The sedimentological expression of transgression–regression cycles upon aeolian–marine margins

Abstract

When compared to their temperate coastal counterparts, sediments deposited and preserved along arid aeolian to shallow-marine margins remain relatively poorly understood, particularly at the scale of lithofacies units and architectural elements. These systems often record evidence for relative sea-level change within sedimentary basins. This work focusses on the Entrada–Curtis–Summerville formations that crop out in central eastern Utah, USA, and provides a detailed analysis of the aeolian Moab Member of the Curtis Formation (informally known as the Moab Tongue) that was impacted by cycles of marine transgressions and regression in the late Jurassic. This study utilises photogrammetry, sedimentary logging and sequence-stratigraphical analysis techniques. Results indicate that four short-lived transgressive-regressive cycles are preserved within the Moab Member, followed by a broad regressive event recorded at the transition between the Curtis and Summerville formations. These cycles relate to changes in the relative sea level of the Sundance Sea and the deflation and expansion of the neighbouring aeolian dune field. During periods of normal regression, marine sediments displayed evidence of tidal and wave action, whereas the continental domain was characterised by growth of the aeolian system. However, when regression occurred within optimal physiographic conditions such as a restricted, semi-enclosed basin, and at sufficient magnitude to outpace erg expansion, this acted to shut-down bedform development and preservation. A rapid restriction of aeolian sediment availability and the inability of the dune field to recover resulted in the formation of deflationary sandsheets, arid coastal plain strata and contemporaneous shallow-marine deposits that are starved of wind-sourced sediments. This study highlights how a rapidly developing high-magnitude regression can lead to the overall retraction of the erg. Deciphering the evolution and sequence stratigraphical relationships of arid aeolian to shallow marine margins is important in both understanding environmental interactions and improving the characterisation of reservoir rocks deposited in these settings.