North-Central Section - 39th Annual Meeting (May 19–20, 2005)

Paper No. 14
Presentation Time: 8:00 AM-12:00 PM


WANINGER, Scott E., Geology, Univ. of Southern Indiana, 8600 University Blvd, Evansville, IN 47712 and DURBIN, James M., Geology, Univ of Southern Indiana, 8600 University Blvd, Evansville, IN 47712,

The stratigraphy and sedimentology of morphologically distinct features exposed in a sand quarry in Spencer County, Indiana indicate a complex history of multiple episodes of deposition and support earlier interpretations (Ray, 1965) that the ridges along the eastern wall of Little Pigeon Creek are silt capped dunes. Four informal units were identified in the study area. Unit 1, the lowermost layer, is a 3-4 m thick yellowish brown, thinly bedded (~ 7 cm) silt interbedded with 1-2 mm thick lamina of dark yellowish brown silt. Unit 2 is an 8.3 m thick fining-upward layer that consists of cross-bedded, very fine sand in 7.5 -10 cm thick layers and scattered 2-20 mm thick beds of coarse silt. Ripples and a range of dip angles (7º-33º) occur at various depths within the unit. Unit 3 is a 1.5 m thick silt that contains features such as mottling, ped structure, the presence of calcite, and < 1 mm black concretions that indicate a paleosol that separates Units 3 and 4. Unit 4 consists of a 1.3 m thick layer with bedded sand and silt at its base. Modern soil development obliterates the bedding close to the surface in Unit 4. Changes in lithology, sediment, and bedding structures indicate four episodes of deposition. Sharp contacts between the units indicate relatively short-lived unconformities. The development of a poorly developed paleosol between Units 3 and 4 indicates a depositional hiatus where weathering rates outpaced deposition. Unit 1 is bedded silt deposited in water. Dune sands (Unit 2) covered Unit 1. Silt rich Unit 3 buried Unit 2, and was then altered by pedogenesis. Lastly, sand interbedded with silt blanketed the paleosol before the modern soil developed in Unit 4.