CHARACTERISTICS AND CONTROLS ON HIGH LATITUDE SEDIMENTATION IN THE CRETACEOUS OF ALASKA AND THE PERMIAN OF ANTARCTICA

We describe two paleopolar clastic successions, the Cretaceous of Alaska and the Permian of Antarctica in order to reveal stratal characteristics and propose controls on high-latitude sedimentation. Both contain fluvial-deltaic deposits with Antarctic strata recording the last icehouse-greenhouse transition and Alaska strata recording sedimentation along the Arctic coastal plain during the Campanian-Maastrichtian greenhouse.

The Prince Creek Formation (Fm), North Slope of Alaska is dominated by meandering rivers with inclined heterolithic stratification (IHS) deposited on lower delta plain splay complexes. Heterolithic floodplains include: 1) crevasse splays, 2) weakly developed clay and ash-rich gleyed entisols and inceptisols with Fe-oxide mottles, ferruginous-manganiferous segregations, and illuvial clay coatings, and 3) dinosaur bonebeds encased in hyperconcentrated flows. Delta fronts contain abundant hyperpycnites. These characteristics, along with stable isotope data from pedogenic siderite, dinosaur tooth enamel, and invertebrates are interpreted as evidence of a seasonally flashy Arctic fluvial system. This discharge variability was a primary control on characteristics from stratal architectures and stacking pattern to microfeatures in paleosols, preserving a highly-heterogeneous system at all scales.

The Mackellar-Fairchild Fms in the Central Transantarctic Mountains preserve deltaic deposits and an up-dip braided fluvial feeder system. The Mackellar-Fairchild delta comprises abundant subaqueous terminal distributary channels, mouth bars composed of hyperpycnites, and thick packages of climbing ripples that alternate with background shelfal siltstone and shale. Although the trace fossil assemblage is high-diversity, most trace fossils are diminutive and exhibit shallow penetration depths and low bed ichnodiversity. These combined characteristics suggest recurring flooding from up-dip fluvial systems punctuated by periods of relative quiescence on the delta front. Discharge variability, likely driven by seasonal floods (freshets), brought sand-rich suspended sediment and freshwater onto the marine delta front from a postglacial braidplain, and was the primary control on sedimentary structures and geometries along the delta front and prodelta.