Static connectivity of fluvial sandstones in a lower coastal-plain setting: An example from the Upper Cretaceous lower Williams Fork Formation, Piceance Basin, Colorado

AAPG Bulletin ◽  
2011 ◽  
Vol 95 (6) ◽  
pp. 899-923 ◽  
Author(s):  
Matthew J. Pranter ◽  
Nicholas K. Sommer
Keyword(s):  
Coastal Plain ◽  
Upper Cretaceous ◽  
Piceance Basin ◽  
Williams Fork ◽  
Williams Fork Formation ◽  
Static Connectivity ◽  
Lower Coastal Plain

Microseismic Fracture Mapping Optimizes Development of Low-Permeability Sands of the Williams Fork Formation in the Piceance Basin

2005 ◽  
Author(s):  
Stephen Lee Wolhart ◽  
Chad Eric Odegard ◽  
Norman Raymond Warpinski ◽  
Charles Kennedy Waltman ◽  
Sean Robert Machovoe
Keyword(s):  
Low Permeability ◽  
Piceance Basin ◽  
Williams Fork ◽  
Williams Fork Formation ◽  
Fracture Mapping

New age constraints on the Late Cretaceous lower Williams Fork Formation, Coal Canyon, Colorado

2021 ◽  
Vol 58 (1) ◽  
pp. 5-26
Author(s):  
Jordan T. Walker ◽  
Andres Aslan ◽  
Rex D. Cole ◽  
Michael T. Heizler
Keyword(s):  
Late Cretaceous ◽  
Volcanic Ash ◽  
New Age ◽  
Piceance Basin ◽  
Weighted Mean ◽  
Analytical Uncertainty ◽  
Marine Strata ◽  
Williams Fork ◽  
Williams Fork Formation ◽  
Stratigraphic Position

The precise age of terrestrial sediments in the Late Cretaceous Williams Fork Formation of western Colorado is poorly constrained due to a paucity of radiometric data. Sanidine and zircon dating of a volcanic ash encased in coal (i.e., the Coal Canyon ash) within the Cameo-Wheeler coal zone of the lower Williams Fork Formation in Coal Canyon, Colorado provides an important new age constraint for the southwestern Piceance Basin. A 10-30 cm thick, light gray, clayey mudstone encased in coal was sampled for both zircon U-Pb and sanidine 40Ar/39Ar geochronology. The presence of numerous euhedral zircon crystals, a lenticular geometry, and a clayey texture suggest that the mudstone is a minimally reworked and slightly altered volcanic ash. Analysis of the euhedral zircon crystals (n=108) in the ash produced a statistically robust U-Pb date with 93 grains yielding a weighed mean age of 74.52 ±0.11 Ma (1σ analytical uncertainty). 40Ar/39Ar sanidine analyses yielded a younger weighted mean age of 73.10 ±0.12 Ma (1σ analytical uncertainty) based on 6 of the 36 grains analyzed. Our preferred age is given by the weighted mean age of the sanidine as it is based on higher precision analyses that can better discriminate older inherited grains that are likely included in the zircon mean-age calculation. Isotopic data for the Coal Canyon ash overlap in age with a K-Ar date of 72.5 ±5.1 Ma for a widespread Williams Fork Formation tonstein, known as the Yampa Bed, found in coal-bearing outcrops and mine workings throughout the northern Piceance and Sand Wash basins and Axial Basin Uplift. Based on the similarity in isotopic age, sedimentologic context and stratigraphic position, we suggest that the Coal Canyon ash and the regionally extensive Yampa Bed are coeval. Additionally, this correlation corroborates that the Cameo-Wheeler coal zone of the Williams Fork Formation in the southwestern Piceance Basin is correlative with the Middle coal zone of the Danforth Hills and Yampa regions. Lastly, this proposed correlation may suggest that the Coal Canyon ash, like the Yampa Bed, correlates with the Baculites reesidei ammonite zone, which is associated regionally with a bentonite dated to 72.94 ±0.45 Ma. Detrital sanidine geochronology of two lower Williams Fork sandstone units that overly the Coal Canyon ash did not produce grains younger than the ash and thus do not quantitatively improve the chronostratigraphy of these specific units. Lastly, the Coal Canyon ash date serves as a basis for future evaluations of the diachroneity of non-marine strata of the Williams Fork Formation.

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