The grain-size-dependent compositional trends of 25 samples of Holocene plutoniclastic sand produced by the physical and chemical weathering of Cretaceous plutonic rocks in arid, semi-arid, and mediterranean (hot summer) climates were determined during this study. These trends, when compared to similar data from plutoniclastic sands produced in a humid temperate mesothermal climate, suggest that arid, semi-arid, and mediterranean (hot summer) climates produce comparatively little alteration of feldspathic to rock-fragment-rich plutoniclastic material. This conclusion, in conjunction with published data, suggests that a climatic threshold exists, beyond which feldspathic to rock-fragment-rich plutoniclastic debris is readily altered to form a sand enriched in quartz. Current data indicate that the critical climatic threshold lies between the humid temperate mesothermal climate typical of South Carolina and North Carolina, and the arid, humid microthermal, and humid mesothermal climates common to the western United States. Data presented here support the use of the climatic-discrimination diagram of L.J. Suttner and P.K. Dutta, and are generally consistent with the earlier work of A. Basu.

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