Please use this identifier to cite or link to this item: http://repositorio.unicamp.br/jspui/handle/REPOSIP/325899
Type: Artigo
Title: Large Barchanoid Dunes In The Amazon River And The Rock Record: Implications For Interpreting Large River Systems
Large barchanoid dunes in the Amazon river and the rock record: Implications for interpreting large river systems
Author: Almeida, Renato Paes de
Galeazzi, Cristiano Padalino
Freitas, Bernardo Tavares
Janikian, Liliane
Ianniruberto, Marco
Marconato, André
Abstract: The interpretation of large river deposits from the rock record is hampered by the scarcity of direct observations of active large river systems. That is particularly true for deep-channel environments, where tens of meters deep flows dominate. These conditions are extremely different from what is found in smaller systems, from which current facies models were derived. MBES and shallow seismic surveys in a selected area of the Upper Amazonas River in Northern Brazil revealed the presence of large compound barchanoid dunes along the channel thalweg. The dunes are characterized by V-shaped, concave-downstream crest lines and convex-up longitudinal profiles, hundreds of meters wide, up to 300 m in wavelength and several meters high. Based on the morphology of compound dunes, expected preserved sedimentary structures are broad, large-scale, low-angle, concave up and downstream cross strata, passing laterally and downstream to inclined cosets. Examples of such structures from large river deposits in the rock record are described in the Silurian Serra Grande Group and the Cretaceous Sao Sebastiao and Marizal formations in Northeastern Brazil, as well as in Triassic Hawkesburry Sandstone in Southeastern Australia and the Plio-Pleistocene Ica Formation in the western Amazon. All these sedimentary structures are found near channel base surfaces and are somewhat coarser than the overlying fluvial deposits, favoring the interpretation of thalweg depositional settings. The recognition of large barchanoid dunes as bedforms restricted to river thalwegs and probably to large river systems brings the possibility of establishing new criteria for the interpretation of fluvial system scale in the rock record. Sedimentary structures compatible with the morphological characteristics of these bedforms seem to be relatively common in large river deposits, given their initial recognition in five different fluvial successions in Brazil and Australia, potentially enabling substantial improvements in facies models for large rivers. (C) 2016 Elsevier B.V. All rights reserved.
The interpretation of large river deposits from the rock record is hampered by the scarcity of direct observations of active large river systems. That is particularly true for deep-channel environments, where tens of meters deep flows dominate. These cond
Subject: Rio Amazonas - Canais fluviais
Dunas
Estruturas sedimentares
Country: Países Baixos
Editor: Elsevier
Citation: Earth And Planetary Science Letters. Elsevier Science Bv, v. 454, p. 92 - 102, 2016.
Rights: fechado
Fechado
Identifier DOI: 10.1016/j.epsl.2016.08.029
Address: https://www.sciencedirect.com/science/article/pii/S0012821X16304587
Date Issue: 2016
Appears in Collections:FT - Artigos e Outros Documentos

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