scholarly journals Alluvial plain dynamics in the southern Amazonian foreland basin

2015 ◽  
Vol 6 (2) ◽  
pp. 2063-2100 ◽  
Author(s):  
U. Lombardo
Keyword(s):  
Sediment Accumulation ◽  
Foreland Basin ◽  
Rural Livelihoods ◽  
Alluvial Plain ◽  
Small Rivers ◽  
Enso Cycle ◽  
Landsat Images ◽  
The Andes ◽  
Seasonally Flooded ◽  
Floodplain Sedimentation

Abstract. Alluvial plains are formed with sediments that rivers deposit on the adjacent flood-basin, mainly through crevasse splays and avulsions. These result from a combination of processes, some of which push the river towards the crevasse threshold, while others act as triggers. Based on the floodplain sedimentation patterns of large rivers in the southern Amazonian foreland basin, it has been suggested that alluvial plain sediment accumulation is primarily the result of river crevasse splays triggered by above normal precipitation events due to La Niña. However, more than 90 % of the Amazonian river network is made of small rivers and it is unknown whether small river floodplain sedimentation is influenced by the ENSO cycle as well. Using Landsat images from 1984 to 2014, here I analyse the behaviour of all the twelve tributaries of the Río Mamoré with a catchment in the Andes. I show that these are very active rivers and that the frequency of crevasses is not linked to ENSO activity. I found that most of the sediments eroded from the Andes by the tributaries of the Mamoré are deposited in the alluvial plains, before reaching the parent river. The mid- to late Holocene paleo-channels of these rivers are located tens of kilometres further away from the Andes than the modern crevasses. I conclude that the frequency of crevasses is controlled by intrabasinal processes that act on a year to decade time scale, while the average location of the crevasses is controlled by climatic or neo-tectonic events that act on a millennial scale. Finally, I discuss the implications of river dynamics on rural livelihoods and biodiversity in the Llanos de Moxos, a seasonally flooded savannah covering most of the southern Amazonian foreland basin and the world's largest RAMSAR site.

scholarly journals Alluvial plain dynamics in the southern Amazonian foreland basin

2016 ◽  
Vol 7 (2) ◽  
pp. 453-467 ◽  
Author(s):  
Umberto Lombardo
Keyword(s):  
Sediment Accumulation ◽  
Foreland Basin ◽  
Rural Livelihoods ◽  
Alluvial Plain ◽  
Small Rivers ◽  
Enso Cycle ◽  
Landsat Images ◽  
The Andes ◽  
Seasonally Flooded ◽  
Floodplain Sedimentation

Abstract. Alluvial plains are formed with sediments that rivers deposit on the adjacent flood-basin, mainly through crevasse splays and avulsions. These result from a combination of processes, some of which push the river towards the crevasse threshold, while others act as triggers. Based on the floodplain sedimentation patterns of large rivers in the southern Amazonian foreland basin, it has been suggested that alluvial plain sediment accumulation is primarily the result of river crevasse splays and sheet sands triggered by above-normal precipitation events due to La Niña. However, more than 90 % of the Amazonian river network is made of small rivers and it is unknown whether small river floodplain sedimentation is influenced by the ENSO cycle as well. Using Landsat images from 1984 to 2014, here I analyse the behaviour of all 12 tributaries of the Río Mamoré with a catchment in the Andes. I show that these are very active rivers and that the frequency of crevasses is not linked to ENSO activity. The data suggest that most of the sediments eroded from the Andes by the tributaries of the Mamoré are deposited in the alluvial plains, before reaching the parent river. The mid-to-late Holocene paleo-channels of these rivers are located tens of kilometres further away from the Andes than the modern crevasses. I conclude that the frequency of crevasses is controlled by intrabasinal processes that act on a yearly to decadal timescale, while the average location of the crevasses is controlled by climatic or neo-tectonic events that act on a millennial scale. Finally, I discuss the implications of river dynamics on rural livelihoods and biodiversity in the Llanos de Moxos, a seasonally flooded savannah covering most of the southern Amazonian foreland basin and the world's largest RAMSAR site.

Late Cretaceous stratigraphy and vertebrate faunas of the Markagunt, Paunsaugunt, and Kaiparowits plateaus, southern Utah

2016 ◽  
Vol 3 ◽  
pp. 229-291 ◽  
Author(s):  
Alan L. Titus ◽  
Jeffrey G. Eaton ◽  
Joseph Sertich
Keyword(s):  
Late Cretaceous ◽  
Foreland Basin ◽  
Alluvial Plain ◽  
Terrestrial Vertebrate ◽  
The North ◽  
Single Region ◽  
The World ◽  
Kaiparowits Plateau ◽  
Fossil Preservation ◽  
Fossil Records

The Late Cretaceous succession of southern Utah was deposited in an active foreland basin circa 100 to 70 million years ago. Thick siliciclastic units represent a variety of marine, coastal, and alluvial plain environments, but are dominantly terrestrial, and also highly fossiliferous. Conditions for vertebrate fossil preservation appear to have optimized in alluvial plain settings more distant from the coast, and so in general the locus of good preservation of diverse assemblages shifts eastward through the Late Cretaceous. The Middle and Late Campanian record of the Paunsaugunt and Kaiparowits Plateau regions is especially good, exhibiting common soft tissue preservation, and comparable with that of the contemporaneous Judith River and Belly River Groups to the north. Collectively the Cenomanian through Campanian strata of southern Utah hold one of the most complete single region terrestrial vertebrate fossil records in the world.

scholarly journals Evaluating the effect of nutrient redistribution by animals on the phosphorus cycle of lowland Amazonia

2018 ◽  
Vol 15 (1) ◽  
pp. 279-295 ◽  
Author(s):  
Corina Buendía ◽  
Axel Kleidon ◽  
Stefano Manzoni ◽  
Björn Reu ◽  
Amilcare Porporato
Keyword(s):  
Amazon Basin ◽  
P Availability ◽  
Phosphorus Cycle ◽  
Terra Firme ◽  
The Andes ◽  
P Content ◽  
Spatial Redistribution ◽  
Soil Age ◽  
Seasonally Flooded ◽  
Lowland Amazonia

Abstract. Phosphorus (P) availability decreases with soil age and potentially limits the productivity of ecosystems growing on old and weathered soils. Despite growing on ancient soils, ecosystems of lowland Amazonia are highly productive and are among the most biodiverse on Earth. P eroded and weathered in the Andes is transported by the rivers and deposited in floodplains of the lowland Amazon basin creating hotspots of P fertility. We hypothesize that animals feeding on vegetation and detritus in these hotspots may redistribute P to P-depleted areas, thus contributing to dissipate the P gradient across the landscape. Using a mathematical model, we show that animal-driven spatial redistribution of P from rivers to land and from seasonally flooded to terra firme (upland) ecosystems may sustain the P cycle of Amazonian lowlands. Our results show how P imported to land by terrestrial piscivores in combination with spatial redistribution of herbivores and detritivores can significantly enhance the P content in terra firme ecosystems, thereby highlighting the importance of food webs for the biogeochemical cycling of Amazonia.

Radiocarbon dating and sedimentation rates in the Holocene alluvial sediments of the northern Bihar plains, India

1996 ◽  
Vol 133 (1) ◽  
pp. 85-90 ◽  
Author(s):  
Rajiv Sinha ◽  
Peter F. Friend ◽  
V. R. Switsur
Keyword(s):  
Sediment Accumulation ◽  
Uttar Pradesh ◽  
Foreland Basin ◽  
Sedimentation Rates ◽  
Near Surface ◽  
Radiocarbon Dates ◽  
Gangetic Plains ◽  
River Terraces ◽  
Short Period ◽  
Two Samples

AbstractSeven radiocarbon dates of carbonate shells and charcoal from the upper two metres of sediment in the Indo-Gangetic plains of northern Bihar, eastern India, can be divided into three groups, with the following approximate ages: 2400±45 a BP (two samples), 1100±45 a BP (four samples) and 765±45 a BP (one sample). This evidence for at least three episodes of sedimentation in the last 2400 a contrasts with evidence of greater ages from similarly near-surface sediments in the middle Gangetic plains of Uttar Pradesh, further west. In these more westerly areas, greater ages and well-developed river terraces point to much more restricted late Holocene sedimentation. Rates of net sediment accumulation calculated using our Bihar ages, spanning a period of the order of 103–104 a, are similar to those calculated for periods of the order of 105–106 a for the Himalayan foreland basin. This suggests that, in the whole basin case, short-period rates higher than the Bihar rates have been compensated by longer than Bihar periods of non-deposition or erosion.

scholarly journals Reconciling Spatial and Temporal Patterns of Cenozoic Shortening, Exhumation, and Subsidence in the Southern Bolivian Andes

2021 ◽  
Vol 9 ◽  
Author(s):  
Nicholas D. Perez ◽  
Ryan B. Anderson ◽  
Brian K. Horton ◽  
Bailey A. Ohlson ◽  
Amanda Z. Calle
Keyword(s):  
Sediment Accumulation ◽  
Foreland Basin ◽  
High Elevation ◽  
Thrust Belt ◽  
Spatial And Temporal Patterns ◽  
Eastern Cordillera ◽  
Sediment Volume ◽  
Bolivian Andes ◽  
Climate Shifts ◽  
Flexural Modeling

The Bolivian Andes are an archetypal convergent margin orogen with a paired fold-thrust belt and foreland basin. Existing chronostratigraphic constraints highlight a discrepancy between unroofing of the Eastern Cordillera and Interandean Zone fold-thrust systems since 40 Ma and the onset of rapid sediment accumulation in the Subandean Chaco foreland after 11 Ma, previously attributed to Miocene climate shifts. New results from magnetostratigraphic, backstripping, erosional volumetric calculations, and flexural modeling efforts are integrated with existing structural and thermochronologic datasets to investigate the linkages between shortening, exhumation, and subsidence. Magnetostratigraphic and backstripping results determine tectonic subsidence in the Chaco foreland basin, which informs flexural models that evaluate topographic load and lithospheric parameters. These models show that Chaco foreland subsidence is consistent with a range of loading scenarios. Eroded volumes from the fold-thrust belt were sufficient to fill the Chaco foreland basin, further supporting the linkage between sediment source and sink. Erosional beveling of the Eastern Cordillera, local intermontane sediment accumulation after 30–25 Ma, and regional development of the high-elevation San Juan del Oro geomorphic surface from 25 to 10 Ma suggest that the western Eastern Cordillera did not store the large sediment volume expected from erosion of the fold-thrust belt, which arrived in the Subandean Zone after 11 Ma. Eocene to middle Miocene foreland basin accumulation was likely focused between the Eastern Cordillera and Interandean Zone, and has been almost completely recycled into the modern Subandean foreland basin. The delay between initial fold-thrust belt exhumation (early Cenozoic) and rapid Subandean subsidence (late Cenozoic) highlights the interplay between protracted shortening, underthrusting, and foreland basin recycling. Only with sufficient crustal shortening, accommodated by eastward advance of the fold-thrust belt and attendant underthrusting of Brazilian Shield lithosphere beneath the Subandes, did the Subandean zone enter proximal foreland basin deposystems after ca. 11 Ma. Prior to the late Miocene, the precursor flexural basin was situated westward and not wide enough to incorporate the distal Subandean Zone. These results highlight the interplay between a range of crustal and surface processes linked to tectonics and Miocene climate shifts on the evolution of the southern Bolivian Andes.

Soil versus Biological Controls on Nutrient Cycling in Terra Firme Forests

2001 ◽  
Author(s):  
Elvira Cuevas
Keyword(s):  
Amazon Basin ◽  
Evergreen Forest ◽  
Water Retention Capacity ◽  
Terra Firme ◽  
Retention Capacity ◽  
Seasonally Dry ◽  
The Andes ◽  
Rio Negro ◽  
Blackwater Rivers ◽  
Seasonally Flooded

Terra firme forests are those that by definition are not permanently or seasonally flooded (terra firme meaning “firm terrain”). This type of forest encompasses the Amazon and Orinoco basins, stretching from the lower slopes of the Andes, east to the Guianas, and south to about 15°S in western Brazil and northern Bolivia (Richards 1996). Structural and compositional variability in these forests in the Amazon basin is very wide as a result of climate differences and geomorphological position. The region is not climatically uniform; the central and much of the southern parts have less and more seasonal rainfall than the eastern and western parts (Walsh 1996). These differences have direct and indirect ecological significance, as phenology and biological processes related to nutrient availability will be strongly influenced by both factors (Cuevas and Medina 1986, 1988, 1990, Medina and Cuevas 1989). Periods of two or more consecutive dry days are ecologically significant in a humid area such as San Carlos de Río Negro, in the northern part of the Amazon, because of low water retention capacity in the widespread sandy soils. In lower geomorphological positions, dry spells of 5-10 days may result in fluctuations of the water table from 0.4-1.0 m (Herrera 1977, Bongers et al. 1985). In areas with a more strongly seasonal climate, roots have been found extending to 18 m depth (Nepstad et al. 1995). This may explain the presence of evergreen forest in the seasonally dry eastern Amazon. Structure and physiognomy of terra firme forests is very similar throughout Amazonia, but floristically it is quite variable due to different compositions in the subbasins of the Amazon’s major tributaries. These subbasins are located within geochemical regions that can be differentiated based on the physicochemical properties of drainage waters (Sioli 1975, Fittkau 1971, Fittkau et al. 1975). Blackwater rivers, such as the Río Negro, drain mostly sandy podsolized soils low in most essential nutrients for plant growth. They are characterized by a high content of humic acids, which remain dissolved because of the predominant low concentrations of polyvalent cations, mainly Ca2+ and Mg2+.

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