Frank R. Rack, Jan Bloemendal, Thomas C.W. Wolf-Welling, Suzanne O'Connell, Michel Cremer, Amelie Winkler, Jörn Thiede, Kevin Black, and Julie Hood


  This paper presents an overview of the physical properties and sedimentologic results from six Ocean Drilling Program Leg 151 sites cored on the Iceland Plateau (Hole 907A), in the Fram Strait region (Sites 908 and 909), and on the Yermak Plateau (Sites 910-912). The primary objective of this paper is to determine to what extent wet bulk density measured using the gamma-ray attenuation porosity evaluator (GRAPE) can be used to interpret textural and compositional changes in sediment accumulation at the various sites around the Nordic Seas and Arctic Ocean. To accomplish this objective, we have first established quantitative relationships between discrete measurements of bulk density and GRAPE bulk density at nine holes and have evaluated the frequency distribution of GRAPE bulk density data at the same holes to detect significant differences between sites. We have also evaluated the frequency distribution of magnetic susceptibility data at these holes because this rock magnetic parameter is most often used in combination with GRAPE measurements for correlation purposes. These two parameters are also used for evaluating compositional and textural changes in sedimentary inputs.
  Composite depth profiles have been developed for three sites (Sites 908, 909, and 911) using both GRAPE bulk density and magnetic susceptibility measurements made on cores from multiple, adjacent holes at these sites. The composite depth profiles provide a more continuous record of property variations in the upper 100 meters below seafloor at a given site than is provided by the data collected at a single hole. The composites also provide the framework for more detailed paleoceanographic and paleoclimatic analyses of the records from these sites (i.e., spectral analysis of time series, astronomic tuning of records, etc.). These activities will be pursued in future contributions related to these data.
  Efforts have been made to identify the sources of variation in the GRAPE bulk density records, and to a lesser extent the magnetic susceptibility records, using the available “ground truth" provided by sedimentologic analyses of discrete samples from selected holes. Textural and mineralogic analyses are compared to GRAPE bulk density records to identify to what extent we are able to explain the density fluctuations in terms of (1) changes in the accumulation of coarse-grained material in various grain-size subfractions, which are primarily transported to the deep sea by sea ice and icebergs during glacial intervals and are influenced by oceanic currents to varying extents, and (2) by changes in the mineralogy and in the relative percentages of various sedimentary inputs, which may provide information about changing source regions for these materials between glacial and interglacial periods in the Nordic Seas and Arctic Ocean.

Date of initial receipt: 5 January 1996
Date of acceptance: 10 May 1996

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