Item Number: SR55
$3.00
Format(s)
Quantity

ABSTRACT: Measurements of the physical properties of the basement complex from well samples, cores, and geophysical logs of deep tests in Indiana, Illinois, and Ohio show : (1) density values from 2.57 to 2.81 gm/cm3 fro granites, 2.86 gm/cm3 for basalt, and 2.70 to 2.90 gm/cm3 for andesites; (2) low magnetic susceptibility for basement rocks (generally less than 0.001 emu), with the highest value 0.010 emu for a gabbro in LaGrange County, Ind.; (3) seismic velocities ranging from 14,113 to 18,868 ft/sec; and (4) apparent electrical resistivity of 7 to 1,000 ohm-meters for the logged intervals. Geophysical surveys of basement features depend in part on predicting contrasts in physical properties between the basement and the overlying Mount Simon Sandstone (Cambrian). Studies of electrical resistivity, porosity, velocity, and gamma-ray logs show that the contact between the Mount Simon Sandstone and the basement complex is a mappable horizon in the northern and eastern parts of Indiana. The density contrast between the Mount Simon Sandstone and the basement complex ranges from 0.1 to 0.2 gm/cm3, and magnetic-susceptibility contrasts range from 0.0 to approximately 0.007 emu. These low contrasts indicate that only major topographic features on the basement are observable by gravity and magnetic surveys. Therefore, the principal sources of gravity and magnetic anomalies observed throughout the state are considered to the lithologic contrasts within the basement complex. If the sources of the anomalies are near the top of the basement complex, the basement structural configuration can be obtained by standard depth calculations. Velocity contrasts between the Mount Simon and the basement complex were used to generate synthetic seismograms that demonstrate that the contact is a seismically mappable horizon in selected areas.



Rudman, A. J., Rupp, J. A. 1993, Geophysical properties of the basement rocks of Indiana: Indiana Geological Survey Special Report 55, 16 p., 5 fig.


You may also like:

Keywords: Mount Simon Sandstone, geophysics, bedrock

Can't find what you're looking for? Feel free to contact us directly:

Publication Sales Office
Indiana Geological and Water Survey
611 North Walnut Grove
Bloomington, IN 47405-2208
812-855-7636 (phone)
812-855-2862 (fax)
IGSINFO@indiana.edu

IGS Return Policy

All sales are final. Materials may not be returned after they have been accepted by the customer. Any discrepencies in mail orders must be reported to IGWS within 10 days of receipt of order.

The Indiana Geological and Water Survey will refund the purchase price and sales tax of products if returned with the original sales receipt within 10 days of receipt of order. Refunds will be issued with the same method of payment as indicated on the original receipt except for cash purchases, which will be refunded by check. Items must be returned in the same condition as purchased. Refunds on digital products and services are not allowed, except for defective media such as CD-ROMs, flash drives, and so on. The customer is responsible for paying shipping costs to return items.