SEQUENCE STRATIGRAPHIC ARCHITECTURE OF THE FRASNIAN CLINE CHANNEL, CENTRAL ALBERTA FRONT RANGES
P.K. Wong, J.A.W. Weissenberger, M.G. Gilhooly, 2017. "SEQUENCE STRATIGRAPHIC ARCHITECTURE OF THE FRASNIAN CLINE CHANNEL, CENTRAL ALBERTA FRONT RANGES", NEWADVANCES IN DEVONIAN CARBONATES: OUTCROP ANALOGS, RESERVOIRS AND CHRONOSTRATIGRAPHY, Ted E. Playton, Charles Kerans, John A.W. Weissenberger
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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.
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NEWADVANCES IN DEVONIAN CARBONATES: OUTCROP ANALOGS, RESERVOIRS AND CHRONOSTRATIGRAPHY
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.