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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
1Manuscript received August 22, 1996;
revised manuscript received May 18, 1998; final acceptance December 4,
1998.
2Instituto Mexicano del Petroleo,
Eje Central Lazaro Cardenas #152 CP 07730 Mexico D.F., Mexico; e-mail:
[email protected]
3Petrobras/Cenpes, Cidade Universitaria,
Ilha Do Fundão, Quadra 7 C.P. 21949-900, Rio de Janeiro-RR, Brazil.
ABSTRACT
The source rocks giving rise to the Jurassic and
Cretaceous oils are associated with marine carbonate environments. In contrast,
the source rocks giving rise to the Tertiary oils are associated with a
marine deltaic siliciclastic depositional setting. Biomarker and isotope
differences observed in the oils derived from marine carbonate environments
can be interpreted in terms of salinity, clay content, and oxygen depletion
variations. These differences provide diagnostic criteria for recognizing
and differentiating five distinct organic-rich depositional regimes as
the sources for these oil types: an anoxic hypersaline marine-carbonate
environment associated with a narrow and shallow semirestricted sea (Oxfordian
age, family 1 oil); an anoxic marine-carbonate environment associated with
a silled basin geometry (Tithonian age, family 2 oils, subtype 2a); an
anoxic marine-carbonate environment associated with a shallow, gentle,
broad marine-carbonate ramp in a distal position (Tithonian age, family
2 oils, subtype 2b); a clay-rich suboxic/anoxic marine-carbonate environment
associated with a carbonate platform in a proximal position (Tithonian
age, family 2 oils, subtype 2c); and an anoxic marine-evaporitic environment
(Early Cretaceous age, family 3 oils). The Tertiary oils (family 4) are
derived from bacterially reworked terrigenous and marine organic source
materials deposited in a marine-deltaic environment.
The Tithonian-related oils in the Mexican southern
side of the Gulf of Mexico accumulated both offshore and onshore and throughout
the stratigraphic column from Kimmeridgian to Pleistocene reservoirs, suggesting
vertical pathways as the principal secondary migration mechanism. The lateral
variations of these oils can be interpreted to reflect the Tithonian paleogeography
in the area and could be useful in predicting differences in the oil compositions.
Geochemical and biological marker analyses of
oils and rock samples from the Sureste basin of Mexico were effective in
identifying and geographically limiting four major oil families related
by age and source rock depositional environment: Oxfordian, Tithonian,
Early Cretaceous, and Tertiary.
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