8. Site 1130¹

Shipboard Scientific Party²

BACKGROUND AND OBJECTIVES

Site 1130 is located on the Great Australian Bight upper slope in 488.0 m of water (Fig. F1). The primary objective at Site 1130 was to intersect and characterize Neogene shelf edge and slope sequences and, particularly, to sample the distal (to contrast with the proximal section at Site 1132) portion of an inferred Paleocene-middle Eocene progradational siliciclastic wedge identified and mapped as seismic Sequence 7 (Feary and James, 1998, reprinted as Chap. 2). This sequence forms an east-west-oriented, elongate sediment body that extends at least 300 km along the Eucla Basin, seaward of a prominent basement high (Fig. F2; see "Seismic Stratigraphy").

Sequence 7 appears to represent the first depositional episode overlying the top Mesozoic erosional event. The uppermost portion of this sequence is probably the seaward equivalent of the middle Eocene Hampton Sandstone found in the subsurface of the onshore Euclato be  Basin. The youngest parts of Sequence 7 were inferred thin, uppermost lower or lowermost middle Eocene mudstones intersected at the base of the Tertiary succession in the Jerboa-1 well (Bein and Taylor, 1981; Stagg et al., 1990), and interpreted by Feary and James (1998, reprinted as Chap. 2) as a thin foredelta apron. This top part of the sequence is an aggradational component reflecting increased accommo-dation space, probably resulting from sediment compaction and sag within the Mesozoic rift basin (Eyre Sub-basin) underlying the Eyre Terrace.

Site 1130 was located to intersect thin portions of Paleogene Sequence 6A and Neogene Sequence 4, overlain by a thick interval of Pleistocene Sequence 2. Regional seismic stratigraphy shows that Sequences 6A and 4 are deep-water carbonate accumulations with lobate and aggradational geometries, respectively (see "Seismic Stratigraphy"). Sequence 2 at Site 1130 offered the opportunity to describe along-slope variations in sedimentation rates and facies, in comparison with the much thicker interval of Sequence 2 intersected at Sites 1127, 1129, and 1131.

The scientific objectives for Site 1130 were to

1. Recover a detailed record of shelf edge siliciclastic deposition at a distal site to evaluate the sedimentary response to Paleogene sea-level fluctuations and to evaluate the complex interaction between sea-level variation, accommodation space, and subsidence;
2. Determine the characteristics of cool-water carbonate facies within the Neogene/Quaternary succession;
3. Determine paleoceanographic parameters within a shelf edge to slope setting from Sequences 2 to 6A to complement other components of the shelf-to-basin transect;
4. Evaluate sea-level control on Neogene/Quaternary facies within an upper slope/shelf edge setting; and
5. Evaluate the diagenetic history and processes within Neogene/Quaternary facies in an upper slope/shelf edge setting.