A QUANTITATIVE BIOSTRATIGRAPHY FOR THE MIOCENE OF TROPICAL SOUTH AMERICA

Neogene sediments are well represented in tropical South America, reaching in some areas, like western Venezuela, approximately 8000 meters of thickness. Despite of this great record, few biostratigraphic researches have been carried out in this region. Only five papers have published in the last 60 years (Germeraad et al. 1968, Regali et al., 1974, Lorente, 1986, Muller et al., 1987, and Hoorn, 1993).

Several biostratigraphic zones were established using traditional biostratigraphic methods based on presence and/or abundance of key species such as Psiladiporites minimus, Verrutricolporites rotundiporus, Echitricolporites maristellae, Crassoretitriletes vanraadshoovenii, Grimsdalea magnaclavata and Asteraceae pollen.

We are analyzing several complete Neogene sections in the eastern foothills of Central Colombia, Urumaco region in western Venezuela, and several isolated outcrops in the Amazonas of Brazil. This new information is combined with all the biostratigraphic data available for the region using Graphic Correlation and Constrained Optimization. Several zones have been produced and compared with those proposed in earlier studies.

Preliminary results have been showed that the Miocene biostratigraphic markers have wider first and last occurrences that earlier studies suggest as well as a strong environmental influence.