Systematic lateral variation in the distribution of fossil mammals in alluvial paleosols, lower Eocene Willwood Formation, Wyoming

1990 ◽  
pp. 135-152 ◽  
Author(s):  
Thomas M. Bown ◽  
K. Christopher Beard
Keyword(s):  
Lateral Variation ◽  
Lower Eocene ◽  
Fossil Mammals ◽  
Willwood Formation

scholarly journals Astronomical climate control on paleosol stacking patterns in the upper Paleocene–lower Eocene Willwood Formation, Bighorn Basin, Wyoming

Geology ◽  
2008 ◽  
Vol 36 (7) ◽  
pp. 531 ◽  
Author(s):  
Hayfaa Abdul Aziz ◽  
Frits J. Hilgen ◽  
Gerson M. van Luijk ◽  
Appy Sluijs ◽  
Mary J. Kraus ◽  
...  
Keyword(s):  
Bighorn Basin ◽  
Climate Control ◽  
Lower Eocene ◽  
Willwood Formation ◽  
Stacking Patterns ◽  
Upper Paleocene

scholarly journals Sandstone body character, river styles, and geomorphology of the lower Eocene Willwood Formation, Bighorn Basin, Wyoming, USA

2021 ◽  
Author(s):  
Youwei WANG ◽  
Timothy Baars ◽  
Hiranya Sahoo ◽  
Joep Storms ◽  
Allard Martinius ◽  
...  
Keyword(s):  
Water Discharge ◽  
Bighorn Basin ◽  
Early Eocene ◽  
Average Width ◽  
Lower Eocene ◽  
Braided Rivers ◽  
Braided Channel ◽  
Facies Associations ◽  
Sinuous Channel ◽  
Willwood Formation

The lower Eocene Willwood Formation of the intermontane Bighorn Basin, Wyoming, USA, is an alluvial red bed succession with a sand content of ca. 20%-25%. The formation has been studied intensively for paleontology, paleoclimate, and sedimentary reconstruction. However, alluvial sandstone bodies and their corresponding river styles remain little characterized and documented. Here, efforts are made to study the characteristics and river styles of sandstone bodies through ca. 300 m of alluvial stratigraphy in the McCullough Peaks outcrop area based on the field data and a georeferenced 3-D photogrammetric model. Four channel facies associations are recognized, and they are ascribed to four river planform styles: distributary channel, massive trunk-shaped channel, braided channel, and sinuous channel, with the latter two styles being the more abundant. The channel sandstone bodies that show the character of sinuous rivers and those of braided rivers differ significantly in average thickness (6.1 m versus 9.0 m) and insignificantly in average width (on average 231 m) and paleoflow directions (on average N003). Braided-character dominated and sinuous-character dominated river styles are seen to alternate in the outcrop, while they show no spatial dependency in the 10 km2 study area. Bighorn Basin margins varied in the early Eocene, with differing tectonic, geological, and topographic characteristics. The observed mixture of river styles may be attributed to differential influences of axial and transverse river systems and/or climate change that controls water discharge and sediment load. An early Eocene geomorphologic reconstruction is constructed summarizing these new and earlier results.

scholarly journals Precession‐scale cyclicity in the fluvial lower Eocene Willwood Formation of the Bighorn Basin, Wyoming (USA)

Sedimentology ◽  
2013 ◽  
Vol 60 (6) ◽  
pp. 1467-1483 ◽  
Author(s):  
Hemmo A. Abels ◽  
Mary J. Kraus ◽  
Philip D. Gingerich
Keyword(s):  
Bighorn Basin ◽  
Lower Eocene ◽  
Willwood Formation

scholarly journals Stratigraphic relationships along the monoclinal eastern base of Bald Ridge and northwestern edge of Wyoming’s Bighorn Basin, U.S.A.

2019 ◽  
Vol 54 (2) ◽  
pp. 47-95
Author(s):  
Jason A. Lillegraven
Keyword(s):  
Upper Cretaceous ◽  
Middle Eocene ◽  
Age Determination ◽  
Bighorn Basin ◽  
Western Basin ◽  
Hinge Line ◽  
Lower Eocene ◽  
Laramide Orogeny ◽  
History Of ◽  
Willwood Formation

ABSTRACT This geologic study is focused on a less than 5 square-mile (ca. 13 km2) tract of public land in northwestern Wyoming, 8 miles (12.9 km) south-southwest of the small town of Clark in Park County. The study area is south of Clarks Fork of Yellowstone River along the eastern base of the topographic feature called Bald Ridge, also known structurally as Dead Indian monocline. Since the Middle Eocene, the study area has been along the northwestern margin of the Bighorn Basin. Prior to that time, the study area existed near the west–east center of the basin. Bald Ridge became elevated late in the Laramide orogeny (no older than the Early Eocene) through east-directed faulting of basement rocks via the extensive Line Creek–Oregon Basin thrust system. As that active faulting occurred, the overlying Phanerozoic strata (Lower Cambrian through Lower Eocene) responded with numerous west-directed, out-of-the-basin thrusts as a new western-basin margin developed along the eastern realm of the newly born Absaroka volcanic field. Most of that deformation occurred after deposition of uppermost levels of the Lower Eocene Willwood Formation. The key purpose of the present paper was to improve the accuracy of mapping of the Jurassic into Eocene stratigraphy along the newly restricted, northwestern edge of Wyoming’s Bighorn Basin. The stratigraphic column in a north–south band along the eastern flank of the Beartooth Mountains and continuing southward into the present study area was markedly deformed and deeply eroded late during the Laramide orogeny. The present small, more southerly study area is structurally and erosionally simpler than its more northerly equivalent. Thus, its study adds important geological information to the history of the northern Cody Arch, a convex-westward string of related basement-involved uplifts extending southward to southwest of the city of Cody. Progressively steepening eastward dips of strata characterize a west-to-east transect from the summit of Bald Ridge (capped by the shallowly dipping, Mississippian Madison Limestone) to the western edge of strongly overturned outcrops of the Eocene Willwood Formation. The Upper Cretaceous Meeteetse Formation is the stratigraphic horizon at which the dips attain vertical or slightly overturned orientations. All consequential faults within the newly mapped area are thrusts, and they show generally westward (out-of-the-basin) displacements. Despite those west-directed displacements, their primary cause was tectonic shortening at depth below Bald Ridge that was directed to the northeast or east-northeast. During the Laramide orogeny, certain thrust planes within the east-dipping Phanerozoic rock column cut down-section stratigraphically (but uphill relative to Earth’s surface) and thereby placed younger strata upon older. The cumulative result, as recognized at several levels within the present area of study, was marked thinning of the total section. For example, surface exposures of the mostly Paleocene Fort Union Formation, 4,000 feet (1,219 m) thick only 7 miles (11.3 km) to the east, was completely eliminated from the local surface stratigraphy by that means. The northern end of Bald Ridge is formed by the highly asymmetric Canyon Mouth anticline. That structure differs strongly in the attitude of its hinge line from the general east-northeast dip of strata cloaking Bald Ridge. The Canyon Mouth anticline’s hinge line plunges steeply to the southeast, and dips on its northeastern flanks are vertical to partly overturned. Surprisingly, hinge lines and flanks of all other anticlinal/synclinal structures recognized within the present map area share those same orientations with Canyon Mouth anticline. These consistent but unexpected differences in orientation from unfolded strata may represent very late events in the history of Laramide strain vectors across the study area. Working in northern parts of this study area, an independent group determining radiometric ages of detrital-zircon grains reported close agreements in age with their host localities in the Early Cretaceous Mowry Shale and Frontier Formation. However, under the present paper’s interpretation of the local stratigraphy, the other workers misidentified formational hosts for all three samplings. That resulted in age-determination errors of depositional history within the Upper Cretaceous section of as much as 28.8 million years.

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