Abstract The early Late Permian Freitag Formation comprises mudrocks, sandstones and thin conglomerates of shallow marine to coastal plain origin, formed along the western margin of the Bowen Basin, Queensland, Australia. The unit is up to 166 m thick in this area, thinning eastward (distally) and southward (laterally) into offshore deposits. The Freitag Formation is considered to be prospective for gas in the northern Denison Trough on the basis of several discoveries in channelized sandstone bodies, the origins and stratigraphic context of which are complex and not fully understood. A re-evaluation of the Freitag Formation, using outcrops, core data, and wireline logs has been completed, and the succession has been subdivided into four unconformity-bounded sequences. The unit, as a whole, can be described as a progradational-retrogradational sequence set, recording a long-term (∼1.5 m.y.) cycle of relative sea-level fall and rise, with shorter-term (?400 k.y.) cycles superimposed on this trend. Depositional facies include non-deltaic, nearshore marine deposits, subaqueous deltaic deposits, and coastal embayment/lagoon deposits. Distinction between these variants is based principally on ichnological criteria. Ichnological signatures throughout much of the formation and in most parts of the study area reflect the overall deltaic aspect of the succession. Key surfaces commonly contain palimpsest trace fossil suites, including many that clearly represent the Glossifungites Ichnofacies. The complex internal architecture is interpreted to be the result of repeated cycles of 10's of meters amplitude relative sea-level fluctuation, possibly related to ice volume fluctuations at the close of the late Paleozoic Gondwanan Ice Age. This revised model for the Freitag Formation suggests that there is an unaddressed potential for gas discoveries in channel sandstones at various levels within the formation.

Abstract: Criteria for recognizing a high-paleolatitude context for sedimentary successions are not widely established. Herein, we provide a facies analysis of the Permian succession of the high-paleolatitude Denison Trough in the southwestern Bowen Basin of Queensland, eastern Australia, and we use this analysis to highlight criteria that may be used to diagnose a high-paleolatitude context in this and other successions. A unified facies scheme for several formations, combining sedimentological and ichnological criteria, recognizes both deltaic and nondeltaic facies within the succession. Whereas a full array of deltaic facies is evident, ranging from distal prodelta to coastal plain, a more limited array of nondeltaic facies is recognized, ranging from shelfal to lower shoreface. The dominance of deltaic facies in the succession suggests that coastlines were overwhelmingly deltaic in aspect. The absence of middle and upper (nondeltaic) shoreface deposits suggests that shallow-water settings were constantly under physico–chemical stresses associated with deltaic efflux, and/or that such deposits were excised by transgressive ravinement following deposition. Deltas were mostly arcuate in planform, consistent with strong wave influence, although some show a more irregular or lobate plan morphology, suggesting significant fluvial influence. Four intervals within the Permian succession (coded P1 to P4) preserve evidence of formation under the direct or indirect (glaciomarine) influence of glacial ice. Palpable evidence of the high-paleolatitude context of the succession is preserved only in these intervals, most commonly in the form of dropstones, glendonite pseudomorphs after ikaite, gravel-grade clasts with modified shapes, and diamictites. In addition to vertical changes into and out of glacial intervals, paleolatitudinal changes in glacially influenced facies are evident across the 25- to 30-degree meridional transect from the Bowen Basin south to the Tasmanian Basin. Outside of glacial intervals P1 to P4, there are few sedimentological or ichnological indicators of high-paleolatitude deposition. Facies characteristics of deposition under glacial influence are therefore crucial to diagnosing the high-paleolatitudinal context of this and other successions.

Abstract The lithological characteristics of wave- and/or storm-dominated delta-front deposits are fundamentally similar to those of facies deposited on the wave-formed shorefaces of strandplain settings. Differentiating ancient shoreface deposits from those that record deposition in proximity to contemporaneous wave-dominated deltas, therefore, is challenging, especially where the facies represent deposits that are intermediate between end-member strandplains and delta fronts. To date, archetypal facies models are inadequate to describe and distinguish between such deposits. The challenge is further accentuated where studies are limited entirely to core and other subsurface data. Depositional processes typical of deltaic settings influence infaunal organisms in subtle but significant ways. The resulting ichnological signatures clearly reflect the innate differences in physicochemical conditions and paleoenvironmental stresses operating in these settings, such as variations in sedimentation rates, substrate consistencies, oxygenation, salinities, energy conditions, increased turbidity levels, and episodic deposition associated with river floods. Lower Permian successions of the Wasp Head, Pebbley Beach, and Snapper Point Formations of the southern Sydney Basin in southeastern Australia are spectacularly exposed in extensive coastal outcrops. The preserved lithologies and many of the primary sedimentary structures are virtually identical to those characteristic of offshore and strandplain shoreface deposits. Integration of the lithological, sedimentological, and subtle ichnological differences, however, demonstrate that these units were deposited under the influence of paleoenvironmental stresses. There is also considerable evidence of very cold climatic conditions and concomitant effects on the depositional environment from ice rafting, which imposed additional paleoenvironmental stresses. For the most part, fair-weather beds closely resemble strandplain shoreface deposits, with trace-fossil suites that are very diverse and contain a mixture of structures that reflect a variety of feeding strategies characteristic of the Cruziana and Skolithos Ichnofacies. Variations in the ichnological signatures, and departures from the archetypal ichnofacies expressions, in the form of sporadic bioturbation levels, reduced assemblage diversities, and reductions in ichnogenera sizes compared to their unstressed counterparts, suggest intermittent physicochemical stresses. Associated storm deposits display many of the sedimentological and ichnological characteristics associated with river influx and deltaic conditions, including: soft-sediment deformation structures and sediment-gravity-flow deposits, recording rapid sediment emplacement; mudstone drapes that are characteristic of hyperpycnally emplaced fluid muds and rapidly flocculated muds that are produced along the zone of mixing at the base of a hypopycnal (buoyant) mud plume; unbioturbated, carbonaceous mudstone interbeds with synaeresis cracks consistent with freshet-induced salinity fluctuations; an abundance of phytodetrital material, and allochthonous wood and large logs; and sandstone beds with “stressed” trace-fossil suites attributable to the Cruziana Ichnofacies, where ordinarily suites representative of the Skolithos Ichnofacies would be expected. These characteristics suggest that fair-weather beds reflect ambient wave shoaling, but during and immediately following storms, increased river discharge strongly influenced the depositional environment and thus the characteristics of the resultant event beds. Overall, the successions are therefore interpreted as wave- and storm-dominated prodelta to proximal delta-front deposits. Variations in storm signature throughout the successions reflect temporal and spatial variations in the preservation and, therefore, abundance of fair-weather beds. Such variations may represent changing storm climates, climatic seasonality, fluctuations in river discharge, increased amalgamation of beds by persistent storm activity, subtle changes in storm tracks with respect to delta-front orientation, and subtle shallowing or deepening along the delta front.

Abstract This study integrates ichnology and sedimentology to refine the palaeoenvironmental and sequence stratigraphic interpretations of the Early Permian Pebbley Beach Formation, in the southern Sydney Basin, Australia. This succession has been interpreted previously to reflect entirely inner to outer shelf and slope environments of deposition. Detailed analysis of the formation reveals ichnological and sedimentological characteristics that contradict a fully marine interpretation. Instead, the interval reflects the vertical superposition and lateral juxtaposition of brackish-water and fully marine units. Marine facies comprise: (1) thoroughly bioturbated muddy siltstone (lower offshore); (2) thoroughly bioturbated sandy siltstone (upper offshore); (3) interbedded bioturbated sandy siltstone and laminated sandstone (delta-influenced offshore transition); (4) thoroughly bioturbated muddy sandstone (distal lower shoreface); (5) interbedded laminated sandstone, bioturbated muddy sandstone and dark claystone (delta-influenced lower shoreface); and (6) bioturbated, laterally variable sandstones (transgressive sand sheets). Estuarine facies comprise: (1) channelized heterolithic sandstone-mudstone (active estuarine channels); (2) sheet-like heterolithic sandstone-mudstone (active estuarine basins); and (3) laminated mudstone (abandoned estuarine channels and basins). The interpreted fully marine deposits contain ichnological suites that exhibit moderate to intense bioturbation, high diversities (31 ichnospecies belonging to 20 ichnogenera), uniform distributions of ichnogenera, and significant numbers of structures reflecting specialized feeding/grazing behaviours. In marked contrast, interpreted estuarine (brackish-water) deposits contain impoverished ichnological suites (9 ichnogenera), show variable but significantly reduced degrees of bioturbation intensity, pronounced variability in ichnogenera distributions and the predominance of a few, simple forms representing simple feeding strategies of resilient trophic generalists. The new analysis allows the recognition of a series of highly top-truncated and condensed sequences (cycles of relative sea-level fall and physical rise), which can be physically correlated over several kilometres. Sequence boundaries typically cut down through shoreface sandstones to directly overlie offshore facies, leading to an interface with little apparent lithological contrast. In the absence of laterally continuous exposure, these surfaces may be recognized by careful ichnofacies evaluation. Thus the re-evaluation presented herein has facilitated a more realistic sequence stratigraphic analysis of the Pebbley Beach Formation.

Abstract Permian sequences in the Denison Trough of Queensland, eastern Australia, are productive conventional gas reservoirs. Previous attempts to interpret the reservoir bodies in terms of depositional environments have relied largely on sedimentary facies analysis and palynology. Sequences have been re-evaluated from a detailed, integrated ichnological and sedimentological perspective, resulting in a significant increase in the precision and resolution of the palaeoenvironmental interpretation. Various marine, coastal and upper delta plain deposits are recognized. Ichnological signatures have facilitated the differentiation of subaqueous delta deposits from those deposited in non-deltaic offshore and shoreface environments. Delta front facies are further subdivided by integrating ichnological and sedimentological data. Permian offshore and shoreface successions in the Denison Trough contain ichnological signatures that exhibit high diversities (25 ichnogenera comprising 32 ichnospecies), moderate to intense levels of bioturbation, uniformity of burrowing, and a wide variety of structures representing specialized feeding strategies. Examples from an additional reservoir dataset, the Tern Formation from the offshore Bonaparte Basin in north Western Australia, also clearly demonstrate the ichnological complexity of Permian shoreface successions. In contrast, Permian deltaic deposits contain ichnological signatures that reflect stressed environmental conditions. Assemblage diversity is reduced (16 ichnospecies), bioturbation intensity is significantly reduced, and uniformity of burrowing is sporadic.

Abstract Hydrocarbons at Norman Wells, Northwest Territories, Canada, are pooled in the Devonian Kee Scarp Formation limestone reef buildup which is 15 mi (25 km) long and 5 mi (8 km) wide. The reef complex began to develop during Upper Middle Devonian time on shale banks of the Hare Indian Formation. Minor variations in sea level localized major reef growth on a thin, open marine platform along basinward edges of the Hare Indian shales. Reef growth proceeded during two major shoaling-upward cycles and was terminated by the advancing clastic sediments of the Canol and Imperial Formations, which serve as the top seal for the reefal buildups. The Kee Scarp reef at Norman Wells attains a maximum thickness of 535 ft (160 m) with a reservoir thickness of 360 ft (110 m). The formation has been divided into four zones, named in ascending order: Kl, K2, K3, and K4. The Kl zone is interpreted as platform, and the K2-K4 zones as reefal buildup. In 1920, Imperial Oil Limited drilled the discovery well for the Norman Wells field near oil seepages at Norman Wells 900 miles (1,500 km) north of Edmonton, Alberta. Oil is stratigraphically trapped in the extreme updip end of the reef buildup. There is no gas cap, and a limited water leg provides no fluid pressure support to assist in producing the oil. The major development plan for producing a portion of the remaining oil at Norman Wells field is discussed in this paper. The plan is based on a recent synergistic geological and engineering study of the reservoir. Information from six oriented cores, well tests, fluid and pressure surveys, outcrop studies, and surface photos has shown that natural vertical fractures present in the reservoir have a strong N30° E orientation. The proposed development plan will make use of the geological and engineering model as well as the directional permeabilities resulting from natural fractures.