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Manganese-bearing rhizocretions in the Willwood Formation, Wyoming, U.S.A.; implications for paleoclimate during the Paleocene-Eocene Thermal Maximum

Daniel T. Woody, Jon J. Smith, Mary J. Kraus and Stephen T. Hasiotis
Manganese-bearing rhizocretions in the Willwood Formation, Wyoming, U.S.A.; implications for paleoclimate during the Paleocene-Eocene Thermal Maximum
Palaios (June 2014) 29 (6): 266-276

Abstract

Changes in the stratigraphic distribution of manganese (Mn)-bearing columnar structures interpreted as rhizocretions indicate a shift in paleohydrological conditions in the Bighorn Basin during the Paleocene-Eocene Thermal Maximum (PETM). While most studies agree that significant warming occurred during the PETM, interpretations differ as to the effects of warming on the paleohydrologic regime. The columns consist of sand and silt cemented by calcite that also contains black, Mn-bearing nodules. The rhizocretions are typically vertically oriented and range from a few cm to over 50 cm in diameter and up to 75 cm tall. They are interpreted to have formed in the rhizospheres of relatively large root systems. The rhizocretions are restricted to intervals, showing only weak paleopedogenic development, that are interpreted as crevasse-splay or avulsion deposits. While such deposits are present throughout the study section at Polecat Bench in the northern Bighorn Basin, Wyoming, the Mn-bearing rhizocretions are found only below and above the PETM interval and within the initial carbon isotope excursion (CIE) marking the onset of the PETM. The abundance of black, Mn-rich nodules (< 1 cm in diameter) in the rhizocretions and presence of other pedogenic features indicate that the soils in which the plants were growing underwent seasonal flooding and repeated redox alternations. Their distribution in similar host deposits throughout the study interval, except for the main body of the PETM, supports climate as the driving factor in preservation of the Mn-bearing rhizocretions. The Mn-bearing rhizocretions support recent studies that suggest transient drying in northern Wyoming during the PETM.


ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 29
Serial Issue: 6
Title: Manganese-bearing rhizocretions in the Willwood Formation, Wyoming, U.S.A.; implications for paleoclimate during the Paleocene-Eocene Thermal Maximum
Affiliation: University of Colorado at Boulder, Department of Geological Sciences, Boulder, CO, United States
Pages: 266-276
Published: 201406
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 59
Accession Number: 2014-086899
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Annotation: NSF grants EAR-0000616, EAR-0228858, and EAR-02293000
Illustration Description: illus. incl. strat. col., geol. sketch map
N44°46'00" - N44°46'00", W108°46'00" - W108°46'00"
Secondary Affiliation: University of Kansas, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 201445
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