Abstract: High-Resolution Biostratigraphy and Paleoecology of Early Miocene Foraminiferal Assemblages from Turbidite Reservoirs in the Campos Basin

Mesquita, A. - Petrobras/Cenpes

The micro-foraminiferal fauna in 16 core samples from deep water turbidite reservoirs of the Campos Basin, Marlim Field, have analyzed qualitative and semi-quantitatively.

The planktonic foraminiferal assemblage belongs to the Globorotalia kugleri biozone, of early Miocene age (23.8 to 21.7 Ma). Besides the presence of the Globorotalia kugleri, common and stratigrafically important species are Catapsydrax dissimilis, Globigerina ciperoensis angustiumbilicata, Globigerinoides primordius,Globoquadrina dehiscens praedehiscens and Globorotalia fohsi peripheroronda.

Four distinct benthonic foraminiferal biofacies A to D, could be defined and correspond to the pre-turbidite, early turbidite pulse, turbidite and post-turbidite sections respectively. Biofacies A, associated with high sea-level hemipelagic sediments of the pre-turbidite section, is characterized by calcareous and agglutinated forms of the middle Bathyal paleobathymetric zone (501-1000 m). Trochammina spp. and Bolivina spp. dominate this biofacies. The agglutinated foraminifera, e. g., Cyclammina sp., Haplophragmoides spp. and Rhizammina sp. have smooth, finely finished testes and are epifaunal and suspension feeders. These characteristics reflect a relatively tranquil environment with weak bottom currents.

Biofacies B contains exclusively calcareous form as Cibicidoides spp., Cibicides spp., Hanzawaia spp., Osangularia sp., Pullenia bulloides and Sphaeroidina bulloides, of the undifferentiated upper Bathyal (201-500 m). Reworked shallower-water species like Amphistegina sp. and Lenticulina sp., are together with autoctone fauna, indication of the high hydrodynamic energy conditions and transport of the material from the platform.

Biofacies C is also calcareous and is characteristic of the shallow part of the upper Bathyal zone (201-300 m). The commom taxa present are Cassidulina sp., Cibicidoides spp., Globocassidulina sp., Gyroidinoides sp., Hanzawaia spp., Melonis pompilioides and Siphonina tenuicarinata. The preservation state denotes transport and/or dissolution.

Biofacies D, from the rich sands lobes from the core top section, has abundant calcareous and frequent agglutinated taxa, coarse infaunal and epifaunal detrital and suspension feeders. The assemblage contains Ammobaculites sp., Bathysiphon spp., Bolivina spp., Bulimina spp., Eggerella sp., Globocassidulina spp., Gyroidina sp., Gyroidinoides spp., Pullenia bulloides and Trochammina sp. They are of the upper Bathyal zone, deep part (301-500 m) and can tolerate higher bottom current intensities than those of the basal section.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil