Sedimentology and stratigraphy of Pennsylvanian and Lower Permian strata (upper Amsden Formation and Tensleep Sandstone) in North-Central Wyoming

The upper Amsden Formation and Tensleep Sandstone are part of a disconformity-bounded stratigraphic sequence, are divisible into twenty-one parasequences, and are composed of fourteen lithofacies. Four dolostone lithofacies and inferred depositional environments are normal-marine skeletal packstone; restricted-subtidal peloidal packstone; peritidal laminated packstone; and paleosol breccia. Eight sandstone lithofacies are offshore hummocky stratified; lower shoreface bioturbated; upper shoreface to foreshore parallel stratified; subaqueous trough cross-stratified; eolian tabular-planar cross-stratified; eolian trough cross-stratified; eolian laminated; and large-scale deformed. Two mudstone lithofacies are offshore polychroma; and marsh to lagoonal variegated.;Repetitive facies patterns. Log-linear modeling and Markov-chain analysis are employed to identify preferred lithofacies transitions. Statistical evidence against random facies stacking is strong. Integration of preferred lithofacies patterns, parasequence stratigraphy and other sedimentologic data leads to a depositional systems interpretation that provides insights into autogenic and allogenic (glacio-eustasy) processes. Facies domain 1 is regarded as the product of a restricted-marine carbonate platform. Facies domain 2 is interpreted as the product of a wave-dominated delta. Facies domain 3 is regarded as the product of a mixed eolian erg and normal-marine carbonate platform. Parasequence boundaries developed during lowered sea level. Rapid sea level rise suppressed carbonate deposition. During slower rise and initial fall of sea level, carbonate autogenic shoaling was wide spread or local variation in detrital input modified environment distribution.;Eolian sedimentology. Dune types responsible for deposition of eolian sandstones are interpreted from geometry of bounding surfaces, distribution of eolian stratification types, and paleodispersal patterns. Three types are: (1) oblique, slightly sinuous crested dune (wavelength = 1-2 km; saddle spacing = 1 km) supporting smaller crescentic dunes and lee-slope spurs; (2) oblique, stright-crested dune (wavelength 0.5-1 km) supporting lee-slope crescentic spurs; and (3) transverse, compound crescentic dune (wavelength = 0.5-1 km; saddle spacing = 0.8 km).;Role of eustasy and subsidence. Eustasy is modeled as the sum of three components: first-order cycle (simplified to a line); second-order cycle (40 my period sine curve); and fourth-order cycle (1.3 my period Fourier series). Eustasy alone results in a net loss of accommodation space and, therefore, is inadequate. Linear subsidence of 8.5 m/my and eustasy provide sufficient accommodation space.