Agradecimentos: The authors are thankful to the careful assessment of the manuscript by the EPSL Editor Martin Frank and thoughtful review and suggestions from Andrew Miall and an anonymous reviewer. Sub-bottom seismic profiling was provided by SALT Sea and Limno Technology. This research was funded...

Agradecimentos: The authors are thankful to the careful assessment of the manuscript by the EPSL Editor Martin Frank and thoughtful review and suggestions from Andrew Miall and an anonymous reviewer. Sub-bottom seismic profiling was provided by SALT Sea and Limno Technology. This research was funded by the São Paulo Research Foundation (FAPESP) through scholarships #2010/51103-6, #2010/51559-0, #2013/02114-3, #2014/09800-2 and Research Grants #2013/01825-3, #2014/16739-8, #12/50260-6 (FAPESP-NSF-NASA Biota/Dimensions of Biodiversity). We also thank CAPES (PROEX-558/2011) and PRFH-PETROBRAS for student scholarships, and CNPq for researcher scholarships (302905/2015-4, 301775/2012-5). This study is a NAP GEO-SEDEX contribution, with the institutional support of the University of São Paulo (PrPesq)

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...

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 São Sebastião and Marizal formations in Northeastern Brazil, as well as in Triassic Hawkesburry Sandstone in Southeastern Australia and the Plio–Pleistocene Içá 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

COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES

558/2011

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ

301775/2012-5; 302905/2015-4

FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP

2010/51103-6; 2010/51559-0; 2012/50260-6; 2013/02114-3; 2013/01825-3; 2014/09800-2; 2014/16739-8

Fechado