Carbonate platform evolution during icehouse periods: A Late Paleozoic (Asselian/Sakmarian) example, Hueco Mountains, west Texas

Detailed study of Early Permian carbonate platforms deposited in the Orogrande Basin during icehouse periods (Hueco Canyon Formation, west Texas) demonstrates the influence of sea-level frequency and amplitude and the effects of topography on carbonate production, facies distribution, ramp evolution and genesis of bounding discontinuities separating depositional packages. Depositional facies were grouped into four facies associations (inner ramp, middle ramp, slope and outer ramp/basin), suggesting deposition along homoclinal and distally steepened ramps. These ramps are placed in a hierarchical scheme of cycle sets, high-frequency sequences and composite sequences studied in detail through the integration of process-sedimentology, geomorphology, sequence stratigraphy and ground penetrating radar (GPR) analysis. The internal architecture of these platforms is characterized by four systems tracts representing sedimentation at particular sea-level stages (highstand, falling stage, lowstand and transgressive systems tracts). Special emphasis was given to the least understood, falling stage systems tracts (that groups all sediments formed during relative sea-level falls) and to the formation of wave-cut terraces and regressive surfaces of marine erosion. GPR was used to increase correlation of discontinuities and differentiate radar facies. The result of integrating outcrop and GPR descriptions is a comprehensive sedimentological and sequence stratigraphic model adapted to the specific nature of carbonate platforms formed during icehouse periods that substantially differs from previously accepted geologic models. Additionally, the overall internal architecture and vertical stacking pattern of cycle sets reveal that these platforms can be generally described by a two-fold template of clinoformal and mounded geometries. This template is a fundamental element to link outcrop, GPR and seismic data based on the possibility that self-similarity could exist between these two scales of observation. Finally platforms sharing a similar two-fold geometrical pattern should be renamed as clino-mounded platforms instead of rimmed platforms or ramps which are used indistinctively for platforms formed during icehouse and greenhouse periods.