Middle Cretaceous greenhouse hydrologic cycle of North America

We present a paleolatitudinal precipitation reconstruction for the greenhou se setting of mid-latitude North America based on the oxygen isotopic compo sition of sphaerosiderites found in middle Cretaceous wetland paleosols. Ou r reconstructed middle Cretaceous delta O-18 values of precipitation are si milar to4 parts per thousand less than values from comparable modern low-el evation coastal settings free of monsoons. The data fit a conceptual model in which the precipitation source for the eastern margin of the Cretaceous Western Interior Seaway of North America is an O-18-enriched oceanic coasta l jet. In this subtropical-tropical setting, mid-Cretaceous precipitation r ates are interpreted to range from similar to 2500 to similar to 4100 mm/yr .