42 Geophysics/Geodynamics (Posters)

Added due to amt of discipline abstracts submitted.

Wednesday, 11 March 2026
9:00 AM - 12:00 PM
RCC, Lower Level Hall

Linking Airborne Electromagnetic Resistivity to Grain-Size Variability in Quaternary Sediments of Crowley’s Ridge, Arkansas

Paper number: 42-6
Program: Technical Sessions
Time: 9:00 AM – 9:00 AM

Authors

Abstract

The Mississippi Embayment is a major hydrogeologic and economic resource that supports municipal, agricultural, and industrial water use across the central United States. Increasing extraction pressures have raised concerns over long-term sustainability, prompting new efforts to better characterize subsurface stratigraphy and aquifer architecture. As part of an ongoing investigation, the USGS collected more than 100,000 km of airborne electromagnetic (AEM) data across the Embayment, including high-resolution coverage along and adjacent to Crowley’s Ridge in eastern Arkansas. Although AEM surveys provide continuous imaging of subsurface conductivity, converting those signals into geologically meaningful facies requires calibration with ground-based datasets. 

To support this calibration, continuous cores were obtained from four boreholes drilled adjacent to AEM flight lines and Crowleys Ridge, two in the Eastern Lowlands and two in the Western Lowlands. Detailed descriptions and high-resolution photography of the cores are in progress, and these along with natural gamma and electromagnetic conductivity borehole logs will be used as direct lithologic and geophysical reference points for interpreting conductivity trends observed in the AEM profiles. This project focuses on integrating these datasets to develop an AEM facies model the upper 75 m of stratigraphy by comparing AEM conductivity signatures to gamma responses, physical core descriptions, and visible sedimentologic changes.

The workflow involves compiling AEM conductivity values at ~2–3 m intervals and extracting equivalent depth intervals from gamma logs and core imagery. Gamma logs and core descriptions are then converted to quantitative metrics suitable for comparison, allowing assessment of how conductivity values vary with lithology, grain size, and depth. Preliminary efforts aim to identify consistent relationships between lower conductivity zones and sandier intervals versus higher conductivity responses associated with finer-grained or more clay-rich units, though analysis is ongoing. By comparing these borehole sites the goal is to determine how mappable these relationships are and to establish a calibration approach that can be applied beyond the borehole control.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411896

© Copyright 2026 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.