Insights into the ancient Mississippi drainage system from detrital zircons analyses of the modern Mississippi deep-sea fan
Tuesday, 16 December 2014
The modern Mississippi deep-sea fan is a large-scale accumulation of Quaternary sediment deposited in the Gulf of Mexico by the modern Mississippi River via the Mississippi delta. The Mississippi River has a well-characterized drainage system extending across North America from the western Rocky Mountains to the Appalachians in the east. Deep-water sand samples of buried channel-fill and lobe deposits of the Mississippi fan from selected Sites of Leg 96 of the Deep Sea Drilling Project (DSDP) and were integrated with USGS piston core samples from the most recent lobe for detrital zircon U-Pb isotopic analysis. Since the modern Mississippi River has a well-known catchment, the detrital zircon age ‘signal’ observed in the deep-water sediments can therefore be used as an actualistic study of the detrital zircon provenance signatures resulting from modern drainage patterns. Based on this approach, we compare this dataset with published data and observe minor variability in the detrital zircon signature through time. Populations sourced from the Western North American Cordillera are consistent through time in terms of ages, however Paleocene sediments are slightly enriched in Yavapai-Mazatzal zircons sourced from southwestern continental U.S.. Grenville- and Appalachian-derived zircons reflect minor variation in sediment input from the Appalachian Mountains and related deposits in the eastern Mississippi River catchment. When compared to published Upper Jurassic Norphlet formation detrital zircon data, the Paleocene published dataset and the newly acquired modern sands are partly depleted of Appalachian-derived zircons. This paucity in Appalachian age zircon in Paleocene-to-modern sediments suggests a reconfiguration of the Mississippi River drainage prior to Tertiary time. Since this realignment, the Mississippi River drainage has remained relatively unchanged. Piston core samples from the most recent lobe yielded zircons indicating a recent influx of Appalachian sources. The direct correlation of modern deep-sea fan to the modern Mississippi River suggests that longshore sediment transport along the Gulf of Mexico margin may be minor. These results test and refine existing paleogeographic, sediment dispersal, and source-to-sink models for the Mississippi drainage system through time.