Calcareous Upper Pleistocene Lowstand Deposits Indicate Shelf/Slope Tectonic Instability

Abstract

Calcareous deposits, including shell, hash, and oolites, have been recorded in Upper Pleistocene lowstand deposits seaward of major rivers such as the Mississippi and the Ganges. These calcareous sediments indicate a major reduction or cessation of terrigenous deposition during lowstand/glacial maximum. Extensive high-energy sediments, including coarse sands and gravels, can bracket thin, low-energy, fine-grained calcareous deposits within lowstand sequences. These various sequences may indicate up to three orders of magnitude of variations in deposition rates. Summarizing glacial lake outbursts/rapid stream rerouting suggests that during final deglaciation there could have been massive outflows at multiple decade to century intervals. Continental glacial oscillations throughout the entire glacial maxima could also have produced massive, short-term floods and deposition rates. Such swings in deposition rates must impact on geologic processes within the underlying sedimentary wedge. Processes impacted include (but are not limited to) compacting, faulting, dewatering, diapiric motion, diagenesis, and heat generation.