Thickness Maps as Criteria of Regional Structural Movement

Abstract

A map depicting the thickness of a sequence of rocks between surfaces that were once flat or relatively flat records the structural movements that occurred between the development of the limiting surfaces. Such an isopachous map is essentially a structure map of the first surface at the time of the second. The accuracy with which such maps reveal the structural movements that took place during the interval depends on how closely the limiting surfaces approached a plane. The deformation is most accurately revealed where the confining surfaces were depositional. Erosional surfaces of low topographic relief may be used to reveal regional warping of broad areas. The relation of the sequence of rocks to underlying and overlying formations determines the time of movement. Isopachous maps that include sequences of formations whose thicknesses were separately controlled by conflicting patterns of folding express a composite of both movements and reveal neither.