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The thickness and character of basal mixing zones in loess with different underlying materials and in different climates were studied in Louisiana and Idaho. Peoria loess in Louisiana is underlain by sandy braided stream deposits, clayey alluvium, and an older Sicily Island loess. In Idaho, materials underlying loess deposits include glacial till, basalt, Pliocene sediments, and a paleosol developed in loess. Multiple criteria, divided into primary and secondary indicators, were used in the identification of basal mixing zones. The primary indicators of basal mixing zones were field morphology and particle‐size distribution. Secondary indicators include total elemental analyses, clay mineralogy, CaCO3 equivalence, exchangeable cations and soil reaction listed in order of decreasing sensitivity. In Louisiana, basal mixed zones varied in thickness from 61 to 124 cm while in Idaho, basal mixed zones were between 8 and 40 cm thick.

The Florida Parishes of southeastern Louisiana (Fig. 1) are bounded on the west by the Mississippi River, on the east by the Pearl River, on the north by the Louisiana-Mississippi state line, and on the south by the Mississippi River deltaic plain. Principal cities include Baton Rouge and New Orleans.

We reconstruct the depositional history of a late Holocene archaeological site, Cowpen Slough (16 CT 147) in the Catahoula Lowlands of east Central Louisiana, and we place that history in regional context. Procedures including grain-size analysis, field descriptions of soil horizons, x-ray diffraction of clay minerals, and total element analysis are employed to build a description of depositional units and parent material present in onsite sediment samples and off-site subsurface core samples. To infer source, results of tests are integrated with radiocarbon dates and Saucier's chronology for this section in the Lower Mississippi Valley. We suggest that between 6000 and 4790 B.P. the Arkansas was the source of sediment present in the archaeological deposit. After 4790 B.P., sediments were deposited by the Mississippi river system. INTRODUCTIONPart of the development of archaeology as a discipline is tied to the earth sciences (Grayson, 1983;Rudwick, 1972). Consequently, as noted by Stein (19871, it is not surprising that archaeologists have a sustained interest in geoarchaeological problems. They use the law of superposition to reconstruct relative chronologies; they employ geomorphology and sedimentology to reconstruct the physical setting of archaeological deposits.According to Stein (19871, interests in site formation processes and midrange theory have led archaeologists to ask more sophisticated questions of archaeological sediments. She suggests that sedimentary characteristics of texture, composition, and structure can inform archaeologists as to source, transport agent, depositional environment, and post-depositional alterations in the deposits.Although not specifically directed toward site formation processes or midrange theory, this paper presents the type of analysis and integration suggested by Stein (1985Stein ( , 1987. Our presentation has several goals.