Origin of unusually thick Heinrich layers in ice-proximal regions of the northwest
Abstract Ten piston cores and a 25 m long giant piston core from the ice-proximal region off Hudson Strait contain Heinrich layers 1 and 2, identified by their sedimentary structure and high detrital carbonate content. Both layers are unusually thick on the upper Labrador slope (3.8^2.1 m) and on th...
| Main Authors: | , , , , |
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| Other Authors: | |
| Format: | Text |
| Language: | English |
| Published: |
2003
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| Subjects: | |
| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1072.7853 http://www-paoc.mit.edu/paoc/papers/hl.thickness.pdf |
| Summary: | Abstract Ten piston cores and a 25 m long giant piston core from the ice-proximal region off Hudson Strait contain Heinrich layers 1 and 2, identified by their sedimentary structure and high detrital carbonate content. Both layers are unusually thick on the upper Labrador slope (3.8^2.1 m) and on the lower slope and rise (1.5^1.0 m). Heinrich layers 1 and 2 can be subdivided into three units. Unit A is restricted to the upper slope and overlies hemipelagic sediment with a gradational boundary. It is 6 1 m thick, dark black to dark gray in color, and made up of coarse ice-rafted sand and granules dispersed in hemipelagic mud with a few faint laminations towards the top. The overlying unit B is up to 3.35 m thick and consists of two facies: (i) centimeter-thick, graded, carbonate-rich mud layers containing dispersed coarser grains in the mud, interpreted as nepheloid-flow deposits with coarse ice-rafted debris, and (ii) carbonate-rich, finely laminated mud layers, which alternate with millimeter-thick laminae of ice-rafted debris. Unit C, up to 0.90 m thick, is devoid of sedimentary structures, and consists of hemipelagic sediment with dispersed dropstones that increase in abundance towards the top of the unit. Data suggest the following sequence of processes could have occurred during the deposition of Heinrich layers in ice-proximal sites. As the Laurentide Ice Sheet grew, it extended through the Hudson Strait ice stream outlet to a floating ice margin near the shelf edge and perhaps beyond to the upper slope, and deposited unit A by releasing dropstones from the basal debris-rich layer. Unit B is interpreted to be the deposits of the combined processes of nepheloid-layer flow, low-density turbidity currents, and massive ice-rafting. Maximum carbonate content ( s 50%), the lightest N 18 O values in very sparse planktonic foraminifera, and low magnetic susceptibility are characteristic of unit B. Unit C is inferred to represent the time of waning supply of fines as nepheloid-flow deposition ceased, while the ... |
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