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                                                             Page 1                =======================================               =      DEEP SEA DRILLING PROJECT      =               =   LONG-CORE SPINNER MAGNETOMETER    =               =  SEDIMENT PALEOMAGNETICS DATA BASE  =               =======================================      I.  INTRODUCTION                                                                      A.  BACKGROUND AND METHODS                                                                          The Deep Sea Drilling Project (DSDP) long-core spinner      magnetometer file contains shipboard data taken by the      Digico long-core spinner magnetometer.  This instrument      measures the direction (declination) and intensity of the      horizontal component of magnetization of the sediment in      unsplit 1.5 meter core sections.  The measurements were made      immediately after the cores were brought aboard.       Leg 47A measurements are from rotary drilled sediment cores.      The remaining measurements are from sediments recovered by      the hydraulic piston corer.       Listings of the computer-processed magnetometer data were      usually included with the Hole Summary Book paleomagnetics      report.  On Legs 70 and 71 the paleomagnetists transcribed      the data from the computer listings to data forms.       To insure compatibility with DSDP plotting routines, records      containing all null data fields were discarded.  For      example, on Legs 68 and 70, measurements at a few levels      yielded no recorded values, but under sedimentolgical notes      "range" meaning "saturated" was printed.  These records were      discarded.       All records are in the same format.  Each record is 81      characters long and represents a single long-core spinner      magnetometer record.    B.  LEGS IN DATA SET         The data base contains data from Legs:  47A, 68, 70, 71, 72,      75 and 90.                                                     DSDP Spinnermag 10/86                                                                   Page 2    C.  BIBLIOGRAPHY         Ryan, W. B. F. and U. von Rad, 1976.  Hole Summary Book for      Leg 47A.  Paleomagnetist:  N. Hamilton.       Montadert, L., and D. G. Roberts, 1976.  Hole Summary Book      for Leg 48.  Paleomagnetist:  E. A. Hailwood.       Gardner, J. V. and W. L. Prell, 1979.  Hole Summary Book for      Leg 68.  Paleomagnetists:  D. Kent and D. Spariosu.       Honnorez, J. and R. P. Von Herzen, 1979.  Hole Summary Book      for Leg 70.  Paleomagnetist:  S. Levi.       Ludwig, W. J. and V. Krasheninnikov, 1980.  Hole Summary      Book for Leg 71.  Paleomagnetists:  J. Salloway and J.      Bloemendal.       Barker, P. F. and R. L. Carlson, 1980.  Hole Summary Book      for Leg 72.  Paleomagnetists:  N. Hamilton and A. Suzyumov.       Hay, W. W. and J. C. Sibuet, 1980.  Hole Summary Book for      Leg 75.  Paleomagnetist:  B. Keating.       Kennett, J. R. and C. C. von der Borch, 1983.  Hole Summary      Book for Leg 90.  Paleomagnetist:  C. E. Barton.    D. DATA RELIABILITY         The user should refer to the Hole Summary Books for complete      discussions of the results and their reliability.        Leg 47A       Site 397A:  The paleomagnetist experimented with using the      long- core spinning unit for Site 397A rotary-drilled cores.      Two suitable 1.5 meter core sections were spun on separate      occasions.  The system worked according to specifications.      It was concluded that major lithological changes could      easily be recognized by intensity values and by swings in      relative declination, which then could be used as a guide to      sampling.        Leg 48       Sites 401 and 402:  A total of seven 1.5 meter      rotary-drilled core sections were measured.  Measurements      were usually taken at 1 cm intervals with triplicate      measurements at each 10 cm point.  The data were included in                                               DSDP Spinnermag 10/86                                                                  Page 3        the Hole Summary Book paleomagnetics section.  The data were      described as mostly unreliable with inconsistent repeat      readings most likely due to slippage of the core-section      within the plastic liner during rotation.  The results were      not included in the data base.        Leg 68       Site 502:  Shipboard personnel attempted to maintain      relative orientation between successive cores, but the      paleomagnetist reports they may have been only partially      successful.  They did maintain relative orientation between      the sections cut from each 4.4 meter core.  Cores were      measured immediately after being brought aboard ship.  "Very      high values of remanent intensity often occur in the      disturbed parts of the core and may be caused by magnetic      grain alignment [due to] sediment shearing, by realignment      of magnetic grains in a relatively strong magnetic field,      perhaps associated with the steel drill string (or possibly      we are detecting the shear pins that fall into the hole      after each core)."       Site 503:  Rust scale from the drill string was a serious      problem.  Dark flecks were concentrated at the top of      virtually every core and the core was smeared inside the      liner to several meters, even in undisturbed portions of the      core.  Rust scale, of course, is highly magnetic.  This was      a serious problem in Hole 503A, but less so in Hole 503B.      Long-core magnetic data from the topmost 1.5 meters of most      cores could not be used because of the rust contamination.      Modification to the corer between Sites 502 and 503 greatly      improved core to core orientation and at Site 503 greater      attention was paid to handling the cores on deck.       In August, 1981, the Leg 68 co-chief scientists forwarded a      list of orientation angles (phi) that go with each core for      Sites 502 and 503.  Phi is the rotation angle measured from      the orientation ring for each core.  The rotation angles      have been entered in the remarks field of Leg 68 sediment      paleomagnetics records.       Leg 70       Site 506:  The paleomagnetist, S.  Levi, states (personal      communication) that he would not have confidence in Leg 70      long-core spinner magnetometer data (especially Site 506)      because of rust contamination and physical disturbance of      the sediment.  However, the data might show trends and gross      differences.  Data for declination and intensity are usually      good beyond the first section, sometimes beyond the top 50      cm of the first section.       Site 507:  Very similar to Site 506.                                               DSDP Spinnermag 10/86                                                                  Page 4         Site 509:  Hole 509 is composed of foram-nanno ooze.  The      results are similar to those at the previous sites.  The      manganese-oxide fragments show weak magnetization intensity.      Hole 509B was composed of layers of MnO2 fragments,      "hydrothermal clays", and foram-nanno oozes.        Leg 71       Site 512:  In most cases an approximate orientation was      preserved between cores.  However, orientation was lost on      Cores 2, 12, and 13.  Large quantities of gravel occurred in      the upper parts of many cores.  The gravel probably fell      down the hole from above.  It produced the relatively high      intensities (often over 1000 microgauss) and the scattered      declinations visible in Section 1 of many of the cores.       Site 514:  Pipe-rust occurred frequently in the cores,      particularly in Section 1, but also in variable quantities      in the lower sections of the cores.  "This problem      constitutes a severe limitation on the use of the long-core      spinner to measure weakly magnetized sediments."        Leg 72       Hole 515A:  "Invariably the upper 50 cm or so of Section 1      from each core gives anomalous declination and intensity      results.  This appears to correlate with evidence of visible      disturbance and is often reflected in the G.R.A.P.E.      determination." Wildly fluctuating values for a single      reading can occur below the first 50 cm of the first      section.  Rust was probably not a factor in the anomalous      readings, as the drill pipe was used for rotary coring at      Hole 515.       Site 517:  Quality of the long-core data at Site 517 is      inferior to that produced for the more cohesive sediments      from Site 515.  Anomalous changes in declination and      intensity were most common in the upper part of a section of      each core.       Results measured on Cores 1 and 2 cannot be directly      compared with the discrete samples because the sections      changed length when rotated.  Sedimentologists in the core      lab tried to reduce the sections to their original length.       Site 518:  The sediments recovered here were generally      firmer than at Site 517.  Cores were carefully inspected for      evidence of voids, soupy disturbance and excessive water      between liner and sediment surface before selection for      spinning.                                                DSDP Spinnermag 10/86                                                                  Page 5        Leg 75       Hole 530B:  Paleomagnetic studies were unsuccessful except      for Core 530B-8, Sections 2 and 3, which did give stable      paleomagnetic directions.  There were three reasons for the      failure:           1) Much of the sediment consisted of debris flows and             turbidites.           2) The sediments were weakly magnetized and in many             cases the noise level of the magnetometer exceeded or             was equal to sample magnetization.  For these reasons             no NRM intensity values are available for Site 530B.           3) There was considerable contamination of sediments             with rust from the drill string.        Leg 90        The objective of the onboard studies was to obtain a      detailed magnetic stratigraphy by making closely spaced      long-core measurements of the horizontal component of NRM      for all HPC cores.  It was not always possible to achieve      this objective and the cores were sampled for subsequent      laboratory studies.  Fluid sections and sections containing      air pockets were not measured.       Hole 587:  Contamination by rust was not a serious problem.      High intensity spikes were attributed to grease spots/rust      particles, although contamination was not always visible in      the section.  Measurements were discontinued after core 7      because of the poor quality of the results.       Site 588:  All well-preserved cores from Holes 588, 588A and      588B were measured with the exception of Hole 588B, cores      10-19.  The Digico magnetometer was noisy and much of the      sediment failed to give a signal significantly higher than      the noise level of the instrument (about 0.1 microgauss at      2**6 spins).  Absolute orientations were obtained on most      cores using the Kuster device.  Declination plots for all      the cores measured were presented in an appendix to the Hole      Summary Book magnetics section.       The Site 588 results were summarized on Summary      Paleomagnetic Measurements forms, copies of which are kept      on microfilm in the DSDP Data Archives.  Measurements were      made at 10 cm steps (2**6 spins).  Below core 588B- 20,      intervals of 20 cm were used.  The Summary Paleomagnetic      Measurements tabulation lists the mean NRM intensity value      with standard deviation of the measurements taken in each      section.  The standard deviations are rather large because                                               DSDP Spinnermag 10/86                                                                  Page 6        of the presence of a small number of high values in the      section.  Thus, the means are much higher than typical      values.  This data file lists the mean value for each      section, but not the standard deviation.       Hole 589:  Paleomagnetic properties are similar to those of      Site 588.  The better consolidated sections were measured      at 20 cm intervals.  The material in core 1 is more strongly      magnetized than the lower cores.  The scattered declinations      of the lower cores are attributed to contamination and the      effect of core liners rather than to instrument noise.                                                                                          DSDP Spinnermag 10/86                                                                  Page 7    II.  FORMAT AND FIELD DESCRIPTIONS      A.  DATA FORMAT      Record length = 81 characters    (originally 85, blank fields removed by NGDC)     COLUMN  FIELD                                          FORMAT    ======  =============================================  ======     1-2    LEG                                            A2     3-5    SITE                                           A3     6      HOLE                                           A1     7-9    CORE                                           A3    10-11   SECTION                                        A2    12-15   TOP INTERVAL DEPTH (cm) (implied decimal pt)   F4.1    16-23   TOP OF CORE DEPTH (meters)                     F8.2    24-31   SAMPLE DEPTH IN HOLE (meters)                  F8.2    32      REPEAT COLUMN                                  I1    33-57   SEDIMENTOLOGICAL NOTES                         A25    58-67   NRM INTENSITY (gauss x 10-6)                   F10.0    68-74   NRM DECLINATION, ANGLES UNCORRECTED (degrees)  F7.0    75-81   NRM DECLINATION, ANGLES CORRECTED (degrees)    F7.0     B.  FIELD DESCRIPTIONS         The definition of leg, site, hole, core and section may be      found in the explanatory notes.  In addition, the special      core designations, as well as the methods of sample labeling      and calculating absolute sample depths are discussed.     INTERVAL DEPTH:       Refers to the depth in centimeters within the section at      which the top or bottom of a measurement was taken.  Values      are encoded with an implicit decimal point.  No bottom      interval depths are given for the measurements in this file.       Measurements are usally made at 10 cm intervals; however,      measurements may be more closely spaced, at 2 cm or 5 cm      intervals, for example.    CORE DEPTH:       The subbottom depth in meters to the top of the core.    SAMPLE DEPTH:       The subbottom depth in meters to the level at which the      measurement was made.                                               DSDP Spinnermag 10/86                                                                  Page 8      REPEAT COLUMN:       The paleomagnetist often returned to make measurements at      higher levels in the section or to repeat measurements      following the usual sequence.  A field has been reserved for      recording repeat measurements.  "0" is entered in the field      if there is only one measurement for an interval.  There is      a "1" for the first repeat measurement, a "2" for the next      repeat and so on.  Records of a section with the same number      in the repeat column are from a single measurement sequence.    SEDIMENTOLOGICAL NOTES:       Only 25 columns were available for the sedimentological      notes.  In encoding, the notes were abbreviated when      necessary.  A note may be continued from the      sedimentological notes field of one record to the same field      on the next record.    NATURAL REMANENT MAGNETISM(NRM) INTENSITY:       NRM intensity is encoded in gauss (c.g.s.  units).  Every      value in the NRM intensity field should be multiplied by      10-6 to arrive at the NRM intensity value.    NRM DECLINATION, ANGLES UNCORRECTED:       The horizontal angle in any given location between true      north and magnetic north.  Values range from 0 to 360 and      are always positive.  The paleomagnetists tried to maintain      relative orientation between successive cores.  Attention      was paid to handling the cores on deck to preserve relative      orientation.    NRM DECLINATION, ANGLES CORRECTED:       This field was used only when the paleomagnetist noted      corrected values.                                                              DSDP Spinnermag 10/86 

Long-core spinner magnetometer : sediment paleomagnetics data base - background and methods

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