Structure and evolution of the East Midlands region of the Pennine Basin

Reduced to pole magnetic anomaly map.

Seismic transect across the Hathern Shelf, Widmerpool Half-graben to Nottingham Platform, showing correlation of the syn-rift sequence in deep boreholes.

Borehole correlation diagram for Tournaisian–Visean strata.

Borehole correlation diagram for Permian strata in the north-eastern part of the region, levelled to Marl Slate reference horizon. Geophysical log codes: GR Gamma ray; DT Sonic log; RHOB Resistivity log.

Map 1 Depth to top of Caledonide basement.

The subsurface of the East Midlands region has been intensively explored by boreholes and seismic surveys on account of its rich resources of coal and hydrocarbons.

This memoir is based on an exhaustive use of such data, acquired during seven decades of exploration, and aims to present a concise review of the tectonic and sedimentary history of the Carboniferous rocks of the East Midlands region.

It is the fourth in a series of subsurface memoirs relating to Upper Palaeozoic basins, and forms a sequel to a previously published account of the adjacent south-west Pennine Basin (Smith et al., 2005).

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Exploration reference

The book will serve as a basic reference source when economic conditions change or new commodities are required, or when new exploration models and exploitation technologies are developed, which once again result in new interest in the region by the exploration industry.

Oilpatch Warrior

Regional review

This account is regional in scope, dealing particularly with the deeper, concealed parts of the Carboniferous and older succession and associated structures, not considered in earlier publications on the Permian to Recent evolution.

It contains a series of structure-contour and preserved-thickness maps at a scale of 1:625 000, which illustrate present-day structure and distribution of rock units..

The accompanying written account is intended both as a regional review, as an explanation and partial amplification of these maps, and as a summary of basin evolution and tectonic history.

Exploration history

During the exploration of northern and central England for oil and gas in the 1970s and 1980s, numerous seismic reflection surveys were carried out.

These provide the principal means of investigating the geological structure and to some extent the stratigraphy of Carboniferous and older rocks below the levels that can be reliably predicted from outcrops, mine workings and most boreholes. In this book, such data have been integrated with as much of the available geological information as possible to produce an account that details the geological evolution of the region from pre-Cambrian to recent times, with particular emphasis on the Carboniferous.

Two-phase development

Carboniferous basin development in the region can be divided broadly into two main phases:

In early Carboniferous times, rapidly subsiding, fault controlled, extensional basins developed between structurally elevated emergent blocks.

Later, a more regional subsidence followed; this was characterised by a general lack of major fault-control, and resulted in submergence and depositional onlap of the earlier structural highs. Platform carbonates developed across the highs whilst argillaceous sedimentation dominated in basinal areas.

In Namurian times, a delta system prograded across the region, mainly from the north and west and supplied enormous quantities of feldspathic clastic material. These delta deposits infilled the remaining topographic depressions and show much variation in facies and thickness. Small deltas also built out into this region from rivers flowing off the London–Brabant Massif to the south, supplying protoquartzitic clastic material.

During Westphalian times, thickness variations were less marked with a more uniform distrubtion of facies.

During Bolsovian (Westphalian C) times, the first effects of the Variscan Orogeny were being felt across the Variscan Foreland. This affected the deposition and distribution of Bolsovian and Westphalian D sequences, culminating, at the end of the Carboniferous, with strong folding in places and partial reversal of some of the earlier basin-controlling normal faults. Deposition ceased with regional uplift and widespread erosion ensued.

A period dominated by extensional faulting occurred from the Permian to early Cretaceous times and was followed by further regional subsidence until early Palaeocene times. Regional uplift with superimposed basin inversion then commenced, and triggered a period of erosion that has probably continued until the present day.

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