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Drifts and ponds of reworked pelagic sediment in part of the southwest Pacific
Lonsdale, P. (1981). Drifts and ponds of reworked pelagic sediment in part of the southwest Pacific. Mar. Geol. 43(3-4): 153-193.
In: Marine Geology. Elsevier: Amsterdam. ISSN 0025-3227; e-ISSN 1872-6151, more
Peer reviewed article  

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  • Lonsdale, P.

    The sediments preserve a record of fluctuations in the geological effect, and by inference the velocity, of the Pacific's western boundary current. An area of 750 km2 sediment drift was studied in detail with 18 cores and observations from a near-bottom instrument. It has rapid vertical and lateral facies changes, from nodule-covered zeolitic clay to radiolarian clay and ooze, related to temporal and spatial changes in rate of deposition of current-transported particles. The source of most of the radiolaria is erosion of older outcrops upstream or current trimming of the drift margins, so the siliceous ooze may be considered a variety of muddy contourite. Small ferromanganese concretions on the surface of a slowly accumulating part of the drift are arranged in long narrow stripes resembling abyssal furrows. Similar patterns, believed to be caused by erosional bedforms, were mapped by side-scan sonars on the corrugated surfaces of ponds of calcareous turbidites. Other pelagic carbonate beds within the drifts were rapidly deposited from thermohaline currents. It may be difficult to distinguish some calcareous contourites from turbidites after textures have been altered by early diagenesis, but identifications based on field relations and topographic situation can be supported by detailed lithologic study. The times of most rapid drift deposition from the bottom current were Late Oligocene-Early Miocene, probably caused by initiation of this western boundary flow from Antarctica, and Late Miocene-Early Pliocene, probably caused by intensified bottom circulation following glacial expansion.

Datasets (2)
  • Global contourite distribution database, version 2, more
  • Global contourite distribution database, version 3, more

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