USGS Open-File Report 94-588
Pliocene of Northwind Ridge, Western Arctic Ocean
- Richard Z. Poore
- U.S.Geological Survey, Reston, VA
- Larry Phillips
- U.S. Geological Survey, Menlo Park, CA
- Dave Schneider
- Woods Hole Oceanographic Institution
- Scott E. Ishman
- U.S. Geological Survey, Reston, VA
The Northwind Ridge is a 500 kilometer long, high-standing fragment of
continental crust in the Canada Basin of the western Arctic Ocean (Grantz,
et al., 1993). The Northwind Ridge is mantled by glacial marine sediments
that preserve a record of changing climatic and paleoceanographic
conditions during the late Cenozoic (Phillips and others, 1992; Poore and
others, 1993, 1994). The thickness of the sediment cap can be up to a few
tens of meters, especially in flat lying areas near the crest. The upper
part of the sediment cap shows distinct banding caused by the alternation
of dark brown muddy beds with gray, olive gray, and tan silty or sandy
muds and, less commonly, pinkish white to white clast-rich coarse layers.
The lower part of the sediment cap consists of more uniform dark brown to
tan muds and silty muds. The section is highly variable and is
complicated by unconformities and winnowed intervals.
We are developing an informal stratigraphic framework for correlating and
dating the Northwind Ridge late Cenozoic sedimentary sequence that relies
on multiple criteria including sediment texture and composition, abundance
and character of microfossils, density core logs, magnetic susceptibility
and magnetostratigraphy. No single core that we have examined contains a
complete section of the sediment cap, but a relatively complete composite
section ranging from the late (?) Miocene to Holocene is evident by
combining the records of several cores.
Calcareous microfossils are only present in a few isolated intervals of
the Pliocene sequence. Initial data suggests that the absence of
calcareous microfossils is due to a shallow CCD.
Sand-sized quartz grains and rock fragments along with coarser drop stones
occur throughout the Northwind Ridge section. We interpret these grains
as evidence for ice-rafting and thus conclude that sea-ice and glacial ice
have been present in the western Arctic since late (?) Miocene. Below the
Gauss/Matuyama boundary grains >2mm and coarser drop stones are rare and
occur sporadically, but they are usually common to abundant in sediments
above the Gauss/Matuyama Chron boundary (fig. 1). This change reflects a
significant increase in the amount of glacial ice reaching the Arctic
beginning at the Gauss/Matuyama boundary. Prior to the Matuyama, glacial
ice was probably minor and intermittently present. Our interpretation of
the Northwind Ridge magnetostratigraphy indicates that the change in ice-
rafting intensity and style in the Northwind Ridge sequence coincides with
increased ice-rafting observed in the North Atlantic and corresponds to
the development of the first large Northern Hemisphere continental ice-
sheets.
References Cited:
- Grantz, A., Hart, P.E., Phillips, R.L., McCormick, M., Perkin, R.G., Jackson, R., Gagnon, A., Li, S., Byers, C., and Schwartz, K.R., 1993, Preliminary results of scientific investigations, USGS cruise PI-93-AR Northwind Ridge and Canada Basin, Arctic Ocean: U.S. Geological Survey Open-File Report 93-389, 34 p.
- Phillips, R.L., Grantz, A., Mullen, M.W., Rieck, H.J., McLaughlin, M.W., and Selkirk, T.L., 1992, Summary of lithostratigraphy and stratigraphic correlations in piston cores from Northwind Ridge, Arctic Ocean, from USCGC Polar Star, 1988: U.S. Geological Survey Open-File Report 92-426, 110 p.
- Poore, R.Z., Phillips, R.L., and Rieck, H.J., 1993, Paleoclimate record for Northwind Ridge, Western Arctic Ocean: Paleoceanography, v. 8, no. 2, p. 149-159.
- Poore, R.Z., Ishman, S.E., Phillips, R.L., and McNeil, D.H., 1994, Quaternary stratigraphy and paleoceanography of the Canada Basin, Western Arctic Ocean: U.S. Geological Survey Bulletin 2080, 32 p.
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