Stratigraphic and Combination Traps Within a Seismic Sequence Framework, Miocene Stevens Turbidites, Bakersfield Arch, California
James S. Hewlett, Douglas W. Jordan, 1993. "Stratigraphic and Combination Traps Within a Seismic Sequence Framework, Miocene Stevens Turbidites, Bakersfield Arch, California", Siliciclastic Sequence Stratigraphy: Recent Developments and Applications, Paul Weimer, Henry Posamentier
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The expression of stratigraphic and combination traps in upper Miocene Stevens turbidite sandstones of the Bakersfield arch, southern San Joaquin Valley, California, can be placed within a depositional sequence framework by integrating seismic, wireline-log, and core data. Insights from this study should reduce exploration risks in this mature basin and serve as exploration analogs in similar sand-rich turbidite systems globally.
Stevens sandstones occur as turbidites within the lowstand systems tracts of three depositional sequences (Coulter, Gosford, and Bellevue) that were deposited in a narrow, deep-water forearc basin. Regional marine-condensed sections containing siliceous shale and cherts separate the lowstand turbidite systems. Turbidites comprising the oldest (Coulter) system were transported by sediment gravity flows through distinct canyons on a sloping deep-water ramp, whereas the stratigraphically younger Gosford and Bellevue turbidite systems were deposited by gravity flows originating on high-relief deltaic slopes. The turbidite systems contain sandy, high-density (primarily) and low-density turbidite and debris-flow deposits in confined and unconfined complexes. Preexisting structural highs and depositional topography influenced the stacking geometries of the turbidite systems.
Four principal stratigraphic and combination stratigraphic/structural trap types in the Stevens turbidites are recognized: (1) permeability (facies) changes from proximal, thick, coarse-grained sandstones to distal, thin, fine-grained, interbedded sandstones and shales that occur on anticlinal flanks and account for the largest accumulations (up to 60 MMBOE); (2) channelized turbidite sandstones that pinch out against structural highs and contain reserves up to tens of MMBOE; (3) numerous small traps (<10 MMBOE) formed by compactional, low-relief, four-way structural closures; and (4) pinch-out of channelized, gully-fill turbidite sandstones within the less-explored middle and lower deltaic slopes of the Santa Margarita Formation.
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Applying depositional sequence stratigraphic concepts to the interpretation of siliciclastic depositional systems is becoming an increasingly important tool in petroleum geology. After a succession of breakthroughs during the 1970s and 1980s, sequence stratigraphic concepts now have entered a phase of intense application and documentation, especially with regard to successful implementation in the field of petroleum geology. Workers have applied these concepts to a variety of databases, ranging from outcrop to cores to electric logs and to multifold seismic data. Clearly, sequence stratigraphic concepts embody–not a rigid model or template–but rather a way of looking at geology. This volume has two purposes: to compile some recent applications of siliciclastic sequence stratigraphic concepts, and to present new studies focused on refining conceptual models. This memoir grew out of a 1991 symposium, "Variations in Depositional Systems Within a Sequence Stratigraphic Framework: Applications to Exploration," organized by the authors at the AAPG annual meeting at Dallas. Robert Loucks and Rick Sarg have edited a companion volume, also published by AAPG,“Entitled Carbonate Sequence Stratigraphy: New Developments and Applications.”