Brown, L. Frank1, Robert G. Loucks1, Ramón H. Treviño1,
Ursula Hammes1
(1) The University of Texas at Austin, Austin, TX
ABSTRACT: Role of Lowstand Deposition in Mobilizing Shale Ridges that Established Successive Shelf Edges, Oligocene Frio Formation (32-23.6 Ma), Gulf of Mexico Basin, South Texas
Rivers entrenched at shelf edges during relative lowstands of sea level served as
sediment point sources. The sediments accumulated in basin-floor fans, slope fans, and
prograding deltaic-wedge systems
. Increasing weight of the sediment load generated growth
faulting that began during mid-slope-fan deposition. Initially, faulting accelerated
accommodation rates in subbasins and increased load stress, which mobilized and forced
deep, water-saturated, muddy facies basinward and upward in response to rotation of
footwall blocks. Extensional faults developed in strata above shale ridges. Growth of
uplifted ridges diminished fault movement enough to permit aggradational slope-fan
deposition to in turn reduce water depths. Subsequently, deltas prograded over slope
systems
that were now sufficiently shallow for deltaic deposition. Minor uplift of shale
ridges and normal fault movement were typically rejuvenated during later cycles.
Individual arcuate (areally concave basinward) growth faults comprise segments of major
strike-aligned regional fault and associated shale-ridge
systems
produced during
temporally equivalent relative sea-level falls. Depositional
systems
that filled subbasins
are genetically identical (although diachronous), with
systems
tracts
becoming younger
basinward. Shale ridges produced paleo-seafloor relief responsible for basinward thinning
of slope fans and delta
systems
. Late lowstand deltaic progradation terminated on the
crest of contemporaneous shale ridges. Consequently, basinward flanks of ridges
progressively served to reestablish younger Frio shelf margins farther basinward,
occurring synchronously with the end of each third-order relative lowstand of sea level.
We suspect that sedimentary-induced tectonics may be a greatly underappreciated key factor
in the origin and evolution of many
types
of sedimentary basins and depositional
systems
.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.