Sedimentation and sediments of Amazonian rivers and evolution of the Amazonian landscape since Pliocene times

Irion, Georg

doi:10.1007/978-94-009-6542-3_7

Cited by 72 publications

(53 citation statements)

References 9 publications

(4 reference statements)

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“…This speciation model is highly flawed for the following reasons: (1) The Belterra clays covering the 180 m terraces in lower Amazonia and previously interpreted as the deposits of a Pliocene "Belterra Lagoon" are apparently nothing but the product of tropical weathering of the underlying bedrock, i.e. residual clays (Irion, 1984a;. Thus the Belterra clays have no paleogeographic significance whatsoever.…”

Section: Lagoon Model or Lake Modelmentioning

confidence: 99%

Hypotheses to explain the origin of species in Amazonia

Haffer¹

2008

Braz. J. Biol.

196

176

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The main hypotheses proposed to explain barrier formation separating populations and causing the differentiation of species in Amazonia during the course of geological history are based on different factors, as follow: (1) Changes in the distribution of land and sea or in the landscape due to tectonic movements or sea level fluctuations (Paleogeography hypothesis), (2) the barrier effect of Amazonian rivers (River hypothesis), (3) a combination of the barrier effect of broad rivers and vegetational changes in northern and southern Amazonia (River-refuge hypothesis), (4) the isolation of humid rainforest blocks near areas of surface relief in the periphery of Amazonia separated by dry forests, savannas and other intermediate vegetation types during dry climatic periods of the Tertiary and Quaternary (Refuge hypothesis), (5) changes in canopy-density due to climatic reversals (Canopy-density hypothesis) (6) the isolation and speciation of animal populations in small montane habitat pockets around Amazonia due to climatic fluctuations without major vegetational changes (Museum hypothesis), (7) competitive species interactions and local species isolations in peripheral regions of Amazonia due to invasion and counterinvasion during cold/warm periods of the Pleistocene (Disturbance-vicariance hypothesis) and (8) parapatric speciation across steep environmental gradients without separation of the respective populations (Gradient hypothesis). Several of these hypotheses probably are relevant to a different degree for the speciation processes in different faunal groups or during different geological periods. The basic paleogeography model refers mainly to faunal differentiation during the Tertiary and in combination with the Refuge hypothesis. Milankovitch ‡ cycles leading to global main hypotheses proposed to explain barrier formation separating populations and causing the differentiation of species in Amazonia during the course of geological history are based on different factors, as follow: (1) Changes in the distribution of land and sea or in the landscape due to tectonic movements or sea level fluctuations (Paleogeography hypothesis), (2) the barrier effect of Amazonian rivers (River hypothesis), (3) a combination of the barrier effect of broad rivers and vegetational changes in northern and southern Amazonia (River-refuge hypothesis), (4) the isolation of humid rainforest blocks near areas of surface relief in the periphery of Amazonia separated by dry forests, savannas and other intermediate vegetation types during dry climatic periods of the Tertiary and Quaternary (Refuge hypothesis), (5) changes in canopy-density due to climatic reversals (Canopy-density hypothesis) (6) the isolation and speciation of animal populations in small montane habitat pockets around Amazonia due to climatic fluctuations without major vegetational changes (Museum hypothesis), (7) competitive species interactions and local species isolations in peripheral regions of Amazonia due to invasion and counterinvasion during cold/warm p...

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Section: Lagoon Model or Lake Modelmentioning

confidence: 99%

Hypotheses to explain the origin of species in Amazonia

Haffer¹

2008

Braz. J. Biol.

196

176

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“…Several authors support marine transgression in Amazonia (e.g., Campbell, 1990;Frailey et al, 1988;Hoorn, 1994;Hoorn et al, 1995;Irion, 1984;Irion et al, 1995). This hypothesis became particularly attractive after publications that recorded marine transgression in Western Amazonia during the late Miocene, with the establishment of an interior seaway derived from the Pacific and/or Caribean sea (Räsänen et al, 1995).…”

Section: Implication Of Geological Factors In the Evolution Of The Ammentioning

confidence: 99%

New geological framework for Western Amazonia (Brazil) and implications for biogeography and evolution

2005

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Although many of the current hypotheses to explain the origin and distribution of the Amazon biodiversity has been based directly or indirectly on geological data, the reconstruction of the geological history of the Amazon region is still inadequate to analyze its relationship with the biodiversity. This work has the main goal to characterize the sedimentary successions formed in the Brazilian Amazon in the NeogeneQuaternary discussing the evolution of the depositional systems through time and analyzing their main controlling mechanisms in order to fill up this gap. Radar image interpretation, sedimentological studies, and radiocarbon dating allowed the mapping of Plio-Pleistocene to Holocene units along the Solimõ es-Amazonas River, Brazil. This integrated work led to the characterization of five sedimentary successions overlying Miocene deposits of the Solimõ es/Pebas Formation, which include the following: Içá Formation (Plio-Pleistocene), deposits Q1 (37,400-43,700 14 C yr B.P.), deposits Q2 (27,200 14 C yr B.P.), deposits Q3 (6730-2480 14 C yr B.P.), and deposits Q4 (280-130 14 C yr B.P.). These deposits occur mostly to the west of Manaus, forming NW-SE elongated belts that are progressively younger from SW to NE, indicating a subsiding basin with a depocenter that migrated to the NE. The reconstruction of the depositional history is consistent with significant changes in the landscapes. Hence, the closure of a large lake system at the end of the Miocene gave rise to the development of a Plio-Pleistocene fluvial system. This was yet very distinct from the modern drainage, with shallow, energetic, highly migrating, braided to anastomosed channels having an overall northeast outlet. This fluvial system formed probably under climatic conditions relatively drier than today's. During the early Pleistocene, there was pronounced erosion, followed by a renewed depositional phase ca. 40,000 14 C yr B.P., with the development of prograding lobes and/or crevasse splays associated with a lake system (i.e., fan-delta) and/or fluvial flood plain areas. After a period of erosion, a fluvial system with eastward draining channels started to develop at around 27,000 14 C yr B.P. The fluvial channels were overflooded in midHolocene time. This flooding is attributed to an increased period of humidity, with a peak between 5000 and 2500 14 C yr B.P. The data presented herein support that, rather than being a monotonous area, the Amazonia was a place with frequent changes in landscape throughout the Neogene-Quaternary, probably as a result of climatic and tectonic factors. We hypothesize that these changes in the physical environment stressed the biota, resulting in speciation and thus had a great impact on modern biodiversity.

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“…However, debate continues over whether the lowland neotropics were cold and dry, or cold and wet (e.g. Colinvaux et al, 2000;Colinvaux et al, 2001;Mon, 1982;Irion, 1984;Räsänen et al, 1987;Salo, 1987) during the late Pleistocene. The paucity of paleoprecipitation data has fostered different views of precipitation at the LGM.…”

Section: Introductionmentioning

confidence: 99%