Complex Architecture in a Low Accommodation Eolian System Stack – Lateral Translation Versus Bedform Climb?

Abstract

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

Contrastingly, the Page Sandstone Formation shows considerable internal heterogeneity from set to system scale as a minimum of six thin (4–33 m) but well defined cycles of deflation to the water-table and growth to a dry coastal erg system occur (Havholm and Kocurek, 1993). This study focused on extensive bluff exposures just NE of Page, Arizona where the up to 60m thick formation was traced along and across depositional strike for >1km². The abundant exposure forms an opportunity to examine the mesoscale/semi-regional architecture of the erg-system stack. We focused upon integrating multiscale (laminae to system scale) dimensional data derived from both traditional outcrop logs and Lidar-generated digital outcrop models. Stratification types, architectural element geometry, facies distributions/proportions and palaeoflow measurements were all mapped to reveal parent dune character.

Distinct set scales and stratification styles 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 was strongly influenced by scour and fill reworking of the sediment pile. We believe this was produced by dry erg migration during lowstands where cresentic duneforms with scour pits of various depth ploughed across a mobile sandy substrate. Here 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 eolian architecture is strongly influenced by translation without obvious climb and where erosional re-working by bedforms of various scales accounts for the depositional architecture.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018