Becklees Sandstone Formation

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Becklees Sandstone Formation (BECK), Carboniferous, Northern England Province[edit]

Becklees Sandstone Formation is part of the Warwickshire Group

Name[edit]

The new name is derived from the Becklees Borehole (BGS Registration Number NY37SE/3) (NY 35166 71578), which proves the greatest thickest of this formation. See Jones and Holliday (2006[1]); Jones et al. (in press[2]).

Lithology[edit]

Interbedded red sandstones (70–90 per cent) and reddish brown mudstones and reddish brown palaeosols including calcretes. Sandstones are fine- to medium-grained, orange brown to bright reddish brown and pinkish brown, moderately to well sorted and typically lack mica. Sandstones are generally cross-bedded and occur in thick successions (10–30 m thick), forming sharp to erosively based channel sandstones in multistorey units, some showing upwards-fining. In hand specimen the sandstones contain noticeably fewer lithic clasts than the underlying Canonbie Bridge Sandstone Formation; this is confirmed by thin section analysis. The sandstones have lower gamma ray API values compared to the underlying Canonbie Bridge Sandstone Formation, with GR values ranging from 39–120 API (mean 77.1, median 74.02 API). Limestones and thin coals are indicated in cuttings descriptions from the Becklees Borehole (see above), although these do not appear to be common and were not recorded at outcrop.

Genetic interpretation[edit]

Deposition on a well-drained alluvial plain with large fluvial systems and rare ephemeral floodplain lakes.

Stratotype[edit]

The formation outcrops at its type locality along the River Esk, Canonbie area, opposite Dead Neuk (NY 39360 76310), where approximately 28 m are present, including the base. Reference sections include outcrops along the River Esk at Mason’s Stream (NY 39813 75760).

Lower and upper boundaries[edit]

The base of the formation occurs at outcrop at (NY 39360 76310) and (NY 39812 75760). It is taken at the abrupt junction where fine- to coarse-grained reddish brown lithic sandstones of the Canonbie Bridge Sandstone Formation are overlain by softer, orange brown, fine- to medium-grained sandstones that lack appreciable lithic grains of the Becklees Sandstone Formation (Figure 8, Column.10). In uncored boreholes the boundary is marked by a shift in the gamma ray log to lower values, reflecting the change in composition from lithic rich (higher GR values) sandstones of the Canonbie Bridge Sandstone Formation to lithic poor, ‘cleaner’ sandstones with lower GR values (Becklees Sandstone Formation). This can be seen for example at 485.3 m depth in the Becklees Borehole (see above) and 214 m depth in the Glenzierfoot Borehole (BGS Registration Number NY37SE/2) (NY 36514 74275). Unusual polygonal cracks have been recorded at the base of the formation along the River Esk at (NY 39360 76310).

The top of the formation is taken at the sharp boundary beneath Permian rocks (Figure 8, Column 10). This marks the Variscan unconformity.

Thickness[edit]

The full thickness of the formation is not proven but ranges from zero to a maximum of 203.6 m in the Becklees Borehole (see above).

Distribution

The formation is restricted to the central parts of the Canonbie Syncline, between the Evertown Borehole (BGS Registration Number NY37NE/14) (NY 36390 75938), the Becklees Borehole (see above), and the Knottyholm Borehole (BGS Registration Number NY37NE/6) (NY 39501 77124).

Age[edit]

Asturian (Westphalian D).

References[edit]

  1. Jones, N S, and Holliday, D W.2006.The stratigraphy and sedimentology of Upper Carboniferous Warwickshire Group red-bed facies in the Canonbie area of S.W. Scotland.British Geological Survey Internal Report, IR/06/043.
  2. Jones, N S, Holliday, D W, and McKervey, J A.In press.Warwickshire Group (Pennsylvanian) red-beds of the Canonbie coalfield, England–Scotland border, and their regional palaeogeographical implications.Geological Magazine.