Finstall Member

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Finstall Member (FNSTL)[edit]

Finstall Member (Old et al., 1991)

Previous nomenclature[edit]

Building Stones (Hull, 1869)

Parent unit[edit]

Helsby Sandstone Formation

Derivation of name[edit]

From the Finstall area (SO 980 700), east of Bromsgrove, Worcestershire.

Type section[edit]

SO 865 639, disused quarry, Hadley, Worcestershire

Reference section[edit]

SO 9619 6816: Sugarbrook No. 3 Borehole. BGS Registered No. SO96NE/30, 67.3 to 206.8 m (Old et al., 1991).

Extant exposures/sections[edit]

Scattered exposures in the Bromsgrove area, south and east of Kidderminster.

Lithology[edit]

The dominant lithology is planar and trough cross-bedded, irregularly bedded and structureless, pale red-brown and greenish grey sandstones. Subordinate lithologies are red-brown and grey-green mudstone and siltstone. The sequence shows repeated fining-upward cycles, from sandstone to mudstone; there is commonly an intraformational conglomerate at the base of each cycle and the upper beds of sandstone are commonly parallel laminated. Sedimentary structures include ripple marks, flute casts, slump structures, mudcracks and convolute bedding. Micaceous bedding planes are common. Bioturbation occurs in the lower part of the member and plant remains and Euestheria have been found in the upper part in the reference section. Elsewhere (1.2) the member has yielded acritarchs, miospores, plant remains, annelids, brachiopods, bivalves, Euestheria, ostracods, and remains of arachnids, fish, amphibians and reptiles.

Lower boundary[edit]

The lower boundary is taken at the base of the cycle above the highest bed of extraformational conglomerate.

Upper boundary[edit]

The upper boundary is taken at the top of the highest significant (>1 m) bed of sandstone with large scale cross bedding.

Thickness[edit]

The thickest known sequence is 139.5 m, in the Sugarbrook No.3 Borehole; the minimum known thickness is 33.6 m, in the Longbridge Laundry Borehole (SP 0201 7847) (Powell et al., 2000).

Age[edit]

Anisian (early Mid Triassic)

Equivalent units[edit]

None

Geographical extent[edit]

The member has only been mapped in the Bromsgrove area of Worcestershire but is likely to extend westwards to Little Witley (SO 78 63), Worcestershire.

Subdivisions[edit]

None

References[edit]