Continental Shelf Sand Ridges: Genesis, Stratigraphy and Petroleum Significance
Nummedal Dag, John R. Suter, 2002. "Continental Shelf Sand Ridges: Genesis, Stratigraphy and Petroleum Significance", Sequence Stratigraphic Models for Exploration and Production: Evolving Methodology, Emerging Models and Application Histories, John M. Armentrout, Norman C. Rosen
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The debate about the origin of sand ridges on modern continental shelves that took place in the 70s and early 80s is now repeating itself with respect to ancient ‘isolated shallow marine’ sand bodies. A review of the multiple interpretations of one such controversial sand body, the Upper Cretaceous Shannon Sandstone of Wyoming, conducted by Suter and Clifton in 1999, concludes: “we cannot, as a result of our analysis, unequivocally disprove any of the interpretations proposed for the Shannon, and we suspect that a collective inability to do so […] is the fuel on which this controversy runs.”
A ‘paradigm shift’ is needed in shelf sand ridge studies at this time, and it is this: shelf sand ridges are composite features. The debate needs to move beyond arguing about the implications of seemingly contradictory implications of the sedimentary structures, to one where the sedimentology is constrained by precise stratigraphic architecture. Numerous studies of modern ridge fields demonstrate that they commonly are separated from their substrate by a ravinement surface, or by a marine erosion surface formed in swales between migrating ridges. It is also clear that that many shelf sand ridges contains cores, or ‘precursors’ of shoreline deposits, the preservation of which is a function of the amount of migration of the ridge after its initial formation at the shoreline.
Shelf sand ridges are potentially major hydrocarbon reservoirs. The cumulative oil production from the Tocito Sandstone fields in the San Juan basin is about 160 MMBO; that from Shannon strata in the Powder River basin is even greater. Hartzog Draw, which is dominantly a Shannon field, has an estimated 400 MMBO in place. Several Middle and Upper Miocene oil fields on the northwest Java shelf also are producing from reservoirs interpreted as shelf sand ridges.
Controversy about outcropping shelf sand ridges will probably continue for some time, because only small parts of the commonly composite ridges are available for examination.