Abstract

Spaced cleavage formed by rock dissolution can represent major amounts of shortening parallel to bedding; much so-called fracture cleavage is of this origin. We classify the solution cleavage developed in Mesozoic pelagic limestones of the Umbrian Apennines into four intensity types (weak, moderate, strong, very strong) on the basis of qualitative attributes and mean spacing of cleavage surfaces. Shortening can be determined from imbricated chert beds and reaches 50% in rocks with very strong cleavage. In the Umbrian Apennines, solution cleavage is commonly associated with detachment thrusts. We describe an example in which the dissolution mechanism “damaged” the rock beneath a thrust by creating closely spaced discontinuities; fragments bounded by these discontinuities were torn up and incorporated in a nearly chaotic shear zone as the thrust sheet moved forward.

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