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Figure 4. Photomicrographs of mudstone, Tulare 34-1, depth interval--7655.5-7657.7 feet.

Left: Overview of texture and porosity in laminated mudstone. Clay-rich matrix hosts abundant silt, carbonaceous stringers, microfossils, and abundant phosphatic debris (arrow). Magenta epoxy fills several layer-parallel-microcracks, some of which may be formed by core relaxation and dehydration. Clay matrix is comparatively tight. Scale bar = 0.5 mm. Plane-polarized light. (40×).

Right: Higher-magnification view of silty mudstone texture illustrates an abundance of discontinuous, horizontal microfractures and patches of microporosity (magenta). Close examination reveals that these microporous lenses (m) are not as clayey and are presumably composed of micro- or cryptocrystalline silica. Microfractures at the top of view are likely induced by dehydration. Also note abundance of pyrite and carbonaceous debris. Scale bar = 0.2 mm. Plane-polarized light. (100×).