Stratigraphy and glacial-marine sediments of the Amerasian Basin, central Arctic Ocean
DAVID L. CLARK, RICK R. WHITMAN, KIRK A. MORGAN, SCUDDER D. MACKEY, 1980. "Stratigraphy and glacial-marine sediments of the Amerasian Basin, central Arctic Ocean", Stratigraphy and Glacial-Marine Sediments of the Amerasian Basin, Central Arctic Ocean, David L. Clark, Rick R. Whitman, Kirk A. Morgan, Scudder D. Mackey
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Thirteen correlatable lithostratigraphic units are recognized in cores recovered from the central Arctic Ocean. The stratigraphic units range in age from late Miocene to Holocene and can be correlated over several hundred thousand square kilometres. Cores were taken from ice-island T-3 during its 1963 to 1973 drift in water depths ranging from 1,069 to 3,820 m. The 13 stratigraphic units, designated A to M, include silty and arenaceous lutites and carbonate-rich, pink-white layers. Three arenaceous lutites are important marker beds in the lower part of the section (A to H), and pink-white layers are distinctive units in the upper section (I to M).
Ages for the units can be calculated by the use of paleomagnetic reversal signatures and by extrapolation of sedimentation rates based on these figures. Units I to M have calculated sedimentation rates that average 1.14 mm/1,000 yr, whereas the sedimentation rates of the older units (A to H) average 0.5 mm/1,000 yr. Pebbles, probably ice-rafted, occur throughout the units. Extrapolation of the sedimentation rate from the Gilbert Polarity Interval 5 reversal indicates that the oldest erratic in undisturbed sediment may have been deposited 5.26 m.y. ago. In general, the arenaceous lutites and pink-white layers represent the highest sedimentation rate and are interpreted to have been deposited during times of increased glacial ice-rafting. Silty lutites may also be principally ice-rafted sediment, but they are believed to represent periods of reduced ice-rafting and lower sedimentation rates.
Four types of glacial-marine sediment can be characterized by silt-clay histograms. The four histogram types (type I, nonsorted; type II, bimodal; type III, clay mode; and type IV, silt mode) reflect differences in the environmental factors that influenced glacial-marine sedimentation. The major process that affected deposition of ice-rafted debris in the Arctic Ocean study area may have been mid-depth oceanic circulation. Little evidence was found to support the hypothesis that the reworking of central Arctic Basin glacial-marine sediment by bottom currents had any major effect on silt-clay distributions.
A mode was observed in the fine to coarse clay particles in most central Arctic Basin glacial-marine sediments. A similar mode was observed for East Pacific Ocean pelagic clay samples. A fine mode in both types of sediment suggests that deposition of clay and fine silt of pelagic or glacial origin occurs uniformly in the deep-sea environments that were sampled.
The geographic distribution of central Arctic Basin glacial-marine sediment types suggests that deposition of ice-rafted coarse sediment dominates sedimentation in the Alpha Cordillera region. In abyssal plain environments, deposition of ice-rafted debris also occurs but is partially masked by turbidite deposition.
The four types of glacial-marine sediment occur in units A to M and support the hypothesis that ice-rafting has been an important mechanism in contributing sediment to the Alpha Cordillera since the late Miocene. In addition, the stratigraphic distribution of these sediments supports the theory that arenaceous lutites represent periods of increased ice-rafting, while silty lutites represent periods of decreased ice-rafting. Central Arctic Basin and non-Arctic marginal sea glacial-marine sediments exhibit similar silt-clay histogram types.
Six intervals of increased Pleistocene glacial ice-rafting are defined. Correlation with periods of continental glaciation is possible, but correlation with marine or terrestrial sequence is difficult because the central Arctic Ocean remained frozen while climatic changes more severely affected lower latitudes. Good correlation with glaciations defined by oxygen-isotope stratigraphy is possible for the most recent times of increased ice-rafting.