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One lithologic category that typically cannot be determined from observation of the split core surface alone is sediment composition. However, this can be determined by examining a small (toothpick‐tip sized) amount of sediment under a binocular microscope and matching the observed grain types to categories of known grain types. This method is called smear slide analysis. The main grain categories that compose marine sediment are minerals and microfossils. Some of the most common grain types are shown in Figure 2.3.

FIGURE 2.3. Photos of minerals, volcanic glass, and microfossils as seen through a petrographic microscope. Bar scale is 50 μm (0.05 mm). Images are from the IODP Digital Reference for Smear Slide Analysis of Marine Mud (Marsaglia et al., 2013, 2015; http://iodp.tamu.edu/publications/TN.html). a = sand‐size quartz grain with conchoidal fracture. b = rectangular grains are feldspar minerals; also shown are quartz grains and rock fragments. c = large flakes of mica (biotite and chlorite), along with smaller quartz and feldspar grains, and opaque rounded grains of pyrite. d = clay minerals, with much larger opaque pyrite grains and a calcite crystal (corner). e = volcanic glass (ash). f = calcareous nannofossils; g = elongate pennate diatoms and round centric diatoms, and diatom fragments; h = Three whole planktic foraminifera, and one very large porous foraminifera fragment, surrounded by calcareous nannofossils; i = radiolaria, with centric diatoms in the background; j = silicoflagellate; k = large sponge spicule surrounded by diatom fragments.

This exercise primarily focuses on composition and texture data observed in smear slides from samples taken from the cores you described in Part 2.2. These data are reported in Table 2.2. The composition data are estimates of the relative abundances of specific grain types (i.e. minerals, microfossils, tiny rock fragments) observed in the smear slides. The textural data are estimates of the relative percentages of sand‐, silt‐, and clay‐sized grains based on smear slide observation. Table 2.2 also includes one type of data that is not from the smear slides – the presence of pebbles observed on the split core. Pebbles (which are large rock fragments) are too large for inclusion in smear slides, but their presence is often indicative of a particular lithology as you will learn in this exercise.

Data Analysis

1 Go to Table 2.2 (smear slide data) and find the row(s) of data that correspond to smear slide samples taken from your core(s). Note that this should be the same core(s) assigned to you in Part 2.2. What are the minerals and fossils in your core(s)? List the mineral and microfossil components below, and circle the photos in Figure 2.3 that show what these grains look like when viewing smear slides through a microscope.

ID of your assigned core(s) (e.g. 112‐687A‐2H)	Minerals present	Microfossils present

1 The composition and texture data from the smear slide data in Table 2.2 will serve as the primary means for determining the lithologic name of the sediment (Mazzullo and Graham, 1988). Read the Box below that describes important information about using the Decision Tree. Then use the Decision Tree (following pages) to determine the lithologic name of the sediment in your core(s):ID of Your Assigned Core(s) __________________________Lithologic Name of the Sediment in the Core(s) __________________________