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Paper No. 285-1
Presentation Time: 9:00 AM-6:30 PM
A LATE CRETACEOUS HIGH-LATITUDE PALEOENVIRONMENTAL AND PALEOECOLOGICAL TRANSECT ACROSS GREENHOUSE ALASKA: A COMPARISON OF THE CHIGNIK, LOWER CANTWELL, AND PRINCE CREEK FORMATIONS, ALASKA, USA
Recent work on the Chignik Formation (Campanian-Maastrichtian) in Aniakchak National Monument, SW Alaska, extends a high-latitude greenhouse transect from the Alaska Peninsula to the North Slope, across ~ 28o of latitude. Along Aniakchak Bay the CF consists primarily of nonmarine alluvial-coastal plain deposits, dominated by meandering fluvial channels, with crevasse splays, small lakes and ponds, and a few thin peat swamps. There is also evidence for tidal influence on the coastal plain, as well as marginal marine and shallow marine deposits. Dark grey to reddish siltstones with root traces, siderite nodules, organic fragments, plant fossils, and coalified logs represent poorly drained paleosols. In places, standing tree trunks are rooted in ancient soils. The vertebrate fossil record consists of tracks and traces, of which 93% of documented sites are attributed to the ichnogenus Hadrosauropodus, a footprint attributed to hadrosaurs. Hadrosaurs ranged in size from full-grown adults to juveniles. There are also rare occurrences of tracks attributed to ankylosaurs and osteichthyans. The Lower Cantwell Formation in Denali National Park, consists primarily of axial braided rivers, alluvial fans, floodplains, ponds and small lakes. Paleosols exist but they are poorly developed. Abundant plant megafossils are present. A rich invertebrate and vertebrate ichnofauna is known from the LCF that includes adult and juvenile forms of hadrosaurs and ceratopsians. The Prince Creek Formation, North Slope, consists primarily of small distributary channels, crevasse splays, small ponds and abundant paleosols. Large meandering channels fed this delta plain distributary network. Paleosols are weakly to moderately well-developed and suggest generally poorly drained conditions punctuated by dry periods, probably related to the seasonal light regime. Plant macrofossils are not abundant but paleosols contain a diverse palynoflora. The PCF has produced thousands of skeletal dinosaur remains. These formations represent different sedimentary environments and landscapes, containing different dinosaur and plant communities. Future details of paleoecology and paleoclimate in the Chignik Formation will provide a fuller picture of regional changes in high latitude greenhouse Alaska during the Late Cretaceous.