Introduction to Small~scale Geological Structures

The small-scale structures referred to in this publication are those structures of tectonic origin that can be observed with the naked eye in the field. Their scale varies broadly between that of the hand-specimen to that of the exposure, or even mountainside. Such structures are the visible effects of rock deformation caused by local stresses and movements which have been induced in the rocks by external tectonic forces of possibly unknown origin. Recognition of these minor structures, and appreciation of their origin and significance assist the field geologist to elucidate the larger-scale geological structures of his area. Commonly some can be used in deciphering the order of strati graphic succession in regions of strongly-folded unfossiliferous beds; and, in ground which has suffered superposed tectonic movements, the minor structures may provide evidence of successive phases or events in the tectonic history. The work contains descriptions of the more common varieties of small-scale tectonic structures, the different ways in which these structures may have been formed, and the limitations of the conclusions which can be drawn from their observation in the field. Gilbert Wilson June 1981 Acknowledgements An outline of much of the material given in this book was delivered at the 'Cinquieme Conference Gustave Dewalque' to the Societe Geologique de Belgique in 1958 and was published in the annals of the society in 1961.

Inhalt
1 Introduction.- 2 Stress and strain.- 3 Structural symmetry.- 4 Structure and stratigraphical succession.- 5 Structures in brittle rocks: tension fractures and shear zones.- 6 Rock cleavage and schistosity: generalities.- 7 Fracture cleavage and strain-slip cleavage.- 8 Flow cleavage, schistosity and lineation.- 9 Boudinage.- 10 Drag-folds and parasitic folds.- 11 Mullion and rodding structures.- 12 Superposed minor structures.- 13 Minor structures and large-scale tectonics.- 14 Conclusions.