Holocene soils and relict paleosols, southern coast ranges,California, USA  

作　　者：W.D.NETTLETON B.R.BRASHER E.C.BENHAM O.A.CHADWICK 

机构地区：[1]USDA-NRCS, NSSC, SSL, Lincoln, NE, 68508 and Dept. of Geography, U. C. Santa Barbara, CA

出　　处：《Chinese Science Bulletin》1999年第S1期15-19,共5页

摘　　要：Thirty-nine soils were studied on Holocene and late Pleistocene geomorphic surfaces.Granodiorite, sandstone, and alluvium derived from these rocks are the parent materials. Climateis Mediterranean. Chamise （Adenostoma faciculatum） is on the drier sites and redwood （Sequoiasempervirens） on the moister sites. Our objectives are twofold, （1） Find if today’s two-season wet-dry, subhumid climate explains the general noncalcic nature of the soils, or if not （2） accept thattheir noncalcic nature results from more moist past climates and define some indicator soilproperties. The depth to carbonate in the soils formed in calcareous materials on Holocenesurfaces corresponds roughly to the average annual depth of water movement, not to the predictedwettest years. We accept then, that the relict paleosols formed under one or more pluvial cyclesbecause they are free of carbonate below their B horizons. Defined levels of pedon clayaccumulation, dithionite-citrate extractable Fe （Fe_d） accumulation in the B horizons, cationexchange capacity at pH 7 （CEC₇） to clay ratios, and the minimum base saturation at pH 7 （BS₇） inthe pedons are useful properties for separating these relict paleosols from the Holocene age soils.A further evidence of the relict nature of the soils on the Pleistocene surfaces is the weatheringreversal noted in these previously weathered materials.Thirty-nine soils were studied on Holocene and late Pleistocene geomorphic surfaces. Granodiorite, sandstone, and alluvium derived from these rocks are the parent materials. Climate is Mediterranean. Chamise (Adenostoma faciculatum) is on the drier sites and redwood (Sequoia sempervirens) on the moister sites. Our objectives are twofold, (1) Find if today's two-season wet- dry, subhumid climate explains the general noncalcic nature of the soils, or if not (2) accept that their noncalcic nature results from more moist past climates and define some indicator soil properties. The depth to carbonate in the soils formed in calcareous materials on Holocene surfaces corresponds roughly to the average annual depth of water movement, not to the predicted wettest years. We accept then, that the relict paleosols formed under one or more pluvial cycles because they are free of carbonate below their B horizons. Defined levels of pedon clay accumulation, dithionite-citrate extractable Fe (Fe_d) accumulation in the B horizons, cation exchange capacity at pH 7 (CEC_7) to clay ratios, and the minimum base saturation at pH 7 (BS_7) in the pedons are useful properties for separating these relict paleosols from the Holocene age soils. A further evidence of the relict nature of the soils on the Pleistocene surfaces is the weathering reversal noted in these previously weathered materials.

关 键 词：geomorphic surfaces WEATHERING PALEOCLIMATES leaching 

分 类 号：P534[天文地球—古生物学与地层学]