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: Lake Hayward is a small coastal hypersaline lake in the Clifton-Preston lakeland system of southwestern Australia. The lake is a Na-Cl-SO 4 brine, compositionally similar to seawater, with a salinity exceeding 200 g/l in summer. Although only 2.75 m deep, it is thermally and chemically stratified between April and January. Groundwater tepees, desiccation features, crusts, gas escape structures, and degrading benthic microbial mats (BMC) occur around the lake margins. Pleistocene carbonate pinnacles acted as nucleation sites for carbonate-precipitating microbialite communities. In the lake center, the surface is covered with non-carbonate precipitating BMC communities, underlain by a thin gypsum layer. The stratigraphy established from 20 cores shows a disconformable transition from Pleistocene eolian coastal-dune sedimentation at the base of the cores to a Holocene limnic swamp. The swamp phase is dated at about 8,000 years BP. Holocene deposition began when rising sea level caused the freshwater swamp to develop over the Pleistocene dune sand and calcretized calcarenite. Wetland conditions became predominant with progressively higher sea level and concomitant rise in water table. Dune barriers were breached and for a short interval Hayward became part of a complex marine inlet with a marine fauna. Gradual lowering of sea level isolated Hayward from the rest of the system. Since 7,000 yr BP, a saline lacustrine environment has prevailed. The lacustrine sediments are laminated and dominated by chemically and biologically precipitated carbonates. Significant amounts of diagenetic dolomite are present. The lake-center cores contain -25 percent TOC. At Lake Clifton, the latest part of a pre-lacustrine marine inlet phase has been dated at between 4,670 and 3,890 yr BP, ending later than at Lake Hayward. Lake Hayward apparently became isolated from the ocean earlier than Lake Clifton and consequently has a longer lacustrine sedimentary record.

Abstract The discovery in 1957 of oil in the remote Swan Hills region, 125 mi northwest of Edmonton, began a wave of exploration similar to that following the 1947 Leduc discovery which started the postwar oil boom in Western Canada. By the end of 1967 more than 1,800 wells had been drilled to explore and develop the Swan Hills region. Drilling has established in-place reserves of more than 5.9 billion bbl of oil and 4.5 trillion ft 3 of gas. Devonian sedimentary rocks unconformably overlie an eroded Cambrian section in the southeast part of the Swan Hills region; in the northwest part of the region, Devonian rocks lap onto the Precambrian granite of the Peace River arch. Three positive features—the Tathlina uplift, Peace River arch, and the Western Alberta ridge—profoundly influenced Middle Devonian Upper Elk Point and Late Devonian Beaverhill Lake sedimentation. An embayment, shielded on the north by the emergent Peace River arch and on the south and west by the nearly emergent Western Alberta ridge, provided an environment conducive to reef development in the central Swan Hills region. Carbonate-bank deposition flanking the Western Alberta ridge in the south and southwestern part of the study area persisted throughout the time of Beaverhill Lake deposition. These beds merge with the overlying Woodbend reef system. Recent changes proposed in Beaverhill Lake nomenclature include the elevation of the Beaverhill Lake to group status and the Swan Hills Member to formation status. The term Swan Hills Formation, as used herein, refers to the reef and carbonate-bank facies of the Beaverhill Lake Group, whereas the term Waterways Formation is applied to the offreef shale and limestone facies. The Swan Hills Formation is considered to be equivalent in age to the Calmut and younger members of the Waterways Formation. The Swan Hills Formation is divided into Light Brown and Dark Brown members. Swan Hills reefs attained a thickness greater than 300 ft, whereas the carbonate- bank facies commonly exceeds 400 ft in thickness. Changing sedimentary and environmental conditions produced a complex reef facies; six major stages are postulated in the development of the undolomitized reef from which the Swan Hills field is producing. Stromatoporoids are the dominant reef-building organisms; abundant Amphipora characterize the restricted lagoonal facies. Although the total impact of Swan Hills production on the provincial economy is difficult to determine, the $184 million paid by the industry to acquire Crown lands in the region during the 10-year period after the initial discovery attests to the economic importance of the Swan Hills producing region.