Site 1193 (proposed Site CS-01A) is located on the Marion Plateau, in 348 m of water ~80 km from the south central Great Barrier Reef margin (Fig. F1). The site is positioned at the intersection of regional seismic line MAR13 (SP 4126) (Fig. F2) and local grid line MAR34 (SP 2241). The total sediment thickness at Site 1193 is 540 m. Holes 1193A, 1193B, and 1193C penetrated to total depths of 515, 138, and 548.5 meters below seafloor (mbsf), respectively. Acoustic basement was recovered in Hole 1193C. Site 1193 was the first Ocean Drilling Program (ODP) site at which the advanced diamond core barrel (ADCB) system was used to drill a sedimentary section. This experiment was planned because recovery in platform carbonates generally is extremely low.
Site 1193 was positioned to recover the sediment sequences making up the middle Miocene northern carbonate platform (Fig. F2) (MP2 of Pigram, 1992). This platform is an important element for the reconstruction of Miocene sea level history because its top marks the last platform growth phase before the major middle to late Miocene sea level fall. Seismic data indicates that the top of the northern platform is an irregular, karstic surface buried under a relatively thin cover of hemipelagic drift deposits (Fig. F2). Seismic geometry further indicates that this platform was established on previously deposited prograding slope sediments, as seen by the inclined reflections underneath the platform (Fig. F2).
The northern edge of this
platform was drilled during Leg 133 (Davies, McKenzie, Palmer-Julson, et al.,
1991). Coring at Sites 816 and 826 showed that the top of the northern platform
consisted of a tropical reefal assemblage deposited in water depths 
20
m. This depth defines the approximate point from which the sea level began to
fall near the middle/late Miocene boundary (Pigram et al., 1992). Results from
Sites 816 and 826 indicated that the top of the northern carbonate platform has
been subjected to subaerial exposure (Davies, McKenzie, Palmer-Julson, et al.,
1991).
Site 1193 provides a record of the total thickness of the eastern edge of this platform, as well as the timing of its growth phases and its exposure. By investigating the hemipelagic sediments overlying the platform, the timing of its burial can be determined. In addition, postcruise analysis on Site 1193 sediments will yield a record of fluid flow and diagenetic processes in this partially dolomitized carbonate platform. The nature of the deeper-water sediments underlying the platform, together with the facies of the basal sediments directly overlying the basement, provide information regarding the timing and processes linked to the initial basement transgression. Finally, Site 1193 provides a lithologic record of the nature of the acoustic basement.
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