ANALYTICAL METHOD

A total of 48 different samples typical of the main sedimentary rock types present in any given section of core in Hole 1014A were analyzed by instrumental neutron activation (INAA). Nine of these samples were chosen as "representative" of the REE distribution patterns. Several centimeter-thick intervals of atypical lithologies (e.g., volcanic ash) near the base of the sequence were purposely omitted. Overall, two main lithologic intervals (subunits) are represented:

  1. Subunit IA (0-140 meters below seafloor [mbsf]) = interbedded clays and foraminifers and nannofossil ooze of Quaternary age, and
  2. Subunit IB (140-449 mbsf) = nannofossil ooze and nannofossil chalk alternating with clays and an increasing amount of calcareous nannofossils, age 5-7 Ma (late Miocene).

Sedimentation rate throughout is estimated at ~79 m/m.y. (Shipboard Scientific Party, 1997).

A combination INAA/total digestion-inductively coupled plasma spectroscopy (ICP) analytical method was chosen because of its high efficiency, sensitivity, and low cost. A 30-g aliquot is encapsulated in a polyethylene vial and irradiated with flux wires and an internal standard at a thermal flux rate of 7 x 1011 n cm-2 s-1, where n equals neutrons. After a 7-day delay to allow Na-24 to decay, the samples are counted on a high-purity Ge detector with a resolution of better than 1.7 KeV for the 1332 KeV Co-60. Using the flux wires, the decay-corrected activities are compared to a calibration developed from multiple certified international reference materials. Corrections are made for interference. The standard is a check on accuracy of the analysis and is not used for calibration purposes.

Detection limits (ppm) and precision (%), respectively, for the REE are as follows: La (0.5; 0.06), Ce (3; 0.27), Nd (5; 0.13), Sm (0.1; 0.04), Eu (0.2; 0.11), Tb (0.5; 0.5), Yb (0.2; 0.1), and Lu (0.05; 0.02).

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