River terraces in the rock record: an overlooked landform in geological interpretation?

Fluvial incision and terracing produces a scale of architectural complexity that is often overlooked in geological interpretations and the
construction of subsurface reservoir models. Results of a 2D seismic forward modelling study demonstrate the difficulties and limitations in resolving
terraces seismically. We propose that terraced sequence boundaries fall readily into a subsurface data resolution gap between seismic and core to wireline
log scale.
Due to limitations in seismic resolution, sequence boundaries are usually interpreted as simple, single surfaces of erosion, for example at the bases of
incised-valley fills. However, modern analogues show that sequence boundaries are in fact often compound in nature. The stratigraphic response to
pulses of incision and aggradation in an incision-dominant phase can result in flights of stair-stepping terraces. In this paper we recognize two distinct
architectural styles: attached and detached terrace flights. Their formation depends on the interplay between the magnitudes of incision versus
aggradation.
We suggest that terraced sedimentary architectures, the nature of the terrace-fill lithology, and any associated pedogenesis impacts upon mesoscale to
macroscale reservoir permeabilities and therefore have implications for subsurface fluid flow. The existence of terraces, in conjunction with the inherent
lack of temporal control in fluvial successions, may help to explain correlation difficulties often encountered and to an extent the compartmentalized
production behavior of some fluvial hydrocarbon reservoirs.