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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS
Distinguished Lecture Tour
Abstract: Ancient Delta System of the Gulf of Mexico Basin
By
Thick, offlapping, terrigenous clastic wedges make up the principal fill of the
Gulf Basin. Proximal parts of these wedges consist of paralic deposits formed either as
large-scale high-constructive delta systems (with related strike systems) or as a series
of smaller high-destructive delta systems. Distal parts accumulated as continental
slope deposits associated with salt diapir fields at the terminus of prograded paralic
systems.
High-constructive delta systems (e.g. Lower Wilcox, Yegua, and Jackson) are
comparable in scale and facies to Holocene Mississippi deltas. They were supplied by
rivers with large-volume sediment discharge; fluvial facies are concentrated locally
along the basin margin. These deltas consist dominantly of fluvial and fluvially-influenced
deposits, with extensive coal-bearing delta plain facies, thick progradational
delta front sand facies, and very thick organic-rich prodelta mud facies. Progradational
sand facies show either lobate or elongate patterns in plan. Delta system
of this type supported extensive strike-fed system comparable to strandplain and barrier
bar systems of the Holocene northwestern Gulf Coast.
High-destructive delta systems (e.g. Upper Wilcox and Frio) are analogous to
the Rhone and other Holocene deltas with significant marine modification (chiefly wave
action) of fluvially-introduced sediments. These deltas were supplied by numerous,
relatively small rivers with moderately high sand load; updip fluvial facies persist
along the entire basin margin. High-destructive deltas are composed of a series of
sand bodies with thickness axes roughly parallel to regional strike. Each of these deltas
consists of local progradational sand facies (channel and channel mouth bars) flanked
marginally by extensive sand units reworked from channel mouth bars. Associated
prodelta mud facies is moderately thick to thin. High-destructive deltas supported
local rather than a really extensive strike-fed systems.
Principal oil and gas reservoirs in high-constructive deltas occur in the progradational
delta front sands with trends controlled by geometry and distribution of these
lobate or elongate sand bodies. Vertical stocking of sand bodies is common, resulting
in rnultipay fields. Trends within these delta system are discontinuous along strike, as
facies between main prograded lobes consist mostly of muds and tight sands. Attendant
growth faulting, salt doming, and mud intrusion cause structural traps. In related
barrier bar and strandplain system, trends are regionally persistent with stratigraphic
traps. Oil and gas trends in high-destructive deltas are defined by local cuspate-trending End_Page 3--------------- coastal barrier sands and downdip progradational channel mouth bars; principal traps
are stratigraphic.
Continental slope systems, making up the distal parts of Gulf Basin terrigenous
wedges, have been penetrated only in younger units of the Basin or in very deep wells.
Systems are comparable in scale, composition, and structural association to modern
continental slope deposits of the northwestern Gulf. Thick and rapidly-deposited delta
systems of the Gulf Basin mobilized underlying deep-seated salt. Principal flowage
was toward the distal front of the prograding systems resulting in distinct diapir fields
coextensive with continental slope systems; minor flowage was toward thinner interdeltaic
areas. Salt mobilization was a significant control in determination of faces
fabric and growth faulting. Younger offlapping units inherited and perpetuated the
tectonic grain established by underlying systems. End_of_Record - Last_Page 4---------------