Upper-bar deposits in large Amazon rivers: Occurrence, morphology and internal structure

Author(s)

Tamura, Larissa N. ^[1] ; Almeida, Renato P. ^[1] ; Galeazzi, Cristiano P. ^[1] ; Freitas, Bernardo T. ^[2] ; Ianniruberto, Marco ^[3] ; Prado, Ariel H. ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Geociencias, Rua Logo 562, Cidade Univ, BR-05508900 Sao Paulo, SP - Brazil

^[2] Univ Estadual Campinas, Fac Tecnol, R Paschoal Marmo 1888, BR-13484332 Limeira, SP - Brazil

^[3] Univ Brasilia, Inst Geociencias, Campus Univ Darcy Ribeiro, BR-71900000 Brasilia, DF - Brazil

• Document type: Journal article
• Source: SEDIMENTARY GEOLOGY; v. 387, p. 1-17, JUN 1 2019.
• Web of Science Citations: 0

Abstract

Although large anabranching rivers are a very common element in the greatest modern drainage basins, the recognition of such systems in the rock record is hampered by insufficient sedimentological information from active rivers. That is particularly the case of bar-top depositional environments in large anabranching rivers, motivating the survey of six selected areas of seasonally emergent bars in the Solimoes and Japura rivers (western Brazilian Amazonia) using Ground Penetrating Radar, Sub Bottom Profiler and Multibeam Echosounder, as well as direct observation sediment sampling. GPR surveys and field observations indicate these bars are dominated by 0.5 to 4 m tall subaqueous dunes with the local presence of metric angle-of-repose bar-side surfaces. Downstream accretion components are characterized by radar facies indicating horizontal to low-angle downstream-dipping cosets of dm-scale to cm-scale cross-strata. Lateral accretion components are characterized by radar facies indicating m-scale high-angle cross-strata sets passing laterally to low-angle and inclined cosets composed of dm-scale cross-strata sets. Upstream accretion components are characterized by radar facies indicating upstream-inclined cosets of m- and dm-scale cross-strata sets with local mud drapes. Preservation of accretionary bar forms in these periodically exposed areas is supported by calculation of the coefficient of variation of peak discharge, which indicates low interannual peak discharge variability over the bar tops. (C) 2019 Elsevier B.V. All rights reserved. (AU)

• FAPESP's process: 16/19736-5 - Quantitative approaches for big river deposits: integrated field geology and 3D photogrammetric models
• Grantee: Bernardo Tavares Freitas
• Support type: Regular Research Grants
• FAPESP's process: 14/16739-8 - Developing facies models for large river systems: processes and products in active bars in the Brazilian Amazon and implications for the paleogeographic reconstructions of the Neogene Amazon and the Mesozoic of Gondwana in NE-Brazil and E-Australia
• Grantee: Renato Paes de Almeida
• Support type: Regular Research Grants
• FAPESP's process: 18/02197-0 - Integrated quantitative models for quaternary fluvial sedimentation and the distribution of the varzea and terra firme biomes in Western and central Amazonia
• Grantee: Ariel Henrique Do Prado
• Support type: Scholarships in Brazil - Master
• FAPESP's process: 17/06874-3 - Fluvial dynamics and sedimentary deposits in the Amazon channel: providing tools to decipher the paleogeographical evolution of Amazonia and deposits of large anabranching rivers in the rock record
• Grantee: Cristiano Padalino Galeazzi
• Support type: Scholarships in Brazil - Doctorate
• FAPESP's process: 16/03091-5 - CHARACTERIZATION OF HETEROGENEITIES AND MODELING OF RESERVOIR ANALOGUES IN FLUVIAL AND EOLIAN DEPOSITS
• Grantee: Liliane Janikian Paes de Almeida
• Support type: Regular Research Grants
• FAPESP's process: 12/50260-6 - Structure and evolution of the Amazonian biota and its environment: an integrative approach
• Grantee: Lúcia Garcez Lohmann
• Support type: BIOTA-FAPESP Program - Thematic Grants