Interpretation of Depositional Processes from Sedimentary Structures in the Cardium Sand

Abstract

ABSTRACT Sedimentary structures in the Cardium Sand record both primary processes of transport and deposition and secondary reworking of the sediment by burrowing organisms. Primary stratification records a dominance of low but constant fluid motion resulting in unidirectional sediment movement at the sediment-water interface. Sedimentary structures recording fallout of sand from suspension and large scale cross-bedding, representing subaqueous dune bedforms, occur only locally. Burrowing is common and has often destroyed primary stratification wherever sand and clay form thinly interbedded sequences. This indicates agitated and aerated water bottoms and low sedimentation rates. Restricted and less aerated conditions existed locally between sand bodies, where trace fossils of non-burrowing organisms living on the sediment surface predominate. Individual sedimentary structures can be interpreted in terms of the process of their formation, but identical processes occur in many environments. However, associated suites of sedimentary structures record the final and dominating processes acting on the sediment prior to final burial, and the vertical succession of these suites reflects the changing pattern of processes with time. Where progradation occurs this vertical succession also reflects the lateral distribution of processes. Thus, vertical succession provides the key to understanding sequential and areal distribution of environmental processes and, together with the areal distribution of lithofacies, leads to the reconstruction of the paleogeographic environment. Interpretations in this paper are in harmony with previous interpretations of the Cardium Sand as a shoal complex in a shallow shelf sea subject to tidal currents.