THE EVOLUTION OF SECTION CONSTRUCTION METHODS IN THRUST BELTS AND HOW TO PRACTICALLY APPLY THEM

Since Chamberlain’s seminal paper the techniques of section construction have developed to where software packages can do a lot of the tedious graphical constructions. How did we get to where we are now and has this really been progress? This depends on the purpose behind the cross section; there are different motivations behind a section to illustrate a thrust system and a structural model for an exploration well.

During the 1950’s and 1960’s hydrocarbon exploration in the Alberta foothills resulted in papers that integrated surface geology, seismic and well data creating models that predicted deeper structural targets beneath shallower thrust sheets. These models ed to very successful exploration programmes, notably by Shell Canada and left a legacy of publications in which the principles used were elegantly described.

In the 1970’s work by the Geological Survey of Canada resulted in examples of balanced, structurally logical sections. These sections illustrated the power of geometrically correct restorable sections and the insights that they can provide into the evolution of a thrust belt.

The focus of research in the 1980’s became three-fold; (1) the quantification of fold geometries and relationships to thrust geometry, (2) the description of fold thrust belt geometries and the development of terminology and (3) systematic “how to construct and balance sections” guidelines. Many classic papers were published that showed cross-sections through a large variety of the worlds fold and thrust belts and also led to the development of software packages to construct and restore cross sections.

Over the last 20 years the basic concepts have been refined and better sections have been published due to ongoing hydrocarbon exploration, better eismic data becoming available and improved remote sensing techniques.

Thus we now have the technology to construct cross-sections with reasonable efficiency this does not however guarantee that the interpretations produced will be correct. A balanced section is merely a section that is restorable and is therefore geometrically feasible. The construction of a good structural cross-section still requires the integration of all of the available data by a structural geologist, a skill that is enhanced by experience and an appreciation of what is fit for purpose.