Soil-landscape and climatic relationships in the middle Miocene of the Madrid Basin

The Miocene alluvial-lacustrine sequences of the Madrid Basin, Spain, formed in highly varied landscapes. The presence of various types of palaeosols allows assessment of the effects of local and external factors onsedimentation, pedogenesis and geomorphological development. In the northern, more arid, tectonicallyactive arca, soils were weakly developed in aggrading alluvial fans, dominated by mass flows. reflecting high sedimentation rates. In more distal parts of the fans and in playa lakes calcretes and dolocretes developed: the former were associated with Mg-poor fan sediments whitc: the latter formed on Mg-rich lake clays exposed during minar lake lowstands. The nonh-east part of the basin had a less arid climate. Alluvial fans in this area were dominated by stream Aood deposits, sourced by carbonate terrains. Floodplain and freshwater lakc deposits formed in distal areas. The high local supply of calcium carbonate may have contributed to the preferential developmenl on calcretes on the fans. Both the fan and floodplain palaeosols exhibit pedofacies relationships and more mature soils developed in settings more distant from the sediment sources. Palaeosols also developed on pond and lake margin carbonates, and led to the formation of palustrine limestones. The spatial distributions and stratigraphies of palaeosols in the Madrid Basin alluvial fans suggest that soil formation was controlled by local factors. These palaeosols differ from those seen in Quatemary fans. Which are characterized by climatically induced periods of stability and instability

Landform, soil, and plant relationships to nitrate accumulation, Central Nevada

Nitrate (NO3 −1) accumulates in Haplocambids and Torrifluvents in inset fan and fan skirt positions in central Nevada. The soils store as much as 17,600 kg of NO3 −1 N ha−1 within the upper 208 cm. This paper provides an explanation. These Holocene soils receive NO3 −1 N from mineralization of organic matter and other NO3 −1 N sources including snowmelt. The NO3 −1 is delivered to soils in the first part of snowmelt in run-off from the higher surfaces. The last part of the melt and the run-off, when sufficient, serve to move the NO3 −1 out of the root zone. Winter fat (Krascheninnikovia lanata), the most valuable winter grazing plant in the Great Basin, is the common plant on NO3 −1 N rich soils. The soils are loamy or sandy and lack horizons restricting water penetration or biological denitrification zones. Hence, some NO3 −1 is free to leach deeply past plant roots. Playas, wet floodplains, deeply gullied inset fans and well-developed soils accumulate little NO3 −1 except where the latter soils are capped by desert pavements and rarely, if ever become saturated with water. Soils with argillic or petrocalcic horizons or duripans on summits of alluvial fan remnants loose NO3 −1 through denitrification, or incorporate it in plants, commonly accumulating less than 50 kg of NO3 −1 N ha−1. These soils however do accumulate salt as shown by their shadscale saltbush Atriplex confertifolia, bud sagebrush Picrothamnus desertorum, and four-wing saltbush Atriplex conescens shrub cover