Geology topics

L. D. McFadden

Publications and source records attributed to L. D. McFadden.

6 recordsLinked to original sources

USGS2017

Influence of late Quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont, Eastern Mojave Desert, California

Radiocarbon dating of late Quaternary deposits and shorelines of Lake Mojave and cation-ratio numerical age dating of stone pavements (Dorn, 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 clay- and 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 increased 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. ?? 1987.

Quaternary Research↗

USGS2017

Rates of soil development from four soil chronosequences in the southern Great Basin

Four soil chronosequences in the southern Great Basin were examined in order to study and quantify soil development during the Quaternary. 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. ?? 1991.

Quaternary Research↗

USGS2017

New optically stimulated luminescence ages provide evidence of MIS3 and MIS2 eolian activity on Black Mesa, northeastern Arizona, USA

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.

Arizona↗

USGS1992

Morphology and genesis of carbonate soils on the Kyle Canyon fan, Nevada, U.S.A.

The physical and chemical properties of soils formed in an arid climate on calcareous alluvium of the Kyle Canyon alluvial fan, southern Nevada, were studied in order to infer the rates and relative importance of various soil-forming processes. These studies included field and microscopic observations and analyses of thin sections, major oxides, extractable iron, and clay minerals. The results are interpreted to reflect five major pedogenic processes: (1) The calcic horizons and calcretes of Kyle Canyon soils form by precipitation of CaCO 3 , derived from eolian dust and alluvium, as clast coats, matrix cement, and massive layers. (2) The A and uppermost B horizons are essentially dust-derived, for they contain large amounts of detrital material not present in the alluvial parent material, and their major-oxide content is similar to that of modern dust. (3) Clay particles are translocated from A into B horizons. (4) Iron-bearing minerals in the near-surface B horizons are slowly oxidized. (5) Carbonate and aluminosilicate grains are both displaced and replaced by pedogenic CaCO 3 ; the silica released by replacement of aluminosilicates may be locally precipitated as amorphous or opaline silica and (or) incorporated into newly formed palygorskite and sepiolite. Rates of soil development at Kyle Canyon are approximate due to uncertainties in age estimates. Some soil field properties change at rates that are similar to rates for soils formed in rhyolitic parent material near Mercury, Nevada. The rate of accumulation of CaCO 3 (3–5 g m −2 yr −1 ) at Kyle Canyon is an order of magnitude faster than that near Mercury, but is comparable to rates calculated for soils in southern New Mexico and Utah.

Nevada↗

USGS1991

Calcic, gypsic, and siliceous soil chronosequences in arid and semiarid environments

We studied three soil chronosequences in the western USA to compare the development of calcic, gypsic, and siliceous soils through time. We compared calcic soils from the Silver Lake playa, southeastern California, gypsic-calcic soils from the Kane Fans in Big Horn County, Wyoming, and siliceous-calcic soils from Forty-mile Wash in southwestern Nevada. In these areas, carbonate, gypsum, and opaline silica appear to be derived primarily from eolian additions and, in advanced stages typical of old soils, are dissolved and precipitated as diagnostic calcic or petrocalcic, gypsic or petrogypsic, and duripan soil horizons. These three precipitates produce somewhat similar morphologic characteristics through time. Morphological stages progress from discrete coatings under clasts, to matrix and around clasts, to significant coatings of clasts and cementation of matrix, to laminar caps above plugged horizons in cases of carbonate and silica. Significant differences among the three soil types include development of color, change of pH, and the depth to which the precipitates begin to accumulate. The tops of gypsic horizons occur below the tops of calcic horizons in simple leaching regimes; the depth to the tops of siliceous horizons is more closely related to the presence and development of argillic horizons.

Conference Paper↗

USGS1990

Brunhes chron excursion/polarity episode recorded during the late pleistocene, Albuquerque Volcanoes, New Mexico, USA

All basaltic lava flows of the Albuquerque Volcanoes (lat.: 35.2°N, long.: 253.2°E), Albuquerque-Belen Basin, New Mexico, record a short excursion/polarity episode. K-Ar isotopic age determinations (weighted average: 155 ± 47 ka) and evaluation of soil profiles on flow surfaces suggest the late Pleistocene ( circa between 250 and 80 ka) as the time of extrusion. Results from 63 sites in a minimum of eight flows yield a mean direction of D = 101.1°, I = -36.1°, α 95 = 1.2° (α 1 95 = 0.7, α 2 95 = 1.2), k = 2219 ( N = 8 flows) and a corresponding virtual geomagnetic pole position (VGP) of 354.1°E, 20.2°S, dp = 0.8°, dm = 1.4° ( A 1 95 = 0.5, A 2 95 = 1.4), and VGP angular standard deviation (ASD) = 1.8°. The unusual magnetization in flows of the Albuquerque Volcanoes is carried by fine-grained [single-domain (SD) and/or pseudo-single-domain (PSD)] low-Ti magnetite and is apparently not a function of complex sub-solidus alteration of magnetic phases. Underlying baked soils contain a relatively low coercivity magnetization with directions comprising two groups. One is roughly antipodal to the lava remanence; the other intermediate between the lava remanence and present field direction. Because all flows yield statistically indistinguishable directions, a field directional path clearly cannot be defined. At the precision level of our age determinations, the Albuquerque feature may correlate with other short polarity episodes or excursions of late Pleistocene age (e.g., Blake or Jamaica). Though characteristically limited in directional morphology, well-dated polarity episodes (i.e. sub-chrons) and excursions recorded in volcanic rocks may provide information on the frequency of significant dynamo instabilities.

New Mexico↗