Pressure-solution deformation of the purgatory conglomerate, rhode island (u.s.a.): quantification of volume change, real strains and sedimentary shape factor

Abstract

Pressure solution has caused substantial volume redistribution within the Purgatory Conglomerate from Rhode Island. Material has been removed from quartzite cobble surfaces parallel to the fold axes and mostly redeposited as fibrous pressure shadows at the long axis terminations of the cobbles. In the hinges of folds, 23% of the mean cobble volume has been removed, and in highly deformed and overturned fold limbs up to 55% volume reduction has occurred. The initial cobble shape and orientation can be measured at an undeformed locality and the deformation path can be easily deduced; thus these are real cobble volume reductions. Apparent volume losses (initial shapes not removed) range from 70% to 89%. Real strains for cobbles (axial ratios ranging from 1:0.65:0.38 to 1:0.47:0.15) have values of e x , e y , e z which range from 0%, −20%, −11% to 0%, −37%, −42%, respectively, depending on structural position. The conglomerate itself has been extended parallel to the fold axes (e r), but the extension is not recorded by the cobble shapes.