Sequence stratigraphic model for epicratonic basin fills in arid settings

Marginal-marine successions deposited in restricted basins under arid conditions are characterised by complex interplay between variable hydrodynamic conditions, localised carbonate-evaporitic production and continental surface processes. In such scenario, climatically driven shifts of depositional belts may result in stratigraphic compartmentalisation through vertical facies and environments dislocation. As importantly, accommodation variations across marine margins can lead to preferential deposition of coeval systems which may ultimately translate into stratigraphic sealing through lateral facies transition. By deciphering the relative influence of allogenic controls upon marine margins stratigraphic architectures in arid and restricted settings and by documenting their sedimentary products, this work provides a generalised sequence stratigraphic model for arid epicratonic basin fills.

Stratigraphic arrangement of mixed paralic deposits is investigated across two margin-perpendicular transects of the Middle to Upper Jurassic San Rafael Group in Utah. Transgressive sequences of the Carmel and the Curtis formations deposited during flooding events of the Sundance Sea are intercalated between the aeolian- to fluvially-dominated low stand deposits of the Entrada Sandstone and the Summerville Formation. Facies changes and sequence stratigraphic surfaces are documented through detailed sedimentary logging and architectural panel interpretations at locations representative of 1) sediment-supply and accommodation controlled continental basin flanks; 2) autogenically overprinted paralic basin margin settings; 3) climatically controlled basin centre. Gamma-ray log data were collected in parts of the basin characterised by differing tectonics settings.

Successions deposited during transgressions are dominantly associated with complex tidal embayments reworking contemporaneous continental sediment deposited further inland and may present contrasting architectural and lithological characteristics linked to variability in basin physiographic settings and climatic conditions. Transgression sequences are generally recorded as composite surfaces in continental basin flank settings although thin fluvial deposits may locally be preserved in the case of favourable accommodation and sediment supply conditions. Sedimentary successions deposited during relative sea-/base-level low stands are characterised by the advance of aeolian systems during aridity maximums and translate basinward to coastal unconfined large-scale alluvial accretion successions. Maximum regression surfaces are associated with terminations of aeolian dune fields. High-frequency climatic fluctuations are preferentially recorded in continental basin flank settings during regressive trends as aeolian dune field growth stages bounded by deflationary supersurfaces. Larger-scale T-R sequential frameworks and their associated spatio-temporal facies evolution are more likely to be controlled by overarching changes in rates of accommodation creation due to foreland basin tectonics. By incorporating spatial facies variations within stacking trends at a basin scale, the proposed model highlights the architectural complexity and facies diversity of depositional sequences within arid epicratonic basins and may constrain reservoir characteristics and associated stratigraphic heterogeneities.