Difference between revisions of "Pendleton Formation"

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Latest revision as of 15:54, 26 July 2021

Pendleton Formation (PENDL), Carboniferous, Midland Valley of Scotland[edit]

Pendleton Formation is part of the Yoredale Group

Name[edit]

The new name Pendleton Formation is proposed to identify all Millstone Grit Group strata of Pendleian age. Pendleton Formation supersedes previous terms such as Pendle Grit Formation and Brennand Grit Formation, used in the Lancaster district for components of the Pendleton Formation (Brandon et al., 1998[1]). The formation coincides with the Skipton Moor Grits of the Bradford district, defined by Stephens et al. (1953)[2].

Lithology[edit]

Fine- to very coarse-grained and pebbly, feldspathic sandstone, interbedded with grey siltstone and mudstone, with subordinate marine black shales, thin coals and seatearths.

Genetic interpretation[edit]

During the Pendleian the fluvial succession of the ‘Bearing Grit’ crossed the Askrigg Block occupying an incised valley (Waters et al., 2009, fig. 10[3]). On reaching the Craven Fault System the marked slope into the Central Pennine sub-basin resulted in deep-water turbidite-fronted deltas prograding into the northern part of the sub-basin, forming the Pendle Grit Member. The deposits typically comprise background sedimentation of thinly interbedded silty mudstones, siltstones and fine-grained sandstones deposited on the submarine prodelta slope. These are cut by massive, laterally impersistent, coarse-grained, pebbly sandstones filling turbidite channels (Aitkenhead et al., 2002[4]). The great thickness of sediments was sufficient to infill the northern part of the basin by late Pendleian times and allow the shallow-water fluviodeltaic coarse-grained, cross-bedded successions of the Warley Wise Grit to extend several kilometres southwards into the basin.

Stratotype[edit]

Partial type sections occur at Pendleton Moor on the west flank of Pendle Hill between Light Clough (SD 7516 3764) (the basal stratotype for the Pendleian Stage) and the excellent section at Mearley Clough (SD 785 411) where the base of the formation is exposed (Earp et al., 1961[5]). At Faugh’s Delph (SD 820 392), the upper part of the formation is exposed with about 30 m of very coarse-grained, massive sandstone of the Warley Wise Grit (Earp et al., 1961[5]).

Lower and upper boundaries[edit]

The base of the formation is taken at the base of the first thick quartz-feldspathic sandstone of Pendleian age, present above the dark grey, carbonaceous, fissile mudstone of the Bowland Shale Formation, which in the north Lancashire area and Bradford–Harrogate districts, is at the base of the Pendle Grit Member, and on the Askrigg Block, is taken at an unconformity of E1c age at the base of the ‘Bearing’ or Lower Howgate Edge Grit (Brandon et al., 1995[6]), overlying the mixed shelf carbonate and deltaic succession of the Yoredale Group (Figure.9, Column 17). The base is taken at the point in the sequence where sandstone becomes predominant.

The top of the formation occurs at the sharp conformable base of the dark grey, fissile mudstone of the Cravenoceras cowlingense Marine Band (E2A1) with eponymous fauna, which is commonly underlain by a thin, fine-grained, calcareous and phosphatic sandstone of the Pendleton Formation (Figure 9, Column 17; Figure 15, Column 5). Locally, in the absence of the Cravenoceras cowlingense Marine Band, the top of the formation is taken at the top of the Warley Wise Grit (north Lancashire area and Bradford–Harrogate districts), the base of the Mirk Fell Ironstones (Stainmore Trough) (Figure 15, Column 2) or the top of the Lower Howgate Edge Grit (northern part of the Askrigg Block).

Thickness[edit]

Lancaster 800.m; Bradford 600.m; southern part of the Askrigg Block up to 45 m thick with a condensed succession. About 30.m thickness is present in the Great Shunner Fell area (Figure.15, Column.3), where the formation is dominated by the Lower Howgate Edge Grit.

Distribution and regional correlation[edit]

The Craven Basin of north Lancashire and north Yorkshire between Lancaster (SD 47 61), Pendle Hill (SD 80 41), Skipton Moor (SE 00 50) and Harrogate (SE 30 55), and also present across the southern part of the Askrigg Block, and in the Masham district (SE 29) (Dunham and Wilson, 1985[7]). The formation passes southward into basinal mudstones of the Bowland Shale Formation (Craven Group).

Age and biostratigraphical characterisation[edit]

Pendleian (E1). The top of the formation is defined at the base of the Cravenoceras cowlingense (E2a) Ammonoid Zone.

Local notes

Within the southern part of the Askrigg Block the formation is dominated by two sandstones, the ‘Bearing Grit’ and overlying Underset (or Top) Grit. These sandstones pass southwards respectively into the thick turbiditic succession of the Pendle Grit Member (PG) (Figure 15, Column 6) (of thinly interbedded silty mudstone, siltstone and fine-grained sandstone, cut by massive, laterally impersistent, coarse-grained, pebbly sandstones) and the Warley Wise Grit (of coarse-grained, cross-bedded sandstone) (see Brandon et al., 1995[6]). In the Great Shunner Fell area, a condensed succession is dominated by the Lower Howgate Edge Grit (Dunham and Wilson, 1985[7]). Within the Stainmore Trough, the Mirk Fell Ganister (MKFG) occurs at the same stratigraphical level as the Lower Howgate Edge Grit of the Askrigg Block (Figure 15, Column 2).

References[edit]

  1. Brandon, A, Aitkenhead, N, Crofts, R G, Ellison, R A, Evans, D J, and Riley, N J.1998.Geology of the country around Lancaster.Memoirs of the Geological Survey of Great Britain, Sheet 59 (England and Wales).
  2. Stephens, J V, Mitchell, G H, and Edwards, W.1953.Geology of the country between Bradford and Skipton.Memoir of the Geological Survey of Great Britain, Sheet 69 (England and Wales).
  3. Waters, C N, Waters, R A, Barclay, W J, and Davies, J R.2009.BGS Stratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore).British Geological Survey Research Report, RR/09/01.
  4. Aitkenhead, N, Barclay, W J, Brandon, A, Chadwick, R A, Chisholm, J I, Cooper, A H, and Johnson, E W (editors).2002.British regional geology: The Pennines and adjacent areas. (Keyworth, Nottingham: British Geological Survey.)
  5. 5.0 5.1 Earp, J R, Magraw, D, Poole, E G, Land, D H, and Whiteman,A J.1961.Geology of the country around Clitheroe and Nelson.Memoir of the Geological Survey of Great Britain, Sheet 68 (England and Wales)
  6. 6.0 6.1 Brandon, A, Riley, N J, Wilson, A A, and Ellison, R A.1995.Three new early Namurian (E1c–E2a) marine bands in central and northern England, UK, and their bearing on correlations with the Askrigg Block.Proceedings of the Yorkshire Geological Society, Vol. 50, 333–355
  7. 7.0 7.1 Dunham, K C, and Wilson, A A.1985.Geology of the Northern Pennine Orefield: Volume 2, Stainmore to Craven.Economic Memoir of the British Geological Survey, Sheets 40, 41 and 50, parts 31, 32, 51, 60 and 61(England and Wales)