XIV.—Submarine Faulting in Kimmeridgian Times: East Sutherland

Abstract

Although it is unlikely that the east of Sutherland will ever rival the west in geological renown, its varied interests have already furnished material for a considerable literature. Attention has been specially focussed upon a down-faulted coastal strip of Mesozoic rocks, which, starting at Golspie, extends north-eastwards for twenty miles through Brora and Helmsdale to the county boundary at the Ord (fig. 1). Golspie itself stands on a narrow outcrop of Trias. Jurassic follows, with a generally ascending sequence that leads up to Kimmeridgian at Kintradwell, a couple of miles north of Brora (fig. 2). Beyond this Corallian reappears, but only for a short distance. Then Kimmeridgian returns and holds the coast-line continuously for nearly nine miles, until, at the Ord, it disappears beneath the sea. The width of the Kimmeridgian exposures is occasionally three-quarters of a mile, but generally much less.

Tsunami deposits in the geological record

“…Coleman (1968) stressed the important process links between tsunami sediment transport, turbidity current flow and the long-term evolution of submarine canyons, arguing that canyon development may be closely linked to tsunami-triggered turbidity current flow. Even earlier, Bailey (1940) had highlighted possible links between turbidity current activity and the evolution of submarine canyons. However, this association between tsunami backwash and offshore turbidity currents has received relatively little modern attention, though an interesting exception is the report by Nanayama and Shigeno (2006) that as the outflow from the 1993 Hokkaido tsunami moved down the submarine shelf slope, it may have generated a turbidity current that deposited a turbidite.…”

“…These accounts have subsequently been followed by a proliferation of papers that describe onshore tsunami deposits from different areas of the world. This wealth of modern 'palaeotsunami' investigations appear to have neglected a much earlier debate concerning the offshore expression of tsunamis and their possible association with turbidity currents (Bailey, 1940;Coleman, 1968). Ironically, as we discuss in the following section, reports of tsunamis preserved in the more ancient (pre-Quaternary) stratigraphic record largely relate to deposits in a marine setting, with few descriptions of onshore tsunamiite deposits.…”

“…Indeed, one of the earliest accounts of a geological tsunamiite relates to the role of tsunami backwash. Bailey and Weir (1932) described an Upper Jurassic (Kimmeridgian) marine sediment sequence in eastern Sutherland, Scotland characterised by extensive beds of boulder deposits, often less than 5 ft in individual thickness. The boulder beds alternate with beds of shale while the top of each boulder bed is "… levelled down with rubble (an abundance of shell fragments) and shelly sand and present a flat surface to the succeeding shale.…”

The structural and diagenetic evolution of injected sandstones: examples from the Kimmeridgian of NE Scotland

“…Between Brora and Helmsdale the succession of boulder beds, carbonaceous siltstones, mudstones and sandstones has received considerable attention (Bailey & Weir 1932;Pickering 1984;Trewin & Hurst 1993). The Kintradwell sandstone dyke (Murchison, 1827) and the surrounding Kimmeridgian host rocks were studied in this area.…”

“…2). It was intruded into a succession of thinly bedded sandstones and carbonaceous silt and mudstones (Bailey & Weir 1932;Roberts 1989). The source for the sandstone dyke is not exposed.…”