An Alternative Model for Producing Levee Topography in Deep-Water Systems Based on Field Studies from the Neoproterozoic Isaac Formation
The objective here is to present an alternative model for the creation of levee topography based on field observations. In the Isaac Formation, medium-bedded strata in the proximal levee thin rapidly over 100's of meters, forming bed surfaces with subtle topography. Similar observations have been reported from other ancient levee systems and are presumed to be responsible for levee topography. In the Isaac Formation, however, this topography becomes infilled and therefore is likely not the major source of levee topography. Instead, thin-bedded turbidites create the topography. These beds have a tabular geometry and terminate abruptly instead of tapering laterally. The upward, progressively more channelward (backstepping) stacking of these thin beds forms a concave-up, lateral-thinning profile. This stacking pattern is a consequence of progressively diminished flow magnitude causing more limited lateral bed extent, which in turn reflects increased channel confinement related to levee growth and reduced overspill into overbank areas.