Composite architecture from a low-accommodation aeolian system stack – lateral translation versus bedform climb?

Aeolian strata are commonly reported as products of unimodal migrating and climbing parent bedforms deposited during the migration of a single co-genetic erg system. Depositional models frequently depict aeolian architecture as homogenous, with set or coset bounded compartments related to largely uniform climbing bedform morphologies.

In contrast, the Page Sandstone Formation shows considerable internal heterogeneity from set to system scale. A minimum of six thin (4-33m) but well defined cycles of deflation to the water-table and growth to a dry coastal erg system occur. Extensive bluff exposures were surveyed over an area >1km2 near Page, Arizona where the formation is 55m+ thick. We focused upon the mesoscale/semi-regional architecture of the system stack. Integration of detailed logs and Lidar-generated digital outcrop models resulted in multiscale dimensional data. Stratification types, architectural element geometry, facies distributions/proportions and palaeoflow measurements were mapped to reveal parent dune character.

Distinct stratification styles and set-scales were observed both across super surface bounded system resets and within super surface bounded co-genetic phases of erg migration, recording the passage of variable parent dune morphologies. Bedform climb is frequently not demonstrable at the scale of the studied outcrops with erosional trough geometries dominating. Our data suggests that accumulation of the Page Sandstone Formation was strongly influenced by scour and fill reworking of the sediment pile. We believe this was produced by dry erg migration during lowstands where crescentic duneforms with scour pits of various depth eroded into a mobile sandy substrate. Preservation was controlled by the relatively rapid stabilization and partial preservation of the individual ergs due to episodic tectono-eustatic water table rise.

This study demonstrates that in dry systems where accommodation space is limited conventional climbing aeolian architecture is juxtaposed with and overprinted by architecture linked to translation without obvious climb and downclimbing dunes, where erosional re-working by bedforms of various scales accounts for much of the depositional architecture.