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Pedogenic Transformation of Fractured Granitic Bedrock, Southern California

^a Jones & Stokes, 2600 V Street, Sacramento, CA 95818 USA
^b Soil & Water Science Program, Dep. of Environ. Sci., Univ. of California, Riverside, CA 92521-0424 USA

View larger version (42K): [in a new window]   Fig 1 Schematic representation of weathered bedrock morphology at the study site showing the location and frequency of intact and bulk samples, and the relative positioning of the five morphologic zones (fill, coating, rind, matrix rind, and matrix) surrounding a typical joint fracture. Fracture dimensions are approximately to scale

View larger version (226K): [in a new window]   Fig 2 Photomicrograph (plane polarized light) of (a) the Cr1 matrix, showing rock-controlled fabric, parallel linear alteration of biotite (B), dissolution pitting of feldspars (F), and clustered distribution patterns of angular quartz grains separated by microcracks and planar voids (pv) infilled with illuvial clay; (b) the Cr3 matrix, showing root channels (rc) contained within planar voids, illuvial clay coatings (cc) and infillings (ci), and root tissue (rt). Photomicrograph (plane polarized light) of (c) the boundary between the matrix rind and fracture rind zones in the Cr1 horizon (MR/R), showing the gefuric c/f related distribution pattern of the fracture rind, the parallel referred orientation pattern (pr) of platy biotite grains in the fracture rind relative to the vertical axis of the joint fracture, a contorted biotite grain (B) in the fracture rind, and sand-sized quartz grains (Q) at the boundary between the matrix-rind and fracture-rind zones fragmenting along planes of weakness corresponding to infilled planar voids (pv); (d) a bow-like, contorted biotite grain in the Cr1 rind; (e) the most common type of fabric in the BCrt rind, showing the gefuric c/f-related distribution pattern, the strong parallel referred orientation pattern of platy biotite and elongate quartz and feldspar grains relative to vertical axis of the joint fracture, and a root channel (rc) running along the boundary between the matrix-rind and fracture-rind zones, (f) the second, less common type of fabric in BCrt fracture rind, showing the gefuric c/f related distribution pattern and crack (ck) and incipient subangular blocky microstructures. Note: photomicrographs c, d, e, and f are oriented so that the vertical axis of the joint fractures is parallel with the long axis of the photomicrographs

View larger version (42K): [in a new window]   Fig 3 Relative proportion of macroporosity (root channels + planar voids) and void coatings and infillings in the matrix, matrix rind, and fracture-rind zones of each weathered bedrock horizon. Error bars are for the entire value bar, (i.e., for macroporosity plot, error bar is for the mean value of channels + planar voids), and represent one standard deviation about the mean. Macropore 0.1-mm diam

View larger version (40K): [in a new window]   Fig. 4 Citrate-bicarbonate-dithionite extractable Fe (Fed) content of the soil and weathered bedrock at the study site. Value bars for a given horizon that are inscribed with different letters differ significantly (P 0.05). Error bars represent one standard deviation about the mean. Error bars are not visible on scale shown. n = 1, and therefore standard deviation could not be calculated

View larger version (36K): [in a new window]   Fig. 5 The OC content of the soil and weathered bedrock at the study site. Value bars for a given horizon that are inscribed with different letters differ significantly (P 0.05). Error bars represent one standard deviation about the mean. . Error bars are not visible on scale shown