Latrubesse,E.M., Cozzuol,M., da Silva-Caminha,S.A.F., Rigsby,C.A., Absy,M.L. and Jaramillo,C.(2010): The Late Miocene paleogeography of the Amazon Basin and the evolution of the Amazon River system. Earth-Science Reviews, 99, 99-124.

『アマゾン盆地の後期中新世の古地理およびアマゾン川河川系の発達』


Abstract
 On the basis of paleontological content (vertebrates and palynology) and facies analysis from river banks, road cuts, and three wells, we have assigned the uppermost levels of the Solimoes(後のoの頭に〜) Formation in western Amazonia, Brazil, to the Late Miocene. The vertebrate fossil record from outcropping sediments is assigned to the Huayquerian-Mesopotamian mammalian biozones, spanning 9-6.5 Ma. Additionally, we present results that demonstrate that deposits in Peruvian Amazonia attributed to Miocene tidal environments are actually fluvial sediments that have been misinterpreted (both environmentally and chronologically) by several authors.
 The entire Late Miocene sequence was deposited in a continental environment within a subsiding basin. The facies analysis, fossil fauna content, and palynological record indicate that the environment of deposition was dominated by avulsive rivers associated with megafan systems, and avulsive rivers in flood basins (swamps, lakes, internal deltas, and splays). Soils developed on the flatter, drier areas, which were dominated by grasslands and gallery forest in a tropical to subtropical climate.
 These Late Miocene sediments were deposited from westward of the Purus arch up to the border of Brazil with Peru (Divisor Ranges) and Bolivia (Pando block). Eastward of the liquitos structural high, however, more detailed studies, including vertebrate paleontology, need to be performed to calibrate with more precision the ages of the uppermost levels of the Solimoes(後のoの頭に〜) Formation.
 The evolution of the basin during the late Miocene is mainly related to the tectonic behavior of the Central Andes (〜3゜-15゜S). At approximately 5 Ma, a segment of low angle of subduction was well developed in the Nazca Plate, and the deformation in the Subandean foreland produced the inland reactivation of the Divisor/Contamata Ranges and tectonic arrangements in the Eastern Andes. During the Pliocene southwestern Brazilian Amazonia ceased to be an effective sedimentary basin, and became instead an erosional area that contributed sediments to the Amazon fluvial system. At that time, the lowland fluvial systems of southwestern Amazonia (the Purus, Jurua and Javari(iの頭は´) basins) become isolated from the Andes by the newly formed north-flowing Ucayali system and south-east flowing Madre de Dios System. It was during the early Pliocene that the Amazon fluvial system integrated regionally and acquired its present appearance, and also when it started to drain water and sediments on a large scale to the Atlantic Ocean.

Keywords: Amazon basin; Amazon River; Late Miocene; Paleogeography; Paleoecology; fossil vertebrates; Palinology; Solimoes(後のoの頭に〜) Formation

Contents
1. Introduction
2. The Solimoes(後のoの頭に〜) Formation
 2.1. Sedimentology revisited
 2.2. Fossil fauna
  2.2.1. Chronology
  2.2.2. The vertebrate diversity
  2.2.3. Summary of diet habits of mammals as environmental indication
  2.2.4. Freshwater mollusks and ostracods
 2.3. Palynology
  2.3.1. Biostratigraphic data
   2.3.1.1. Well IAS-32-AM
   2.3.1.2. Well IAS-19-AM
   2.3.1.3. Well IAS-27-AM
   2.3.1.4. Outcrops samples
    2.3.1.4.1. Patos, Upper Acre River
    2.3.1.4.2. Barranco da Elizete, Upper Acre River
    2.3.1.4.3. Murici, Upper Acre River
    2.3.1.4.4. Niteroi(oの頭に´), Lower Acre
  2.3.2. Paleoenvironmental considerations
3. Amazonia during the Late Miocene
 3.1. Correlation of the Solimoes(後のoの頭に〜) Formation with others lithostratigraphic units of South America
 3.2. The Amazon basin: evolutionary approach
4. Conclusions
Acknowledgments
References


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