Stratigraphical framework for the Middle Jurassic strata of Great Britain and the adjoining continental shelf

Barron, A.J.M.; Lott, G.K.; Riding, J.B. ORCID: 2012 Stratigraphical framework for the Middle Jurassic strata of Great Britain and the adjoining continental shelf. Nottingham, UK, British Geological Survey, 177pp. (RR/11/006)

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The Stratigraphy Committee of the British Geological Survey (BGS) is undertaking a review of stratigraphical classification for all parts of Great Britain. Several Stratigraphical Framework Committees (SFC) have been established to review problematical issues for various parts of the stratigraphical column. Each SFC has the following terms of reference: • To review the lithostratigraphical nomenclature of designated stratigraphical intervals for a given region, identifying problems in classification and correlation. • To propose a lithostratigraphical framework down to formation level that can be used as a central reference by geologists working in the region concerned. • To organise peer review of the scheme. • To present the results in a document suitable for publication. • To ensure that full definitions of the lithostratigraphical units are held in the web-accessible BGS Lexicon of Named Rock Units for the areas of responsibility covered by the SFC. The process of erecting a framework requires decisions to be taken about correlations and equivalences leading to a simplified nomenclature. Inevitably, many names will be rendered obsolete. The frameworks are lithostratigraphical and though each is set against a chronostratigraphical reference column, the finer points of the chronostratigraphy of the succession are not the prime concern. The predominantly Middle Jurassic rocks discussed in this report have been considered by the Jurassic Stratigraphical Framework Committee under the leadership initially of M G Sumbler (who compiled an initial draft in 2003) and, after 2001, A J M Barron. The report introduces a lithostratigraphical framework to formation level for the Middle Jurassic succession of Britain and adjoining offshore areas. It applies to the main outcrops and subcrops (where the strata are present at depth), and the offshore occurrences. It follows on, with an extended geographical brief, from the stratigraphical framework report for the Lower Jurassic of England and Wales (Cox et al., 1999). The onshore distribution has been divided into six depositional areas; the Wessex–Weald Basin, the Cotswolds, the East Midlands Shelf, the Cleveland Basin, the Moray Firth and the Hebrides, although for practical reasons the essentially arbitrary lateral limits of the first three may differ for various stratigraphical levels. The economic importance and availability of natural and man-made exposures of Middle Jurassic strata has resulted in well over 200 years of research attempting to classify them. Much of this work occurred long before guidance was available for best practice in naming lithostratigraphical units, and there has been a haphazard approach to the establishment of the hierarchy of units. From an early, relatively simple framework, subsequent publications have greatly added to the complexity of the nomenclature. Often this reflected the localised nature of research with different names being applied to essentially the same unit in different areas. Also, previously laterally contiguous deposits have been separated, eroded or concealed by post-Jurassic tectonic, igneous or sedimentary events and processes. Chapter 1 of this report is an introduction to the Middle Jurassic Series and the included proposals. It indicates the principles for the development of the new lithostratigraphical scheme and sets out the key publications used for reference. Chapter 2 summarises the structural and palaeogeographical setting of Great Britain through the Middle Jurassic and sets out the definitions, history and development of the basins. Chapter 3 briefly describes the key techniques (principally biostratigraphy) for correlation of successions, and sets out the basis for the establishment of the chronostratigraphical framework. Chapter 4 outlines the development of the lithostratigraphical framework. The fifth (Chapters 5 to 8) and largest part of the report provides a fuller description of the stratigraphical framework for each of the six onshore groups – the Inferior Oolite, Great Oolite, Ravenscar and Ancholme groups in England, and the Great Estuarine and Sutherland groups in Scotland, subdivided as appropriate into regions and/or palaeogeographical provinces. Each entry includes a description of the origin and history of the nomenclature, rank and subdivisions, principal lithologies, type area and reference sections, geographical extent, lower and upper boundary, thickness, age range, environment of deposition and key references. Chapter 9 gives a concise account of the framework for the offshore regions, related to the onshore sequences. Definitions of the offshore Fladen, West Sole, Brent and Humber groups and their component formations are not given as the full schemes are formally and satisfactorily published elsewhere (Lott and Knox, 1994; Richards et al., 1993; Ritchie et al., 1996).

Item Type: Publication - Report
Programmes: BGS Programmes 2010 > Geology and Landscape (England)
ISBN: 9780852726952
Funders/Sponsors: NERC
Date made live: 05 Mar 2012 15:25 +0 (UTC)

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