The BGS Lexicon of Named Rock Units — Result Details

Summer Isles Formation

Computer Code: SUMI Preferred Map Code: notEntered
Status Code: Full
Age range: Holocene Epoch (QH) — Holocene Epoch (QH)
Lithological Description: Predominantly dark olive grey (5Y 3/2) to very dark greyish brown (2.5Y 3/2), very soft to soft, bioturbated to homogeneous, silty mud with sporadic shells and shell fragments. Base of unit locally marked by a very coarse, poorly sorted, carbonate gravel (shell hash) and muddy, slightly sandy and shelly sand. Coarse sandy and gravel lag on shallow marine banks.
Definition of Lower Boundary: Unconformable and commonly erosional on the Annat Bay Formation and/or older underlying glacial units.
Definition of Upper Boundary: Present-day sea bed.
Thickness: Mostly less than 5 m thick, but up to 12 m thick in outer Loch Broom, associated with a discrete sediment drift.
Geographical Limits: Predominantly recognised as partial fills in the glacially overdeepened deep-water basins landward of the Summer Isles, i.e. Tanera, Coigach, North Annat, South Annat, South-East Annat, Skerries and South Priest basins, as well as Loch Broom and inner Little Loch Broom. Also occurs as seismically unresolvable lag deposit on the shallow marine banks.
Parent Unit: Not Entered (?)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  57.8655 deg N, 05.1063 deg W. BGS vibrocore 57-06/267, between seabed and 2.06 m below seabed, inner Loch Broom. Stoker, M S and Bradwell, T. In press. Quaternary geology of the Summer Isles region - a brief explanation of the marine environment map. Sheet Explanation of the British Geological Survey. 1:50 000 Special Sheet Summer Isles (Scotland). 
Reference(s):
Stoker, M S and Bradwell, T. In press. Quaternary geology of the Summer Isles region - a brief explanation of the marine environment map. Sheet Explanation of the British Geological Survey. 1:50 000 Special Sheet Summer Isles (Scotland). 
Stoker, M S, Bradwell, T, Howe, J A, Wilkinson, I P & McIntyre, K. 2009. Lateglacial ice-cap dynamics in NW Scotland: evidence from the fjords of the Summer Isles region. Quaternary Science Reviews, 28, 3161-3184. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable