Radiographic Investigation of Laminated and Ripple Cross-Laminated Flysch Sandstones, Ouachita Mountains, Oklahoma

Abstract

ABSTRACT The radiographs of horizontally laminated and ripple cross laminated sandstones from the Paleozoic flysch of the Ouachita Mountains show the very details of their internal structures. The pattern of horizontal laminae inside flute casts is related to the flow direction and, therefore, can be used as a paleocurrent indicator. The current ripples are of three dimensional, truncated, and mostly nonclimbing type, indicating deposition from a traction current rather than from a suspended load. All samples studied document the conformity of paleocurrent directions deduced from internal structures and those measured on sole marks. This means that sole marks were cut by the same currents that deposited the horizontally and cross-laminated sand. The number of smaller and larger changes in the flow regime, such as the multiple alternation of laminae and the change from horizontal lamination into current ripples, evident on radiographs of a single bed, document that periods of sedimentation alternated with periods of non-sedimentation and erosion. There is an open question whether these breaks in sedimentation resulted from fluctuations within one turbidity current or from the long-term activity of different sedimentary processes.