Carbon and oxygen isotopic composition of selected limestones and fossils

Paleosalinities in ancient brackish water systems determined by 87Sr/86Sr ratios in carbonate fossils: A case study from the Western Canada sedimentary basin

“…The generally contrasting S'*O values between seawater ( O%O, SMOW) and freshwaters ( > -25%0), and 6 "C differences in dissolved inorganic carbon (DIC) between seawater ( -O%O, PDB) and freshwaters (-12 to -32%0), is the basis for distinguishing marine and freshwater sediments through stable isotope analysis of carbonate fossils and limestones (Clayton and Degens, 1959;Keith and Weber, 1964). Several authors investigated an extension of this approach to cover transitional brackish waters (Sacket and Moore, 1966;Mook and Vogel, 1968;Mook, 1970), demonstrating the approximately conservative behavior of oxygen and carbon isotopes in the seawater-freshwater mixing zone.…”

Geochemical Characteristics and Paleoenvironmental Signi cance of the Ordovician Paleokarst Reservoir in the Maigaiti Slope of Tarim Basin

“…When the relative burial volume of organic carbon was higher than the amount of oxidation, more 12 C entered the organic carbon, which made the δ 13 C value of the marine carbonatite rocks in the same period move toward the positive direction. Also, the increasing salinity of the deposition in the water medium would have caused increases in carbonatite δ 13 C (Clayton and Degens, 1959;Keith and Weber, 1964); atmospheric precipitation and terrestrial freshwater injection would have caused δ 13 C value decreases. Oxygen isotopes are greatly influenced by the temperature and the concentration of the medium.…”

Geological Survey research 1972

“…The oxygen of th e limestones presumably became lighter through isotopic exchange with fresh water that percolated through them for a long time (Degens and Epstein, 1962;Ke ith and Weber , 1964;Tan and Hudson , 1971). Good examples of Graf (1960), Keith and Weber (1964 ), and Degens (1969). Numbered samples are discussed in the texl.…”