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Unconformities and age relationships, Tongue River and older members of the Fort Union Formation (Paleocene), western Williston Basin, U.S.A.

2004; University of Wyoming; Volume: 39; Issue: 2 Linguagem: Inglês

10.2113/39.2.113

0010-7980

Edward S. Belt,

Geochemistry and Geologic Mapping

Research Article| January 01, 2004 Unconformities and age relationships, Tongue River and older members of the Fort Union Formation (Paleocene), western Williston Basin, U.S.A. Edward S. Belt; Edward S. Belt * 1Department of Geology, Amherst College, Amherst, MA 01002, U.S.A. *Author to whom correspondence should be addressed esbelt@amherst.edu Search for other works by this author on: GSW Google Scholar Joseph H. Hartman; Joseph H. Hartman 2Department of Geology and Geological Engineering, and Energy & Environmental Research Center, University of North Dakota, Grand Forks, ND 58202, U.S.A. Search for other works by this author on: GSW Google Scholar John A. Diemer; John A. Diemer 3Department of Geography and Earth Sciences, University of North Carolina, Charlotte, NC 28223, U.S.A. Search for other works by this author on: GSW Google Scholar Timothy J. Kroeger; Timothy J. Kroeger 4Department of Biology and Geology, Bemidji State University, Bemidji, MN 56660, U.S.A. Search for other works by this author on: GSW Google Scholar Neil E. Tibert; Neil E. Tibert 5Department of Geology, Smith College, Northampton, MA 01063, U.S.A. Search for other works by this author on: GSW Google Scholar H. Allen Curran H. Allen Curran 5Department of Geology, Smith College, Northampton, MA 01063, U.S.A. Search for other works by this author on: GSW Google Scholar Author and Article Information Edward S. Belt * 1Department of Geology, Amherst College, Amherst, MA 01002, U.S.A. Joseph H. Hartman 2Department of Geology and Geological Engineering, and Energy & Environmental Research Center, University of North Dakota, Grand Forks, ND 58202, U.S.A. John A. Diemer 3Department of Geography and Earth Sciences, University of North Carolina, Charlotte, NC 28223, U.S.A. Timothy J. Kroeger 4Department of Biology and Geology, Bemidji State University, Bemidji, MN 56660, U.S.A. Neil E. Tibert 5Department of Geology, Smith College, Northampton, MA 01063, U.S.A. H. Allen Curran 5Department of Geology, Smith College, Northampton, MA 01063, U.S.A. *Author to whom correspondence should be addressed esbelt@amherst.edu Publisher: University of Wyoming Received: 05 Jul 2003 Revision Received: 08 Jul 2004 Accepted: 05 Nov 2004 First Online: 03 Mar 2017 Online ISSN: 1555-7340 Print ISSN: 1555-7332 UW Department of Geology and Geophysics Rocky Mountain Geology (2004) 39 (2): 113–140. https://doi.org/10.2113/39.2.113 Article history Received: 05 Jul 2003 Revision Received: 08 Jul 2004 Accepted: 05 Nov 2004 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Edward S. Belt, Joseph H. Hartman, John A. Diemer, Timothy J. Kroeger, Neil E. Tibert, H. Allen Curran; Unconformities and age relationships, Tongue River and older members of the Fort Union Formation (Paleocene), western Williston Basin, U.S.A.. Rocky Mountain Geology 2004;; 39 (2): 113–140. doi: https://doi.org/10.2113/39.2.113 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyRocky Mountain Geology Search Advanced Search Abstract An unconformable relationship is observed within the Paleocene Fort Union Formation in the western Williston Basin at the contact between the Tongue River Member and the underlying Lebo and Ludlow Members. Isotopic dates and pollen biozone data reported here are integrated with previously published data. A new correlation of these facies results in a revised history of localized depositional and tectonic events. One unconformity occurs at this lithological contact in the Pine Hills (PH), Terry Badlands (TB), and Ekalaka (E) areas west of the Cedar Creek anticline (CCA), and another unconformity occurs at the same lithological contact in the Little Missouri River (LMR) area east of the CCA. The two unconformities differ in age by about two million years. The older is the U2 and the younger is the U3, which initially were recognized in the Ekalaka area of southeastern Montana (Belt et al., 2002). The U2 crops out in the TB, PH, and E areas, where at least 85 m of Tongue River strata bearing palynomorphs characteristic of biozone P-3 are found above the unconformity. Radiometric dates from strata (bearing palynomorphs characteristic of biozone P-2) below the U2 range in age from 64.0 to 64.73 Ma. The U2 unconformity west of the CCA thus occurs in strata near the base of the lower P-3 biozone.The U3 crops out in the LMR area (east of the CCA), where only 13 m of strata characterized by the P-3 pollen biozone occur above it. Radiometric dates from an ash <1 m above the U3 in that area range in age from 61.03 to 61.23 Ma, and the P-3/P-4 pollen biozone boundary is located 13 m above the ashes. The U3 thus occurs in strata characterized by upper parts of the P-3 pollen biozone east of the CCA. The U3 is also identifiable in the middle of the ca. 200 m-thick Tongue River Member west of the CCA, where mammal sites 40 to 80 m above it are Tiffanian-3 in age. The strata below this unconformity are tilted gently to the northwest; strata above the unconformity are flat lying. This mid Tongue River unconformity probably correlates with the unconformity at the base of the Tongue River Member in the LMR area east of the CCA, where a Ti-2 mammal site (the "X–X" locality) occurs <10 m above it.Depositional and tectonic events can be summarized using North American Mammal Age nomenclature as a relative time scale. From latest Cretaceous through Puercan time, paleodrainage was toward the east or southeast, in the direction of the Cannonball Sea. The Black Hills did not serve as an obstruction at that time. During early Torrejonian time, the Miles City arch (MCA) and Black Hills were uplifted and partially eroded, leading to the U2 unconformity. When deposition resumed, paleodrainages shifted to a northeasterly course. During middle and late Torrejonian time, facies of the lower Tongue River ("Dominy") sequence and the Ekalaka Member of the Fort Union Formation were deposited in the middle of a subbasin between the MCA and the CCA. Simultaneously, smectite-rich components of the Ludlow Member were being deposited east of the CCA. During latest Torrejonian time, uplift of the Black Hills tilted the "Dominy" sequence toward the northwest and local erosion led to the U3 unconformity. Following this tilting, during Tiffanian time, deposition of the upper Tongue River ("Knobloch") sequence shows continuity from western North Dakota across eastern Montana and into the northern Powder River Basin. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.