Isotopic Study of Siderite Concretion, Tuscarawas County, Ohio

Abstract

A carbonate concretion from the shale bed overlying the No. 5 coal of Pennsylvanian age in Tuscarawas County is composed of siderite and contains pyrite, barite, sphalerite and traces of calcite in its interior and in fractures. The siderite has 8I 3C= +0.65%o, Sr=289 ppm and 87Sr/86Sr=0.7110±0.0009- These results indicate that the siderite was deposited from brackish water in the pore spaces of the sediment and discredit the hypothesis that the carbonate ions originated by oxidation of peat or organic material. The barite has 8 S=— 4.6%o, indicating that it was not precipitated from sea water. Pyrite and sphalerite have 8 S= — 10.8%o and — 4.6%o, respectively, and were not deposited in isotopic equilibrium with each other. The sulfur in all three minerals is enriched in l6S as a result of bacterial reduction of sulfate to sulfide.