Open AccessChemostratigraphic implications of spatial variation in the Paleocene‐Eocene Thermal Maximum carbon isotope excursion, SE Bighorn Basin, Wyoming
Author(s) -
Baczynski Allison A.,
McInerney Francesca A.,
Wing Scott L.,
Kraus Mary J.,
Bloch Jonathan I.,
Boyer Doug M.,
Secord Ross,
Morse Paul E.,
Fricke Henry C.
Publication year - 2013
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/ggge.20265
Subject(s) - geology , chemostratigraphy , isotopes of carbon , paleontology , isotopic shift , excursion , carbonate , δ13c , stable isotope ratio , isotope , total organic carbon , chemistry , physics , organic chemistry , quantum mechanics , political science , environmental chemistry , law
The Paleocene‐Eocene Thermal Maximum (PETM) is marked by a prominent negative carbon isotope excursion (CIE) of 3–5‰ that has a characteristic rapid onset, stable body, and recovery to near pre‐CIE isotopic composition. Although the CIE is the major criterion for global correlation of the Paleocene‐Eocene boundary, spatial variations in the position and shape of the CIE have not been systematically evaluated. We measured carbon isotope ratios of bulk organic matter ( δ 13 C org ) and pedogenic carbonate ( δ 13 C carb ) at six PETM sections across a 16 km transect in the SE Bighorn Basin, Wyoming. Bed tracing and high‐resolution floral and faunal biostratigraphy allowed correlation of the sections independent of chemostratigraphy. The onset of the CIE in bulk organic matter at all six sections occurs within a single laterally extensive geosol. The magnitude of the CIE varies from 2.1 to 3.8‰. The absolute and relative stratigraphic thickness of the body of the CIE in bulk organic matter varies significantly across the field area and underrepresents the thickness of the PETM body by 30%–80%. The variations cannot be explained by basinal position and instead suggest that δ 13 C org values were influenced by local factors such as reworking of older carbon. The stratigraphic thickness and shape of the CIE have been used to correlate sections, estimate timing of biotic and climatic changes relative to the presumed carbon isotope composition of the atmosphere, and calculate rates of environmental and biotic change. Localized controls on δ 13 C org values place these inferences in question by influencing the apparent shape and duration of the CIE.