Jansen, Eystein

Mayer, Larry A.

Shipboard Scientific Party

English

UNH Scholars' Repository

University of New HampshireUniversity of New Hampshire Scholars' RepositoryAffiliate Scholarship Center for Coastal and Ocean Mapping1991GRAPE Density Records and Density CyclicityEystein JansenUniversity of BergenLarry A. MayerUniversity of New Hampshire, larry.mayer@unh.eduShipboard Scientific PartyFollow this and additional works at: https://scholars.unh.edu/ccom_affilPart of the Oceanography and Atmospheric Sciences and Meteorology Commons, and theSedimentology CommonsThis Conference Proceeding is brought to you for free and open access by the Center for Coastal and Ocean Mapping at University of New HampshireScholars' Repository. It has been accepted for inclusion in Affiliate Scholarship by an authorized administrator of University of New HampshireScholars' Repository. For more information, please contact nicole.hentz@unh.edu.Recommended CitationJansen, E., Mayer, L.A., and the Shipboard Scientific Party, 1991, GRAPE density records and Density Cyclicity, in, Berger, W.H., andKroenke, L., eds., Proceedings of the Ocean Drilling Program, vol. 130, pp. 553-558.Kroenke, L. W., Berger, W. H., Janecek, T. R., et al., 1991Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 13013. GRAPE DENSITY RECORDS AND DENSITY CYCLICITY1E. Jansen,2 L. Mayer,3 and Shipboard Scientific Party4The gamma-ray attenuation porosity evaluator (GRAPE)component of the multisensor track (MST) unit on board theJOIDES Resolution measures the saturated bulk density of sedi-ments by relating the attenuation of gamma rays in a core sam-ple to that of a standard with known density (aluminum). Afterreaching thermal equilibrium, unsplit core sections are routinelyrun through the MST system. The sampling density chosen forthe MST during Ocean Drilling Program (ODP) Leg 130 (about2-3 cm) provides a near-continuous measurement of sedimentdensity by means of the GRAPE equal to a resolution of 0.5-3 k.y, depending on the sedimentation rate.Comparisons of GRAPE density values with discrete labora-tory density measurements and downhole density logs show thatabsolute GRAPE density estimates are higher than both labora-tory and logging density measurements; however, the downholetrends in the density data are very coherent. The constant offsetbetween the GRAPE data and density measurements made byother means indicates that the offset is a function of the calibra-tion of the GRAPE system. The extremely high sample resolu-tion of the GRAPE makes it possible to use these data for anumber of purposes:1. To perform hole-to-hole correlations at a specific site, eval-uating the continuity of the recovered section over core breaks.This provides a rapid method for splicing sections from onehole into missing sections in another hole or, alternatively, toevaluate possible double coring of a particular interval. GRAPEcorrelations can be made to depths as great as 300 m below sea-floor (mbsf)> well beyond the depth of useful magnetic suscepti-bility measurements.2. To perform fine-scale, site-to-site correlations, especiallyin intervals with high signal-to-noise ratios or identifiable vari-ability patterns.3. To provide high-resolution records of environmental vari-ations. Density variations in pelagic sediments are driven bychanges in dissolution, winnowing, and dilution of carbonateby terrestrial material and opal; they therefore reflect pale-oceanographic and paleoclimatic conditions.The raw GRAPE data for Sites 803-807 were checked forquality, using the GRAPEFIX routine on the shipboard VAXcomputer system. Because of the slow passage of the sectionthrough the MST system required by magnetic susceptibility mea-surements, a number of GRAPE density measurements were of-ten performed at a particular level. Multiple measurements wereaveraged using the program DECIMATE. This program waslater transferred to and is now operative on the VAX system.1 Kroenke, L. W., Berger, W. H., Janecek, T. R., et al., 1991. Proc. ODP, Init.Rβpts., 130: College Station, TX (Ocean Drilling Program).2 Section B, Department of Geology, University of Bergen, Allegaten 41, N-5007 Bergen, Norway.3 Department of Oceanography, Dalhousie University, Halifax, Nova Scotia,Canada B3H4J1.4 Shipboard Scientific Party is as given in the list of participants preceding thecontents.The raw GRAPE data commonly display very low densities inthe upper portions of a core. In most cases, these low-densityintervals correspond to intervals that contain disturbed andsoupy sediments or flow-in.As a first pass, an additional set of GRAPE data files wereproduced in which data points that came from intervals de-scribed as disturbed by the visual core description were elimi-nated. This was done for the section cored with the advancedhydraulic piston corer (APC) of at least one hole at each site,and it effectively eliminates most of the apparent variance re-lated to coring disturbance. To increase the signal-to-noise ratiofurther, these data were smoothed by a 10-point Gaussian filter;the smoothed data sets are displayed in Figures 1 and 2. As isseen in Figure 1, there is no clear evidence of cyclicity at thecore length interval (9.5 m), indicating that most of the distur-bance signal that results from core breaks has been removed. Insome cases, however, the upper parts of some cores still retainanomalously low densities, probably a result of subtle coringdisturbances that are not obvious to visual examination.Despite clear hole-to-hole and site-to-site differences in theGRAPE records, the high-frequency variations in the GRAPErecords indicate that there is strong potential for detailed hole-to-hole as well as site-to-site correlations. Preliminary shipboardstudies based on the visual correlation of GRAPE records indi-cate that, in particular, the upper ~ 100 m of the section are themost promising for correlation as they display the highest am-plitudes and have intervals with distinct variability patterns. InFigure 2, we have plotted records from Holes 806B and 807A,which roughly cover the interval from 1 to 2 Ma, based on ship-board biostratigraphy. It is evident from this example that thedensity variations at the two sites show essentially the same pat-tern over this interval, with a very regular cyclic appearance.Using the preliminary shipboard age information, time-se-ries analyses with the SPECMAP program package (Imbrie etal., 1984) were conducted on data from Holes 803B and 806B.These studies document that the GRAPE variance is closely con-centrated in narrow frequency bands corresponding to the 100,41, and 23 ka Milankovitch periodicities, and that the GRAPEsignal is coherent with global oxygen isotope records (Imbrie etal., 1984) over the last 1 Ma at each of these frequency bands.An example of these preliminary time-series analyses is shownin Figure 3. The analysis further documents a trend of evolving100-ka variation at the expense of 41-ka spectral power throughthe Pleistocene, in the same manner that has previously beendocumented for oxygen isotope records (Ruddiman et al., 1986).This indicates that the environmental mechanisms that governsediment density variations are linked with the ice ages and theglobal climate system and are strongly influenced by orbitalforcing.Shipboard studies were limited to testing the utility of theGRAPE data, and these results need more testing and develop-ment during shore-based studies. Of prime importance is theneed to arrive at a clear understanding of the specific factorsthat control the short-term density variations in Ontong JavaPlateau sediments. In addition, the more refined and accuratetime scales evolving from postcruise studies must be imple-553E. JANSEN, L. A. MAYER, SHIPBOARD SCIENTIFIC PARTY1.5Grape density (g/cm3)1.6 1.7 1.8B Grape density (g/cm3)1.6 1.7 1.81300 —350 1— 601Figure 1. GRAPE density data from Hole 806B plotted vs. sub-bottom depth. A. The upper 350 mbsf. B. Blown-up section with detail of the intervalfrom 30 to 60 mbsf. The data are smoothed by a 10-pt Gaussian filter.men ted. Shipboard work, however, has already established thelarge potential for extremely high-resolution records of environ-mental change that can be extracted from the GRAPE.REFERENCESImbrie, J., Hays, J. D., Martinson, D. G., Mclntyre, A., and Mix,A. C , 1984. The orbital theory of Pleistocene climate: support froma revised chronology of the marine δ 1 8 θ record. In Berger, A., Im-brie, J., Hays, J., Kukla, G., and Salzman, B. (Eds.), Milankovitchand Climate: Understanding the Response to Astronomical Forcing(Vol. 1): Dordrecht-Boston-Lancaster (D. Reidel Publ. Co.), 269-305.Ruddiman, W. R., Raymo, M., and Mclntyre, A., 1986. Matuyama41,000-year cycles: North Atlantic Ocean and Northern Hemisphereice sheets. Earth. Planet. Sci. Lett., 80:117-129.Ms 130A-113554GRAPE DENSITY RECORDS201.5Grape density (g/cm3)1.6 1.7 1.825303540i l l i l l I I IB Grape density (g/cm3)15 16 1.7151 i i i i i i r1.8202530l I I IFigure 2. Smoothed GRAPE density data from Holes 806B (A) and 807A (B) plotted vs. sub-bottom depth. The selected depth intervals roughlycover the period from 1 to 2 Ma in both holes.555E. JANSEN, L. A. MAYER, SHIPBOARD SCIENTIFIC PARTY100.0010.001.000.100.01wSj?ECMAP StackIΘ 806B GRAPECoherency100K50K 25K 16.6K 12.5K0.10.010.00110"40.04 0.08 0.12 0.16Frequency (cycles/sample interval)0.21 0 5Figure 3. Example of a cross-spectral analysis of the smoothed GRAPErecord from the upper 25 mbsf in Hole 806B vs. the global stack of trop-ical planktonic δ 1 8 θ (SPECMAP stack; Imbrie et al., 1984). TheGRAPE data used in the analysis were sampled at a constant samplinginterval of 2000 yr. The results are preliminary and are based on theshipboard age model for this hole.556

GRAPE Density Records and Density Cyclicity

https://scholars.unh.edu/cgi/viewcontent.cgi?article=1028&context=ccom_affil

GRAPE Density Records and Density Cyclicity

Abstract

Similar works

Full text

Available Versions

UNH Scholars' Repository