6. Dispersal and Preservation of Tectonically Generated Alluvial Gravels in Sedimentary Basins
- Cathy Busby3 and
- Antonio Azor4
Published Online: 30 JAN 2012
Copyright © 2012 Blackwell Publishing Ltd
Tectonics of Sedimentary Basins: Recent Advances
How to Cite
Allen, P. A. and Heller, P. L. (2011) Dispersal and Preservation of Tectonically Generated Alluvial Gravels in Sedimentary Basins, in Tectonics of Sedimentary Basins: Recent Advances (eds C. Busby and A. Azor), John Wiley & Sons, Ltd, Chichester, UK. doi: 10.1002/9781444347166.ch6
Department of Earth Science, University of California, Santa Barbara CA 93106, USA
Departamento de Geodinámica, Universidad de Granada, Campus de Fuentenueva, s/n, 18071 Granada, Spain
- Published Online: 30 JAN 2012
- Published Print: 30 DEC 2011
Print ISBN: 9781405194655
Online ISBN: 9781444347166
- syntectonic conglomerates;
The dispersal of coarse gravel from source regions into sedimentary basins is commonly viewed as a hallmark of tectonic activity. Criteria for recognition of syn-tectonic conglomerates include characteristic architectural patterns, progradation of the gravel front, and the rate of down-system fining. However, interpretations of tectonic timing from such deposits need to consider the dynamic framework of the sediment routing system transporting the sediment from source to sink. The time scales of processes associated with gravel production and transport can be significant and, as a result, dilute the fidelity of the rock record as a recorder of tectonic activity.
Signals of coarse-grained sediment release are transformed during propagation through the sediment routing system. One of the most important methods of transforming a sediment release signal is by the buffering effect of local storage in alluvial river systems. The long-term stratigraphic impact of the release of gravel into sedimentary basins is also influenced by the relation between the frequency of the signal released from the source and the response time of the receiving basin. Few studies have evaluated the time lags of gravel deposition across basins. Results from a foreland basin setting in Spain suggest that lag times of 105 to 106 years take place, increasing with down-system distance from the source of gravel.
Erosional and depositional landscapes perturbed by tectonics, such as the change of slip rate on a major border fault resulting from segment linkage, undergo a transient response the duration of which depends on climatic parameters, rock erodibility, and system size, but is commonly of order 106 years. Numerical models and field studies suggest that an important part of the variability in stratigraphic successions results from this transient behavior before the establishment of new steady-state conditions.
The gravel supplied to sedimentary basins is dispersed down-system, but is also selectively extracted to build stratigraphy. Major controls on the rate of downstream fining are the discharge of the sediment supply, its grain-size distribution, and the spatial distribution of the rate of tectonic subsidence. Rapid rates of tectonic subsidence close to the source cause rapid rates of downstream fining and short depositional system lengths, whereas low rates of tectonic subsidence stretching over long down-system distances promote commensurately low rates of downstream fining.
The coupling between the erosional landscape of the source region and the depositional landscape of the sedimentary basin is currently a rich and challenging area of research. The effects of erosion and sediment deposition on the localization and reactivation of tectonic deformation is currently being investigated at a variety of scales.