Biostratigraphy of the La Pica Formation (Late Miocene to Early Pliocene): Paleoenvironments and Reworking Problems

Dennis Sánchez and Igor Rodríguez
Exploration, PDVSA, Puerto La Cruz, Venezuela

The La Pica Formation is observed in the Northern Monagas area from Santa Bárbara to Pedernales oilfields, in the Delta Amacuro State, Eastern Venezuela Basin. In the type section the formation is divided into an upper part composed of intercalations of fissile, gray and occasionally silty shales, often showing a reddish-brown banding, probably due to siderite staining, with very few beds of fine grained sandstones and carbonaceous inclusions. The lower part is also characterised by the same type of shales and fine to medium grained “salt and pepper” sandstones, with a thin bed of hard, greenish gray, arenaceous and micaceous limestone below.

A micropaleontological study is carried out in core samples from the type locality (La Pica-1 Well) and 10 other wells. All the taxa were identified, photographed and abundance were calculated in terms of percentages for each specie. The general aspect of the microfauna varies geographically. Towards the west between the Santa Bárbara and Pedernales oilfields, the agglutinated forams are small-sized, white colour and poorly preserved. From Pedernales to the east (offshore) the size of these forms considerably increase, turning brown in colour and shows a very good preservation. Calcareous foraminifera are very scarce and small. Additionally a mixed shallow and deep water assemblages are observed at some intervals in the west. This, combined to the fact that in some wells the same stratigraphic intervals are completely barren (showing only micro molluscs) allow to interpret a reworked origin for the deep water microfauna found in the La Pica Formation towards the east.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas