CHARACTERIZING QUATERNARY SEDIMENTS FOR MULTIUSE DECISION MAKING

With the increased demand for geologic information and the proliferation of sophisticated desktop computing capabilities, the need for Quaternary scientists to provide a complete characterization of sediment assemblages is more critical than ever if geologic information is to be fully utilized. A recent 3D mapping project in central Illinois demonstrates the range of applications that can be addressed in an area with a complex glacial succession, and emphasizes the data quality that is required. Using over 500 data points, we: 1) created a 3D lithostratigraphic model of the mapping area and used it to generate a series of maps and visualizations for basic lithostratigraphic understanding; 2) cut profiles through this 3D model along alternative highway alignments to evaluate the underlying sediment distribution for alternative highway corridors; 3) described the distribution of sands and gravels to assist in development of the required Environmental Impact Statement for road construction; and, 4) documented the textural characteristics of each unit to assist various construction design efforts. In addition, the 3D lithostratigraphic model can be used with transition probability and Markov chain models to develop 3D hydrofacies/hydraulic conductivity models for use in groundwater flow and contaminant transport projects, and aggregate resource potential can be more accurately assessed based on facies descriptions and sand-and-gravel geometry developed from the model. Detailed information about the Quaternary succession was required to create these predictive tools, including: 1) stratigraphic correlation of driller’s logs and outcrop descriptions; 2) detailed lithologic characterization for each unit (i.e., facies, matrix texture, size and frequency of clasts, the occurrence and characteristics of cementation, etc.); 3) observations or conceptual models of textural changes within facies assemblages comprising each stratigraphic unit; 4) observation or conceptual models of spatial and geometric relationships between facies assemblages based on stratigraphic correlation between outcrops and driller’s logs; 5) conceptual models of depositional environments; and 6) evaluation of the uncertainty in the data and subsequent uncertainty within maps, cross sections, and conceptual models.