Geochemical model of δ18O of pedogenic calcite versus latitude and its application to Cretaceous palaeoclimate

Oxygen isotopic data for Early (Aptian) and Late (Maastrichtian) Cretaceous palaeosol calcite as a function of palaeolatitude of the Western Interior of North America plot in the modern winter-precipitation field, which, along with vertic features, may suggest a winter-wet palaeoclimate. Steeper, positive slopes for the Cretaceous curves compared to the modern curves may be attributable to greater latitudinal gradients in mean annual temperature and soil temperature in the Cretaceous compared to today, and/or to a greater degree of evaporation in Cretaceous soils at low latitudes compared to the modern earth. Distinguishing between these possibilities will require a more complete understanding of the variables that affect oxygen isotopes in pedogenic calcite, as well as better Cretaceous terrestrial palaeoclimate proxies with which to compare the isotopic data.