In addition to performing a multichannel seismic survey campaign, the site survey cruise AGSO 0209, FR03/99 (April/May 1999) for Ocean Drilling Program Leg 194 collected a series of gravity cores, with a maximum length of 4 m, at the future sites of the proposed Marion Plateau drill sites. Two years later, during Leg 194, scientists cored several hundred-meter-thick successions of Neogene sediments at these locations. The almost undisturbed water/sediment interface in the short cores of the site survey cruise offer the opportunity to analyze the modern sedimentation at a high-resolution scale and comparison with the Leg 194 results from the deeper subsurface.
Sediment geometries seen on the seismic data revealed that in the modern environment, the bathymetric depression between the two Marion Plateau carbonate platforms is infilled, the topography is flattened, and strong currents are sweeping the plateau surface (Isern and Anselmetti, 2001). Consequently, it is not obvious whether sedimentation is still ongoing or whether the modern depositional pattern differs from the Neogene situation, where a morphologic depression was present.
Coring sites are located on a seismic line imaging the Southern Marion Platform (SMP) and its adjacent slope/plateau areas (Table T1; Fig. F1). Deeper-water depositional environments northwest and southeast of the SMP are composed of hemipelagic periplatform sediments in modern water depths from 320 to 343 m. Seafloor photographs (Isern, Anselmetti, Blum, et al., 2002) show no (sites CS-03 and 1197/CS-08) to moderate (sites CS-09 and 1198/CS-05) sediment ripples, reflecting differing degrees of current activity.
Site survey gravity cores were used to characterize the composition of seafloor and subseafloor sediments, a requirement for the operational planning of Leg 194. The sediments collected were also used to characterize the modern depositional regime, based on carbonate and organic carbon data, stable oxygen and carbon isotopic data from bulk sediment, and biostratigraphic information using calcareous nannofossils. These data are presented in this report.