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The lower Miocene is a period of significant sediment input to the Gulf of Mexico (GOM) Basin that accompanied tectonic and climatic changes in North America. However, the resulting sediment pathways from continental upland sources to basinal sink remain poorly constrained. We employ detrital zircon (DZ) U-Pb and (U-Th)/He double dating to define both basement provenance and the exhumation histories of detrital source regions.
We have collected samples from outcrops across the northern Gulf, from Texas to Florida, in order to discriminate sediment pathways. Most of our data show a mixture of source terranes, including Oligocene volcanic centers, Cordilleran Arc, Laramide uplifts, Grenville, Mid-Continent, Yavapai-Mazatzal, and Appalachian-Ouachita as major provinces and Wyoming and Superior regions as minor provinces. However, major DZ age peaks vary greatly between different samples, providing a means to differentia drainage systems. Five major sediment input pathways are defined: the Paleo-Rio Grande, Paleo-Red, Paleo-Mississippi and Paleo-Tennessee rivers and a local river system in Florida draining from Appalachians. The Paleo-Rio Grande and Paleo-Red rivers show a significant sediment input from Oligocene volcanic centers, Laramide uplift regions and the Cordilleran Arc, whereas the Paleo-Tennessee River received most of its sediments from Appalachian-Ouachita and Grenville basement. The Paleo-Mississippi River lies within a transitional zone between western and eastern North American drainage systems.
By integrating (U-Th)/He ages we can further distinguish first order volcanic zircons from recycled zircons. This can increase the ability to discriminate different drainage systems because the recycled zircons come from source terranes that are different from the original basement in which they formed. For example, two different Grenville-age zircon sources are differentiated by our U-Pb and (U-Th)/He ages. Sediments in Texas show a mixed zircon source from both local Grenville basement (Llano uplift) and eastern Appalachian Grenville basement, recycled via the Colorado Plateau. In contrast, sediment in Louisiana lacks sediment sourced directly from Llano uplift, indicating a well-defined drainage system divide between Texas and Louisiana boundary.