The δ13C and δ18O values of well-preserved carbonate rhizoliths (CRs) provide detailed insights into changes in the abundance of C3 and C4 plants in response to approximately decadal-scale changes in growing-season climate. We performed stable isotope analyses on 35–40 CRs sampled at 1-cm intervals from an 18-cm-thick paleosol formed in southern Illinois during Wisconsin interstadial 2. Minimum δ13C values show little variation with depth, whereas maximum values vary dramatically, and average values show noticeable variability; maximum δ18O values vary less than the minimum δ18O values. These findings indicate that a diverse and stable C3 flora with a limited number of C4 grass species prevailed during this interval, and suggest that the maximum growing-season temperatures were relatively stable, but minimum growing-season temperatures varied considerably. Two general patterns characterize the relationships between the δ13C and δ18O values obtained from the 1-cm samples. In some cases, low δ13C values correspond to low δ18O values and high δ13C values correspond to high δ18O values, suggesting that cooler growing-season temperatures favored C3 and warmer growing-season temperatures favored C4 plants. In other cases, low δ13C values correspond to high δ18O values, likely suggesting that wetter growing-season conditions were favorable to C3 plants. The high density of well-preserved CRs in this paleosol provides a unique opportunity to study detailed ecological responses to high-resolution variability in growing-season climate.

Matrix-supported diamicton and uniform to laminated, silty, fine-grained sediment deposited from about 42,500 to 27,600 cal yr B.P. under slackwater conditions nearly filled two caves in southwestern Illinois. At some point, most of the sediment was flushed from the caves and from about 22,700 to 4000 cal yr B.P. floods deposited a drape of sandy and silty sediment on remnant slackwater successions, cobbly alluvium, and bedrock (especially from 7700 to 4000 cal yr B.P.). Clay mineral analyses of the slackwater cave sediment reveal a provenance of chiefly Petersburg Silt, a smectite- and illite-rich proglacial lacustrine unit present in the overlying Illinois Episode glacial succession. Today, remnants of the ancient subterranean slackwater deposits nearly fill several secondary passages and in at least two locations, cover a cobble-mantled strath terrace 1.3 to 1.5 m above active stream channels. Slumping and sinkhole formation appear to have been important mechanisms for deposition of the ancient subterranean deposits. Slumping of these surficial deposits and associated vegetation can occur along the flanks of sinkholes (in addition to sinkhole formation) and enter caves; however, the finer organics, some of them comminuted during transport into the caves, become part of the cave alluvium. This finer organic fraction is the modern analog of the humified organic matter disseminated in slackwater sediment dated in this investigation by radiocarbon methods. Twenty-four 14C ages on humified organic matter provide chronologic control. The δ13C values of the organic matter reflect the proportion of C4-type to C3-type vegetation growing in and around swallets and sinkholes at the time of redeposition. Drought-tolerant C4-type vegetation was more prevalent relative to C3-type vegetation from 42,500 to 31,200 cal yr B.P. compared to conditions from 28,800 cal yr B.P. to the present. The δ13C values are consistent with the results from other investigations of speleothems and organic matter from loessial paleosols.

Four anthraquinones were isolated from the foliose lichen, Lasallia papulosa (Ach.) Llano. Two of the anthraquinones are known compounds, previously isolated from Lasallia papulosa, while the other two were reported previously as secondary metabolites from laboratory-cultured Nephroma laevigatum, and are isolated here for the first time from lichens in their natural habitat. All compounds were characterized by UV spectrophotometry, mass spectrometry, 1H NMR and 13C NMR. The products were identified as 7-chloroemodin, valsarin (7-chloro-5-hydroxyemodin), 5-chloro-1-O-methylemodin and 5-chloro-1-O-methyl-ω-hydroxyemodin.