Slump Folds and Early Structures, Northeastern Newfoundland Appalachians

Abstract

Analysis of conditions necessary for submarine slope failure shows that submarine slumping is to be expected in eugeosynclinal belts where rapidly deposited muddy sediments are shocked by earthquakes. The physical properties of the sediments and variability of available stresses during submarine sliding appear conducive to irregular, localized deformation and a similar style of folding. In the Appalachian eugeosynclinal belt of Newfoundland, Upper Ordovician flysch greywacke is characterized by abundant mesoscopic slump folds. These tolds typically display variable style, varying wave lengths, and curvilinear hinges and are localized between undisturbed strata. Axes of slump folds commonly parallel both the paleocurrent directions determined from sole marks and also the early fold axes in preflysch strata, Therefore, the flysch trough is interpreted as an early synclinorial structure of Taconian age having contemporaneous submarine slides. Later, main-phase Acadian folds and cleavage are often concordant with slump-fold axes and axial surfaces; commonly it is difficult to distinguish between mesoscopic slump and Acadian folds. Thus slump folds could be misinterpreted as early or main-phase tectonic structures. These data suggest that the earliest, "" episode of folding in areas of superposed deformation be interpreted cautiously, particularly with regard to origin, extrapolation of scale, regional significance, and variation with respect to structural level. A strict distinction between sedimentary and tectonic structures seems unrealistic because the close relationship of tectonics and sedimentation in mobile belts assures widespread prelithification deformation.