The prediction and modelling of subsurface fluvial stratigraphy

This review is an attempt to assess the current 'state-of-the-art' for techniques of subsurface fluvial stratigraphic analysis. It begins with a brief overview of the requirements of subsurface analysis, the limitations of the data available, and the difficulties presented by fluvial deposits in this context, then moves onto an examination of the philosophy behind modelling and the approaches that can be taken. Models are idealized representations of reality established to assist the understanding of complex natural phenomena and processes; they should be designed to have both descriptive and interpretative value. In addition, and of particular value in the exploitation of economic resources, models should also have predictive power in that they should enable deductions to be made about the properties at locations for which measurements have not been taken.A wide range of alternative approaches are currently employed. These include: conceptual techniques like facies modelling and sequence stratigraphic analysis; direct numerical modelling from observations including methods such as palaeohydrology, surface (interpolation) methods, geostatistics and fractals; simulation methods such as using Markov statistics and deterministic process studies; and indirect numerical modelling such as probabilistic simulation, and the use of outcrop analogues. Each of the techniques is briefly described, and its strengths and weaknesses analysed. Subsurface prediction typically incorporates a combination of modelling philosophies in hybrid methodologies, such as a combination of forward process models based on parameters obtained from initial, inverse modelling of the data. This is probably the way forward, such as combining stochastic with process-based simulations.The validity of subsurface models depends directly on the quality of the data and the assumptions made. Current modelling approaches are fundamentally limited because of our lack of adequately detailed knowledge about present-day rivers systems