The Rio Grande Fan: A Sand-Rich Braided Distributive System in the Gulf of Mexico: A Modern Analog for the Frio and Wilcox Formations

Multiple canyons provide coarse-grained sediment from adjacent mountain sources to deposit the Rio Grande Fan on a continental-slope plateau. Multiple surface and subsurface channel pathways are influenced by salt diapirism and drainage into an enlarged channel entering the Perdido Canyon. The result is a widespread distribution of channels throughout the fan and then convergence of channels at the end of the fan. Echo character and cores suggest the potential for good connectivity in this sand-rich fan. The seismic and sedimentary facies, relatively steep fan gradient (1:250), and incised rather than leveed, channels, indicate that the Rio Grande Fan is probably a braided sand-rich fan. This type of fan is rare and contrasts with other mud-rich Gulf of Mexico (GOM) Fans. For example, Bryant Fan is fed by a chain of 15 mini-basins that exhibit seismic facies of: 1) mass transport deposit (MTD) wedges and sheets, 2) incised, ponded and perched turbidites, and 3) bypass channelized facies. The mini-basin pathway through Bryant Canyon traps MTD mud; this results in non-bifurcated, aggrading and stacked channel systems that extend across the Bryant Fan to feed single distal depositional lobes of ~ 30 km in length. The Rio Grande Fan distributive system also differs significantly from the Mississippi Fan, which is fed by massive failures of the 20 km-wide gullied Mississippi Canyon. The failures and mud-rich sediment source result in multiple mid-fan channel bifurcations, outer fan channel splays, and a fan composed of half MTD and half turbidite deposits. The distributive systems of the Rio Grande Fan may provide an analogue for some Deepwater Paleogene Frio and Wilcox deposits in the northwestern GOM.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California