Pa. Comet et al., STERANE AND TRITERPANE PATTERNS AS DIAGNOSTIC-TOOLS IN THE MAPPING OFOILS, CONDENSATES AND SOURCE ROCKS OF THE GULF-OF-MEXICO REGION, Organic geochemistry, 20(8), 1993, pp. 1265-1296
Four hundred and eighty-one Gulf of Mexico oils and condensates can be
subdivided into nine major families based on their sterane (m/z 217,
218) and triterpane (m/z 191, 177) biomarker mass chromatogram pattern
s. These families are (1) carbonate-sourced oils reservoired in Jurass
ic-Cretaceous reservoirs onshore and Plio-Pleistocene reservoirs offsh
ore, (2) Austin Chalk reservoired oils, (3) Tuscaloosa oils, (4) Wilco
x reservoired oils (La), (5) South Texas Palaeogene reservoired oils,
(6) Mississippi delta oils, (7) post-mature oils of uncertain affiniti
es, (8) migration contaminated oils (showing attributes of a mixing of
immature and post-mature sources), and (9) oils and condensates lacki
ng biomarkers. Each oil family is concentrated in specific age-defined
producing trends, ranging in age from Jurassic to Pleistocene. For Te
rtiary reservoirs, these producing trends shift geographically with ti
me, in a manner analogous to the clockwise migrating Cenozoic depocent
er model for the northern Gulf of Mexico. At least six ages of marine
source rock deposition may be implicated in the genesis of these oils
(1) The Kimmeridgian-Oxfordian (including Smackover and Norphlet forma
tions), (2) The Aptian (including Pine Island, Bexar and Sunniland for
mations), (3) The Albian (Paluxy formation), (4) The Cenomanian-Turoni
an (including Eagle Ford and Tuscaloosa formations), (5) The Coniacian
Santonian (Eagle Ford and Austin Chalk), and (6) The Palaeocene (Wilc
ox, Midway, Sparta formations). The Jurassic and Cretaceous source roc
ks correspond to described oceanic anoxic events of probable global si
gnificance. This paper will concentrate on describing the biomarker pa
tterns of the oils and postulated source rocks, but due to reasons of
space, isotopic, elemental and other data will only be briefly discuss
ed.