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Fiorillo A.R.,Perot Museum of Nature and Science | McCarthy P.J.,University of Alaska Fairbanks | Flaig P.P.,University of Texas at Austin
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2015

The Prince Creek Formation of northern Alaska is the most abundant source of polar dinosaur remains in the world, and now, corroborating data from this well-studied rock unit allow for making inferences about the paleoecological preferences for these extinct polar animals. The rock unit records high-latitude, alluvial sedimentation and soil formation on a low-gradient, muddy coastal plain. Compound and cumulative andic Entisols and Inceptisols 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 indicate periodic waterlogging, anoxia, and gleying, consistent with a high water table. In contrast, Fe-oxide mottles, ferruginous and manganiferous segregations, bioturbation, and less common illuvial clay coatings indicate recurring oxidation and periodic drying out of some soils. An integrated reconstruction of pedogenic processes and biota suggests that this ancient Arctic coastal plain was influenced by seasonally fluctuating water table levels and floods, and in distal areas, marine waters. Four of the five bonebeds in this study are from more distal areas, represented by lower delta plain facies, while the fifth bonebed is from a more proximal part of the basin, represented by a somewhat better drained coastal plain facies.Bonebeds in the distal areas are dominated by Edmontosaurus sp. while the more proximal bonebed is dominated by the remains of the ceratopsian Pachyrhinosaurus perotorum. The distribution of these bonebeds, sedimentological facies, paleosols, and biota suggests that Pachyrhinosaurus may have preferred more upland environments while Edmontosaurus preferred lowland, deltaic environments. This distribution may be the result of physiological adaptation to the pronounced seasonality provided by polar terrestrial ecosystems. In contrast to a preferred habitat distribution of these large herbivores, the large predatory dinosaur Nanuqsaurus hoglundi seems to have had a more ubiquitous distribution across the landscape. © 2015 Elsevier B.V.

Fiorillo A.R.,Perot Museum of Nature and Science | McCarthy P.J.,University of Alaska Fairbanks | Hasiotis S.T.,University of Kansas
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2015

Latest Cretaceous strata of the lower Cantwell Formation, Denali National Park, central Alaska Range, contain an abundance of megafloral remains and invertebrate and vertebrate trace fossils. Though dominated by herbivorous dinosaur footprints, the abundance and diversity of fossil bird tracks are unique. We present newly discovered crayfish burrows from several areas along a 50. km transect with Denali National Park. Most crayfish burrows from the lower Cantwell Formation are preserved only in cross-section and range from approximately 5-10. cm in diameter. Where preserved in full relief and terminations present, burrow depth is generally. <. 50. cm. Burrow morphology is similar to burrow morphology of modern freshwater crayfish (Cambaridae).The Cantwell Formation fills the Cantwell Basin, a 135. km-long and up to 35. km-wide, east-west trending basin, bracketed by the Hines Creek Fault to the north and the McKinley Fault to the south. Basin fill comprises up to 4000. m of continental deposits, interpreted as braided rivers, alluvial fans, floodplains, swamps, and ponds.Crayfish burrows provide evidence of water table level, soil moisture fluctuations, as well as insight into mean annual temperatures at the time of deposition of the lower Cantwell Formation, a Late Cretaceous high-latitude paleoecosystem. Despite a relatively high latitudinal setting (~. 71°N paleolatitude), the Late Cretaceous (i.e., Campanian-Maastrichtian) mean annual temperature, based on the distribution of similar present-day crayfish burrows, was more like that of southernmost Ontario, Canada, where the northernmost burrowing crayfish are found today. The burrow depth suggests (1) no permafrost was present, and (2) the phreatic zone was ~. 30-50. cm below the paleo-ground surface. Based on the presence of these crayfish burrows, the paleoclimate is interpreted as humid continental (Köppen scheme), with average summer high temperatures between 25. °C and 28. °C and average winter low temperatures between -6. °C and 0. °C. These estimates compare somewhat favorably with previous CLAMP estimates of a warm monthly mean temperature of 17.08 +/- 1.6. °C and a cold monthly mean temperature of -2.31 +/- 1.9. °C. © 2015 Elsevier B.V.

Salazar Jaramillo S.,University of Alaska Fairbanks | McCarthy P.J.,University of Alaska Fairbanks | Trainor T.P.,University of Fairbanks | Fowell S.J.,University of Alaska Fairbanks | Fiorillo A.R.,Perot Museum of Nature and Science
Journal of Sedimentary Research | Year: 2015

Paleosols formed from weathering of alluvial mudstones in the Late Cretaceous (Maastrichtian) Prince Creek Formation, North Slope Alaska, are dominated by detrital smectite, discrete illite, kaolinite, chlorite, quartz, and pedogenic illite-smectite (I/S) mixed-layer clays. In the fine clay fraction (< 0.2 μm) illite-smectite mixed-layer clay is the main clay mineral and is interpreted as pedogenic in origin, whereby the I/S is a product of illitization of inherited smectite during weathering and pedogenesis. We consider the detrital clay minerals to be derived from pre-existing sediments eroded from the Brooks Range, mixed with reworked volcanic ash-fall-derived bentonites. In the Prince Creek Formation, smectitic parent materials were deposited by epiclastic volcanic ash-rich alluvium that accumulated on imperfectly drained floodplains. Diagenetic transformation of smectite to illite is unlikely in the Prince Creek Formation, in as much as maximum burial temperatures never exceeded ∼ 48°C. The predominance of bentonite-derived smectite (> 80%), low bulk density, phosphorus accumulation, Fe and Al mass-balance trends, and the presence of Fe-Al-humus complexes in one paleosol profile is interpreted as evidence of andic soil properties, and these paleosols are interpreted, therefore, as Andept-like alluvial soils. These results demonstrate that clay mineralogical studies, in conjunction with geochemical data of paleosols, can be used to identify paleoandic soil properties which have not been widely recognized in the ancient rock record. Alternating wetting and drying conditions, required to form pedogenic I/S in these alluvial paleosols, resulted from a highly seasonal moisture regime in the Late Cretaceous Arctic. Copyright © 2015, SEPM (Society for Sedimentary Geology).

Fiorillo A.R.,Perot Museum of Nature and Science | Hasiotis S.T.,University of Kansas | Kobayashi Y.,Hokkaido University
Geology | Year: 2014

The discovery of a new tracksite of mostly hadrosaurid dinosaur footprints, made by a herd living in an ancient high-latitude continental ecosystem, provides insight into the herd structure and behavior of northern polar dinosaurs and perspective on populations of large-bodied herbivores in an Arctic greenhouse world. This tracksite occurs in the Upper Cretaceous Cantwell Formation in the Alaska Range (Denali National Park, Alaska, United States), and it is the largest tracksite known from this far north. Preservation of the tracksite is exceptional: most tracks, regardless of size, contain skin impressions and they co-occur with well-preserved plant fossils and invertebrate trace fossils of terrestrial and aquatic insects. Statistical analyses of the tracks show that individuals of four different age classes of hadrosaurids lived together in a large social group. Our research results independently corroborate the growth curve for hadrosaurids proposed by paleohistologists that suggests that these dinosaurs experienced a period of rapid growth early in their life history. © 2014 Geological Society of America.

Flaig P.P.,University of Texas at Austin | Fiorillo A.R.,Perot Museum of Nature and Science | McCarthy P.J.,University of Alaska Fairbanks
Palaios | Year: 2014

The Cretaceous coastal plain of Arctic Alaska contains the richest concentration of high-latitude dinosaurs on Earth. Three bonebeds (Liscomb, Byers, Sling Point) are found in paleopolar (82°-85° N) coastal-plain deposits of the Prince Creek Formation on Alaska's North Slope. 40Ar/39Ar analysis of a tuff below the oldest bonebed (Sling Point) returned an age of 69.2 ± 0.5 Ma indicating a maximum early Maastrichtian age for these bonebeds. Bonebeds are overwhelmingly dominated by partially articulated to associated late-stage juvenile Edmontosaurus sp. Bone is rarely found in channels; instead highdensity accumulations are preserved on floodplains in laterally extensive, muddy alluvium. Bone size grading is vertically nonuniform and most bones are in hydraulic disequilibrium with the surrounding clay-rich matrix. Bones exhibit little evidence of rounding, weathering, predation, or trampling, suggesting short-distance transport and rapid burial. Because these bonebeds are unlike typical debris-flow or streamflow deposits, the mechanism for bonebed emplacement remained poorly understood. All bonebeds contain a current-rippled siltstone containing the largest bone overlain by a distinctive mudstone encasing smaller bones, bone fragments, and subparallel-aligned plant fragments that appear ''frozen in flow'' within the muddy matrix. We recognize that these bonebeds exhibit a recurring facies pairing and bipartite division of flow consistent with deposition by finegrained viscous hyperconcentrated flows. We suggest that exceptional discharge events entrained mud and ash stored on point bars and floodplains, increasing suspended-sediment concentrations in rivers and generating erosive hyperconcentrated flows that transported the remains of scores of juvenile dinosaurs onto floodplains adjacent to distributary channels. © 2014, SEPM (Society for Sedimentary Geology).

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