ABSTRACT The South Jasper Basin was a major locus of carbonate deposition during the Frasnian, and its sedimentary record is extensively exposed in the Alberta Rocky Mountains. This study places many of its classic outcrops into a sequence stratigraphic framework for the first time. New descriptions of 18 outcrop sections, lateral tracing of stratigraphic geometries, and correlation to a regional sequence stratigraphic–biostratigraphic framework form the basis of the interpretations. The sequence stratigraphic evolution of the study area consists of a second-order, transgressive–regressive depositional sequence, composed of eight composite (third-order) depositional sequences and their constituent high-frequency (fourth-order) sequences. One lowest Famennian third-order sequence is briefly described. The composite sequences are correlated from the northwestern margin of the Southesk Cairn carbonate complex at Toma Creek to time-equivalent strata exposed in the Nikanassin Range. Exposures in the Nikanassin Range include a carbonate shelf prograding southeast into the South Jasper Basin. Stratigraphic architecture of the carbonate platforms was influenced by relative sea-level change within the second-order sequence and timing of basin fill in the Jasper Basin. Extensive euxinic shale deposition occurred in the mid-Frasnian, with its maximum extent coinciding with the second-order Maximum Flooding Surface (MFS), in the Woodbend 2.3 high-frequency sequence. Stratigraphic architecture generally follows the second-order trend, but significant deviations from that trend are observed at both the composite and high-frequency sequence scale. Basinally restricted wedges of shallow-water carbonate occur above third- and fourth-order sequence boundaries during the second-order transgression. Slowing relative sea-level rise in the second-order highstand was reinforced by third- and fourth-order relative falls to produce complex stratigraphic architecture at the platform margins. Offlapping strata with basinally restricted shelf margin deposits and falling stage geometries are uniquely well exposed in the Nikanassin Range, allowing detailed reconstruction of sea-level fluctuations in the second-order highstand. Restricted marine circulation onto the carbonate platforms and basin filling in the late Frasnian coincided with extensive siliciclastic silt deposition in the study area. Silt was deposited during third- and fourth-order lowstands, bypassed into the basin and was reworked during intermittent inundation of the carbonate platforms.

Abstract Carbonate strata were widely deposited in the Alberta Basin during the Frasnian. These are well exposed in the Alberta Rocky Mountains and regionally extensive in the adjacent subsurface. This study places many of its classic outcrops from the Cascade (Burnt Timber) Channel to the South Jasper Basin into a single sequence stratigraphic framework for the first time. This framework is correlated from outcrop to subsurface using sequence stratigraphic and biostratigraphic data. Improved confidence in the stratigraphic interpretation is based on new measured sections tied to photographic panoramas, combined with detailed mapping of lithofacies and stratal patterns of continuously exposed platform to basin transitions in outcrop. These data are correlated with new and revised core and well-log interpretations from the Alberta subsurface. Ten third-order composite sequences and their constituent high-frequency (fourth-order) sequences span the uppermost Givetian through Frasnian strata of the Alberta Basin. They reflect stratigraphic architecture typical of a (second-order) depositional sequence: transgression followed by regression, or basin opening and filling. The eight youngest composite sequences are defined from the Cline Channel and Jasper Basin areas using stratal and facies stacking patterns and regional correlation of sequence boundaries and maximum flooding surfaces, integrated with conodont biostratigraphy. Most sequence boundaries observed are subaerial exposure surfaces, seen in outcrop or inferred from onlap of tidal-flat or reef margin deposits onto foreslope facies. The basin was filled asymmetrically by mixed carbonate–clay successions that form dominant east to west prograding strata. Two main types of sediment comprise the basin fill: extrabasinal clay and intrabasinal carbonate. Composite sequences (CSs) and high-frequency sequences (HFSs) can be confidently correlated from outcrop to subsurface. A combination of well-log and outcrop cross sections, integrated with biostratigraphy, support these correlations. These regional (time) surfaces allow better understanding of basin evolution and architecture. The influence of the second-order sequence dominates the accommodation setting and is expressed in the architecture of composite and high-frequency sequences. For example, the tripartite character (lowstand–transgressive–highstand) of CSs in the lower and middle part of the sequence is followed by the appearance of a distinct falling stage component in the upper part of the Frasnian. An increased frequency of truncation surfaces and offlapping strata is consistent with diminishing accommodation. With progressive basin infill and shallowing paleobathymetry, foreslope declivity decreased from a minimum of 10° to less than 1.5° as the depositional system became more ramp-like. This is accompanied by a change of lowstand geometry from wedge to tabular shaped. Deposition of coarser terrigenous clastics was also limited in most of the basin to the lower part of the second-order sequence, except at CS and HFS. Restricted marine circulation onto the carbonate platforms and basin filling in the upper part of the Frasnian coincided with extensive siliciclastic silt deposition in the study area, particularly in the Jasper Basin, where an influx of terrigenous silt formed mixed carbonate–siliciclastic deposits. Silt was deposited during third- and fourth-order lowstands, bypassed into the basin, and reworked during intermittent inundation of the carbonate platforms. Beyond the basic transgressive–regressive architecture of the second-order (Givetian–) Frasnian sequence, we document detailed observations such as (1) controls affecting the onset, cessation, and extent of euxinic shale deposition in the mid-Frasnian and its relation to the second-order maximum flooding surface; (2) the relative speed and distribution of illitic basin fill within the second-order highstand; (3) the effect of basin fill and off-platform sediment transport on regional and local carbonate platform architecture, such as the configuration of in situ carbonate lowstands, initiation of reefs along favorable fairways, and overall margin stacking patterns; and (4) the magnitude of relative sea-level falls associated with the development of sequence boundaries. A comparison to previously established Frasnian sequence stratigraphic schemes within the basin is extended to other basins in Europe and Australia.