Relief peels in the study of palaeoflood slack-water sediments

The use of slack-water sediments as palaeostage indicators in palaeoflood hydrological analysis requires detailed sedimentological description. Conventional descriptions have relied mainly on field descriptions of slack-water profiles. However, this method often fails to reveal important detail. By employing the well-established technique of relief peels, modified for use in slack-water sediment studies, the problem of insufficient data recovery from slack-water deposits was successfully overcome during a palaeoflood hydrological investigation of South African rivers. The use of relief peels showed that this technique is a useful, and in some cases, indispensable aid in the description and interpretation of palaeoflood deposits. For example, relief peels have shown that slack-water sediments are for the most part not massive exhibiting mainly flat lamination. This indicates that slack-water sedimentation was characterised by moderate rates of deposition rather than sudden or rapid rates. Relief peels have also shown that the base of tributary back-flooded slack-water sediments often contain intraformational rip-up clasts. This indicates that reworking of the existing slack-water sediments is a common process during tributary back-flooding. chnique was particularly effective in enhancing sedimentary structure and in differentiating between interpalaeoflood, non-palaeoflood and intraflood pulses. Relief peels can also be stored permanently as a surface sample of the slack-water sequence to be retrieved for later study.