Peace River Formation Research Articles

First report in the fossil record of a shark tooth embedded in a pinniped bone

There are now many examples in the fossil record of shark bite marks preserved on biogenic materials including coprolites, ammonoids, sea star ossicles, an echinoid, and bone and calcified cartilage. These exceptional fossils document evidence of exploratory behavior, active predation, and/or scavenging. However, only a small subset report on the presence of shark teeth embedded in fossilized bone or cartilage. Although a few shark tooth-marked seal bones are known from the fossil record, no direct evidence of predation or scavenging in the form of a shark tooth embedded in a fossil seal bone has yet been documented. Herein, we describe the first shark tooth embedded in a seal (Phocidae Gray, 1821) bone, a calcaneum (CMM-V-6964), that was surface collected in Mosaic’s South Fort Meade Mine, Hardee County, Fort Meade, Florida, United States. The isolated bone originated from within the Bone Valley Member of the Peace River Formation (Hawthorn Group). The partial tooth is identified as having come from an Early Pliocene great white shark, Carcharodon carcharias (Linnaeus, 1758). This discovery also represents the first C. carcharias tooth ever found embedded in a fossil bone. The embedded tooth may have come about as a result of active predation or scavenging. The extant macropredatory sharks, Carcharodon carcharias (great white shark), Notorynchus cepedianus (Péron, 1807) (sevengill shark), Somniosus microcephalus (Bloch & Schneider, 1801) (the Greenland shark), and Somniosus antarcticus Whitley, 1939 (sleeper shark), are known to actively prey upon seals (Pinnipedia Illiger, 1811). If this peculiar fossil association resulted from active predation, the seal did not survive the encounter because there is no evidence of healing in the area around the embedded shark tooth.

Syn-depositional oil seeps in the Late Albian Paddy Member of the Peace River Formation (Early Cretaceous), north-central Alberta

Abstract Controversy exists regarding the timing of emplacement of oil in the giant Athabasca and Peace River oil sands. Bitumen-cemented sandstones are present in the late Albian Paddy Member of the Peace River Formation; some cemented sandstones formed burrowed firmgrounds and reworked intraclasts, showing that oil was reaching surface by about 101–102 Ma. Estuarine and shallow-marine sandstones of the Paddy Member are exposed on the Peace and Heart rivers in the vicinity of the town of Peace River. Bitumen-cemented sandstone occurs in four stratigraphic settings: 1) An in-situ cement forms locally bedding-transgressive, sheet-like masses in cross-bedded estuarine sandstone; 2) A bitumen-cemented and heavily burrowed layer, 30–60 cm thick, lies immediately beneath a marine transgressive surface and shows that oil infiltrated downward into, and cemented, the upper surface of a shoreface sandbody. The firm sand was subsequently exhumed by transgressive erosion, fractured and burrowed by arthropods; 3) Rounded pebble- to cobble-sized clasts of bitumen-cemented sand lie on the floor of a tidal channel, and the channel floor surface is also stained and burrowed. This case suggests floating oil infiltrated the channel floor at low tide, subsequently hardening prior to erosion and burrowing; 4) Rounded cobble-to boulder-size clasts of bitumen-cemented sandstone, up to 1 m wide and 0.5 m thick, lie on a regional marine ravinement surface cut on the uppermost Paddy shoreface sandstone. The sand was permeated with oil, top-down, then oxidized to form a tough bitumen cement. The bituminous sand was subsequently scoured by waves during marine transgression to form a boulder lag that is enclosed in transgressive marine claystone. All four of these examples show that oil was reaching the Earth’s surface during Paddy time where it infiltrated porous sands to a depth of several decimetres, subsequently degrading and oxidizing to form a tough ‘asphalt pavement’ that attracted a burrowing firmground fauna and was eroded into cohesive intraclasts weighing many tens of kilograms. Pyrolysis proved the bitumen cement to be degraded oil, but it was not possible to identify the source-rock using gas chromatography-mass spectrometry. The Paddy ‘asphalt pavements’ are comparable to cements that form in beach sediments in the wake of catastrophic spills from tanker groundings. A direct analogue is provided by Eocene estuarine sediments in Dorset, U.K. There, bitumen-cemented estuarine sands also formed firmgrounds and intraclasts on channel-floor and marine transgressive surfaces.

Tectonic, eustatic and climatic controls on marginal‐marine sedimentation across a flexural depocentre: Paddy Member of Peace River Formation (Late Albian), Western Canada Foreland Basin

AbstractIn north‐central Alberta and adjacent British Columbia, clastic strata of the middle to late Albian Peace River and Shaftesbury formations were deposited in alluvial to shallow‐marine environments across the foredeep of the Western Canada Foreland Basin. A high‐resolution, log and core‐based allostratigraphic framework for the Paddy Member of the Peace River Formation established nine allomembers, PA to PI, bounded by flooding surfaces and apparently equivalent non‐marine surfaces. Within the estimated 2 Myr. duration of the Paddy, allomembers allow the evolving palaeogeography and changing relationship between accommodation and sedimentation rates to be analysed on time‐steps on the order of 105 years. Paddy strata fill an arcuate depocentre ca 300 km wide, across which the rocks thin eastward from 125 m to ca 5 to 10 m. The northern part of the basin is occupied by muddy, offshore marine deposits that pass abruptly southward into a linear, WSW‐ENE‐trending body of sandstone deposited in a wave‐dominated barrier‐strandplain, at least 350 km long. Extending >200 km to the south of the strandplain was a region of shallow brackish to freshwater lagoons and lakes that graded to the SW into alluvial facies. Within the lagoon region, few‐m thick, elongate and patchy sandstones represent river‐dominated deltas. In allomembers PA to PG, these sandstones are concentrated in the west and south, implying supply from the western Cordillera. In allomembers PH and PI, sandstones are mainly in the east and have a distinctive, quartz‐rich composition. They can be correlated eastward into the coeval Pelican Formation, and were sourced probably from the Canadian Shield on the opposite side of the basin. In the western foredeep, alluvial rocks comprise aggradational, unconfined floodplain deposits with ribbon sandstones, dissected, on at least nine separate levels, by palaeovalleys that are confined to the proximal foredeep. Valleys are 10 to 30 m deep, few km wide, and filled with multi‐storey channel‐bars of pebbly coarse sandstone or conglomerate. Valleys cut down from well‐developed interfluve palaeosols that record a falling and then rising water table. Alternating aggradation and degradation, and advance and retreat of the alluvial gravel front is attributed to cycles of varying rainfall intensity, rather than tectonism or eustasy. Apparently, coeval transgressive‐regressive successions in the lagoon and marine regions are attributed to few‐m scale eustatic changes. On the NE margin of the basin, tidal sandstone fills a northward‐opening estuary cut on the basal Paddy unconformity. This sandstone contains the first well‐documented specimens of Gnesioceramus comancheanus (Cragin), proving contemporaneity with at least part of the marine Joli Fou Formation to the east. Paddy allomembers change shape upward from short blunt wedges, through more acutely tapered wedges, to sheets. This change reflects initially rapid flexural subsidence, attributed to active thickening of the adjacent orogenic wedge. A waning rate of deformation permitted wider dispersal of sediment across the basin, driving broad isostatic subsidence beneath increasingly sheet‐like rock bodies. A major hiatal surface, VE3, records non‐deposition or subtle erosion attributed to erosional unloading and uplift of the adjacent orogen. A subsequent marine transgression is attributed to renewed thickening of the tectonic wedge that triggered deposition of marine mudstone that thickens westward from 0 to >110 m over 300 km. A postulated Milankovitch‐band climatic control on both local gravel supply (via fluctuating rainfall), and shoreline movement (via ?Antarctic glacio‐eustasy or groundwater storage), might account for cycles of alternating incision and aggradation in the alluvial realm. The same mechanism may also explain why shallow‐marine units such as the Cretaceous Viking and Cardium formations contain abundant conglomerate in lowstand shoreface deposits (higher river discharge), yet have highstand shorelines dominated by sandstone (lower river discharge).

Early Cretaceous (?early late Albian) echinoderms from northeastern British Columbia, Canada

An echinoderm association is reported from the ?early late Albian Paddy Member of the Peace River Formation of British Columbia, Canada. The association includes Frasericrinus mauricensis gen. et sp. nov., two additional distinctive crinoid column types, a poorly preserved asteroid, and an umbilical fragment of the cephalopod Stelckiceras. This is the first report of a Cretaceous isocrinid from North America. The echinoderm fossils are from the top of a succession of storm-deposited sandstones and mudstones (Boulder Creek Formation) that can be correlated southward into nearshore and terrestrial facies of the Paddy Member of the Peace River Formation. The echinoderm fossils were buried (and probably lived) about 12–14 km from the contemporaneous shoreline in an estimated water depth of 10–20 m. Integration of biostratigraphic and allostratigraphic schemes suggests that the echinoderms are of earliest late Albian age. The association of the echinoderm fauna with ammonites of Boreal affinity indicates deposition in northern waters, although the presence of Tethyan inoceramids in apparently coeval Paddy Member strata 270 km to the east suggests that northward-advancing water from the Gulf of Mexico had reached northwestern Alberta, if not actually merged with the Boreal embayment. The nearshore occurrence of Cretaceous stalked crinoids is indicative of an asynchronous, gradual migration of stalked crinoids to deep-water habitats, to which they are restricted in modern oceans.

Allostratigraphy and paleogeography of the Harmon and Cadotte members of the Peace River Formation (Middle Albian), west-central Alberta and adjacent British Columbia

Abstract The mudstone-dominated Harmon and sandstone-dominated Cadotte members of the Peace River Formation were deposited during the middle Albian in the southern end of a Boreal marine embayment that occupied the foredeep of the Western Canada Foreland Basin. Sandstone of the Cadotte Member represents a shoreface environment and has traditionally been interpreted as the updip equivalent of offshore Harmon mudstone. Allostratigraphic correlation, based on marine flooding surfaces and unconformities shows that the Harmon alloformation can be divided into five regionally-mappable allomembers. Similar erosion surfaces allow the Cadotte alloformation to be divided into three allomembers. The new allostratigraphy shows that the informal Harmon and Cadotte alloformations do not have an interfingering relationship and hence are not genetically related. Harmon and Cadotte allomembers have been mapped over about 100 000 km2, but show no evidence of stratal lap-out or depositional topography; it is concluded that deposition took place on a shallow marine ramp of very low relief. The vertical stacking of Harmon and Cadotte allomembers across the foredeep indicates that rates of accommodation and sediment supply remained in approximate equilibrium throughout deposition of these units. In the far southern and eastern parts of the study area, changing gamma ray log response suggests that marine deposits of both the Harmon and Cadotte alloformations grade laterally into coeval coastal plain deposits that are mapped in outcrop as Gates Formation whereas in subsurface wireline log picks, these rocks are usually included in the Upper Mannville Group. The lateral boundary between offshore mudstone and coeval nearshore muddy sandstone can be mapped within individual Harmon allomembers; the mudstone to sandstone boundary has a lobate to cuspate pattern in plan view, suggesting that, at the southern extremity of the ‘Harmon Sea’ rivers built elongate deltas in a very shallow-water, low wave-energy setting. Lenticular, sharp-based sandstone bodies 17–42 m thick hang from allomember bounding surfaces in both the Harmon and Cadotte alloformations; these sandbodies probably represent paleovalley fills. Valley incision may have been linked to relative sea-level changes that also gave rise to the marine transgressive surfaces that are traceable over the entire study area. In the east, both the Cadotte and Harmon alloformations are completely truncated by a bevelling unconformity at the base of the Paddy and the laterally-contiguous Joli Fou alloformation.

Allostratigraphy of the Peace River Formation (Albian) in north-western Alberta and adjacent British Columbia

Abstract The middle to upper Albian Peace River Formation was deposited at the southern end of the ‘Hulcross Sea’, an embayment of the Boreal Ocean that occupied the foredeep of the Western Canada foreland basin. The Peace River Formation can be allostratigraphically divided by numerous, regionally-mappable erosion surfaces, recognizable both in wireline logs, core, and outcrop. We propose recognition of the informal Harmon, Cadotte and Paddy alloformations, bounded by four regionally-mappable marine transgressive surfaces, HE0, CE0, PE0 and VE3 in ascending order. The Harmon alloformation consists predominantly of marine mudstone, and is divided into five allomembers bounded by marine flooding surfaces and/or thick bentonites. The Harmon forms a wedge thinning from >145 m in the SW to 5 m in the NE over approximately 300 km. There is no geometric evidence of a sigmoidal geometry, or that allomembers downlap onto a single, distinct surface. Deposition took place on a very low-gradient and low-relief marine ramp, strongly influenced by storms. The Cadotte alloformation consists of well-sorted swaley cross-stratified sandstone and was deposited on a wave-dominated strandplain shoreface. Ravinement surfaces divide the Cadotte into three, sheet-like allomembers, each typically about 10 m thick. Allomembers CA and CB are mainly fine-grained sandstone whereas allomember CC is dominantly medium-grained sandstone with abundant pebble conglomerate. Towards the north, sandstone grades laterally into heterolithic facies indicative of an offshore setting. The Paddy alloformation lies unconformably on the Cadotte, and comprises an array of facies, with alluvial and lagoonal deposits predominant in the south. Further north, sandstone indicative of a wave-influenced strandplain shoreline forms a belt trending WSW-ENE across the middle of the area; heterolithic offshore marine deposits lie to the north. The Paddy alloformation comprises nine allomembers, PA to PI, that onlap progressively onto the basal unconformity PE0 from SW to NE. The pronounced wedge shape and muddy lithology of the Harmon implies rapid flexural subsidence and largely vertical aggradation whereas the sheet shape of the Cadotte suggests a lower rate of subsidence when high-frequency eustatic change may have driven rapid regressions and transgressions. The lower Paddy allomembers PA to PF are strongly wedge-shaped, suggestive of renewed tectonically-driven subsidence whereas upper allomembers PG to PI are more sheet-like, suggesting that a tectonic load exerted a less important influence and instead, more uniform regional isostatic subsidence took place, driven by the load of the eastward-encroaching sediment body. Sandstone-rich Paddy strata are abruptly overlain, at the VE3 unconformity, by a blanket of dark marine mudstone that forms the basal part of the lithostratigraphic Shaftesbury Formation; the mudstone between the VE3 and VE4 surfaces is of upper Viking age, and has a pronounced wedge geometry which implies a major new pulse of flexural subsidence in the west.

Revised stratigraphy, regional correlations and new bentonite radiometric ages for the Albian Loon River Formation, Fort St. John Group, northwestern Alberta

Abstract Although the mudstone-dominated Loon River Formation of northwestern Alberta has clear value as a mappable lithostratigraphic unit, its limits have previously not been well defined. The formation definition is here brought into line with the North American Stratigraphic Code with the delineation of upper, lower and lateral boundaries, and the definition of a composite type section with its lower part in the cored well 00/14-18-123-19W5M/0, and an upper part consisting of outcrop sections along the Boyer and Ponton rivers. Wireline-log, core and outcrop correlations indicate that regional transgressive/flooding surfaces TS1 and TS11, which respectively mark the base of the Spirit River Formation and top of the Peace River Formation in the Peace River area, mark the base and top of the Loon River Formation farther north. Transgressive/flooding surface TS9, at the top of the Spirit River Formation in the south, can be traced northward as an allostratigraphic surface to subdivide the Loon River Formation into lower and upper intervals. The Spirit River and laterally equivalent lower Loon River interval form a northward prograding and thinning clastic wedge. New biostratigraphic data and correlation with the Spirit River Formation indicate that the lower Loon River Formation is of Early to Middle Albian age. In contrast, the Peace River–upper Loon River interval is thicker to the north. Initial mapping of discontinuities within the upper Loon River Formation indicates that it may consist of a series of northward offlapping sedimentary wedges. New U–Pb and 40Ar/39Ar ages for two bentonite beds, age-diagnostic dinocysts, and foraminifera of the Haplophragmoides multiplum Subzone indicate a Middle Albian age for the basal part of the upper Loon River Formation and confirm wireline-log correlation with the basal Harmon Member of the Peace River Formation to the south. The age of the uppermost part of the upper Loon River Formation is less certain. Foraminifera indicative of the Late Albian Miliammina manitobensis Zone and Late Albian dinocysts in samples from the overlying Shaftesbury Formation provide an upper age limit, and these strata may be as young as Upper Albian.

Nearshore articulate crinoid from the Albian of Alberta, Canada (Early Cretaceous, Echinodermata)

During the middle Albian, a southward incursion of the Boreal Ocean flooded northern Alberta and adjacent British Columbia, forming a large embayment known as the Hulcross Sea. Marine mudstones of the Hulcross Formation and Harmon Member of the Peace River Formation record transgression, whereas sandstones of the Cadotte Member of the Peace River Formation record shoreline regression to the north. Abundant hummocky and swaley lamination in the Cadotte sandstone attest to the influence of storms on a shallow shelf. The Cadotte sandstone undergoes a lateral facies change from mud-free shoreface sandstone in the south to heterolithic offshore facies in the north. An articulated crinoid was found within a hummocky sandstone bed about 15 km seaward (north) of the shoreface-shelf facies transition. The articulated state of the crinoid indicates that it was buried very rapidly, and never exhumed. The arms through 20 mm of the column are preserved, but because the details of the aboral cup are not well preserved, this specimen must be left in open nomenclature. The elliptical columnals with a concave latus in the distal portion of the preserved column ally this specimen to the Bourgueticrinida, although with details of the aboral cup lacking and other characters atypical for Mesozoic bourgueticrinids, the Canadian specimen is placed in Bathycrinidae indeterminate. The oldest previously recorded bathycrinids were from the Upper Cretaceous (Maastrichtian), thus this report extends their range to the Lower Cretaceous (Albian).

Counter point bar deposits: lithofacies and reservoir significance in the meandering modern Peace River and ancient McMurray Formation, Alberta, Canada

AbstractCounter point bar deposits in the meandering Peace River, North‐central Alberta, Wood Buffalo National Park, are distinct from point bar deposits in terms of morphology, lithofacies and reservoir potential for fluids. Previously referred to as the distal‐most parts of point bars, point bar tails and concave bank‐bench deposits, counter point bar deposits have concave morphological scroll patterns rather than convex as with point bars. The Peace is a large river (bankfull discharge 11 700 m3 sec−1, width 375 to 700 m, depth 15 m, gradient 0·00004 or 4 cm km−1) in which counter point bar deposits are dominated by silt (80% to 90%), which contrasts with sand‐dominant (90% to 100%) point bar deposits. Beginning at the meander inflection (transition from convex to concave), counter point bar deposit stratigraphy thickens as a wedge‐like architecture in the distal direction until the deposit is nearly as thick as the point bar deposits. The low permeability silt‐dominant lithofacies in counter point bar deposits will limit reservoir extent and movement of fluids in both modern and ancient subsurface fluvial deposits. In the exploration and extraction of bitumen and heavy oil in subsurface fluvial rocks, identification and mapping of reservoir potential of point bar deposits and counter point bar deposits is now possible in the fluvial‐dominated tidal estuarine Lower Cretaceous Middle McMurray Formation, North‐east Alberta. Recent geophysical advances have facilitated imaging of some ancient buried point bar deposits and counter point bar deposits which, on the basis of morphological shape of sedimentary bodies observed from seismic amplitude, can be interpreted and mapped as depositional elements or blocks that contain associated sandstone or siltstone dominant lithofacies, respectively. As counter point bar deposits exhibit poor permeability and thus limit reservoir potential for water, natural gas, light crude, heavy oil and bitumen, counter point bar deposits should be avoided in resource developments. Geophysical imaging, interpretation and mapping of point bar deposit and counter point bar deposit elements provide new opportunities to improve recovery of bitumen and heavy oil and reduce development costs in subsurface cyclic steam stimulation and steam‐assisted gravity drainage projects by not drilling into counter point bar deposits.

Naturally occurring arsenic in the Miocene Hawthorn Group, southwestern Florida: Potential implication for phosphate mining

To understand the mineralogical association, concentration, and distribution of arsenic (As) in the Hawthorn Group, the chemical and mineralogical composition of 362 samples that were collected from 16 cores in southwestern Florida were examined in detail. In the study area, the Hawthorn Group consisted primarily of a basal carbonate unit (the Arcadia Formation) and an upper siliciclastic unit (The Peace River Formation). The Peace River Formation contains appreciable amounts of phosphate and is currently being exploited for phosphate ore. Samples were taken from cores of each formation at intervals of 7.5 m. In addition, to the interval samples, sections likely to have high As concentrations, such as zones with pyrite crystals, hydrous ferric oxides, green clays, and organic material, were collected and analyzed. Bulk As concentrations were determined by hydride generation-atomic fluorescence spectrometry (HG-AFS) after digestion with aqua regia (3:1 HCl and HNO 3). The elements Fe, Al, Si, Mg, Ca, S, and P were measured on the same solutions by inductively coupled plasma optical emission spectrometry (ICP-OES). The identification of discrete minerals was aided by scanning electron microscopy (SEM) and chemical compositions within the sample matrix and in individual minerals were obtained by electron-probe microanalysis (EMPA). This detailed mineralogical and geochemical study demonstrated that: (1) As in the Hawthorn Group varied from formation to formation and was mostly concentrated in trace minerals, such as pyrite; (2) average As concentrations significantly changed from 8.8 mg/kg ( σ = 8.6 mg/kg) in the Peace River Formation to 3.0 mg/kg ( σ = 3.7 mg/kg) in the Tampa Member of the Arcadia Formation. Arsenic concentrations for all Hawthorn samples varied from 0.1 to 69.0 mg/kg; (3) pyrite, with one exception, occurred as framboids and was unevenly distributed throughout the Hawthorn Group; (4) pyrite framboids were located inside a francolite (carbonate fluorapatite) matrix with As concentrations as high as 3730 mg/kg and as a trace mineral in the sediment matrix concentrations varying from <1 to 8260 mg/kg; (5) hydrous ferric oxides (HFO) contained As concentrations as high as 540 mg/kg; (6) francolite, organic material, and clays contained substantially less As than pyrite; (7) thus, the release of As from pyrite could pose a potential problem for the phosphate industry.

Reconstructing a Mid-Cretaceous Landscape from Paleosols in Western Canada

Abstract The Albian Stage of the mid-Cretaceous was a time of equable climate conditions with high sea levels and broad shallow epeiric seas that may have had a moderating affect on continental climates. A Late Albian landscape surface that developed during a regression and subsequent sea-level rise in the Western Canada Foreland Basin is reconstructed on the basis of correlation of paleosols penetrated by cores through the Paddy Member of the Peace River Formation. Reconstruction of this landscape refines chronostratigraphic relationships and will benefit future paleoclimatological studies utilizing continental sphaerosiderite proxy records. The paleosols developed in estuarine sandstones and mudstones, and they exhibit evidence of a polygenetic history. Upon initial exposure and pedogenesis, the Paddy Member developed deeply weathered, well-drained cumulative soil profiles. Later stages of pedogenesis were characterized by hydromorphic soil conditions. The stages of soil development interpreted for the Paddy Member correlate with inferred stages of pedogenic development in time-equivalent formations located both basinward and downslope (upper Viking Formation), and landward and upslope (Boulder Creek Formation). On the basis of the genetic similarity among paleosols in these three correlative formations, the paleosols are interpreted as having formed along a single, continuous landscape surface. Results of this study indicate that the catena concept of pedogenesis along sloping landscapes is applicable to ancient successions. Sphaerosiderites in the Paddy Member paleosols are used to provide proxy values for meteoric δ18O values at 52° N paleolatitude in the Cretaceous Western Interior Basin. The meteoric δ18O values are used to refine existing interpretations about the mid-Cretaceous paleolatitudinal gradient in meteoric δ18O values, and the mid-Cretaceous hydrologic cycle.

A Completion Solution for the Paddy Reservoir in Northeast British Columbia: A Case Study

Abstract The Paddy reservoir, located near the Foothills of the Rocky Mountains in northeast British Columbia, Canada, is a fluvioestuarine valley-filled sandstone that has moderate to high permeability. Evidence of tectonic stress has been observed during hydraulic fracture treatments in the form of excessive wellbore friction and net pressures. Historically, attempts to fracture-stimulate these wells has been difficult due to the inability to generate sufficient fracture width necessary for proppant placement. This paper presents a completion solution for the Paddy reservoir in northeast British Columbia that enabled successful placement of propped fracture treatments. Pressure response of past fracture treatments were analysed to understand the cause of past failures, and to quantify the influence of tectonicallyinduced stress. A recommended completion solution is presented which includes orientated perforating to reduce near-wellbore friction and a process for designing fracture treatments to enable successful placement of proppant. Field examples of the new completion technique are presented which show that near-wellbore friction was reduced by 50%, and that up to four times the amount of proppant was placed in the formation compared to previous treatments. Pressure match simulation results from the fracture treatments are also presented. Geologic Summary The Paddy Member forms the upper portion of the Peace River Formation and is distributed over the Peace River area of northwest Alberta and northeast British Columbia. It is underlain by dominantly coarse-grained shoreface deposits of the Cadotte Member and overlain by marine shales of the Shaftesbury Formation. The Paddy Member is made up of thinly bedded sandstones and shales with occasional thin coals. In the study area, the Paddy is approximately 40 m thick. Reservoir quality, incised valley sandstones located in the upper part of the unit are up to 18 m thick. They are dominantly fine to medium and occasionally coarse grained, fairly quartz-rich sandstones with 10 - 30% chert and other lithic grains. Beds are from centimetre to metre scale in thickness and show small to large-scale trough cross lamination. Where bedding thickness is reduced, millimetre scale wavy shale laminae are common and are often incorporated into stylolitic concentrations, which greatly reduce vertical permeability. The cleaner sandstones were probably deposited under fluvial conditions with some tidal influence where thin shale laminae are common. The dominant cement in these sandstones is quartz, which substantially occludes intergranular porosity in the study area. Small amounts of carbonate cements also occur but are rarely volumetrically important. In addition to intergranular porosity, a significant amount of microporosity has been generated through the dissolution of detrital grains, primarily chert. The abundance of microporosity in these sandstones, together with low water saturations indicated by wireline log analysis, may be the origin of the widely held concern that the Paddy reservoir is susceptible to formation damage through water blocking. Core from the study area indicates that porosity in the Paddy reservoir ranges up to 20%, with associated permeability to air at minimal confining pressure of several hundred millidarcies. A minimum porosity cutoff for pay is taken at approximately 8 - 9%, which is typically associated with 1 md permeability.

Stratigraphic Significance of Ooidal Ironstones from the Cretaceous Western Interior Seaway: The Peace River Formation, Alberta, Canada, and the Castlegate Sandstone, Utah, U.S.A.

Ooidal ironstones form prominent units, and an appreciation of their sedimentological and stratigraphic significance is important for the interpretation of sedimentary successions. Ooidal ironstones from the Albian Paddy Member of the Peace River Formation, Alberta, Canada, and the Campanian Castlegate Sandstone of the Mesaverde Group in Colorado have been analyzed. The ooidal ironstones are associated with a major sequence boundary and subsequent transgressive surface. Both are interpreted to have been deposited under conditions of low net sediment accumulation in well-oxygenated bottom-water conditions, with episodic storm events reworking the sediments. The Paddy Member ironstone is interpreted to have been deposited in an estuarine environment, and the Castlegate ironstone is interpreted to have been deposited in a shallow-marine environment. Both ironstones are dominated by berthierine ooids and grain-rimming and pore-filling siderite, with later ferroan dolomite and calcite in the Castlegate ooidal ironstone. Petrographic, geochemical, and isotopic evidence, coupled with thermodynamic considerations, indicates that the ooidal ironstone mineralogy formed during suboxic diagenesis. The conditions required for suboxic diagenesis were extensive sediment reworking and slow net sediment accumulation rates. We propose that these conditions arose as a result of marine transgression during the initial relative sea-level rise following the development of a sequence boundary. Ooidal ironstone formation ceased once sedimentation rates increased and transgression deepened water depths considerably. These results illustrate the association between ooidal ironstones and major stratal surfaces in sedimentary successions, and highlights the complexity that early diagenesis at such surfaces can take.

Abstract: Sequence Stratigraphy of the Late Miocene-Early Pliocene Peace River Formation, Southwestern Florida

ABSTRACT Platform-wide carbonate deposition ceased on the south Florida Platform during the early Pliocene for a period of about one m.y. A sequence of late Miocene-age shallow marine sediments containing mixed carbonates and siliciclastics was succeeded by an early Pliocene-age, predominantly siliciclastic, deltaic sequence within the Peace River Formation to temporarily end carbonate deposition on the southern interior part of the Florida platform. The Peace River Formation was deposited from about 11 to 4.3 Ma. It is separated from the underlying, middle Miocene Arcadia Formation by an unconformity with a hiatus of 2 to 4 m.y. The unconformity separating the shallow marine sequence (late Miocene) from the overlying deltaic sequence (early Pliocene) has a hiatal gap of 2 to 6 m.y. depending on geographic location. The unconformity between the upper Peace River Formation and the overlying Tamiami Formation shows a distinctive change in bedding orientation and lithology, but only a minimal hiatus occurs (perhaps 0.2 m.y.). The late Miocene sequence contains a series of shallow marine shoaling-upward parasequences 1 to 9 (depending on location) that are either transgressive or regressive. The early Pliocene sequence is a single prograding deltaic deposit that pinches out from north to south in the central part of the platform.

New Tertiary stratigraphy for the Florida Keys and southern peninsula of Florida

Seven lithologic formations, ranging in age from Oligocene to Pleistocene, were recently penetrated by core holes in southernmost Florida. From bottom to top, they are the early Oligocene Suwannee Limestone; late-early Oligocene-to-Miocene Arcadia Formation, basal Hawthorn Group; late Miocene Peace River Formation, upper Hawthorn Group; newly proposed late Miocene-to-Pliocene Long Key and Stock Island Formations; and Pleistocene Key Largo and Miami Limestones. The rocks of the Suwannee Limestone form a third-order sequence. Although the entire thickness was not penetrated, 96 m of Suwannee core from one well contains at least 50 vertically stacked, exposure-capped limestone cycles, presumably related to rapid eustatic fluctuations while experiencing tropical to subtropical conditions. The Arcadia Formation is a composite sequence containing four high-frequency sequences composed of multiple vertically stacked carbonate cycles. Most cycles do not show evidence of subaerial exposure and were deposited under more temperate conditions, relative to the Suwannee Limestone. The Arcadia Formation in southernmost Florida is bounded by regional unconformities representing third-order sequence boundaries. Post-Arcadia transgression produced a major backstepping of sediment accumulation above the upper sequence boundary of the Arcadia Formation. The Peace River Formation, composed of diatomaceous mudstones, has been identified only beneath the Florida peninsula and is not present beneath the Florida Keys. Deposition occurred during marine transgressive to high-stand conditions and a local phosphatization event (recorded in northeast Florida). The transgression is possibly related to a global rise in sea level, which resulted in upwelling of relatively cooler, relatively nutrient-rich water masses onto the Florida Platform. It is proposed that the absence of Peace River sediments beneath the Keys is due to sediment bypass of the upper surface of the Arcadia, a result of sediment sweeping by an ancestral Florida current. During late Miocene to Pliocene time in the Florida Keys, siliciclastics of the Long Key Formation and fine-grained carbonates of the Stock Island Formation prograded toward the southern edge of the Florida Platform and downlapped onto the regional unconformity at the top of the Arcadia. Shallow-marine Pleistocene limestones (Key Largo and Miami Limestones), deposited during tropical to subtropical conditions, drape over accretionary successions of the Long Key and Stock Island Formations.

A Neogene Mixed Siliciclastic and Carbonate Foundation for the Quaternary Carbonate Shelf, Florida Keys

ABSTRACT New core holes and marine seismic profiles show the distribution and paleoenvironments of a siliciclastic foundation sandwiched between the much-studied Quaternary carbonates of the Middle and Upper Florida Keys and Oligocene to Miocene carbonates of the Arcadia Formation, a distance of some 160 km. Throughout this area the Quaternary carbonates are generally no more than 30 m thick and are underlain by up to 145 m of Plio-Pleistocene mixed limestones and sands, and marine siliciclastics (Peace River Formation). Quartz sands, days, and minor reworked phosphatic grains of the Peace River are the distal deposits of an almost peninsula-wide blanket that interrupted prolonged Tertiary carbonate deposition in southernmost Florida. In the Lower Keys the Peace River siliciclastics change fac es to very fine- to fine-grained carbonates composed of bioclastic, planktonic-foraminiferal grainstones and packstones. The position of the present southern Florida shelf margin, with its discontinuous coral reefs, is determined by the seaward paleoslope of siliciclastics and/or carbonates of the Plio-Pleistocene section defined in the Florida Keys. Lithostratigraphy of five continuous cores on the Keys and southeastern mainland, each about 300 m long, combined with numerous well logs and sample descriptions from the Keys and mainland, establish the southern limit of Peace River siliciclastics to at least the Middle Keys. The well data show intervals of quartz of coarse sand to granule size localized as a north-south pathway of maximum paleocurrents that extend from the central part of the peninsula approximately 350 km to the Middle Keys. This pathway of maximum paleocurrents, about 100 km wide, is interpreted as the palimpsest record of unusually strong, southward-moving shoreline and channeled deposition or a giant prograding spit. The ultimate source of these siliciclastics is from the Appalachians, approximately 1000 km to t e north. We propose that the Plio-Pleistocene marine siliciclastics and carbonates (including the Peace River Formation) recovered in wells on the Keys extend seaward beneath the present southern Florida outer shelf and are present in seismic profiles acquired across the shelf-margin slope. A series of profiles forming an offshore traverse from the Lower to Upper Keys show seaward-dipping clinothems that locally dip obliquely to the arcuate strike of the Florida Keys. These clinothems downlap on a prominent reflector that can be traced to an exposed submarine surface of upper Tertiary carbonates, the Pourtales and Miami Terraces. Some reflectors show configurations similar to contourites, and others, to channels. We contend that southward entry of the siliciclastics into southernmost Florida w s deflected eastward by west-to-east channeled flow of an ancestral Florida Current.

Provenance of the Lower Cretaceous Paddy Member (Peace River Formation), Northwestern Alberta

ABSTRACT Most natural gas reservoirs in the Albian Paddy Member (Peace River Formation) in northwestern Alberta produce from quartzarenite sandstone. The provenance of this quartzarenite has been enigmatic, especially considering that in the underlying Cadotte and Falher members quartz may only comprise 40%. Petrographic analysis, including light and heavy minerals and cathodoluminescence colouration of quartz was carried out. Other framework grains include chert and feldspar, generally being 2% or less, with traces of metamorphic and plutonic rock fragments. The heavy mineral suite is dominated by tourmaline, zircon and rutile with lesser amounts of kyanite and staurolite. Most Paddy quartz grains luminesce reddish-brown and purple with fewer bright blues. The Paddy polycrystalline quartz grains were likely derived from thrust sheets which exposed quartz-rich units such as the Precambrian upper Miette and Misinchinka groups and/or Lower Cambrian Gog Group. The minor amount of chert was likely derived from Upper Paleozoic carbonates. Plutonic rock fragments suggest some granitic to granodioritic sources, likely the Hogem, Cassiar and Pitman batholiths in north-central British Columbia. Potash feldspar indicates limited exposure of felsic magmatic rocks and/or high-grade metamorphic sources. Schistose and phyllitic rock fragments were derived from metamorphic sources. Polycrystalline quartz types and Basu plots indicate quartzitic source areas having low to medium grades of metamorphism as well as plutonic sources. Red-brown cathodoluminescence quartz colours also indicate a low-grade metamorphic origin. The heavy minearl suite, particularly kyanite and staurolite, point to areas near the Hogem and Cassiar batholiths as probable source areas. An estimate of the proportions of rock types in the source terrain of the Paddy Member is sedimentary - 60%, metamorphic - 30% and plutonic 10%. RESUME La plupart des reservoirs de gaz du Membre Albian Paddy (Formation Peace River) du nord-ouest de l'Alberta produisent a partir du gres quartzite. L'origine de ce quarzite fut enigmatique, surtout si l'on considere que la teneur en quartz des membres sous-jacents Cadotte et Falher est de 40%. L'analyse petrographique, incluant les mineraux legers et lourds et la cathodoluminescence des couleurs du quartz, a ete effectuee. Les autres grains de masse comprennent le chert et le feldspath, d'une teneur generalement de 2% ou moins, avec des traces de fragments de roches metamorphiques ou plutoniques. Le cortege de mineraux lourds est domine par la tourmaline, le zircon et le rutile avec des quantites plus petites de cyanite et de staurotide. La plupart des grains de quartz du Membre Paddy vus sous un rayon de lumiere paraissent rouge-brun, violet et moins souvent bleu vif. Les grains de quartz polycristallin du Membre Paddy proviennent vraisemblablement des nappes de charriage qui exposent les unites riches en quartz tel que le Precambien superieur des groupes Miette et Misinchinka et/ou du Cambrien inferieur du Groupe Gog. La faible quantite de chert provient probablement des carbonates du Paleozoique superieur. Les fragments de roches plutoniques suggerent des origines granitiques a granodioritiques, probablement les batholites du Hogem, du Cassiar et du Pitman du centre-nord de la Colombie-Britannique, le feldspath potassique indique l'exposition limitee de roches magmatiques de couleur claire et/ou dont l'origine est a grade metamorphique eleve. Les fragments de roches d'origines schisteuses et feuilletees proviennent d'une origine metamorphique. Les differents types de quartz polycristallins et le diagramme de Basu indiquent que les regions d'origine quartzitique ont un grade metamorphique et d'origine plutonique de faible a moyen. La cathodoluminescence de la couleur rougebrune du quartz indiquent egalement une faible teneur d'origine metamorphique. Le cortege de mineraux lourds, surtout de cyanite et de staurotide, pointe vers les regions pres des batholites de Hogem et de Cassiar comme etant des regions d'origines probables. Les proportions evaluees de roches types dans le terrain d'origine du Membre Paddy sont comme suit: 60% sedimentaire, 30% metamorphique et 10% plutonique. Traduit par Marie Louise Tomas End_Page 482------------------------

Shale Diagenesis: A Case Study from the Albian Harmon Member (Peace River Formation), Western Canada

AbstractShales have often been cited as the source of authigenic material that occurs in coarser grained sediments, but there are few comprehensive studies of diagenesis in shales that rigorously attempt to determine if they are sources for potentially mobile constituents or if they retain those constituents within the shale body. The silicate diagenesis of a Lower Cretaceous marine mudstone, the Harmon Member, was investigated by determining the bulk chemistry, clay mineral compositions and mineral modes using standard analytical techniques and linear programming. Changes in mineralogy are observed in hemipelagic laminated mudstones (LM) that are attributable to diagenesis despite relatively constant bulk compositions. These include authigenic kaolinite formation and illitization of detrital muscovite, K-feld-spar and authigenic kaolinite. No diagenetic trends in mineralogy are observed in rapid and episodically deposited transition zone (TZ) sediments because of primary (depositional) mineralogical variability. Diagenetic changes in mineral modes for shales of the Harmon Member are small, suggesting that silicate diagenesis proceeds under relatively “closed system” conditions. The occurrence of authigenic quartz suggests that much of the Si released from the dissolution of quartz and chert is precipitated within the Harmon Member. Al, Ti, and K apparently are conserved. Burial induced increase in temperature is inferred to be the primary control on silicate diagenesis within the Harmon Member.

Estuarine Deposits of the Albian Paddy Member (Peace River Formation) and Lowermost Shaftesbury Formation, Alberta, Canada

ABSTRACT Outcrop exposures of the Peace River Formation in northwestern Alberta contain evidence of significant relative sea-level fluctuations that occurred during the middle to late Albian. These include Paddy Member channels that incised into the Cadotte Member shoreline deposits and the subsequent estuarine-frill. The upper Cadotte Member contact is irregular and siderite-cemented; it has been scoured into and infilled by sandstone of the Paddy Member. The lower sandstone of the Paddy Member is crossbedded, with abundant comminuted, carbonaceous debris. Channels cut into the Cadotte Member are up to 5 m deep and are locally overlain by in situ coal and roots. The channels are infilled with alternating couplets of moderately to intensely bioturbated sand and mud which form inclined h terolithic stratification: mud plugs are also present. Internally these sands are ripple and parallel cross-laminated. This part of the Paddy Member is interpreted as estuarine fill that resulted from a relative sea-level rise. The channel fill is overlain by intensely bioturbated, locally rooted, finely interbedded sandstone, siltstone and shale, with minor reworked bentonites, interpreted as tidal flat deposits. Tidal flat sediments are overlain by 2 to 3 m of scoured, parallel-laminated sandstone and capped by 1.5 m of planar-tabular crossbedded sandstone interpreted as shoreface and transgressive, estuary-mouth deposits, respectively. Evidence for tides throughout the Paddy Member includes inclined heterolithic stratification, mud couplets, reactivation surfaces, reversing paleoflows and compound crossbeds. The incised channels and related fill are correlative with a sequence of paleosols 300 km southwest in the Boulder Creek Formation. A brackish influence is indicated by the presence of a few species of peridinioid dinoflagellates occurring in abundance at certain levels and the trace fossil assemblage. The Paddy Member is overlain by marine mudstone of the Shaftesbury Formation. A 20 to 30 cm thick, wave-rippled layer of fish teeth, fish bones and pebbles, near the base of the Shaftesbury Formation, can be traced along the Peace River for at least 75 km. The layer of fish remains is interpreted as transgressive lag.

Biostratigraphy of the Albian Paddy Member (Lower Cretaceous Peace River Formation), Goodfare, Alberta

Thirty-seven taxa of arenaceous foraminifera, recovered from cores of the upper part of the Paddy Member (Peace River Formation) and the superjacent lower Shaftesbury Formation in the Goodfare area of northwestern Alberta, are assigned to the lower part of the Verneuilina canadensis Subzone of the Miliammina manitobensis Zone of the Lower Cretaceous (upper Albian). A stratigraphic hiatus of eight foraminiferal subzones is implied between the Paddy Member and subjacent Cadotte Member. Progressive transgression of the M. manitobensis sea is reflected by a succession of four faunules of foraminifera and trace fossils. Shallow-water facies and reduced salinity are indicated for the Paddy environment, and a return to normal salinity during deposition of the overlying Shaftesbury Formation. A distinctive Miliammina–Ammotium faunule is figured from the upper part of the Paddy Member.