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Geomorphic and Stratigraphic Records of the Composite Evolution of Submarine Channels

Abstract

To gain a better understanding of fundamental submarine channel processes and products, we explore geomorphic and stratigraphic records of deep-sea channelized systems through the lenses of modern Earth surface and latest Quaternary continental margins of the west coast of North America, and outcrops of the Cretaceous Magallanes Basin, Chile. Channelized sedimentary systems offshore of the west coast of North America show a breadth of geomorphology and stratigraphic architecture, including channel reaches of varying sinuosity, levees, terraces within channels, and sediment waves in incipient channels and along thalwegs of well-developed channels. Repeat bathymetric surveys of submarine channels in fjords of British Columbia and the Monterey Canyon underscore the transience of fine-scale detail in channelized geomorphology, and sedimentary processes likely active during channel evolution, such as the frequent, multi-phase bed reworking, local deposition, and bypass of turbidity currents. Submarine channel deposits of the Tres Pasos Formation, Chile, include uniquely preserved thin-bedded and fine-grained channel margin units, the deposits of which drape or lap onto the composite edge of the channelform, as well as scours of diverse scales. These characteristics reveal a complex, multi-phase and multi-scale history of incision and bypass of turbidity currents. The stratigraphic evidence for dynamic sedimentary processes of channel evolution in this system is consistent with observations of submarine channels offshore of the west coast of North America. These geomorphic and stratigraphic records provide evidence of the full channel evolutionary cycle, from inception through protracted maintenance by predominantly bypassing sediment gravity flows, to terminal infill with sediment. The primary function of submarine channels is sediment transfer; the stratigraphic record is biased by the sand-rich products of shorter-lived channel filling and abandonment. Our integrated approach of deciphering channelized sedimentary processes, based on modern and ancient analogs, provides a more complete understanding of fundamental submarine sediment-routing processes, as well as insights into channel connectivity and facies heterogeneity.