The Influence of Valley Morphology On the Rate of Bayhead Delta Progradation

Abstract

Bayhead deltas exist between the fluvial and central-basin depositional environments of many incised-valley-fill successions. Prior work has shown that tributary junctions in flooded incised valleys provide ''pinning points'' or locations of stabilization for bayhead deltas during transgression. The purpose of this study is to examine the influence of tributary junctions on the behavior of bayhead deltas during regression. This influence is examined by using a simple numerical model that incorporates established relationships for systematic changes in valley geomorphology downstream. In addition, the model incorporates important observations regarding the controls on water depth in wave-dominated estuarine central basins, which in part controls sediment accommodation. Water depth in the central basin of wave-dominated estuaries with high suspended sediment loads is a function of the width of the central basin parallel to the prevailing wind direction (fetch). A direct relationship is observed between the width of the central basin parallel to the prevailing wind direction and water depth based on data from modern estuaries in North America, Europe, and South America. Our model shows that bayhead-delta progradation rates increase at tributary confluences and larger deltas prograde at faster rates than smaller deltas. In the case of two tributary bayhead deltas fed by systems of the same size coming together, the combined bayhead delta progrades 17.6% faster. This study provides one more example of the importance of autogenic processes in influencing stratigraphic architecture and the rate of shoreline changes.

Autogenic delta progradation during sea-level rise within incised valleys

“…Bayhead deltas have first been attributed to external factors such as wave action, punctuated sea-level rise or increases in sediment flux (Zaitlin et al, 1994;Thomas and Anderson, 1994;Holz, 2003;Greene et al, 2007), but they could also result from autogenic processes (Simms and Rodriguez, 2015). Here, we build on this idea and show that bayhead deltas can result from the interplay between sediment supply and the evolving geometry of incised-valleys during steady base-level rise to create an autogenic stratigraphic pattern.…”

Early Holocene transgressive palaeogeography in the Po coastal plain (northern Italy)

“…The morphology of the transgressed surface is a key factor controlling estuary development and evolution (Heap & Nichol, 1997;Dillenburg et al, 2000;Rodriguez et al, 2005;Abrahim et al, 2008;Anderson et al, 2008;Rossi et al, 2011;Simms & Rodriguez, 2015). Low-gradient transgressive surfaces favour rapid landward shifts of facies, whereas the presence of structural highs may limit the emplacement of transgressive deposits (Cattaneo & Steel, 2003).…”

Complex coastal change in response to autogenic basin infilling: An example from a sub‐tropical Holocene strandplain

“…Wright & Burchette, ); river downcutting or avulsions (e.g. Muto & Steel, ; Jerolmack & Paola, ); interactions between local wave climates and shoreline progradation (Ashton & Giosan, ) or in situ reef development (Andrade et al ., ); subsidence caused by fluid extraction (Poland & Davis, ; Holzer & Galloway, ) or substrate compaction (Meckel et al ., ; Törnqvist et al ., ); or local geological and geomorphic controls on accommodation availability during transgression or regression (Simms & Rodriguez, ).…”