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Clastic Domains of Sandstones in Central/Eastern Venezuela, Trinidad, and Barbados: Heavy Mineral and Tectonic Constraints on Provenance and Palaeogeography

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Clastic Domains of Sandstones in Central/Eastern Venezuela, Trinidad, and Barbados: Heavy Mineral and Tectonic Constraints on Provenance and Palaeogeography Please do not cite until published. Expected early 2009. In: James, K., Lorente, M. A. & Pindell, J. (eds) The geology and evolution of the region between North and South America, Geological Society of London, Special Publication. Clastic domains of sandstones in central/eastern Venezuela, Trinidad, and Barbados: heavy mineral and tectonic constraints on provenance and palaeogeography James Pindell1,2, Lorcan Kennan1, David Wright3, and Johan Erikson4 1. Tectonic Analysis Ltd., Chestnut House, Duncton, West Sussex, GU28 0LH, UK 2. Also at: Dept. Earth Science, Rice University, Houston, TX 77002, USA 3. Department of Geology, University of Leicester, Leicester, LE1 7RH, UK 4. Department of Natural Sciences, St. Joseph’s College, Standish, ME 07084, USA Corresponding first author: [email protected] Supplementary material: Location maps and detailed heavy mineral data tables are available at http://www.geolsoc.org.uk/SUP00000 Abstract: Current models for the tectonic evolution of northeastern South America invoke a Palaeogene phase of inter-American convergence, followed by diachronous dextral oblique collision with the Caribbean Plate, becoming strongly transcurrent in the Late Miocene. Heavy mineral analysis of Cretaceous to Pleistocene rocks from Eastern Venezuela, Barbados and Trinidad allow us to define six primary clastic domains, refine our palaeogeographic maps, and relate them to distinct stages of tectonic development: (1) Cretaceous passive margin of northern South America; (2) Palaeogene clastics related to the dynamics of the Proto-Caribbean Inversion Zone before collision with the Caribbean plate; (3) Late Eocene–Oligocene southward-transgressive clastic sediments fringing the Caribbean foredeep during initial collision; (4) Oligocene–Middle Miocene axial fill of the Caribbean foredeep; (5) Late Eocene–Middle Miocene northern proximal sedimentary fringe of the Caribbean thrustfront; and (6) Late Miocene–Recent deltaic sediments flowing parallel to the orogen during its post-collisional, mainly transcurrent stage. Domain 1–3 sediments are highly mature, comprising primary Guayana Shield- derived sediment or recycled sediment of shield origin eroded from regional Palaeogene unconformities. In Trinidad, palinspastic restoration of Neogene deformation indicates that facies changes once interpreted as north to south are in fact west to east, reflecting progradation from the Maturín Basin into central Trinidad across the northwest-southeast trending Bohordal marginal offset, distorted by about 70 km of dextral shear through Trinidad. There is no mineralogical indication of a northern or northwestern erosional sediment source until Oligocene onset of Domain 4 sedimentation. Palaeocene–Middle Eocene rocks of the Scotland Formation sandstones in Barbados do show an immature orogenic signature, in contrast to Venezuela-Trinidad Domain 2 sediments, this requires: (1) at least a bathymetric difference, if not a tectonic barrier, between them; and (2) that the Barbados deep-water depocentre was within turbidite transport distance of the early Palaeogene orogenic source areas of western Venezuela and/or Colombia. Domains 4–6 (from Late Oligocene) show a strong direct or recycled influence of Caribbean Orogen igneous and metamorphic terranes in addition to substantial input from the shield areas to the south. The delay in the appearance of common Caribbean detritus in the east, relative to the Palaeocene and Eocene appearance of Caribbean-influenced sands in the west, reflects the diachronous, eastward migration of Caribbean foredeep subsidence and sedimentation as a response to eastward-younging collision of the Caribbean Plate and the South American margin. Current kinematically rigorous Cenozoic models for the evolution of northeastern South America invoke a Palaeogene tectonic phase due to inter-American convergence followed by diachronous dextral oblique collision with the Caribbean Plate (Pindell et al. 1991, 2006; Perez de Armas 2005), which became strongly transcurrent in the Late Miocene (Pindell et al. 1998, 2005). In eastern Venezuela and Trinidad, the collision and subsequent shear between the Caribbean Plate and South America (Fig. 1) juxtaposed, imbricated and offset former palaeogeographic elements, hindering Pindell et al., in press 2009, PREPRINT Trinidad, Venezuela. Barbados heavy minerals and palaeogeography Page 1 -68° -67° -66° -65° -64° -63° -62° -61° -60° -59° -58° -57° -56° -55° -54° 16° 16° Lesser Edge of Carib. crust Caribbean Antilles Tiburón Rise Arc 15° Plate 15° Proto-Caribbean Inversion Zone 14° Grenada 14° Venezuela S. Carib. Foldbelt intra-arc Post-Aptian Basin Aves Basin BARBADOS oceanic crust 13° Ridge 13° “Atlantic” fracture 12° Bohordal zones (post-95 Ma) 12° Fault Greater Tobago Margarita Demerara Fracture Zone Cariaco Paria 11° Basin pull-apart Caribbean Prism 11° TRINIDAD Columbus 10° V. de Cura Serrania 10° Urica F. Oriental Basin Pre-Aptian Guarico Belt Guyana Transformoceanic crust Cret. shelf edge blind Carib Maturín Basin Los Bajos F. 9° underthrust Orinoco Delta 9° Guarico Basin VENEZUELA Guyana Shield 8° 8° -68° -67° -66° -65° -64° -63° -62° -61° -60° -59° -58° -57° -56° -55° -54° Fig. 1. Key tectonic features of the Eastern Caribbean region, including Central and Eastern Venezuela and Trinidad, and key features referred to in the text. The background for the map is the satellite gravity of Smith and Sandwell (1997). Today, Caribbean crust lies east of Tobago and under Barbados. This crust and the Caribbean accretionary prism have over-ridden much of the proposed Proto-Caribbean Inversion Zone, which is only exposed today in the area south of Tiburón Rise. The positions shown on this map are based on three-dimensional restoration of features mapped on seismic tomography (after Pindell et al. 2007a). Pindell et al., in press 2009, PREPRINT Trinidad, Venezuela. Barbados heavy minerals and palaeogeography Page 2 reconstruction of former depositional systems. Correct reconstruction of these is important because certain palaeogeographic aspects pertain directly to petroleum exploration. For example, fluvial- depositional systems and turbidite fairways may contain good quality reservoir sandstone packages that can drive hydrocarbon exploration efforts. Previous work has demonstrated three general principles regarding the provenance of sandstones in northeastern South America (see Figs 2–4 for stratigraphic summaries): (1) South America was the predominant source for most clastic sediments, which are typically quartz prone and mineralogically mature; (2) a less mature Caribbean mineral association began in the Caribbean foredeep basins at the following times: Palaeocene in western Venezuela, Eocene in Central Venezuela, and Oligocene in Eastern Venezuela-Trinidad, indicating the diachronous advance of the Caribbean Plate from the west; and (3) the Palaeogene clastic units of Barbados were derived from relatively high-grade metamorphic (e.g. sillimanite-bearing) rocks, probably from the South American craton or Andes, but also include minerals of probable Caribbean origin such as glaucophane (Senn 1940; Gonzales de Juana et al. 1980; Kasper & Larue 1986; Socas 1991; Kugler 2001). These observations allow the regional stratigraphic units to be understood in the context of the basic Caribbean-South America collisional model (e.g. Dewey & Pindell 1986; Kasper & Larue 1986; Pindell et al. 1988, 1998). However, there has been no systematic attempt to use heavy minerals to test such concepts as the diachroneity of collision, or the possible existence of a Proto-Caribbean prism/thrustbelt (proposed by Pindell et al. 1991, 2006). This study attempts to fill this void, and to define the cause-and-effect relationship between the regional stratigraphic units and tectonic evolution. We have collected and analysed the heavy mineral content of 118 sandstone and siltstone samples from the Cretaceous and Cenozoic of Eastern Venezuela, Trinidad and Barbados, supported by petrographic examinations of sand grain composition of these and many other samples, to determine sandstone composition variations through the stratigraphic column. In addition, we have studied thin sections and obtained X-ray diffraction data (T. Rieneck & W. Maresch, Universität Bochum, Germany pers. comm. 2007) on field and core samples from the three countries on distinctive red, rounded pebbles and less rounded rip up clasts, informally referred to as “cherries”. In Trinidad, these are particularly characteristic of the Cretaceous (Barremian–Albian) Cuche Formation in the Central Range and probably the similarly aged Toco Formation on the north coast, and are also found in (albeit less-oxidized) coarse intervals of the younger Gautier Formation. They are also found in the (possibly) Late Eocene to earliest Oligocene Plaisance Conglomerate and the basal part of the Mount Harris section of the eastern Central Range in Trinidad, and we have found them in one outcrop of the Oligocene–Early Miocene Nariva Formation sandstone. In Venezuela, they occur in the (possibly) Early Oligocene Lechería beds north of Barcelona. Additionally, we have examined (XRD, thin sections) the dark “clasts” of similar size and shape in the Galera Formation shales that have been previously considered possible precursors for the “cherries” of younger formations (Higgs 2006, 2009). The new heavy mineral and petrographic analyses augment those previously published, and along with the XRD results and previously published modal point count data are integrated
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