CLIMATE INTERPRETATION OF THE PALEO-ARCTIC PRINCE CREEK FORMATION ALASKA DURING THE MIDDLE-MAASTRICHTIAN GLOBAL WARM PERIOD

We present a geochemical record of palynomorphs and clay minerals from paleosols of the paleo-arctic Prince Creek Formation and interpret the data in the context of the Middle-Maastrichtian warming event (MME). We reconstruct paleoprecipitation and estimate meteoric water in the greenhouse arctic using major oxides and stable isotopes of carbon and oxygen. A radiometric age of 69.2 +/- 0.5 Ma from a tuff in the Prince Creek Formation, exposed along Alaska's Colville River, suggests the presence of the MME (~69 Ma). The MME has recently been identified in the coeval lower Cantwell Formation, Denali National Park, Alaska, allowing a comparison of precipitation between central and northern Alaska during the same time period. Using paleoprecipitation equations from geochemical data (climofunctions), we obtained a mean annual precipitation value of 1254 ±181 mm/yr, which falls within the 577.49 – 1791.01 mm/yr range derived from stable carbon isotope analysis of palynological separates. The δ¹⁸O values of smectite from bentonite beds cluster around ~ +5‰. The δ¹⁸O value of meteoric water calculated from bentonitic smectite is ~ -24‰, assuming a mean annual temperature of 6.3°C. This indicates δ¹⁸O-depleted precipitation, as expected for high latitudes during the Late Cretaceous. The age and meteoric water composition derived from analyses of bentonitic smectite, and the precipitation and temperature derived from pedofeatures of the paleosols, strongly supports the hypothesis that increased latent heat transport during the MME intensified the hydrological cycle and resulted in depleted δ¹⁸O values of precipitation in the paleo-arctic compared to Central Alaska.