Lying within an arid climatic belt La Posta Soil Profile #3 consists of from bottom to top (1) an R-horizon composed ofhypidiomorphic granular granodiorite (Q33P60,), (2) a 5.08-cm-thick C-horizon composed of partially altered granodioritic material(Q33F60K7,), and (1) a 2032-om-thiok dark brovm plant-supporting A-horizon (Q41P52K7). Previous work has shown that the C and A horizons are depleted in Ca, Na, Sr, and Ba relative to the unweathered R-horizon. This result has been interpreted to be the result of dissolution and removal of plagioclase during the development of the C and A horizons. Using a 10-step statistical protocol I evaluated the statistical significance of the above chemical changes. The results of my work suggest that between the R and C horizons Si, Ca, K, Na, Ba, Zn, Rb, and Sr show a statistically significant loss in elemental mass while Fe shows a gain at the 95% confidence level. These results translate into an overall loss in total mass of -7.6%+/-5% per 100 grams of rock. Between the R and A horizons Si, Ca, Mg, Na, P, Ba, Zr, Ga, Zn, and Sr show a statistically significant loss in elemental mass while Mn and Y show a gain at the 95% confidence level. These results translate into an overall loss in total mass of -10%+/-6% per 100 grams of rock. Thus, the results of my work support previous studies that show that even in an arid climate there is evidently sufficient moisture to produce significant degradation and removal of plagioclase during pedogenesis.
