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Abstract

Fluvial systems possess a range of scaling relationships that reflect drainage basin controls on water and sediment flux. In hydrocarbon exploration and production, scaling relationships for fluvial deposits can be utilized to constrain environmental and sequence stratigraphic interpretations, as well as predict the lateral extent of fundamental reservoir flow units.

This study documents the scales of channel fills, channel bars, channel belts, and coastal plain incised valleys from well constrained Quaternary fluvial systems. Data on channel fill and storey to channel belt scales have been compiled from published thicknesses for sinuous to straight single channel systems, and spatial dimensions have been measured from Google Earth and ArcGIS georeferenced geologic maps. Fluvial systems included in this database span 3 orders of magnitude in drainage area, from continental scale systems to small tributaries, and span tropical to subpolar climatic regimes (Fig. 1).

Figure 1.

Scaling relationships for Quaternary systems that relate discharge, drainage basin size, channel belt thickness, and channel belt width.

Figure 1.

Scaling relationships for Quaternary systems that relate discharge, drainage basin size, channel belt thickness, and channel belt width.

One component of this study focused on trunk stream reaches upstream from backwater effects, so as to minimize inclusion of distributive, highly avulsive systems. The other component investigates channel belt and channel patterns within backwater zones.

All scaling relationships are represented by statistically significant power laws, and absolute dimensions are scaled to drainage area. A key criterion for scaling fluvial dimensions to drainage basin includes sampling comparable upstream locations as width, thickness, and width to thickness ratios vary substantially upstream of backwater compared to within backwater zones. Additionally, dimensions of channel fills, point bars and channel belts, and incised valleys define distinct populations. Mean width to thickness ratios for channel fills are ~10:1, whereas channel belts commonly range from 20-250:1 depending upon sinuosity. Scales of quaternary examples compare well with previous compilations of channel belt scales interpreted in the ancient record, and with theory.

Comparison of these quaternary scaling relationships with width to thickness trends observed in the Mungaroo Formation suggest that the fluvial channel belts of the Mungaroo Formation reside in a downdip (probably backwater) location of the fluvial system. Furthermore, the largest drainage basin or catchment area for the Mungaroo fluvial system was relatively large (on the order of hundreds of thousands of square kilometres), but included many smaller drainage systems.

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