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PSA Sequence Stratigraphic Framework for the Lower Cretaceous North Carolina Coastal Plain, Southeastern U.S.A
By
Richard Sunde1 and Brian P. Coffey2
Search and Discovery Article #50044 (2007)
Posted June 18, 2007
*Adapted 
from
poster
presentation at AAPG Annual convention, Long Beach, California, April 1-4, 2007.
1Simon Fraser University, Burnaby, British Columbia, Canada ([email protected])
2Simon Fraser University, Vancouver, British Columbia, Canada ([email protected])
A lithology-based sequence
stratigraphic framework for the little studied Lower Cretaceous mixed
carbonate-siliciclastic sediments of the subsurface Albemarle Basin is
presented. Thin sections produced of well cuttings from exploration wells were
analyzed to characterize lithology, fossil components, depositional facies, and
diagenetic events because the study interval is entirely confined to the deep
subsurface in a basin lacking core control. Data was then used in conjunction
with wireline logs to document the facies abundance and stacking patterns.
Integration of 2D seismic data and biostratigraphic control allowed regional
correlation of major transgressive-regressive events between wells, resulting in
the generation of a sequence stratigraphic framework for the onshore basin.
Results show the following
dominant lithofacies (listed from shallow to deep): sandstone, skeletal
sandstone; variably sandy mollusk packstone/grainstone; siltstone;
unfossiliferous and diatomaceous shales; skeletal wackestone; variably sandy
(quartz and glaucony) lime mudstone, and marl.
Comparison of observed facies
with cores and wireline logs from the Baltimore Canyon and Southeast Georgia
Embayment confirms the sequences consist of upward-shoaling siliciclastic
shorefaces, with basal-open shelf mollusk-rich carbonates often marking
transgressive events. Basin-scale depositional trends indicate greater
accumulation of the carbonate facies in the southern basin, with increased fine
siliciclastic material to the north. This trend may reflect a major
siliciclastic point-source in the vicinity of the ancestral Chesapeake region.
The depositional
and diagenetic models generated from this research provide valuable insight into
the facies and reservoir properties in coeval offshore units comprising frontier
exploration targets along the Atlantic coast of the U.S. and Canada.
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The presence of wide, strike parallel facies belts suggests a high wave energy influence.
Two general stacking patterns have been recognized: Clastic-Dominated
(usually the HST of the sequences): An early quartz-sandy, molluscan-skeletal
packstone defines a transgressive lag. This is overlain by shales and
siltstones grading up into Carbonate-Dominated (usually the TST of sequences): An early molluscan skeletal packstone defines a transgressive lag. This is overlain by a peloidal-rich packstone possessing variable amounts of marl, lime mud, and other skeletal fragments (un-abraded brachiopods, bryozoans, and rare echinoderms). This in turn is overlain by a mollusk packstone that likely represents sub-fair-weather wave-base rudist accumulations. The sequence is capped by a molluscan-ooid grainstone to packstone, miliolid packstone to wackestone, quartz-sandy lime mud, algal laminites, and rarely evaporates. This stacking pattern and lack of abundant encrusting allochems suggest a carbonate ramp depositional architecture. Clastic-rich beds may represent tempestite events, or temporary carbonate sedimentation hiatuses (short-lived sea-level regressions).
Detailed petrographic study of well Basin-scale depositional trends indicate increased accumulation of carbonate facies in the south, with increased siliciclastic material in the northern regions of the basin. The trend is consistent with trends observed offshore. Namely, the sediments of the Southeast Georgia Embayment to the south are carbonate-dominated while the Baltimore Canyon Trough to the north is clastic-dominated. Despite North Carolina’s tropical setting during the Lower Cretaceous, a significant portion of the studied sediments indicate depositional environments akin to clastic prograding shorefaces (bases are marked by mollusk-rich transgressive lags). Intervals dominated by carbonates most often occur during transgression, or in the distal basinward portions of the basin.
Brown, P.M.,
J.A. Miller, and F.M. Swain, 1972, Structural and stratigraphic
framework and spatial distribution of
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