Site U1463

Abstract

Background and objectives 1 Operations 6 Lithostratigraphy 13 Biostratigraphy and micropaleontology 23 Geochemistry 26 Paleomagnetism 30 Physical properties 35 Downhole measurements 39 Stratigraphic correlation 50 References IODP Proceedings 2 V o l u m e 3 5 6 recovered and the thrusters and hydrophones were pulled back into the ship's hull before beginning the transit to Site U1464. The total time spent on Site U1463 was 147.0 h (6.13 days). Overall, the APC system penetrated 840.3 m and recovered 835.29 m (99.4%) and 189.1 m was cored with the HLAPC system with 189.69 m of material recovered (100.3%). The XCB system cored 265.0 m and recovered 126.56 m (47.8%). The overall recovery for Site U1463 was 89.0%. Hole U1463A After offsetting the vessel from the beacon, preparations for coring in Hole U1463A (18°57.9181′S, 117°37.4217′E) commenced. The APC/XCB system was assembled. Given the previous difficulty with the mudline core at IODP Sites U1459 and U1462 (broken and bent core barrels, respectively), we decided to begin coring operations with the XCB coring system. An XCB core barrel was dressed with a core liner and dropped in preparation for beginning Hole U1463A. We tagged the seafloor and calculated the water depth to be 145.8 meters below sea level (mbsl). Hole U1463A was started at 1925 h on 12 September 2015. The first XCB core barrel returned empty (Core 356-U1463A-1X) and a second barrel was dropped. Core 2X recovered 8.59 m of soft mud. We decided to abandon Hole U1463A in order to begin a new hole (U1463B) with the APC system. Hole U1463A advanced 19.4 m and recovered 8.59 m of core (44.3% recovery). Hole U1463A ended at 2030 h. The total time spent on Hole U1463A was 9.75 h. Hole U1463B Hole U1463B (18°57.9190′S, 117°37.4340′E) began at 2100 h on 12 September 2015 with recovery of a mudline core (7.88 m). The water depth was calculated to be 145.4 mbsl. We recovered Cores 356-U1463B-1H through 30H to 271.2 m DSF. The HLAPC system was then deployed and we recovered Cores 31F through 33F to 284.4 m DSF, at which depth piston coring refusal was reached. The XCB coring system was deployed and coring continued from Core

Site U1464

“…The overlap between RCB and APC coring continues beyond 310 m CSF-A to the bottom of Hole U1464B (317 m CSF-A) and suggests an offset of 400-650 m/s between the two coring methods. A similar discrepancy was also noted between APC and XCB coring at Site U1463, where XCB-cored sediments showed higher P-wave velocities than APC-cored sediments in an overlapping stratigraphic interval between holes (see Physical properties in the Site U1463 chapter [Gallagher et al, 2017d]).…”

“…Variations in most minor elements show similar trends between Sites U1463 and U1464 ( Figure F20 in the Site U1463 chapter [Gallagher et al, 2017d]; Figure F22). Downhole trends of boron and lithium have relatively constant values shallower than ~40 m CSF-A, then gradually increase with depth until ~270 m CSF-A, and then decrease toward 318 m CSF-A ( Figure F22).…”

“…GRA bulk densities (ρ) and MAD bulk densities tend to be indistinguishable for the uppermost 100 m CSF-A. However, as was the case at Site U1463 (see the Site U1463 chapter [Gallagher et al, 2017d]), bulk densities estimated using MAD methods tend to be lower than those estimated by GRA between 100 and 317 m CSF-A ( Figure F30). We believe that this is a result of variations in mineral- Figure F28.…”

“…AF cleaning of up to 20 mT revealed a persistent negative inclination trend from the top of the succession to ~210 m CSF-A (Core 356-U1464D-23H), where there is an overall shift toward shallower inclination values and more frequent positive inclination intervals. A possible explanation for this trend is that characteristic remanent magnetization was better characterized deeper than ~210 m CSF-A by the AF cleaning up to mT because of a change in magnetic mineralogy, similar to the transition at ~275 m CSF-A in magnetic mineralogy characteristics of sediments from Hole U1463B (see the Site U1463 chapter [Gallagher et al, 2017d]).…”

Expedition 356 summary

“…Biostratigraphic zone boundary ages are shown. Age-depth model was produced from select biostratigraphic datums (see Table T6 in the Site U1463 chapter [Gallagher et al, 2017g]) (solid circles = calcareous nannofossil, open circles = planktonic foraminifer). Sedimentation rates assume a linear sedimentation rate between datums.…”