Papers by Leslie McFadden
Quaternary Research, 1989
SSSA Special Publication, 1991
Abstract A considerable amount of progress in the understanding of the factors that control the g... more Abstract A considerable amount of progress in the understanding of the factors that control the genesis of calcic soils has been made by integration of field and laboratory studies supplemented by numerical modeling. Modeling of pedogenic carbonate accumulation using a compartment model strategy has produced simulated depth functions similar to those observed in field investigations and emphasizes the significance of varying eolian dust flux and soil pCO 2 on the magnitude and depth of carbonate accumulation. Recent ...
Encyclopedia of Soil Science, Second Edition, 2005
Quaternary Research, 1987
Radiocarbon dating of late Quaternary deposits and shorelines of Lake Mojave and cation-ratio num... more Radiocarbon dating of late Quaternary deposits and shorelines of Lake Mojave and cation-ratio numerical age dating of stone pavements (Darn. 1984) on the adjacent Soda Mountains Piedmont provide age constraints for alluvial and eolian deposits. These deposits are associated with climatically controlled stands of Lake Mojave during the past 15,000 yr. Six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and Piedmont surfaces, as well as on soil-geomorphic data. All but one of these stratigraphic units were deposited in response to time-transgressive climatic changes beginning approximately 10.000 yr ago. Increased eolian flux rates occurred in response to the lowering of Lake Mojave and a consequent increase in fine-sediment availability. Increased rates of deposition of eolian fines and associated salts influenced pedogenesis. stone-pavement development, and runoff-infiltration relations by (1) enhancing mechanical weathering of fan surfaces and hillslopes and (2) forming clayand silt-rich surface horizons which decrease infiltration. Changes in alluvial-fan source areas from hillslopes to piedmonts during the Holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less-permeable soils. Inferred increases in early to middle Holocene monsoonal activity resulted in high-magnitude paleo-sheetflood events on older fan pavements; this runoff triggered Piedmont dissection which, in turn, caused increased sediment availability along channel walls. Thus, runoff-infiltration changes during the late Quaternary have occurred in response to eolian deposition of fines, pedogenesis, increased sheetflood activity in the Holocene, and vegetational changes which are related to many complicated linkages among climatic change, lake fluctuations, and eolian, hillslope, and alluvial-fan processes. C' 1987 University of Washington.
Quaternary Research, 1991
Four soil chronosequences in the southern Great Basin were examined in order to study and quantif... more Four soil chronosequences in the southern Great Basin were examined in order to study and quantify soil development during the Quatemary. Soils of all four areas are developed in gravelly alluvial fans in semiarid climates with 8 to 40 cm mean annual precipitation. Lithologies of alluvium are granite-gneiss at Silver Lake, granite and basalt at Cima Volcanic Field, limestone at Kyle Canyon, and siliceous volcanic rocks at Fortymile Wash. Ages of the soils are approximated from several radiometric and experimental techniques, and rates are assessed using a conservative mathematical approach. Average rates for Holocene soils at Silver Lake are about 10 times higher than for Pleistocene soils at Kyle Canyon and Fortymile Wash, based on limited age control. Holocene soils in all four areas appear to develop at similar rates, and Pleistocene soils at Kyle Canyon and Fortymile Wash may differ by only a factor of 2 to 4. Over time spans of several millennia, a preferred model for the age curves is not linear but may be exponential or parabolic, in which rates decrease with increasing age. These preliminary results imply that the geographical variation in rates within the southern Great Basin-Mojave region may be much less significant than temporal variation in rates of soil development. The reasons for temporal variation in rates and processes of soil development are complexly linked to climatic change and related changes in water and dust, erosional history, and internally driven chemical and physical processes. 0 1991 University of Washington.
Quaternary Research, 2011
Lower slopes of the Sandia Mountains are characterized by granitic corestone topography and weath... more Lower slopes of the Sandia Mountains are characterized by granitic corestone topography and weatheringlimited slopes with thin grusy colluvium and weakly developed soils. In contrast, thick soils with illuvial clay and pedogenic carbonate have developed below aplite outcrops. Aplite is resistant to chemical decomposition, but physically weathers to blocky clasts that enhance surface roughness and erosional resistance of colluvium, promoting accumulation of eolian fines. Thick B horizons on aplite slopes indicate limited erosion and prolonged periods of stability and soil development. Accretion of eolian material limits runoff and prevents attainment of a steady-state balance between soil production and downslope transport.
Quaternary Research, 2011
Eolian deposition on the semiarid southern Colorado Plateau has been attributed to episodic aridi... more Eolian deposition on the semiarid southern Colorado Plateau has been attributed to episodic aridity during the Quaternary Period. However, OSL ages from three topographically controlled (e.g. falling) dunes on Black Mesa in northeastern Arizona indicate that eolian sediments there were deposited in deep tributary valleys as early as 35-30 ka, with most sand deposited before 20 ka. In contrast, the oldest OSL ages for sand sheets fall within the Pleistocene-Holocene climatic transition (~12-8 ka). Thus most eolian sediment accumulated on Black Mesa under climatic conditions that were in general cooler, moister, and more variable than today, not more arid, pointing to a considerable increase in sediment supply.
Quaternary Research, 1992
Geomorphology, 2010
The formation of cracks is a fundamental first step in the physical weathering of rocks in desert... more The formation of cracks is a fundamental first step in the physical weathering of rocks in desert environments. In this study we combine new field data from the Mojave (U.S.), Gobi (Mongolia) and Strzelecki (Australia) deserts that collectively support the hypothesis that meridional cracks (cracks with orientations not readily attributable to rock anisotropies or shape) in boulders or cobbles form due to tensile stresses caused by directional heating and cooling during the sun's daily transit. The new studies indicate that rock size, surface age, and latitude play important roles with respect to their influence on rock fracture. Rock size and pavement surface age exert an influence on the development of rock cracks as the average clast size of mature desert pavements may be at or below the threshold-clast size for thermal cracking of rocks. Latitude-controlled seasonal temperature variations play a key role, as demonstrated by: 1) tightly clustered mean resultant orientations that differ by latitude, as predicted in , and 2) very cold wintertime temperatures and strong diurnal gradients that may favor crack development in wintertime, given the likelihood for strong clast heating during early morning hours. The consistent evidence for meridional cracks in surfaces of diverse age and desert environments, climate, vegetation, and distance of clast transport indicate that directional insolation may play the key role in initially generating and propagating rock fractures, rather than a secondary role as implied in recent field and modeling studies of physical weathering in deserts.
Geology, 1995
ABSTRACT The formation of stone pavements, a ubiquitous gravel armor mantling landforms in arid r... more ABSTRACT The formation of stone pavements, a ubiquitous gravel armor mantling landforms in arid regions of the world, has been previously attributed to erosion by wind and water or alternating shrinking and swelling of soil horizons, implying that gravel is concentrated at the land ...
Geology, 1988
... and Christ, 1965; Drever, 1982; McFadden and Tinsley, 1985; Marion et al., 1985), although th... more ... and Christ, 1965; Drever, 1982; McFadden and Tinsley, 1985; Marion et al., 1985), although the solubility of nonpure carbonates may be lower or higher (Suarez, 1981). Compartment temper-atures are those at which the calcite reactions occur. ...
Geological Society of America Bulletin, 1985
Geological Society of America Bulletin, 1995
... Bigioggero,; Sergio Chiesa,; Andrea Zanchi,; Attilio Montrasio,; and Luigina Vezzoli. The Cer... more ... Bigioggero,; Sergio Chiesa,; Andrea Zanchi,; Attilio Montrasio,; and Luigina Vezzoli. The Cerro Mencenares volcanic center, Baja California Sur: Source and tectonic control on postsubduction magmatism within the Gulf Rift. Geological Society of America Bulletin , September, 1995 ...
Geoarchaeology, 2006
Dozens of Paleoindian sites, including the Boca Negra Wash (BNW) Folsom site (LA 124474), are sca... more Dozens of Paleoindian sites, including the Boca Negra Wash (BNW) Folsom site (LA 124474), are scattered across a basalt plateau (the West Mesa) on the western side of the Albuquerque Basin, and adjacent uplands. The BNW site, like many others in the area, is located near a small (~60 ϫ 90 m) playa basin that formed in a depression on the basalt surface and was subsequently covered by an eolian sand sheet (Unit 1) dated by OSL to ~23,000 yr B.P. Most of the basin fill is ~2 m of playa mud (Units 2 and 3) dating ~13,970 14 C yr B.P. (17,160-16,140 cal yr B.P.) at the sand-mud interface to ~2810 14 C yr B.P. (~2960-2860 cal yr B.P.) at the top. C/N ratios suggest that the BNW playa basin probably held water more often during the Folsom occupation; stable carbon isotope values indicate C3 vegetation was more common as well, but C4 grasses became dominant in the Holocene. Cores extracted from four playa basins nearby revealed a similar stratigraphy and geochronology, documenting presence of wetlands on playa floors during the Paleoindian occupation of the area.
Earth and Planetary Science Letters, Jul 31, 1994
A model is presented describing the factors and processes which determine the measured 14 C ages ... more A model is presented describing the factors and processes which determine the measured 14 C ages of soil calcium carbonate. Pedogenic carbonate forms in isotopic equilium with soil CO 2. Carbon dioxide in soils is a mixture of CO 2 derived from two biological sources: respiration by living plant roots and respiration of microorganisms decomposing soil humus. The relative proportion of these two CO 2 sources can greatly affect the initial 14 C content of pedogenic carbonate: the greater the contribution of ...
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Papers by Leslie McFadden