Dudley D. Rice, Donald L. Gautier, 1983. "Shelf Sandstones", Patterns of Sedimentation, Diagenesis, and Hydrocarbon Accumulation in Cretaceous Rocks of the Rocky Mountains, Dudley D. Rice, Donald L. Gautier
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Two types of sandstones are differentiated in offshore shelf sequences that are dominated by siltstone and shale. The first type consists of thin beds or laminae of sandstone interbedded with siltstone and shale. This type of lithology is widespread and forms unconventional hydrocarbon reservoirs. The second type of shelf sandstone occurs as thick, elongate bodies that are interpreted to have been deposited as sand ridges and are comparable to coastal sandstones in some ways. They are conventional reservoirs for oil and gas, and the isolated sand ridges form stratigraphic traps that are enclosed by potential source rocks. Important features of this latter type of sandstone are: (1) they occur at considerable distances (hundred of miles) from the shoreline, (2) they form coarsening-upward sequences that show no evidence of subaerial exposure, (3) they are restricted generally to progradational sequences, and (4) they were deposited on a relatively flat, muddy shelf as elongate bodies with features indicating southward transport.
The shelf sandstones are interpreted to have been deposited on the storm-dominated western shelf of the Western Interior seaway. Sediment was transported by south-flowing geostrophic currents induced by strong winds associated with winter storms. Thin beds and laminae of sandstone interbedded with siltstone and shale were deposited as currents accelerated and decelerated with time as storms passed. Sand was probably concentrated as sand ridges on minor topographic highs by flow expansion and deceleration over these features. Deposits generally coarsen upward because current perturbation and wave agitation were intensified as the sand ridges grew.