Abstract 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.

Abstract The Prince Creek Formation is an Upper Cretaceous, dinosaur-bearing, high-latitude alluvial succession deposited on an ancient coastal-plain that crops out in bluffs along the Colville, Kogosukruk, and Kikiakrorak Rivers of northern Alaska. Studies that document the complex stratigraphy and architecture of high-latitude alluvial systems deposited under greenhouse conditions are extremely rare. It is exceptionally uncommon to find extensive, accessible outcrops that also contain numerous Arctic dinosaur fossils; hence the Prince Creek Formation is of great significance not only to sedimentologists but also to paleontologists involved in reconstructing high-latitude dinosaur habitats. Maastrichtian strata of the Prince Creek Formation record deposition on a tidally influenced high-latitude coastal-plain in (i) first-order meandering trunk channels, (ii) second-order meandering distributary channels, (iii) third-order fixed (anastomosed?) distributary channels, and (iv) on floodplains. Conglomerate and medium- to coarse-grained multistory sandbodies are found exclusively in regionally restricted 13–17-m-thick fining-upward successions (FUSs) that display inclined heterolithic stratification (IHS) capped by finer-grained, organic-rich facies. These relatively thick FUSs are interpreted as first-order meandering trunk channels. Thinner (2–6-m thick), single-story, heterolithic sheet sandbodies composed predominantly of IHS and including abundant mud-filled channel plugs are the most frequently encountered channel form. Trough cross-lamination at the base of the IHS records paleoflow at high angles relative to the dip of the inclined beds, indicating that lateral accretion of point-bars was the principal depositional mechanism. These single-story sandbodies are interpreted as second-order meandering distributary channels. Fine-grained 1.5–3.0-m-thick, ripple cross-laminated ribbon sandbodies deposited mainly by vertical accretion above an arcuate erosion surface and containing only minor IHS are interpreted as third-order fixed (anastomosed?) distributary channels. Thinner (0.2–1.0-m-thick) current-rippled sheet sands and silts are interpreted as small-scale crevasse splays and levees. Organic-rich siltstone and mudstone, carbonaceous shale, coal, bentonite, and tuff are interpreted as deposits of lakes, ponds, swamps, marshes, mires, paleosols, and ashfall on floodplains. Heterolithic sheet sandstones deposited by small, sinuous meandering distributary channels typically appear lenticular along strike, commonly incise into pre-existing distributary channels, and interfinger with and incise into organic-rich floodplain facies. Fixed, ribbon-form (anastomosed?) distributaries incise either into meandering distributaries or into floodplain facies, with numerous ribbons typically preserved in tiers at the same stratigraphic level. Spatial relationships between channel types, and between channels and floodplain facies, indicate that the bulk of deposition took place on crevasse-splay complexes adjacent to trunk channels. Crevasse-splay complexes were constructed by the lateral migration of sinuous meandering distributaries and the vertical filling of fixed (anastomosed?) distributaries, with splay complexes separated from each other by organic floodplain facies. Flow in meandering distributaries and fixed (anastomosed?) distributaries may have been contemporaneous. Alternatively, fixed (anastomosed?) distributaries may record the initial or waning stages of flow during splay-complex formation or abandonment. IHS composed of rhythmically repeating, coarse-to-fine couplets of current-rippled sandstone and siltstone or mudstone is found in all three types of channels. The rhythmic and repetitive nature of these couplets together with relatively thick, muddy fine-grained members in couplets suggest that flow in channels was likely influenced by tidal effects. Drab colors in fine-grained sediments, abundant carbonaceous plant material, and common siderite nodules and jarosite suggest widespread reducing conditions on poorly drained floodplains influenced, in more distal areas, by marine waters. However, carbonaceous root traces found ubiquitously in all distributary channels and most floodplain facies along with common Fe-oxide mottles indicate that the alluvial system likely experienced flashy, seasonal, or ephemeral flow, and a fluctuating water table. The flashy nature of the alluvial system may have been driven by recurring episodes of vigorous seasonal snowmelt in the Brooks Range orogenic belt as a consequence of the high paleolatitude of northern Alaska in the Late Cretaceous.

Fossils within accreted terranes are typically used to describe the age or origin of the exotic geologic blocks. However, accretion may also provide new pathways for faunal exchange between previously disconnected landmasses. One such landmass, the result of accretion, is Beringia, that entity encompassing northeastern Asia and northwestern North America and the surmised land connection between the two regions. The present concept of Beringia as a Quaternary subcontinent includes a climatic component in the form of glacial advances and retreats driving changes in sea level. These changes may have facilitated exchanges of marine biota between the Pacific Ocean and Arctic Basin, or exchanges of terrestrial faunas and floras between Asia and North America. The Beringian ecosystem includes specializations of the flora and fauna, especially in the vertebrate fauna. A review of tectonic reconstructions and the striking taxon-free parallel patterns in data on the Cretaceous and Quaternary fauna and flora suggest that a generalized concept of Beringia should be formally extended back in time to the Cretaceous. A significant shift in emphasis of defining variables occurs with this extension. Climate, in the form of meteorological phenomena, and geologic history are important variables in the previously recognized definition of Beringia. The extension of Beringia into the Cretaceous implies that Beringia is rooted in its accretionary rather than its climatic history; in other words, the geographic pattern as the result of tectonics is the defining parameter for Beringia.