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doi:10.2204/iodp.proc.320321.105.2010

Stratigraphic correlation and composite section

Special Task Multisensor Logger (STMSL) data were collected at 5 cm intervals from Holes U1333B and U1333C and compared to the WRMSL data obtained at 2.5 cm intervals from Hole U1333A to monitor coring in Holes U1333B and U1333C in real time. Cores for the final composite section were depth-shifted on the basis of the magnetic susceptibility data at 2.5 cm resolution from the WRMSL track. Magnetic susceptibility and GRA density data were used for correlating among holes at Site U1333. The magnetic susceptibility data proved to be the most useful correlation parameter because of the higher signal-to-noise ratio compared to the GRA data. The high amplitude variations in magnetic susceptibility in the three holes drilled at Site U1333 permitted construction of a complete composite section to Core 320-U1333B-14H-7, 50 cm (131.20 m CSF), at a composite depth of ~150 m CCSF-A (Fig. F27). Offsets and composite depths are listed in Table T31, and the sections of core used for the splice are identified in Table T32. We avoided using intervals with significant disturbance or distortion for the composite record (see "Paleomagnetism;" Table T11). Very low magnetic susceptibility amplitudes made the splicing process challenging at ~115 m CCSF-A (at 220 revised meters composite depth [rmcd] in Fig. F28). However, preliminary correlation to the Site 1218 magnetic susceptibility record (Shipboard Scientific Party, 2002b) suggests a complete stratigraphic section and demonstrates that little, if any, material is missing (Fig. F28).

The Site U1333 splice can be used as a sampling guide to recover a single sedimentary sequence between 0 and 150 m CCSF-A, although it is advisable to overlap a few decimeters from different holes when sampling to accommodate anticipated ongoing development of the depth scale. Stretching and compression of sedimentary features in aligned cores indicates distortion of the cored sequence. Because much of the distortion occurs within individual cores on depth scales of <9 m, it was not possible to align every single feature in the magnetic susceptibility, GRA, NGR, and color reflectance records. However, at crossover points along the splice (Table T32) care was taken to align highly identifiable features from cores in each hole.

A growth factor of 1.15 was derived by linear regression for all holes at Site U1333, indicating a 15% increase in CCSF-A relative to CSF depth (Fig. F29). We used this value to calculate the CCSF-B (see "Corrected core composite depth scale" in the "Methods" chapter) depth presented in Table T31 to aid in the calculation of mass accumulation rates.

We calculated sedimentation rates using paleomagnetic and biostratigraphic datums (Table T33; Fig. F10; see "Biostratigraphy" and "Paleomagnetism") on the CCSF-B depth scale to obtain values compatible with the actual recovered length. Paleomagnetic reversals are used to calculate the average linear sedimentation rates (LSRs) for Site U1333 through most of the section. Calcareous nannofossils, foraminifers, and radiolarians are present throughout the entire section and were used in addition to the magnetostratigraphy in establishing age control (Fig. F10).

The LSR at Site U1333 in the radiolarian and nannofossil oozes of lithologic Units II and III vary between ~4 and 6 m/m.y. in the middle and upper Eocene, increase to ~13 m/m.y. in the lower Oligocene, and remain at ~6.6 m/m.y. in the upper Oligocene and lower Miocene part of the section.

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