Paleoclimate and paleoenvironment of the Prince Creek and Cantwell formations, Alaska: Terrestrial evidence of middle Maastrichtian Greenhouse Event.

摘要

I studied the paleoclimate and paleonvironmental conditions of the Prince Creek Formation, North Slope Alaska, and the lower Cantwell Formation in Denali National Park, Alaska. I used data from pollen analysis, clay mineral analysis and stable isotope analysis of clay minerals and organic matter applied to paleosols of the Prince Creek Formation. In the lower Cantwell Formation, I reconstructed the sedimentary environment, produced a terrestrial carbon stable isotope record and obtained a ∼ 69.5 Ma radiometric age for the lower Cantwell Formation.;Clay analysis in the Prince Creek Formation indicates that the genesis of the paleosols was strongly influenced by the properties of the parent material and that an epiclastic bentonitic source contributed to the development of non-allophanic properties, which suggests the presence of Andept-like paleosols. Paleosols formed on the floodplains of the Prince Creek Formation reveal features attributed to wet-dry cycles as a result of seasonal flooding, perhaps due to snow melt in the ancestral Brooks Range. Carbon and oxygen isotope analyses, and the geochemistry of paleosol Bw/Bt horizons indicate mean annual precipitation values between 745.56 and 1426.88 +/-221.38 mm/yr and mean annual temperatures of 12 +/-4.4 °C. The meteoric water delta18O value calculated from smectite at a 6.3 °C mean annual temperature is ∼ -24 ‰. The calculated value is delta18O-depleted as is expected for high latitudes during the Late Cretaceous.;Sedimentary facies analysis suggests that The East Fork measured section of the lower Cantwell Formation was likely deposited in the distal part of an alluvial fan. A new U-Pb age of 69.5 +/-0.7 Ma from bentonites and carbon isotope values of bulk sedimentary organic matter and wood fragments indicates that a greenhouse event, known as the mid-Maastrichtian Event (MME), is recorded at the East Fork of the Toklat River Section. A mean annual precipitation value of ∼ 517.92 +/-134.44 mm/yr was obtained from delta 13C terrestrial organic matter.;The coeval nature of the lower Cantwell Formation (∼69.5 Ma) and the Prince Creek Formation (∼69.2 Ma) suggests that the MME likely affected the Prince Creek Formation as well. In the Prince Creek Formation, the age, precipitation, temperature and meteoric water composition from bentonite smectites are consistent with increased precipitation due to an intensified paleo-arctic hydrological cycle, which may have been the result of increased latent heat transport during the mid-Maastrichtian greenhouse episode.