The BGS Lexicon of Named Rock Units — Result Details

Hartfield Formation

Computer Code: HTFD Preferred Map Code: HTFD
Status Code: Full
Age range: Cisuralian Epoch (PLC) — Cisuralian Epoch (PLC)
Lithological Description: Red, laminated and cross-laminated silty sandstone interbedded with pebbly sandstone and lenses of breccio-conglomerate. The sandstone is medium- to thick-bedded, silty, medium- to fine-grained with small [<0.5mm] detrital mica flakes and including many frosted and rounded quartz grains. Intervals of pebbly sandstone and breccia occur within the sandstone, not necessarily at the top of the sandstone beds. The clasts are pebble sized, mostly tabular and platey and aligned parallel or near parallel to bedding, defining a crude lamination, and matrix supported in red sandy siltstone or silty sandstone. The clast composition is red or grey mudrock, grey micaceous wacke sandstone, cream-coloured quartzite and, locally, deeply weathered basalt and amygdaloidal basalt. The Formation may also include interbeds of brick red, dune cross-bedded, fine- or very fine-grained sandstone without detrital mica grains.
Definition of Lower Boundary: The basal strata unconformably overlie, or are faulted against, rocks of Lower Palaeozoic age. The underlying sequences are commonly steeply inclined, well-indurated, fine-grained wacke sandstone and mudrock and have a marked angular discordance with the overlying, shallowly inclined strata of the Hartfield Formation.
Definition of Upper Boundary: Strata of the Hartfield Formation are conformably overlain by brick-red sandstone of the Corncockle Sandstone Formation. The boundary is picked at the base of a continuous sequence of fine-grained, well sorted sandstone with large scale cross-bedding and single grain "pin stripe" lamination typical of the overlying Formation.
Thickness: The thickness of the Hartfield Formation from the mapped extent in Kinnel Water [NY0679 9246] to [NY0671 9163] and Mollin Burn [NY 0575 9223] to [NY 0605 9141] is approximately 150m and 170m, respectively.
Geographical Limits: Lochmaben Basin, Dumfriesshire, southwestern Scotland [Southern Uplands].
Parent Unit: Stewartry Group (STEW)
Previous Name(s): Moffat Breccia Formation [Obsolete Name And Code: Use HTFD] (MOFB)
Hartfield Breccia Formation (-2248)
Alternative Name(s): none recorded or not applicable
Type Section  Exposures in the banks of the Kinnel Water approximately 0.5km upstream and downstream of Hartfield Farm [NY 0670 9215]. 
Brookfield, M E, 1978. Revision of the Stratigraphy of Permian and Supposed Permian Rocks of Southern Scotland. Geologische Rundschau, Vol.67, p.110-143. 
British Geological Survey. 2004. St Ann's. Sheet NY09SE. Bedrock. 1:10 000. [Edinburgh Geologial Survey.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used: