NEW INSIGHTS IN THE 3D MAPPING OF THE LEMONT FORMATION IN WILL AND COOK COUNTIES, ILLINOIS

A county with urban, suburban, and rural environments, Will County is located at the confluence of moraines within the Joliet sublobe, including the Minooka Moraine (oldest) as well as the outboard Lake Border Moraine (the Tinley Moraine). Preliminary mapping has identified evidence of three glacial diamictons units: the Yorkville and Haeger Members, Lemont Formation, and the Wadsworth Formation. The Haeger Member, known for its relatively coarse particle-size distribution (from boulders to silt, low clay), and high dolomite content. The Haeger Member occurs in between finer-textured (silty and clayey) diamictons of the older Yorkville Member and younger Wadsworth Formation. The physical characteristics of diamictons comprising the Yorkville and Wadsworth units are similar, both being gray, with little sand, and abundant silt and clay in the matrix. A stratigraphic problem has been tracing the Haeger unit in the subsurface. Where it pinches out to the east and south of the well-known Lemont Section, separating the Yorkville from the Wadsworth units may not be possible. Buried by diamicton of the Wadsworth Formation, determining the southern boundary of the Haeger Member and its associated sorted sediment, is an important aim of an ongoing 3D geologic mapping program. New subsurface data and the discovery of new sections should be allow reassessment of depositional environments, correlation, and extent of the Haeger in this area. A thick unnamed tongue of outwash was consistently found between the Wadsworth Formation and the Yorkville Member in the central part of Will County. If the basal part of this tongue included the Haeger Member, this sand and gravel unit would be correlated with the Beverly Tongue of the Henry Formation. The main objective of this study is to reconstruct the complex successions of ice marginal deposits by a 3D modelling approach, and utilized surface LiDAR data. The model integrates surficial sediments maps and borehole logs using GIS and GeoScene3D.