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Abstract

By linking provenance indicators, estimated sediment supply, and depositional rate to exhumation episodes, it is possible to reconstruct timing and location of source to sink depositional pathways. The lower Miocene (LM; 23-15Ma) is an episode of voluminous sediment input to the Gulf of Mexico from erosion of North American interior highlands (Galloway, 2009; Galloway et al., 2011). This interval has gained increased attention from the oil and gas industry because of hydrocarbon potential beneath the thick salt canopy. However, inferred sediment transport pathways for this interval are based on consideration of likely river courses through known paleogeomorphological elements (Galloway et. al., 2011). Furthermore, provenance is mainly based on traditional petrographic methods (e.g., QFL diagrams), which have large uncertainties owing to degradation of sediment grains by transportation, weathering, and subsurface diagenesis. Major tectonic reorganization in the western interior of North America together with rejuvenation of the Appalachian Mountains in the east further complicates lower Miocene provenance analysis. More robust data are required to understand the progressive eastward shift of source terranes and its influence on sediment dispersal to the deep-water basin, where extensive allochthonous salt canopies can hinder direct seismic observation of sediment dispersal pathways.

The dual constraint provided by crystallization age (U-Pb) and cooling age (U-Th/He) greatly increases the accuracy and precision of provenance interpretations. We therefore integrate detrital zircon. U-Pb, and U-Th/He dating to reveal not only sediment provenance, but also the exhumation histories of the detrital source regions. Only limited U-Pb dating has been done in the Gulf of Mexico (Mackey et al., 2012 and Craddock et al., 2013) and U-Pb and U-Th/He double dating has not yet been applied here. We have collected 15 outcrop samples from Texas and Louisiana for U-Pb and U-Th/He analysis. Preliminary U-Pb results indicate that there are several major source terranes including the Oligocene volcanic field, Laramide uplift, Cordilleran Arc, Grenville, Mid-Continent, and Yavapai-Mazatzal terranes. Minor provinces, including Appalachian-Ouachita, Wyoming, and Superior regions, are also recorded. However, by combining U-Pb ages with U-Th/He ages, we identify several recycled zircons with more complex transportation, deposition, and exhumation histories. Exhumation histories indicate that the large numbers of zircons formed during the Sevier-Nevadan orogenies were recycled to the GOM rather than transported there directly. In addition, our data show that Grenville age zircons deposited in Louisiana were probably recycled through the Colorado Plateau from their original source in the Appalachian Mountains. In contrast, volcanic sources are readily identified because their U-Pb age is close to their U-Th/He age. Detrital zircon double dating is therefore greatly enhancing our understanding of tectonic movement, provenance changes and the evolution of sediment transport axes for the important lower Miocene interval in the Gulf of Mexico.

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