The seabed geomorphology and geological structure of the Firth of Lorn, western Scotland, UK, as revealed by multibeam echo-sounder survey
2015
This paper presents recently collected swath bathymetry from the Firth of Lorn.
553 km2 of data were collected during 2012–2013 as part of the INIS Hydro (Ireland, Northern
Ireland and Scotland Hydrographic Survey) programme.
The area proves to consist of bedrock-dominated seabed, divided into narrow, stratigraphicallyconstrained
and glacially-over-deepened basins. The bedrock is composed of late Proterozoic
Dalradian metasediments overlain unconformably by Old Red Sandstone (ORS) sediments and
lavas of ?Silurian-age. The central region of the Firth of Lorn is dominated by a vertical cliff, up
to 150 m high and extending for approximately 24 km. This feature, here termed the Insh Fault,
may have originated as a Dalradian extensional fault, been reactivated as an ORS feature and now
forms a fault-line scarp with resistant ORS rocks on the downthrown side, flanking the more deeply
eroded metasediments exposed in the basin. Tertiary intrusives are common, in particular, swarms
of Paleocene dolerite dykes exposed on the sediment-free bedrock surfaces, and can be traced for
many kilometres.
Evidence for past glaciation is widespread, manifest in the extensive erosion of the bedrock
platforms and the abundance of well-preserved moraines and over-deepened basins. The survey
region includes the Corryvreckan Whirlpool and Great Race, beneath the tidal flows of which occur
submarine dunes.
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