Mathematics – Logic
Scientific paper
Aug 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005gecoa..69.3813g&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 69, Issue 15, p. 3813-3829.
Mathematics
Logic
12
Scientific paper
Concentrations of oceanic and atmospheric oxygen have varied over geologic time as a function of sulfur and carbon cycling at or near the Earth’s surface. This balance is expressed in the sulfur isotope composition of seawater sulfate. Given the near absence of gypsum in pre-Phanerozoic sediments, trace amounts of carbonate-associated sulfate (CAS) within limestones or dolostones provide the best available constraints on the isotopic composition of sulfate in Precambrian seawater. Although absolute CAS concentrations, which range from those below detection to ˜120 ppm sulfate in this study, may be compromised by diagenesis, the sulfur isotope compositions can be buffered sufficiently to retain primary values. Stratigraphically controlled δ34S measurements for CAS from three mid-Proterozoic carbonate successions (˜1.2 Ga Mescal Limestone, Apache Group, Arizona, USA; ˜1.45 1.47 Ga Helena and Newland formations, Belt Supergroup, Montana, USA; and ˜1.65 Ga Paradise Creek Formation, McNamara Group, NW Queensland, Australia) show large isotopic variability (+9.1‰ to +18.9‰, -1.1‰ to +27.3‰, and +14.1‰ to +37.3‰, respectively) over stratigraphic intervals of ˜50 to 450 m. This rapid variability, ranging from scattered to highly systematic, and overall low CAS abundances can be linked to sulfate concentrations in the mid-Proterozoic ocean that were substantially lower than those of the Phanerozoic but higher than values inferred for the Archean. Results from the Belt Supergroup specifically corroborate previous arguments for seawater contributions to the basin. Limited sulfate availability that tracks the oxygenation history of the early atmosphere is also consistent with the possibility of extensive deep-ocean sulfate reduction, the scarcity of bedded gypsum, and the stratigraphic δ34S trends and 34S enrichments commonly observed for iron sulfides of mid-Proterozoic age.
Gellatly Anne M.
Lyons Timothy W.
No associations
LandOfFree
Trace sulfate in mid-Proterozoic carbonates and the sulfur isotope record of biospheric evolution does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Trace sulfate in mid-Proterozoic carbonates and the sulfur isotope record of biospheric evolution, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Trace sulfate in mid-Proterozoic carbonates and the sulfur isotope record of biospheric evolution will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-955362