--> ABSTRACT: Siliceous Sedimentation on Kerguelen Plateau: Combined Results from Ocean Drilling Program Legs 119 and 120, by Frank R. Rack, Alan Pittenger, Millard Coffin, and Anders Solheim; #91022 (1989)
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Previous HitSiliceousNext Hit Sedimentation on Kerguelen Plateau: Combined Results from Ocean Drilling Program Legs 119 and 120

Frank R. Rack, Alan Pittenger, Millard Coffin, Anders Solheim

Legs 119 and 120 of the Ocean Drilling Program drilled 11 sites on the Kerguelen Plateau to complete a latitudinal transect across this high-latitude bathymetric feature. Measurements of index properties (bulk density, grain density, water content, and porosity) are combined with shipboard lithologic descriptions to provide a qualitative and quantitative overview of the diatom-rich sedimentary units drilled.

The Kerguelen Plateau can be divided into two domains. The northern portion, designated the Kerguelen-Heard Plateau (KHP), generally lies in water depths of less than 1,000 m. The southern portion, designated the Southern Kerguelen Plateau (SKP), lies in water depths generally ranging between 1,500 and 2,000 m.

Sites 736 and 737, located on the KHP near Kerguelen Island, are characterized by thick sequences of diatom ooze. The diatom ooze exhibits high measured water contents (75-80%) and porosities (85%). The low grain density of the amorphous silica in diatom frustules results in relatively low values of bulk density (1.2-1.4) as compared to nannofossil ooze (1.6 g/cm3).

Drilling at Site 747, on the southern KHP, recovered diatom ooze overlying nannofossil ooze and chalk. The increasing downhole percentage of calcareous Previous HitmicrofossilsNext Hit creates steep gradients in measured bulk density (1.19-1.75 g/cm3), water content (91.5-31.4% g/cm3), and porosity (97.1-53.1%). Sites 738, 744, and 748 on the northern part of the SKP all recovered slightly thinner upper sequences of diatomaceous ooze (with calcareous Previous HitmicrofossilsNext Hit) than at Site 747.

Thin units, representing possible surficial "lag" deposits containing diatom ooze at Sites 749 and 750, overlie thick sequences of nannofossil ooze and chalk with chert. Sites 745 and 746 are located off the SKP in water depths greater than 4,000 m. Thick sequences of diatom ooze deposited below the present-day carbonate compensation depth and containing a significant clay component in the deeper facies was recovered at both sites.

Preliminary results at Site 751 reveal a pattern of shifting Previous HitsiliceousTop and calcareous pelagic sedimentation across this geographic location over time. Index properties reflect the changing composition of microfossil assemblages with depth. These data may provide significant paleo-oceanographic information for this area of the Southern Ocean during the Neogene.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.