The evolution and stratigraphic architecture of fluvio-lacustrine deltas: reservoir characteristics from the Red River Delta, Lake Texoma and the Denton Creek Delta, Grapevine Lake, TX

Abstract

Elongate, single-channel, non-bifurcating deltas are currently forming in many lakes throughout the United States. The Red River Delta forms an elongate, single-delta into Lake Texoma, sourced by a sand-rich, bedload dominated river system. Current models of delta formation suggest muddy rivers can form elongate deltas due to a lack of sand to form mouth bars, driving bifurcation, but do not explain a mechanism for a sandy river to form a non-bifurcating delta. We propose a model for elongate, single-channel deltas based on a process of grain-size separation within the delta channel, resulting in a sand starved river mouth that cannot bifurcate. Our results indicate that elongate, non-bifurcating deltas should be formed by muddy and sandy rivers alike, and therefore may represent the default delta. Field mapping at Lake Texoma and Grapevine Lake show that these single-channel deltas are found to be associated with overbank sand sheets that emanate laterally from the channel axis. These wings are interpreted to be blowout wings (after Tomanka, 2013) and are a modern example of lacustrine hyperpycnites (after Zavala, 2006). These wings are thin (10-40 cm) and laterally continuous, with lengths and widths spanning several hundred meters from the channel, and aspect ratios reaching 2,480 m wide per 1 m thickness. Blowout wings are found to scale to the formative depositional system, with dimensions corresponding to 5 times the channel width. The recognition of blowout wings greatly increases the potential static connectivity of fluvial bodies by connecting otherwise isolated channels through a network of laterally extensive wings. Adding blowout wings into the lexicon of high-accommodation fluvial depositional models should be considered for subsurface exploration.