Abstract

Because meteoric water δ18O values decrease with decreasing ambient temperature and increasing latitude, δ18O 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° to 83°. Mean δ18O values for meteoric cements and speleothems both show the same negative correlation with paleolatitude. The δ18O 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 δ18O 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 δ18O values of meteoric calcite (δ18Omcl) and seawater (δ18Osw) by using the equations Tcoastal =13.3 ±32.6[-0.231- 0.0613(δ18Omcl + δ18Osw)½ and Tinland =17.8 ±16.2[-0.572 - 0.1233(δ18Omcl + δ18Osw)½, where T is temperature in °C. Calcite precipitated from coastal meteoric water at temperatures between 0 and 25 °C will exhibit a narrow range in δ18O(-6‰ to -4‰, where δ18Osw = 0‰). The δ18O of calcite precipitated from inland meteoric water will be sensitive to paleotemperature, ranging from -14‰ to -5‰ (where δ18Osw = 0‰) for temperatures of 0 to 25 °C.

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