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Aragonite-calcite seas; quantifying the gray area

Uwe Balthasar and Maggie Cusack
Aragonite-calcite seas; quantifying the gray area
Geology (Boulder) (December 2014) 43 (2): 99-102


Oscillations between the dominance of aragonite and calcite in abiotic marine CaCO (sub 3) precipitates throughout Earth history are closely coupled with the evolution of Earth's seawater composition and represent the environmental context in which organisms evolved their ability to biomineralize. The most important factor controlling these Phanerozoic oscillations in CaCO (sub 3) polymorph composition is the ratio of Mg:Ca in seawater, which is thought to separate aragonite and calcite precipitation along a distinct temperature-controlled threshold. A sharp threshold, however, is contradicted by overlapping aragonite and calcite precipitation fields at a range of experimental conditions. Here we present experimental data that enable us to quantify the proportions of CaCO (sub 3) polymorphs as a function of Mg:Ca ratio and temperature. This allows us to convert published Mg:Ca ratio proxy data and models of the Phanerozoic Mg:Ca ratio into proportions of abiotic CaCO (sub 3) polymorphs at a given temperature, and thus provides a temperature-corrected view of aragonite-calcite sea conditions. In this revised view, abiotic calcite precipitation was inhibited during aragonite sea intervals at temperatures above 20 degrees C, whereas calcite sea intervals were characterized by the co-precipitation of aragonite and calcite in environments above 20 degrees C. This continuous prominence of aragonite precipitation in Phanerozoic warm-water environments explains the Phanerozoic increase of aragonite over calcite skeletal composition in calcifying organisms.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 43
Serial Issue: 2
Title: Aragonite-calcite seas; quantifying the gray area
Affiliation: University of Glasgow, School of Geographical and Earth Sciences, Glasgow, United Kingdom
Pages: 99-102
Published: 20141219
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 36
Accession Number: 2015-007629
Categories: HydrochemistryStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2015041
Illustration Description: illus. incl. 1 table
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2022, 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: 201504
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