Lessons from the Modern
Published:January 01, 2011
2011. "Lessons from the Modern", From River to Rock Record: The preservation of fluvial sediments and their subsequent interpretation, Stephanie K. Davidson, Sophie Leleu, Colin P. North
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Holocene rivers have a high degree of morphological variability, and many researchers see a continuum of channel forms that are transitional between end-member planforms such as braided, meandering, or straight. Individual rivers also show a high degree of longitudinal and vertical (through time) variability, as a result of changes in base level, climate, tectonics, tributary contribution, and/or valley slope. This high degree of variability in plan-view morphology of Holocene rivers is generally not reflected in interpretations of ancient fluvial deposits, which continue to be interpreted as meandering or braided. Many of these interpretations are suspect because of myths about modern rivers and because the characteristics described bear little relationship to plan-view morphology. Modern fluvial facies models are built around the nature and type of channel bars. Knowledge of the architecture of bar forms and their occurrence in Holocene river channels has been greatly enhanced in the past two decades with data gained from ground-penetrating radar (GPR) studies. In spite of our expanded data base for modern rivers and their deposits we still need additional data on width-to-thickness ratios and architecture of deposits of aggrading river systems.
A review of the literature suggests that data on channel bar deposits is lacking in most studies of ancient fluvial deposits. The few research efforts that describe paleochannel bars in 3D and 2D exposures of ancient fluvial deposits suggest that there was considerable variability in paleochannel form within a given formation. Our focus in the study of ancient fluvial deposits should shift from interpreting planforms to description and interpretation of preserved bar forms and how river systems evolved. In this regard many ancient fluvial sheet sandstones need to be re-examined.
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From River to Rock Record: The preservation of fluvial sediments and their subsequent interpretation
Over the last couple of decades, fluvial geomorphology and fluvial sedimentary geology have been developing in parallel, rather than in conjunction as might be desired. This volume is the result of the editors' attempt to bridge this gap in order to understand better how sediments in modern rivers become preserved in the rock record, and to improve interpretation from that record of the history of past environmental conditions. The catalyst for the volume was a conference with the same that was hosted at the University of Aberdeen School of Geosciences, in Aberdeen, Scotland, on 12-14 January 2009. The conferences brought together a broad spectrum of geomorphology and sedimentology researchers, from academia and industry. This interdisciplinary mix of experts considered and discussed ideas and examples ranging through timescales from the annual movement of individual river bars to sequence stratigraphic analysis of major sedimentary basins spanning millions of years. The articles in this volume are a mixture of novel concepts, new evaluations of the perceived wisdom about rivers and their sediments, and improved understanding derived from recent experience in interpreting the rock record. This volume usefully illustrates the current state of knowledge and will provide a stimulus for further research, particularly work that integrates geomorphological and sedimentological approaches and emphasizes crossdisciplinary communication.