Figure 1. General map of Leg 178 with ship track.
Figure 2. Bathymetric chart of the Antarctic Peninsula Pacific margin with Leg 178 sites marked (bathymetry in meters). SM = seamount.
Figure 3. Schematic figure of tectonic and glacial elements of the Antarctic Peninsula margin and sites drilled during Leg 178.
Figure 4. Graph and maps of ice-sheet size and location at mean sea-level temperatures 5, 9, 10, 15, 19, and 20 Kelvin (K) above present. The maps indicate where margin sedimentation might be sensitive to particular stages of ice-sheet growth. Antarctic Peninsula glaciation appears to have developed during the last 5-9 K of cooling (from Huybrechts,1993).
Figure 5. Sequence model of deposition on shelf and slope through a glacial cycle (adapted from Larter and Barker, 1989, 1991b). Unsorted till is deposited on the slope (foresets) during glacial maxima and on the shelf (topsets) during retreat. Pelagic or hemipelagic sediment is deposited on the slope and rise during interglacials. With re-advance, some or all shelf topsets may be eroded.
Figure 6. Schematic drawing of the processes active during glacial half-cycles, leading to the development of hemipelagic sediment drifts on the continental rise (adapted from Rebesco et al., 1997). The unstable component of unsorted upper-slope deposits forms first debris flows, then turbidity currents. The fine fraction is suspended and entrained in ambient bottom currents to be deposited downcurrent. Drifts are built above the level of the dendritic pattern of turbidity current channels because (in the case of the Antarctic Peninsula margin and perhaps elsewhere) subsequent turbidity currents erode the deposited sediment everywhere except upon the drifts and maintain the steeper drift slopes at the limit of stability.
Figure 7. Part of multichannel seismic (MCS) reflection profile I95-137 across Site 1095. S.P. = shotpoint.
Figure 8. Summary of lithostratigraphic, magnetostratigraphic, and biostratigraphic findings in Leg 178 sediment drift sites. The record of magnetic susceptibility and natural gamma-ray attenuation is shown for comparison.
Figure 9. Depth-age profile determined from geomagnetic reversals and diatom and radiolarian datums. Paleomagnetic data were drawn from analysis of split-core (X's) and geologic high sensitivity magnetic tool (GHMT) logging data (diamonds). Separate curves for split-core (thin line) and GHMT magnetic data (heavy broken line) are interpolations that pass through all data points within each data set and match the slopes at those points. Diatom and radiolarian datum intervals are marked with an upright triangle at the base (B = base/first occurrence) and an inverted triangle at the top (T = top/last occurrence). TC = top of common occurrence/last common occurrence. P. sulcata abundance is shown with gray shaded bars. The hole is barren of microfossils below ~520 mbsf. Mean sedimentation rates (underlined) determined for the three intervals show an uphole decrease.
Figure 10. Part of MCS reflection profile I95-130A across Site 1096 (see location in Figure 1096 B-4). Note the bottom-simulating reflector at about 700 ms TWT below the seafloor, interpreted as the opal-A to opal-CT transition. S.P. = shotpoint.
Figure 11. Depth-age relationship for Site 1096 based on geomagnetic reversals (X) and diatom (solid symbols) and radiolarian (open symbols) datums. Paleomagnetic data were drawn from shipboard analysis of cores. Intervals of diatom and radiolarian datums are marked with an upright triangle at the base and an inverted triangle at the top. In labels indicating species identity, B = base/first occurrence and T = top/last occurrence. Sedimentation rates (underlined) for selected intervals are adjacent to the corresponding curve. Vertical solid arrows indicate dominant age diagnostic fossil type (biosiliceous vs. calcareous) for respective intervals of this site. The dashed vertical line below B Fragilariopsis interfrigidaria datum interval indicates range of published ages for this datum.
Figure 12. A. Part of MCS reflection profile IT92-114 across Site 1101 (see location in Figure 1101-B-1B). B. Seismic stratigraphic record at location of proposed site APRIS-05A (proximal site on Drift 4). C. Seismic stratigraphic record at location of proposed site APRIS-06A (distal site on Drift 4). S.P. = shotpoint.
Figure 13. Depth-age profile determined from geomagnetic reversals and diatom and calcareous nannofossil datums. The curve fit to the paleomagnetic data is an interpolation that passes through all data points within the data set and matches the slope at those points. Diatom and calcareous nannofossil datum intervals are marked with solid (diatom) and open (nannofossil) triangles. B = base/first occurrence, T = top/last occurrence.
Figure 14. Location of Site 1097 on single-channel seismic reflection profile PD88-04 (Bart and Anderson, 1995) across the continental shelf seaward of Adelaide Island, Antarctic Peninsula.
Figure 15. Summary of facies recovered at Site 1097, associated biofacies, and environmental interpretation. Representative cores are identified at top.
Figure 16. Continental shelf transect. Location of Sites 1100, 1102, and 1103 on MCS reflection profile I95-152 across the continental shelf seaward of Adelaide Island, Antarctic Peninsula. S.P. = shotpoint.
Figure 17. Simplified lithostratigraphy at Site 1103 showing lithofacies.
Figure 18. Bathymetry and location of site-survey seismic reflection profiles on Palmer Deep. Tracks of the 3.5-kHz sub-bottom profiles obtained by the JOIDES Resolution are indicated by the thickest bold line.
Figure 19. Generator Injector (GI) air-gun seismic profile I97H-228G (A) across Palmer Deep Site 1098, Basin I, and (B) across Palmer Deep Site 1099, Basin III (modified from Camerlenghi et al., in press).
Figure 20. Lithostratigraphic columns for Sites 1098 and 1099.
Figure 21. Summary of biostratigraphic findings and correlation in Leg 178 continental rise sites.
Figure 22. Relative abundances of chlorite, illite, and mixed-layer clays in sediments from the continental shelf (Site 1097) and rise (Sites 1095, 1096, and 1101) analyzed on Leg 178.
Figure 23. Downhole logs of hole diameter, total natural gamma, bulk density, porosity, resistivity, sonic velocity (see text), and magnetic susceptibility from Hole 1103A, with core measurements of natural gamma, bulk density, porosity, sonic velocity, and magnetic susceptibility.
Figure 24. Biostratigraphic summary of shelf sites (Holes 1097A, 1100D, and 1103A), based on shipboard observation, with seismic correlation. Light gray horizons show materials of very rare diatom occurrence. Dark gray horizons show intervals barren of microfossils. Age assignment of S3 at Hole 1097A is based on benthic foraminifers, diatoms, and radiolarian biostratigraphy. The depths of seismic reflectors at Hole 1103A are refined with logging information.
Figure 25. Magnetostratigraphic summary for Leg 178 continental rise sites.