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Distinguishing between sudden and gradual extinctions in the fossil record; predicting the position of the Cretaceous-Tertiary iridium anomaly using the ammonite fossil record on Seymour Island, Antarctica

Charles R. Marshall
Distinguishing between sudden and gradual extinctions in the fossil record; predicting the position of the Cretaceous-Tertiary iridium anomaly using the ammonite fossil record on Seymour Island, Antarctica
Geology (Boulder) (August 1995) 23 (8): 731-734

Abstract

A simple method, employing 50% confidence intervals, may be used to distinguish sudden from gradual extinctions. In cases where the fossil record is consistent with a sudden disappearance, the expected position of the extinction horizon may also be determined. Analysis of the fossil ammonites on Seymour Island shows that their pattern of disappearances is consistent with a sudden mass extinction at the Cretaceous-Tertiary (K-T) boundary, even though a literal reading of the fossil record shows they disappeared gradually over a stratigraphic interval 10-50 m below the boundary. It is striking that the iridium anomaly on Seymour Island falls within the stratigraphic interval determined by the 50% confidence intervals to be the most likely place for the K-T boundary (assuming there was a sudden disappearance of ammonites at the boundary). However, a computer simulation of the Seymour Island ammonite fossil record indicates a wide range of other extinction scenarios, including gradual extinctions ranging over as much as 20 m (alpha = 0.05), that are consistent with the ammonite fossil record; without saturation collecting near the K-T boundary it will be impossible to distinguish between gradual and sudden extinction scenarios for the Seymour Island ammonites based on the ammonite fossil record alone.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 23
Serial Issue: 8
Title: Distinguishing between sudden and gradual extinctions in the fossil record; predicting the position of the Cretaceous-Tertiary iridium anomaly using the ammonite fossil record on Seymour Island, Antarctica
Affiliation: University of California at Los Angeles, Department of Earth and Space Sciences, Los Angeles, CA, United States
Pages: 731-734
Published: 199508
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 13
Accession Number: 1995-053234
Categories: StratigraphyGeochemistry of rocks, soils, and sediments
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
S64°45'00" - S63°00'00", W58°00'00" - W56°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 199519
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