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Barbados
Barbados is located in the southeast of the Antillean region, about 2000 km from Jamaica. It differs from islands of the Lesser Antilles in lying away from the convex side of the island arc and in having a sedimentary, not volcanic, origin, being situated at the summit of the Lesser Antillean accretionary prism (Speed, 1994; Machel, 1999; Donovan with Harper, 2005). The allochthonous Tertiary rocks of the accretionary prism underlie the entire island, but only form about 10 per cent of its outcrop, which is largely limited to the Scotland District in the northeast of Barbados. These deposits have yielded rare micromorphic brachiopods (Harper, 2002b). The remaining 90 percent of the island’s outcrop consists of autochthonous Pleistocene reef limestones that occur as three principal terraces, distinguished topographically as the Upper (oldest), Middle and Lower (youngest) Coral Rock (Poole & Barker, 1983; for a discussion of the historical development of ideas on the age and genesis of these limestones, see Donovan & Harper, 2002). The age of these units is Pleistocene; Trechmann considered the fauna of the basal Coral Rock to have a “pre-Pleistocene aspect” (1937, p. 358; see also 1958, p. 433; Donovan, 2003). These terraces are constructional reef features that preserve the original coral zonation of the reef structure (e.g., Mesolella, 1967; Mesolella et al., 1970). They represent the product of reef growth during the complex interaction of tectonic uplift and fluctuations of sea level during the Pleistocene. Apart from brachiopods, the fauna includes benthic foraminiferans, bryozoans, benthic molluscs (Trechmann, 1937; Jung, 1968), echinoids and astropectinid asteroids (Donovan, 2000), the boring Entobia isp. (produced by clionid sponges) in some molluscs, and rarer pteropods, crabs (Collins & Morris, 1976) and arcoscalpellid barnacle plates. The following brachiopod localities are known from the Coral Rock (Fig. 3).
Locality B1 - Skeete’s Bay, Whitehaven – Brachiopods have been collected from the northwest side of Skeete’s Bay, Whitehaven, parish of St. Philip, southeast Barbados (approximately 59º 27’ 00” W 13º 10’ 00” N; see also Trechmann, 1937, pp. 346, 357, text-fig. 3; Donovan with Harper, 2005, fig. 6). It is a coastal exposure of the basal Middle Coral Rock (484,000-127,000 years old; Poole & Barker, 1983) that rests unconformably on the Tertiary Oceanic Group; the basal position suggests a mid Pleistocene age. The brachiopods from Whitehaven were collected in August 1997 and June 2002, mainly from well-lithified float blocks on the beach and also from the lowermost 2 m of the section. The lithology, fauna and preservational style of the fossils in the Middle Coral Rock at this locality are reminiscent of the lower Pleistocene Manchioneal Formation of Jamaica (Donovan et al., 2002).
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Fig. 3. Simplified geological map of Barbados (modified after Donovan with Harper, 2005, fig. 1; redrawn and modified after Speed et al., 1991, fig. 2). Key to tectono- and lithostratigraphic units (for explanation, see Speed, 1994): open stipple = basal complex; vertical ruling = diapiric melange; O = Oceanic nappes; UCR = Upper Coral Rock; MCR = Middle Coral Rock; LCR = Lower Coral Rock. The First High Cliff (1HC) separates the LCR and MCR; the Second High Cliff (2HC) separates the MCR and UCR. Key to place names and brachiopod localities: AQ = Arawak Cement Quarry (B4); B = Bridgetown; C = Cluffs Bay (B2); RP = Spring Bay, south of Ragged Point (B3); SB = Skeete’s Bay (B1). |
Locality B2 - Cluffs – Cluffs Bay, parish of St. Lucy, west of North Point and the Animal Flower showcave, is reached on a track to the coast. Care must be taken at this locality (approximately 59º 37’ 48” W 13º 19’ 38” N; Donovan with Harper, 2005, fig. 7), with narrow ledges perched at the unconformity between the Miocene Oceanics and the basal Middle Coral Rock. Trechmann (1937, p. 344) published a measured lithological section, and (p. 349) listed a fauna of benthic molluscs, pteropods and brachiopods from this locality that is much less diverse than that from Whitehaven; it is unclear whether this is an artefact of the easier access at the latter locality. Tichosina sp. cf. T. bartletti (Dall) (Harper, 2002a) was the only brachiopod recognised at Cluffs Bay.
Locality B3 - Spring Bay, south of Ragged Point – At Spring Bay, south of Ragged Point, parish of St. Philip (approximately 59º 26’ 00” W 13º 09’ 35” N; Donovan with Harper, 2005, fig. 6), the Tertiary/Quaternary (= Middle Coral Rock) unconformity is well-exposed (see Trechmann, 1937, p. 345). A horizon of Tichosina shells is exposed above the beach on the south side of the bay.
Locality B4 - Arawak Cement Quarry – The Arawak Cement Quarry (Lower Coral Rock), parish of St. Lucy (approximately 59º 38’ 47” W 13º 17’ 6” N; Donovan with Harper, 2005, fig. 7), on the west coast of northern Barbados, has yielded a single shell of Argyrotheca sp. This locality was not known to Trechmann (1937).
Other localities – Trechmann (1937, p. 349) tabulated the occurrences of molluscs and brachiopods in the basal Coral Rock. Brachiopods were recognised from seven localities. Apart from Localities B1-B3, mentioned above, Trechmann found brachiopods at Spring Hill, Caledonia, Chimborazo, and Loamfield and Hopefield (not marked on Fig. 3).