Jointing, Linears, and Lineaments - the Basement Connection

S. Parker Gay, Jr.

Although some geologists understand the basic connection between basement faults, jointing, linears, and lineaments, many do not, and a few even disparage the idea of a connection, in spite of well-documented proofs dating from the 1960's and 1970's. Briefly, small meter-scale movements of basement faults under recently lithified sedimentary rock create joints. These joints are parallel and cover large areas because the underlying basement faults (actually shear zones) are parallel and cover large areas. Most areas of earth's continental crust are underlain by three or more basement fault sets, thus resulting in multiple directions of jointing. However, some joints are not related to basement and result from later stresses in the sedimentary section that create folding and faulting. Basement-created joints are not evenly spaced, and where they are more numerous due to inhomogeneities in the sedimentary section and/or where groundwater is channeled along them, airphoto and Landsat lineaments result - features which are parallel to, but not necessarily coincident with, the underlying causative basement faults. Additional movement of some of the basement faults will, of course, result in fracturing and the formation of faults, folds, stratigraphic features, linears, and lineaments that are directly coincident with the underlying faults. Later migration of ore fluids and gas and oil into these structures can result in economic deposits important to man.

AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012