Neotectonics in the northern equatorial Brazilian margin

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• 作者：Dilce F. Rossetti^a ; ^{rossetti@dsr.inpe.br} ; Lena S.B. Souza^b ; ^{lenabarata@yahoo.com.br} ; Renato Prado^c ; ^{renato@iag.usp.br} ; Vagner R. Elis^c ; ^{vagnelis@iag.usp.br}
• 关键词：Neogene ; Late Quaternary ; Electrical resistivity ; Ground penetrating radar ; Sedimentation ; Northern Brazil ; Geotectonic model
• 刊名：Journal of South American Earth Sciences
• 出版年：2012
• 期刊代码：50_08959811
• 类别：ear
• 出版时间：August, 2012
• 卷：37
• 期：Complete
• 页码：175-190
• 文件大小：4874 K

摘要

An increasing volume of publications has addressed the role of tectonics in inland areas of northern Brazil during the Neogene and Quaternary, despite its location in a passive margin. Hence, northern South America plate in this time interval might have not been as passive as usually regarded. This proposal needs further support, particularly including field data. In this work, we applied an integrated approach to reveal tectonic structures in Miocene and late Quaternary strata in a coastal area of the Amazonas lowland. The investigation, undertaken in Maraj贸 Island, mouth of the Amazonas River, consisted of shallow sub-surface geophysical data including vertical electric sounding and ground penetrating radar. These methods were combined with morphostructural analysis and sedimentological/stratigraphic data from shallow cores and a few outcrops. The results revealed two stratigraphic units, a lower one with Miocene age, and an upper one of Late Pleistocene-Holocene age. An abundance of faults and folds were recorded in the Miocene deposits and, to a minor extent, in overlying Late Pleistocene-Holocene strata. In addition to characterize these structures, we discuss their origin, considering three potential mechanisms: Andean tectonics, gravity tectonics related to sediment loading in the Amazon Fan, and rifting at the continental margin. Amongst these hypotheses, the most likely is that the faults and folds recorded in Maraj贸 Island reflect tectonics associated with the history of continental rifting that gave rise to the South Atlantic Ocean. This study supports sediment deposition influenced by transpression and transtension associated with strike-slip divergence along the northern Equatorial Brazilian margin in the Miocene and Late Pleistocene-Holocene. This work records tectonic evidence only for the uppermost few ten of meters of this sedimentary succession. However, available geological data indicate a thickness of up to 6聽km, which is remarkably thick for an area regarded as a passive margin.