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Centre for Earth and Environmental Science Research

Upper Cretaceous of Venezuela: integrating chemostratigraphy and biostratigraphy

Executive Summary
ResearchersDr Ian Jarvis (Principal Investigator): CEESR
Ms Sandra Crespo de Cabrera (Co-PI): PDVSA
Funding Body/SourcePDVSA
DurationOctober 1999-August 2008
Project SummaryVenezuela is the worlds fifth largest oil producer, mostly sourced from Late Cretaceous rocks deposited around 90 million years ago. The precise age, depositional conditions, and palaeoceanographic setting that led to the accumulation of these important deposits remains hotly debated.
This project is employing a multidisciplinary approach that integrates well-established micropalaeontological methods with new geochemical techniques to improve our understanding of the processes leading to petroleum source rock and reservoir formation in northern South America.

Location of some study sections in western and eastern Venezuela

Cretaceous of Venezuela

Most Cretaceous sediments in Venezuela were deposited on a passive continental margin, with conditions alternating between clastic and carbonate-dominated systems. Environments varied from shallow-water to bathyal.

Deposition of organic-rich mudrocks and carbonates was widespread and occurred for long time periods, extending in some areas from the Cenomanian - Santonian (100 - 84 Ma). These sediments, which include the world-famous La Luna Formation, constitute the source rocks for most of the oil discovered to date in Venezuela.

Laminated organic-rich carbonate facies La Luna Formation

Correlation has traditionally been accomplished using conventional biostratigraphy, particularly foraminifera, but in Venezuela this approach is severely limited by environmental controls on these organisms. Consequently, the stratigraphy of many areas is poorly known, especially where marked lateral facies changes occur.

This project is employing stable-isotope and elemental chemostratigraphy, tied to detailed foraminiferal biostratigraphy, to improve stratigraphic resolution of key petroleum source-rock and reservoir intervals. Carbon isotope chemostratigraphy based on analysis of the organic fraction in particular, is providing excellent new constraints for regional and inter-continental correlation.

Objectives are to

  • establish a biostratigraphic, chronostratigraphic, chemostratigraphic and palaeo-environmental framework for the Upper Cretaceous of Venezuela, which will allow the identification and correlation of potential petroleum source rocks and reservoirs
  • refine existing models for the geological evolution of northern South America during the Late Cretaceous


Journal papers

Jarvis, I., Mabrouk, A., Moody, R.T.J. & Crespo de Cabrera, S.C., 2002. Late Cretaceous (Campanian) carbon isotope events, sea-level change and correlation of the Tethyan and Boreal realms. Palaeogeography, Palaeoclimatology, Palaeoecology, 188: 215-248.

Crespo de Cabrera, S.C., Sliter, W.V. & Jarvis, I., 1999. Integrated foraminiferal biostratigraphy and chemostratigraphy of the Querecual Formation (Cretaceous), Eastern Venezuela. Journal of Foraminiferal Research, 29: 487-499.

Conference presentations

Crespo de Cabrera, S.C. & Jarvis, I., 2002. Foraminiferal biofacies and morphogroups from the Upper Albian - Maastrichtian eastern Venezuela Basin: a palaeoceanographic and palaeoenvironmental study. AASP-TMS-NAMS Joint Meeting Exploration Biostratigraphy Abstracts, September 2002, London.

Crespo de Cabrera, S.C. & Jarvis, I., 2004. High resolution stable isotope stratigraphy from the Albian - Campanian of Venezuela. 32nd International Geological Congress Abstracts Part 1, 178-10, 829.

Crespo de Cabrera, S.C. & Jarvis, I., 2005. Elemental chemostratigraphy of Upper Cenomanian to Santonian source rock sediments from the eastern Venezuela Basin: a useful tool for high-resolution correlation. AAPG International Conference & Exhibition: New Tracks to New Highs, September 2005, Paris.

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