The BGS Lexicon of Named Rock Units — Result Details

Lower Old Red Sandstone Group

Computer Code: LORS Preferred Map Code: LORS
Status Code: Full
Age range: Early Devonian Epoch (DL) — Early Devonian Epoch (DL)
Lithological Description: The coarsening-upwards succession comprises red floodplain mudrocks, with common calcrete, and sandstones ranging from high-sinuosity channelised deposits to low-sinuosity, braided stream deposits, the latter including sheet flood sandstones and laterally accreted sandbodies. These represent increasingly proximal alluvial deposition, culminating in coarse conglomerate fan deposits locally.
Definition of Lower Boundary: The base of the group is placed at the appearance of red beds in the late Silurian. In the Marloes peninsula of south-west Pembrokeshire, the base of the group is placed at the conformable junction of the tidal deposits of the Gray Sandstone Group and the overlying Red Cliff Formation. Elsewhere, the base of the group is traditionally placed at the base of the Ludlow Bone Bed, a thin, lenticular phosphatised lag deposit at the base of the littoral Downton Castle Sandstone Formation.
Definition of Upper Boundary: The upper boundary is a major regional unconformity, above which Upper Devonian rocks of the Upper Old Red Sandstone Group overstep the Lower Old Red Sandstone Group.
Thickness: The Lower Old Red Sandstone Group is up to 4200 m thick in the Pembroke peninsula and up to about 2000 m thick elsewhere.
Geographical Limits: At outcrop in the West Midlands [e.g. Clee Hills SO 58 83], Welsh Borderland [e.g. Ludlow SO 45 75] and southeast [e.g. Monmouthshire SO 41 07], south central Wales [e.g. Brecon Beacons SO 04 21] and Pembrokeshire [e.g. SS 02 98].
Parent Unit: Old Red Sandstone Supergroup (ORS)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
none recorded or not applicable
Reference(s):
none recorded or not applicable
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E246 E251 E005 E236 S109 S109 S115 S115 S087