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Author Evolution, Mesoproterozoic Marine ♦ Linda C. Kah, A. ♦ Timothy W. Lyons, B. ♦ John T. Chesley, C.
Source CiteSeerX
Content type Text
File Format PDF
Subject Domain (in DDC) Computer science, information & general works ♦ Data processing & computer science
Subject Keyword Northern Baffin ♦ Bylot Island ♦ Ga Carbonate-evaporite Succession ♦ Ga Grenville ♦ Northern Baffin Island ♦ Organic Carbon ♦ Biospheric Oxygenation ♦ Bylot Supergroups ♦ Mesoproterozoic Carbon Cycling ♦ O2 Level ♦ Society Cliff Formation ♦ Similar Paleoproterozoic ♦ Isotopic Shift ♦ Carbon Isotopic Composition ♦ Seawater Evaporation ♦ Caso4 Precipitation ♦ Marine Gypsum ♦ Marine Carbonate Rock ♦ Significant Change ♦ Enhanced Burial Flux ♦ Carbonate Precipitation ♦ Bylot Supergroup ♦ Increased Oxygenation ♦ Peritidal Carbonate ♦ Basin Development ♦ Limited Ca2 Availability ♦ Marine Carbonate Saturation ♦ Inorganic Carbon ♦ Geologic Record ♦ Isotope Event ♦ Minor Siliciclastic Rock ♦ Marine Caso4 ♦ Gypsum Bed ♦ Hypothesized Mesoproterozoic Oxygenation Event ♦ Positive Shift ♦ Carbonate Platform ♦ Ga Society Cliff Formation
Abstract A 4 ‰ positive shift in the carbon isotopic composition of the oceans, recorded globally in marine carbonate rocks at 1.3 Ga, suggests a significant change in Mesoproterozoic carbon cycling. Enhanced burial fluxes of organic carbon, relative to inorganic carbon, implied by this isotopic shift may have resulted in increased oxygenation of the Earth’s biosphere, as has been suggested for similar Paleoproterozoic and Neoproterozoic carbon isotope events. This hypothesized Mesoproterozoic oxygenation event may be recorded in the geologic record by the appearance of the oldest preserved, laterally extensive, bedded marine CaSO4 evaporites in the 1.2 Ga Grenville and Bylot supergroups. Speculation that the appearance of extensively preserved marine gypsum and/or anhydrite reflects increased biospheric oxygenation has been challenged, however, by the hypothesis that CaSO4 precipitation prior to the Mesoproterozoic may have been inhibited by significantly higher marine carbonate saturation, which would have facilitated carbonate precipitation and effectively limited Ca2+ availability during seawater evaporation (Grotzinger, J.P., 1989. Controls on Carbonate Platform and Basin Development, vol. 44, SEPM, Tulsa, OK, pp. 79–106), regardless of O2 levels. The 1.2 Ga Society Cliffs Formation (Bylot Supergroup, northern Baffin Island) consists of 720 m of peritidal carbonates, evaporites, and minor siliciclastic rocks. Evaporites occur predominantly in the lowermost 300 m of the Society Cliffs Formation, where gypsum beds (1–250 cm thick) constitute up to 15 % of the
Educational Role Student ♦ Teacher
Age Range above 22 year
Educational Use Research
Education Level UG and PG ♦ Career/Technical Study
Publisher Date 2000-01-01