Terminal Distributary Channels and Delta Front Architecture of River-Dominated Delta Systems

Abstract

Using modern and ancient examples we show that river-dominated deltas formed in shallow basins have multiple coeval terminal distributary channels at different scales. Sediment dispersion through multiple terminal distributary channels results in an overall lobate shape of the river-dominated delta that is opposite to the digitate Mississippi type, but similar with deltas described as wave-dominated. The examples of deltas that we present show typical coarsening-upward delta-front facies successions but do not contain deep distributary channels, as have been routinely interpreted in many ancient deltas. We show that shallow-water river-dominated delta-front deposits are typically capped by small terminal distributary channels, the crosssectional area of which represents a small fraction of the main fluvial ''trunk'' channel.Recognizing terminal distributary channels is critical in interpretation of river-dominated deltas. Terminal distributary channels are the most distal channelized features and can be both subaerial and subaqueous. Their dimensions vary between tens of meters to kilometers in width, with common values of 100-400 m and depths of 1-3 m, and are rarely incised. The orientation of the terminal distributary channels for the same system has a large variation, with values between 123u (Volga Delta) and 248u (Lena Delta). Terminal distributary channels are intimately associated with mouth-bar deposits and are infilled by aggradation and lateral or upstream migration of the mouth bars. Deposits of terminal distributary channels have characteristic sedimentary structures of unidirectional effluent flow but also show evidence of reworking by waves and tides.

Punctuated Sediment Discharge during Early Pliocene Birth of the Colorado River: Evidence from Regional Stratigraphy, Sedimentology, and Paleontology

“…Bright et al, 2016;O'Connell et al, 2017). Broadly channelized cross-bedded sandstone bodies represent terminal distributary channels, and tabular-bedded silt and fine sand accumulated in channel-mouth bars of a low-gradient delta front system (e.g., Olariu and Bhattacharya, 2006;Ahmed et al, 2014). Desiccation cracks and weak paleosols provide evidence for intermittent subaerial exposure in mudflats of the prograding Colorado River delta plain.…”

The morphology and evolution of channels on the Wax Lake Delta, Louisiana, USA

“…Several studies document consistent downstream trends in the width and depth of established deltaic channels [Andrén, 1994;Olariu and Bhattacharya, 2006;Edmonds and Slingerland, 2007;Edmonds et al, 2011b;Sassi et al, 2012]. However, only a few studies have documented channel network evolution through time.…”

Outcrop architecture of a fluvio-lacustrine succession: Upper Triassic Yanchang Formation, Ordos Basin, China

“…Shallow-water deltas in lake basins have been the subject of considerable study in recent years (Keighley et al, 2003;Keighley and Flint, 2008;Olariu et al, 2006Olariu et al, , 2010Turner and Tester, 2006;Zou et al, 2010). The Ordos Basin is commonly cited as an example of a shallow-water deltaic system (Zou et al, 2010;Deng et al, 2013).…”

“…Outcrop and seismic data from multiple studies demonstrate the existence of progradational configurations of most delta-front bodies, whether in marine or lake basins (Overeem et al, 2003;Olariu and Bhattacharya, 2006;Olariu et al, 2010;Turner and Tester, 2006;Jacob et al, 2010;Beate et al, 2010). Based on the type of basin, the gradient of the accumulation surface, and ratio between the rate of generation of accommodation via subsidence and the rate of sediment accumulation on the delta front, sand-body stacking patterns indicative of progradation can take the form of oblique, sigmoid and low-angle shingled arrangements (Berg, 1982;George, 1990).…”