The headward extent of fluvial landforms and associated vegetation on massanutten mountain, Virginia
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Abstract Variation in fluvial landforms and associated vegetation in the headward (upstream) direction has received little study and the controlling factors are not well understood. The relations among channel gradient, basin area, stream order, and the headward extent of fluvial landforms and vegetation was studied in 18 small basins and larger nearby stream reaches in the Massanutten Mountain area, northern Shenandoah Valley, Virginia. Low‐order streams were traversed to their basin heads. Notice was made of the point or region of the disappearance of fluvial landforms. Indicator species were used to confirm landform identification. The studied landforms include the channel bar, channel shelf, floodplain, and terraces. Basin geomorphic characteristics were determined from topographic and geologic maps and ground surveys. Results suggest that gradient is the most important factor controlling the development of fluvial landforms. Floodplains have not developed along stream reaches where average channel gradients exceed 0.15. Channel shelves and associated vegetation occur farther upstream than floodplains.Keywords:
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Point bar
This chapter contains sections titled: Introduction Description of the Lena Drainage Basin A Periglacial Environment Floodplain, Delta and Periglacial Landforms Fluvial Dynamics and Landforms Thermal Erosion and its Impact on the Fluvial Forms Impact of Climatic Change on the Hydrosystem Conclusion References
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Although commonly found in deserts, our knowledge about inverted relief landforms is very limited. The so-called 'Gravel Body' in the northern Kumtagh Desert is an example of an inverted relief landform created by the exhumation of a former fluvial gravel channel. The common occurrence of these landforms indicates that fluvial processes played an important role in shaping the Kumtagh Desert in the past 151 ka. A physical model is presented to reconstruct the palaeohydrology of these fluvial channels in terms of several measurable parameters including terrain slope, boulder size, and channel width. Combining the calculated palaeoflood depth, the maximal depth of channel bed eroded by wind, and the current height of inverted channels with the age of the aeolian sediments covered by gravels, the local wind erosion rate is estimated to be 0.21–0.28 mm/year. It is shown that wind erosion occurring in the Kumtagh Desert is no more severe than in adjacent regions. Since the modern Martian environment is very similar to that of hyperarid deserts on Earth, and Mars was once subjected to fluvial processes, this study will be helpful for understanding the origin of analogous Martian surface landforms and their causative processes. Copyright © 2015 John Wiley & Sons, Ltd.
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Fluvial deposits on the palaeo-fluvial terraces of Danxia landform areas were dated by using TL technique. Tectonic uplift rates were obtained by dividing the heights of the paIaeo-fluvial terraces above current average water level. The geomorphic ages were then calculated from the tectonic uplift rates and the relative heights of Danxia strata. The cliff retreating rates were deduced from the geomorphic ages and the cliff valley width. Finally the continent erosional rates were estimated by surveying the sediment volume that had been eroded out with the geomorphic ages. This study is a new attempt in geomorphology to step from qualitative description to quantitative determination of earth surface landform processes.
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In this study, data obtained from the Lower Cretaceous McMurray Formation in the central Athabasca Oil Sands, northeastern Alberta, Canada, are examined and used to establish the architecture of stacked fluvial and estuarine tidal bar deposits. A total of 13 distinguishable facies (F1–F7, F8a–F8b, and F9–F13) corresponding to stacked fluvial and estuarine deposits are recognized. These facies are then reassembled into four facies associations: fluvial deposits, tidal flat, tidal bar complex, and tidal bar cap. Of these, the lower fluvial deposits show a highly eroded channel lag and tidal influences in the cross-stratified sand and wavy interbeds. The fluvial deposits pass upwards into upper tidal-dominated tidal flats and a massive homogeneous tidal sand bar complex. Very thick tidal-influenced facies (F8a–F8b, up to 22 m) caused by semi-diurnal and semi-lunar cycles are also observed in tidal flats. Based on studies of the facies and facies associations, a three-dimensional (3-D) architecture model is finally established and used to analyze the internal distribution of the stacked fluvial and estuarine deposits. This is the first time that a 3-D model of the paleo-estuary tidal bar has been constructed. The results of this study will assist future research analyzing the architecture of stacked fluvial and estuarine deposits.
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Geomorphologic features and sediment distribution from meander-belts informs our understanding of ancient deposits, with specific application to predicting heterogeneity in petroliferous strata. The point bar to counter-point bar transition has been of recent interest and its common occurrence in modern fluvial environments suggests that they are often over-looked and under-recognised in ancient datasets. In this study, six point bar to counter-point bar transitions are examined along meander bends from rivers with varying channel scale, discharge and tidal influence. The data indicate that observed trends of grain-size fining from point bar to counter-point bar are consistent regardless of channel scale, discharge and tidal influence. High net sand to gross thickness (> 0.7) point bars and low net-to-gross counter-point bars (< 0.3) are documented. The average decrease in net-to-gross across the transition is 57%; the transition length scales to channel size and is approximately three times channel width. Tidally-influenced counter-point bar deposits are recognised despite the absence of concave scroll patterns in tidal flat areas. The lack of scroll bar topography contributes to the challenges in identifying counter-point bar deposits in tidally-influenced settings. Recognising and predicting heterogeneity related to the point bar to counter-point bar transition in ancient fluvial and tidal-fluvial deposits is considered, with specific implications for steam chamber growth during development of the Athabasca Oil Sands, Alberta, Canada.
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The Huesca fluvial fan (Miocene, Ebro Basin, Spain) contains a low-gradient, mixed-load fluvial system. A detailed outcrop study of its meandering river deposits shows that the preservation of elongate channel-floor sandstone ribbons is common and that these deposits create a continuous along-stream sand-to-sand connectivity between successive crescent-shaped sandy point-bar accumulations on both sides of the channel. The combined appearance of the sandstone resembles a string of beads consisting of a thin, sinuous ribbon with thick and wide protuberances on either side. The studied meandering river sandstone bodies are laterally amalgamated and vertically stacked with a net-to-gross (N/G) ratio of about 40%. They occur in 1–1.5-km (0.62–1-mi)-wide, northeast–southwest-oriented elongate meander belts occupying paleochannels. Beyond these belts, the sandstone is limited to isolated bodies with a very low N/G ratio.
A generic model of the string-of-beads geometry, based on the outcrop data analysis, showed a significant increase of bulk rock volume for the connected string of beads compared with the model of isolated point bars.
The outcrop results demonstrate the potential for channel-floor sandstone bodies to be preserved in a low-gradient, mixed-load fluvial system and their importance in connecting point-bar units in an along-stream direction. We recommend that fluvial reservoir architecture modeling programs include a function that allows the connectivity between channel-floor and point-bar architectural elements. This may greatly impact the estimated reservoir volumes and recovery factors in primary and secondary production as well as influence the sweep efficiency of enhanced recovery technologies.
Marinus E. Donselaar received his M.Sc. degree in geology from the University of Utrecht and his Doctor of Science degree in reservoir geology from Delft University of Technology, both in the Netherlands. He worked at the Comparative Sedimentology Division at the University of Utrecht. Since 1987, he has been a lecturer in sedimentology at Delft University of Technology. His research interests are in the modeling of fluvial and barrier island reservoir architecture. Irina Overeem has a Ph.D. from the Faculty of Civil Engineering and Geosciences, Delft University of Technology, Netherlands, where she was an assistant professor in geological modeling from 2005 to 2007. Her research focuses on the numerical modeling of fluviodeltaic processes. Over the last six years she has held a position at Institute of Arctic and Alpine Research (INSTAAR), and she is presently working at the Community Surface Dynamics Modeling Facility at the University of Colorado.
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The headward extent of fluvial landforms and associated vegetation on massanutten mountain, Virginia
Abstract Variation in fluvial landforms and associated vegetation in the headward (upstream) direction has received little study and the controlling factors are not well understood. The relations among channel gradient, basin area, stream order, and the headward extent of fluvial landforms and vegetation was studied in 18 small basins and larger nearby stream reaches in the Massanutten Mountain area, northern Shenandoah Valley, Virginia. Low‐order streams were traversed to their basin heads. Notice was made of the point or region of the disappearance of fluvial landforms. Indicator species were used to confirm landform identification. The studied landforms include the channel bar, channel shelf, floodplain, and terraces. Basin geomorphic characteristics were determined from topographic and geologic maps and ground surveys. Results suggest that gradient is the most important factor controlling the development of fluvial landforms. Floodplains have not developed along stream reaches where average channel gradients exceed 0.15. Channel shelves and associated vegetation occur farther upstream than floodplains.
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On the basis of field deep exploration channel surveying and combined with drilling, well logging and sampling analysis, in accordance with landforms, sediments, sedimentary structure, distribution of grain size, logging trace, the fluvial deposits of morden Nen river is divided into seven sedimentary microfacies: shingle bar, overbank, swamp of braided river, point bar, levee, floodfan, washland of meander river. The deposits of mordern Nen river are distinctively composed of coarse\|grained braided fluvial sequence overlying fine\|grained low energy meandering fluvial sequence.
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