Geologic Magnetic Data Processing
ODP Logging Contractor: LDEO-BRG
Location: Eratosthenes Sea Mount (Eastern Mediterranean)
Latitude: 34° 4.104' N
Longitude: 32° 43.524' E
Logging Date: April, 1995
Bottom Felt: 2564 mbrf (used for depth shift to sea floor)
Total Penetration: 600.3 mbsf
Total Core Recovered: 72.3 m (14 %)
GHMT Logging Runs
Two passes were recorded. Processing was performed on pass 1, open-hole section (89.7-580.8 mbsf).
Wireline heave compensator was used to counter ship heave resulting from the mild sea conditions.
The FMS calipers show a circular hole with variations from 12 to 18 inches. The raw susceptibility has been corrected for hole diameter variations using the FMS caliper.
The GHMT logs have been interactively depth shifted with reference to NGT from DIT/SDT/HLDT/CNTG/NGT run, and to the sea floor (- 2564 m). The program used is an interactive, graphical depth-match program, which allows to visually correlate logs and to define appropriate shifts. The reference and match channels are displayed on the screen, with vectors connecting old (reference curve) and new (match curve) shift depths. The total gamma ray curve (SGR) from the NGT tool run on each logging string is used to correlate the logging runs most often. In general, the reference curve is chosen on the basis of constant, low cable tension and high cable speed (tools run at faster speeds are less likely to stick and are less susceptible to data degradation caused by ship heave). Other factors, however, such as the length of the logged interval, the presence of drill pipe, and the statistical quality of the collected data (better statistics is obtained at lower logging speeds) are also considered in the selection.
A list of the amount of differential depth shifts applied at this hole is available upon request.
A double drift of the total induction signal is present at this hole. The pipe effect is visible on the total induction signal from the top of the logged section to about 180 mbsf. The total induction signal (MAGB) has been corrected for the presence of drill pipe.
The GHMT crosses carbonatic formations.
The data correspond to upper Cretaceous (Santonian to Maastrichtian) from 380 to 170 mbsf, to middle Eocene from 170 to 130 mbsf, and to Early Pliocene above for the logged section. Two sedimentary hyatuses are present at 170 and 130 mbsf. Below 380 mbsf, the cores are barren of fossils, so no age is given (from shipboard studies).
Proposed interpretation of GHMT data
No shipboard magnetostratigraphic result is available from core analysis for the depth interval logged with the GHMT. The interpretation of GHMT data should be performed jointly with detailed paleomagnetic and/or biostratigraphic studies.
Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 160. For further questions about the logs, please contact:
E-mail: Cristina Broglia