A Potential High-Latitude Signature on a Cretaceous Paleopolar Coastal Plain: Flashiness Evidenced by Recurring Facies, Sedimentary-Pedogenic Structures and Isotopic Trends in the Prince Creek Formation of Arctic Alaska During a Greenhouse

Abstract

The Prince Creek Fm (Maastrichtian) of Alaska, deposited at 80–85° north paleolatitude, preserves an Arctic paleopolar Greenhouse ecosystem. We suggest that distinctive, recurring facies and sedimentary-pedogenic structures coupled with isotopic trends are evidence of a high-latitude signature on this low-gradient, muddy coastal plain. Strata record deposition in meandering trunk channels, meandering-fixed distributaries, and associated floodplains. Crevassing was common and splay complexes make up the bulk of sandy deposits. Inclined heterolithic stratification (IHS) and carbonaceous root traces are found in all channels. Although IHS is interpreted to record tidal-influence, ubiquitous roots on all IHS may also evidence a flashy system with regular discharge fluctuations. Entisols-Inceptisols are drab-colored and contain carbonaceous material and Fe-oxide depletion coatings indicating waterlogging and anoxia, consistent with a high water table. Fe-oxide mottles, ferruginous segregations, bioturbation, and illuvial clay coatings indicate recurring oxidation and periodic drying-out of soils. These compound-cumulative soils experienced repeated wetting and drying, with soil formation repeatedly interrupted by alluviation. Common pedogenic illite/smectite in ash-rich Prince Creek soils also suggest weathering and alternating wetting-drying. Bonebeds on floodplains exhibit a recurring facies pairing consistent with deposition by viscous hyperconcentrated flows. We suggest that exceptional discharge events, generated by seasonal snowmelt in the nearby Brooks Range increased suspended sediment concentrations and generated recurring, erosive hyperconcentrated flows. Hyperpycnites have also been identified in prodelta deposits of the genetically-linked shallow-marine sediments of the Schrader Bluff Fm. Stable oxygen isotope analysis of dinosaur tooth enamel and pedogenic siderite suggest that δ18O depleted water ingested by dinosaurs, and meteoric water from siderite, result from increased rainout linked to increased latent heat transfer to the poles, an intensified hydrological cycle, and snowmelt. δ18O and δ13C values from authigenic aragonite in brackish-water invertebrates likely record seasonal fluctuations attributed to drainage from high altitude freshwater sources. We interpret these characteristics to record a seasonally flashy system, which is the high-latitude signature in the Prince Creek Fm likely driven by the paleopolar light and temperature regime.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015