Detalied magnetotelluric study of the northern part of Subandean fold belt, Bolivia

Abstract

A detailed magnetotelluric survey was carried out in the northern part of Subandean fold belt, Bolivia, with the main goal of better understanding of the geological structure of the sedimentary basin and petroleum system in the study area. An improvement of magnetotelluric technology was developed aimed at better imaging of resistivity structures in fold belt. A new static shift correction procedure and a new multistage unconstrained and constrained 2D inversion workflow was suggested and successfully implemented. In addition, the original 3D inversion approach was developed and its efficiency for fold belt geological settings was shown.Advances in magnetotelluric technology made it possible to obtain new geological information about the structure of the sedimentary cover in the study area. Two resistivity structural levels differing in resistivity were outlined. The boundary between levels corresponds to the top of the Carboniferous-Devonian formations, which is one the principle detachments in the northern part of Subandean fold belt. The topography of the top of the lower structural level does not correlate with structures in the upper structural level and with structures outlined by surface geology in most of the survey area. A large numbers of fault zones are outlined in the upper structural level, narrow anticlines are characterized by complicated structure (palm-tree structures).Magnetotellurics gives the most reliable position of the buried axes of anticlinal disharmonic folds, which opens up the possibility of constructing more reliable geological models using joint inversion of magnetotelluric data together with other geophysical data, first of all seismic data. Application of magnetotellurics in fold basins as complimentary to 2D seismic geophysical technology gives possibility to increase reliability of geological interpretation.