Influence of lowstand eolian erosional processes on stratigraphic completeness: Sequence stratigraphy of the upper member of the Hermosa Formation (Upper Pennsylvanian), Paradox Basin, southeast Utah

The Paradox Basin of southeast Utah is characterized by a Late Pennsylvanian stratigraphic sequence consisting of cyclic interbeds of marine carbonate, and nonmarine carbonate and siliciclastic rocks. Consideration of the physical aspects of each facies, along with the preferred shoaling succession of marine facies within fifth-order parasequences (established through Markov Chain Analysis), allows reconstruction of the areal distribution of marine depositional environments and accordingly the determination or relative water depths. An understanding of the relative water depths associated with each facies makes it possible to identify component systems tracts within fourth-order sequences; fourth-order sequences often consist of transgressive and highstand marine parasequence sets disconformably overlain by nonmarine lowstand deposits. Furthermore, the association of facies within sequences suggests that these fourth-order cycles in turn define a deepening and shallowing third-order cycle. This third-order cycle is likewise superimposed onto a second-order episode of long-term accommodation loss. It is possible that the relatively high frequency fifth and fourth-order cycles may be attributed to the waxing and waning of Gondwana glaciers, while the longer-term second and perhaps third-order cycles reflect variations in tectonic accommodation provided by subsidence of the Paradox Basin. Implicit to this interpretation is the ability to correlate the observed allocycles basinwide. While the second and third-order cycles are readily correlated across the basin, the fourth and fifth-order cycles are only occasionally correlatable even on a local scale. This anomaly may be explained by the arid climate of the Paradox Basin during Late Pennsylvanian time which induced a stagnation of groundwater movement. Subsequently, shallow marine packstones and grainstones were not lithified by meteoric diagenesis. During fourth-order lowstands, the unconsolidated marine sediments left exposed to terrestrial processes on the shelf were deflated by the wind and reworked into eolian dunes downwind. As a result, the marine record was partially or totally stripped away, thereby making correlation of fourth and fifth-order cycles difficult if not impossible