MICROMORPHOLOGY AND FABRIC OF SANDY LOAM TILL, WEST-CENTRAL WISCONSIN

Micromorphology of till is reported mostly from fine-grained, loamy tills. We examined thin sections of red, sandy loam, Superior Lobe till from west-central Wisconsin to (1) catalogue micromorphological features found in sandy till, (2) compare sand-grain fabric with pebble fabric, and (3) attempt to gain insight on till genesis from these observations. The till investigated was deposited by the Superior and Chippewa Lobes and has an average sand:silt:clay ratio of 70:20:10.

Micromorphological features identified include predominantly coated and crushed grains, but also unit partings, necking, rotational structure, and tails. None of these features were able to differentiate till units whose genesis had been suggested by other means, such as pebble fabric, stratigraphic setting, and geomorphic occurrence. This suggests to us that many of these features may be inherited from earlier stages of till development.

Sand-grain fabrics show dominant azimuth modes to be parallel to those derived from pebble fabrics. However, fabrics strengths, measured as eigenvalues, show no correlation between pebble fabrics and sand-grain fabrics. Therefore, fabric strength measured from till thin sections reflects different depositional processes than do strengths from pebble fabrics. This observation supports a contention of Benn (1994) that till-depositional processes are different for different grain sizes.