Eastern Section Meeting

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What's Lurking in the Basement? Recent insight into basement features in Indiana


The basement rocks of Indiana belong to the Eastern Granite-Rhyolite Province which is believed to be primarily anorogenic granite. The nature of the rocks that immediately overly basement is not well understood due to a paucity of data, although several deep wells have indicated the presence of mafic rocks and possible Precambrian sediments. Outside of several large fault zones, few major structures have been identified in Indiana's basement.

In 2012 CountryMark undertook a project to study the relationships between basement structure and petroleum accumulations in the shallower section. A review of Indiana area public domain aeromagnetic and gravity data was followed by the recording of a high resolution aeromagnetic (HRAM) survey over several counties in SW Indiana. The HRAM data identified a large hook-shaped anomaly, along with a linear basement anomaly which indicate a possible northwest extension to the Mt Carmel fault beyond its current mapped extent. Three ~20 mile long seismic lines were recorded in order to further investigate the nature of these magnetic anomalies. Interpretation of the seismic suggests the ‘hook’ feature is a plunging Precambrian anticline, with an approximate depth to the peak of the anticline of 7,000 below ground surface. Despite this depth, there are several positive correlations between this basement structure and potential structural traps in the shallower section. Seismic also indicates the presence of a distinct reflector (a possible unconformity) below the Mt Simon Formation. Below this possible unconformity are layered reflectors that appear to onlap against the Precambrian anticline. Do these deep reflectors represent Precambrian sediments? The Precambrian Middle Run Formation of Ohio has recorded gas and oil shows. Could there be potential for petroleum in the Precambrian of Indiana?