Continental Terraces and Related Cratonic Accumulations
Multiple rapid sea level changes of the past two million years have resulted in major changes in the processes and structures that prevailed for tens of millions of years of pre-Quaternary time during the building of massive midplate continental margins. These changes have hindered interpretations of preQuaternary, or what may be called normal, growth processes and structures to the extent that fallacious concepts of the genetic processes have evolved. We submit that an idealized non-Quaternary midplate continental margin would have a shore zone of prograding beaches but would be devoid of estuaries. Barriers and lagoons would exist primarily in association with delta complexes. Muddy shelf facies would prevail, as no mechanism exists for moving sands out of the shore zone to the shelf in significant quantities. Slopes would be largely smooth and prograding by slow pelagic, hemipelagic, and low-density turbid layer deposition. Erosion by turbidity currents and slumping would be uncommon and largely restricted to the vicinity of a few large long-lived submarine canyons. Axiomatically, the rise would be poorly developed and appear lobate in the form of discrete deep-sea fans off the canyon mouths. Terrigenous turbidites would be mainly confined to these fans.