Difference between revisions of "Stockdale Farm Formation"

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Stockdale Farm Formation (STFA), Carboniferous, Midland Valley of Scotland[edit]

Name[edit]

The formation is named after Stockdale Farm, Stockdale, east of Settle. It was first proposed by Arthurton et al. (1988)[1] for a succession proved in the Halsteads (Cominco S2) Borehole (BGS Registration Number SD86SW/6) (SD 8491 6345) and the Stockdale Farm (Cominco S7) Borehole (BGS Registration Number SD86SE/6) (SD 8541 6378), both of which are located on the Settle Sheet.

Lithology[edit]

The formation comprises an informal lower member of thinly interbedded laminated dolostone, dolomitic–siliciclastic siltstone, mudstone and laminated anhydrite, which is overlain by an informal middle member of interbedded sandstone, siltstone, mudstone and thin limestone. The sandstones are arkosic pale grey, fine-grained, micaceous and carbonaceous, and the limestones are dark grey micrites with subordinate packstones and wackestones. An upper informal member comprises interbedded limestone, siltstone and mudstone, lithologically similar to the middle member, but lacking sandstones.

Genetic interpretation[edit]

Alluvial plain and marginal marine flats subject to periodic desiccation and fluctuating salinity, in a semi-arid climate.

Stratotype[edit]

The type section of the formation is the Halsteads (Cominco S2) Borehole (see above) from about 389.35 m to the base of the bore at 426.35 m depth. A reference section, proving the upper and middle parts of the formation, is the Stockdale Farm (Cominco S7) Borehole (see above) from about 169.9.m to the base of the bore at 309.9 m depth.

Lower and upper boundaries[edit]

The base of the formation is not seen, but it is possibly an angular unconformity above Lower Palaeozoic sandstone, siltstone and mudstone.

The top of the formation is a deeply fissured surface marking a significant non-sequence. It is overlain by conglomerates of the Chapel House Limestone Formation and underlain by limestone, siltstone and mudstone of the Stockdale Farm Formation (Figure 15, Column 6).

Thickness[edit]

Known only in boreholes (see above), the formation is greater than 165 m thick.

Distribution and regional correlation[edit]

The formation occurs in the Askrigg Block–Craven Basin ‘Transition Zone’. It is possibly equivalent to the Roddlesworth Formation of the Central Lancashire High (see Waters et al., 2009)[2].

Age and biostratigraphical characterisation[edit]

Tournaisian to Chadian. The macrofauna is generally poor except in the top 12 m where it includes Delepinea sp. and Michelinia megastoma (see Arthurton et al., 1988[1]). The topmost 11 m of the formation include the typical early Chadian (Tournaisian) foraminifers Palaeospiroplectammina mellina, Endothyra danica, Lugtonia monilis and Spinoendothyra mitchelli (Arthurton et al., 1988[1]).

Formal subdivisions[edit]

Arthurton et al. (1988[1]) proposed three members, in ascending order: the Halsteads Shales-with-Anhydrite, Stockdale Farm Sandstones and Shales, and Stockdale Farm Limestones and Shales. This nomenclature is unacceptable as two of the members duplicate the name of the formation and the lithological epithets are unsuitable. As these units are recorded only in the subsurface, no attempt has been made during this study to formalise the definition of these units as members.

References[edit]

  1. 1.0 1.1 1.2 1.3 Arthurton, R S, Johnson, E W, and Mundy, D J C.1988.Geology of the Country around Settle.Memoir of the British Geological Survey, Sheet 60 (England and Wales)
  2. 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.