Difference between revisions of "Magnetotellurics case history: Precambrian overthrust (Northwestern Colorado)"

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==Survey results==
 
==Survey results==
  
[[file:applying-magnetotellurics_fig16-7.png|thumb|{{figure number|1}}An 11-station MT profile across the thrust. Drafted from data from Mills.<ref name=ch16r5 />]]
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[[file:applying-magnetotellurics_fig16-7.png|thumb|300px|{{figure number|1}}An 11-station MT profile across the thrust. Drafted from data from Mills.<ref name=ch16r5 />]]
  
 
The MT station near the drill hole (see diagram [[:file:applying-magnetotellurics_fig16-7.png|Figure 1]]) shows a thin, near-surface conductor on top of the resistive Precambrian thrust sheet. This is a wedge of Quaternary and [[Tertiary]] sediments. Beneath the thrust, a thick conductive section of Cretaceous sediments is observed.
 
The MT station near the drill hole (see diagram [[:file:applying-magnetotellurics_fig16-7.png|Figure 1]]) shows a thin, near-surface conductor on top of the resistive Precambrian thrust sheet. This is a wedge of Quaternary and [[Tertiary]] sediments. Beneath the thrust, a thick conductive section of Cretaceous sediments is observed.

Revision as of 20:14, 13 May 2014

Exploring for Oil and Gas Traps
Series Treatise in Petroleum Geology
Part Predicting the occurrence of oil and gas traps
Chapter Applying magnetotellurics
Author Arnie Ostrander
Link Web page
Store AAPG Store

MT can be used in an overthrust environment to delineate conductive sediments beneath a resistive thrust plate. It is often difficult to acquire good-quality seismic data in an overthrust area where high-velocity (high-resistivity) rocks overlie low-velocity (low-resistivity) sediments.

The Precambrian overthrust in the Bear Springs area of northwestern Colorado is an example.[1]

Survey results[edit]

Figure 1 An 11-station MT profile across the thrust. Drafted from data from Mills.[1]

The MT station near the drill hole (see diagram Figure 1) shows a thin, near-surface conductor on top of the resistive Precambrian thrust sheet. This is a wedge of Quaternary and Tertiary sediments. Beneath the thrust, a thick conductive section of Cretaceous sediments is observed.

Figure 1 is an 11-station MT profile across the thrust.

Structural details[edit]

These data provide the following structural details:

  • Thickness of Quaternary and Tertiary cover
  • Thickness of Precambrian thrust sheet
  • Thinning of Cretaceous sediments to the south
  • Depth to top of Paleozoic sediments
  • No differentiation between Paleozoic and basement

A very detailed subsurface structural map could be obtained in this area using a 3-D grid, controlled-source MT survey depicting the Precambrian/Cretaceous thrust contact and the top of the Paleozoic section.

See also[edit]

References[edit]

  1. 1.0 1.1 Mills, A., 1994, Zephyr Geophysical Services, personal communication.

External links[edit]

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Magnetotellurics case history: Precambrian overthrust (Northwestern Colorado)
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