QUASI-FLEXURAL FOLDING OF PSEUDO-BEDDING

A prominent limestone formation within the Pindos Group (exposed on Mt. Lykaion, Peloponnese) displays pervasive evenly spaced pseudo-bedding produced during burial diagenesis in late Cretaceous. The pseudo-bedding is expressed by primary stylolitic surfaces lined with insoluble residue and marked by cm-scale teeth oriented essentially normal to true bedding. Pseudo-bedding is especially pronounced in outcrops due to deep weathering of insoluble residue. Stylolite formation was driven by high stress concentrations at grain contacts under gravitational loading. Stylolites evolved through mass transfer creep involving material dissolution, diffusion, and reprecipitation. Apparent bedding contacts are actually welded contacts. Individual stylolite surfaces and pseudo-beds are seen in large outcrops to wedge out laterally. Evenness of pseudo-bedding is a function of self-organized feedback during dissolution creep. Layer-parallel shortening of the pseudo-beds is recorded in short transverse secondary tectonic stylolites, each confined to individual pseudo-beds and oriented perpendicular to the pseudo-beds. Teeth of these tectonic stylolites are oriented parallel to pseudo-bedding. The folding that followed layer-parallel shortening may appear to be wholly flexural-slip, with magnitude of slip a function of pseudo-bed thickness and dip. However, high resistance to shear along primary stylolite surfaces, and the lateral ‘wedge-outs’ of pseudo-beds, made it impossible for shortening by folding to be accommodated exclusively by flexural-slip. Diffusive mass transfer compensated via pressure dissolution of the limestone. The folding thus is ‘almost’ or ‘partly’ flexural slip, and conforms to quasi-flexural folding, a rarely-cited category of folding in the Donath and Parker (1964) classification. Where slip surfaces along pseudo-bed surfaces abruptly tip out, or where friction along them was excessively high, the quasi-flexural mechanism at Mt. Lykaion relied on buckling, mass interpenetration of pseudo-beds, stylo-faulting, stylo-duplexing, and mass dissolution to make up for slip deficit. Disharmony, a characteristic of quasi-flexural folding, reflects the abrupt spatial transformations from slip-dominated to dissolution- and buckling-dominated structures.