The Cretaceous (Early Maastrichtian), dinosaur-bearing Prince Creek Formation (Fm.) exposed along the Colville River in northern Alaska records high-latitude, alluvial sedimentation and soil formation on a low-gradient, muddy coastal plain during a greenhouse phase in Earth history. We combine sedimentology, paleopedology, palynology, and paleontology in order to reconstruct detailed local paleoenvironments of an ancient Arctic coastal plain. The Prince Creek Fm. contains quartz-and chert-rich sandstone and mudstone-filled trunk and distributary channels and floodplains composed of organic-rich siltstone and mudstone, carbonaceous shale, coal, and ash-fall deposits. Compound and cumulative, weakly developed soils formed on levees, point bars, crevasse splays, and along the margins of floodplain lakes, ponds, and swamps. Abundant organic matter, carbonaceous root traces, Fe-oxide depletion coatings, and zoned peds (soil aggregates with an outermost Fe-depleted zone, darker-colored Fe-rich matrix, and lighter-colored Fe-poor center) indicate periodic waterlogging, anoxia, and gleying, consistent with a high water table. In contrast, Fe-oxide mottles, ferruginous and manganiferous segregations, bioturbation, and rare illuvial clay coatings indicate recurring oxidation and periodic drying of some soils. Trampling of sediments by dinosaurs is common. A marine influence on pedogenesis in distal coastal plain settings is indicated by jarosite mottles and halos surrounding rhizoliths and the presence of pyrite and secondary gypsum. Floodplains were dynamic, and soil-forming processes were repeatedly interrupted by alluviation, resulting in weakly developed soils similar to modern aquic subgroups of Entisols and Inceptisols and, in more distal locations, potential acid sulfate soils. Biota, including peridinioid dinocysts, brackish and freshwater algae, fungal hyphae, fern andmoss spores, projectates, age-diagnostic Wodehouseia edmontonicola, hinterland bisaccate pollen, and pollen from lowland trees, shrubs, and herbs record a diverse flora and indicate an Early Maastrichtian age for all sediments in the study area. The assemblage also demonstrates that although all sediments are Early Maastrichtian, strata become progressively younger from south to north.

A paleoenvironmental reconstruction integrating pedogenic processes and biota indicates that polar woodlands with an angiosperm understory and dinosaurs flourished on this ancient Arctic coastal plain that was influenced by seasonally(?) fluctuating water table levels and floods. In contrast to modern polar environments, there is no evidence for periglacial conditions on the Cretaceous Arctic coastal plain, and both higher temperatures and an intensified hydrological cycle existed, although the polar light regime was similar to that of the present. In the absence of evidence of cryogenic processes in paleosols, it would be very difficult to determine a high-latitude setting for paleosol formation without independent evidence for paleolatitude. Consequently, paleosols formed at high latitudes under greenhouse conditions, in the absence of ground ice, are not likely to have unique pedogenic signatures.