Hole 1087C was planned to be logged with a full suite of sensors to continuously characterize the sedimentary changes, to correlate the lithostratigraphy with other sites, and to provide data for core-log integration. Unfortunately, the logging tool string could not be retrieved after the first run, which ended operations at Hole 1087C (see "Operations" section, this chapter).
Hole 1087C was logged with one tool string (seismostratigraphy,) which included the NGT, LSS, DIT, and TLT sondes. The logs were run downhole and uphole from 492 mbsf (total depth) to 80 mbsf, where the tool string got stuck at the bottom of the pipe. The natural gamma-ray intensity is the only parameter measurable through the pipe, but it should be interpreted only qualitatively in this interval. The pipe was set at 87 mbsf and pulled up to ~57 mbsf during logging. The wireline logging heave compensator was not used because of rough sea conditions.
The lithologic succession recovered from Hole 1087C is controlled mainly by changes in the nature and intensity of biogenic production vs. the type and amount of detrital input. It is characterized by small changes in sediment composition and compaction, which should be reflected in the log physical properties measurements. Despite the uniform lithostratigraphy defined from core observations and smear-slide studies (see "Lithostratigraphy" section, this chapter), the good quality and high resolution of the downhole measurements allow us to identify numerous sedimentary changes in the logged formation (Fig. 23).
Lithostratigraphic Unit II at the very bottom of the hole is characterized by higher gamma-ray intensity, resistivity, and acoustic velocity, with a transition which fits with the boundary between lithostratigraphic Units II and I (see "Lithostratigraphy" section, this chapter). In this formation, the acoustic velocity is >2200 m/s for a 2-m-thick interval at ~455 mbsf. Between 350 and 300 mbsf, a progressive decrease in both gamma-ray intensity and resistivity corresponds to the higher carbonate content of the sediment (see "Organic Geochemistry" section, this chapter). Above this depth, the general trend of velocity values mainly reflects downhole compaction and lithification. Uranium content shows a distinct increase uphole, beginning near 200 mbsf and reaching a plateau near 120 mbsf.
Besides these general trends, the 370–350 and 140–120 mbsf intervals are characterized by high values of gamma-ray intensity, resistivity, and uranium content, with drastic excursions for gamma-ray intensity below 300 mbsf. These intervals might reflect abrupt changes in the ratio between clastic and biogenic components, as they show up simultaneously in internal parameters. Diagenesis could enhance or modify such lithologic changes, as suggested by high resistivity and steady velocity values between 370 and 350 mbsf.
The downhole measurements of the two neighboring holes are very similar, despite the higher sedimentation rate observed at Site 1085 in the Mid-Cape Basin. Both general trends and details can be correlated between the two sites, as shown by the gamma-ray intensity (Fig. 24). Despite the higher sedimentation rate, gamma-ray intensity is higher and the amplitude of general shifts is sharper in the Mid-Cape Basin.