Scaling Relationships for Channel Fills, Channel Belts and Incised Valleys: Insights from Quaternary Systems
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, point and channel bars, channel belts, and coastal-plain incised valleys from well-constrained Quaternary fluvial systems.
Data on channel-fill and point-bar to channel-belt scales were compiled from published thicknesses for sinuous single-channel systems, with spatial dimensions measured from GoogleEarth. 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 sub-polar climatic regimes. Channel-fill and channel-belt scales were measured upstream from backwater effects, so as to minimize inclusion of distributive, highly avulsive systems. Scales of incised valleys were derived from well-constrained published examples that are known to have formed during the last 100 kyr glacio-eustatic cycle.
All scaling relationships are represented by statistically-significant power laws, with absolute dimensions that scale to drainage area, but distinct clustering occurs between channel fills, point bars and channel belts, and incised valleys. Mean width-to-thickness ratios for channel fills are ~10:1, whereas point bars commonly range from 70-250:1. Coastal-plain incised valleys from the last glacio-eustatic cycle range from 25-150 m in thickness, and a few kilometers to more than 80 km in width, with width-to-thickness ratios of ~600-800.
Scales of Quaternary examples compare well with previous compilations of channel-belt scales interpreted in the ancient record, and with theory. However, the smallest Quaternary incised valleys in our database reside in the uppermost part of the domain of published compilations of ancient incised valleys, with ancient examples overlapping significantly with both interpreted channel fills and channel belts. When interpreted within the context of this database from modern systems, we suggest many ancient examples may have been overinterpreted, which in turn suggests a persistent lack of objective criteria for differentiating channel fills, channel belts, and incised valleys.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California