A novel method for estimating sandbody compaction in fluvial successions

Clastic sedimentary successions are subject to variable amounts of compaction, which causes a decrease in both the thickness and porosity of sand-rich depositional units. Methods for estimating the degree of sediment compaction are needed for characterizing changes in the geometry and petrophysical properties of depositional elements in relation to their burial history. Conventional methods for estimating compaction of rock successions through the application of several empirical equations return estimations whose uncertainties can be significant, and integrative approaches that can produce reliable estimations are therefore desirable. To this end, a new method is proposed here for the estimation of the degree of compaction of sandbodies in ancient channelized fluvial successions. For outcropping fluvial successions, the compacted geometry of channel-fill margins cut into non-cohesive deposits can be measured, whereas the decompacted angle of repose of the material originally forming the channel banks can be estimated experimentally. Sediment compaction can therefore be estimated by comparing the observed geometry of the uppermost part of a channel-fill margin with the angle of repose of the non-cohesive bank material. The proposed method has been applied to three different sand-prone fluvial successions seen in outcrop, for the purposes of (i) illustrating the approach, and (ii) testing it through a comparison of its estimations against results produced by a conventional method based on thin-section observations. The comparison demonstrates that the two methods yield similar results, highlighting how the proposed approach can be readily applied to the assessment of compaction in clastic successions, for scopes of both pure and applied geological research.