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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
2006. The American Association of Petroleum Geologists. All rights reserved.
DOI:10.1306/10130505037
Sequence
-stratigraphic
analysis
of Eocene clastic foreland basin deposits in central Lake Maracaibo using high-resolution
well
correlation and 3-D seismic data
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Alejandro Escalona,1 Paul Mann2
1Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, 4412 Spicewood Springs Road, Building 600, Austin, Texas 78759; [email protected]
2Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, 4412 Spicewood Springs Road, Building 600, Austin, Texas 78759; [email protected]
ABSTRACT
Eocene clastic rocks of the Maracaibo Basin were deposited in an asymmetrical foreland basin formed during the oblique Paleogene collision between the Caribbean and South American plates. In this study, we use more than 300 wells and 2000 km2 (772 mi2) of seismic data in the central Maracaibo Basin to produce a detailed sequence
-stratigraphic interpretation of the Eocene Maracaibo foreland basin.
The base of the Eocene stratigraphic succession in the central Maracaibo area is characterized by an approximately 250-m (820-ft)-thick, aggradational succession of fluviodeltaic sandstone overlain by an approximately 600-m (1968-ft)-thick retrogradational succession of shallow-marine shale and sandstone containing minor progradational units. The upper part of the foreland basin sequence
is marked by an approximately 100-m (328-ft)-thick aggradational succession of fluviodeltaic sandstone. In the approximately 1000-m (3280-ft)-thick Eocene section, we interpreted 17 parasequence sets, 6 genetic sequences, and 1 depositional
sequence
. Only one classic
sequence
boundary was interpreted within the Eocene section that marks the boundary between the retrogradational shallow-marine section and the overlying aggradational fluviodeltaic succession. Based on the stratigraphic architecture and thickening trends of several of the parasequence sets, we conclude that the main source of clastic sedimentation was located on the South America craton south of the Maracaibo Basin, instead of along the thrusted, north-northeastern margin of the basin as proposed by previous workers.
A lack of recognition of classic sequence
boundaries suggests that Eocene clastic rocks of the central Maracaibo foreland basin were not subaerially exposed during most of the Eocene, and that their stratigraphic architecture was controlled by tectonic subsidence related to thrusting along the northeastern edge of the foreland basin. Eustasy was not an important control on the stratigraphic evolution of the foreland basin until its middle Eocene aggradational period that marked the end of foreland basin subsidence.
Well
logs and three-dimensional seismic data show that depositional environments on the Eocene delta plain and shelf of the central Maracaibo foreland basin were dominated by fluvial and tidal processes that are similar to modern depositional processes of the Orinoco delta in eastern Venezuela.
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