Gravity and magnetic field characteristics and hydrocarbon prospects of the Tobago Basin

The Tobago Basin, which is located offshore northern Venezuela with a southern margin close to Trinidad and Tobago, has an area of approximately 59,600 km². The Tobago Basin has relatively favourable hydrocarbon prospects, and to date, exploration work has mainly concentrated on small areas of the southwestern portion of the basin. To conduct a comprehensive study of the structural framework of the basin and the characteristics of the basement in order to identify prospective zones for hydrocarbon exploration, shipborne‐measured and satellite‐measured gravity data, shipborne‐measured magnetic data, and aeromagnetic survey data were analysed. A regularisation filtering method was used to separate and obtain regional and residual gravity and magnetic anomalies. Directional gradients of gravity and magnetic anomalies and the total horizontal gradient and vertical second derivative of gravity anomalies were employed to extract information about fault structures. Regression analysis methods were used to determine the basement depth. The geological significance of the gravity and magnetic fields was examined, the structural framework of the basin was assessed, the basement depth was estimated, and favourable hydrocarbon exploration prospects within the basin were identified. The results show that the Tobago Basin contains complex structures consisting mainly of two groups of faults trending in northeasterly and northwesterly directions and that the major northeasterly trending faults control the main structural configuration and depositional system within the basin. The basement of the Tobago Basin has deep rises and falls. It can be divided into the following four secondary tectonic units: the western sub‐basin, the central uplift area, the southern sub‐basin, and the northeastern sub‐basin. The central uplift area and northeastern sub‐basin are most likely to have developed hydrocarbon accumulations and should be targeted for further exploration.     

“Racism in a Melting Pot…?” Trinidadian mid-life transnational migrants’ views on race and colour-class on return to their homes of descent

This paper deals with second-generation, one-and-a-half generation and “prolonged sojourner” Trinidadian transnational migrants, who have decided to ‘return’ to the birthplace of their parents. Based on 40 in-depth interviews, the paper considers both the positive and critical things that these youthful transnational migrants report about returning to, and living in, this multi-ethnic plural society and the salience of racial and colour-class stratification as part of their return migration experiences. Our qualitative analysis is based on the narratives provided by these youthful returnees, as relayed “in their own words”, presenting critical reflections on racism, racial identities and experiences as transnational Trinidadians. It is clear that it is contexts such as contemporary working environments, family and community that act as the reference points for the adaptation “back home” of this strongly middle-class cohort. We accordingly encounter a diverse, sometimes contesting set of racial issues that emerge as salient concerns for these returnees. The consensus is that matters racial remain as formidable legacies in the hierarchical stratification of Trinidadian society for a sizeable number. Many of our respondents reported the positive aspects of racial affirmation on return. But for another sub-set, the fact that multi-ethnic and multi-cultural mixing are proudly embraced in Trinidad meant that it was felt that return experiences were not overly hindered, or blighted by obstacles of race and colour-class. For these returnees, Trinidad and Tobago is seen as representing a 21st century “Melting Pot”. But for others the continued existence of racial divisions within society - between ethnic groups and among those of different skin shades - was lamented. In the views of these respondents, too much racial power is still ascribed to ‘near-whiteness’. But for the most part, the returnees felt that where race played a part in their new lives, this generally served to advantage them. However, although the situation in Trinidad appears to have been moderated by assumptions that it remains a racial ‘Melting Pot’, the analysis strongly suggests that the colour-class system of stratification is still playing an essential role, along with racial stereotyping in society at large.     

Developers in the public interest? The role of urban development corporations in the Anglophone Caribbean

Urban centres in the Caribbean face a wide variety of infrastructural and planning challenges. One of the key strategies that has been adopted by national governments to address these challenges is the formation of urban development corporations. These are governmental agencies with powers to facilitate urban regeneration in specific areas. This paper examines the history, role and function of urban development corporations in Jamaica, Antigua and Barbuda, and Trinidad and Tobago. The Urban Development Corporation (UDC) was formed in Jamaica in 1968, the St John's Development Company (SJDC) in Antigua and Barbuda was created in 1986, and the Urban Development Corporation of Trinidad and Tobago (UDeCOTT) was established in 1994. These bodies share the characteristic of having far-reaching planning and development powers within specific areas. For example, the SJDC is able 'to acquire, manage, or dispose of lands and to lay out, construct, and maintain roads, buildings, public parks, piers, car parks, and other public amenities' within specified designated areas, whilst Jamaica's UDC is empowered 'to carry out and/or secure the laying out and development of "designated areas". These three urban development corporations can be seen to act as developers in the public interest, as agents of modernisation, and as responses to neoliberalisation. However, whilst they have succeeded in effecting large-scale transformations to the urban landscape, this has often been achieved through a top-down development process with exemption from planning regulations and little accountability to the residents of the cities.     

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in harbor sediments from Sea Lots, Port-of-Spain, Trinidad and Tobago

Concentrations of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were determined in nearshore marine surficial sediments from three locations in Trinidad. Sediments were sampled at Sea Lots on the west coast, in south Port-of-Spain Harbor, south of Sea Lots at Caroni Lagoon National Park, and on Trinidad’s east coast at Manzanilla. Total PCB concentrations in Sea Lots sediments ranged from 62 to 601 ng/g (dry weight {dw}), which was higher than at Caroni and Manzanilla, 13 and 8 ng/g dw, respectively. Total OCP concentrations at Sea Lots were ranged from 44.5 to 145 ng/g dw, compared with 13.1 and 23.8 n/g (dw), for Caroni and Manzanilla respectively. The concentrations of PCBs and of some OCPs in sediments from Sea Lots were above the Canadian interim sediment quality guidelines. To date, this data is the first report on the levels of PCBs and other organochlorine compounds from Trinidad and Tobago.     

Evolution of the Grenada and Tobago basins and implications for arc migration

The tectonic mechanisms controlling how volcanic arcs migrate through space and geologic time within dynamic subduction environments is a fundamental tectonic process that remains poorly understood. This paper presents an integrated stratigraphic and tectonic evolution of Late Cretaceous to Recent volcanic arcs and associated basins in the southeastern Caribbean Sea using seismic reflection data, wide-angle seismic refraction data, well data, and onland geologic data. We propose a new tectonic model for the opening of the Grenada and Tobago basins and the 50-250-km eastward jump of arc volcanism from the Late Cretaceous Aves Ridge to the Miocene to Recent Lesser Antilles arc in the southeast Caribbean based on the mapping of three seismic megasequences. The striking similarity of the half-graben structure of the Grenada and Tobago basins that flank the Lesser Antilles arc, their similar smooth basement character, their similar deep-marine seismic facies, and their similar Paleogene sediment thickness mapped on a regional grid of seismic data suggest that the two basins formed as a single, saucer-shaped, oceanic crust Paleogene forearc basin adjacent to the now dormant Aves Ridge. This single forearc basin continued to extend and widen through flexural subsidence during the early to middle Eocene probably because of slow rollback of the subducting Atlantic oceanic slab. Rollback may have been accelerated by oblique collision of the southern Aves Ridge and southern Lesser Antilles arc with the South American continent. Uplift and growth of the southern Lesser Antilles arc divided the Grenada and Tobago basins by early to middle Miocene time. Inversion of normal faults and uplift effects along both edges of the Lesser Antilles arc are most pronounced in its southern zone of arc collision with the South American continent. The late Miocene to Recent depositional histories of the Grenada and Tobago basins are distinct because of isolation of the Grenada basin by growth and uplift of the Neogene Lesser Antilles volcanic ridge.     

The karstlands of Trinidad and Tobago, their land use and conservation

The karst landscapes of Trinidad and Tobago, although restricted in area, present a previously undocumented array of tropical karst landforms, including karren, caves, springs, valley systems, and a range of dolines or sinkholes, including an area of polygonal cockpit karst. The karstlands are located primarily in the Northern and Central Ranges of Trinidad and in the southwestern portion of Tobago, and they have developed on carbonate rocks ranging in age from Jurassic to Quaternary. Associated with them is a range of vegetation types and faunal communities, many of which have been much altered by human land management, including forestry and agriculture. Quarrying has destroyed much of the karst in the western part of Trinidad, and urban development and tourism have taken their toll too, especially in the Lowlands of western Tobago. Little of the karst is incorporated within existing protected areas.     

Land-based nutrient enrichment of the Buccoo Reef Complex and fringing coral reefs of Tobago, West Indies

Tobago’s fringing coral reefs (FR) and Buccoo Reef Complex (BRC) can be affected locally by wastewater and stormwater, and regionally by the Orinoco River. In 2001, seasonal effects of these inputs on water-column nutrients and phytoplankton (Chl a), macroalgal C:N:P and δ¹⁵N values, and biocover at FR and BRC sites were examined. Dissolved inorganic nitrogen (DIN, particularly ammonium) increased and soluble reactive phosphorus (SRP) decreased from the dry to wet season. Wet season satellite and Chl a data showed that Orinoco runoff reaching Tobago contained chromophoric dissolved organic matter (CDOM) but little Chl a, suggesting minimal riverine nutrient transport to Tobago. C:N ratios were lower (16 vs. 21) and macroalgal δ¹⁵N values higher (6.6‰ vs. 5.5‰) in the BRC vs. FR, indicating relatively more wastewater N in the BRC. High macroalgae and low coral cover in the BRC further indicated that better wastewater treatment could improve the health of Tobago’s coral reefs.     

Palaeoecology and significance of barnacles in the mid-Pliocene Balanus Bed of Tobago,West Indies

The Balanus Bed of the Rockly Bay Formation (mid-Pliocene) of Tobago is a sequence of orange-brown sands with laterally equivalent muds. The invertebrate macrofauna is dominated by the balanid barnacle Megabalanus tintinnabulum (Linnaeus) sensu lato, with associated oysters, pectinaceans, gastropods, bryozoans, regular echinoids, and rare crabs and sharks. Vertical burrows in muddier substrates are good evidence that this assemblage was living littorally or shallowly sublittorially. Previous analyses of the Rockly Bay Formation of the type area have erroneously suggested that it represents a lenticular deposit. It is now recognized to be a transgressive unit, unconformable on the underlying Mesozoic basalts. The sediment of the Balanus Beds was derived from the in situ weathering of basalts, producing a gradation from sandy (near shore) to muddy substrates. Balanids grew singly on the weathering basalt, but suitable substrates for attachment in the muddy environment were rare, so barnacles are found clustered in close association. The primary substrates for attachment in the muddy environment were disarticulated balanid plates, mollusc valves and small pebbles. Although the base of the Formation is not seen in Rockly Bay, a basal conglomerate overlain by a horizon of dissociated valves of the large ark Anadara patricia (Sowerby) is exposed in nearby Little Rockly Bay. Apart from the two fossiliferous horizons mentioned, the Formation is barren of marine microinvertebrates. The Rockly Bay Formation appears to have formed in response to the mid-Pliocene rise in sea level. Horizons dominated by balanids may be useful indicators of sea-level rise, at least in the Neogene, Darwin's ‘Age of Barnacles’.