Volcanic Sunset-Glow Stratum: Origin

Abstract
A piston core taken off of the coast of Oregon in 358 meters of water contained an indurated calcareous layer composed partly of dolomite with a composition Ca58.7Mg41.3. Dolomites of this chemical composition are typical of the supratidal environment. However, the dolomite has isotopic composition δ018 = 5.8 per mille, δC13 = 35.1 per mille relative to the Chicago PDB-I standard. The unusual carbon isotope ratio is similar to that of calcites produced as a byproduct of bacterial breakdown of hydrocarbons.