Correlations of Sediment Lithostratigraphy, Downhole Logs, and Seismic Reflectors at Site 418

Abstract

We have correlated the spectral gamma-ray log from the 324-m sediment section at Hole 418A with core data from Holes 418A and 418B to develop a more detailed lithostratigraphic model for Site 418 and a more precise correlation of lithologic boundaries with seismic reflections. In general, log-unit boundaries can be resolved to within about 1 m (below seafloor). Except for lithologic Unit III, all units defined by coring are well defined by the logs and depths to unit boundaries defined by logging are consistent with constraints imposed by the cores. The logs also indicate the existence of several subunits not defined by coring. Each of five reflectors correlates with a unit boundary. In particular, reflectors at 0.21 and 0.29 s (two-way traveltime, below seafloor), which have been identified as horizon A c and horizon 0 by Senske and Stephen (this volume), correlate with the base of the Eocene clays of Unit IV and with the top of the "black clay" sequence, Unit VI.

Site Synthesis Report of DSDP Sites 417 and 418

“…From the latter, they predicted a prominent reflection -0.-1 sec above basement. During ODP Leg 102 logging of Hole 418A, the only physical property log which gave satisfactory results in the sediment section was the gamma ray neutron porosity (Shipboard Scientific Party, 1986;Carlson et al, 1988b). (Table 1).…”

Site synthesis report of DSPP sites 417 and 418

“…Senske and Stephen (1988) correlated stratigraphy at Hole 418A to single-channel digital profiles (Figure 12). Carlson et al (1988b) used the gamma ray log collected on ODP Leg 102 to make detailed correlations between Hole 418A stratigraphy and an analog profile. The seismic stratigraphy of the region has been discussed from a basin-wide perspective by , Tucholke and Mountain (1979), and Mountain et al (1985).…”

“…From the latter, they predicted a prominent reflection -Q.1 sec above basement. During ODP Leg 102logging of Hole 418A, the only physical property log which gave satisfactory results in the sediment section was the gamma ray neutron porosity (Shipboard Scientific Party, 1986;Carlson et al , 1988b).…”

“…Digital copies of the Schlumberger data are available from the Borehole Research Group at Lamont-Doherty Geological Observatory. Carlson et al (1988b) used the gamma ray log to revise unit boundaries in the sediment section (Figure 29). They used an empirical travel time-depth relation for deepsea sediments to correlate unit boundaries to seismic reflection events (Figure 30).…”