| Summary: | Plate 1 Relative abundance clay size CaCO3; Plate 2 Weight percent clay size CaCO3; Plate 3 Relative percent illite; Plate 4 Relative percent expandable; Plate 5 Relative percent chlorite; Plate 6 Relative percent kaolinite. Base map source not given Clay mineral analyses were performed on 392 bottom samples of recent marine sediments that were collected as part of an environmental study conducted by the Bureau of Land management during the 1975-76 academic year. Relative abundances of illite, expandable clay minerals, chlorite and kaolinite were determined by semiquantitative x-ray diffraction analytical procedures. Abundance of clay-size calcite was also determined semiquantitatively from x-ray diffraction patterns. Relative abundances of clay minerals and calcite were plotted on maps and contoured to show distribution patterns. Clay minerals have been shown to be detrital in nature, derived from the adjacent continental landmass and islands. Coccolithophorida as well as benthonic and planktonic foraminifera are the principal if not sole source of the CaCO3 present in the clay fraction of recent sediments. The interaction of several factors controls distribution of clay minerals and clay-size calcite in recent marine sediments of the California Continental Borderland: (1) bathymetry, (2) variations in clay mineral grain size, (3) variations in abundance in source area (both CaCO3 and clay minerals, (4) major ocean currents, and (5) near-shore wave controlled currents (including onshore/offshore components and longshore components. The major relationship between clay-size CaCO3 and clay minerals is a masking effect each has on the other. Close to the continent the high influx of clay minerals in sediment from rivers effectively masks the presence of calcite. On the outer banks and ridges, the influx of terrigenous clay minerals is diminished owing to increased distance from shore—and as result, organically-derived calcite becomes the dominant constituent of the clay-size sediment fraction. San Diego State ...
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