Strontium-isotopic signatures reflect an origin of dolomite by fresh-water effluent: The pine plains formation (Wappinger Group, Cambrian) of southeastern New York

Abstract

Dolostones of the Pine Plains Formation of Late Cambrian age from a continental margin of the Appalachian Basin formed in a peritidal setting. The strontium-isotopic signature of this hypersaline dolostone shows that the waters responsible for precipitating this dolomite were fresh-water effluents derived from a granitic continental crust. In interbedded black dolostones of reducing or anoxic setting the carbon-isotopic ratio shows enrichment in the lighter isotope. In the absence of land plants such13C depletions indicate that photosynthetic communities, such as fresh-water, terrestrial or soil cyanobacteria or bacteria were present. If δ13C reflects depositional conditions, so should the strontium-isotopic composition. Cambrian sea water was not intimately involved in precipitating this dolomite. Dolomite formed by fresh-water effluent under conditions of low stand of sea level. An alternative interpretation is that the original isotopic composition of the marine dolomite was not retained, and that the elevated strontium-isotope composition reflects fabric-retentive replacement of precursor dolomite in a meteoric fluid system. The studied dolostones exhibit the highest87Sr/86Sr ratios ever reported in Paleozoic carbonate deposits.