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doi:10.2204/iodp.proc.336.202.2014

Results

Geochemical data

Hole U1382B

Hole U1382B is characterized by high Al, Si, and K contents both in the uppermost 12 m and lowermost 5 m of sediment (Fig. F1). At ~56 and 62 meters below seafloor (mbsf), two smaller but still significant peaks of these elements were identified. Both Fe and Mn concentrations are highest in the uppermost 12 m and lowermost 5 m. Foraminiferal sands are most abundant in the uppermost 30 m, with a particularly thick layer between 15 and 25 mbsf. Where XRF scanning was possible, these sandy intervals display very low Mn, Fe, Al, and K concentrations (Fig. F1) and high Ca counts.

Hole U1383D

Unlike in Hole U1382B, the variability of Al, Si, and K in Hole U1383D is much less pronounced, with only slightly increased intensities in the uppermost few meters of the sediment pile. Fe and Mn count rates show a broader range, with increased concentrations near the top of the drilled section. Significant enrichment of these elements toward the sediment/basement interface was not detected in Hole U1383D (Fig. F2). Ca intensities negatively correlate with intensities of all other elements. Despite variable Ca intensities (i.e., calcium carbonate contents), actual layers of foraminiferal sand are rare in Hole U1383D and completely absent below 20 mbsf (Table T1).

Hole U1384A

Downhole element distribution patterns in Hole U1384A resemble those of Hole U1382B and contrast those of Hole U1383D. Al, Si, and K are enriched near the top and bottom. The same trend is observed for Fe and Mn (Fig. F3). Ca intensities are negatively correlated with those of all other elements. Eleven intervals of foraminiferal sand are spread across the entire depth of the hole (Table T1).

Hole 1074A

Downhole element distribution patterns of Hole 1074A resemble those of Holes U1382B and U1384A. Again, Al, Si, K, Fe, and Mn are enriched near the top and bottom of the sediment pile (Fig. F4). The distribution of foraminiferal sand in Hole 1074A differs from that in the other three holes (Table T1). There are numerous (29) and mostly very thin (1–5 cm) layers in the uppermost 56 m of the drilled sequence but no sand at all between 56 mbsf and the bottom of the hole.

Lithostratigraphy

The results of core logging and X-ray scanning were used to construct lithologic charts employing the criteria given in “Methods and materials” (Figs. F1, F2, F3, F4). These charts illustrate the lithologic sequence and highlight the variations in the lithostratigraphy between different sites in the North Pond area. Lithologies of Holes U1382B, U1384A, and 1074A resemble each other, with illite and Mn nodules (and occasionally magnetite) occurring at the top and bottom of each respective core. However, core from Hole U1383D does not show any of these features near the sediment/basement interface. Furthermore, a significant magnetite layer (likely represented by ultramafic basement rocks) was identified in Hole U1382B at ~49–54 mbsf. In general, rock debris is most abundant at Site U1382, intermediate at Sites U1383 and 1074, and absent at Site U1384. The occurrence of foraminiferal sand layers is highly variable with respect to both vertical distribution within individual holes and lateral distribution between the different sites. Sand appears to be scarce in the lowermost sections of all cores, where clay contents seem to be greatest.

The particularly strong enrichments of Fe and Mn in the bottom sections of Holes 1074A and U1384A are noteworthy. Detailed geochemical studies are required to test if these enrichments are related to upwelling of basement fluids in the northwestern part of North Pond.

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