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Abstract

U-Pb dating of detrital zircons in fluvial sandstones provides a method for reconstruction of drainage basin and sediment routing systems for ancient sedimentary basins. This paper summarizes a detrital-zircon record of Cenomanian paleodrainage and sediment routing for the Gulf of Mexico and U.S. midcontinent. Detrital zircon data from Cenomanian fluvial deposits of the Gulf of Mexico coastal plain (Tuscaloosa and Woodbine formations), the Central Plains (Dakota Group), and the Colorado Front Range (Dakota Formation) show the Appalachian-Ouachita orogen represented a continental divide between south-draining rivers that delivered sediment to the Gulf of Mexico, and west- and north-draining rivers that delivered sediment to the eastern margins of the Western Interior seaway. Moreover, Cenomanian fluvial deposits of the present-day Colorado Front Range were derived from the Western Cordillera, flowed generally west to east, and discharged to the western margin of the seaway. Western Cordillera-derived fluvial systems are distinctive because of the presence of Mesozoic-age zircons from the Cordilleran magmatic arc: the lack of arc zircons in Cenomanian fluvial deposits that dis-charged to the Gulf of Mexico indicates no connection to the Western Cordillera.

Detrital zircon data facilitate reconstruction of contributing drainage area and sediment routing. From these data, the dominant system for the Cenomanian Gulf of Mexico was an ancestral Tennessee River (Tuscaloosa Formation), which flowed axially through the Appalachians, had an estimated channel length of 1200-1600 km, and discharged sediment to the east-central Gulf of Mexico. Smaller rivers drained the Ouachita Mountains of Arkansas and Oklahoma (Woodbine Formation), had length scales of <300 km, and entered the Gulf through the East Texas Basin. From empirical scaling relationships between drainage-basin length and the length of basin-floor fans, these results predict significant basin-floor fans related to the paleo-Tennessee River system and very small fans from the east Texas fluvial systems. This predictive model is consistent with mapped deep-water systems, as the largest fan system was derived from rivers that entered the Gulf of Mexico through the southern Mississippi embayment.

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