Mid-continental USA Gridded Maps of Loess Thickness: Readme file
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              World Data Center for Paleoclimatology, Boulder
                                and 
                   NOAA Paleoclimatology Program
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NOTE: PLEASE CITE ORIGINAL REFERENCE WHEN USING THIS DATA!!!!!

NAME OF DATA SET: Mid-continental USA Gridded Maps of Loess Thickness
LAST UPDATE: 6/2001 (Original Receipt by WDC Paleo)  

CONTRIBUTORS: Karen E. Kohfeld and Daniel R. Muhs


IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2001-049

SUGGESTED DATA CITATION: Kohfeld, K. E. and Muhs, D. R., 2001,
Mid-continental USA Gridded Maps of Loess Thickness, 
IGBP PAGES/World Data Center for Paleoclimatology 
Data Contribution Series #2001-049.  
NOAA/NGDC Paleoclimatology Program, Boulder CO, USA. 


ORIGINAL REFERENCE: Kohfeld, K. E., and Harrison, S. P., 2001. 
DIRTMAP: The geologic record of dust. 
Earth-Science Reviews, Vol. 54 (1-3) (2001) pp. 81-114.


GEOGRAPHIC REGION: Mid-continental North America
PERIOD OF RECORD: Approximately 34 - 10 ka BP


LIST OF FILES: 
Readme_Kohfeld2001.txt (this file), 
Table1_codes.xls, Table2_data.xls (Microsoft Excel Format),
Table1_codes.txt, Table2_data.txt (Tab-delimited ASCII format).

DESCRIPTION:  
Late Wisconsin (Peoria) Loess of the mid-continental USA represents the 
thickest deposition of last glacial loess, ranging from trace amounts 
(< 1 m) to accumulations as thick as 40-50 m in parts of western Nebraska 
and western Iowa. Accumulation of Peoria Loess coincides primarily with 
the last glacial period, although accumulation was not synchronous across 
the entire mid-continental region. The maximum-limiting of Peoria Loess 
range from approximately 30-34 ka (organic matter from the uppermost 
Roxana Silt and Gilman Canyon Formation) to 20-22 ka in other regions.  
The actual time period of deposition varies from region to region 
(see e.g. Muhs and Bettis, 2000; Bettis et al., submitted).

Although a map of loess thickness across the mid-continental USA has 
been made (Thorp and Smith, 1952; republished in generalized form by 
Ruhe, 1983), this compilation is now more than 50 years old and has 
never been assembled as a digital data set, allowing for a 
representation of loess as a geomorphological feature that can be 
directly compared with regional model simulations over North America. 
The purpose of digitizing loess thickness is to provide this information 
as part of the DIRTMAP data base (Kohfeld and Harrison, 2001), 
to demonstrate spatial changes in accumulation across the 
mid-continental USA, and to make it available to the geomorphology, 
Quaternary and earth system modeling communities.  

DATA DOCUMENTATION

Loess thicknesses were digitized from twelve maps produced for the 
U.S. Geological Survey (USGS) on a 0.1 x 0.1 degree grid. These maps 
are part of the USGS Quaternary Atlas Series and have a scale of 1:1,000,000.  
However loess thicknesses for some of the map are presented as insets at 
considerably smaller scale.  In addition, although some maps have new 
compilations of loess thickness (e.g. Hallberg et al., 1991; 
Swinehart et al., 1994), at 1:1,000,000, others are simply derived from 
the earlier compilation of Thorp and Smith (1952). Original maps were produced 
using either a Lambert Conformical Conic (Copeland et al., 1988; 
Farrand et al., 1984; Holbrook et al., 1990; Lineback et al., 1983; 
Miller et al., 1988; Whitfield et al., 1993) or a Modified Polyconic 
(Denne et al., 1993; Goebel et al., 1983; Gray et al., 1991; 
Hallberg et al., 1991; Pope et al., 1990; Swinehart et al., 1994) Projection. 
The USGS maps cover the general region of Peoria Loess accumulation in the 
mid-continental USA, spanning a 1500-km-long east-west belt from Nebraska 
to Ohio (102-84°W) and a 1500-km north-south belt from Wisconsin to Indiana 
(30-46°N).  Aeolian sand in Nebraska is excluded from this map, as they are 
not included on the survey map for this region. However, where aeolian sands 
were included as part of the USGS maps, they were incorporated into this 
dataset (e.g. Wisconsin).

Three data codes represent thickness of the Peoria Loess. Compilations for the 
USGS maps were completed primarily by state geological surveys and do not have 
uniform thickness intervals. As a result, the complete coding is extremely 
detailed (1-32 divisions).  We have preserved this original coding (Figure 1), 
in order to be as consistent as possible with the original data.  We have also 
provided two condensed codes in which similar depth intervals are incorporated 
into the same code (Figures 2 and 3).  The explanations of the data codes are 
provided in Table 1.  Table 2 contains the digitized data.



Table1_codes.xls contains the following columns: 
Thickness	Group Code 1	Condensed Code 2	Condensed Code 3
"Thickness" is the interval provided on the original map.  
The codes relate the information provided in Table 2 to the original loess 
thicknesses provided in the USGS maps.

Table2_data.xls contains the following columns: 
Longitude	Latitude	Map	Group Code 1	Condensed Code 2	Condensed Code 3
Longitude and Latitude provide location information for each point.
"Map" provides information about the original map area from which the 
data were digitised.  The codes are related to the original loess thicknesses 
provided in the survey maps in Table 1.

Figure 1 - Uses all coded data
Figure 2 - Uses Condensed Code 2
Figure 3 - Uses Condensed Code 3



ADDITIONAL REFERENCES:
Bettis , E. A., III, Muhs, D. R., Roberts, H. M. (submitted, 2001) 
The last glacial record of loess deposition in the North American 
midcontinent, Quaternary Science Reviews.

Copeland, J., Charles W., Rheams, K. F., Neathery, T. L., Gilliland, 
W. A., Schmidt, W., William C. Clark, J., and Pope, D. E. (1988). 
Quaternary Geologic Map of the Mobile 4° x 6° Quadrangle, United States. 
In "Quaternary Geologic Atlas of the United States, 
Miscellaneous Investigations Series." (G. M. Richmond, D. S. Fullerton, 
and D. L. Weide, Eds.). U.S. Geological Survey.

Denne, J. E., Luza, K. V., Richmond, G. M., Jensen, K. M., Fishman, W. D., 
and E. G. Wermund, J. (1993). Quaternary Geologic Map of the Wichita 
4° x 6° Quadrangle, United States. In "Quaternary Geologic Atlas of the 
United States, Miscellaneous Investigations Series." (G. M. Richmond, 
and A. C. Christiansen, Eds.). 
U.S. Geological Survey.

Farrand, W. R., Mickelson, D. M., Cowan, W. R., and Goebel, J. E. (1984). 
Quaternary Geologic Map of the Lake Superior 4° x 6° Quadrangle, United States 
and Canada. In "Quaternary Geologic Atlas of the United States, Miscellaneous 
Investigations Series." (G. M. Richmond, and D. S. Fullerton, Eds.). 
U.S. Geological Survey.

Goebel, J. E., Mickelson, D. M., Farrand, W. R., Clayton, L., Knox, J. C., 
Cahow, A., Hobbs, H. C., and Matt S. Walton, J. (1983). Quaternary Geologic Map 
of the Minneapolis 4° x 6° Quadrangle, United States. In "Quaternary Geologic 
Atlas of the United States, Miscellaneous Investigations Series." 
(G. M. Richmond, and D. S. Fullerton, Eds.). U.S. Geological Survey.

Gray, H. H., Bleuer, N. K., Lineback, J. A., Swadley, W. C., Richmond, G. M., 
Miller, R. A., Goldthwait, R. P., and Ward, R. A. (1991). Quaternary Geologic 
Map of the Louisville 4° x 6° Quadrangle, United States,. In "Quaternary 
Geologic Atlas of the United States, Miscellaneous Investigations Series." 
(G. M. Richmond, and D. S. Fullerton, Eds.). U.S. Geological Survey.

Hallberg, G. R., Lineback, J. A., Mickelson, D. M., Knox, J. C., Goebel, J. E., 
Hobbs, H. C., Whitfield, J. W., Ward, R. A., Boellstorf, J. D., Swinehart, J. B., 
and Dreeszen, V. H. (1991).  Quaternary Geologic Map of the Des Moines 4° x 6° 
Quadrangle, United States. In "Quaternary Geologic Atlas of the United States, 
Miscellaneous Investigations Series." (G. M. Richmond, D. S. Fullerton, and 
A. C. Christiansen, Eds.). U.S. Geological Survey.

Holbrook, D. F., Gilliland, W. A., Luza, K. V., Pope, D. E., Wermund, E. G., 
Miller, R. A., Bush, W. V., Jensen, K. N., and Fishman, W. D. (1990). 
Quaternary Geologic Map of the Vicksburg 4° x 6° Quadrangle, United States. 
In "Quaternary Geologic Atlas of the United States, Miscellaneous Investigations 
Series." (G. M. Richmond, D. S. Fullerton, and D. L. Weide, Eds.). 
U.S. Geological Survey.

Lineback, J. A., Bleuer, N. K., Mickelson, D. M., Farrand, W. R., and Goldthwait, 
R. P. (1983). Quaternary Geologic Map of the Chicago 4° x 6° Quadrangle, 
United States. In "Quaternary Geologic Atlas of the United States, Miscellaneous 
Investigations Series." (G. M. Richmond, and D. S. Fullerton, Eds.). 
U.S. Geological Survey.

Miller, R. A., Maher, S. W., Charles W. Copeland, J., Rheams, K. F., 
LeNeathery, T., Gilliland, W. A., Friddell, M. S., Nostrand, A. K. V., 
Wheeler, W. H., Holbrook, D. F., and Bush, W. V. (1988). Quaternary Geologic Map 
of the Lookout Mountain 4° x 6° Quadrangle, United States. In "Quaternary Geologic 
Atlas of the United States, Miscellaneous Investigations Series." (G. M. Richmond, 
and D. S. Fullerton, Eds.).  U.S. Geological Survey.

Muhs, D. R., and Bettis, E. A. (2000). Geochemical variations in Peoria Loess of 
western Iowa indicate paleowinds of midcontinental North America during last 
glaciation.  Quaternary Research 53, 49-61.

Pope, D. E., Gilliland, W. A., and Wermund, E. G. (1990). Quaternary Geologic Map 
of the White Lake 4° x 6° Quadrangle, United States. In "Quaternary Geologic Atlas 
of the United States, Miscellaneous Investigations Series." (G. M. Richmond, 
D. L. Weide, and D. W. Moore, Eds.).  U.S. Geological Survey.

Ruhe, R. V. (1983). Depositional environment of Late Wisconsin loess in the 
midcontinental United States. In "Late-Quaternary Environments of the United States." 
(J. H. E. Wright, Ed.), pp. 130-137. The Late Pleistocene. 
University of Minnesota Press, Minneapolis.

Swinehart, J. B., Dreeszen, V. H., Richmond, G. M., Tipton, M. J., Bretz, R., 
Steece, F. V., Hallberg, G. R., and Goebel, J. E. (1994). Quaternary Geologic Map 
of the Platte River 4° x 6° Quadrangle, United States. In "Quaternary Geologic Atlas 
of the United States, Miscellaneous Investigations Series." (G. M. Richmond, Ed.). 
U.S. Geological Survey.

Thorp, J., and Smith, H. T. U. (1952). Pleistocene eolian deposits of the 
United States, Alaska, and parts of Canada: National Research Council Committee 
for the Study of Eolian Deposits. Geological Society of America, New York.

Whitfield, J. W., Ward, R. A., Denne, J. E., Holbrook, D. F., Bush, W. V., 
Lineback, J. A., Luza, K. V., Jensen, K. M., and Fishman, W. D. (1993). 
Quaternary Geologic Map of the Ozark Plateau 4° x 6° Quadrangle, United States,. 
In "Quaternary Geologic Atlas of the United States, Miscellaneous Investigations 
Series." (G. M. Richmond, and D. L. Weide, Eds.). 
U.S. Geological Survey.