IODP Proceedings    Volume contents     Search

doi:10.2204/iodp.proc.339.205.2019

Materials and methods

Of the three holes drilled at Site U1387, we analyzed Holes U1387A and U1387C. The intervals analyzed for Hole U1387A (344.34–345.67, 350.44–351.31, and 351.42–351.53 meters below seafloor [mbsf]) were cored using the extended core barrel (XCB) system. Hole U1387C was cored using the rotary core barrel (RCB) system for the intervals analyzed (347.64–349.85, 351.36, and 352.7 to ~460 mbsf). Stratigraphic correlation at this site was revised in the early to middle Pleistocene sequence based on stable isotope data and supported by X-ray fluorescence (XRF) data, resulting in a corrected meters composite depth (mcd) scale (Voelker et al., 2018). In general, the stable isotope data show that the sequence of the revised splice does not contain a hiatus (see the “Methods” chapter [Expedition 339 Scientists, 2013a]) but just small coring gaps (Voelker et al., 2018). The calcareous nannofossil events identified here were observed in smear slides prepared using microscope slides and coverslips that were mounted with Norland optical adhesive. These slides were observed using standard light microscope techniques on a Zeiss Axiophot and with a polarizing microscope Leica DMRP at ×1250 and ×1000 magnification. A minimum of 200 fields of view (FOVs) were examined for each sample in cross-polarized and plane-transmitted light.

Bioevent ages were assigned based on the occurrence of calcareous nannofossils in the samples analyzed. Estimates of the abundance of calcareous nannofossils were determined as follows:

  • VA = very abundant (>100 specimens per FOV).
  • A = abundant (11–100 specimens per FOV).
  • C = common (1–10 specimens per FOV).
  • F = few (1 specimen per 2–10 FOVs).
  • R = rare (1 specimen per ≥11 FOVs).
  • B = barren.

Abundances of individual taxa or groups of calcareous nannofossils were categorized as follows:

  • D = dominant (>20 specimens per FOV).
  • A = abundant (11–20 specimens per FOV).
  • C = common (1–10 specimens per FOV).
  • F = few (1 specimen per 2–10 FOVs).
  • R = rare (1 specimen per ≥11 FOVs).
  • P = present (abundance not quantitatively determined).

Calcareous nannofossil events were defined based on abundance patterns of the index species and recognized as lowest occurrence (LO), lowest common occurrence (LcO), highest common occurrence (HcO), and highest occurrence (HO).

Table T1 provides details on all data collected.