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Paleoclimatic inferences from paleopedology and magnetism of the Permian Maroon Formation loessite, Colorado, USA

Kristy L. Tramp, G. S. Soreghan and R. Douglas Elmore
Paleoclimatic inferences from paleopedology and magnetism of the Permian Maroon Formation loessite, Colorado, USA
Geological Society of America Bulletin (June 2004) 116 (5-6): 671-686

Abstract

The Maroon Formation in the eastern Eagle Basin (Colorado) consists of >700 m of lithified loess with >200 paleosols interpreted as Protosols and Argillisols on the basis of field, petrographic and geochemical data. Additionally, magnetic susceptibility aids assessment of the intensity of pedogenesis. Bulk magnetic susceptibility (Chi (sub b) ) through the section repeatedly fluctuates between low values (average 3.51 X 10 (super -8) + or - 1.59 X 10 (super -8) m (super 3) /kg) in parent loessite and higher values (average 5.70 X 10 (super -8) + or - 2.70 X 10 (super -8) m (super 3) /kg) in paleosols. Moreover, magnetic susceptibility positively correlates with abundance of clay-sized material as well as Al (sub 2) O (sub 3) and K (sub 2) O and effectively distinguishes Protosols and Argillisols. Low-temperature demagnetization indicates the presence of ultra-fine-grained magnetite. The integration of geochemical, petrographic, and rock magnetic data suggest that changes in magnetic susceptibility reflect pedogenesis and relate primarily to climate- and time-dependent pedogenic production and concentration of ultra-fine-grained magnetite. The Maroon Formation loess and associated soils accumulated in an overall arid system, documented in part by formation of incipiently formed paleosols developed into Argillisols by eolian clay and carbonate additions rather than by in situ clay formation. However, the paleosols showing bulk magnetic susceptibility values of greater than 200 Chi (sub b) document a high-frequency (10 (super 4) -10 (super 5) yr) fluctuation between arid times of loess accumulation and slightly wetter times of reduced silt influx and resultant pedogenesis. This fluctuation likely reflects glacial-interglacial climate shifts that operated in low-latitude Pangea during icehouse conditions. These results suggest that climate-related magnetic susceptibility variations within loess successions can be preserved and useful in very ancient (pre-Pliocene-Pleistocene) sequences.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 116
Serial Issue: 5-6
Title: Paleoclimatic inferences from paleopedology and magnetism of the Permian Maroon Formation loessite, Colorado, USA
Affiliation: Rice University, Department of Earth Science, Houston, TX, United States
Pages: 671-686
Published: 200406
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 102
Accession Number: 2004-054254
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2004077
Illustration Description: illus. incl. sects., geol. sketch map
N39°15'00" - N39°25'00", W107°10'00" - W107°00'00"
Secondary Affiliation: University of Oklahoma, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200416
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