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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 63 (1979)

Issue: 3. (March)

First Page: 411

Last Page: 411

Title: Glacial-Marine Trace- and Body-Fossil Associations, Upper Yakataga Formation (Pliocene-Pleistocene), Gulf of Alaska: ABSTRACT

Author(s): John M. Armentrout

Article Type: Meeting abstract


Glacial-marine deposits of the Yakataga Formation are characterized by six associations of trace and body fossils. These associations can be directly compared to modern associations within the tidewater-fiord and marine-shelf environments in the Gulf of Alaska, and allow definition of specific paleoecologic conditions.

Inner-shelf sandstones are extensively bioturbated by a community characterized by the infaunal pelecypods Siliqua and Spisula and the epifaunal gastropod Neptunea. Distinct trace fossils are absent.

Open-shelf siltstones are also extensively bioturbated. Epifaunal body fossils of the gastropod Colus and small ophiuroids are abundant. The infaunal pelecypods Mya and Panomya are locally common. Trace fossils include rare small vertical burrows and large pelecypod burrows parallel with and oblique to bedding planes.

Major channel systems within the upper Yakataga Formation are interpreted as fiord deposits. The fiord deposits have three rock-fossil associations. Rhythmically bedded siltstones and sandy siltstones have an infaunal community of the pelecypods Acila and Macoma. Distinct trace fossils are absent. "Massive" siltstones are extensively bioturbated, have locally abundant large burrow networks, and typically have locally abundant body fossils of the epifaunal gastropods Beringius, Colus, and Musashia, as well as small ophiuroids. Within the siltstone sequences of fiord deposits are thin, graded sandstones. These thin sandstones have an associated body-fossil community of shallow-burrowing Nuculana and Clinocardium and trace fossils of small vertical escape burrows, bed-top pelecypod resti g impressions, and pelecypod foot-push trails.

A sixth faunal association consists of epifaunal organisms such as serpulid worms and barnacles that are attached to the upper surface of glacially derived dropstones.

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