LATE QUATERNARY DELTA EVOLUTION IN THE NORTHERN GULF OF MEXICO

During the previous interglacial-glacial transition and associated sea-level fall, the larger rivers of the Northern Gulf of Mexico region (Rio Grande, Colorado, Brazos, western Louisiana, west Mobile/Pascagoola, east Mobile, Perdido/Escambia, and Apalachicola rivers) constructed large deltas on the shelf. This indicates significantly greater sediment flux rates (up to an order of magnitude) compared to the modern shelf setting. In general, sediment input to the shelf increased as sea-level fell, but temporal and spatial differ-ences in sediment discharge resulted from differences in the coastal plain sediment storage capacity of rivers and to the extent of cannibalization of older (Oxygen Isotope Stage 5) deltas. If climate regulated sediment dis-charge during this time interval, the effects of falling sea level overshadowed climate-controlled variability. Abandonment of deltas associated with some of the larger rivers (e.g. Brazos, western Louisiana and Lagniappe deltas) prior to the maximum low-stand resulted in an absence of lowstand delta and slope fans in these regions. Other fluvial feeders, such as the Rio Grande and Colorado rivers, remained fixed in their locations throughout the interglacial/glacial eustatic cycle and constructed lowstand delta and slope fan complexes. Not every shelf-margin delta is a lowstand delta and not every shelf-margin delta is connected to a lowstand fan. Transgressive, backstepping deltas are associated with those rivers with the largest sediment fluxes (Mississippi, Rio Grande, Colorado, Brazos and Apalachicola). The growth of these deltas was short-lived and diachronous, reflecting different climatic influence across the Gulf Coast region.