Abstract Three-dimensional seismic data enable geoscientists to image the stratigraphic record along selected stratal or time slices. These slices provide detailed images of the planform geometry of ancient depositional systems and environments. In this presentation we attempt to provide a partial answer to the question: what kind of information do nonmarine channel and valley patterns and parameters convey regarding sediment load, channel stability, structural or climatic history of the area, and palaeochannel and reservoir architecture? Geomorphologists have long recognized four basic channel patterns: straight, meandering, braided and anastomosing. They have also developed a classification based on aerial pattern and sediment load. This relationship seems straightforward; however the patterns form a continuum with a great deal of complexity related to degree and character of sinuosity, braiding and anabranching. For example an equal-width sinuous pattern suggests moderate to high lateral stability, and low bed load to suspended load deposits. A wide bend sinuous pattern suggests low to moderate lateral stability, and higher bed load to suspended load deposits. Because of convergence and divergence, interpretation of controls on palaeochannel patterns is difficult. Nevertheless, a better understanding of the various controls on modern river morphology and dynamics can produce useful information regarding palaeo-systems. For example, river type (straight, braided, meandering and anastomosing) depends upon upstream controls such as geologic history (glaciated v. non-glaciated systems), tectonics (relief), lithology (sediment type) and climate (hydrology and vegetation), and downstream controls such as base-level (up and down) and length (avulsion). In addition, factors such as bedrock, active tectonics, floods and vegetation cause considerable pattern variability. Only by taking into account the effect of these controls and by using all available data can there be more predictive and interpretive explanations of seismic data.

Abstract The sequence stratigraphic model, with its initial emphasis on eustatically driven controls on sedimentary sequences, has generated considerable interest in the ultimate controls on alluvial successions. Arguments regarding controls on alluvial sequences have been ongoing for many decades. Proposed controls include global (eustatic) or local base-level fluctuation, climate, tectonics, and sediment supply. Since sediment supply is in general a function of one or more of the other three controls, the possible number can be reduced to three. Most models and explanations for fluvial successions are too simplistic. They attempt to explain these successions on the basis of a single controlling factor. Additionally the models commonly fail to take into account modern geomorphic concepts of complexity and ignore the fact that controls other than base-level fall can produce incision and that base-level lowering does not always result in incision and rejuvenation of a fluvial system. They also fail to realize that base-level fluctuations may have their greatest effect only in the lower reaches of a fluvial system and that the amounts of sediment produced by incision alone cannot account for the volume of sediment observed in most stratigraphic sequences. For these reasons it is difficult to justify the application of systems tracts designations to upstream portions of fluvial valley-fill successions. Field and analog experiment studies demonstrate the difficulty of distinguishing various controls in fluvial systems because (1) similar erosional and depositional features and sequences can be produced by different processes and vice versa and (2) different levels of sensitivity may result in a minor, a major, or no response of a system to an extrinsic perturbation.

Abstract Two main aspects of rivers relate to the interpretation of the last deglaciation. One involves changes of channel morphology, as affected by climatic and hydrologic controls. The other is the record preserved in the valley alluvium. Although intimately related, the two topics will be considered separately in this chapter because they involve different approaches to river history. The fluvial record of the period 18 to 6 ka is complex and fragmentary, and therefore it does not provide an unequivocal basis for interpreting climate change and ice retreat. However, the current understanding of rivers is sufficiently detailed so that conclusions about past hydrologic conditions can be made if a paleochannel can be described quantitatively or if the sequence of valley fill deposits is complete. Herein lies the greatest problem, for much of the necessary information is commonly obscured or incomplete. Generally, paleochannels are destroyed by erosion or buried by deposition, and older fluvial deposits are removed by erosion, so that inferences regarding past hydrologie and climatic conditions can rarely be made. Even when this is possible the results are frequently inconsistent with conclusions reached elsewhere, partly because the nature and degree of climate change varied in North America. In addition, different rivers and even reaches of the same river respond differently to similar changes of discharge and sediment load. Hence, even if morphologic or sedimentologic changes can be completely documented, they do not necessarily provide a basis for a general interpretation of climatic or hydrologie change. Some of the problems of this type of interpretation are summarized below (for a discussion see Schumm, 1984, 1985).

Abstract The width ( w ) depth ( d ), meander wavelength ( l ), gradient ( s ), shape ( w / d ), and sinuosity ( P ) of stable alluvial river channels are dependent on the volume of water moving through the channel ( Q w ) and the type of sediment load conveyed through the channel ( Q s ). and Empirical equations developed from data collected along modern alluvial rivers permit calculation of the effects of changes of hydrologic regimen ( Q w , Q s ) on channel morphology. Conversely, these relations permit estimation of paleochannel gradient, meander wavelength, sinuosity, and discharge from the dimensions of the paleochannel as exposed in cross section. The recognition of paleochannels within valley-fill or other complex fluvial deposits is a major problem, but criteria for the delineation of paleochannel cross-sectional shape and dimensions have been developed from studies of shapes and sediment characteristics of Australian paleochannels.