Science Applications, Inc., McLean, Virginia.
The isotopic composition of strontium in non-marine carbonate rocks: the Flagstaff Formation of Utah*
Article first published online: 14 JUN 2006
Volume 26, Issue 2, pages 271–282, April 1979
How to Cite
NEAT, P. L., FAURE, G. and PEGRAM, W. J. (1979), The isotopic composition of strontium in non-marine carbonate rocks: the Flagstaff Formation of Utah. Sedimentology, 26: 271–282. doi: 10.1111/j.1365-3091.1979.tb00354.x
Laboratory for Isotope Geology and Geochemistry Contribution No. 39.
- Issue published online: 14 JUN 2006
- Article first published online: 14 JUN 2006
- Manuscript received 8 March 1978; revision received 25 August 1978
The isotopic composition of strontium in surface water in continental basins is determined primarily by the geology of the basin and to a lesser extent by climatic conditions. Consequently, the 87Sr/86Sr ratios of brines in such basins can change only as a result of changes in the geology or climate. This principle of isotope geology was studied by analysis of a suite of non-marine carbonate rocks from the Flagstaff Formation (Palaeocene-Eocene) of Utah. The samples were collected from a section in Fairview Canyon of Sanpete County. They include both limestone and dolomite and were selected to have low non-carbonate residues. The concentrations of strontium in calcites averages 383 ± 128 p.p.m., while those of dolomites increase from 354 ± 74 p.p.m. in the lower 43 m of section to a maximum of 2259 p.p.m. higher up. The increase in the strontium content of dolomite is interpreted as evidence for a change from steady-state to progressively more evaporitic conditions. Two dolomites have isotopic compositions of oxygen expressed as δ18O = -2.75‰ (relative to the PDB standard) and are enriched in 18O relative to two calcites whose average δ18O value is -9.9‰. The 87Sr/86Sr ratios of the carbonate minerals range from 0.70890 to 0.71260. These values are clearly greater than the 87Sr/86Sr ratio of marine carbonates of Early Eocene age which is 0.70744. The variation of the 87Sr/86Sr ratio in this section of the Flagstaff Formation is real and reflects the occurrence of geological events which changed the isotopic composition of Sr entering Lake Flagstaff. The non-carbonate fractions of six carbonate rocks and one sandstone fit a straight line on the strontium mixing diagram in co-ordinates of initial 87Sr/86Sr and 1/Sr concentration. These results suggest that the isotopic composition of strontium in Lake Flagstaff may have been modulated by periodic input of volcanogenic detritus of felsic composition.