Title of Presentation: Was it Really the Orinoco?

Date: Thurs 28th Jan, 2010.
Venue: Valpark Chinese Restaurant
Time: 11:30am - 1pm
Lunch will be provided.

Was it Really the Orinoco?

Thirty years after R.M. Stainforth first questioned the notion of a dominant paleo-Orinoco sediment source for Trinidad Pliocene sandstones (his “Miocene”), it still remains a popular and “logical” interpretation largely because of the proximity and sheer size of the modern Orinoco delta (Stainforth 1978). Mineralogical attributes from Pliocene sediments of the Cruse, Manzanilla, Springvale, Morne L'Enfer and Mayaro formations suggest however that the paleo-Orinoco source was subordinate to a second clastic source with closer mineralogical ties to the Caribbean Mountain belt (Northern Range and its extension in eastern Venezuela).  It is proposed that this mountain belt was a significant source for these Pliocene sediments and its contribution to Trinidad basins has been grossly underestimated in past and current literature.  This assertion arose from a mineralogical analysis of 54 Cenozoic sandstone samples that were compared to the modal composition of modern sands in and around the Orinoco drainage basin and Caribbean Mountains. In particular, the lowered ZTR index relative to Paleogene sandstones and abundance of chloritoid, epidote and detrital chlorite are not typical of Orinoco-derived sands, past and present.  The assertion is further supported in the framework detrital fraction by a relative increase in metamorphic lithic fragments, pebbles of metamorphic-derived quartz and arguably, increased feldspar content.  There are also facies changes across basins and paleocurrent orientations within Pliocene sediments that cannot be ignored.   

A Caribbean Mountain provenance may have been disguised from popular interpretation by the immense structural complexity that now exists between source and sink. Andean-derived Pliocene sediments should however not be surprising given (1) the oblique foreland basin geometry and (2) similar changes in provenance recognized from northwest Brazil and western Venezuela coincident with Neogene uplifts across western and northern South America.  The Caribbean Mountain belt represents the most easterly expression of these uplifts and had a similarly profound effect on clastic sediment composition, although much later in the Trinidad stratigraphy than observed to the west.  Pliocene paleogeographic reconstructions should ideally be constrained by integrated analyses (e.g. mineralogy, high-resolution 3D seismic data, facies reconstructions) as it is a simplistic notion to assume a sole paleo-Orinoco source for younger Trinidad strata based on proximity, isopachs or areal extent of the modern Orinoco delta.  

Hasley Vincent (MSc., Ph.D.)

Reference

Stainforth, R. M., 1978, Was it the Orinoco?  AAPG Bulletin, v. 62; no. 2; p. 303-306

Dr. Hasley Vincent’s Bio 

Hasley Vincent holds a BSc. degree in Geology from the University of the West Indies, Jamaica, a MSc. Degree in Petroleum Geoscience from Imperial College, London and a Ph.D. from Dalhousie University, Canada.  He is currently employed as a Geologist at the Ministry of Energy and Energy Industries, prior to which, he held posts in Halliburton and Petrotrin.  Research interest focuses on advancing the utility of sedimentology to the local stratigraphy and geoscientific community and the architecture of depositional systems as they relate to hydrocarbon exploration and development.  Fieldwork experience includes the sedimentology of deepwater to terrestrial successions around Trinidad and Barbados.