SUMMARY Good documentation of uncomplicated tectonic faulting in the Coal Measures of north-east Derbyshire has enabled fault planes and zones to be isolated for detailed study, both laterally and vertically. Systematic variations in throw and hade are revealed by contouring the fault planes for these properties, and typical patterns are described. The individuality shown by faults is emphasised.
SUMMARY Two differing mudstone suites, in places with an intervening non-sequence, overlie the Clowne Seam. The earlier suite is localised, and includes the Clowne Marine Band at its base. The overall succession represents an onlap relationship with the peat, commencing with near-marine creeks and bays and continuing with fresher waters containing a prolific ostracod and bivalve fauna. Total submergence of the Clowne peat was achieved during the deposition of the later suite, which has no marine affinities. This progressive flooding is related to thickness and petrographic variations in the underlying coal, which locally includes quartzitic lenses (‘ quarzlagen ’). The possible origins of these lenses are reviewed.
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.
The Silkstone Rock (Westphalian A, Langsettian) is a major multistorey channel sandstone formed in a delta plain environment with minimal marine influence. It occupies up to three interseam intervals in the east Pennine coalfield, England, and exceeds 50 m in thickness and 15 km in width at its maximum development, which is larger than many Westphalian channel sand bodies. The high ash content of coal adjacent to the channel belt indicates that regional peat accumulation took place contemporaneously with the existence of the channel system. The major channel system fed a number of minor channels during different interseam intervals, and conducted sediment and water into nearby delta plain lakes, via lacustrine delta and crevasse splay systems. These minor channels, which show a range of fills, are sub-parallel and show lateral offset stacking, suggesting that differential compaction was an important control on their location. The major channel belt acted as a long-lived distributary system that flowed towards the east, away from the overall basin depocentre, with its position being controlled mainly by deltaic processes.
SUMMARY 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.
We welcome this publication on vitrinite reflectance [VR] in British Carboniferous coals. There has been no unifying account for many years; the article demonstrates the value of inter-disciplinary and international collaboration. However, its brevity precludes a comprehensive review of available data and publications, and massed National Coal Board (NCB) data are excluded, which would greatly enhance understanding of maturity variations through the rock-volume, at different rates in very varied coalfields. Nor does the article include VR data from many modern boreholes drilled in un-mined areas - records available at the British Geological Survey (BGS).
The Westphalian A and B of the Pennine Basin is one of the most intensely studied sedimentary successions in the UK owing to its economic importance in the coal and hydrocarbon industries. Previous studies of this interval have utilized the wealth of mining data available to accurately correlate sand bodies and deterministically map their regional extents in a two-dimensional framework. This paper expands on one particular study by taking the same data used by previous workers and digitally processing them into a format that is readable by an oil industry reservoir modelling programme (IRAP-RMS). A three-dimensional deterministic model has then been constructed to allow visualization and analysis of the resulting facies geometries in three dimensions, with the aim of gaining an improved understanding of the geometry and architecture of a major multistorey fluvial sandbody. Application of these techniques has allowed for enhanced visualization and interrogation of the Pennine Basin interval, previously not possible using traditional two-dimensional techniques. Understanding of the Silkstone Rock and its relationship to other facies has improved, because erosion at the base of the unit can be demonstrated to truncate coals and single-storey channel-fills that represent an earlier depositional phase. The visualization of this relationship is not possible from a single two-dimensional section, and the three-dimensional model therefore clarifies stratal relationships.
The Ochil Fault, one of the most prominent tectonic features in the Midland Valley of Scotland, juxtaposes Lower Devonian volcanic rocks against late Westphalian strata, implying a possible vertical displacement of up to 4 km. The Kincardine Basin in its hanging-wall, although actively subsiding during the greater part of the Silesian, trends generally N–S, perpendicular to the Ochil Fault, and its Silesian sedimentary record shows little sign of tectonic control by that fault. It is proposed that the Ochil Fault was initiated, possibly as a sinistral strike-slip feature, in the Devonian, but acted as a sidewall fault during the early evolution of the Kincardine Basin, attributed to extension on a hypothetical pre-Brigantian fault along the Bo'ness Line on the east side of the basin until late Namurian times, when active extension ceased. Both faults were probably buried during late Namurian and Westphalian times. Reactivation of the Ochil Fault during end-Carboniferous N–S extension, dated by quartz-dolerite emplacement, was responsible for probably at least 2 km displacement. including the presently visible footwall uplift. It is suggested that the hanging wall may have contained a Permian basin, now removed.
This paper re-introduces a forgotten subject, cannel coal, formed within very low gradient mire drainage systems. A minute part of the British Carboniferous rock volume, cannel was prized in the early Industrial Revolution for oil and gas, notably hydrogen. In this paper it is revisited to reveal under-reported palaeogeography, using modern mining and drilling data to give regional depositional insights. The focus is on the English East Midlands, in the SE of the Pennine Basin. Early literature on other areas emphasized deposition in small lakes, assuming little connectivity. In the East Midlands, large lake deposits are connected by cannel-filled channels, from the basin's southern margins up to 100 km north into Yorkshire. Interplays with fluvio-clastic systems are spread over a subtle but simple palaeoslope, north and NE to the Gainsborough Trough sub-basin, with negligible structural disturbance during deposition of the Pennine Coal Measures Group. A gentle basement tilt is indicated. Mire drainage tangential to the central basin invites discussion on wider issues, including marine flooding into the basin. Mire longevity is discussed, this also being relevant to research on contaminant contents through coal-forming times.
Abstract One of the characteristics of all operating coalbed methane fields is the considerable variation in producibility success within these fields and even between adjacent wells, suggesting that very site-specific controls are operating. The most likely control in many coalfields is geological structure, particularly faults, which can divide the ground into fluid migration pathways and zones with bypassed, retained gas. Apart from the faulted zone itself adjacent ground will have been subject to dilational or contractional strain, and the strain profiles on either side of the fault will have their own individual permeability characteristics which may be further modified by subsequent burial history. Although any one well will be site-specific, this introductory paper seeks to describe the general ways in which modern understanding of faults and their associated strained ground can contribute to better well spacing and detailed siting and therefore a greater proportion of successful completions.
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