Use of multiple oxygen isotope proxies for elucidating Arctic Cretaceous palaeo-hydrology
Stable oxygen isotope analysis of siderite and dinosaur tooth enamel phosphate from the Campanian–Maastrichtian Prince Creek Formation, Alaska, USA, are analysed to determine the palaeohydrology of the ancient Colville Basin north of the Ancestral Brooks Range. δ18O of freshwater siderites relative to V-PDB ranges between −14.86 and −16.21‰. Dinosaur tooth enamel δ18O from three different sites (Kikak–Tegoseak, Pediomys Point, Liscomb) range between +3.9‰ and +10.2.0‰. δ18Ometeoric water are calculated from δ18Osiderite that formed at seasonal temperatures ranging from −2 to 14.5 °C, with a mean annual temperature of 6.3 °C. At 6.3 °C, the δ18Ow calculated from siderite ranged between −22.23 and −20.89‰ V-SMOW. Ingested water compositions are estimated from dinosaur teeth assuming body temperatures of 37 °C and local relative humidity of 77.5%, resulting in values ranging from −28.7 to −20.4‰ V-SMOW, suggesting consumption of meteoric water and orographically depleted runoff from the Brooks Range. The ranges in calculated δ18Ometeoric water are compatible between the two proxies, and are mutually corroborating evidence of extremely 18O-depleted precipitation at high latitudes during the Late Cretaceous relative to those generated using general circulation models. This depletion is proposed to result from increased rainout effects from an intensified hydrological cycle, which probably played a role in sustaining polar warmth.