--> Lower Miocene Sediment Dispersal Pathway From Onshore to Offshore, Gulf of Mexico: Insight From Detrital Zircon Geochronology

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Lower Miocene Sediment Dispersal Pathway From Onshore to Offshore, Gulf of Mexico: Insight From Detrital Zircon Geochronology

Abstract

The lower Miocene (23-15Ma) is a major episode of sediment input to the Gulf of Mexico (GOM) from erosion of North American interior highlands. Recent major discoveries of deep water lower Miocene reservoirs (sub-salt) have attracted much attention to sediment dispersal pathway from hinterland source to deep water sink. However, mapping of sediment routing is usually complicated by widespread salt canopies. In this study, we use detrital zircon as an approach to study sediments provenance and trace sediment pathway from source areas to depositional sink. Nineteen onshore samples collected along northern Gulf margin were analyzed for U-Pb isotopes. U-Pb age spectra including 2192 zircon grain analyses suggest that Rocky Mountains, Great Plains and Miocene volcanic terranes in southwestern North America (e.g. Trans-Pecos) are the major source terranes for western GOM, whereas Appalachian Mountains are major source terranes for eastern GOM. In addition, these samples can be divided into four groups according to their distinct zircon U-Pb age spectra. Unique age spectrum of each group indicates different source terranes and drainage river networks. Major fluvial axis of the Paleo Rio Grande, Houston-Brazos, Red, Mississippi, Tombigbee, and Apalachicola rivers can be differentiated as each river carried distinct zircon signals. Five additional offshore samples were collected from shelf and slope environment of early Miocene. These offshore samples are located in downdip of major fluvial-deltaic depocenters. Their zircon U-Pb age spectra display a good correlation with onshore samples. Such feature suggests zircon signals are consistent from onshore fluvial to deep water environment, even though longshore currents reworking and mixing were probably intense along the central and much of the northwestern Texas coast in early Miocene. Therefore, a sediment routing way from hinterland source via fluvial-delta to ultimately deep water sink could be well established by detrital zircon analysis. This study provides an alternative way to connect deep water sediments to onshore fluvial deposits under circumstance where dispersal way is obscured by salt movement and longshore currents.