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Late Maastrichtian and Danian Ostracode Faunas from Northern Alaska: Reconstructions of Environment and Paleogeography

Elisabeth M. Brouwers and Patrick De Deckker
PALAIOS
Vol. 8, No. 2 (Apr., 1993), pp. 140-154
DOI: 10.2307/3515168
Stable URL: http://www.jstor.org/stable/3515168
Page Count: 15
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Late Maastrichtian and Danian Ostracode Faunas from Northern Alaska: Reconstructions of Environment and Paleogeography
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Abstract

A 300-m sequence of well-exposed fossiliferous outcrops in bluffs along the Colville River, northern Alaska, has yielded diverse, well-preserved Maastrichtian and Danian ostracode assemblages. High-latitude faunas of this age are uncommon, so that this locality provides a unique opportunity to reconstruct an ancient arctic environment. The Maastrichtian strata are nonmarine flood-plain deposits and contain diverse terrestrial and aquatic fossils. The paleoenvironment was a broad, flat, water-saturated delta plain with a diverse herbaceous ground cover, emergent and subaquatic vegetation, and a dry ground upland microthermal forest of deciduous coniferous and broad-leaved plants. The nonmarine ostracodes indicate a ground-water system with elevated salinity of marine composition. The Danian strata are predominantly marginal-marine and shallow-marine and include an abundant and diverse invertebrate fauna. The paleoenvironment was a mild- to cold-temperate shallow ocean dominated by reduced salinity, terrestrial influence, and frequent storm activity. Sediments and faunas show a gradual shift upsection from lagoonal and bay facies to inner shelf facies. During the Maastrichtian and early Paleocene, polar terrestrial and marine assemblages consisted predominantly of endemic organisms that were adapted to the cool temperatures, seasonal low light conditions, and geographic isolation characteristic of northern high-latitude environments. Some of the nonmarine arctic ostracode genera are believed to represent their oldest geologic occurrence, suggesting that the genera perhaps evolved in northern Alaska during the Late Cretaceous. These "arctic" genera migrated southward during the Tertiary and constitute some of the more typical Nearctic fossil and recent nonmarine genera of the temperate middle latitudes.

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