Book chapter
Megafan environments in northern South America and their impact on Amazon Neogene aquatic ecosystems
Amazonia, Landscape and Species Evolution: A Look into the Past, pp 162-184
01 Jan 2010
Featured in Collection : UN Sustainable Development Goals @ Drexel
Abstract
A megafan is a low-angle, partial cone of fluvial sediments that can reach hundreds of kilometres in length. Its size and depositional processes differentiate the megafan from alluvial fans and deltas. Megafans are a mesoscale, entirely continental depositional feature. This landform has received little attention in either modern or palaeogeographic reconstructions of northern South America. We present a model for landscape development in Neogene Amazonia examining the role of the 'inland delta' or megafan. This environmental setting should be taken into account in mesoscale palaeogeographic reconstructions because it is so widespread in modern foreland landscapes in South America and elsewhere. We describe both megafan and multi-megafan patterns, the latter introduced by means of a roughness map of northern South America, which also assists in identifying landscapes of different types. We distinguish seven landscape phases; in each we evaluate a specific set of physical environmental processes in megafan settings that have biological significance. The processes are based primarily on stream avulsion, but also on stream incision and drainage-net breakdown. We conclude that fluvial sedimentation of the Andean foreland depression probably was accomplished primarily by megafan sedimentation, with declining estuarine and lacustrine sedimentation as the Neogene progressed. Because megafans are often juxtaposed, hydrological connections between neighbouring megafan rivers were probably repeatedly established - with all the associated biological ramifications of range expansion, population mixing, introgression, reinforced genetic isolation and competition. Regional connections between suites of nested megafans, and between major drainage basins, probably existed at times via critically situated megafans. Some modern fish distributions coincide with the mountain-front zone of megafan development, suggesting that megafan-mediated biological processes could have contributed to speciation. Accordingly, our attempt to reconstruct Miocene and younger landscapes in greater detail, with the benefit of the modern megafan analogue, seems justified.
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Details
- Title
- Megafan environments in northern South America and their impact on Amazon Neogene aquatic ecosystems
- Creators
- M. Justin Wilkinson - Jacobs Engineering GroupLarry G. Marshall - Arizona Museum of Natural History, 53 North, Macdonald St., Mesa AZ 85201, USAJohn G. Lundberg - Drexel UniversityMikhail H. Kreslavsky - University of California, Santa Cruz
- Contributors
- C Hoorn (Editor)F P Wesselingh (Editor)
- Publication Details
- Amazonia, Landscape and Species Evolution: A Look into the Past, pp 162-184
- Publisher
- Wiley; CHICHESTER
- Number of pages
- 23
- Resource Type
- Book chapter
- Language
- English
- Academic Unit
- Academy of Natural Sciences of Drexel University
- Web of Science ID
- WOS:000337463900011
- Scopus ID
- 2-s2.0-84886156973
- Other Identifier
- 991019335321604721
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- Collaboration types
- Domestic collaboration
- Web of Science research areas
- Evolutionary Biology
- Geosciences, Multidisciplinary