dsolread.doc	5/1/95

Quaternary Soils and Dust Deposition in Southern Nevada and 
California
Marith C. Reheis, Jonathan C. Goodmacher, Jennifer W. Harden, Leslie D. McFadden, Thomas 
K. Rockwell, Ralph R. Shroba, Janet M. Sowers, and Emily M. Taylor 
Abstract
  Eolian dust constitutes most of the pedogenic material in late Pleistocene and Holocene 
soils of many arid regions.  Comparison of the compositions and influx rates of modern dust with 
the eolian component of dated soils at 24 sites in southern Nevada and California yields 
information on:  (1) the composition and influx rate of dust in late Pleistocene and Holocene soils, 
(2) paleoclimate and its effects on the genesis of aridic soils, especially with regard to "dust 
events", (3) the timing and relative contribution of dust from playa sources versus alluvial sources, 
and (4) the effects of accumulation of fines in soil horizons.
The A and B horizons of soils formed on gravelly alluvial-fan deposits in the study area are 
similar to modern dust in grain size, content of CaCO3 and salt, major oxides, and clay 
mineralogy; thus, they are interpreted to consist largely of eolian dust.  The major-oxide 
compositions of the shallow soil horizons are nearly identical to that of the modern dust, but the 
compositions of progressively deeper horizons approach that of the parent material.  The clay 
mineralogy of modern dust at a given site is similar to that of the Av horizons of nearby Holocene 
soils, but is commonly different from the mineralogies of deeper soil horizons and of the Av 
horizons of nearby Pleistocene soils.  These results are interpreted to indicate that (1) dust both 
accumulates and is transformed in Av horizons with time, and (2) that clay minerals can be 
transformed in only 10,000 years or less.
Changes in soil-accumulation rates provide insights into the interplay of paleoclimate, dust 
supply, and soil-forming processes.  Modern dust-deposition rates are more than large enough to 
account for middle and late Holocene soil-accumulation rates at nearly all sites.  However, the early 
Holocene soil-accumulation rates in areas near late Pleistocene pluvial lakes are much higher than 
modern rates and clearly indicate a dust-deflation and -deposition event that caused rapid formation 
of fine-grained shallow soil horizons on late Pleistocene and early Holocene deposits.  We interpret 
late Pleistocene soil-accumulation rates to indicate that dust-deposition rates were low during this 
period but that increased effective moisture during the late Wisconsin favored translocation of clay 
and CaCO3 from the surface to deeper in the soil profile.  Calculated pre-late Pleistocene rates are 
very low in most areas, mainly due to a pedogenic threshold that was crossed when accumulations 
of silt, clay, and CaCO3 began to inhibit the downward transport of eolian material, but in part due 
to erosion.
INTRODUCTION
  The presence of eolian dust in soils and the relative contribution of dust to soil formation 
in both arid and humid areas has been debated for decades.  Most researchers now agree that dust 
is a ubiquitous component of soils formed in arid areas, although some argue that calcareous dust 
does not contribute significantly to the content of pedogenic calcium carbonate in some localities.  
Many studies have also shown that eolian dust is an important component of soils in subhumid to 
humid areas.  In arid and semiarid areas, eolian dust also plays a significant role in geomorphic 
processes.  For example, desert pavements, ubiquitous features in arid regions, form when eolian 
dust accumulates beneath a surface layer of stones; this process acts to smooth initially rough 
surfaces.  Once formed, however, the reduced porosities of dust-rich horizons lead to increased 
runoff and erosion, which increases surface roughness.  Detailed studies of dust influx facilitate 
studies of paleoclimate based on modelling of soil-forming processes such as translocation of 
pedogenic carbonate.
Most research on the eolian component of soils has focused on identifying the presence of 
dust and estimating its proportion relative to soil parent materials and in-situ weathering products.  
Approaches have included (1) assuming that most or all of a specific pedogenic component is dust-
derived because it is not present in the parent material and is not likely to be formed in large 
quantities by chemical weathering of the parent material (such as CaCO3 and gypsum); (2) 
estimating the content of dust in soils versus the parent material using trace elements or isotopes; 
(3) comparing the mineralogy of dust and soils with parent material; and (4) using 
micromorphological techniques to identify foreign components or characteristic shapes of grains.
Despite general agreement on the importance of dust to soil genesis, few studies have 
compared modern rates of dust deposition to estimated amounts of dust in soils of known age to 
compare the compositions and deposition rates of modern dust to dust in soils.  Quantitative 
comparisons are important to studies of soil genesis, paleoclimatic reconstruction from soil 
properties, and soil chronosequences used to estimate the ages of surfaces and deposits.  For 
example, soils that formed downwind of a large dust source may be significantly better developed 
than soils of the same age that formed in sheltered areas.
A project to study modern dust deposition in southern Nevada and California was initiated 
in 1984 to provide data on modern dust composition and influx rates for use in a numerical model 
relating soil carbonate to paleoclimate and in soil-chronosequence studies in the southern Great 
Basin and Mojave Desert (fig. 1) in support of tectonic and stratigraphic investigations for the 
Yucca Mountain Project.  In this paper, we relate the composition of modern dust to soil properties 
and compare modern rates of dust influx with late Pleistocene and Holocene rates estimated from 
soils at 24 sites in southern Nevada and California.  A companion paper relates modern dust data 
from these and an additional 31 sites to climate, source area, and source lithology.

List of files in the database and general contents:

All *.doc files are in Word for Windows 1.0, all *.xls files are in Excel 3.0.

dsolread.doc	Modified abstract and introduction for soil-dust paper (in review) and list of files.
dsolproc.doc	Sampling and laboratory procedures for soil datafiles; equations; references for 
procedures and for some data from published sources
dsolfoot.doc	Footnotes, comments, and definitions of abbreviations and acronyms in soil files.

dsolloc.xls	Site data for soil profiles:  soil locations, type and lithology of parent material, 
corresponding dust-trap number, and estimated climate data.
dsoldes.xls	Field descriptions of soils.
dsindprn.xls	Calculated soil-development-index values of soils.
dsolab.xls	Laboratory data for soil horizons.
dsolpw.xls	Calculations of soil profile weights of silt, clay, CaCO3, and salt.
dsolox.xls	Major-oxide data for Kyle Canyon, Silver Lake, and Wilson Creek soils.
dsolmin.xls	Clay mineralogy of soils (mostly culled from cited publications).
averate.xls	Average soil accumulation rates of silt, clay, CaCO3, and salt.
intrate.xls	Interval soil accumulation rates of silt, clay, CaCO3, and salt.
intrtdev.xls	Averages and standard deviations of interval soil accumulation rates.