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Low seasonality in central equatorial Pangea during a late Carboniferous highstand based on high-resolution isotopic records of brachiopod shells

Andy Roark, Ethan L. Grossman and Joseph Lebold
Low seasonality in central equatorial Pangea during a late Carboniferous highstand based on high-resolution isotopic records of brachiopod shells
Geological Society of America Bulletin (September 2015) 128 (3-4): 597-608

Abstract

The relationship between Permian-Carboniferous glacial cycles and low-latitude climate remains a subject of vigorous debate. This study investigated seasonality and regional environmental variability in a portion of central equatorial Pangea during a late Pennsylvanian highstand using stable isotope and trace-element analyses of brachiopod shells from the Virgilian Ames Member of the Conemaugh Group in the Appalachian Basin, U.S.A. Well-preserved, thick-shelled Neospirifer dunbari specimens were serially sampled across growth bands to elucidate a record of seasonal variability during the life of the organisms. Because Neospirifer only colonized this marginal basin during near-maximum highstands, when stable, near-marine salinities were established, these data are a direct proxy for intra-annual climate fluctuations during interglacial times. Neospirifer specimens show remarkably little internal chemical variability, with delta (super 18) O generally fluctuating by 0.4 ppm or less and delta (super 13) C fluctuating by less than 1.5 ppm within a single specimen. Moreover, total delta (super 18) O variability between all specimens is only approximately 1.5 ppm. This lack of variation reflects a homogeneous, nonseasonal to weakly seasonal climate during the Ames highstand. Both delta (super 18) O and delta (super 13) C are approximately 1.5 ppm lower than those of other Virgilian specimens from regions with a more proximal connection to the open ocean, suggesting at least moderate freshwater influence in the Appalachian Basin during this time, although salinities remained close enough to marine levels to maintain stenohaline fauna. Thus, brachiopod seasonal records indicate normal moist tropical conditions during this penultimate Carboniferous interglacial, with no evidence for strong monsoonal variations in temperature or rainfall.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 128
Serial Issue: 3-4
Title: Low seasonality in central equatorial Pangea during a late Carboniferous highstand based on high-resolution isotopic records of brachiopod shells
Affiliation: Texas A&M University, Department of Geology and Geophysics, College Station, TX, United States
Pages: 597-608
Published: 20150914
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 91
Accession Number: 2015-096624
Categories: StratigraphyIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch map
N38°25'00" - N42°00'00", W84°49'60" - W80°31'60"
N39°43'00" - N42°17'60", W80°31'60" - W74°40'00"
N37°15'00" - N40°40'00", W82°30'00" - W77°45'00"
Secondary Affiliation: West Virginia University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201541
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