Sugarbrook Member

From Earthwise
Jump to navigation Jump to search

Sugarbrook Member (SGBK)[edit]

Sugarbrook Member (Old et al., 1991)

Previous nomenclature[edit]

Waterstones (Binney, 1846) Passage Beds (Richardson, 1928) Waterstones Group (Wills, 1970)

Parent unit[edit]

Helsby Sandstone Formation

Derivation of name[edit]

From the Sugarbrook Pumping Station site [SO 961 681], to the south-west of Bromsgrove, Worcestershire.

Type section[edit]

SO 9619 6816: Sugarbrook No. 3 Borehole (BGS Registered No. SO96NE/30), 22.9 to 67.3 m (Old et al., 1991).

Reference sections[edit]

None

Extant exposures/sections[edit]

Scarce exposures in the Bromsgrove area, south and east of Kidderminster (Mitchell et al., 1962; Old et al., 1991).

Lithology[edit]

The dominant lithology is pale red-brown and greenish grey sandstones. The sandstones are finer grained than in the underlying Finstall Member and large-scale cross-bedding is virtually absent. Interbedded red-brown and grey-green mudstones and siltstones are more common than in the Finstall Member. The sequence shows repeated fining-upward cycles, from sandstone to mudstone; intraformational conglomerates occur throughout. Sedimentary structures include ripple marks, flute casts, slump structures, mud cracks and convolute bedding. Micaceous bedding planes are common. In the type section bioturbation, plant remains and Euestheria have been found in the lower about15m, and acritarchs and pseudomorphs after halite occur above that level.

Lower boundary[edit]

The lower boundary is taken above the highest significant (>1 m) bed of sandstone with large scale cross bedding of the underlying Finstall Member.

Upper boundary[edit]

The upper boundary is taken at the top of the highest significant grey sandstone bed, above which red mudstones and siltstones of the MMG predominate over sandstone.

Thickness[edit]

The thickest known sequence is 24.4 m, in the Sugarbrook No. 3 Borehole.

Age[edit]

Anisian (early Mid Triassic)

Equivalent unit[edit]

Tarporley Siltstone Formation (pars.), MMG

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]