The BGS Lexicon of Named Rock Units — Result Details

Hildasay Sandstone Member

Computer Code: HIYS Preferred Map Code: notEntered
Status Code: Full
Age range: Late Paleocene (GPL) — Late Paleocene (GPL)
Lithological Description: The Hildasay Sandstone Member is dominated by mudstones and sandstones mostly of progradational shallow marine facies, but ranging from paralic 'delta-top' facies in proximal sections to 'prodelta' facies in distal sections. Paralic 'delta-top' facies are represented by claystones, mudstones, siltstones and sandstones of highly variable facies, with thin lignites. The more distal 'progradational' successions have not been encountered in cores, but appear from cuttings descriptions to be dominated by grey mudstones and siltstones interbedded with fine to coarse grained sandstones. The beds are mostly organized into upward-coarsening cycles, clearly identified on wireline-log character.
Definition of Lower Boundary: The base of the Hildasay Sandstone Member is defined by a downward change from sandstone to mudstone within a gradational lithological transition. The underlying mudstone forms the base of a large-scale upward-coarsening cycle (unit F2) and is normally recognizably thicker than the mudstones within the overlying and underlying sandstone members.
Definition of Upper Boundary: In most sections the top of the Hildasay Sandstone Member is defined by a downward change from mudstone to sandstone and is marked by a sharp downward decrease in gamma-ray values.
Thickness: The member reaches a maximum thickness of 203 m in well 205/9-1.
Geographical Limits: UK north west margin. The Hildasay Sandstone Member is positively identified only in sections in the central part of the area to the west of the Flett Ridge, where it can be recognized by the occurrence of sandstones below the Balder Formation and above the Apectodinium spp. acme biomarker. The absence of the Apectodinium spp. acme biomarker in many marginal sand-rich sections of the Flett Formation may indicate equivalence with the Hildasay Sandstone Member, but alternatively may reflect facies control.
Parent Unit: Flett Formation (FLET)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea well 206/02- 1A: 2226 – 2393 m (7303 – 7850 ft) (Knox et al., 1997). 
Reference Section  North Sea well 206/01- 2: 2420 – 2572 m (7940 – 8438 ft) (Knox et al., 1997). 
Reference(s):
Knox, R W O'B, Holloway, S, Kirby, G A and Baily, H E. 1997. Stratigraphic nomenclature of the UK North West Margin. 2. Early Paleogene lithostratigraphy and sequence stratigraphy. British Geological Survey, Nottingham. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable