--> ABSTRACT: Carboniferous Stratigraphic Analysis in the Subandean Foothills and the Plains of Tarija Basin-Bolivia, by A. F. Viera and R. M. Hernandez; #90906(2001)

Datapages, Inc.Print this page

A. F. Viera1 and R. M. Hernandez2

1Pluspetrol E&P, Buenos Aires, Argentina
2XR Exploracionistas, Salta, Argentina

ABSTRACT: Carboniferous Stratigraphic Analysis in the Subandean Foothills and the Plains of Tarija Basin-Bolivia

According to well data, outcrops and 2D and 3D seismic information, a regional sequential stratigraphic analysis is developed for the Carboniferous Interval of the Southwest sector of the Tarija Basin.

The area of study lies between Santa Cruz de la Sierra to the North, the Charagua, Aguarague and Parabanon ranges to the West, the Pilcomayo River to the South and the Chaco Plains to the East.

The Carboniferous depositional cycle lasts approximately 74 million years. Its deposits are influenced in part by glaciation.

The distribution of the sedimentary infilling is directly related to the advance or retreat of the glaciers and to the eustatic variations and the accommodation space generated.

The base of the Carboniferous is an important erosive unconformity generated on the Devonian age deposits corresponding to the Iquiri Fm. The top is an erosive unconformity showing a very important paleoclimatic change represented by Permian eolian sediments belonging to the Cangapi Fm.

Based on seismic interpretation two Megasequences have been defined. The limit between them is a regional erosive unconformity characterized by the development of important paleovalleys. These paleovalleys indicate the major advance of the glacial systems during the Carboniferous.

It is assumed that this unconformity corresponds in age to the Mississippian Pennsylvanian limit.

The lower Megasequence, of Mississippian age, shows marine influence by the association of facies defined in outcrops, especially in its early stage. For the Upper Megasequence, of Pennsylvanian age, continental environments prevail.

Seismically interpreted, erosive limits allow the subdivision of these two Megasequences in two sequences of third-order respectively.

Each one of the four defined sequences (SSQ1, SSQ2, SSQA and SSQB) is formed by deposits corresponding to the development of the Lowstand system tract and the Transgressive system tract .

The basal section of each sequence comprises deposits of subaerial and subaqueous outwash and deltaic deposits, which are lithologically represented by diamictites, sandstones and shales eventually. The top section of each sequence represents the infilling of these eroded paleovalleys plus the flood plain deposits. Lithologically these are represented by sandstones and shales.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado