Organic delta/sup 13/C varies slightly with salinity in microbial mats at Guerrero Negro, Baja California, Mexico: Implications for stromatolite /sup 13/C values
Organic carbon preserved in Precambrian stromatolites has delta/sup 13/C values typically in the range -19 to -35, whereas microbial mats growing today in marine hypersaline environments have delta/sup 13/C values in the range -6 to -14. This /sup 13/C shift has been attributed to selective preservation of isotopically light organics, a decline in atmospheric CO/sub 2/ levels, or the restriction of microbial stromatolitic communities to hypersaline environments in the Phanerozoic due to grazing pressures in lower salinity environments. The salinity argument requires that the organic delta/sup 13/C of microbial mats increases with salinity, perhaps ranging from -20 to -35 in less saline water to -6 to -14 in hypersaline waters. Microbial mats inhabit those Guerrero Negro salt works ponds with salinities between 5.0 and 13.0%. Carbonate alkalinities in the ponds range from 2.7x10/sup -3/ moles/L (4%) to 3.6x10/sup -3/ moles/L (13%). Microcoleus mats' organic delta/sup 13/C vary from -12.4 to -14.2 with no clear dependence upon salinity. Aphanothece mats appear to be 1 to 2 permil enriched, relative to Microcoleus mats. The data suggest that salinity effects are insufficient by themselves to cause the /sup 13/C differences observed between Precambrian stromatolites and modern microbial mats.
- Research Organization:
- NASA-Ames Research Center, Moffett Field, CA (USA)
- OSTI ID:
- 6610882
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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580400* - Geochemistry- (-1989)