Gravel sheet (basal or gravel lag)

Position: In-channel

 

Form

Relatively homogenous, thin/tabular bedload sheets that are deposited across the bed. Often coarse-grained and poorly sorted. May consist of an array of gravel bedforms such as pebble clusters and ribs.

 

Process description

Deposited under uniform energy conditions in highly sediment charged rivers. Generally indicates transport capacity-limited or competence-limited conditions due to oversupply of sediment. Surficial gravel bedforms are subject to frequent removal and replacement by floods as the sheet moves downstream as a pulse. May represent residual deposits that form a basal lag or a diffuse gravel sheet, reflecting rapid deposition and/or prolonged winnowing. May be armoured.