QUATERNARY RESEARCH 46, 19–26 (1996) ARTICLE NO. 0040 Absence of Glaciation in Illinois during Marine Isotope Stages 3 through 5 B. BRANDON CURRY Illinois State Geological Survey, 615 E. Peabody Dr., Champaign, Illinois 61820 AND MILAN J. PAVICH United States Geological Survey, Mail Stop 955, National Center, Reston, Virginia 22092 Received October 25, 1995 tope record (and its proxy record of global ice volume) there- A 10 Be inventory and 14 C ages of material from a core from fore do not necessarily coincide with ages from the sediment northernmost Illinois support previous interpretations that this record from Illinois (Fig. 1). The discordance between ma- area was ice free from ca. 155,000 to 25,000 yr ago. During much rine isotope events and Illinois terrestrial records appears to of this period, from about 155,000 to 55,000 yr ago, 10 Be accumu- correlate with volumes of global glacial ice smaller than lated in the argillic horizon of the Sangamon Geosol. Wisconsinan those of large glacial events such as stages 2 and 6 (Shack- loess, containing inherited 10 Be, was deposited above the Sanga- leton, 1987). For example, late Altonian loess (Roxana Silt), mon Geosol from ca. 55,000 to 25,000 yr ago and was subsequently deposited chiefly from 45,000 to 30,000 years ago (McKay, buried by late Wisconsinan till deposited by the Lake Michigan 1979; Curry and Follmer, 1992; Leigh and Knox, 1993) has Lobe of the Laurentide Ice Sheet. The Sangamonian interglacial no distinct deep sea cold-corollary (Fig. 1) and occurred stage has been correlated narrowly to marine oxygen isotope sub- stage 5e; our data indicate instead that the Sangamon Geosol when there was at least 35% less global ice than during developed during late stage 6, all of stages 5 and 4, and early stage maximum stage 2 conditions (Shackleton, 1987). 3.  1996 University of Washington. The Sangamonian interglacial stage has long been corre- lated presumptively with marine isotope stage 5 (Follmer, 1983). However, Richmond and Fullerton (1986) restricted INTRODUCTION the Sangamonian Stage (and implicitly, development of the Sangamon Geosol) to substage 5e (130,000 to 123,000 yr The history of Quaternary climatic change interpreted ago; Martinson et al., 1987). Currently, the only numerical from the sediment record of glaciated midwestern North ages of Sangamonian material in the type area of central America has evolved as understanding of sedimentation pro- Illinois have been determined by electron spin resonance cesses, pedology, and chronology has improved (Leverett, methods (ESR) from the Hopwood Farm locality (Fig. 2). 1899; Frye and Willman, 1973; Ruhe, 1976; Clark et al., Ages of a mastodont molar include 71,000 { 8000 yr, 91,000 1993). For deposits beyond the range of reliable radiocarbon { 12,000 yr, and 120,000 { 15,000 yr depending on the dating (ca. 35,000 yr ago; Curry and Follmer, 1992), lack uranium-uptake model used to calculate the age (Blackwell of numerical ages has resulted in poorly tested correlations et al., 1990). Although the ESR ages fall largely in the range among glaciated midwestern North America successions of stage 5, their uncertainty precludes correlation with any (Clark and Lea, 1986; Kempton et al., 1985; Clark et al., substage of stage 5. Hence, the age of the Sangamonian 1993). Confirmation of correlations is now possible, how- Stage in its type area remains poorly known. ever, as ages determined from relatively recent techniques Critical to assessing the age of the Sangamon Geosol is (e.g., thermoluminescence (TL), aminostratigraphy, electron determination of the age of its Illinoian loessial or other spin resonance, U-series, and 10 Be inventories) are critically glacigenic parent material. Widely assumed to have been evaluated and compared (e.g., Markewich et al., in press). deposited during marine isotope stage 6 (Follmer, 1983), With the exception of the last glaciation, the southern Illinoian sediments have been dated numerically for only margin of the Laurentide Ice Sheet did not necessarily wax two sites in Illinois. At the Hopwood Farm locality (Fig. 2), and wane in sync with other sectors of the ice sheet during ESR ages on Sangamonian enameloid gar scales 0.1 to 1.3 the last two glacial–interglacial cycles (Clark et al., 1993). Ages of climatic shifts indicated by the marine oxygen iso- m below the ESR-dated mastodont molar discussed above 19 0033-5894/96 $18.00 Copyright  1996 by the University of Washington. All rights of reproduction in any form reserved.