Uinta Piceance Basin stratigraphic column

The Mowry Shale is an

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145& ...

geologic

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

. The formation was named for Mowrie Creek, northwest of Buffalo in

Johnson County, Wyoming Johnson County is a county in the north central part of the U.S. state of Wyoming. At the 2020 United States Census, the population was 8,447. The county seat is Buffalo. Kaycee is the only other incorporated town in the county. Johnson Count ...

Description

The Mowry Shale or Fish-scale Beds because of the abundance of fish scales, is a dark-gray, siliceous shale that weathers silver gray; it is 10-70 m thick. 40Ar/39Ar of sanidine from a bentonite yielded an age of 97.17 +/-0.69 Ma, thus is Cenomanian in age. Fossils indicate the Mowry was deposited during the early stages of the Western Interior Seaway.

Age

In so much as the Mowry was observed to lie above formations that were originally thought to be associated with the difficult to date upper Dakota units, especially Newcastle Sandstone, the Mowry was previously thought to be of

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in ...

age. However, recent studies, particularly of fossil pollens and spores, have dated the Mowry to the late-

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0 ...

. In many locations, the Mowry is bounded above by the Clay Spur bentonite, which is assigned the radiometric date of 97 million years, the upper Mowry may extend into the earliest Cenomanian.

Paleontology

Invertebrate fossils known include the ammonites ''Metengonoceras aspenanum'', ''Metengonoceras teigenense'', ''Neogastroplites americanus'', and ''Neogastroplites muelleri''. Isolated, lenticular accumulations of fish bones, scales, teeth and coprolites are thought to represent storm lag deposits formed by winnowing of the seafloor and concentration of the bones in bottom scours. The following fish species have been identified from the Mowry: an unnamed caturid, an unnamed ichthyodectid, ''Clupavus'' sp., ''Enchodus'' sp., ''Apateodus'' sp., an unnamed alepisaurid'','' and ''Xenyllion'' ''zonensis''. ''Xenyllion'' is the oldest acanthomorph (spiny-rayed) teleost in North America.Stewart, J.D. and Hakel, M., 2006. Ichthyofauna of the Mowry Shale (Early Cenomanian) of Wyoming. In, Lucas, S.G., and Sullivan, R.M. (editors), Late Cretaceous Vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35, p.161-163.

Dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

remains diagnostic to the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

have been recovered from the formation.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607.

Distribution

The Mowry outcrops or occurs at depth in parts of

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of the ...

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

North Dakota North Dakota () is a U.S. state in the Upper Midwest, named after the indigenous Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minnesota to the east, ...

South Dakota South Dakota (; Sioux: , ) is a U.S. state in the North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Lakota and Dakota Sioux Native American tribes, who comprise a large po ...

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...

and

Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to t ...

. It occurs within the following geologic regions:Mowry Shale
/ref> *

Big Horn Basin The Bighorn Basin is a plateau region and intermontane basin, approximately 100 miles (160 km) wide, in north-central Wyoming in the United States. It is bounded by the Absaroka Range on the west, the Pryor Mountains on the north, the Big ...

* Central Montana Uplift * Chadron Arch *

Denver Basin The Denver Basin, variously referred to as the Julesburg Basin, Denver-Julesburg Basin (after Julesburg, Colorado), or the D-J Basin, is a geologic structural basin centered in eastern Colorado in the United States, but extending into southeast ...

* Green River Basin * Montana Fold Belt * North Park Basin *

Powder River Basin The Powder River Basin is a geologic structural basin in southeast Montana and northeast Wyoming, about east to west and north to south, known for its extensive coal reserves. The former hunting grounds of the Oglala Lakota, the area is very s ...

* Sweetgrass Arch *

Uinta Uplift The Uinta Mountains ( ) are an east-west trending chain of mountains in northeastern Utah extending slightly into southern Wyoming in the United States. As a subrange of the Rocky Mountains, they are unusual for being the highest range in the co ...

Williston Basin The Williston Basin is a large intracratonic sedimentary basin in eastern Montana, western North Dakota, South Dakota, southern Saskatchewan, and south-western Manitoba that is known for its rich deposits of petroleum and potash. The basin is a ...

* Wind River Basin * Yellowstone Province

References

* Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. . Shale formations of the United States Cretaceous Montana Cretaceous geology of Wyoming {{US-geologic-formation-stub

Description

Age

Paleontology

Distribution

See also

References