcrop just east of Faringdon. This has been traced SE from the outcrop extent for at least 8 km in the subsurface towards Wantage. It has an estimated maximum downthrow to the SW of ca 40 m. Contrary to previous interpretations, this fault was probably active during Kimmeridge Clay deposition.

The second feature is the Faringdon Trough, an erosional palaeovalley filled with at least 50 m of marine Lower Greensand sediments. The Trough trends SSE from Faringdon and cuts deeply through the Kimmeridge Clay to reach the underlying Corallian. A subtle structural feature, here named the Baulking Fault, has a throw of < 10 m and its movement was probably pre-Cretaceous, but it seems to have influenced the path and geometry of the Faringdon Trough, dividing it into two segments. Contrary to previous interpretations, subsurface mapping suggests that the main Trough has a broad U-shape in cross-section with a planar base where it rests on resistive Corallian limestone. Along its margins depositional dips of up to 9° have been widely recorded in the Lower Greensand sediments.

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通过地下测绘确定法林顿海槽的结构环境和几何形状

我们利用 80 多个钻孔的数据和地表地质信息，对位于西牛津郡法林顿和旺塔吉之间的白马谷科拉伦至高尔特（上侏罗世至下白垩世）沉积物的地下结构和地层进行了解释。该地区沉积物向东南方向的平缓区域倾角被两个主要地貌打断。第一条是法林顿断层，最初是在法林顿以东的露头处确定的。该断层从露头处开始向东南方向延伸，在地下至少延伸了 8 公里，一直延伸到旺塔吉。据估计，该断层向西南方向的最大下倾角约为 40 米。与之前的解释相反，该断层很可能在金默里奇粘土沉积期间就已开始活动。第二个地貌是法林顿槽，这是一个侵蚀性古山谷，其中充满了至少 50 米深的下绿砂岩海洋沉积物。海槽从法林顿向东南方向延伸，深深地穿过基姆里奇粘土，到达下层的科拉利亚岩。一个微妙的结构特征在此被命名为鲍尔金断层（Baulking Fault），其倾角为 10 米，其运动可能发生在白垩纪之前，但它似乎影响了法林顿海槽的走向和几何形状，将其分为两段。与之前的解释相反，地下测绘表明，主海槽的横截面呈宽阔的 U 形，底部为平面，位于具有阻力的科拉利亚石灰岩上。在下绿砂岩沉积物中广泛记录了其边缘高达 9° 的沉积倾角。

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来源期刊

Proceedings of the Geologists Association 地学-地质学

CiteScore

2.70

自引率

8.30%

发文量

审稿时长

6-12 weeks

期刊介绍： The Proceedings of the Geologists'' Association is an international geoscience journal that was founded in 1859 and publishes research and review papers on all aspects of Earth Science. In particular, papers will focus on the geology of northwestern Europe and the Mediterranean, including both the onshore and offshore record. Following a long tradition, the PGA will focus on: i) a range of article types (see below) on topics of wide relevance to Earth Sciences ii) papers on aspects of Earth Science that have societal relevance including geoconservation and Earth management, iii) papers on palaeoenvironments and palaeontology of the Mesozoic and Cenozoic, iv) papers on aspects of Quaternary geology and climate change, and v) papers on the history of geology with particular reference to individuals that have shaped the subject. These topics will also steer the content of the themes of the Special Issues that are published in the PGA.