Sedimentary facies and processes of deposition: Ice Island cores, Axel Heiberg Shelf, Canadian Polar Continental Margin

Abstract

The sedimentological features are described of 24 piston and gravity cores recovered at depths from 140 to 283 m beneath the perennial ice cover of the Arctic Ocean, north of Axel Heiberg Island. Sample sites are located between Nansen and Sverdrup channels, along the drift path of the Canadian Ice Island. Eight facies are characterized and interpreted, as follows: (A) Soft, yellow-brown structureless pebbly sandy mud/silty mud interpreted as strongly bioturbated hemipelagic muds with ice-rafted meltout and fallout deposits; (B) burrowed sandy silty/clayey mud interpreted to be the result of slow continuous suspension fallout concommitant with bioturbation; (C) wispy, laminated sandy silty mud due to slow continuous suspension fallout with bioturbation punctuated by sudden deposition from nepheloid flows or fine-grained turbidity currents; (D) laminated sandy silty mud formed by underflow, turbidity current and suspension fallout; (E) firm, dark grey/olive grey-brown pebbly sandy/silty mud comprising ice-rafted debris or debris flow deposits; (F and G) indurated, reddish brown/ochre and black pebbly sandy mud/silty mud comprising exposed bedrock; and (H) firm, grey and brown structureless silty mud interpreted as suspension deposits with rare ice rafting. The indurated facies F and G occur on a topographic high on the inner shelf. This topographic high is interpreted as an offshore bank which may have provided a sedimentary source during deposition. Facies H is restricted to deeper cores within Nansen and Sverdrup channels, representing a possibly older relict deposit. Other facies show broad correlations throughout the study area. Facies A, B and C are more common in the upper parts of cores, Facies D and E in the lower parts of cores. Deposition by gravity flows in a realm of normal hemipelagic sedimentation is a more important process than fallout and wasting of ice shelves and icebergs. Reworking by waves and bottom currents is minimal. The present facies model compares well with those for other high arctic areas, including Baffin Island fjords and the continental rise of Canada Basin in the western Arctic Ocean. No till facies were cored on the Axel Heiberg Shelf, indicating that this part of the shelf was probably not inundated by grounded ice during the last glaciation. The most abundant mineral in the coarse fraction (> 63 μm) of the samples selected is common quartz. The mafic minerals are far less common than quartz and feldspar, reflecting the instability of these grains; however, igneous augite, typically clinopyroxene, occurs in all samples. Rock fragments include fresh and altered basalt and gabbro, metamorphic and granitic rock fragments and a wide variety of sedimentary rock fragments, including mudstone, sandstone, chert and limestone. The variation of shape and composition of rock and mineral fragments within and between facies suggests a mixed source area dominated by a plutonic terrain. The plutonic and metamorphic rock fragments were probably derived from Pearya, whereas the sedimentary rock fragments were eroded from the Franklinian Mobile Belt and Sverdrup Basin. The occurrence of augite suggests a nearby volcanic source, probably Ellesmere Island. The present data indicate that the source terrains did not vary significantly during the time of the facies distribution of the Axel Heiberg Shelf.