112-9 Improved mapping of shallow geology: ground-based geophysics to support airborne electromagnetics.

Session: Geophysics in Investigating and Exploring for Mineral, Energy and Groundwater Resources (Posters)

Poster Booth No.: 243

Presenting Author:

Lillian Drager

Authors:

Drager, Lillian¹, Fanning, Aiden², Kiene, Lani³, Ortman, Caleb⁴, Young, Steven⁵, Balikian, Riley⁶, Thomason, Jason F.⁷, Mwakamanyale-Gilkie, Kisa⁸, Malone, David H.⁹

(1) Illinois State University, Normal, Illinois, USA, (2) Illinois State University, Normal, Illinois, USA, (3) Illinois State University, Normal, Illinois, USA, (4) Illinois State University, Normal, IL, USA, (5) Illinois State Geological Survery, University of Illinois, Champaign, Illinois, USA, (6) Illinois State Geological Survey, University of Illinois, Champaign, IL, USA, (7) Illinois State Geological Survey, University of Illinois, Champaign, IL, USA, (8) Illinois State Geological Survery, University of Illinois, Champaign, Illinois, USA, (9) Illinois State University, Normal, IL, USA,

Abstract:

Electrical resistivity tomography (ERT) and ambient seismic data, analyzed using the horizontal-vertical spectral ratio (HVSR) technique, were gathered to refine an existing interpretation of the bedrock surface topography and shallow geology in northern Illinois. Recently-acquired helicopter time-domain electromagnetic (HTEM) data give new insights into subsurface geologic features. The distribution of unconsolidated geological material and the relief of the local bedrock topography are important controls on the shallow groundwater flow system in the study area. Thus, we enhanced the interpretation of these HTEM data using ground-based geophysical data. HVSR data were acquired to refine bedrock topography, and the ERT data imaged materials above bedrock. We collected ~7 kilometers of ERT data across a local deeply incised bedrock valley and its tributaries. We also acquired closely-spaced (160 meters) HVSR soundings coincident with the ERT profiles. The interpretations help better define local bedrock tributary topography and better characterize the geometry of shallow sand and gravel aquifers in the valley itself. We calibrated these data with local water well records and geologic core descriptions to help ground-truth the newly acquired HTEM data. Collectively, ground-based geophysical data, coupled with geologic test-holes and HTEM data, greatly improved our understanding of local aquifers and water resources. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9917

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