Application of Laser Diffraction Grain‐Size Analysis to Reveal Depositional Processes in Tidally Influenced Systems

Siiro, Petri; Räsänen, Matti; Gingras, Murray K.; Harris, Chad R.; Irion, George; Pemberton, S. George; Ranzi, Alceu

doi:10.1002/9781444304350.ch10

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“…The difference in height between the down‐dip end and the up‐dip end can reach at least 3 to 5 m (FA1, FA3). In terms of lithology and bedforms, the members are more uniform although they become finer‐grained up‐dip (Siiro et al. , 2005).…”

Section: Discussionmentioning

confidence: 99%

Tidal and seasonal controls in the formation of Late Miocene inclined heterolithic stratification deposits, western Amazonian foreland basin

et al. 2007

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Upper Miocene strata in the Acre sub-basin, Brazil, consist dominantly of various types of inclined heterolithic stratification and pedogenic horizons. These strata were sedimentologically and ichnologically described to: (i) study different temporal controls responsible for inclined heterolithic stratification generation and their variation in a distal-proximal trend; and (ii) delineate the depositional setting. For this purpose, nine representative outcrops were sedimentologically and ichnologically studied, and their facies associations described. Thickness variations of the heterolithic strata of various orders (lamina, lamina bundles and beds) were analysed by statistical methods (Fourier transform). The deposits were interpreted as tidally and seasonally influenced estuarine or delta-related and continental strata. The inclined heterolithic stratification deposits represented vastly different settings ranging from tidally dominated, brackish-water ichnofossils-bearing channels to seasonally controlled, articulated Purussaurus (a freshwater alligator) fossilbearing channels. Several time cycles were distinguished in the strata, including semi-diurnal, fortnightly and seasonal. Tidal imprint was best observed in low-energy brackish-water settings, whereas seasonal rhythmicity was distinguishable throughout the depositional system. However, the latter was most apparent in riverine channels proximal to the inferred fluvio-tidal transition. The different temporal controls commonly had distinguishable impact on sedimentological and ichnological properties in the studied sediments. The differing properties included: (i) the degree and nature of lateral variability with respect to lithology and bedforms in inclined heterolithic stratification; (ii) the lateral continuity of inclined heterolithic stratification; (iii) the nature of sedimentary contacts between the inclined heterolithic stratification members; (iv) thickness variation of inclined heterolithic stratification members within a set; (v) the cyclicities observed in inclined heterolithic stratification series; (vi) the degree of bioturbation; (vii) the types of trace fossils observed; and (viii) the distribution of bioturbation in adjacent inclined heterolithic stratification members.

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Section: Discussionmentioning

confidence: 99%

Tidal and seasonal controls in the formation of Late Miocene inclined heterolithic stratification deposits, western Amazonian foreland basin

et al. 2007

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“…In the geological map presented in Figure 1c, it can be seen that the extension of the anabranching structure is limited by the Nauta unit on the eastern side (unit resistant to fluvial erosion), which consists of layers of clay bed, including sand and lignite beds [33]. On the western side, the Muyuy anabranching structure is framed by alluvial floodplains denoted as alluvial deposits, formed by the migrating channels characterized with scroll bars [32].…”

Section: Geologic Backgroundmentioning

confidence: 99%

Detecting the Planform Changes Due to the Seasonal Flow Fluctuation and 2012 Severe Flood in the Amazon River near Iquitos City, Peru Based on Remote Sensing Image Analysis

Angulo

Lee

2022

Water

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The Upper Amazon River forms an anabranching planform, which has been found to have significant changes in migration rate and river morphology. Previous studies have elaborated long-term evolution of the anabranching systems; however, research on the influence of the water level on temporal changes in anabranching is absent. According to the theory of river hydraulics, fluvial scour usually occurs when the shear force possessed by the high flow exceeds the resistance of the streambank. In contrast, deposition occurs when the tractive force of the low flow is insufficient to overcome the forces of gravity and friction. This study investigated the Muyuy anabranching planform change of the Upper Peruvian Amazon River due to the seasonal flow fluctuations and a severe flood in 2012. The Muyuy anabranching area is located 20 km upstream of Iquitos City, Peru. Landsat images from the wet and dry seasons in 2008, 2009, 2012, and 2013 were collected. The images were classified into three land cover classes (water, bare soil, vegetation and others) based on NDVI analysis. Quantitative analysis of the erosion/deposition shows that deposition is more noticeable than erosion in the Muyuy anabranching area. Considerable deposition can be found on the island of the anabranching system, and the streambank erosion occurred in the outer (concave) side of the main channel. This phenomenon of river erosion and deposition consistently occurred in 2008 and 2009 because of the periodical variation among the wet and dry seasons. However, prominent erosion was observed in 2012 and it was recognized to be caused by the severe flood. Furthermore, the extensive island was formed in 2013, which means substantial depositions accumulated in the recession of the 2012 flood.

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“…It has nearly the same distribution of formations as defined by Räsänen et al (). It can be observed that the anabranching structure is confined by the Pebas unit on the left (formation resistant to fluvial erosion), which is composed of blue smectilic clay beds intercalated with sand and lignite beds (Siiro et al , ). On the right‐hand side of the Iquitos anabranching structure, there is an alluvial floodplain (denoted as alluvial deposits by Räsänen et al (), which was formed by scroll bars of migrating channels.…”

Section: Study Areamentioning

confidence: 99%

Planform dynamics of the Iquitos anabranching structure in the Peruvian Upper Amazon River

Mendoza

Abad

Frias

et al. 2016

Earth Surf Processes Landf

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The upper reach of the Amazon River has a very dynamic morphology, with the highest rates of migration observed in the entire Amazon River. It has an anabranching channel pattern which alternates between a condition of single channel and anabranching structures; in particular, the anabranching structure near Iquitos City shows an interesting channel behavior. Its channels migrate at different rates, where there are processes of narrowing and widening, and also collision and development of new channels. The temporal evolution of the Iquitos anabranching structure is described during the period from 1985 to 2014. The study is carried out by using satellite images to track the migration patterns, which are contrasted to the underlying geological units in the valley. Bathymetry of the structure and several velocity transects were obtained during a field campaign prior to the 2012 historic flood event. This information allowed for numerical modeling in order to compute the hydrodynamic flow field that complements the temporal analysis, aiming to understand the planform migration patterns after the 2012 flood event. It is observed that the geological units play an important role in modulating the migration rates and planform development of the channels. The channels in the structure are in contention to be the main channel, which become the secondary channel after migration. This causes the channels to experience a rise in bed elevation and narrowing of the channel itself; if this trend continues for several more years, these channels will detach from the Iquitos anabranching structure, thus forming paleo‐channels. This geomorphic process is important for horizontal and vertical soil heterogeneity along the floodplain. In general, the analysis shows a complex interaction between the underlying geological units, flow structure, morphology of the bed and planform migration. Copyright © 2016 John Wiley & Sons, Ltd.

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Application of Laser Diffraction Grain‐Size Analysis to Reveal Depositional Processes in Tidally Influenced Systems

Cited by 3 publications

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Tidal and seasonal controls in the formation of Late Miocene inclined heterolithic stratification deposits, western Amazonian foreland basin

Tidal and seasonal controls in the formation of Late Miocene inclined heterolithic stratification deposits, western Amazonian foreland basin

Detecting the Planform Changes Due to the Seasonal Flow Fluctuation and 2012 Severe Flood in the Amazon River near Iquitos City, Peru Based on Remote Sensing Image Analysis

Planform dynamics of the Iquitos anabranching structure in the Peruvian Upper Amazon River

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