STRATIGRAPHY AND SEDIMENTOLOGY OF THE ALLUVIAL FLOOR OF WESLEY CHAPEL GULF, ORANGE COUNTY, INDIANA

Wesley Chapel Gulf (a.k.a Elrod Gulf) is a distinctive karst collapse feature with an alluviated floor deposited as the Lost River karst drainage network floods. Clyde Malott described the Gulf, considered probable origins of the feature, and estimated sediment thickness of the alluvial floor (1932, 1952). Powell (1986) built upon Malott's work, linking the rise responsible for the alluvial floor of the Gulf to the Lost River. We present data on the thickness of sediments, and a generalized stratigraphic framework for the alluvial floor as determined from two soil cores. We also hypothesize about the rates of alluviation of the Gulf floor based upon examination of paleosols and sediment analysis. Core A, approximately 76.2 m (250 ft) from the rise, encountered limestone bedrock at a depth of 10.4 m (34 ft). Core B, 15.3 m (49.5 ft) from the rise, recovered 10.2 m (33 ft) of sediment before encountering saturated sediments not recoverable with our equipment. Examination of the sediment cores revealed the presence of two units, an upper unit, and a lower unit, each with distinctive characteristics and separated from one another by a minor paleosol that marks an unconformity. The two units indicate a probable shift in sediment deposition, perhaps attributable to climate or anthropogenic influences. The lower unit exhibits thin (1 mm) varve-like bedding, with alternating organic-rich silt and low organic loam. The well preserved thin bedding and the lack of distinctive paleosols is interpreted as evidence for frequent flood events that allowed deposition to outpace the homogenizing effects of pedogenesis. The upper unit is a sandy to silty loam, with localized silt beds and organic sediments. Minor paleosols in this unit suggest short-lived depositional hiatuses that allowed some pedogenesis. Comparison of particle size data between Cores A and B indicates that sediments become finer distal from the rise, interpreted as evidence of the influence of the Lost River rise on alluvial deposition.