Sellafield Member

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Sellafield Member (SELF)[edit]

Previous nomenclature[edit]

  • Kirklinton Sandstone (Dixon et al., 1926)
  • Ormskirk Sandstone Formation (Institute of Geological Sciences, 1977)

Parent unit[edit]

Helsby Sandstone Formation

Derivation of name[edit]

From the Sellafield area of Cumbria

Type section[edit]

NY 04506 00184: Sellafield Borehole 13B, Cumbria. BGS Registered No. NY00SW/42, 0 to 176.42 m.

Reference sections[edit]

  • NY 0280 0310 to 0255 0274: River Calder, Cumbria (Barnes et al., 1994).
  • NY 034 012: Seascale Scar, Cumbria (Gregory, 1915).

Extant exposures/sections[edit]

Very scarce exposures in the Sellafield–Seascale–Drigg area, west Cumbria.

Lithology[edit]

The dominant lithology is a red-brown, weathering to orange-brown, fine-grained, well-sorted sandstone with well-rounded grains of aeolian origin. It is commonly cross-bedded. This aeolian dune facies is interbedded with an interdune facies comprising well-cemented, fine-to medium-grained, poorly sorted sandstone with common wavy silty laminae. Small-scale convolutions, loading and dewatering structures are common.

Lower boundary[edit]

The lower boundary is taken at the sharp upward change from fine-to coarse-grained fluvial sandstone in the underlying part of the Helsby Sandstone Formation to medium-grained, aeolian sandstone. In borehole geophysical logs it is marked by an upward decrease in gamma-ray values and an upward decrease in sonic velocity. Both log signatures are more serrated than in the underlying part of the Helsby Sandstone Formation.

Upper boundary[edit]

The upper boundary is not seen but will be marked by the incoming of dominantly red-brown mudstones and siltstones of the Mercia Mudstone Group.

Thickness[edit]

The thickest known sequence is 176.42 m, in the Sellafield 13B Borehole.

Age[edit]

Anisian (early Mid Triassic)

Equivalent unit[edit]

Helsby Sandstone Formation (pars.)

Geographical extent[edit]

The member only crops out between Drigg and Sellafield on the Cumbrian coast.

Subdivisions[edit]

None

References[edit]