The BGS Lexicon of Named Rock Units — Result Details

Ynyslas Formation

Computer Code: YNYSS Preferred Map Code: notEntered
Status Code: Full
Age range: Holocene Epoch (QH) — Holocene Epoch (QH)
Lithological Description: Stratified, unconsolidated, fine- to medium-grained, quartz sand with shell debris.
Definition of Lower Boundary: Commonly unconformable on Flandrian or Late Devensian superficial deposits. In the type area it overlies Flandrian storm beach gravels in the west and peat in the east; locally, it overlies bedrock (Godwin, 1943).
Definition of Upper Boundary: Generally the ground surface, but locally, contact with overlying Flandrian deposits. In the type area the formation is locally overlain by Tidal Flat Deposits (British Coastal Deposits Group).
Thickness: Exceptionally to 10.5m in the type area, but generally less and in accordance with the topographic expression of dune forms (Cave and Hains, 1986).
Geographical Limits: Cardigan Bay; principally at Morfa Bychan, Morfa Harlech, Morfa Dyffryn, Poppit Sands, Whitesands Bay and Freshwater West.
Parent Unit: British Coastal Deposits Group (COAS)
Previous Name(s): Kenfig Formation (KNFIG)
Blown Sand (BSA)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Mostly active dune complex consisting of a narrow strip behind the storm beach from Borth to Aberlerry Farm [SN 609 910], widening northwards to about 1km north of Foel-ynys [SN 607 929] and terminating at Twyni Bach. Relict, older sandhills occur at [SN 612 899]. Cave and Hains, 1986. The deposits developed in response to exposed beach deposits being blown inland by prevailing winds. 
Reference(s):
Godwin, H. 1943. Coastal peat beds of the British Isles and North Sea. Journal of Ecology, Vol.31, 199-247. 
Bowen, D Q, 1999. Wales. Chapter 7 in Bowen, D Q (Editor), A revised correlation of Quaternary deposits in the British Isles. Geological Society of London Special Report, No.23. 
Cave, R and Hains, B A. 1986. Geology of the country between Aberystwyth and Machynlleth. Memoir of the British Geological Survey, Sheet 163 [England and Wales]. [London: HMSO.]. 148pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E244 E209 E193 E163 E149 E135 E119 E134