Frizington Limestone Formation
Frizington Limestone Formation is part of the Great Scar Limestone Group
The name is derived from Frizington Parks Quarry, west Cumbria. Barclay et al. (1994) proposed the name Frizington Limestone for the exposed correlative, the Seventh Limestone (Eastwood et al., 1931; Arthurton and Wadge, 1981). Akhurst et al. (1997) treated the Frizington Limestone with formational status.
In west Cumbria the Frizington Limestone Formation consists of thin- to thick-bedded tabular limestones with thin shale interbeds (Barclay et al., 1994). The lower part of the formation displays intensely bioturbated, mainly thin- to medium-bedded, sandy and silty limestone with rhizoliths, fenestral lime mudstones and tabular to hummocky cross-bedded sandstones. This is overlain by a foraminiferal-rich, mainly medium- to thick-bedded, bioclastic packstone and grainstone with abundant micritised peloids, common lithostrotionoid sheets, and thin shale and sandy limestone beds. Palaeokarst surfaces and calcrete and mudstone palaeosols are present within the upper part of the formation.
The lower part of the formation was deposited within a peritidal environment; the overlying beds were deposited in a shallow marine setting with periodic emergence.
The Sellafield 3 Borehole (BGS Registration Number NY00SW/35) (NY 02596 02646) between 1515.75 and 1615.45 m depth below the rotary table provides a partial type section (including the base) comprising mostly bioclastic packstones, with lesser grainstones, sandy limestones at some levels and some thin sandstones. A few fenestral lime mudstones occur, mostly towards the base of the formation (see Barclay et al., 1994). A reference section is at Frizington Parks Quarry (disused), west Cumbria (NY 0405 1560) where about 26 m of the lower part of the formation are seen, though not the base, which is thought to be within 10.m of the lowest beds seen. The simplified sequence comprises a lower part about 9 m thick of bioclastic sandy limestones interbedded with packstones and grainstones, a middle portion about 12 m thick of mainly grainstones with brachiopod ‘hashes’ and coral horizons, and an upper part, poorly exposed, about 5 m thick of sandstones and thin shales (see Barclay et al., 1994).
Lower and upper boundaries
In north and west Cumbria the base of the formation, which is marked locally by conglomeratic sandstone, rests either disconformably on the Martin Limestone Formation (with Arundian strata missing), or directly on the conglomerates of the Courceyan Marsett Formation and lavas of the Cockermouth Volcanic Formation (Figure 9, Column 13; Figure 14, Columns 1, 2). Locally, the formation may directly overlie Lower Palaeozoic rocks.
In north Cumbria the top of the formation is taken immediately beneath the ‘Sixth Shale’, which comprises the base of the Sixth Limestone unit, Eskett Limestone Formation. In the Uldale area (NY 2560 3700) the top is a palaeosol containing a thin coal seam (Eastwood et al., 1968). In west Cumbria, calcretes, palaeokarst surfaces and terrigenous deposits are evidence of emergence and subaerial exposure at the top of the formation beneath the Urswick Limestone Formation. Here, early Asbian strata are missing.
The formation is 50–100 m thick in west Cumbria.
Distribution and regional correlation
The formation occurs in west and north Cumbria between Whitehaven and Penrith. The western limit is truncated below the Permo–Triassic basal unconformity. The eastern limit is taken at the Kirk Rigg Fault, along the line of the A66 highway, west of Penrith (McCormac, 2001).
Age and biostratigraphical characterisation
Holkerian. The presence of foraminifer Pojarkovella nibelis in the Sellafield boreholes (Barclay et al., 1994) is indicative of the Cf5 Zone. The palaeokarst surfaces and calcrete and mudstone palaeosols present within the upper part of the formation indicate that periodic emergence preceded a period of nondeposition during late Holkerian and early Asbian times.
- Barclay, W J, Riley, N J, and Strong, G E.1994.The Dinantian rocks of the Sellafield area, West Cumbria.Proceedings of the Yorkshire Geological Society, Vol. 50, 37–49.
- Eastwood, T, Dixon, E E L, Hollingsworth, S, and Smith, B.1931.The geology of the Whitehaven and Workington District.Memoir of the Geological Survey, Sheet 28 (England and Wales).
- Arthurton, R S, and Wadge, A J.1981.Geology of the country around Penrith.Memoir of the Geological Survey of Great Britain, Sheet 24 (England and Wales).
- Akhurst, M C, Chadwick, R A, Holliday, D W, McCormac, M, McMillan, A A, Millward, D, and Young, B.1997.Geology of the west Cumbria district.Memoir of the British Geological Survey, Sheets 28, 37 and 47 (England and Wales).
- Eastwood, T, Hollingworth, S E, Rose, W C C, and Trotter, F M.1968.Geology of the country around Cockermouth and Caldbeck.Memoir of the Geological Survey of Great Britain, Sheet 23 (England and Wales).
- McCormac, M.2001.The Upper Palaeozoic rocks of the Shap and Penrith district, Edenside, Cumbria.British Geological Survey Research Report, RR/01/10.