Denis Lavoie

Exposure to seismic survey alters blue whale acoustic communication

The ability to perceive biologically important sounds is critical to marine mammals, and acoustic disturbance through human-generated noise can interfere with their natural functions. Sounds from seismic surveys are intense and have peak frequency bands overlapping those used by baleen whales, but evidence of interference with baleen whale acoustic communication is sparse. Here we investigated whether blue whales (Balaenoptera musculus) changed their vocal behaviour during a seismic survey that deployed a low-medium power technology (sparker). We found that blue whales called consistently more on seismic exploration days than on non-exploration days as well as during periods within a seismic survey day when the sparker was operating. This increase was observed for the discrete, audible calls that are emitted during social encounters and feeding. This response presumably represents a compensatory behaviour to the elevated ambient noise from seismic survey operations.

Hydrothermal dolomitization in the Lower Ordovician Romaine Formation of the Anticosti Basin: significance for hydrocarbon exploration

This study deals with the diagenetic evolution of dolostones of the Romaine Formation, from cores and outcrops on Anticosti and Mingan islands, and reports evidence for hydrocarbon migration in secondary porosity generated by high temperature / hydrothermal alteration. Four types of calcite (grouped into early (C1) and late (C2) assemblages) and six types of dolomite (grouped into 3 different (D1, D2 and D3) assemblages) are distinguished. According to fluid-inclusion and stable C-O isotope data, the early calcite group, which consists of sedimentary micrite, replacement microspar and early pore-filling calcite records near surface diagenetic environments. Early and pervasive replacement dolomites (RD1 and RD2 in the first dolomite (D1) assemblage) were formed during early burial, and are not related to porosity generation. Later replacement dolomites (RD3 and RD4 in the second dolomite (D2) assemblage) and pore-filling dolomite cements (PD1 and PD2 in the third dolomite (D3) assemblage) as well as minor sphalerite were formed from warm, saline fluids, which were likely hydrothermal in origin. Vuggy porosity was produced through brecciation and fracturing, and through some dissolution of the D1 dolomite assemblage by these hydrothermal fluids. Intercrystalline porosity was also created during formation of the D2 dolomite assemblage. The vugs were partly occluded by late-stage pore filling dolomite and calcite cements, pyrite and barite. Bitumen droplets in vugs together with hydrocarbon inclusions recorded in C2 calcite and in contemporaneous barite indicate a hydrocarbon migration event after the porositygenerating processes. The brecciation / leaching of a precursor dolomite host is uncommon in hydrothermal dolomite hydrocarbon fields, but is recognized in the adjacent coeval pool in Newfoundland. This type of alteration in the Ordovician carbonates with the presence of a rich hydrocarbon source rock and favourable maturation are key elements for the on-going exploration efforts in this basin.

Dolomitization of the Lower Ordovician Aguathuna Formation carbonates, Port au Port Peninsula, western Newfoundland, Canada: implications for a hydrocarbon reservoir

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.

Sedimentologic, Diagenetic and Tectonic Evolution of the Saint-Flavien Gas Reservoir at the Structural Front of the Quebec Appalachians

ABSTRACT The Beekmantown Group (Lower Ordovician) of the Saint-Flavien reservoir has produced 162x106 m3 (5.7 bcf) of natural gas between 1980 and 1994. The conversion of the field into gas storage was initiated in 1992 and the pool became operational in 1998. Integration of structural and sedimentologic features, carbonate and organic matter petrography and geochemistry for 13 drill holes is used to define a tectonic-sedimentologic-diagenetic model for porosity evolution in these reservoir dolostones. The Beekmantown Group consists of numerous fifth-order shallowing-upward cycles 1.0 to 7.0 m thick (average of 2.4 m). Each cycle consists of a basal shale deposited during the initial flooding of the platform which was subsequently covered by a shoaling succession of subtidal and intertidal limestones to intertidal dolostones. Early dolomitization has produced intercrystalline porosity and preserved some moldic pores in the intertidal facies. Near surface, post-dolomite karstification has created vugs that were subsequently filled by early marine calcite fibrous cement based on the 18O and 13C ratios of calcite. Early burial elements consist of horizontal stylolites, pyrite and sphalerite. Late migrated bitumen was thermally altered or vaporized as native coke under deep burial conditions exceeding 240°C, partly due to overthrusting of Appalachian nappes. Under these conditions, breccias and fractures were generated and subsequently filled with K-feldspar, quartz, illite, and xenomorphic and poikilotopic calcite. The 18O of the poikilotopic calcite and homogenization temperature of coeval fluid inclusions indicate formation under high temperatures (Th about 260°C). Horizontal shear zones and marcasite-rich vertical stylolites were produced during folding and thrusting. Dissolution has preferentially affected late fracture-filling calcite and generated most of the actual porosity during or soon after the Taconian Orogeny. The relationship between the occurrence of smectite and this type of porosity indicates the low temperature condition of this dissolution (T <100°C). Porosity in the Saint-Flavien reservoir has been mostly produced by fracture-controlled, late to post-Taconian dissolution of early to late calcite in the intertidal dolomitic slightly porous facies at the top of rhythmic cycles that compose the Beekmantown Group. End_Page 126------------------------

Massive dolomitization of a pinnacle reef in the Lower Devonian West Point Formation (Gaspe Peninsula, Quebec): An extreme case of hydrothermal dolomitization through fault-focused circulation of magmatic fluids

Devonian pinnacle reefs of the West Point Formation in Gaspe Peninsula (eastern Canada) were built on paleotectonic highs in a foreland basin. Of the nine pinnacles known in outcrop, one is dolomitized and occurs at the junction of two Acadian faults. The petrography of the dolomitized facies has revealed the presence of three dolomite phases and one late calcite cement. A first dolomite phase of small crystals is volumetrically minor; the following dolomite phase dominates and consists of centimeter-size replacive saddle dolomite crystals that contain fluid inclusions with homogenization temperatures ranging between 301 and 382C. The third dolomite consists of millimeter- to centimeter-size saddle dolomite crystals that fill late fractures; this phase is characterized by lower temperature fluid inclusions (159–171C). A lower temperature calcite phase (107–123C) fills some voids. Fluid inclusions are saline (8.7 to 13.3 wt.% NaClequiv). The dolomite and calcite phases are characterized by very negative 18OVPDB (Vienna Peedee belemnite) values (between 19 and 14) and negative 13CVPDB values (between 8 and 1). The replacive saddle dolomite phase originated from a fluid with very positive 18OVSMOW (Vienna standard mean ocean water) values (+8), whereas the following dolomite and calcite precipitated from fluids with lower 18OVSMOW values (+3.4 and +4.5). We propose that fault-focused circulation of magmatic fluids is responsible for the very high-temperature massive dolomite replacement of the calcite host, and high-temperature burial fluids later used fractures to circulate in the dolomitized host to precipitate late dolomite and calcite. Regionally, hydrocarbon migration is recognized at the time of late calcite cementation.

Diagenetic history and porosity evolution of Upper Carboniferous sandstones from the Spring Valley #1 well, Maritimes Basin, Canada–implications for reservoir development

Abstract Eighty-two core samples were collected from the Spring Valley #1 well which penetrates the Upper Carboniferous strata in the Late Devonian–Early Permian Maritimes Basin. The strata consist of alternating sandstones and mudstones deposited in a continental environment. The objective of this study is to characterize the relationship of sandstone porosity with depth, and to investigate the diagenetic processes related to the porosity evolution. Porosity values estimated from point counting range from 0% to 27.8%, but are mostly between 5% and 20%. Except samples that are significantly cemented by calcite, porosity values clearly decrease with depth. Two phases of calcite cement were distinguished based on Cathodoluminescence, with the early phase being largely dissolved and preserved as minor relicts in the later phase. Feldspar dissolution was extensive and contributed significantly to the development of secondary porosity. Quartz cementation was widespread and increased with depth. Fluid inclusions recorded in calcite and quartz cements indicate that interstitial fluids in the upper part of the stratigraphic column were dominated by waters with salinity lower than that of seawater, the middle part was first dominated by low-salinity waters, then invaded by brines, and the lower part was dominated by brines. Homogenization temperatures of fluid inclusions generally increase with depth and suggest a paleogeothermal gradient of 25 °C/km, which is broadly consistent with that indicated by vitrinite reflectance data. An erosion of 1.1–2.4 (mean 1.75) km of strata is inferred to have taken place above the stratigraphic column. δ 18 O values of calcite cements (mainly from the late phase) decrease with depth, implying increasing temperatures of formation, as also suggested by fluid-inclusion data. δ 13 C values of calcite cements range from −13.4‰ to −5.7‰, suggesting that organic matter was an important carbon source for calcite cements. A comparison of the porosity data with a theoretical compaction curve indicates that the upper and middle parts of the stratigraphic column show higher-than-normal porosity values, which are related to significant calcite and feldspar dissolution. Meteoric incursion and carboxylic acids generated from organic maturation were probably responsible for the abundant dissolution events.

Early Devonian Marine Isotopic Signatures: Brachiopods from the Upper Gaspe Limestones, Gaspe Peninsula, Quebec, Canada

ABSTRACT Brachiopods from the Upper Gaspe Limestones (Gaspe Peninsula, eastern Canada) document the isotopic geochemistry (18O, 13C, and 87Sr/86Sr) of marine calcites for the Siegenian and Emsian stages (Early Devonian). Nonluminescent brachiopods (NLB) from five species of a deep-water benthic community show a narrow range of 13C values (+1.3 to + 1.7, average + 1.5) and a much wider range of 18O values (-2.7 to -4.6, average -3.7) that partially overlaps the field of luminescent brachiopods. This is probably related to retention of fabric during diagenesis despite oxygen-isotope exchange. The heaviest 18O values for nonluminescent brachiopods (-3.3 Siegenian; -2.7, Emsian) are interpreted as the signature of marine low-Mg calcite. The 18O values for the Gas e brachiopods suggest a negative 18O shift at the end of the Early Devonian. The heaviest 18O values documented by previous workers for late Early Devonian (Emsian) brachiopods cluster around -4.5 a figure that differs by 1.8 from the heaviest value for Gaspe brachiopods. This difference is most likely related to the growth of the Gaspe brachiopods in deeper and cooler seawater, as suggested by independent sedimentologic and biologic evidence, rather than a 7°C warming of ocean surface temperatures or a rapid (< 7 ma) shift in the 18O of seawater in a period of nonglaciation. The 87Sr/86 data for Early Devonian brachiopods fill the Early Devonian gap in the Burke et al. (1982) curve for Devonian seawater. The Siegenian value is slightly more radiogenic than the younger Emsian ones, and support a continuous decrease in 87Sr/86Sr values from latest Silurian to Middle Devonian time.

Stratigraphy and structure of the Laurentian rifted margin in the northern Appalachians: A low-angle detachment rift system

The Neoproterozoic–Early Cambrian rifted margin of eastern Laurentia is framed by promontories and embayments defined by northeast-trending rifts offset by northwest-trending 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.

Brittle fault evolution of the Montréal area (St Lawrence Lowlands, Canada): rift-related structural inheritance and tectonism approached by palaeostress analysis

The Montreal area belongs to the St Lawrence Lowlands, a Cambrian Early Ordovician passive margin of the Iapetus Ocean, later covered by Appalachian Middle to Upper Ordovician foreland deposits. A structural and palaeostress analysis has been carried out in order to reconstruct its tectonic evolution. The structural map has been revised with new data. Palaeostresses are reconstructed based on inversion of fault slip data, and these results are independently corroborated by the microstructural study of calcite mechanical twinning. Field relationships are used to establish the relative chronology of fractures and to deduce the motion on regional faults. The reconstructed structural and tectonic evolution brings to light some relationships between structural inheritance and tectonic events that have affected the area since Early Palaeozoic times. An early NW–SE extension is responsible for N040-trending faults along the northern border of the St Lawrence Lowlands, and for N090- and N120-trending faults cross-cutting the Montreal area. This extension is followed by WNW–ESE and NNW compressions, which have induced reverse motion on pre-existing faults and generated strike-slip conjugate faults. Subsequent NE–SW and NNW–SSE-directed extensions have reactivated previous faults with normal to strike-slip motions. A late NE–SW compression is recorded in the Monteregian plutons. Compressions in WNW–ESE and NNW directions are consistent with Appalachian collisional tectonism, but N040- and N090-trending faults cross-cut Appalachian folds and foreland deposits. Although the early NW–SE extension is consistent with the collapse of the Iapetan margin in Early Palaeozoic times, most of the present geometry of the St Lawrence Lowlands could be attributed to Mesozoic tectonism, recorded as nearly N–S-directed extensional events.

Multiple-stage diagenetic alteration and fluid history of Ordovician carbonate-hosted barite mineralization, Southern Quebec Appalachians

Lower Ordovician bioclastic limestone of the Upton Group, southern Quebec Appalachians, hosts stratabound Ba-Zn-Pb mineralization. The Upton Group, a mixed platform carbonate-siliciclastic-volcanic succession, is exposed as windows within the tectonically overlying Cambrian siliciclastics of the Granby Nappe. Mineralization consists mostly of barite and minor amounts of sulfides (sphalerite, pyrite, galena, and chalcopyrite), in addition to calcite, quartz and bitumen cements. It is hosted by a bioclastic limestone which is interbedded with and capped by a black calcareous shale, and underlain by a mudstone-siltstone-volcanic succession and a lower poorly fossiliferous limestone. The lower limestone recorded early extensive dolomitization followed by meteoric alteration (dedolomitization, sulphate dissolution, vadose cements, soil pisoids, etc.), and burial diagenesis (recrystallization, fracturation, and cementation). The vadose gravitational calcite cements yield δ18OPDB values of −8.4 to −11.0‰ andδ13CPDB values of +2.4 to +2.8‰. The thin soil profiles with pisoids have a δ18OPDB value of −8.2‰ and a δ13CPDB value of +2.0‰. These data suggest an evaporative18O-enrichment of near-surface trapped soil moisture (vadose water) in a rock-dominated diagenetic system. The recrystallized limestone hasδ18OPDB values of −11.4 to −15.5‰ and near Early Ordovician marine δ13CPDB values of −0.2 to +2.5‰. These data suggest a final stabilization of the limestone from high temperature fluids in a rock-dominated diagenetic system. The mineralized bioclastic limestone shows rare evidence of early submarine cementation which is overprinted by significant post-depositional recrystallization and hydrothermal alteration. The latter resulted in the generation of secondary porosity and precipitation of a subhedral barite cement, a bladed barite cement, and fracture-filling barite. Fracture- and void-filling calcite, sulfides, quartz and bitumen cementation followed barite mineralization. Pre-barite syntaxial calcite overgrowths on crinoids yieldδ13CPDB values of −3.9 to −15.0‰ andδ18OPDB values of −13.7 to −14.8‰. Post-barite sparry calcite cement and fracture-filling calcite haveδ13CPDB values of −2.6 to −13.0‰ and −2.4 to −17.9‰, respectively, andδ18OPDB values of −13.6 to −14.2‰ and −14.0 to −15.8‰, respectively. The δ18O values suggest relatively high-temperature re-equilibration in a deep-burial environment. The variable and depleted13C values appear to reflect fluid-rock interaction and addition of significantδ13C-depleted CO2 from thermochemical sulphate reduction of organic matter. Mixing of reduced, hot basinal brines with oxidizing sulphate-rich fluids resulted in barite precipitation.