The BGS Lexicon of Named Rock Units — Result Details

Chillesford Church Sand Member

Computer Code: CFB Preferred Map Code: CFS
Status Code: Full
Age range: Antian/Bramertonian Stage (QN) — Antian/Bramertonian Stage (QN)
Lithological Description: The Chillesford Church Sand Member comprises well sorted,fine-to medium-grained,micaceous,buff to pale brown,quartz sand.It is commonly decalcified, but locally patches of shell material are preserved, notably in the Chillesford Church Pit [TM 3829 5231] where the deposit was formerly termed the 'Scrobicularia Crag' due to an abundance of this bivalve. The member is characterised by planar bedding and small-scale ripple cross-stratification. Mud laminae, flasers and intraclasts occur sporadically and much of the sequence is strongly bioturbated and contains prominent vertical burrows. A depositional environment of tidal sand flats is probable.
Definition of Lower Boundary: The Chillesford Church Sand Member overlies the typically coarser grained, and generally more red-brown (green at depth where glauconite has not been oxidized), Red Crag Formation without any marked discontinuity.
Definition of Upper Boundary: The Chillesford Church Sand Member passes upwards through a gradational interbedded transition into the Chillesford Clay Member, which consists predominantly of clays and silts.
Thickness: Up to 13m.
Geographical Limits: The Chillesford Church Sand Member has only been mapped seperately in southern East Anglia. Farther north, in central East Anglia it has not been possible to map the Chillesford Church Sand Member separately from the Red Crag Formation and the deposits have been mapped as Crag Grup (undivided).
Parent Unit: Norwich Crag Formation (NCG)
Previous Name(s): Chillesford Beds [Obsolete Name and Code: Use CFB] (-3914)
Chillesford Sand [Obsolete Name and Code: Use CFB] (-119)
Chillesford Sand Member [Obsolete Name and Code: Use CFB] (-2069)
Alternative Name(s): Chillesford Member
Stratotypes:
Type Section  1.42 to 6.82m depth in Wantisden Hall Borehole BGS Registered No. TM35SE/62.[TM 3601 5215] Zalasiewicz and Mathers,1985 
Reference(s):
Mathers, S J and Zalasiewicz, J A. 1988. The Red Crag and Norwich Crag formations of southern East Anglia. Proceedings of the Geologists Association, Vol.99, 261-278. 
Zalasiewicz, J A and Mathers, S J. 1985. Lithostratigraphy of the Red and Norwich crags of the Aldeburgh-Orford area. Southeast Suffolk Geological Magazine, Vol.122, 287-296. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E225