pure and applied geophysics

, Volume 116, Issue 4, pp 913–930

Small faults formed as deformation bands in sandstone

  • Atilla Aydin
Article

DOI: 10.1007/BF00876546

Cite this article as:
Aydin, A. PAGEOPH (1978) 116: 913. doi:10.1007/BF00876546

Abstract

Small faults with displacements of a few millimeters or centimeters are abundant in the Entrada and Navajo Sandstones, in the San Rafael Desert, Utah, where they are important primary structures, preceding the development of large faults with displacements of several meters or tens of meters. The small faults contain no surfaces of discontinuity, rather they occur asdeformation bands about one millimeter and tens or hundreds of meters long, and across which the displacements are distributed. Two zones with different modes of deformation can be distinguished within a deformation band: an outer zone where the matrix, including pores and matrix material, deforms; and an inner zone, about 0.5 mm thick, where the sand grains fracture and further consolidation takes place. Fracturing of the grains is controlled by contact geometry; the grains tend to split into subgrains along lines connecting contact points between the grains. Then the angular subgrains, which are readily fractured, are further granulated and mixed with the matrix. The final product is the deformation band, with much smaller grain size, poorer sorting, and lower porosity than the original parent sandstone. The sandstone on either side of a deformation band is almost undisturbed-fractures are rare there — so that deformation is highly localized within the band. The material within a deformation band apparently strain hardens as a result of the deformation; perhaps this is why the shear displacement across a deformation band is at most a few centimeters.

Key words

Fault structures Deformation bands Entrada and Navajo Sandstores 

Copyright information

© Birkhäuser Verlag 1978

Authors and Affiliations

  • Atilla Aydin
    • 1
  1. 1.Department of GeologyStanford UniversityStanfordUSA
  2. 2.Department of GeologyIstanbul Technical UniversityIstanbulTurkey