SEDIMENTOLOGY, ICHNOLOGY, AND SEQUENCE STRATIGRAPHY OF THE MIOCENE OFICINA FORMATION, ORINOCO OIL BELT, EASTERN VENEZUELA BASIN
Date
2017-02-01
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0001-5865-3635
Type
Thesis
Degree Level
Masters
Abstract
The Lower Miocene Oficina Formation is widely distributed in the subsurface of the Orinoco Oil
Belt of eastern Venezuela. Despite its economic importance as one of the most important
hydrocarbon reservoirs worldwide, little is known about its sedimentologic, ichnologic and
sequence-stratigraphic aspects. Sedimentary facies, trace fossils, depositional environments,
stratal stacking patterns and surfaces of sequence stratigraphic significance have been analyzed in
the Junín and Boyacá areas. The Oficina Formation is subdivided here into three members:
Lower, Middle, and Upper. The Lower Member consists mainly of lowstand fluvial braidedchannel
deposits filling an incised valley. No evidence of marine conditions is present and the
only biogenic structures detected are root trace fossils present at the top of a few fining- and
thinning- upward channelized units. The Middle Member is much more heterogeneous, both
vertically and laterally, comprising high-sinuosity estuarine-channel, tidal-flat, tidal-creek and
tidal-sandbar deposits, stacked to form a retrogradational package and representing the
transgressive systems tract. The Middle Member is characterized by widespread evidence of tidal
influence (e,g, inclined heterolithic stratification) and by the presence of the impoverished
Cruziana Ichnofacies and the Skolithos Ichnofacies, both reflecting brackish-water conditions.
This member is thought to represent deposition in an estuarine system. The Upper Member
consists predominantly of highstand delta-plain deposits, stacked forming a progradational
pattern. These deposits locally show intense bioturbation with a predominance of continental
trace fossils, illustrating the Scoyenia Ichnofacies. Deltaic deposits display a mixed influence of tides and river processes. Previous studies invariably assumed a deltaic model for the whole Oficina Formation. However, integration of sedimentologic, ichnologic, and sequencestratigraphic
datasets suggests a more complex depositional evolution, comprising a fluvioestuarine
valley incised during a fall in sea level that became filled during the lowstand and
subsequent transgression, culminating with deltaic progradation during the highstand.
Description
Keywords
Fluvioestuarine, Orinoco Oil Belt , Oficina Formation
Citation
Degree
Master of Science (M.Sc.)
Department
Geological Sciences
Program
Geology