Site U1455

Abstract

Contents 1 Site summary 3 Background and objectives 3 Operations 7 Lithostratigraphy 16 Biostratigraphy 17 Paleomagnetism 20 Geochemistry and microbiology 23 Physical properties 27 Downhole measurements 28 Stratigraphic synthesis 33 References C. France-Lanord et al. Site U1455 IODP Proceedings 2 V o l u m e 3 5 4study Himalayan erosion was found, although it was not recovered at Site U1451 for the same period. In this particular depth interval, further detailed sedimentary analyses may shed light on the causes for the depositional facies being different from Pliocene and Pleistocene times and may help to determine whether the absence of levees originated from a change in sediment supply or transport pathways or from other factors. OperationsWe cored three holes at Site U1455. Holes U1455A and U1455B each consist of a single mudline core; the cores penetrated to 0.9 and 6.9 m DSF, respectively. Hole U1455C consists of coring in three intervals: 0-122.3 m DSF (advanced piston corer [APC] and half-length APC [HLAPC] systems), 359.8-431.4 m DSF (HLAPC system), and 773.0-949.0 m DSF (RCB system). The uppermost interval of Hole U1455C consists of APC and HLAPC coring and four 4.8 m advances without coring (19.2 m). Cores 1H-24F penetrated 103.1 m in this interval and recovered 89.82 m of sediment (87%). We drilled 237.5 m without coring from 122.3 to 359.8 m DSF and then resumed continuous HLAPC coring. Cores 26F-41F penetrated from 359.8 to 431.4 m DSF (71.6 m) and recovered 48.82 m of sediment (68%). After dropping a free-fall funnel (FFF) and retrieving the drill string to switch to the RCB system, we reentered Hole U1455C and drilled ahead without coring from 431.4 to 773.0 m DSF. We RCB cored from that depth to 949.0 m DSF. Cores 43R-60R penetrated 176.0 m and recovered 59.36 m of sediment (34%). Coring ended on 28 March 2015 at 1435 h when the operational time for the expedition expired. LithostratigraphyAs at other Expedition 354 sites, lithologic differences between units and variations in grain size and bed thickness reflect cycles of proximal turbidity current channel activity and abandonment. Sand intervals may represent interlevee "sheet flows" (e.g., Curray et al., 2003), whereas finer grained fractions are more likely preserved in leveed sections. Calcareous clay units reflect cessation of proximal channel activity, but the intervals also resemble episodes of minor increase in siliclastic deposition.Coring in Hole U1455C was divided into three segments. The uppermost segment (from the seabed to 120.51 m core depth below seafloor [CSF-A]) is principally composed of micaceous quartz-rich siliciclastic sediments, many containing typical characteristics of turbidites (sharp base, normal grading, and laminations). In this segment, the lower sand units are overlain by 13.5 m of calcareous clay covered by a 45.86 m thick section of sand and mud turbidites. There are two glassy volcanic ash layers at 5.68-5.75 and 82.80-82.89 m CSF-A. The second recovered segment of Hole U1455C (359.80-431.39 m CSF-A) is also pr...