Site 1126 is located on the eastern Eyre Terrace upper slope in 783.8 m of water (Fig. F1). This site was designed to intersect Cenozoic seismic Sequences 2, 3, and 4 and Lobes 1 and 3 of Sequence 6A (Feary and James, 1998, reprinted as Chap. 2) and to intersect as much of the upper part of the Cretaceous section as time permitted (Fig. F2). The target depth at this site was a high-amplitude reflector of probable Cenomanian age, estimated before drilling (on the basis of stacking velocities) to be at 525 meters below seafloor (mbsf). Because this was also the first ODP site in this basin, it provided the opportunity to establish a basic stratigraphy for the Cenozoic sequences that could then be refined at later sites.
The principal objectives at this site were (1) to collect a detailed record of Paleogene-lower Neogene temperate to subtropical midlatitude sedimentation in an upper slope environment and (2) to recover a record of marine flooding of the evolving rift basin in Cenomanian time. Seismic interpretation (Feary and James, 1998, reprinted as Chap. 2) indicated that the lowermost Cenozoic sequence at this site (Sequence 6A) should be broadly contemporaneous with the Eocene?-middle? Miocene carbonate platform exposed on land and underlying the modern mid-inner shelf. Although seismic data show that a significant portion of this time interval (Sequence 6A, Lobe 2) is missing at this location, Site 1126 represents an ideal opportunity to sample the upper (Lobe 3) and lowermost (Lobe 1) parts of the deep-water sequence deposited apparently contemporaneous with this platform. Despite the absence of Lobe 2 at this location, it is likely that these deeper water deposits should contain a more complete sequence than coeval shallow-water sediments, without lowstand hiatuses.
This site also constitutes an upper slope component of the Leg 182 shelf-to-basin transect, designed to address a number of paleoceanographic problems: (1) the relationship between circulation patterns in the deep ocean and on the shelf during times of warm vs. cold oceanic conditions, (2) the precise timing and nature of the opening of the Tasman Gateway, (3) the evolution and effect of the Leeuwin Current, and (4) the relationship between primary productivity and cool-water carbonate development. In addition, Site 1126 presented an opportunity to use in situ heat-flow measurements (using a combination of Adara temperature tool and Davis-Villinger temperature probe [DVTP]) integrated with core thermal conductivity data to characterize the heat flow regime in the eastern Eyre Terrace.
The relatively thin Cenozoic sequence at this location offered an opportunity to recover the uppermost part of the Mesozoic section, shown to be of Cenomanian age in the nearby Jerboa-1 exploration well. Although Jerboa-1 yielded a record of this interval in the form of ditch-cutting fragments, a fully cored section through this interval was sought to clarify facies relationships and the biostratigraphy of this nearshore marine interval.
The principal drilling objectives at Site 1126 were to
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