Review and synthesis of the role of structural arches in the Brazilian Amazon lowlands

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

J. Sage,III Wagner (Creator)

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East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: In tropical South America , the interplay of tectonics , climate , and base-level influences terrestrial sedimentary processes of modern rivers and their antecedents , leading to transport of large volumes of sediment through Amazonia. Ultimately , this sediment is either preserved as basin fill along the major axes of long-lived sedimentary basins or transported offshore. Because outcrops are rare and chronologies are not well established , little is known about the non-petroleum-bearing , shallow Meso-Cenozoic strata of Amazonia. Geologic data from previous studies were integrated with the new seismostratigraphic analysis (seismic , geophysical log , and gravimetric data) to develop an overarching geologic framework for Amazonia. The Meso-Cenozoic strata of four sedimentary basins in the Brazilian Amazon lowlands (Acre , Solimōes , Amazonas and Marajó Basins) were analyzed because this period holds key information about the tectonic and stratigraphic history , which led to the evolution of the neotropical rainforest and the eventual establishment of the late Miocene , eastward flowing , trans-continental Amazon (trans-Amazon) drainage. New seismostratigraphic data attests to the stratigraphic history and the tectonic driving mechanisms , geometry , and timing of structural arch uplift. Structural arches inhibited eastward sediment transport , thus west-to-east hydrologic continuity between the Andes , the Amazon lowlands , and the equatorial Atlantic Ocean. Contractional stresses in central Amazonia reactivated and inversed Proterozoic rift graben blocks , which caused uplift of the Paleozoic Purus Arch. Late Jurassic Juruá and Late Cretaceous-Cenozoic Andean orogenic loading in western Amazonia caused uplift of the Iquitos Arch (and other similar Andean forebulges). Rift flank uplift in eastern Amazonia occurred during Early Cretaceous extension of the South Atlantic Ocean. This tectonic framework combined with the stratigraphic relationships between the isochronous Miocene Solimōes , Alter do Chǎo and the Barreiras Fms. (defined by lithology and provenance). This geologic model differs from some researchers (Figueiredo et al. , 2010 , 2009; Hoorn et al. , 2010) but is consistent with the literature review of Caputo and Soares (2016) , which suggests that Andean-sourced sediment reached the Atlantic Ocean in the late Miocene as a result of , not the over-topping of the Purus of Iquitos Arches , but instead the Gurupá Arch. Finally , this study also provided the framework for subsequent geochronology and provenance studies to be undertaken as part of a trans-continental , stratigraphic drilling expedition designed to recover complete Amazonian Meso-Cenozoic sequences.

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Language: English

Date: 2017

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