AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Provenance of the Lower Miocene Interval in the Northern Gulf of Mexico Basin: Insights From Detrital Zircon U-Pb and (U-Th)/He Double Dating

Abstract

The lower Miocene (LM; 23–15Ma) is an interval during which voluminous sediments were eroded from North American interior highlands and transported into deep water of the Gulf of Mexico Basin. Rich hydrocarbon resources are found in LM reservoirs, including an evolving play beneath the thick salt canopy. Complex salt structures and degradation of seismic imaging beneath the salt canopy makes it difficult to identify sediment sources and track dispersal pathways. We employ detrital zircon (DZ) U-Pb and (U-Th)/He double dating to define both basement provenance and exhumation histories of detrital source regions. Outcrop samples and drilling core materials have been collected along the northern Gulf coast, to discriminate sediment pathways. Samples from Texas and Louisiana are dominated by relatively young zircons from 25 - 300 Ma, mainly sourced from Oligocene volcanic centers, regions of Laramide uplift and the Cordilleran Arc. Minor age populations of 1.5 - 1.3 Ga and 1.8 - 1.6 Ga zircons indicate an additional source from the Yavapai-Mazatzal basement and granitic intrusions in the southwestern U.S. Zircon ages of 1.3 - 1.0 Ga are also common and probably represent recycled materials from the southwestern U.S., originally sourced from eastern Grenville basement. Samples from Mississippi and Florida show distinct age distributions, with most ages from 1.3 - 1.0 Ga and 300 – 100 Ma, indicating a dominant Appalachian source. The provenance signal changes gradually from west to east across the northern GOM margin. The DZ age populations suggest five drainage systems associated with different source terranes, including the Paleo-Rio Grande, Paleo-Red, Paleo-Mississippi, and Paleo-Tennessee rivers and a local river system in Florida draining from the Appalachians. These signals are robust provenance indicators for deepwater sediment source analysis. Sediment recycling is a common issue that complicates provenance interpretations. We integrate (U-Th)/He ages to distinguish recycled zircons from direct-source zircons. 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 Grenville zircons sourced directly from the Llano uplift, indicating a well-defined drainage system divide between Texas and Louisiana.