Dredged Rock Samples from the Alpha Ridge, Arctic Ocean: Implications for the Tectonic History and Origin of the Amerasian Basin


The Amerasian Basin of the Arctic Ocean conceals one of the few unresolved plate tectonic puzzles on Earth, with important implications for the geologic history of the vast adjoining shelfal regions. Until we are able to scientifically drill the most controversial parts of the Amerasian Basin seafloor, many questions about its age and origin will remain unanswered. To address the plate tectonic origin of the Amerasian Basin, we dredged steep escarpments along the Alpha Ridge, a bathymetric ridge that extends across the Amerasian Basin. The Alpha Ridge is dissected by structures that have been characterized by seismic reflection and which appear to be normal fault-bound linear ridges and basins. The Alpha Ridge has been described as a hot spot track, an oceanic plateau, and a possible spreading center. Dredged samples taken in 1985 from the central Alpha Ridge were determined to be highly altered fragmental basalt and yielded a Late Cretaceous 40Ar/39Ar whole rock age which agreed with the conventional models for a purely volcanic/oceanic origin of the Alpha Ridge (Forsythe and others, 1986; Lawver et al., 2002). Dredged rock samples were taken by the icebreaker USCGC Healy (HLY0805, Mayer and Armstrong, 2008) and included samples from a steep slope of a subsidiary ridge in the south central Alpha/Mendeleev Ridge complex. The fresh broken surfaces of large blocks of rock and the lithologic similarity of the rocks recovered suggest an outcrop was sampled. The recovered rocks included interbedded red sandstones and ochre mudstones with well-defined bedding and sedimentary structures. Preliminary shipboard analysis suggests they may be tuffaceous and/or derived from volcanic sources, and may possibly be continental in origin. Further analysis and descriptions will be carried out in the coming months to determine their age and depositional environment. The results of this analysis and their possible implications for the origin of the Alpha Ridge and tectonic history of the Amerasian Basin will be presented.


Center for Coastal and Ocean Mapping

Publication Date


Journal or Conference Title

Fall Meeting, American Geophysical Union (AGU)


89, Issue 53

Conference Date

Dec 15 - Dec 19, 2008

Publisher Place

San Francisco, CA, USA


American Geophysical Union Publications

Document Type

Conference Proceeding