Methane-Derived Marine Carbonates of Pleistocene Age

Abstract
In some calcium carbonate-bearing sandstones from the edge of the continental shelf off the northeast United States, the δC 13 range is from -30 and -60 per mil for both aragonite and high-magnesium calcite. The δC 13 of coexisting shells of Modiolus sp. is normal (+ 1.7 to -2.7 per mil). The δO 18 values of around + 3.5 per mil in all samples suggest deposition at temperatures around 0°C. Quaternary methane oxidized either chemically or microbiologically to carbon dioxide is the probable source of carbon in these carbonates.