Controls on the apex location of large deltas

Adrian J Hartley,Gary S Weissmann,Louis Scuderi

doi:10.1144/jgs2015-154

Adrian J Hartley, Gary S Weissmann + Show 1 more

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https://doi.org/10.1144/jgs2015-154

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Abstract

The majority of sediment transport to the world's oceans is routed via large deltas. We examine controls on delta apex location using a database of 84 of the world's largest deltas. Of the dataset, 94% of apices are controlled by either bedrock valleys (80%) or Pleistocene alluvial valleys (14%), suggesting that the principal control on modern apex development is valley exit and/or bedslope-mediated avulsion and not hydrodynamic backwater length. Valley exit control on large delta apex location may have been as important in the rock record as it is today, and should be considered as a key control on delta development. Supplementary material : Tabulated data on backwater length and apex type for studied deltas available at https://doi.org/10.6084/m9.figshare.c.3469770

Highlights

Controls on the apex location of large deltasThe majority of sediment transport to the world’s oceans is routed via large deltas. We examine controls on delta apex location using a database of 84 of the world’s largest deltas
Our data indicate that the apex location of >90% of modern deltas is fixed by the position of a feeder valley cut through either bedrock or Pleistocene strata, with many of the Pleistocene valleys representing an extension of older bedrock valleys (e.g. Volga, Fig. 3)
Analysis of 84 of the world’s largest modern deltas indicates that the apices of 94% of the deltas are located at the mouth of bedrock or Pleistocene alluvial valleys

Summary

Controls on the apex location of large deltas

The majority of sediment transport to the world’s oceans is routed via large deltas. We examine controls on delta apex location using a database of 84 of the world’s largest deltas. Chow 1959; Paola & Mohrig 1996; Jerolmack & Swenson 2007; Chatanantavet et al 2012) The identification of this scaling relationship has important implications for predicting sandstone body development in the subaerial part of modern and ancient deltas. 75% of the suspended sand fraction is lost 100 km downstream of the apex (Allison et al 2012) and predictable changes in channel belt migration rates and width/thickness ratios occur over this distance (Blum et al 2013; Fig. 1) If these relationships hold for all deltas, identification of the nodal avulsion point should help in predicting reservoir and aquifer distribution as well as in constraining palaeogeographical reconstructions. Channel depth was taken from published information and for most examples included an average depth over the apex–shoreline length Where this was not available, reliable depth measurements for portions of the river close to the apex were used.

Apex location of large deltas

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Discussion

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