Samples were collected from Cores 182-1130A-14H, 15H, and 16H and prepared for the following analyses.
Twenty samples between 125.2 and 150.5 mbsf were prepared for thin section by cutting a 5-g piece and placing the sample into a disposable phenolic ring (1 in x 7/8 in). Samples were air dried for two weeks. Dry samples were impregnated with epoxy and cut into final 30-µm-thick slides. Thin sections were analyzed under petrographic light microscope, and lithologies were grouped into lithofacies based on texture, grain size, sorting, and grain types.
Grain sizes of 30 samples were determined by using a Sedigraph 5100 particle-size analysis system. Approximately 1.5 g of sample was put in water and sonicated for 10-20 s. The limiting range for analysis was 125-25 µm, and each sample was run for 20 min. A problem with this method is that sand-sized particles fall outside the range. For instance, some of the planktonic foraminifers are coarser than silt size, and their size did not get recorded. The grain counts of sieved samples and the thin section point counts complement this method and provide an insight into the coarser fraction.
Forty samples from representative depths were analyzed for grain composition using thin section as well as sieved material coarser than 68 µm. The two analyses illustrate the differences between classic point counts of lithified and unlithified sediments. The components identified are benthic and planktonic foraminifers, sponge spicules, bryozoan fragments, tunicates, echinoids, radiolarians, and ostracodes. In a broad sense, the term skeletal grain is used to define bioclastic fragments, most likely mollusk and small bryozoans, which we could not recognize in thin section or in grain counts.
Forty samples from representative depths were weighed and diluted in distilled water. The samples were washed and sieved in a 68-µm metal mesh (U.S. Standard). The coarse-grained fraction (>68 µm) was collected, air dried, weighed, and compared with the initial weight. The coarse fraction was then studied for grain composition. Grain counts (400 per sample) were done by using a stereoscope at a magnification of 40x on a 1 mm x 1 mm colored grid constructed on a cotton paper and pasted on filter paper. All grains were picked from the sample and placed on covered paper slides using a thin brush.
Twenty thin sections were investigated for grain composition under a Nikon petrographic microscope using a Hacker Instruments counter. Two hundred points per thin section were counted. The point counter was set at a step length of 0.5 mm at 20x magnification. Grains or matrix centered in the objective were counted.
Forty-three samples from cores were analyzed for concentrations of aragonite, high-magnesium calcite (HMC), low-magnesium calcite (LMC), dolomite, and quartz by X-ray diffraction (XRD). A small amount (~0.5 to 1.0 g) of sample was mixed with distilled water and placed on a glass using a plastic pipette. The powdered smear mount of the sample was then allowed to dry at room temperature and placed in a Scintag PADV X-ray diffractometer at 40 Kv and 50 mA housed at the S.W. Bailey X-Ray Diffraction Laboratory at the Department of Geology and Geophysics, University of Wisconsin-Madison. The peak areas for each relevant mineral were determined by scanning a smear mount between 24 and 32°2
(CuK
radiation). Percentage composition was calculated following methodology established by Peter Swart (University of Miami) and taking into account the ratio of peak areas from the samples and standards. Standards, also provided by Peter Swart, were run each time a new set of samples was analyzed. The samples are assumed to be composed only of dolomite, LMC, HMC, and aragonite.
