METEORIC SPHAEROSIDERITE LINES AND THEIR USE FOR PALEOHYDROLOGY AND PALEOCLIMATOLOGY

Sphaerosiderite, a morphologically distinct millimeter-scale spherulit ic siderite (FeCO3), forms predominantly in wetland soils and sediment s, and is common in the geologic record. Ancient sphaerosiderites are found in paleosol horizons within coal-bearing stratigraphic intervals and, like their modern counterparts, are interpreted as having formed in water-saturated environments. Here we report on sphaerosiderites f rom four different stratigraphic units, each of which has highly varia ble C-13 and relatively stable O-18 compositions. The unique isotopic trends are analogous to well-documented meteoric calcite lines, which we define here as meteoric sphaerosiderite lines. Meteoric sphaeroside rite lines provide a new means of constraining ground-water delta(18)O and thus allow evaluation of paleohydrology and paleoclimate in humid continental settings.