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Loess Distribution as Revealed by Mineral Variations¹

ABSTRACT

The apparent physical uniformity of various loess deposits has often led in the past to conclusions of uniform composition and constant rate of deposition for loess formations. These assumptions have been used in many evaluations of soil development and in explaining the distribution of various soils. The existence of identifiable increments of characteristic composition within Peoria Loess not only indicates compositional variations but permits evaluation of the regional distribution of individual loess increments. Unique mineralogy (particularly clay-mineralogy) of the loess increments is attributed to major changes in the origin of valley loess source sediments.

The consistent identification and pattern of four distinct zones within Peoria Loess in Illinois east of the Illinois River Valley reveal that the rate of loess deposition has not been constant. Rather, the upper younger loess increments are most dominant and more widely distributed and therefore most important as soil forming material. This implies that the soils of the maturity or development sequence in Illinois have all formed in the same relatively young increment of Peoria Loess. The characteristies of these soils which vary from weakly- to moderately-developed Udolls to very strongly-developed Albaqualfs cannot be attributed to their age differences.

¹ Contribution from the Dep. of Agronomy, Univ. of Illinois, Urbana. Part of a thesis submitted by the senior author in partial fulfillment of the requirements of the Ph.D. degree at the Univ. of Illinois. Presented before Div. S-5 and S-9, Soil Science Society of America, Aug. 19, 1971 at New York, N.Y.

² Formerly Graduate Fellow and Professor, University of Illinois, respectively.

Received for publication August 11, 1972. Accepted for publication December 11, 1972.