Sedimentary Coastal Zones from High to Low Latitudes: Similarities and Differences
We live in a world where the loss of sea ice and thawing of coastal grounds in the north, and renewed marine transgression and an increase in the frequency of extreme weather events globally, are becoming commonplace. This volume presents a timely examination of coasts, the geological environment at particular risk as global warming brings on this new reality. In 23 papers, low lying, mainly siliciclastic coasts are reviewed, described and analysed under a variety of climates in quasi-stable tectonic settings along passive, trailing-continental edges from Polar Regions to the Tropics. Examples include coasts of the Arctic seas, temperate to tropical eastern shores of the Americas, western Portugal, Mediterranean, Persian Gulf, South Africa and Australia. The entire coastal zone is considered, ranging from geophysical processes and products to biological entities including the adaption of inhabitants of various climatic zones. Knowledge of the state of the coasts now, and how the coastal plain has evolved since the Late Pleistocene, is crucial for any realistic planning for the future.
Fluvial sediment supply, mud banks, cheniers and the morphodynamics of the coast of South America between the Amazon and Orinoco river mouths
Published:January 01, 2014
Edward J. Anthony, Antoine Gardel, Nicolas Gratiot, 2014. "Fluvial sediment supply, mud banks, cheniers and the morphodynamics of the coast of South America between the Amazon and Orinoco river mouths", Sedimentary Coastal Zones from High to Low Latitudes: Similarities and Differences, I. P. Martini, H. R. Wanless
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The overarching morphosedimentary control on the coast of South America between the Amazon and Orinoco rivers is the massive muddy discharge of the Amazon (from c. 754×106 to 1000×106 t a−1). This mud supply by the world’s largest river reflects sediment sourcing from the Andes, weathering in a tropical–equatorial climate and the extremely high water discharge (ca 173 000 m3 s−1). Amazon mud forms an estuarine mega-turbidity maximum on the shelf that feeds the growth of a subaqueous delta. About 15–20% of this mud forms coastal banks that migrate towards the mouth of the Orinoco, which has constructed a large subaerial delta. This muddy coast exhibits interspersed beaches and cheniers constructed from sand supplied by the smaller rivers and by the Orinoco, and is characterized by extremely large spatio-temporal geomorphic variability resulting from intense wave-reworking of the migrating banks, mangrove colonization and destruction, and erosion in interbank areas. These dynamic processes also drive important biogeochemical recycling, enhancing coastal productivity while efficiently remineralizing organic matter and promoting authigenic mineral formation. This muddy coast is being impacted by human-induced changes, in Guyana in particular. The Amazon–Orinoco coast provides an analogue for muddy, wave-dominated shorefaces in the geological record.