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delta (super 13) C depth profiles from Paleosols across the Permian-Triassic boundary; evidence for methane release

Evelyn S. Krull and Gregory J. Retallack
delta (super 13) C depth profiles from Paleosols across the Permian-Triassic boundary; evidence for methane release
Geological Society of America Bulletin (September 2000) 112 (9): 1459-1472

Abstract

Stable carbon isotopic analyses of organic carbon (delta (super 13) C) in individual paleosol profiles from Permian-Triassic sequences of Antarctica reveal systematic isotopic variations with profile depth. These variations are in many cases analogous to those in modern soils, which are functions of redox conditions, soil development, and degree and type of microbial decay. In modern soils, these isotopic depth functions develop independently from vegetation changes (C (sub 3) versus C (sub 4) vegetation) and can be diagnostic of soil orders. This study shows that soil-intrinsic functions can be preserved in the delta (super 13) C values of paleosols as old as 260 Ma and constitute valuable data for paleoecological interpretations. A large carbon isotopic offset of as much as 10 per mil in whole paleosol profiles across the Permian-Triassic boundary indicates significant changes in the soil biogeochemistry and the soil-atmosphere system. Early Triassic paleosols are distinctive in their extremely low delta (super 13) C values (to -42 per mil) and often show an anomalous delta (super 13) C depth distribution compared to both Permian paleosols and modern soils. Highly depleted delta (super 13) C values, as the ones in Early Triassic paleosols, are suggested to be associated with microbial methane oxidation (methanotrophy). This hypothesis implies increased methane concentrations in the Early Triassic soil-atmosphere system. Increased atmospheric methane was probably partly responsible for the global carbon isotopic shift documented in marine and terrestrial sediments across the Permian-Triassic boundary.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 112
Serial Issue: 9
Title: delta (super 13) C depth profiles from Paleosols across the Permian-Triassic boundary; evidence for methane release
Affiliation: University of Oregon, Department of Geological Sciences, Eugene, OR, United States
Pages: 1459-1472
Published: 200009
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 106
Accession Number: 2000-075455
Categories: StratigraphyIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 1 table, sketch map
S85°00'00" - S85°00'00", E135°00'00" - E135°00'00"
S77°00'00" - S76°30'00", E159°00'00" - E160°00'00"
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: 200024
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