Search

Abstract Upper Ordovician biohermal mounds of the Red Head Rapids River Formation in the Hudson Bay Basin consist of microbial and sponge boundstone and cementstone. The cementstone is made up of isopachous layers and botryoids of former aragonite now calcite. Secondary dissolution porosity and small fractures are cutting through the bioherm. Secondary pore-fillings consist of drusy calcite cement and subsequent bitumen. The δ18O VPDB and δ13C VPDB values of late cements are invariably more negative than those of the marine cements. Fluid inclusion microthermometry documents the presence of two distinct populations of homogenization temperatures, one in secondary pore-filling burial calcite cement (T h average 93 ± 10 °C) and a second one in recrystallized marine calcite cements (T h average 118 ± 25 °C). The combined δ18O VPDB and T h data suggest that burial cements precipitated from a fluid having δ18O SMOW values between +0.5 and −2‰, whereas the marine cement data indicate resetting of the fluid inclusions in the presence of a high temperature, δ18O SMOW heavy brine (+2.5 to +12‰). The lower temperature fluid inclusions of the late pore-filling cement agree with recent Apatite Fission Track data suggesting early oil window temperature at maximum burial. The higher T h values recorded in the marine cement represent resetting of initial or entrapment of new fluid inclusions from fracture-controlled circulation of basement-derived fluids. The petrographic and geochemical data suggest that fracture-controlled high temperature brine circulation occurred after the inception of burial and recrystallization of original marine aragonite to calcite, which resulted in the generation of significant secondary porosity that was later filled by lower temperature burial cements and hydrocarbons. [ABSTRACT FROM AUTHOR]

The acid extractable organics (AEOs) containing naphthenic acids (NAs) in groundwater overlying undeveloped shale gas (Saint-Édouard region) and tight oil (Haldimand sector, Gaspé) reservoirs in Québec, Canada, were analysed using high resolution Orbitrap mass spectrometry and thermal conversion/elemental analysis – isotope ratio mass spectrometry. As classically defined by C n H 2n+Z O 2 , the most abundant NAs detected in the majority of groundwater samples were straight-chain (Z = 0) or monounsaturated (Z = −2) C 16 and C 18 fatty acids. Several groundwater samples from both study areas, however, contained significant proportions of presumably alicyclic bicyclic NAs (i.e., Z = −4) in the C 10 -C 18 range. These compounds may have originated from migrated waters containing a different distribution of NAs, or are the product of in situ microbial alteration of shale organic matter and petroleum. In most groundwater samples, intramolecular carbon isotope values generated by pyrolysis (δ 13 C pyr ) of AEOs were on average around 2–3‰ heavier than those generated by bulk combustion (δ 13 C) of AEOs, providing further support for microbial reworking of subsurface organic carbon. Although concentrations of AEOs were very low (<2.0 mg/L), the detection of potentially toxic bicyclic acids in groundwater overlying unconventional hydrocarbon reservoirs points to a natural background source of organic contaminants prior to any large-scale commercial hydrocarbon development. [ABSTRACT FROM AUTHOR]

Unconventional tight to shale reservoirs vary from tight sandstone/siltstone to organic-rich mudstone/shale, commonly with mixed lithologies. In such reservoir systems, matrix pores and organic pores with different origins and distinct physical and chemical properties co-exist for hydrocarbon storage. Traditional resource assessment methods, designed for conventional reservoirs, cannot handle the two pore systems properly. This study proposes a dual-porosity model to respond to the need for a new method in assessing hydrocarbon resource potential in such reservoir systems. The dual-porosity model treats the two types of pores separately and derives the resource estimates from different sources of data, thus better characterizing unconventional reservoirs with complicated pore systems. The new method also has the flexibility of assessing resource potential for the entire spectrum of mixed lithologies ranging from a complete tight to a pure source rock (organic–rich shale/mudstone) reservoir. The proposed method is illustrated through the assessment of the in-place petroleum resource potential in the Upper Ordovician Utica Shale of southern Quebec, Canada. The results of the application suggest that the proposed approach effectively handles the two pore systems in tight-shale reservoirs effectively and provides a useful tool for estimating resource potential in unconventional plays. [ABSTRACT FROM AUTHOR]

New magnetic and seismic datasets offer a unique opportunity to document the geometry of the Appalachian front in a poorly studied segment of the orogen. Interpretation of high-resolution magnetic data allows, for the first time, the documentation of the contact between the autochthonous St Lawrence Platform and the Appalachians and highlights the regional significance of previously poorly documented ENE faults that experienced post-Ordovician strike-slip motion. Seismic data reveal tectonic slices in the foreland domain underlying the Appalachians and show that the depth of the décollement at the base of the Appalachian tectonic wedge varies significantly. Taken together, geological, magnetic and seismic data suggest that the geometry of the Appalachian front exhibits significant variations in map and cross-section views and recorded a polyphased structural history. [ABSTRACT FROM AUTHOR]

Abstract: Production of hydrocarbons from Canadian shales started slowly in 2005 and has significantly increased since. Natural gas is mainly being produced from Devonian shales in the Horn River Basin and from the Triassic Montney shales and siltstones, both located in northeastern British Columbia and, to a lesser extent, in the Devonian Duvernay Formation in Alberta (western Canada). Other shales with natural gas potential are currently being evaluated, including the Upper Ordovician Utica Shale in southern Quebec and the Mississippian Frederick Brook Shale in New Brunswick (eastern Canada). This paper describes the status of shale gas exploration and production in Canada, including discussions on geological contexts of the main shale formations containing natural gas, water use for hydraulic fracturing, the types of hydraulic fracturing, public concerns and on-going research efforts. As the environmental debate concerning the shale gas industry is rather intense in Quebec, the Utica Shale context is presented in more detail. [Copyright &y& Elsevier]

Mg isotopes are used to better understand the genesis of hydrothermal saddle dolomite cements in Lower Paleozoic successions in Canada. These cements occur in fault-bounded dolostones that overlay lithologically diverse basement rocks; Ordovician dolomite lies over the Precambrian craton, whereas the Silurian and Devonian dolomites overlay a succession of tectonically accreted sedimentary, volcanic and ultramafic units of Cambrian to Ordovician age. Lower Silurian saddle dolomites have the most negative δ26MgDSM3 values of our dataset (–3.25 to –1.13‰), and plot in two distinct groups: a strongly negative subset that characterizes higher temperature (175°C) dolomites, and a less negative subset for lower temperature (153°C) dolomites. Upper Ordovician saddle dolomites precipitated at significantly lower temperatures (102°C), and their δ26MgDSM3 values range from –1.26 to –0.71‰. Lower Devonian saddle dolomites formed at very high temperature (350°C) and have δ26MgDSM3 values ranging from –1.29 to –0.78‰. No experimental data on high temperature (100–350°C) fluid-dolomite Mg isotope fractionation factors have been published, and recent research suggests that no significant fractionation occurs between diagenetic fluids and dolomites at high temperatures in closed to semi-closed diagenetic systems. Our results indicate that the isotopic signature of diagenetic fluid is the primary control for the δ26MgDSM3 values in these high-temperature dolomites. [ABSTRACT FROM AUTHOR]

Abstract: The Hudson Strait–Evans Strait–Foxe Channel (HEF) is a major composite topographic feature that connects Hudson Bay and Foxe Basin with the Labrador Sea. Hudson Strait is underlain by several fault-controlled sub-basins with a half-graben geometry. The sedimentary succession in the sub-basins is thicker than the one preserved onshore and reaches a maximum of ∼2.6 km in the eastern part of the Hudson Strait. The lower part of the offshore succession correlates with Paleozoic rocks exposed in nearby islands but the nature and age of the upper part remains poorly constrained. Faults have a clear morphological expression, strike WNW and ENE, dip predominantly toward the north and record an extensional tectonic event that predates an episode of shortening. A model is proposed linking half-graben development to the initial stages of extension in the future Labrador Sea and subsequent inversion to the kinematic decoupling of the Labrador Sea from the Canadian landmass by the Ungava Fault Zone. [Copyright &y& Elsevier]

Carbonates representing different depositional and diagenetic settings (near-surface to deep burial), including modern sabkha, were collected from the Lower Ordovician St. George Group in eastern Laurentia (western Newfoundland, Canada). Based on petrographic examination, three dolomite phases were identified: D1 dolomicrite (crystals ranging from 4 to 50μm), D2 dolomite (50 to 150μm) and D3 saddle dolomite (≥500μm). They occur as replacements and cements, and exhibit dull (for D1 and D3) to zoned (for D2) luminescence. The occurrence of near-micritic dolomites (D1) suggests that dolomitization started at low temperatures under near-surface conditions during an early stage of diagenesis, whereas microthermometric studies of the D2 and D3 dolomites confirmed their formation at higher temperatures, on average, of 112±19°C and 153±30°C, respectively, under deeper burial conditions. The D1 dolomicrite yields an average δ26Mg value of −1.92±0.30‰ (DSM3), which is slightly more negative than those of the D2 dolomite with −1.75±0.34‰ (DSM3) and D3 saddle dolomite with −1.58±0.31‰ (DSM3). The slightly more positive δ26Mg values of the higher-temperature dolomites (D2 and D3) suggest insignificant kinetic fractionation and slight overprinting by 26Mg-enriched diagenetic fluids recirculating in siliciclastic and 26Mg-rich crustal rocks under closed to semi-closed diagenetic conditions. The Sr-isotope signatures support the formation of D1 dolomicrite in an early diagenetic stage and the REE compositions of the investigated dolomites favor their formation in semi-closed to closed diagenetic systems with fluid compositions evolving by circulation through crustal rocks with progressive burial. Furthermore, the Mg isotopes suggest that the lime mudstones of the St. George Group had an algal origin, whereas the D2 dolomite was sourced and subsequently altered mostly from the D1 dolomicrites of the succession. [ABSTRACT FROM AUTHOR]

Abstract: The Phanerozoic Hudson Bay Basin is a large intracratonic basin that is almost completely encircled by Precambrian rocks of the Canadian Shield. The preserved sedimentary succession is up to 2500m thick and consists mainly of Upper Ordovician to Upper Devonian limestones, dolostones, evaporites and minor siliciclastics that were deposited in shallow marine conditions. Backstripping, based on new paleontological data and well correlations, reveals an irregular subsidence history marked by several periods of exhumation. In seismic data, the Hudson Bay Basin appears to have a relatively simple geometry, characterized by a lower sedimentary package cut by high-angle faults, overlain by a saucer-shape, essentially underformed upper sedimentary package. Normal (or transtensional) faults imaged on seismic reflection profiles provide clear evidence for crustal extension during deposition of the older sedimentary packages or slightly later, indicating that the basin is, at least partly, extensional in nature. However, significant changes in the depocenter location during the Paleozoic and variable exhumation values required by new maturation data indicate that other mechanisms influenced the subsidence/exhumation history of the basin. In particular, the influence of far-field events and dynamic topography transmitted by large-scale mantle flow in the continental interior (creating long-wavelength tilting and unconformities) is suspected but not yet proven. [Copyright &y& Elsevier]

Abstract: Nearly 2000 pockmarks with diameters ranging from a few tens of meters up to 700m are present on the seafloor of the St. Lawrence Estuary in eastern Canada. Coring of some pockmarks resulted in the recovery of various-sized and shaped carbonate concretions in a predominantly silty mud matrix. Petrographic and geochemical data on four authigenic carbonate concretions are reported as well as data from shell material in the unconsolidated sediment. Video observations and echo-sounder images indicate that the sampled pockmarks are actively gas venting. The video images show significant look-alike microbial mats in areas where gas is venting. The carbonate concretions are primarily made up of carbonate cements with varying percentage of shell fragments, micrite particles and fine-grained clastics. Orthorhombic crystal morphology and diagenetic fabrics including isopachous layers and botryoids characterize the aragonite cement. Oxygen isotopes ratios for the cement crusts do not record any thermal anomaly at the site of precipitation with δ 18OVPDB ratios (+3‰) in equilibrium with cold (5°C) deep marine waters, whereas significant negative δ 13CVPDB ratios (−9.9 to −33.5‰) for cement and shell material within concretions indicate that the carbonates largely derive from the microbial oxidation of methane. The δ 13CVPDB ratios of aragonite shells (−2.7 to −5.6‰) taken from unconsolidated sediments at some distance from the concretions/vents show variable dilution of HCO3 − with negative δ 13CVPDB ratios derived from microbial oxidation of methane with isotopically normal (0‰) marine bicarbonate. These results are in agreement with other lines of evidence suggesting that pockmarks formed through the recent and still active release of gas from a reservoir within the Paleozoic sedimentary succession. [Copyright &y& Elsevier]

Highly brecciated carbonate-rich serpentinites (or ophicalcites) of Early Ordovician age in the Dunnage Zone of Quebec are host to fracture-fill, high-temperature (80–230 °C) carbonate cements. Away from, or crosscut by the fractures, centimetre- to decimetre-thick crusts made up of massive to laminated micrite, peloidal layers and threads are associated with low-temperature botryoidal calcite cements. The peloidal masses are characterized by a clotted texture that is reminiscent of interpreted fossilized Ordovician microbial communities. The ophicalcite contains carbonate botryoids, morphology commonly found at shallow reefal margins but also at modern cold CH4 seeps and recently documented at hot CH4 vents from serpentinite, such as the modern Lost City hydrothermal field in the Atlantic Ocean. The δ18OVPDB ratios of the calcite botryoids and peloidal layers indicate formation and (or) precipitation out of cold Ordovician deep-marine waters. To the contrary of botryoids at cold methane seeps, the botryoids associated with the modern and Ordovician hot vents do not show the negative δ13CVPDB ratios indicative of microbial isotopic fractionation. Therefore, any microbial-derived HCO3– has been overwhelmed by the isotopically heavier marine-derived carbon during the open-system diagenesis. Carbonate-rich serpentinites should be carefully revisited in the search for evidence of microbial life in the Precambrian, as the negative δ13CVPDB ratios used as fingerprints of biological activity are not always reliable. Des serpentinites riches en carbonates (ou ophicalcites) datant de l’Ordovicien précoce, dans la zone de Dunnage du Québec, contiennent des ciments de carbonates de haute température (80 à 230 °C) qui remplissent des fractures. En s’éloignant des fractures ou recoupées par celles-ci, des croûtes d’épaisseur centimétrique à décimétrique formées de micrite massive à laminée, de couches et de filaments à péloïdes sont associées à des ciments de calcite botryoïdale de basse température. Les masses de péloïdes sont caractérisées par une texture grumeleuse qui suggère une interprétation de communautés microbiennes fossilisées datant de l’Ordovicien. L’ophicalcite contient des carbonates botryoïdaux, une morphologie souvent retrouvée en bordures de récifs de faible profondeur mais aussi documentée à des sites modernes d’émanations froides de CH4 et récemment à des sites d’évents chauds de CH4 développés sur des serpentinites tels que le champ hydrothermal « Lost City »dans l’Océan Atlantique. Les rapports δ18OVPDB des calcites botryoïdale et des couches à péloïdes indiquent une formation et (ou) une précipitation à partir des eaux marines froides et profondes ordoviciennes. À l’opposé des botryoïdes associés aux émanations froides de méthane, les botryoïdes associés aux évents de hautes température modernes et ordoviciens ne montrent pas les rapports négatifs δ13CVPDB indiquant un fractionnement microbien isotopique. Donc, toute quantité de HCO3– d’origine microbienne a été dilué dans le réservoir isotopique de carbone marin plus lourd lors de la diagenèse en milieu ouvert. Les serpentinites riches en carbonates devraient être soigneusement réétudiées lors de la recherche de preuves supportant l’activité microbienne au Précambrien puisque les rapports négatifs δ13CVPDB utilisés en tant qu’empreintes d’activité biologique ne sont pas toujours fiables. [ABSTRACT FROM AUTHOR]

The Lower Ordovician St. George Group of western Newfoundland consists mainly of shallow-marine-platform carbonates (~500 m thick). It is formed, from bottom to top, of the Watts Bight, Boat Harbour, Catoche, and Aguathuna formations. The top boundary of the group is marked by the regional St. George Unconformity. Outcrops and a few cores from western Newfoundland were sampled at high resolution and the extracted micritic materials were investigated for their petrographic and geochemical criteria to evaluate their degree of preservation. The δ13C and δ18O values of well-preserved micrite microsamples range from –4.2‰ to 0‰ (VPDB) and from –11.3‰ to –2.9‰ (VPDB), respectively. The δ13Ccarb profile of the St. George Group carbonates reveals several negative shifts, which vary between ~2‰ and 3‰ and are generally associated with unconformities–disconformities or thin shale interbeds, thus reflecting the effect of or link with significant sea-level changes. The St. George Unconformity is associated with a negative δ13Ccarb shift (~2‰) on the profile and correlated with major lowstand (around the end of Arenig) on the local sea-level reconstruction and also on those from the Baltic region and central Australia, thus suggesting that the St. George Group Unconformity might have likely had an eustatic component that contributed to the development–enhancement of the paleomargin. Other similar δ13Ccarb shifts have been recorded on the St. George profile, but it is hard to evaluate their global extension due to the low resolution of the documented global Lower Ordovician (Tremadoc – middle Arenig) δ13Ccarb profile. [ABSTRACT FROM AUTHOR]

Abstract: Together, recent gravity and high-resolution aeromagnetic datasets are used to qualitatively investigate the upper- and middle-crustal geometry of the Middle Paleozoic Gaspé belt in the northern Appalachians. Long-wavelength potential field anomalies define two sub-basins that are divided by northeast trending gravity highs. For each sub-basins, gravity lows correlate with the youngest rock units. Maps that highlight anomalies associated with near surface features, at the expense of those related to deeper sources, provide an important supplement to the spatially discrete observations derived from bedrock mapping. Analysis of such maps indicates that the sub-basins are characterized by different structural patterns and that faults trending obliquely compared to the main structural grain have been previously underestimated. The geometry of the Gaspé belt as revealed by this integrated geophysical and geological study bears similarities with orogens exhibiting lateral extrusion. This geometry is interpreted as the result of a heterogeneous strain regime in front of an indenter corresponding to the Early Paleozoic Gander/Dunnage crustal block. The indentation tectonic model is supported by: 1) the various strike and kinematic of faults that suggest a strongly heterogeneous strain regime; 2) the greater geological complexity and the occurrence of faults with a significant thrust component in front of the indenter; 3) the predominance of dextral strike-slip faults in the eastern Gaspé Peninsula that result in lateral material transport away from the indenter; 4) the location of abundant Devonian magmatic dykes, sills and stocks in a fault-bounded zone that experienced local extension; 5) the occurrence of block rotation. [Copyright &y& Elsevier]

The Lower Ordovician Aguathuna Formation (~100 m thick) is formed of shallow-marine carbonates, which constitute the uppermost part of the St. George Group of western Newfoundland. Sedimentation was paused by a major subaerial exposure (St. George Unconformity), which likely developed a significant pore system in the underlying carbonates by meteoric dissolution. The sequence has been affected by multiphase dolomitization that caused complex changes in the rock porosity. The Aguathuna dolomites are classified into three main generations ranging in crystal size between ~4 µm and 2 mm. The occurrence of fabric-retentive dolomicrites implies that dolomitization likely started during the early stages of diagenesis. Although dolomitization is pervasive in the upper part of the formation and significantly occludes the pores, some intervals in the lower part have higher porosity. The development of lower permeable layers overlain by an impermeable (seal) cap suggests a possible potential diagenetic trap. Unlike sabkha deposits, the Aguathuna carbonates do not have evaporite interlayers. Furthermore, the low Sr contents (~96 ppm) and the δ18O values of earlier dolomites (–3.3‰ to –6.9‰ VPDB (Vienna Pee Dee Belemnite)) are also difficult to reconcile with a brine origin. The Sr/Ca molar ratios (0.0067–0.0009), calculated for the earliest dolomitizing fluid, suggest a modified seawater origin, likely mixed sea and meteoric waters. The least radiogenic 87Sr/86Sr values of the earliest dolomite are consistent with those of early Ordovician seawater, which supports an early-stage diagenesis. Petrography, geochemistry, and fluid inclusions of the late dolomites suggest precipitation at higher temperatures (~73–95 °C) in deeper burial environments from hydrothermal solutions. [ABSTRACT FROM AUTHOR]

The post-Taconian units in the Quebec and northern New Brunswick Appalachians constitute the Gaspé Belt and geological studies have mostly focussed on its eastern Quebec segment. Biostratigraphic data indicate that the succession in southern Quebec is no older than Late Silurian and extends into the Early Devonian. Two distinct stratigraphic assemblages are present. The first assemblage (Saint-Luc, Cranbourne, and Lac Aylmer formations, and Glenbrooke Group) unconformably overlies the Humber and Dunnage zones. The units show a basal alluvial conglomerate that passes progressively to deeper marine facies upsection, which have recorded a post-Late Silurian transgressive event. The second assemblage (Saint-Francis Group and Frontenac Formation) is faulted against either Dunnage units or autochthonous post-Taconian units. It locally unconformably overlies units of the Dunnage Zone; the succession shows progressively deeper marine conditions upsection and also has recorded a post-Late Silurian transgressive event. The biostratigraphic framework suggests that some of the units that were assumed to be vertically stacked are rather laterally equivalent. Independant evidence supports the hypothesis that the Gaspé Belt in southern Quebec formed after the collapse of the Taconian orogen in Late Silurian time. This event is ascribed to the Salinian Orogeny. The framework from southern Quebec is incorporated in a regional scenario. The Gaspé Belt experienced a Pridolian–Lochkovian sea-level rise. In Pragian time, shallower marine conditions were established in southern Quebec, whereas in the Gaspé Peninsula, the shallower conditions only occurred in early Emsian time. [ABSTRACT FROM AUTHOR]

The Lower Devonian Compton Formation is the uppermost unit of the St. Francis Group in the Connecticut Valley – Gaspé synclinorium of southern Quebec. The Compton Formation is composed of three informal members. Five distinct sedimentary facies have been recognized in the lower two members of the Compton Formation. High-energy, shallow-marine, and channel sands dominate the Milan member. The overlying Lac Drolet member consists of below wave base mud and silt deposits with abundant turbidite sand. The Milan member is interpreted to represent deposits of a river-dominated delta-front environment, whereas the Lac Drolet member is suggestive of below storm-wave base pro-delta deposits. The transition from the Milan member to the Lac Drolet member is correlated with the deepening event recognized in coeval succession in the Gaspé Peninsula and known as the T2 event. There, the coeval Indian Point Formation is interpreted to represent pro-delta sediments. The new paleogeographic map for the Lochkovian illustrates the development of deltaic lobes from northern Gaspé to southern Quebec. In Lochkovian, deltaic regimes were established in southern Quebec and northeastern Gaspé, whereas the intervening successions (western Gaspé Peninsula – New Brunswick) experienced significant synsedimentary tectonic collapse. [ABSTRACT FROM AUTHOR]

The Appalachian Forelands and Platform NATMAP (National Geoscience Mapping Program) project in eastern Canada is a multi-discipline and multi-organization research endeavour aimed at the understanding of the evolution and architecture of the ancient continental margin of Laurentia. This Canadian Journal of Earth Sciences Special Issue presents some recent research progress for our knowledge of the Silurian–Devonian Gaspé Belt of that ancient margin. [ABSTRACT FROM AUTHOR]

The Taconian Humber Zone stretches from western Newfoundland to southern Quebec. The Early Cambrian slope succession in Newfoundland is found in the Curling Group, whereas in Quebec, various units were deposited during that first time slice. Biostratigraphic data allow correlation of the Curling Group with the Labrador Group in Newfoundland and with the newly time-constrained slope succession in Quebec. The end of the rift drift transition is marked by a sea-level lowstand at the end of the Early Cambrian. The Middle Cambrian to latest Early Ordovician passive margin history recorded five cyclic sea-level fluctuations. Three of these cycles are recorded in the shallow-marine Middle to Late Cambrian platform (Port au Port Group) and slope sediments preserved in the Cow Head and Northern Head groups in Newfoundland. The biostratigraphic information assists correlation with Cambrian passive margin units in Quebec. Major sea-level lowstands are recognized along the continental margin in early-middle Late Cambrian (Steptoan) and in late Late Cambrian (Sunwaptan). Even if the Quebec succession can be tied with its Newfoundland correlative, some significant differences in the nature of Upper Cambrian slope conglomerates argue for a tectonic control on the depth of erosion of the Cambrian continental margin. The Lower Ordovician record of the passive margin consists of two depositional cycles (Tremadocian-Arenigian) separated by a sea-level lowstand. This last event is well expressed in platform succession and is also recognized in conglomerate units found in the slope succession. [ABSTRACT FROM AUTHOR]

The Trenton Group (Late Ordovician), the youngest carbonate unit in the Taconic foreland basin of southern Quebec, is a tripartite unit with a distinctive coarse-grained middle part, the Deschambault Formation. Lithofacies of the Deschambault Formation are domimited by coarse-grained bioclastic/intraclastic limestones; finer-grained lithofacies are ubiquitous but subordinate. The complete spectrum of lithofacies indicates sedimentation ranging from above fairweather- to below storm-wave base. Skeletal components are indicative of the modern temperate-water bryomol association. Non-skeletal elements are represented by peloids and intractasts. Accretion rates from areas of continuous sedimentation were low (<14 cm/10[SUP3] years). From sedimentological and faunal evidence, it is proposed that the Late Ordovician Deschambault ramp was bathed by temperate waters. The model compares favourably with modern cool-water shelves rimming the southern edge of the Australian continent. Palaeomagnetic data locate southern Quebec in a low latitudinal setting during the Late Ordovician. Upper Ordovician facies distribution in eastern Canada and progressive disappearance of some faunal provinces through Late Ordovician time are used to conclude that the initiation of the Late Ordovician glaciation that covered most of Gondwana was instrumental in easing northward movement of cold oceanic currents. This resulted in the rapid contraction of the southern hemisphere warm-water tropical belt from a 30° latitudinal-wide zone in the early Caradoc to a 15° zone in the late Caradoc. [ABSTRACT FROM AUTHOR]

The current understanding of the Paleozoic petroleum system in Hudson Bay Basin remains far from complete due in no small part to the uncertainty in locally-calibrated generation and migration models underpinned with reliable source rock kinetic data. To improve the petroleum systems model, four representative immature organic-rich calcareous shales of Late Ordovician age from onshore outcrops surrounding the Hudson Bay were analysed to characterize their source rock generation kinetics. To constrain uncertainty due to laboratory measurement errors in kinetic parameter estimation, six heating rates were used in the pyrolysis experiments for each sample, resulting in 24 kinetic datasets that reduce uncertainty from both source rock heterogeneity and inherited laboratory measurement errors. Under the assumed geological time and geothermal framework, application of the kinetic models resulted in internally consistent generation histories, suggesting that the source rock started to generate oil when temperature reached 100 °C. It is likely where the maximum burial depth excessed 3000 m, the source rocks were in oil generation window with kerogen transformation ratio varying in a range between 52 and 78%. The modeled source rock maturity range from the immature outcrop samples is supported by bulk rock geochemistry data from cuttings of the source rock interval in offshore wells with high S1 peaks, large humps on the left shoulder on S2 curves, typical feature of FID pyrograms in the oil window. Comparison of the kinetic behavior of the samples in this study with those of typical marine Type I, Type II and Type IIS source rocks under laboratory condition and the assumed geological time/temperature framework suggests that kerogen converts to oil in a lower temperature range than those typical normal marine Type II source rock. We attribute the moderate sulfur content (likely high sulfoxide/thiophene ratio) and presence of kerogen component groups that are more prone to cleavage at low temperature as the cause for low temperature onset of hydrocarbon generation. [ABSTRACT FROM AUTHOR]

The Appalachian Forelands and Platform NATMAP project in eastern Canada is a multi-discipline and multi-organization research endeavour aimed at the understanding of the evolution and architecture of the ancient continental margin of Laurentia. The Canadian Journal of Earth Sciences special issue presents some recent research progress for our knowledge of the Cambrian-Ordovician segment of that ancient margin. [ABSTRACT FROM AUTHOR]

• δ13C-δ18O-Δ 47 characterize methane-derived bivalve shells and cements from an Estuary. • Seep shells show full isotopic equilibrium due to slow precipitation. • Cements show unique Δ 47 and δ18O positive offsets from marine signals. • Cements define a new differential disequilibrium domain for natural carbonates. • This isotope study refines the basis for interpreting ancient seep carbonates. Recent studies using the CO 2 carbonate clumped isotope (13C-18O-16O, i.e., Δ 47) paleothermometer and bulk isotopes (δ13C, δ18O) have brought new insights into the prevailing conditions during carbonate formation around marine methane seeps. These studies mostly revealed δ18O or paired δ18O and Δ 47 disequilibria between precipitating minerals, water and DIC species. Here, we have sampled bivalves and cements from two modern, slow-release methane seeps located in the St. Lawrence Estuary. The bivalve shells have marine isotopic signals, whereas the cements show wide Δ 47 (up to +0.05‰) and minor δ18O (+0.8‰) positive offsets relative to marine equilibrium, with a narrow δ13C range (−33.5 to −31.1‰). The observed isotopic trends show that, unlike in previous studies, the aragonite shells precipitated at full isotopic equilibrium, whilst the cements suggest differential disequilibrium precipitation. We propose that the suite of results were generated by distinct Δ 47 and δ18O pathways, as supported by DIC-water isotopic exchange numerical experiments. The observed trends typify slow rates of methane oxidation and carbonate precipitation from residual gas with high-δ18O and low-Δ 47 values after methane-derived CO 2 diffusion. Overall, we suggest that the shells represent potential archives of seep conditions, and that the seep cements define a new Δ 47 and δ18O domain widening the known spectrum of marine conditions producing natural carbonates. Our results, compiled with literature data, help refine the basis for interpreting carbonate precipitation mechanisms in ancient seeps or other geological settings. [ABSTRACT FROM AUTHOR]

The author discusses his involvement on the Canadian Urological Association (CUA) Patient Information Brochure Project. Through this, CUA could develop a product with improved graphic, text content, and established printed patient information materials to urologists. He finds that the brochures scored better in readability compared to other subspecialty organizations.

Dissolved methane concentrations in shallow groundwater are known to vary both spatially and temporally. The extent of these variations is poorly documented although this knowledge is critical for distinguishing natural fluctuations from anthropogenic impacts stemming from oil and gas activities. This issue was addressed as part of a groundwater research project aiming to assess the risk of shale gas development for groundwater quality over a 500-km2 area in the St. Lawrence Lowlands (Quebec, Canada). A specific study was carried out to define the natural variability of methane concentrations and carbon and hydrogen isotope ratios in groundwater, as dissolved methane is naturally ubiquitous in aquifers of this area. Monitoring was carried out over a period of up to 2.5 years in seven monitoring wells. Results showed that for a given well, using the same sampling depth and technique, methane concentrations can vary over time from 2.5 to 6 times relative to the lowest recorded value. Methane isotopic composition, which is a useful tool to distinguish gas origin, was found to be stable for most wells, but varied significantly over time in the two wells where methane concentrations are the lowest. The use of concentration ratios, as well as isotopic composition of methane and dissolved inorganic carbon (DIC), helped unravel the processes responsible for these variations. This study indicates that both methane concentrations and isotopic composition, as well as DIC isotopes, should be regularly monitored over at least 1 year to establish their potential natural variations prior to hydrocarbon development. [ABSTRACT FROM AUTHOR]

The abundance of carbonate minerals in rocks is an important element for petroleum geochemists, geologists and engineers to consider during hydrocarbon exploration and production. Carbonate minerals can be related to the depositional environments of the source rocks and hence the type of organic matter that can be subsequently modified through diagenetic processes. The total carbonate content in shales can also be used to deduce their fracability as reservoir rock for shale gas/oil extraction. At present, mineralogical analysis by X-ray diffraction (XRD) is the most widely used technique in the oil and gas-related petrophysical and geochemical laboratories for identifying and quantifying carbonate minerals in rock samples. In contrast, the use of the total mineral carbon content parameter MinC (%) from Rock-Eval analysis has been limited despite (1) the parameter's effectiveness as demonstrated through instrument and methodology development; and (2) the presence of a large volume of Rock-Eval results due to its widespread use in the oil and gas industry. In this study, we acquired XRD and Rock-Eval analytical results on over nine hundred rock samples ranging from Ordovician to Cretaceous age from four petroleum sedimentary basins in Canada. Least-squares regression analyses produce empirical equations with R 2 values greater than 0.92 for the correlations between XRD total carbonate contents and the Rock-Eval MinC (%) values of six different suites of samples. This indicates that the MinC (%) values generated by Rock-Eval 6 and other instruments of similar capability can be used with confidence for estimating the amounts of total carbonates in sedimentary rock samples. While the correlation between the two types of carbonate content measurements is geology-specific, a global linear regression model (R 2 of 0.97) based on the large combined data set has been proposed for approximating the total carbonate abundances based on Rock-Eval MinC (%) values. [ABSTRACT FROM AUTHOR]

A large, resistant buildup at the top of the Upper Ordovician (Hirnantian?) Red Head Rapids Formation on Southampton Island (Nunavut, Arctic Canada) is dominated by massive boundstone and cementstone facies. These massive facies have more in common with the sponge-microbial reefs that dominated worldwide in the Early Ordovician, including the following primary components: early calcified sponge material, microbial elements, and synsedimentary cement. A close spatial relationship between sponge and microbial framework elements suggests that a poorly preserved decaying sponge framework provided substrates for the attachment and development of microbes and that the microbes played essential roles as reef consolidators. Centimetre-scale colonial metazoans are present and locally intergrown with the sponge and microbial components. Other mound-dwelling invertebrates or calcareous algae are rare. Although altered now to calcite, cement fabrics suggest that aragonite was ubiquitous as seafloor precipitate. Prior to its subaerial exposure in the latest Ordovician, the Red Head Rapids Formation buildup developed on the margin of a shallow-marine evaporative epicratonic basin where a diverse community of reef-building metazoans was unable to flourish. [ABSTRACT FROM AUTHOR]

Rock-Eval pyrolysis has been widely accepted by the petroleum industry as a useful technique for a quick, easy and cost effective source rock evaluation. However, there are misconceptions and misuse of some of the existing Rock-Eval parameters due to implicit underlying assumptions or poor understanding of the limitations, which could lead to erroneous conclusions. Data interpretation from a perspective of hydrocarbon generation kinetics may facilitate better interpretation of the hydrocarbon generation capacity of a source rock from its thermal stability and transformational behaviors. We present a model-assisted approach for data interpretation, from which data scatters can be viewed not only for the remaining petroleum generation potential of individual samples, but also for data specific thermal decomposition path as a whole to verify whether the data come from a single kerogen population with similar kinetics and associated generation potentials. Moreover, we propose a concept of dimensionless TOC and S2 variables that effectively removes the thermal maturity overprint in the traditional TOC vs. S2 plot used for the determination of the kerogen type. The dimensionless variables are defined by rescaling the parameters against their original values before thermal decomposition. On a dimensionless plot, data points from the same genetic population of source rocks align on a single line regardless of their thermal maturation levels. This article demonstrates the methods and the proposed approaches for studying oil generation kinetics and resource potential using traditional Rock-Eval data through examples from selected producing and potential shale gas plays in Canadian sedimentary basins and elsewhere. [ABSTRACT FROM AUTHOR]

The Utica Shale is a potential unconventional tight gas reservoir from southern Quebec. The Utica Shale is a calcareous shale with intervals of fine-grained siltstone with total organic content of 1.2 wt.% (median, n = 408). The major organic matter constituents are migrabitumen and zooclasts (chitinozoan and graptolite) macerals. The primary kerogen is characterized as marine due to the presence of chitinozoan and marine-derived prasinophyte algae such as Tasmanites . A significant portion of the bulk organic matter is dominated by migrabitumen. The present hydrocarbon potential (S2, mg HC/g Rock) of the Utica Shale is largely controlled by distribution of solid migrabitumen throughout the unit. Hydrogen Index (HI) declines with increasing maturity, which is controlled by greater burial from shallow to deep sections. Oxygen Index (OI) remains low in most samples, which is attributed to lack of terrestrial input. However, organic lean intervals show significantly inflated OI due to interference of mineral carbon (possibly siderite). Random reflectance measurements on matrix/solid bitumen and chitinozoans are robust indicators of thermal maturity. The maturity ranges from the late oil window in the shallow Utica to the wet and dry gas windows in the intermediate and deep Utica, respectively. The results suggest that matrix bitumen formed during migration and dissemination of hydrocarbon into the clay fraction of the rock. This is associated with significant bacterial sulfate reduction possibly in the early stages of generation and migration of oil. It appears that the porous siltstone facies in the deeply buried section of the Utica Shale acts as a reservoir for the migrated bitumen from organic-rich strata within the section and/or possibly overlying source rock. [ABSTRACT FROM AUTHOR]

Abstract: The Anticosti Basin is a large, predominantly marine sedimentary basin centered within the northern Gulf of St. Lawrence. Poor-quality vintage seismic reflection data collected more than 25 years ago in the offshore part of the basin failed to depict its geometry. However, recently acquired multibeam bathymetry and magnetic data can be used in combination with high-resolution seismic lines to map the Paleozoic succession within the Honguedo Strait. The upper part of the offshore sedimentary succession consists of approximately 1140m of sediments younger than those exposed on Anticosti Island. The offshore part of the basin includes a 40km wide fold and fault belt sub-parallel to the coastline of the Gaspé Peninsula. The structural style is characterized by broad open synclines, narrow anticlines and NW-striking faults with dextral strike separations, which bears similarities to that of the Gaspé belt that formed mainly during the Middle Devonian Acadian Orogeny. This study indicates that the Appalachian deformation front is located to the north of its classically inferred location. Moreover, it suggests that the curvature of the early Paleozoic assemblages in the Gulf of St. Lawrence is partly a late (Devonian) feature. An improved understanding of the offshore architecture of the basin may help to develop new paleogeographic reconstructions and hydrocarbon exploration models in this under-explored frontier basin. [Copyright &y& Elsevier]

The 15-km-long Matane pockmark train belongs to a series of NNE-striking alignments of pockmarks mapped on the seafloor of the St. Lawrence Estuary. It includes 109 pockmarks that show a complete transition from well-defined, relatively deep (up to 8.6 m), crater-like depressions to subtle, partly buried morphological features, suggesting that pockmarks have formed at different periods along the whole alignment and that the location of fluid release has changed through time. On seismic profiles, pockmarks are characterized by vertical seismic chimneys that root in the (fractured?) hinge zone of an open anticline within the autochthonous Palaeozoic rocks of the St. Lawrence Platform. In absence of a geochemical characterization of expelled gas, the relationship between the Matane pockmark train and the anticline in a domain characterized by mature source rocks is the strongest evidence for the genetic link between pockmarks and the release of gas from an active hydrocarbon system or a reservoir located in the Palaeozoic succession. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The nature and extent of potential source bodies associated with prominent, regional-scale gravity and magnetic anomalies in the northern Québec Appalachians are investigated through forward modeling. Potential field anomalies are interpreted to be the geophysical expression of basalt flows extruded during the Neoproterozoic to Cambrian rifting of Laurentia, prior to opening of lapetus. Geophysical modeling provides substantial new constraints on seismic and structural crosssections and the map distribution of volcanism. This study indicates that the volcanism was significantly more widespread than previously recognized. Basaltic rocks form a sheet up to 4 kilometers thick, transported on the main Taconic décollement. Most of this sheet is deeply buried and overlain by a thick pile of Paleozoic sediments. Later tectonic modifications by backthrusting and hinterland-directed normal faulting as well as by Acadian strike-slip faulting substantially changed the geometry of the transported volcanic rocks and the structural style both across and along the strike of the orogen. The extension of the gravity anomaly under the St. Lawrence River also suggests that the Ordovician deformation front is 20 to 30 kilometers further to the north than previously interpreted. [ABSTRACT FROM AUTHOR]

The Neoproterozoic-Early Cambrian rifted margin of eastern Laurentia is framed by promontories and embayments defined by northeast-trending rifts offset by northwesttrending transforms. A regional first-order synthesis of the available stratigraphic data in the northern Appalachians reveals significant along-strike variations in the thickness, composition, age, and facies of synrift and early postrift stratigraphy. These variations are consistent with models for low-angle detachment rift systems and allow for resolution of regional structures specific to low-angle detachments, including upper-plate margins, lower-plate margins, and transform faults that bound zones of oppositely dipping low-angle detachments. [ABSTRACT FROM AUTHOR]

Abstract: The seabed of the St. Lawrence Estuary is characterized by many fluid releasing features. On multibeam bathymetric images these features correspond to crater-like depression (pockmarks) predominantly found on the northwestern shoulder of the ∼300m deep Laurentian Channel, as well as on the channel floor. Aligned pockmarks, which define segments up to 12km long, are frequent in the Laurentian Channel, whereas they are preferentially associated with submarine landslides on the northwestern shoulder of the channel. On high-resolution seismic profiles, pockmarks found in the Laurentian Channel are characterized by seismic chimneys that may be traced down to the autochthonous Paleozoic rocks (St. Lawrence platform), suggesting a thermogenic origin for the gas. On the northwest shoulder of the Laurentian Channel, the seismic signature of pockmarks does not extend downward to the reflector that corresponds to bedrock (St. Lawrence platform and/or Grenvillian province) suggesting, together with high sedimentation rate, a biogenic origin for the gas. These results are discussed in the light of the data collected in the onshore parts of the St. Lawrence platform and suggest the presence of a mature hydrocarbon source. The conclusions are supportive arguments for the hydrocarbon prospectivity of both the onshore and offshore segments of the Paleozoic autochthonous domain (St. Lawrence platform). [Copyright &y& Elsevier]

In the vicinity of the Town of Gaspé, the relationships between the Silurian-Devonian sedimentary succession of the Gaspé Belt and the Humber and the Dunnage zones are complex. To unravel these relationships, we used high-resolution aeromagnetic data and regional gravimetric data coupled with field tectonostratigraphic information. The magnetic vertical derivative located several magnetic anomalies associated with near-surface features in the Silurian–Devonian cover sequence. In particular, a conglomerate with magnetic fragments that overlies the Late Silurian Salinic Unconformity is clearly recognizable. Large ovoid anomalies of significant intensity located in the Silurian–Devonian sedimentary cover area cannot be associated with any known geological feature. The interpretation of the high-pass and low-pass filtered aeromagnetic survey indicates that the ovoid anomalies originate below the Silurian–Devonian cover sequence. The most significant of the ovoid anomalies is associated with a gravimetric anomaly. It is proposed that these geophysical anomalies are probably associated with ultramafic and (or) volcanic rocks correlative in the subsurface with outcrops of the Cambrian–Ordovician lithologies of the Lady Step Complex and (or) the Shickshock Group. [ABSTRACT FROM AUTHOR]

Presents a study which reconstructed the tectonic evolution of Montréal, Canada using structural and palaeostress analysis. Structural geology of the Montréal area; Inverse analysis of fault slip data; Structural implications for the Montréal area.

The Charlevoix area, which is host to an impact structure of Devonian age, straddles the boundaries among crystalline rocks of the Grenville Province, the Cambrian-Ordovician sedimentary succession of the St. Lawrence Platform, and accreted units of the Appalachian orogen. The area features well-developed supracrustal fault systems attributed to impact cratering. A major fault system oriented from northeast to northwest consists of normal faults marked by cataclastic and gouge breccias and, less frequently, by pseudotachylyte. Detailed mapping of faults both within and outside the Charlevoix impact crater suggests that brittle faulting occurred both before and after impact cratering. Polymictic fault breccias occurring along some supracrustal faults are the clearest evidence of impact-related fault rocks in the Charlevoix area. The St-Laurent fault, trending to the northeast, represents a major structure interpreted as being related to Late Proterozoic - early Paleozoic rifting of the lapetus Ocean. However, the St-Laurent fault crosses the Charlevoix impact crater without major deflection, suggesting post-impact reactivation. The fault systems in the Charlevoix area are interpreted to be pre-impact structures related to the opening of the Iapetus Ocean, most of which have also been reactivated during the Devonian cratering event and in post-impact time, the latter most likely coeval with the Atlantic Ocean rifting in Mesozoic time. [ABSTRACT FROM AUTHOR]

Although computed tomography (CT-Scanning) has been regularly applied to core analyses in petroleum geology, there is still a need to improve our ways to document porosity and porosity distribution in the entire pore scale spectrum, from the tens of nanometer to the meter-scale. Porosity imaging is particularly crucial for complex and heterogeneous rocks such as hydrothermally altered and fractured carbonates. The present work proposes an improved method using medical-CT to reliably estimate reservoir porosity. An in-house core-flooding setup allowed to analyse several individual core samples, scanned simultaneously (dry and saturated), as well as continuous core sections up to 1.5 m long. Without any prior knowledge of samples, three-dimensional alignment and subtraction of the two data sets (dry and saturated states) results in the generation of 3D porosity matrices. The methodology tested on a large set of reference core material shows a strong correlation between conventional gas porosimetry techniques and porosity from CT-scan. The added value of the porosity measurements by CT-scan is, first of all, the generation of 3D images of pore network, allowing to assess spatial attributes of macropores, their distribution and connectivity. Secondly, the CT-scan method also provides continuous porosity profile at the millimetric scale. Both developments are crucial for the understanding of reservoir rock properties. • Combined core-flooding setup and medical-CT give porosity for heterogeneous material. • Reference core material were tested and included 8 different lithologies. • The new CT methodology developed strongly correlates with conventional gas porosimetry. • 3D porosity matrices and continuous porosity profiles at submillimetric scale are produced. [ABSTRACT FROM AUTHOR]

Cyclopentanone is an important platform chemical for various industrial syntheses. It has been recently reported as a major product in biomass cellulose-derived biofuels but has rarely been reported in geochemical research. We report here the abundant occurrence of cyclopentanone, 2-cyclopenten-1-one and their alkyl derivatives in pyrolysates of organic-rich shales. Closed system pyrolyses at temperatures from 290 °C to 350 °C have been carried out on thermally immature organic-rich shale samples of Ordovician and Devonian age from Canada. GC–MS analyses of the pyrolysates show that cyclopentanones, 2-cyclopenten-1-ones and phenols dominate over hydrocarbons in the low temperature hydrous pyrolysates, and their abundance relative to hydrocarbons decreases with increasing thermal maturation. However, these low molecular weight cyclic ketones are only minor components compared with hydrocarbons in anhydrous pyrolysates, indicating that water has played an important role in the formation of these oxygen-containing compounds. In addition, n -alkan-2-ones in the range of C 6 –C 35 are also detected in the hydrous pyrolysates, but they are at much reduced concentrations compared with the cyclic ketones. The potential precursors in the shale and the likely chemical reaction mechanism for the formation of these cyclic ketones are discussed in detail in the paper. [ABSTRACT FROM AUTHOR]

In many unconventional hydrocarbon systems, organic matter (OM) substantially contributes to total porosity of the rock that led to a positive correlation between total organic carbon (TOC) and porosity. While organic porosity is an important reservoir property of unconventional hydrocarbon systems, TOC of these rocks consists of different macerals or petrographic fractions. These TOC fractions can be geochemically divided and quantified by the revised, extended slow heating (ESH) Rock-Eval analysis. This study discusses the contribution of different fractions of OM on porosity variation in the mature to overmature Utica Shale in southern Quebec, using ESH Rock-Eval analysis, helium pycnometery, scanning electron microscopy (SEM), and X-ray diffraction (XRD) mineralogy. Selected samples from three wells at depths of ∼400, 700, and 2000 m, covering a range of thermal maturity from late peak oil window (VRo eqv. ∼1%) to dry gas zone (VRo eqv. ∼2.1%) were analyzed in this study. The predominant OM constituents are solid bitumen, chitinozoans, and minor graptolites with mean TOC of 1.1 ± 0.4 wt. %. The mean porosity for oil and gas window samples decreases with depth from 3.9 ± 0.9 to 2.6 ± 0.5%, respectively. The SEM images reveal that organic porosity is limited to pores developed in solid bitumen, while regardless of thermal maturity, chitinozoans have a non-porous structure throughout the oil to dry gas window. This observation suggests that the impact of thermal maturity on porosity is different for different OM fractions (i.e., macerals), leading to different contribution of OM fractions to total porosity. The latter conclusion is further supported by the improved correlation observed between the solid bitumen fraction and porosity compared to TOC-porosity correlation for oil window samples. Our entire data set suggests that OM (i.e., bitumen fraction), especially in the dry gas window, is not the major controlling factor on the total porosity in the Utica Shale, whereas, intergranular porosity has the dominant control on total porosity. This observation suggests that the hydrocarbon storage potential may largely reside in inorganic pores rather than organic pores in the analyzed intervals of the Utica Shale. The decrease in total porosity observed from shallower samples (i.e., oil window) to deeper samples (i.e., dry gas window) also suggests that intergranular porosity is the dominant porosity component, which decreases with burial. [ABSTRACT FROM AUTHOR]

The S1 peak generated by Rock-Eval analysis of source rock and reservoir interval core and cuttings samples has been routinely employed for in-place hydrocarbon resources assessment by petroleum geochemists, geologists and even engineers. Significant evaporative loss of gaseous and light hydrocarbons (up to C 10 ) can occur during core and cuttings collection and storage, and subsequent sample preparation in the laboratory before instrumental analysis. Consequently a correction to the S1 values is needed in order to obtain a more accurate estimate of the resources. To investigate the effect of evaporative loss on both the amount and the composition of the hydrocarbons retained in shale, a time-series of Rock-Eval and thermal desorption-gas chromatography (TD-GC) analyses have been carried out on an organic-rich Devonian Duvernay Formation shale core sample from the Western Canada Sedimentary Basin (WCSB) and an organic-lean Ordovician Lotbinière Formation shale core sample from Quebec, Canada. The results suggest that the content of total organic carbon (TOC) may play an important role in retaining and preserving light hydrocarbons in sedimentary rocks. A total loss of gaseous and light liquid hydrocarbons up to C 9 is shown to take place within 21 h of sample preparation for the low TOC (<1%) Ordovician Lotbinière shale when the powdered sample was left exposed to the open air, accounting for a 38% decrease in its Rock-Eval S1 peak. The Rock-Eval S1 peak can be reduced by 29% even if the powdered sample has been stored in a sealed container for just over a week. In contrast, the volatile loss has been found to occur at a much slower rate for the high TOC (>11%) Devonian Duvernay shale core sample. After 360 h of exposure to the open air, the powdered Duvernay shale sample shows only 15% decline in its Rock-Eval S1 peak, and still contains high relative concentrations of C 7 –C 9 hydrocarbons. In addition, the evaporative loss of some isomers of C 5 –C 7 hydrocarbons from the organic-rich shale is not fully in agreement with their GC retention/elution behavior, but appears to be partially controlled by their adsorption/desorption on the organic matter and mineral matrix. This suggests that the C 5 –C 8 gasoline range hydrocarbon parameters should be used with caution for oil–oil correlation for unconventional shale and tight petroleum systems. While the findings in this study validate the current industrial practice that targets organic-rich and mature shale intervals for unconventional shale gas and oil exploration because of their large hydrocarbon storage capacity, the results also have an important implication that high TOC content may adversely affect the production efficiency of shale and tight hydrocarbon reservoirs due to the strong adsorption of hydrocarbons by the high maturity organic matter. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper is to present the first step of a new approach to make a map of radonprone areas showing different potential radon emission levels in the Quebec province. This map is a tool intended to assist the Quebec government in identifying populations with a higher risk of indoor radon gas exposure. This map of radon-prone areas used available radiogeochemical information for the province of Quebec: (1) Equivalent uranium (eU) concentration from airborne surface gamma-ray surveys; (2) uranium concentration measurements in sediments; and (3) bedrock and surficial geology. Positive proportion relationships (PPR) between each individual criterion and the 1417 available basement radon concentrations were demonstrated. It was also shown that those criteria were reliable indicators of radon-prone areas. The three criteria were discretized into 3, 2 and 2 statistically significant different classes respectively. For each class, statistical heterogeneity was validated by Kruskal–Wallis one way analyses of variance on ranks. Maps of radon-prone areas were traced down for each criterion. Based on this statistical study and on the maps of radon-prone areas in Quebec, 18% of the dwellings located in areas with an equivalent uranium (eU) concentration from airborne surface gamma-ray surveys under 0.75 ppm showed indoor radon concentrations above 150 Bq/m3. This percentage increases to 33% when eU concentrations are between 0.75 ppm and 1.25 ppm and exceeds 40% when eU concentrations are above 1.25 ppm. A uranium concentration in sediments above 20 ppm showed an indoor radon concentration geometric mean of 215 Bq/m3 with more than 69% of the dwellings exceeding 150 Bq/m3 or more than 50% of dwellings exceeding the Canadian radon guideline of 200 Bq/m3. It is also shown that the radon emission potential is higher where a uranium-rich bedrock unit is not covered by a low permeability (silt/clay) surficial deposit. [Copyright &y& Elsevier]

The article presents a case study of a 10 year old boy who had fallen over a hockey stick and hurt his flank. He suffered cardiac arrest after 10 minutes of arrival to hospital which led to the need of intubation. During emergency laparotomy it was noticed that the spleen and liver were normal though there was expanding retroperitoneal hematoma. Blood supply to left kidney was stopped which helped in stabilizing his blood pressure. His condition stabilized and was discharged after five days.

Four roadcuts southwest of Sussex, New Brunswick, expose a nearly 70 m-thick stratal package from the Hiram Brook Member of the Albert Formation (Horton Group, Tournaisian). Detailed sedimentological logging and analytical work has been undertaken on the southernmost of the roadcuts. Interbedded sandstone and mudstone in the lower and upper intervals of the succession have been interpreted as the deposits of lacustrine deltas, shorelines, and fluvial systems. The medial interval is almost entirely of mudstone and interpreted as offshore lacustrine. A log of the total gamma ray (GR) shows a typical response; low readings are most frequent in the upper interval where coarser-grained sandstone is more prevalent. Higher readings occur in the muddier parts of the lower interval, and the medial intervals that lack a diagenetic carbonate overprint. The response is mirrored in the spectral readings for potassium (K) and thorium (Th). However, several peak uranium (U) readings anomalously correspond to low spectral K and Th values and thus, also, to total GR readings since U is of an order of magnitude less abundant than K in the rock. The anomalies correlate well with beds observed to be darker and more dolomitic. Such beds also record highest total organic carbon (TOC) -- ongoing XRD analysis will also determine if there is covariance with any mineralogical changes. It is generally accepted that U values vary in a positive relationship with organic-rich strata, since dissolved U compounds are scavenged by anoxic-decaying organic matter. However, because Albert Formation (and other) lacustrine strata contain abundant K- and Th-bearing minerals, organic-rich shale frequently does not correspond to peak total GR and may be misinterpreted in standard petroleum well logs where only total GR is recorded. [ABSTRACT FROM AUTHOR]

The Watts Bight Formation in western Newfoundland consists of a Lower Ordovician succession of shallow-water carbonates and has been extensively dolomitized. These dolomites occur as both replacements and cements and are associated with complex changes in the rock porosity and permeability. Early replacement micritic dolomites (D1) are finely crystalline and indicate that dolomitization began during early stages of diagenesis. The calculated δ18O values of the earliest (D1) dolomitizing fluids (–6.4‰ to –9.5‰ VSMOW, Vienna Standard Mean Ocean Water) fall between the estimated δ18O values of Tremadocian seawater and meteoric waters and suggest mixing-zone dolomitization. A second phase of coarsely crystalline (up to 400 μm) dolomite (D2) replaces D1 dolomite and early calcite and is associated with enhancement in porosity and permeability through the development of intercrystalline pores. A late-stage saddle dolomite (D3) and late burial calcite cements significantly occluded the pores in some horizons. Petrography, fluid inclusions, and geochemistry show that D2 and D3 dolomites formed from warm (65–125 °C) saline (10 to 25 eq. wt.% NaCl + CaCl2) hydrothermal fluids. The calculated δ18Ofluid of D2 ranges from –4.5‰ to 3.6‰ VSMOW, and for D3 dolomites, calculated δ18Ofluid ranges from 1.4‰ to 8.4‰ VSMOW, suggesting an influx of basinal brines. The occurrence of high porosity associated with D2, combined with the laterally sealing tight limestone beds, presence of favourable source rocks, and thermal maturation, may suggest that the Watts Bight carbonates are possible potential hydrocarbon reservoirs and suitable targets for future hydrocarbon exploration in western Newfoundland. [ABSTRACT FROM AUTHOR]

Hydrothermally dolomitized carbonate samples from the Lower Silurian Sayabec Formation in northwestern Gaspé Peninsula (lac Matapédia syncline) have been analyzed using X-ray Computed microTomography (micro-CT). This technique records spatial variations in the X-ray attenuation coefficient that may correspond to mineral and pore distributions in the rock. Preliminary micro-CT scans were undertaken at relatively low X-ray energy (<100 keV) and successfully imaged the fracture porosity. In addition, calcite was manifested by regions of greater X-ray attenuation than dolomite. At such energies the photoelectric effect is primarily responsible for attenuation and the attenuation coefficient is a function of the effective atomic number (Zeff ), - with attenuation increasing with Zeff. Consequently, mineral grains that are sufficiently large to be resolved by the instrument, and display contrasting Zeff can be distinguished in a CT scan. In this case, the contrast in Zeff between calcite (15.88) and dolomite (13.94) is sufficient to distinguish between the two minerals, though the presence of Fe in ferroan dolomite would decrease the Zeff contrast. Micro-CT analysis of samples from potential carbonate petroleum (or groundwater) reservoirs therefore has the potential to not only assist in the non-destructive quantification of porosity, but also to track variation in diagenetic overprinting. [ABSTRACT FROM AUTHOR]