The concealed Upper Palaeozoic rocks of Berkshire and South Oxfordshire

Foster, Dave G.; Holliday, D. W.; Jones, C. M.; Owens, Bernard; Welsh, A.

doi:10.1016/s0016-7878(89)80057-4

Cited by 22 publications

(15 citation statements)

References 14 publications

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“…Lavas, sills and small vents of Westphalian A to C age are found along the southern margin of the WalesLondon-Brabant High (Waters et al 1994); sills and lavas are found in the Westphalian C/D sequences of Oxfordshire, and in the earlier Westphalian of Berkshire (Poole 1977;Foster et al 1989). Igneous features are known to have produced a range of associated fault styles, for example radial and ring patterns around vents, including the crypto-volcanic vents interpreted by Barnett (1985).…”

Section: Faults Resulting Solely From Syn-depositional Igneous Processesmentioning

confidence: 99%

The identification of syn-depositionally-active structures in the coal-bearing Upper Carboniferous of Great Britain

Rippon

1998

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The Upper Carboniferous coalfields of Great Britain occupy various tectonic settings. Excellent data sets allow detailed analysis of any relationship between structure and the depositional patterns. Syn-depositional movement can be identified on a basin scale, and also at the scale of individual faults. However, with the exception of the Scottish Midland Valley, definitive evidence for syn-depositional movement on specific structures is relatively rare, and especially so in the English Pennine Basin. In particular, there is a general scarcity of detailed structural control on coal-depositional patterns. The environments in which coals formed would have been much more sensitive to subtle ground movements than the higher energy environments of the major channel belts. The precursor peats were widespread and commonly diachronous, and probably spanned around half the available time and space during Westphalian deposition across the Pennine Basin. The rarity of localized structural controls on coal patterns is therefore firm evidence of rarity of specific syn-depositional faulting throughout the sedimentary volume. Using mining data mainly from the Pennine Basin and the Midland Valley, this account discusses examples of likely, and less likely syn-depositional features, and proposes structural and sedimentological critieria for systematic assessment.Much of the British Silesian (Upper Carboniferous) is coalbearing, particularly the strata of mid-A to mid-C Westphalian age. Significant earlier coals are present in Dinantian and Namurian successions in northern Britain, while Westphalian D coals are widespread within the coalfields of southern England and South Wales (Fig. 1). The main sequences have been extensively explored and mined, and many publications describe the regional geology, structural setting, and sedimentology. However, there is little published on syn-depositional movements and associated structures, and the existing literature does not assess the prevalence, or rarity, of movement and its effects on deposition; naturally, authors have reported examples of likely movement, rather than its absence.

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Section: Faults Resulting Solely From Syn-depositional Igneous Processesmentioning

confidence: 99%

The identification of syn-depositionally-active structures in the coal-bearing Upper Carboniferous of Great Britain

Rippon

1998

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“…Across the MMC, they overlie a surface already greatly eroded by the Acadian Unconformity but also overstep the Lower Coal Measures and the feather edge of the Carboniferous Limestone in the Reading Coal Basin. The preserved area of the Warwickshire Group subcrop beneath the Variscan Unconformity has been mapped from boreholes by Dunham & Poole (1974) and Foster et al (1989), but examination of seismic data indicates that it once covered a much larger area and, although there appears to be regional thinning towards the NE (Poole 1977) (Fig. 10b) there is little evidence of a depositional margin to the north or east.…”

Section: The Warwickshire Groupmentioning

confidence: 99%

“…Away from the complexities of the Oxfordshire Thrust Zone, the Warwickshire Group shows regional tilting prior to Variscan erosion. Olivine-bearing basalts and dolerite, with dolerite sills, have been described from the Lower and Middle Coal Measures of the Reading Coal Basin (Foster et al 1989) but there is seismic evidence of an apparent igneous intrusion uplifting and breaking through the Warwickshire Group on the NE margin of the Oxfordshire Coalfield at about National Grid Reference [45200 24600]. This shows as a pronounced negative on both the published reduced-to-pole magnetic field −2 and 10 km continuation residual maps (Busby et al 2006) but does not appear to have any significant effect on the residual gravity maps.…”

Section: The Warwickshire Groupmentioning

confidence: 99%

Seismostratigraphic analysis of Paleozoic sequences of the Midlands Microcraton

Butler¹

2018

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A regional review of publicly available seismic reflection lines and wells enables the identification across the Midlands Microcraton (MMC) of four Paleozoic seismostratigraphic megasequences, bounded by the Shelveian, Acadian, Symon and Variscan unconformities. The southern boundary of the MMC is drawn at a line of major change in pre-Permian subcrop, and most of central southern England is considered underlain by Paleozoic rocks of MMC character. The Lower Silurian Shelveian Unconformity cuts down through Ordovician and Cambrian rocks to the Precambrian and largely defines the distribution of these rocks in the region. However, more than 2500 m of Tremadoc shales are preserved SW of Swindon. Above the Shelveian, a characteristic shallow-marine Silurian is overlain by up to 3000 m of Old Red Sandstone facies, preserved in a northsouth-orientated syncline. The Acadian Unconformity cuts down through folded Lower Paleozoic rocks, with the Frasnian transgression overlying Precambrian in places. Little Carboniferous was deposited across the MMC until uppermost Westphalian-Stephanian Warwickshire Group sandstones and coals were laid down across the erosion surface of the Symon Unconformity. The northern boundary of thin-skinned Variscan thrusting can be interpreted on seismic data but appears to have had little effect on the regional pre-Permian subcrop.This paper presents the results of a regional review of the area of the Midlands Microcraton (MMC) using the digital, post-stack seismic lines, and well and borehole formation tops and times (Fig. 1), freely available to academic users through the UK Onshore Geophysical Library (UKOGL), together with lithological descriptions from released wells. This area has been of little interest for oil and gas exploration over the past 25 years, and the details of the Paleozoic rocks are not widely known. Few seismic lines have been recorded over the eastern and westernmost parts of the MMC, and lines recorded over the rest of the area vary greatly in vintage and quality. However, many of the lines in the central area show remarkably good detail of both Lower and Upper Paleozoic sequences and tectonic events. Interpretation has enabled the identification of four major unconformities, which define the distribution of Paleozoic rocks beneath the Permian and Triassic cover across the MMC. It has also enabled the recognition of a series of 'packages' of seismic character that can be used to identify the four seismostratigraphic megasequences separated by these unconformities. It is hoped that the information presented here will stimulate interest in the area and lead to more detailed studies for both commercial and academic purposes.

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“…Communication between South Wales and the English Midlands through mid-A to mid-C Westphalian times was inferred by Trueman (1947) and Wills (1956) on the basis of faunas and intervening remnant outcrops; further similarities in the coal sequences suggest some common external control on overall base level in all depositional areas. There may have been additional communication through Oxfordshire into the southern province in Berkshire, where Westphalian A-C Coal Measures are known (Foster et al 1989). The High was overstepped by later Westphalian sequences; Peace & Besly (1997) describe the structural evolution of the Variscan foreland and the High through late Carboniferous times.…”

Section: The Regional Setting: Comparisons With South Walesmentioning

confidence: 99%

Variscan structures in the Kent Coalfield, southeast England, and their regional significance

1997

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The Upper Carboniferous Kent Coalfield lies concealed beneath various Mesozoic formations, its southern areas lying about 20 km north of the commonly accepted position of the main Variscan Deformation Front. However, despite intense intra-coal deformation, the existing literature is ambivalent about compressional Variscan features in Kent, the general view being that coal deformation is largely the product of the depositional environment. The main deformation is interpreted here as the result of Variscan compression, the structural style being imposed by the sandstone-dominated lithology. This conclusion is necessitated by the regularity of deformational structures revealed by mine workings, and supported by coal sequence irregularities suggestive of thrusting, especially in the lower Westphalian strata, all of which is paralleled in parts of the South Wales Coalfield. The Kent data indicate that, as in South Wales, a zone of thrusting many tens of kilometres wide lies in advance of the main deformation front. Structural trends are consistent with an overall swing in the front from east–west across much of central-southern England, to more northwest–southeast across northeastern France. This swing may represent a transpressional transfer zone, within which stress deflection and block rotation produced thrust vergence oblique to the overall direction of maximum compression.

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The concealed Upper Palaeozoic rocks of Berkshire and South Oxfordshire

Cited by 22 publications

References 14 publications

The identification of syn-depositionally-active structures in the coal-bearing Upper Carboniferous of Great Britain

The identification of syn-depositionally-active structures in the coal-bearing Upper Carboniferous of Great Britain

Seismostratigraphic analysis of Paleozoic sequences of the Midlands Microcraton

Variscan structures in the Kent Coalfield, southeast England, and their regional significance

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