REVISITING THE NORTH AMERICAN TERRESTRIAL OXYGEN ISOTOPE GRADIENT AND CONSTRUCTION OF A METEORIC WATER OXYGEN ISOSCAPE

Albian to Cenomanian (113-94Ma) aged rocks were deposited during the gradual increase and peak of global hothouse temperatures. These temperatures promoted the intensification of the hydrologic cycle (relative to cold-house) that promotes an increased latent heat transportation to the poles. This build up to the super-greenhouse of the Cretaceous Thermal Maximum and the Maximum itself, coincided with major, global hydrologic cycle changes. The increased storm strength as seen in global increased hummocky-strata wavelengths corresponds to a likely propensity for eddy diffusion over advection-based processes to drive the oxygen isotopic fractionation dispersal over the western North American landmass similar to the Paleocene-Eocene Thermal Maximum. Contrary to previous research, the resulting oxygen isotopic gradient would be shallower than today, not steeper as suggested by an intensified Rayleigh distillation. As a dominance of eddy diffusion processes would result in a conservation of enriched marine isotopic signals, the oxygen isotopic gradient would reflect a shallow oxygen isotopic gradient. A shallow oxygen isotopic gradient has been derived using updated geospatial techniques (ArcGIS), and continental plate reconstruction (GPlates and PALEOMAP). An updated 2^nd order polynomial equation of:

δ¹⁸O_{meteoric water}= -0.0015(°lat²) - 0.1753(°lat) + 2.5924

where lat = paleo-latitude, was derived from an updated amalgamation of reclaimed and repurposed oxygen isotopic data originating from a variety of continental archives ranging from phosphatic crocodile enamel, turtle shell phosphate, pedogenic sphaerosiderite nodules, pedogenic calcium carbonate nodules, and clays. This gradient is also paired with an interpolated map of the meteoric water oxygen isotopic landscape (isoscape) of a slice of the North American western interior of the continent, stretching from northern Mexico to southern Canada. The isoscape indicates that the dominant pattern of the meteoric-water derived oxygen isotopic distribution on the North American landmass is a north-south latitudinal gradient with a likely moisture source originating from the ancient Gulf of Mexico.