A CONTINENTAL PROVENANCE SHIFT OF LOWER MIOCENE FORMATION IN THE GULF OF MEXICO BASIN: INSIGHT FROM DETRITAL ZIRCON GEO- AND THERMOCHRONOMETRY

The lower Miocene (LM; 23-15Ma) is an episode of voluminous sediment input to the Gulf of Mexico (GOM) from erosion of North American interior highlands, which form deepwater reservoirs of the offshore areas of the GOM. The provenance of LM is mainly based on petrographic method (QFL) and consideration of likely river courses through known paleogeomorphological elements. However, petrographic methods 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 LM provenance analysis.

We present detrital zircon U-Pb and (U-Th)/He data from sediments collected along entire northern Gulf coast outcrops to better understand the provenance changes from west to east and its influence on sediments distribution. Our data shows the lower Miocene unit receives a significant input of zircons with U-Pb ages from 25 Ma to 3 Ga. Samples from Texas and Louisiana shows a great proportion of zircons coming from Oligocene volcanic centers, Laramide uplift region, Cordilleran Arc, while sediments in Mississippi, Alabama and Florida shows more contributions from Appalachian-Ouachita and Grenville basement. Zircons from Mid-Continent, Yavapai-Mazatzal terranes are also important components of our age data both in samples from western and eastern GOM. Therefore, a continental provenance shift from western North America (mainly Rocky Mountains and Cordillera Arc region) to eastern Appalachian Mountains could be inferred from our U-Pb dating. Also our data greatly increase the capability to identify different drainage system in Miocene time. Five major drainage systems, including Paleo-Rio Grande, Paleo-Red River, Paleo-Mississippi River, Paleo-Tennessee River and local river system in Florida drained from Appalachians, are identified by distinct U-Pb ages population within samples along strike in GOM. In addition, combined with (U-Th)/He ages we can further identify first order volcanic and recycled zircons, which greatly enhance our understanding of tectonic movement, provenance changes and the evolution of sediment transport axes for the important LM interval in the GOM.