Recognition of High-Frequency Sequences in the Kenilworth Member of the Blackhawk Formation, Book Cliffs, Utah
David R. Taylor, Richard W.W. Lovell, 1991. "Recognition of High-Frequency Sequences in the Kenilworth Member of the Blackhawk Formation, Book Cliffs, Utah", Sequence Stratigraphy Applications to Shelf Sandstone Reservoirs: Outcrop to Subsurface Examples, J. C. Van Wagoner, C. R. Jones, D. R. Taylor, D. Nummedal, D. C. Jennette, G. W. Riley
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Shallow marine strata of the Campanian Kenilworth Member, cropping out in the Book Cliffs of east-central Utah, were examined from their updip to downdip depositional limits. Thirty-one outcrop sections were measured recording facies, stratal surfaces, and paleoflow indicators. These data were used to interpret the depositional environments and to develop a chronostratigraphic framework for the Kenilworth. The geometry of stratal surfaces and the continuity of sandstones were traced between measured sections using binoculars and photographic panoramas of cliff exposures.
A variety of depositional environments were identified in the Kenilworth including fluvial channels, coastal plain, foreshore, shoreface, offshore transition/offshore marine and deltaic. The vertical and lateral associations of these depositional environments indicate the presence of several parasequences separated by regionally correlative marine-flooding surfaces.
Five wave-dominated shoreline parasequences were recognized, each with a north-south to northwest-southeast paleoshoreline orientation. The oldest four parasequences are stacked as a progradational parasequence set and are interpreted to be part of the highstand systems tract. A regional erosional surface overlies the highstand systems tract and east-west trending fluvial channel systems incise into the underlying shoreface deposits. The erosional surface was traced basinward where deltaic deposits occur above a coarse-grained lag. The extensive erosional surface is interpreted to be a sequence boundary which formed in response to a relative sea-level fall. The coarse-grained lag and deltaic deposits in the basin are interpreted to be part of the lowstand systems tract. A major flooding surface occurs above the lowstand and was traced updip beneath a backstepped wave-dominated shoreline parasequence of the transgressive systems tract.
Sandstones of the Kenilworth Member are thus interpreted to comprise parts of two high-frequency sequences. A sequence boundary occurs within the Kenilworth and separates the highstand systems tract of an older sequence from the lowstand and transgressive systems tract of a younger sequence. The sequence boundary can be recognized by changes in parasequence stacking patterns, regionally extensive erosional truncation, and a basinward shift of facies. The magnitude of the relative sea-level fall that occurred during deposition of the Kenilworth is estimated to be at least 60 feet, based on the amount of fluvial channel incision observed at the sequence boundary. This magnitude of relative sea-level fall resulted in a basinward shift in facies of about 10 miles. The resultant paleoslope is interpreted to be 0.07 degrees, which is comparable to depositional slopes on the present day Gulf of Mexico shelf.
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The Lower Sego provides an opportunity to study well-exposed, high-frequency sequences and their systems tracts. Criteria for identification of sequence boundaries will presented. Sequences and their boundaries will be contrasted with parasequences and their bounding surfaces. The Upper and Lower Sego contain well-exposed tidal deposits within the lowstand systems tracts of high-frequency sequences. These tidal deposits and their relationship to incised valleys and systems tracts will be examined. The incised valley interpreted to form during relative falls in sea level will be contrasted with distributary channels related to autocyclic mechanisms.
0.0 Leave the parking lot of the Grand Junction Hilton. Grand Junction , Colorado. Turn left onto Horizon Drive. Pass under the 1-70 bridge, Turn left into the entrance ramp for 1-70 west.
0.2 Enter 1-70 heading west toward the Colorado –Utah State line. For the next 20 miles the Interstate will parallel the Colorado River flowing along the west side of the Grand Valley. The Interstate is built on the gray Cretaceous Mancos Shale. To the west of the Colorado River are the red cliffs of the Colorado National Monument. The Monument is operated by the National Park Service. These cliffs are the eastern edge of the Uncomahgre Uplift. As you drive north along the Interstate, the steeply dipping eastern limb of the Uncomahgre is clearly visible. This tight monoclinal fold is the result of horizontal compressional tectonics associated with Laramide deformation (Heyman, 1983). The red rocks in the Mounment include, from stratigraphically oldest to youngest: the Chinle Formation forming the lower, less resistant slops, the Wingate formation forming the massive cliffs up to 400 feet thick , the Kayenta Formation overlain by an unconformity along which the Navajo and Curtis Formations are missing , the Summerville and Entrada Formations, and the Morrison Formation consisting of fluvial sandstones and associated mudstones, within which some of the earliest dinosaur bones in North America were discovered in the late 19th century. The Jurassic Morrison Formation is unconformably overlain by the brown, Cretaceous, coal-bearing Dakota Sandstone. The Dakota caps many of the high mesas within the Mounment and forms well-exposed dip slopes along the Interstate in the vicinity of the exit to Mack, Co..