27 Geochemistry, Organic (Posters)

Sunday, 31 October 2010
8:00 AM - 6:00 PM
Hall D

PRELIMINARY BIOCHEMICAL CHARACTERIZATION OF THE LOWER JURASSIC ORGANIC-RICH FACIES OF THE LUSITANIAN BASIN (PORTUGAL)

Paper number: 27-11
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

  • Ricardo L. Silva Presenting Author
    Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Coimbra, N/A
  • Frederico S. da Silva
    Instituto de Geociências, Centro de Ciências Matemáticas e da Natureza, Universidade Federal do Rio de Janeiro, Rio de Janeiro, N/A
  • João G. Mendonça Filho
    Instituto de Geociências, Centro de Ciências Matemáticas e da Natureza, Universidade Federal do Rio de Janeiro, Rio de Janeiro, N/A
  • Luís V. Duarte
    Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Coimbra
  • Taís F. Silva
    Instituto de Geociências, Centro de Ciências Matemáticas e da Natureza, Universidade Federal do Rio de Janeiro, Rio de Janeiro, N/A
  • Rui Ferreira
    Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Coimbra, N/A

Abstract

In this work we present the biochemical characterization (protein, carbohydrate and lipid content) of several black-shales of the Lusitanian Basin Lower Jurassic organic-rich facies supported by organopetrographic, geochemical and thermal maturation integrated analysis.

Lipids, in terms of relative proportion, tend to dominate over the carbohydrates and proteins, indicating that diagenesis has affected the original composition of Organic Matter (OM). For example, at Peniche, lipid relative content varies from 67.2 to 96.7% and the increase in this component corresponds to a decrease in carbohydrates, from 30.2 to 0.6%. Proteins show little variation, from 2.6 to 4.4%. Thermal maturation assessment indicates that the studied sedimentary series have reached the final stages of diagenesis but not, or barely, reached catagenesis. The question is: has diagenesis affected these biochemical compounds to an extent that it is impossible, for instance, to use them in OM characterization? Optical observation indicates that Amorphous Organic Matter (AOM) is the kerogen dominant group. Higher lipid content is observed in samples where AOM seems to result from the microbiological reworking, by heterotrophic bacteria, of autotrophic-photosynthetic microbial mats while a lower content relates to AOM resulting from microbial degradation of mixed marine (e.g. phytoplankton) and continental components. The correlation between the biochemical data and some of the optically determined characteristics of kerogen seems to favour the idea that the approach used here may be a viable working tool in the study of such ancient sedimentary environment with no present-day counterpart.