PITTELLI, ROSINA, and ISBELIA DURAN, Maraven, S.A., Caracas, Venezuela
ABSTRACT: Patterns of Foraminiferal and Nanoplankton Abundance and Diversity as a Tool for Sequence Stratigraphy Analysis of the Eocene in Western Venezuela
Detailed micropaleontological and nanoplankton studies have been integrated with wireline logs and lithology to define middle to upper Eocene sequence stratigraphy for three wells in the Andes Foothills Area. An estimate of the relative abundance of each species was made for both foraminifera and calcareous nanoplankton, standard sample preparation included processing of a uniform volume of well cuttings. Data consists of 6 faunal/floral checklists recording the occurrence of foraminiferal and calcareous nanoplankton species. The faunal/floral diversity, abundance and discontinuity, together with glauconite concentration, helped to define the Sequence Boundaries and the Maximum Flooding Surfaces. These discontinuities were calibrated for age, and were compared with the ages of the Seq ence Boundaries of Haq et al. (version 1992). The Lutetian-Bartonian stage (middle Eocene) sediments consists of glauconitic marls and limestones and shales, representing a sequence of transgressive, condensed and highstand regressive deposits that underlie a regional unconformity (SB 39.5). These sediments are assigned to Planktonic Zones P10 -P14 (Blow, 1979) and Nanoplankton Zones NP 15 - NP 17 (Martini, 1971). The Priabonian stage (upper Eocene) sediments assigned to Planktonic Zones P15-P17 and Nanoplankton Zones NP18-NPl9, contains mainly claystones and scattered quartzose silts and sand beds, consisting of slope fan deposits and lowstand regressive deposits, underlying a regional unconformity (SB 30). The position of biostratigraphic boundaries is influenced by the paleogeographic setting and paleoenvironmental conditions.
AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.