Site 27

Abstract

The northern margin of the Demerara Abyssal Plain is bordered by a low ESE-WNW trending rise known as the Barracuda Ridge. North of South America, the eastern margin of the Demerara Abyssal Plain is formed by the Barbados Ridge. An extensive sedimentary section of the Barbados Ridge is exposed on the island of Barbados and consists of a series of radiolarian to planktonic foraminiferal and calcareous nannofossil biogenic sediments interlayered with ash beds. This series, known as the Oceanic Formation, has been described in detail by Jukes, Brown and Harrison (1892), Beckmann (1953) and Saunders and Cordey (1968). The pelagic sediments of the Oceanic Formation range in age from Lower or Middle Eocene through Miocene, and rest with angular and erosional unconformity on complex contorted flysch-like sedimentary strata, almost devoid of fossils, referred to as the Scotland Group. The nature of the sediments and basement in the northern part of the Demerara Abyssal Plain to the east of the Barbados Ridge has been thought to differ markedly from those to the west and south. Profiler records along a traverse at about 16°N latitude, made by H.M.S. Vidal in 1965 (Collette et al, 1969), show the sediments to the east, in the northern part of the Demerara Abyssal Plain, to have a different appearance from those of the Barbados Ridge; the underlying "basement" is not as smooth as is typical for regions adjacent to the continental margin off eastern North and South America (Ewing et al., 1966). To determine the nature of the sediments and "basement," Site 27 was selected on the northern margin of the Demerara Abyssal Plain, south of the Barracuda Ridge. At the site, a rather rough "basement" is overlain by 0.3 to 0.6 second of acoustically transparent sediment. The site also lies in the region traversed by the

Tectonics and sedimentation interactions in the east Caribbean subduction zone: An overview from the Orinoco delta and the Barbados accretionary prism

“…The thickness of the recent Quaternary sediments filling the Barracuda trough is very high (locally higher than 2 sTWT, corresponding probably to more than 2 km; Patriat et al, 2011; Pichot et al, 2012; Fig. 11), which is consistent with the data collected at DSDP drilling site 27 (Bader et al, 1970) and…”

Pleistocene Mass Transport Deposits Off Barbados Accretionary Prism (Lesser Antilles)

“…2). According to the stratigraphic record reported at Site 27 (Bader et al, 1970) and other regional studies (Wright et al, 1984;Dolman, 2000), the quaternary succession generally comprises interbedded distal turbidites within hemipelagic sediments. The Quaternary sequence onlaps against a progressive unconformity (horizon H02) ( Fig.…”

“…The ANTIPLAC cruise was designed to cross these DSDP-ODP drilling sites. Because of the highest amount of quaternary sediments recovered at Site 27 (Bader et al, 1970) this site is of particular importance to study recent sedimentation processes occurring seaward of the Barbados accretionary prism. Considering velocity laws from previous studies in the area (Bangs et al, 1990;Dolman, 2000), borehole depth and stratigraphic boundaries reported at Site 27 were converted into time (Patriat et al, 2011;Pichot et al, 2012;).…”