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):
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. 
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. 
Godwin, H. 1943. Coastal peat beds of the British Isles and North Sea. Journal of Ecology, Vol.31, 199-247. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E244 E209 E193 E163 E149 E135 E119 E134