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.

Abstract This study applies high-resolution sequence stratigraphy, biostratigraphy, and magnetic susceptibility (MS) stratigraphy to better constrain correlation of upper Middle and Upper Devonian strata and geologic events in western Alberta, Canada. We also explore the potential of MS stratigraphy as a long-range correlation tool and paleoclimatic or oxygen isotope proxy. High-resolution MS data from slope and basin deposits near the isolated Miette and Ancient Wall platforms provide insight into patterns of carbonate- platform development and infilling of the Devonian Alberta basin. Our MS data, combined with conodont and brachiopod biostrati-graphic data and sequence stratigraphy, provides additional control on the relative timing of five major and fifteen higher-frequency MS excursions and nine depositional sequences. Sea-level events that initiated deposition of seven of nine late Givetian-early Famennian third order depositional sequences in western Alberta coincide with Devonian transgressive-regressive (T-R) cycles IIa-2 to IIe. Eight of these form the main sequence stratigraphic architectural units of the isolated Miette and Ancient Wall platforms. Sea- level events were identified based on significant sequence stratigraphic horizons, including exposure and marine flooding surfaces, and were biochronologically calibrated using combined conodont and brachiopod biostratigraphy. Identification of sequence boundaries and differentiation of highstand and lowstand slope and basinal deposits was based on the geometry, mineralogy, and clast content of redeposited carbonate units. The magnetic-susceptibility signature of slope and basin facies is also shown to vary systematically within the sequence stratigraphic framework. Spikes in the MS record coincide with events associated with lowstand or initial transgression. The MS stratigraphy displays a consistent pattern across the Alberta basin, with generally higher MS values toward the east. The MS signature is generally low in the late Givetian and early Frasnian (through MN Zone 9) but displays a major bimodal MS increase in the middle to late Frasnian (MN zones 10-11). MS values return to generally lower levels during the late Frasnian (MN zones 12-13) and early Famennian. This general pattern of increasing followed by decreasing MS is interpreted to indicate variations in delivery of magnetically susceptible terrigenous material. The highest MS values correlate directly to the lithologic change associated with an influx of fine-grained siliciclastics in the Mount Hawk Formation. The generally consistent pattern of MS change across the Alberta basin points toward the utility of MS stratigraphy as a regional correlation tool. Several other positive MS excursions documented here are also associated with increased detrital input and are coeval with decreasing or low oxygen isotope values (increasing or high paleotemperatures) reported from both Laurasia and Gondwana. This relationship implies a paleoclimatic linkage with increasing temperatures and weathering rates resulting in higher detrital input and higher MS values. Published oxygen isotope data are too coarse to conduct high-resolution comparison with our MS data, but the parallel trends noted here suggest that further research on the use of MS as an oxygen isotope or paleoclimate proxy is warranted. The MS signature of coeval Devonian rocks from highly condensed sections in Morocco displays a shape structure similar to our data and reinforces arguments that MS stratigraphy has potential as a long-range correlation tool.