Geologic Magnetic Data Processing
ODP logging
contractor: LDEO-BRG
Hole: 1052E
Leg: 171B
Location: Blake Nose (NW Atlantic Ocean)
Latitude: 29° 57.0794' N
Longitude: 76° 37.609' W
Logging date: February, 1997
Bottom felt: 1355 mbrf
Total penetration: 684.8 mbsf
Total core recovered: 544.8 m (60.2 %)
GHMT
Logging Runs
Two passes (main and repeat) were recorded. Processing was performed on the main pass, open-hole section (236.5-676.2 mbsf).
Wireline heave compensator was not available on Leg 171B. Sea conditions were moderate, with sea swells in the order of 1 m.
The hole diameter varies from 10 to 11 inches in the logged section. The raw susceptibility has been corrected for hole diameter variations.
The original logs have been interactively depth shifted with reference to NGT from DIT/APS/HLDT/NGT run and to the sea floor (- 1353 m). The amount of depth shift to the sea floor corresponds to the water depth as seen on the logs and differs 2 m from the drillers' "bottom felt" depth. 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.
Log
Quality
The total induction signal (MAGB) has been corrected for the presence of drill pipe. Numerous spikes are present on the total induction signal in the lower part of the logged section (470-680 mbsf), which are correlated to low values of the NMRT outer voltage.
Lithology
The GHMT was recorded through lithologic units III to V:
- Unit III (top of the logged section to 301.6 mbsf): Nannofossil claystone; calcareous claystone with zeolite; Nannofossil, foraminifer, and calcareous chalk w/ clay (late to early Paleocene).
- Unit IVA (301.6-388.6 mbsf): Clayey nannofossil chalk; nannofossil chalk with clay (late Maastrichtian).
- Unit IVB (388.6-477.4 mbsf): Nannofossil chalk; nannofossil chalk with clay (late Maastrichtian).
- Unit VA (477.4-511.8 mbsf): Silty claystone; clayey siltstone with nannofossils (Cenomanian to Late Albian).
- Unit VB (511.8-633.5 mbsf): Laminated black shale; clayey limestone with foraminifers and quartz; silty claystone (late Albian).
- Unit VC (633.5 mbsf to bottom of the logged section): Clayey siltstone, silty claystone; siltstone with carbonate grains: bioclastic and lithic grainstone (late Albian).
Age
information
The logged section corresponds to biozones CP3 to CC8b, as inferred from nannofossil data onboard.
Proposed
interpretation of GHMT data
Paleomagnetic chrons C27r to C34n (bottom to top) have been determined from comparison with core measurements of the paleo-inclination made on board.
The numerous spikes present in the data recorded in the lower part of the hole lead to artifacts in the computation of the correlation slope.
Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 171B. For further questions about the logs, please contact:
Cristina
Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia