Oxygen isotopes in meteoric calcite cements as indicators of continental paleoclimate

Because meteoric water delta (super 18) O values decrease with decreasing ambient temperature and increasing latitude, delta (super 18) O values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures. To test this, we compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from Devonian to modern and in paleolatitude from 3.5 degrees to 83 degrees . Mean delta (super 18) O values for meteoric cements and speleothems both show the same negative correlation with paleolatitude. The delta (super 18) O vs. latitude trend for these carbonates is almost identical to that predicted for modern inland environments, but differs from the trend for coastal environments. This suggests that the ground water controlling the ultimate composition of meteoric cement is derived predominantly from inland recharge.If it is assumed that the modern meteoric water delta (super 18) O vs. temperature relation is valid for the past and that insignificant evaporation occurred prior to carbonate precipitation, then coastal and inland paleotemperatures can be calculated from the delta (super 18) O values of meteoric calcite (delta (super 18) O (sub mcl) ) and seawater (delta (super 18) O (sub sw) ) by using the equations T (sub coastal) =13.3 + or -32.6[-0.231- 0.0613(delta (super 18) O (sub mcl) + delta (super 18) O (sub sw) ) (super 1/2) and T (sub inland) =17.8 + or -16.2[-0.572 - 0.1233(delta (super 18) O (sub mcl) + delta (super 18) O (sub sw) ) (super 1/2) , where T is temperature in degrees C. Calcite precipitated from coastal meteoric water at temperatures between 0 and 25 degrees C will exhibit a narrow range in delta (super 18) O(-6ppm to -4ppm, where delta (super 18) O (sub sw) = 0ppm). The delta (super 18) O of calcite precipitated from inland meteoric water will be sensitive to paleotemperature, ranging from -14ppm to -5ppm (where delta (super 18) O (sub sw) = 0ppm) for temperatures of 0 to 25 degrees C.