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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Depositional Systems and Oil and
Gas Plays in the Late
Cretaceous Olmos Formation, South Texas
By
The Late Cretaceous Olmos Formation of South Texas
continues to be an active exploration target 60 years after oil
was first discovered in this clastic assemblage. This shallow,
oil-proven formation was deposited on a broad, wave-influenced shelf. Sand accumulated in two depocenters. Initial
deposition took place in a western depocenter with an early
phase of wave-dominated deltaic sedimentation. Deposition of
the strike-elongate delta was followed by two cycles of high-constructive
deltaic deposition during which time sediments
prograded beyond the Early Cretaceous shelf edge. These
three deltaic complexes together compose the Catarina delta
system
. The focus of sedimentation then shifted eastward to
the Big Foot delta
system
. Again, wave-dominated deltaic
sedimentation was followed by two episodes of high-constructive
but wave-modified delta formation. Sands not retained in
the Big Foot delta
system
were transported alongshore to the
west where they constructed a thick retrogradational coastal/
interdeltaic complex for which the name Rocky Creek barrier/
strandplain
system
is proposed.
Regional uplift with concomitant erosion removed much
of the updip facies tracts of the Olmos. This truncated section
was unconformably covered by Escondido shelf mudstones
thereby creating conditions favorable for stratigraphic entrapment
of hydrocarbons migrating updip from the deeper basin
through permeable deltaic sandstones. This stratigraphic-trap
play is the most prolific of the seven oil and gas plays in the
Olmos Formation. Six other plays produce oil and gas from a
variety of
structural
traps but most of the remaining oil
production is from the Charlotte fault zone. Youthful shelf-edge
gas, condensate, and oil plays are highly productive and
together with wildcat prospects farther basinward, offer the
best potential for continued high-level production from this
mature province.
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