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Alexander, Jan 
ORCID: https://orcid.org/0000-0002-2830-2727, Fielding, Chris and Argiro, Adam
(2024)
Towards a new generation of fluvial facies models for the interpretation of ancient deposits, based on inter-annual peak discharge variance of modern rivers.
Sedimentology.
ISSN 0037-0746
(In Press)
Abstract
Fluvial facies models based on river planform are flawed and not fully fit for purpose. An alternative approach to classifying fluvial deposits is based on river discharge characteristics. A recent paper showed that the co-efficient of variance of annual peak discharge (CVQp) correlates well with the characteristics of preserved alluvium for a suite of modern rivers. Here, the database of rivers is expanded and augmented, and the utility of this statistic confirmed. For modern rivers, plotting the running-value of CVQp for a set interval (for example, 30 years) over a longer discharge record shows that the statistic varies both spatially and temporally. The CVQp can rise abruptly at a given location in response to a single flow event if that event is significantly larger than is common in that river. Such abrupt changes in CVQp are superimposed on longer-term patterns of more gradual change stimulated by environmental factors or anthropogenic effects such as dam construction. If the period of calculation for CVQp is relatively short, ‘anomalous’ events appear more frequently. Sequential studies of modern rivers indicate that such anomalous events have a high probability of being preserved in the alluvial record of the river, and suggest that, over the timeframes of channel filling and abandonment, they may constitute the dominant (characteristic) portion of the record in high CVQp systems. Since flow events with strongly peaked hydrographs (flashy discharges) are more common in high CVQp systems and leave a record dominated by upper flow regime stratification styles, it follows that the alluvial record of high CVQp rivers will be dominated by upper flow regime stratification. In contrast, in lower CVQp systems the occurrence of an event that changes the running CVQp value significantly may form a distinct event deposit, and the temporarily changed CVQp is unrepresentative for the duration of the channel’s life. The dominance of upper flow regime stratification, together with decreased preservation of identifiable macroform structure, increased lateral lithological heterogeneity, and in many cases increased preservation of in situ tree fossils in channel deposits of higher CVQp rivers, forms the basis for a series of new facies models for low, moderate, high, and very high/ultra-high CVQp alluvial systems and deposits. The new models can be applied to ancient successions either in combination with traditional, planform-based models, or not. These models provide information about ancient palaeoenvironmental conditions, and changes in such conditions over time at various scales via stratigraphic investigations.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | alluvial, discharge variability, fluvial facies models, planform, preservation potential |
| Faculty \ School: | Faculty of Science > School of Environmental Sciences University of East Anglia Research Groups/Centres > Theme - ClimateUEA |
| UEA Research Groups: | Faculty of Science > Research Groups > Geosciences |
| Depositing User: | LivePure Connector |
| Date Deposited: | 24 Sep 2024 12:55 |
| Last Modified: | 24 Sep 2024 12:55 |
| URI: | https://ueaeprints.uea.ac.uk/id/eprint/96796 |
| DOI: | issn:0037-0746 |
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