The Devonian stratigraphic record contains a wealth of information that highlights the response of carbonate platforms to both global-scale and local phenomena that drive carbonate architecture and productivity. Signals embedded particularly in the Middle-Upper Devonian carbonate record related to biotic crises and stressed oceanic conditions, long-term accommodation trends, and peak greenhouse to transitional climatic changes are observed in multiple localities around the world and temporally constrained by biostratigraphy, highlighting distinct and impactful global controls. Devonian datasets also stress the importance of local or regional phenomena, such as bolide impacts, the effects of terrestrial input and paleogeography, syn-depositional tectonics, and high-frequency accommodation drivers, which add complexity to the carbonate stratigraphic record when superimposed on global trends. The unique occurrence of well-studied and pristinely preserved reefal carbonate outcrop and subsurface datasets, ranging across the globe from Australia to Canada, allows for a detailed examination of Devonian carbonate systems from a global perspective and the opportunity to develop well-constrained predictive relationships and conceptual models. Advances in the understanding of the Devonian carbonate system is advantageous considering, not only the classic conventional reservoirs such as the pinnacle reefs of the Alberta Basin, but also emerging conventional reservoirs in Eurasia, and many unconventional plays in North America. The papers in this volume provide updated stratigraphic frameworks for classic Devonian datasets using integrated correlation approaches; new or synthesized frameworks for less studied basins, reservoirs, or areas; and discussions on the complex interplay of extrinsic and intrinsic controls that drive carbonate architectures, productivity, and distribution. The 13 papers in this special publication include outcrop and subsurface studies of Middle to Upper Devonian carbonates of western Canada, the Lennard Shelf of the Canning Basin, Western Australia, and the western USA.

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 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 The southeast and northwest margins of the Frasnian (Upper Devonian) Cline Channel are preserved in excellent and continuous outcrop exposures at both Cripple Creek and Wapiabi Gap in the Alberta Rocky Mountains. Accretionary and interfingering platform margins allow detailed definition and correlation, from platform to basin, of significant sequence stratigraphic surfaces. Eight Frasnian third-order composite sequences are defined using stratal and lithofacies stacking patterns, regional correlation of sequence boundaries, and maximum flooding surfaces, constrained by conodont biostratigraphy. They form part of an upper Givetian–Frasnian second-order transgressive–regressive depositional sequence. Most sequence boundaries observed show subaerial exposure. Others are inferred from stratal architecture, e.g., onlap of tidal-flat or reef margin deposits onto foreslope lithofacies. The Cline Channel was filled asymmetrically from southeast to northwest along the described/studied transect. Progradation of platform margins is on a substrate of platform-derived fine-grained carbonates and extrabasinal clays that form argillaceous carbonates and calcareous shales. Stacking patterns of the composite sequences vary across the Cline Channel. On the southeast side, the second-order Givetian–Frasnian cycle is characterized by initial retrogradation followed by aggradation to retrogradation in the upper mid-Frasnian, and finally, progradation in the upper Frasnian. On the northwest side, the overall stacking pattern is aggradational. With progressive basin filling, platform edges evolved from rimmed boundstone and/or grainstone to mainly grainstone. Foreslope declivity decreased from a minimum of 10° (WD3) to less than 1.5° (WI1) reflecting more ramp-like foreslopes. Coincident with this change, lowstand geometry evolved from wedge shaped to tabular. Where slope gradients were high, lowstands are wedges, less extensive and abutting antecedent highstands. With development of ramp-like geometries, lowstands became tabular and were detached from their antecedent shelf edges with even minor falls of relative sea level. Gentle slope gradients and larger areas for shallow-water carbonate production facilitated extensive lowstand development. Assignment of strata into systems tracts of ramp-like systems is facilitated by subregional correlation. Decreasing accommodation within the second-order highstand is indicated by reduction in composite sequences (CSs) thickness and replacement of open marine with platform-interior strata as the basin shallowed and filled. Composite sequences became more asymmetric, developing thin, offlapping falling stage systems tracts in the late Frasnian, accompanied by a higher frequency of lowstands. Continuous outcrop exposures permitted the amount of relative sea-level fall to be estimated for the bounding surfaces of several CSs. Relative sea-level falls ranged from 9 to ~40 m.

Abstract: The Carson Creek North Field is an Upper Devonian isolated reef-rimmed buildup in the Swan Hills Formation of the subsurface Western Canada Sedimentary Basin. The Swan Hills Formation belongs to the Beaverhill Lake Group, which contains three regionally defined sequences. The sequence boundaries at the base of the middle sequence (BHL2.1 SB) and the upper sequence (BHL3.1 SB) are present within the Carson Creek North buildup, dividing it into three evolutionary stages (lower atoll stage, upper atoll stage, and shoal stage). The BHL2.1 SB is a locally exposed surface at the top of the lower atoll stage, during which the Carson Creek North buildup evolved from a low-angle ramp to a steep-sided reef margin enclosing a restricted lagoon. The BHL3.1 SB is a regional subaerial exposure surface at the top of the upper atoll stage, also known as the intra-Swan Hills unconformity (ISHU). The upper atoll stage consists of backstepping reef margin cycles, and the shoal stage overlying the ISHU contains backstepping ramps culminating in drowning of the Carson Creek North buildup; therefore, the ISHU occurs within a continuously backstepping margin succession. The ISHU demonstrates ~13 m of paleotopographic relief within the Carson Creek North buildup, yet it is not associated with a regressive margin. The Beaverhill Lake Group also contains shallow-water carbonates in the southeastern part of the Western Canada basin (Eastern Shelf) that are partly equivalent to the Swan Hills Formation. The Eastern Shelf carbonates are separated from Carson Creek North by more than 100 km across the Waterways shale basin. A regressive facies succession is present just below the BHL3.1 SB in the Eastern Shelf area, followed by an intrabasin lowstand corresponding to a hiatus during which paleotopography developed on the ISHU at Carson Creek North. The Eastern Shelf succession thus contains the missing regression across the ISHU at Carson Creek North. The lowstand was followed by gradual regional flooding that included deposition of the Carson Creek North shoal stage ramps. Stratigraphic comparisons among Carson Creek North, the Swan Hills Formation, and the Eastern Shelf areas indicate that regional differential subsidence patterns and initial basin floor topography were the most likely reasons for the divergent stratigraphic architecture. The origin of the ISHU itself remains unresolved, but it could be linked to a global eustatic event near the base of the Frasnian Stage, enhanced by tectonic activity in the Western Canada Basin.

ABSTRACT Carbon stable isotope data from western Canada, in combination with biostratigraphic control and astrochronologic constraints from magnetic susceptibility data, provide insight into the pace and timing of the Frasnian–Famennian (F–F; Late Devonian) biotic crisis. In much of the world, this event is characterized by two organic–rich shales, which display geochemical anomalies that indicate low-oxygen conditions and carbon burial. These events, commonly referred to as the Lower and Upper Kellwasser events (LKE and UKE), have been linked to the expansion of deeply rooted terrestrial forests and associated changes in soil development, chemical weathering, and Late Devonian climate. The δ 13 C data generated from organic matter record a 3 to 4‰ positive excursion during each event. These data and other geochemical proxy data reported elsewhere corroborate hypotheses about enhanced biological productivity, driven by terrigenous input under exceptionally warm climatic conditions. In this hypothesis,a boom in primary production leads to successive development of anoxic bottom water conditions, decreased biotic diversity, and net transfer of carbon from the atmosphere to the ocean floor. Despite the importance of the F–F events, a precise chronology for the events is lacking due to limited biostratigraphic resolution. Each of the F–F events falls within one conodont zone, with durations estimated on the order of 0.5 to 1.0 Myr. The LKE occurs very high in Frasnian Zone (FZ) 12, while the UKE begins within FZ 13B, just below the F–F boundary. A previous analysis of high-resolution magnetic susceptibility data from the studied sections in western Canada identified 16.5 eccentricity cycles, each lasting 405 kyr, within the Frasnian strata and one in the earliest Famennian. The present study reports δ 13 C anomalies associated with the LKE and UKE in the same sections. The LKE and UKE intervals comprise 7 to 8 and 13 to 13.5 m of stratigraphic section, respectively. Based on our analysis, this implies that they represent only one 405-kyr eccentricity cycle or less.We estimate that the duration of the LKE was a bit more than half of a long eccentricity cycle (~200–250 kyr), while the UKE was more protracted, lasting a full long eccentricity cycle (~405 kyr). The onset of both events is separated by one-and-a-half 405-kyr eccentricity cycles, indicating that they occurred about 500 to 600 kyr apart. This work demonstrates the utility of magnetic susceptibility, or other long time-series proxy data, used in conjunction with astronomical calibration to provide insight into the pacing of significant events in geologic time.

ABSTRACT: The Upper Devonian Grosmont reservoir in Alberta, Canada, is the world’s largest heavy oil/bitumen reservoir hosted in carbonates, with an estimated 400 to 500 billion barrels of “Initial Oil In Place” at average depths of about 250 to 400 m. Our study is part of a more comprehensive effort to evaluate the Grosmont reservoir through geological, geophysical, and petrophysical methods in order to determine the most advantageous method(s) of exploitation. The reservoir is a carbonate–evaporite system. The carbonates of the Grosmont were deposited during the Late Devonian on an extensive platform and/or a ramp in five or six cycles. Evaporites are interbedded with the carbonates at several stratigraphic levels. These evaporites, informally referred to as the “Hondo Formation,” have received scant attention or were ignored in most earlier studies. However, they may play a crucial role regarding the distribution of the most porous and/or permeable reservoir intervals via dissolution, as permeability barriers to compartmentalize the reservoir during or after hydrocarbon migration, and as a source of dissolved sulfate for microbial hydrocarbon degradation. Most Hondo primary evaporites are anhydrite that formed subaqueously as well as displacively and/or replacively very close to the depositional surface. Secondary/diagenetic sulfates were formed from primary sulfates much later and under considerable burial. The locations of primary evaporite deposition were controlled by a shift from carbonate platform or ramp deposition over time. At present the primary sulfates occur in a number of relatively small areas of about 10 by 20 km to 20 by 30 km, with thicknesses of a few meters each. If these areas represent the depositional distribution, the primary evaporites were deposited in a series of large, shallow subaqueous ponds (salinas). Alternatively, the primary evaporites were deposited in a more extensive lagoon, and their present distribution represents the remnants after postdepositional, mainly karstic dissolution. The evaporites would have acted as intraformational flow barriers up until the time of dissolution, which may be a factor in the development of compositional differences of the bitumens contained at various stratigraphic levels. In the eastern part of the Grosmont reservoir the evaporites appear to be dissolved and replaced by solution-collapse breccias and bitumen-supported intervals of dolomite powder. In the western part of the reservoir the sulfates may form effective reservoir seals on the scale of the sizes of former brine ponds. However, it is likely that hydrocarbons bypassed them wherever the carbonates had sufficient permeability and/or where the marls were breached by faults and/or karstification.

Abstract: Devonian reef complexes are spectacularly exposed in a series of limestone ranges along the northern margin of the Canning Basin in Western Australia and have become known as “The Devonian Great Barrier Reef.” The geological literature on these rocks dates back to 1884, and systematic research on them began during the late 1930s. Since then, many individuals and organizations have progressively increased knowledge of the stratigraphy and paleontology of the reef complexes, although one study concluded that they are products of “dynamic metamorphism.” Comprehensive research by the Geological Survey of Western Australia and its coworkers culminated in 2009 with the publication of a detailed account of the surface geology of the reef complexes and their associated terrigenous conglomerates. This article presents an overview of the research into the reef complexes, focusing on the key milestones and developments in knowledge and concepts.

Abstract: High-resolution, time-significant correlations are integral to meaningful stratigraphic frameworks in depositional systems but may be difficult to achieve using traditional sequence stratigraphic or biostratigraphic approaches alone, particularly in geologically complex settings. In steep, reefal carbonate margin-to-slope systems, such correlations are essential to unravel shelf-to-basin transitions, characterize strike variability, and develop predictive sequence stratigraphic models—concepts that are currently poorly understood in these heterogeneous settings. The Canning Basin Chronostratigraphy Project integrates multiple independent data sets (including biostratigraphy, magnetostratigraphy, stable isotope chemostratigraphy, and sequence stratigraphy) extracted from Upper Devonian (Frasnian and Famennian) reefal platform exposures along the Lennard Shelf, Canning Basin, Western Australia. These were used to generate a well-constrained stratigraphic framework and shelf-to-basin composite reconstruction of the carbonate system. The resultant integrated framework allows for unprecedented analysis of carbonate margin-to-slope heterogeneity, depositional architecture, and sequence stratigraphy along the Lennard Shelf. Systems tract architecture, facies partitioning, and stacking patterns of margin to lower-slope environments were assessed for six composite-scale sequences that form part of a transgressive-to-regressive supersequence and span the Frasnian–Famennian (F–F) biotic crisis. Variations are apparent in margin styles, foreslope facies proportions, dominant resedimentation processes, downslope contributing sediment factories, and vertical rock successions, related to hierarchical accommodation signals and ecological changes associated with the F–F boundary. We present these results in the form of carbonate margin-to-basin sequence stratigraphic models and associations that link seismic-scale architecture to fine-scale facies heterogeneity. These models provide a predictive foundation for characterization of steep-sided flanks of reefal carbonate platform systems that is useful for both industry and academia. This study emphasizes the utility of an integrated stratigraphic approach and the insights gained from better-constrained facies and stratal architecture analysis, insights that were not achievable with traditional sequence stratigraphic or biostratigraphic techniques alone.

ABSTRACT Making reliable correlations and sequence stratigraphic interpretations can be challenging in depositionally complex settings due to depositional heterogeneity and data-set limitations. To address these issues, the Canning Basin Chronostratigraphy Project documented the development of a high-resolution, chronostratigraphic correlation framework across different depositional environments in the Upper Devonian (Frasnian–Famennian) of the Lennard Shelf, Canning Basin, by integrating stable isotope chemostratigraphy, biostratigraphy, magnetostratigraphy, and sequence stratigraphy. This integrated data set allows for a rare, detailed look at the carbon isotope record, and specifically its potential as a sequence stratigraphic interpretation tool and its application to improve correlation capabilities, both of which have implications for better understanding of the depositional history of the Lennard Shelf. For platform-top settings, a sequence stratigraphic framework was constructed using stacking pattern analysis constrained by the paleomagnetic reversal record. In slope settings, where depositional variability and a lack of platform-top control have historically hindered our ability to recognize and correlate systems tracts, carbon isotope chemostratigraphy (in conjunction with conodont biostratigraphy and magnetostratigraphy) proved to be a useful chronostratigraphic tool because primary marine δ 13 C values were well preserved. Using the paleomagnetic reversal record, with additional age control from walkout correlations to key outcrop sections, we were able to confidently correlate from the platform-top into the slope. Evaluation of the slope isotope record, within the projected sequence stratigraphic framework from the platform-top, revealed that variations in δ 13 C values corresponded to changes in sea level. Using this relationship, isotopic trends were used as a proxy for delineating systems tracts in slope sections without direct platform-top control. In turn, this improved correlations through heterogeneous slope facies and also allowed for a refined sequence stratigraphic interpretation of Famennian strata in the Canning Basin. Results from this work also allowed us to develop a model that attempts to explain the observed relationships among global carbon cycling, sea-level fluctuations, and paleoceanographic conditions during the Late Devonian.

Abstract: High-resolution chronostratigraphic correlation using elemental chemostratigraphy in platform carbonates is typically difficult to achieve. Here, elemental chemostratigraphy is used to correlate between two platform-top, carbonate-dominated field sections from the narrow Lennard Shelf that existed on the NE margin of the Canning Basin, Western Australia, during the mid-late Frasnian. The correlation, constrained by magnetic polarity reversals and physical ground truthing, is based on recognition of distinctive cyclical “stacking patterns” defined by changes in concentrations of the trace element zirconium (Zr). Zr concentrations are controlled by the amount of the heavy mineral zircon in the sediments, which is derived from a terrigenous source and is diagenetically very stable. The stacking patterns in the lower part of the study sections display gradually upward-increasing values of Zr to a maximum, followed by an almost immediate fall to a minimum. In the upper part of the study interval, the cycles are more symmetrical, with both gradually increasing and decreasing portions. The point at which the change in Zr stacking pattern occurs in the two sections is synchronous and occurs in association with a supersequence maximum flooding surface. The correlation based on maximum and minimum Zr values throughout the two sections is demonstrated to be chronostratigraphic by comparison with correlations based upon paleomagnetism and physical ground truthing. When element ratios commonly used as provenance and paleoclimate proxies are plotted, the variations between closely spaced samples are greater than any systematic variations throughout the study intervals. Therefore, no isochemical chemozones can be defined, implying that during deposition of the study intervals, there were no long-lived changes in sediment provenance or paleoclimate that the elemental chemistry can detect. The work presented here shows that the standard approach of defining isochemical chemozones for chemostratigraphic correlation is not always appropriate. However, an approach using cyclical changes in elemental variables for chemostratigraphic correlation between two closely spaced sections is chronostratigraphically valid. The greater challenge is in application of the same approach to more widely spaced sections, potentially in different facies of a carbonate setting.

ABSTRACT The effects of bolide impacts on carbonate platform sedimentation and stacking patterns are poorly understood, partly because the geological evidence for marine impact sites is typically unavailable. Givetian–Frasnian carbonates in southern Nevada contain a continuous record of sedimentation before, during, and after the Devonian (Frasnian) Alamo impact event (382 Ma), evidenced mainly by the regional Alamo Breccia Member of the Guilmette Formation. Two transects arranged from seven stratigraphic sections measured through the lower ~300 m of the Guilmette Formation record environmental lithofacies deposited from peritidal to deep subtidal zones. Stacking patterns of peritidal and subtidal cycles indicate four relatively high-frequency sequences superimposed on the larger-magnitude eustatic Taghanic onlap of the Kaskaskia sequence. Sequences are interpreted based on facies proportions and cycle stacking trends because of a lack of prominent erosional surfaces developed on the Frasnian greenhouse shelf. Lateral correlation of facies and cycle stacking indicates that the Alamo impact took place during the late phase of sedimentation during deposition of “Sequence 3” in the Guilmette Formation. Underlying facies and surfaces were obliterated and excavated during the impact, resulting in truncated terminations of sequence boundary and maximum flooding zones. Eustatic sea-level rise during the late Frasnian resulted in an overarching shoreline backstep and deepening of vertical facies associations prior to the Alamo impact. Additional accommodation was gained instantaneously as a result of the Alamo impact, which formed a local, steep-sided basin and shifted the slope break of the platform margin. Postimpact sedimentation within the Alamo crater is characterized by condensed sections of continuously deposited thin-bedded mudstones with pelagic (tentaculites) fauna. Thick shoreface sandstones were deposited in a lowstand clastic wedge as the last phase of crater fill in the study area. While accommodation and depositional environment changed dramatically at the impact site, long-term sedimentation trends immediately outside of the impact site were unaffected by the Alamo event, demonstrating that the forces that control overall carbonate platform growth and evolution (tectonics, climate, oceanography, biology) are of far greater importance than even regional-scale physical perturbations such as meteor impacts.

ABSTRACT: Understanding of very thick Late Devonian shelf strata in Idaho is hindered by formation terminologies. Interpreted genetically, and in combination with lower accommodation settings in Montana, strata reveal craton-to-basin geometries and analogues similar to other western Laurentian basins. The Jefferson Formation Birdbear Member and Three Forks Formation in Montana are correlated to the Jefferson Grandview Dolomite in Idaho using regional sequence stratigraphic surfaces. A new stratigraphic framework defines three widely deposited latest Frasnian sequences and Early Famennian intrashelf basin paleogeography. Peritidal to marine mixed siliciclastic and carbonate rocks of the Middle Devonian lower Jefferson Formation in Idaho are overlain by the Frasnian Dark Dolomite. These rocks are overlain by similar lithologies, including thick evaporite solution breccias of the latest Frasnian and Early Famennian upper Jefferson Formation. Latest Frasnian sequences are similar to Nisku–Winterburn sequences in western Canada. Overlying Famennian successions are correlatives to the Three Forks Formation Logan Gulch Member in Montana and the Palliser–Wabamun units of Alberta. Biohermal Dark Dolomite in the central Lemhi Range and Borah Peak area of the Lost River Range was deposited west of the Lemhi Arch, with buildups also established on ramps near the shelf break in the Grandview Canyon area (Grandview Reef). During onset of the Antler Orogeny, prior to deposition of the Middle Famennian Three Forks Trident Member and widespread disconformities, a latest Frasnian outer shelf barrier formed above the Grandview Reef. Cyclic, heterolithic, peloidal western Grandview Dolomite facies were deposited and are ~330 m thick, although correlative facies of the Jefferson D4 through D6 members are twice as thick behind the shelf edge in the central Lemhi and Borah Peak area. Lower Grandview Dolomite black subtidal carbonate and Nisku buildups (Gooseberry Reef) formed in three late Frasnian sequences and under a basal Famennian sequence boundary. At this time, the Lemhi Arch foundered, but remained unstable—it was termed the “Beaverhead Mountains uplift.” An intrashelf basin dominated midshelf paleogeography during the Early Famennian, accommodating thick shallow water barrier sandstone, solution-collapse breccia, and restricted marine dolostone and limestone of the upper Grandview Dolomite. Crinoid packstone beds near the top of the Jefferson Formation occur below the Three Forks Trident Member in the Lost River Range. Similar nodular, crinoidal limestone with cephalopods occurs under an unconformity with the Sappington Formation in the Beaverhead Mountains. These rocks were previously called the False Birdbear and were grouped with the Jefferson Formation; however, they comprise their own ~15-m-thick sequence and are unrelated to the rarely fossiliferous and dolomitized upper Grandview Dolomite. Open marine shale–limestone sequences of the 80-m-thick Trident Member were deposited on the Idaho shelf above and below regional surfaces and hiatuses. These rocks were variably accommodated on reactivated paleohighs and in local seaways on the craton margin. An unconformity developed on the outer Idaho shelf in the latest Devonian during deposition of the Sappington Formation on the Lemhi Arch and in the Central Montana Trough. Sappington strata were either not deposited on the western shelf or accumulated under deep water conditions and were eroded during regional Mississippian basin inversion and turbidite deposition.