|
|||||
|
|
Reaction, relaxation and lag in natural sedimentary systems: General principles, examples and lessons |
|
| Authors: | JRL Allen |
| Abstract: | Natural sedimentary systems are process-response systems in which hierarchical configurations on the sedimentary surface are given character, maintained and translated because some of the energy supply is expended, that expenditure resulting in material transfers and transports. The energy supply to most types of system generally varies on several different time scales. Consequently, a complex of reaction and relaxation effects marks the operation of these systems, the equilibrium of which can be defined only in terms of explicit time scales. Mathematically, the existence of these lag effects introduces non-uniqueness into the operation of natural systems, which is best represented and assessed in terms of phase diagrams. Many aspects of the behaviour of natural systems are in conformity with this theoretical model. The transport of suspended sediment in rivers and tidal flows ordinarily differs in phase from the aqueous discharge. Bed forms in tidal and river currents lag the changing flow conditions, by extents to a modest degree predictable by the model. Lag effects also mark wave-dominated sedimentary environments. Spatial lag effects, in which flow properties differ in phase from bed configurations, are critical to the dynamics of many kinds of bed form, including dunes, flute marks, and stream meanders. The ubiquity of lag effects, and the multiple time-scales of natural sedimentary systems, call into question aspects of current practice in the study of sedimentary environments and, as well, much of the way in which experimental and analytical studies are designed and used in sedimentology. |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ | |