Submarine canyon morphology records river dynamics and seascape evolution, Pleistocene Mississippi canyons

Utilizing time- and depth-migrated 3D seismic-reflection data, we mapped the basal unconformities of ten Pleistocene submarine canyons on the present-day Louisiana shelf. Excluding the Bryant and modern-day Mississippi canyon, these features have not previously been mapped or described in detail. Despite significant variability in the overall canyon shape, with incision depths of 0.2–1.1 km, widths of 6–12 km, and upstream incision lengths of 40–100 km from the shelf edge, the basal thalweg widths remain consistent, ranging between 200 m and 250 m. This suggests a similar sediment input for all ten systems: the paleo-Mississippi River. Consequently, we interpret these canyons to be a record of Mississippi River migration across the Pleistocene coastal plain.

We measured canyon morphologies (i.e., cross-sectional areas, incision depths, and thalweg longitudinal profiles) to interpret the spectrum of canyon maturity and longevity within this succession. Radiocarbon dating indicates that the modern Mississippi Canyon initiated between 50,000 and 30,000 BP, remaining active until 7500 BP. This age control provides a benchmark for assessing the longevity of ancestral Mississippi canyons based on morphology. Deep, wide incisions, like for the modern Mississippi Canyon, indicate longer-lived systems of sufficient duration to develop a mature axial channel belt with larger average cross-sectional areas. Conversely, shallower and narrower incisions represent shorter-lived systems that were abandoned before a wider, deeper channel belt could evolve.