Methane-Derived Marine Carbonates of Pleistocene Age

In some calcium carbonate-bearing sandstones from the edge of the continental shelf off the northeast United States, the $\delta $C$^{13}$ range is from -30 and -60 per mil for both aragonite and high-magnesium calcite. The $\delta $C$^{13}$ of co-existing shells of Modiolus sp. is normal (+ 1.7 to -2.7 per mil). The $\delta $O$^{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.