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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Stratigraphic Characteristics and
Sandstone Distribution of the Hackberry
Depositional System (Mid-Oligocene),
S.E. Texas and S.W. Louisiana:
A Sand-Rich Slope-Fan Complex
By
The Hackberry depositional system has been long recognized by Gulf Coast geologists by its anomalous deepwater fauna, rapid lateral variation in sandstone thicknesses, and prominent basal erosional unconformity. Hackberry sandstones also serve as major hydrocarbon reservoirs in many fields in southeast Texas and southwest Louisiana. A vertical succession through the Hackberry typically shows the basal erosional surface overlain by a variably sandy interval, informally termed the lower Hackberry sands, and capped by a thick deep-water interval, the Hackberry shale.
High-quality seismic data
indicate that the Hackberry
has a distinctive seismic signature. This seismic signature
permits the Interpretation of Hackberry lithologic characteristics
in a sequence stratigraphic framework. Key elements
of the seismic signature include: (1) a series of half-graben-like
slumps, marking the updip limit of the Hackberry
depositional system, and representing the failure of an
immediately pre-existing shelf edge, (2) a basal erosional
surface, in some places channelized as deep as 1800 ft. and
cutting as deeply as the Eocene, representing a prominent
sequence boundary upon which the Hackberry was
deposited, and (3) a pronounced downlap surface with well-developed
suprajacent clinoform geometries, best developed
in updip positions and representing a maximum flooding
surface within the Hackberry shale.
Most Hackberry sandstone is confined to the lower
Hackberry :,and interval immediately above the sequence
boundary. The Hackberry sandstone isopach shows
numerous linear to ovoid-shaped areas of thickly developed
sandstone separated by areas of little or no sandstone. In
some places, linear sandstone depocenters can be related
to eroded and channelized slope paleotopography that is
discernable seismically. Elsewhere, linear areas of thickly
developed sandstone are not associated with a clear
erosional expression on seismic records and may represent
broadly linear, aggradational turbidite fills in paleolow
positions. Other, more irregular to ovoid-shaped sand
patterns represent ponded aggradational deposits in intraslope
paleolow areas and basins. Paleontologic
data
strongly
suggest that this system was deposited at the time of the
large mid-Oligocene sea-level lowstand shown on the Haq et
al. (1987) coastal onlap curve. Deposition of lower Hackberry
sands commenced when fluvio-deltaic systems bypassed
the foundered shelf edge and sediment-gravity flows
ensued through a tortuous network of upper slope channels,
gullies, and other paleolows. Collectively, these deposits
represent the upper and middle portions of a sand-rich
slope-fan complex.
REFERENCE
Haq, B. U., Hardenbol, J., and Vail, P. R., 1987, Chronology of fluctuating sea levels since the Triassic. Science, v. 235. p 1156-1167.
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