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 δC13 range is from -30 and -60 per mil for both aragonite and high-magnesium calcite. The δC13 of co-existing shells of Modiolus sp. is normal (+1.7 to -2.7 per mil). The δO18 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.