Changes in coarse fraction, calcium carbonate, and total organic carbon (TOC)
accumulation rates and wt% define four different Neogene climatic and oceanographic
regimes for the deep-water Fram Strait area (Site 909). These changes are not as well developed
in intermediate water depth at Site 908, possibly indicative of differences in current velocities at
the two sites. Stage I, upper lower to middle Miocene (Site 909, 838-1062 meters below
seafloor[mbsf]; 17.5-10.85 m.y.), sediments consist of a fining-upwards sequence of mass-wasted
sediments, interbedded with laminated and bioturbated sediments. Tectonic influences are the
dominant control on these sediments, which were deposited before the initiation of sustained
bottom-water flow through Fram Strait.
Stage II, from middle to upper Miocene (Site 909, 838-368 mbsf; 10.95-5.7 m.y.; Site 908, 185-167 mbsf; 6.2-5.7 m.y.), shows the greatest variation in bulk and coarse fraction accumulation rates. It consists of two step-wise increases in bulk accumulation rate, followed by a rapid decrease. In each sequence after the increase begins, the number of layers with high nonbiogenic carbonate increases, and an increase in the amount and variability of the coarse fraction follows. When the accumulation rate decreases, the coarse component decreases first, followed by a decrease in nonbiogenic carbonate and then the total accumulation rate decrease follows. The changes are most likely a result of the initiation and/or major increase of glaciation and the build-up of ice sheets, accompanied by changes in bottom-water strength. The first dropstones were recovered during Stage III, upper Miocene to middle Pliocene (Site 909, 368-200 mbsf; Site 908, 167-104 mbsf; 5-7 to 2.8 m.y.), during which the coarse fraction accumulation rates are low (<1000 gcm-2m.y.-1). In fact there is surprisingly little variation in coarse fraction accumulation. However, higher accumulation rates and a slight increase in coarse components is observed at Site 908 4.2-2.8 Ma. Stage IV, middle Pliocene to the present (<2.8 m.y.), from 200 to 0 mbsf at Site 909 and from 105 to 0 mbsf at Site 908, contains high-amplitude variations in coarse fraction and %TOC attributable to glacial-interglacial fluctuations. With the exception of very low rates between 1.1 and 2.0 m.y. at Site 908, coarse fraction accumulation rates are higher at Site 908 than at Site 909, and they may indicate changes in bottom-water strength and/or different source areas.
Date of initial receipt: 6 July 1995
Date of acceptance: 18 December 1995
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