A field guide to Barbados (Part 6): Central Barbados
Stephen K Donovan (The Netherlands)
Stop 1. Waterford District, near Codrington Agricultural Station (approx. 59º 36’ 8” W 13º 6’ 49” N; Fig. 1)
The area considered in the final part of this guide is outlined in A field guide to Barbados (Part 1): Introduction (Donovan & Harper, 2010, fig. 1e) and Fig. 1 in this article. As with other articles in this series, the starting point is Bridgetown.
From the ABC Highway, turn southwest towards Bridgetown on Highway 3. In the area of the turnoff towards Codrington Agricultural Station (on the right), in the parish of St Michael, examine the road cutting, starting at the southwest corner and walking northeast.
This is Stop 6 of Humphrey & Matthews (1986, p. 101), in the Middle Coral Rock, just above the First High Cliff and dated at 194,000 years old. The succession shows a range of reef-related biologically-determined facies (that is, sedimentary rocks deposited in environments defined by their organic content). The lowermost part of the cutting exposes an Acropora cervicornis facies with caliche (a hardened deposit of calcium carbonate) crusts (Humphrey, 1997, fig. 11-5).
The staghorn coral, A. cervicornis (Lamarck), is succeeded by the elkhorn coral, Acropora palmata (Lamarck), which occurs in a reef crest facies in association with encrusting red algae. The sediment between clasts is locally poorly cemented. A change to a sandy, backreef lagoonal facies with Montastrea annularis is, in turn, succeeded by branching coralline algae and Porites porites (Pallas), the clubbed finger coral.
Stop 2. Dayrells Reef Tract, northeast of Hothersal Turning (approx. 59º 34’ 52” W 13º 8’ 20” N; Fig. 1)
Retrace the route northeast to the ABC Highway, which is crossed. Follow Highway H3, which involves taking a right fork at Hothersal Turning and a left at the turning for St George’s Church. The section at Dayrells, in the parish of St Michael, is a further road cutting. Examine it by starting at the southwest corner and walking northeast.
This is Stop 5 of Humphrey & Matthews (1986, p. 100; Humphrey, 1997, fig. 11-7), in the Middle Coral Rock, just below the Second High Cliff and dated at 320,000 years old. Fore reef deposits in the southwest part of the cutting are, unusually for the Coral Rock, through a zone dominated by Montastrea annularis buttress zone. This is associated with an Acropora palmata reef crest facies, in which a subaerial exposure surface is discernable.
Stop 3. Harrison’s Cave (approx. 59º 34’ 29” W 13º 10’ 54” N; Fig. 1)
Continue northeast on Highway H3 and, a little over 1km further on, take the left turn towards Applewhaites. At the end of this road, turn left at the T-junction and, within 300m, turn right towards Proutes. About 500m further on, take the left turning to Hopewell. This road is somewhat winding. Turn right (almost due north) towards Holy Innocent’s Church and Sturges. Both Harrisons Cave and Welchman Hall Gully (Stop 4), in the parish of St Thomas, are signposted and close to each other. Follow the minor road to Harrisons Cave and park.
Harrison’s Cave is the most impressive cave known in Barbados and has been developed as a major tourist attraction since the mid-1970s (Fig. 2). The cave is developed within the outcrop of the Upper Coral Rock (Poole & Barker, 1983), only about 1km to the south of the edge of the Scotland District and close to the highest point of the island, Mount Hillaby (340m; Gordon et al., 1986, p. 116).
The limestone in this area varies between 52 and 66m in thickness (National Conservation Commission of Barbados, undated, p. 12). The tour of the caves is by the so-called ‘tram’ – a series of carriages hauled by a battery electric vehicle along a roadway, which follows the former course of underground streams that are now diverted (Ali, 1996, p. 222).
Stop 4. Welchman Hall Gully
Return to the main Highway H2 and follow signs to nearby Welchman Hall Gully (Fig. 3).
This gully, over 1km in length, is a collapse feature in the Upper Coral Rock and has been developed as a botanical garden by the Barbados National Trust (Fig. 3). The geologist will appreciate the range of limestone solution and precipitation features seen along the walls of the gully (Fig. 4), allowing examination, in daylight, of structures seen underground at the previous stop. Features include a prominent dripstone pillar about 1.25m in diameter, formed by the union of a stalactite and its associated stalagmite.
Stop 5. Horse Hill (approx. 59º 32’ 33” W 13º 11’ 43” N; Fig. 1)
From Welchman Hall Gully, travel northeast on Highway H2 and then turn right (southeast) on the Highway H3A to Blackmans and Coffee Gully. At this point, turn left (north to northeast) on Highway H3. The exposure at Horse Hill, in the parish of St Joseph, is northwest of St Joseph’s Girls School and about midway between District F Police Station and Bowling Alley.
This locality is a high-sided road cutting, which runs northeast and downhill in the Upper Coral Rock (Fig. 5).
A rubbly Porites? biofacies at the top of the hill trends down into in situ, close packed coral heads further down the hill and rubble beds at the bottom. Donovan & Veale (1996) described the shallow water, irregular echinoids, Echinoneus cyclostomus Leske and Brissus sp. cf. B. unicolor (Leske) from this locality (Fig. 6).
This stop is within the outcrop area of the Upper Coral Rock (Poole & Barker, 1983), above the Second High Cliff. Radtke et al. (1988, appendix 1) obtained electron spin resonance dates from aragonitic corals in a traverse across the Second High Cliff to the south of the present study area. These vary from 310,000 to 642,000 years, in broad agreement with the dates obtained by He/U dating (Bender et al., 1979). Whatever the precise age of the Highway 3 specimens, they seem certain to be greater than 250,000 years old (Mesolella et al., 1969) – the quoted dates fall in the range of the middle Pleistocene (Harland et al., 1990, fig. 3.17).
Stop 6. Hackleton’s Cliffs (approx. 59º 32′ 36″ W 13º 11′ 51″ N; Fig. 1)
Turn around and travel back up onto the central limestone upland. Turn left towards Malvern on the road at the top of Hackleton’s Cliff. Follow the road signs to the viewpoint at Hackleton’s Cliff, overlooking Bathsheba.
This viewpoint was visited during the first excursion at Stop 4 in Donovan & Harper (2010), but there is no finer place to take a last look at the geology of Barbados (Fig. 7).
References
Ali, A. 1996. Barbados: Just Beyond Your Imagination. Hansib Caribbean, St. John’s, Antigua: 319 pp.
Bender, M.J., Fairbanks, R.G., Taylor, F.W., Matthews, R.K., Goddard, J.G. & Broecker, W.S. 1979. Uranium-series dating of the Pleistocene reef tracts of Barbados. Geological Society of America Bulletin, 90: 577-594.
Donovan, S.K., including a joint contribution with Harper D.A.T. 2005. The geology of Barbados: a field guide. Caribbean Journal of Earth Science, 38 (for 2003): 21-33.
Donovan, S.K. & Harper, D.A.T. 2009. Geological localities explained 2: Barbados. Geology Today, 25: 151-158.
Donovan, S.K. & Harper, D.A.T. 2010. A field guide to Barbados (Part 2): coastal geology of southeast Barbados. Deposits, 24: 28-33.
Donovan, S.K. & Veale, C. 1996. The irregular echinoids Echinoneus Leske and Brissus Gray in the Cenozoic of the Antillean region. Journal of Paleontology, 70: 632-640.
Gordon, M.J., Johnson, J.D., Payne, P.B. & Mottley, W. 1986. Modern cultural aspects of Barbados’s geology. In: 11th Caribbean Geological Congress Barbados — 1986. Field Guide, Barbados, July 1986: 105-125. Government Printing Department, Bridgetown, Barbados.
Harland, W.B., Armstrong, R.L., Cox, A.V., Craig, L.E., Smith, A.G. & Smith, D.G. 1990. A Geologic Time Scale 1989. Cambridge University Press, Cambridge: 263 pp.
Humphrey, J.D. 1997. Geology and hydrogeology of Barbados. In: Vacher, H.L. & Quinn, T.M. (eds), Geology and Hydrogeology of Carbonate Islands: 381-406. Elsevier, Amsterdam.
Humphrey, J.D. & Matthews, K.K. 1986. The Pleistocene coral cap of Barbados. In: 11th Caribbean Geological Congress Barbados — 1986. Field Guide, Barbados, July 1986: 85-105. Government Printing Department, Bridgetown, Barbados.
Mesolella, K.J., Matthews, R.K., Broecker, W.S. & Thurber, D.L. 1969. The astronomical theory of climatic change: Barbados data. Journal of Geology, 77: 250-274.
National Conservation Commission of Barbados. undated. Harrison’s Cave Barbados. National Conservation Commission, Bridgetown: 20 pp.
Poole, E.G. & Barker, L.H. 1983. The Geology of Barbados. 1:50,000 sheet. Directorate of Overseas Surveys and Government of Barbados, St. Michael.
Radtke, U., Grün, R. & Schwarz, H.P. 1988. Electron spin resonance dating of the Pleistocene coral reef tracts of Barbados. Quaternary Research, 29: 197-215.