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GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, VOL. 1, NO. 12, 1054, doi:10.1029/2000GC000095, 2000

Geologic evidence for a mantle superplume event at 1.9 Ga

Kent C. Condie

Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801


David J. Des Marais

Ames Research Center, M/S 239-4, Moffett Field, California 94035-1000


Dallas Abbott

Lamont-Doherty Earth Observatory, Palisades, New York 10964


Abstract

Both preserved and restored areal distributions of Proterozoic marine intracratonic, passive margin, and platform sediments show a prominent peak at ∼1.9 Ga, indicating that shallow marine sediments were widespread on the continents and that sea level was high at this time. The chemical index of alteration in shales deposited at this time was high, suggesting warm climates, possibly due to enhanced CO2 levels in the atmosphere. High sea level and warms climate may also explain an abundance of black shale, banded iron formations, and shallow marine phosphate deposits and an increase in the number of occurrences and diversity of stromatolites in general and microdigitate stromatolites at 1.9 Ga. All of these observations are consistent with a 1.9-Ga superplume event. The occurrence of only a minor positive carbon isotope shift in marine carbonates at 1.9 Ga indicates that the relative rates of burial of organic and oxidized carbon remained about the same as at present. Slightly low 87Sr/86Sr isotopic ratios in seawater at 1.9 Ga reflect increased mantle input of Sr from the proposed superplume event, whereas higher ratios at 1.85–1.75 Ga may reflect increased input of continental Sr from a growing supercontinent. The first massive sulfate evaporites in the geologic record at 1.8–1.6 Ga follow the possible 1.9-Ga superplume event. This may reflect an increase in both oxidation state and carbonate deposition in the oceans as plume-related volcanism wanes.

Received 10 July 2000; accepted 8 November 2000; published 5 December 2000.

Keywords: Mantle plumes; sea level; superplume; carbon isotopes; black shales.

Index Terms: 1610 Global Change: Atmosphere (0315, 0325); 1635 Global Change: Oceans (4203); 1824 Hydrology: Geomorphology (1625); 9619 Information Related to Geologic Time: Precambrian.

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 276938 bytes)

Citation: Condie, K. C., D. J. Des Marais, and D. Abbott (2000), Geologic evidence for a mantle superplume event at 1.9 Ga, Geochem. Geophys. Geosyst., 1(12), 1054, doi:10.1029/2000GC000095.