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Detailed geophysical and geological measurements were conducted during a site-survey cruise to Sites 646 and 647 in the Labrador Sea. These included gravity, magnetic, bathymetry, high-resolution and deep-penetration seismic reflec­ tion, seismic refraction, and heat-flow measurements. A second cruise, which was not so extensive, involved collection of high-resolution seismic-reflection measurements and of sediment cores in Baffin Bay at Site 645. A limited number of piston cores were also collected at Sites 646 and 647. The seismic data from these cruises have been used to identify a number of prominent reflectors that show different characteristics among the sites. Magnetic, gravity, and seismic data have been used to differentiate between rough and smooth basement topography at the Labrador sites. We suggest that the changes in basement character resulted from the change in the direction of spreading. High-resolution seismic data at the Baffin Bay site suggest the possibility of a slump feature in the top 90 m of the section near the site. INTRODUCTION Sites 646 and 647 in the Labrador Sea and Site 645 in Baffin Bay were selected for drilling during Leg 105 of the Ocean Drill­ ing Program (ODP). These sites were selected on the basis of compiled information from a large amount of geological and geophysical data collected by the Bedford Institute of Oceanog­ raphy, other research institutions, and the oil exploration indus­ try over the past 20 yr. However, additional data at each site were needed to obtain detailed knowledge of the underlying structure and geology so that the locations of these sites could be assessed from safety and pollution points of view. This study describes the details and results of the cruises aboard the re­ search vessel Hudson (operated by the Bedford Institute of Oceanography) undertaken in 1984 and 1985 to the Labrador Sea and Baffin Bay, respectively. The correlation of drilling re­ sults to data at each of these sites and their implications to the paleoceanography and tectonic development of these regions are dealt with elsewhere in this volume and will not be repeated here. We present here most of the seismic data collected at these sites, to make them easily accessible. Unlike the Labrador Sea sites, adequate multichannel seis­ mic data existed for the Baffin Bay site, and additional data were not required to assess its suitability before drilling. How­ ever, to extend the drilling results for the upper 200 m section at this site to the neighboring regions, high-resolution seismic and coring data were collected in the vicinity of this site on a cruise aboard the Hudson in 1985. These data are also included here. Drilling at these Labrador Sea and Baffin Bay sites was pro­ posed (1) to study the tectonic development of these regions, (2) to study the history of deepand surface-water paleocirculations through these regions, and their connection to the Arctic and Atlantic oceans, and (3) to study the paleoclimatic condi1 Srivastava, S. P., Arthur, M., Clement, B., et al., 1989. Proc. ODP, Sci. Results, 105:College Station, TX (Ocean Drilling Program). 2 Geological Survey of Canada, Atlantic Geoscience Centre, Bedford Inst. of Oceanography, Dartmouth, Nova Scotia B2Y 4A2, Canada. 3 Department of Oceanography, Dalhousie University, Halifax, Nova Scotia B3H4J1, Canada. 4 Department of Oceanography, Seoul National University, Seoul 151, Korea. 5 Departement de Sciences de la Terre GEOTOP, Universite du Quebec a Mon­ treal, CP 8888 Succursale "A," Montreal, Quebec H3C 3P8, Canada. tions and the timing and frequency of climatic oscillations, par­ ticularly glacial and interglacial cycles that prevailed in these re­ gions. Details of these objectives together with some background information on the geological and paleoenvironmental setting of these basins were described by Srivastava, Arthur, et al. (1987). The first objective for drilling in the Labrador Sea was to sample the basement rock to get an estimate of the date of the magnetic anomaly sequence, thereby resolving much of the un­ certainty in the record of seafloor spreading in this region. Base­ ment cannot be reached easily in most of the Labrador Sea be­ cause of a substantial sediment cover. Site 647 in the southern Labrador Sea (Fig. 1) was chosen because of a thin section of Neogene and Paleogene sediments. Another reason for selecting this site location was that it lies near enough to the CharlieGibbs Fracture Zone, where maximum effects from the incur­ sions of waters from the North Atlantic, the Norwegian-Green­ land Sea, and the Arctic Ocean are thought to have taken place. We expected that the study of sedimentary column here would provide valuable information about paleocirculation through this region. Another site, 646, southwest of Greenland (Fig. 1) was chosen because it lies in a region where the maximum effect of the Norwegian Sea Overflow Water (NSOW) was expected, and because the top of the older Paleogene section lies at a shal­ low depth. Thus, this site was an ideal place for studying the on­ set of deep, cold, bottom-water currents in the North Atlantic. As in the Labrador Sea, sediment thicknesses in most parts of Baffin Bay exceed 5 km, thereby rendering the basement in­ accessible to drilling. Thus Site 645, on the western margin of Baffin bay, off the southwest coast of Baffin Island (Fig. 1), was chosen where syn-rift and early post-rift sediments lie at subbottom depths of less than 2000 m. We hoped that drilling into these sediments would provide the age and subsidence history of early post-rift sediments, which are important for deciphering the tectonic history of this region as well as its paleocirculation. DATA COLLECTION METHODS Figure 2 shows the ships' track lines, along which detailed measure­ ments were made during the cruise to the Labrador Sea. Navigation dur­ ing this cruise and another cruise to Baffin Bay was maintained using the Bedford Institute of Oceanography Integrated Navigation System (BIONAV), consisting of an Austron 5000 passive ranging LORAN-C system, a Marconi CMA 72 transit doppler satellite receiver, and the ship's log and gyrocompass integrated through an HP21-E computer.

Results of Detailed Geological and Geophysical Measurements at ODP Sites 645 in Baffin Bay and 646 and 647 in the Labrador Sea