Search

Fluid inclusions in diagenetic cements in Upper Jurassic--Lower Cretaceous sandstones offshore Nova Scotia provide constraints on the fluid migration history in gas reservoirs of the Scotian basin. Diagenetic minerals from six wells in the Venture field were analysed by optical petrography, scanning electron microscopy (SEM), and electron microprobe. A total of 122 primary and secondary fluid inclusions were analysed from different cements. Primary aqueous inclusions in quartz overgrowths have homogenization temperatures([T.sub.h)] of 111.8 ± 7.1 °C (1σ) and in later carbonate cements 126.5 ± 2.1 °C; inclusions in both cements are highly saline (16-26.1 wt.% NaCl equivalent). Secondary aqueous and hydrocarbonbearing inclusion trails crosscutting silica cement and detrital quartz have [T.sub.h] of 121.6 ± 13.6 °C and low salinities (8.7 ± 6.0 wt.%). Secondary carbonic inclusions have C[O.sub.2] melting temperatures (-56.6 ± 0.1 °C) and [T.sub.h](-9.3 ± 0.8 °C) indicating a high-density carbonic phase. Late carbonate cements in the same sandstone units vary in chemical composition in different wells, and connected reservoirs show similar late carbonate assemblages, suggesting that the late carbonate cementation may be partly controlled by the reservoir fill and spill sequence. Silica and late carbonate cementation involved highly saline fluid flow, likely at about ~135 Ma. Hydrocarbon migration postdated silica cementation and was associated with secondary fracturing, suggesting that it corresponded to the onset of overpressure. Les inclusions de fluides dans les ciments diagenetiques de gres datant du Jurassique superieur--Cretace inferieur au large de la Nouvelle-Ecosse fournissent un cadre pour l'historique de la migration des fluides dans des reservoirs de gaz du bassin neo-ecossais. Des mineraux diagenetiques de six puits dans le champ Venture ont ete analyses par petrographie optique, microscopie electronique a balayage (SEM) et microsonde electronique. En tout, 122 inclusions primaires et secondaires de fluides provenant de differents ciments ont ete analysees. Les inclusions aqueuses primaires dans des excroissances de quartz ont des temperatures d' homogeneisation ([T.sub.h])de 111,8 ± 7,1 °C (1σ) et, dans des ciments carbonates plus tardifs, elles ont des [T.sub.h] de 126,5 ± 2,1 °C; les inclusions dans les deux ciments sont hautement salines (16 a 26,1 % poids en equivalent NaCl). Des trainees d'inclusions porteuses d'hydrocarbures et aqueuses secondaires recoupant le ciment de silice et le quartz detritique ont des [T.sub.h] de 121,6 ± 13,6 °C et de faibles salinites (8,7 ± 6,0 % poids). Les temperatures de fusion du C[O.sub.2](-56,6 ± 0,1 °C) et de [T.sub.h](-9,3 ±0,8 °C) des inclusions carboniques secondaires indiquent une phase carbonique a densite elevee. Les ciments carbonates tardifs dans les memes unites de gres ont des compositions chimiques qui varient selon les differents puits et des reservoirs relies montrent des assemblages carbonates tardifs similaires, suggerant que la cimentation carbonatee tardive puisse etre en partie controlee par la sequence de remplissage et de deversement du reservoir. La silice et la cimentation tardive par des carbonates impliquaient un ecoulement de fluides hautement salins, il y a probablement ~135 Ma. La migration des hydrocarbures a eu lieu apres la cimentation par de la silice et elle est associee a une fracturation secondaire, suggerant qu' elle corresponde avec le debut de la surpression. [Traduit par la Redaction], Introduction Fluid inclusions can record the migration of fluids, including hydrocarbons, through a basin during cement precipitation and microfracture annealing. These can be examined using microthermometry, ultraviolet microscopy, and other [...]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Diagenetic cements have been studied in conventional core of Lower Cretaceous sandstone from the Glenelg, Chebucto and Thebaud fields in the Sable Subbasin, offshore Nova Scotia. The spatial and temporal distribution of diagenetic cements and para-sequences has been constrained in relationship to lithofacies, depth and the well position in both the distal (Glenelg and Chebucto) and proximal (Thebaud) parts of the basin. Clay minerals in the sandstones include early grain-coating clays, kaolin, illite and chlorite. Grain-coating illitic clays occur in Glenelg N-49 forming coated grains cemented, initially, by Fe-rich calcite (CI), then low Fe-calcite (CII). Kaolinite occurs as booklets and vermicular stacking textures. It fills large inter-granular pores in the Chebucto well and in some samples from Thebaud I-93 and Thebaud #3. Kaolinitized mica exhibits expanded texture that inflates into adjacent intergranular pores. Illite occurs also as fibrous crystals, which in the Chebucto K-90 well are included by ankerite. Fe-rich chlorite (chamosite) rims are found only in the Thebaud samples examined and demonstrably have developed from earlier Fe-rich clay. Early pore-filling chlorite occurs in contact with detrital quartz and lithoclast grains and is often associated with illite. Both this chlorite and chlorite rims are formed around quartz grains lacking quartz overgrowths. Quartz cement (overgrowths) is well developed principally in medium and coarse sandstones. It postdates kaolinite cement and predates most of the other cements. Carbonate cements (calcite, Fe-calcite, Mg-calcite, ankerite and siderite) are the major cementing minerals filling the large intergranular pores in Glenelg, Chebucto and Thebeaud wells. In Glenelg H-59, two siderite cements were defined; the earliest one is formed by large and corroded crystals and it is low in Mg. The late microcrystalline siderite (< 10 µm) is Mg-rich (8 to 9%). It forms the tiny crystals that fringe detrital grains and fill intercrystalline micropores between quartz and Fe-calcite cement. In Thebaud I-93 siderite nodules contain less Mg than the siderite cement (1%, 8.5% respectively). The neo-formation of framboidal pyrite in carbonate cement indicates a burial under both reducing and alkaline conditions. In samples from the Glenelg field, perthite is partially replaced by Fe-calcite, with only K-feldspar patches and albite left. Rare traces of francolite (samples with 1 to 6 wt.% P2O5) are found in the Glenelg wells associated with illite and calcite cements. These observations on diagenetic minerals are related to the position of host sediments within parasequences. Coated grains are restricted to transgressive system tracts. Abundant early kaolinite and siderite are found principally in sandstones immediately beneath transgressive system tracts, particularly in cross-bedded coarse channel sandstones.Early calcite cement, predating quartz overgrowths, is found principally in bioturbated sandstones and mudstones with bioclasts, typical of the HST. [ABSTRACT FROM AUTHOR]

New models of magnetic data are presented that provide insight into the early stages of rifting and breakup between Morocco and Nova Scotia. The margins, which began forming during the Late Triassic rifting and Middle Jurassic separation of the North American and African plates, display considerable variability in deeper crustal structure, faulting style, and basin geometry along their length. The central and northeastern portions of the Nova Scotia margin show characteristics of a magma-poor margin, with a high degree of crustal thinning and a complex ocean-continent transition zone with little direct evidence of volcanism. In contrast, the margin to the southwest of Nova Scotia has clearly recognized characteristics of a volcanic-style rifted margin, including seaward-dipping reflector (SDR) sequences that are interpreted as rift-related volcanic flows overlying basement. These SDRs are coincident with a strong linear magnetic anomaly, the East Coast Magnetic Anomaly (ECMA), which shares many characteristics with the West African Coast Magnetic Anomaly (WACMA). Both magnetic anomalies change character and diminish in amplitude northward along the margins. The new models show the expected decrease in magnetic source material towards the northeastern end of the margin and suggest that modest amounts of igneous material, emplaced at or near the edge of the thinned continental crust, will satisfy the observed anomalies in this magma-poor section of the margin. These new interpretations and supporting evidence indicate volcanism was a factor along much of the margin during early rifting between Nova Scotia and Morocco. [ABSTRACT FROM AUTHOR]

In this study, we build on a foundation of previous biostratigraphic studies for the Scotian Basin, offshore eastern Canada, by conducting new quantitative multidisciplinary biostratigraphic studies of the Mesozoic sections in eight wells: Bonnet P-23, Chebucto K-90, Cohasset L-97, Glenelg J-48, Glooscap C-63, Mohican I-100, South Desbarres O-76, and South Griffin J-13. These wells were chosen to provide good spatial coverage, stratigraphic penetration, and correlation with the seismic grid. We have also evaluated pre-existing biostratigraphic data and undertaken the well-log sequence-stratigraphic interpretation of Upper Triassic to Cenozoic sediments in 16 additional wells using a consistent multidisciplinary event scheme derived from the new wells. Key to the dating of some horizons has been integration of the palynology and micropaleontology (disciplines mostly used previously on the Scotian Margin) with new nannofossil data. Simultaneously we have closely integrated the biostratigraphic results with lithofacies, well-log, and seismic interpretations. Using this integrated approach, we have identified nine regionally mappable sequence-stratigraphic events (unconformities and maximum flooding surfaces, or MFSs): the Intra-Oligocene Unconformity; the Ypresian Unconformity; the Turonian/Cenomanian Unconformity; the Late Albian Unconformity; the Aptian/Barremian Unconformity; the Intra-Hauterivian MFS; the Near-Base Cretaceous Unconformity; the Tithonian MFS; and the Top-Callovian MFS. Additional events of local extent were also recognized in some wells. Our study has led to significant revision of some previous lithostratigraphic picks. The Early Jurassic on the Scotian Margin remains poorly resolved and may be represented by an unconformity on much of the basin periphery. [ABSTRACT FROM AUTHOR]

We have established a new plate kinematic model of the central and North Atlantic oceans between North America, Africa, Meseta, Iberia, Flemish Cap, and Galicia Bank from Late Triassic to Late Cretaceous to better understand the nature and timing of rifting of Nova Scotia and Morocco conjugate continental margins since Late Triassic. The maps of salt distributions at the Sinemurian-Pliensbachian limit (190 Ma; after salt deposition) and in middle Bajocian (170 Ma) show that an area of the Nova Scotia margin is devoid of allochthonous salt and that an area of similar size located oceanward of the West African Coast Magnetic Anomaly shows salt deposits, suggesting that a portion of the Nova Scotia margin with its overlying salt deposits could have been transferred onto the Moroccan side right after the formation of the conjugate East Coast Magnetic Anomaly and West African Coast Magnetic Anomaly. Seven paleogeographic maps, from Late Triassic to Late Cretaceous, are presented with structural elements and magnetic lineations. They show that the connection between the Central Atlantic and the Tethys, with an aborted rift between Iberia and North America ending in the north against the Flemish Cap - Galicia Bank dam, started to deepen at the end of the first rifting phase (190 Ma ago) after the rupture of the thinned continental crust. It is only during the Early Cretaceous, after the rupture of the Flemish Cap - Galicia Bank dam, that the deep connection around Iberia was finally established between the Central and North Atlantic, the Tethys, and the Bay of Biscay. [ABSTRACT FROM AUTHOR]

Early Cretaceous volcanism is widespread in the eastern Scotian Basin. The stratigraphic position of volcanic rocks within wells was re-evaluated and the volcanological character of the rocks was refined by study of cuttings and well logs. Hauterivian-Barremian volcanic rocks on the SW Grand Banks and Aptian-Albian volcanic rocks in the Orpheus Graben and SE Scotian Shelf resulted from Strombolian type eruptions. More extensive Hawaiian type flows were mapped from seismic profiles near the Mallard and Brant wells on the SW Grand Banks and they appear to have been derived from local basement highs with a positive magnetic anomaly interpreted as volcanic centres. Igneous rocks in the Hesper well on the SE Scotian Shelf are the erosional remnant of basaltic flows that terminated at the paleoshoreline. They correlate with basalt flows both in extensive outcrop on Scatarie Ridge and in several Orpheus Graben wells. The interpretation of the Hesper basalts as an erosional remnant of more extensive basalt flows is consistent with detrital petrographic evidence for substantial uplift of the inboard part of the Scotian Basin in the Hauterivian-Aptian. Widespread volcanic activity indicates a regional and long-lived magma source, which resulted in elevated regional heat flow. Effects of this heat flow are seen in sedimentary rocks of the Sable Subbasin and it had a discernable impact on hydrocarbon maturation. [ABSTRACT FROM AUTHOR]

Sources of Tithonian-Albian sediment in the Scotian Basin are interpreted from detrital zircon geochronology to test previous hypotheses about the sources and pathways of sediment to thick deltaic successions that are important hydrocarbon reservoirs. Sediment provenance influences reservoir quality, but also provides information on tectonism during rifting of the North Atlantic Ocean. More than 760 zircons were dated by laser ablation U-Pb methods from nine offshore wells and one borehole on land and were characterized by external morphology, internal zoning, and Th/U ratio. A Meguma terrane source to the LaHave Platform was confirmed by peaks in detrital zircon abundance at 550-650 Ma, 1.0-1.2 Ga, and ∼2.1 Ga. Samples from the Sable Subbasin show a large peak in detrital zircon abundance at ∼1050 Ma, with lower peaks from 400-650, ∼1480, ∼1650, ∼1860 Ma and 2.7 Ga, characteristic of inboard Appalachian terranes of Laurentide affinity. Many late Paleozoic to Neoproterozoic zircons are euhedral or subhedral, and apparently first cycle, as are a few older zircons that indicate transport from the rising rift shoulder in southern Labrador as far north as the Makkovik Province (∼1860 Ma). About half the zircons are rounded and polycyclic. Samples from the Abenaki Subbasin are similar, but late Paleozoic to Neoproterozoic zircons are rare and ∼40% of the Mesoproterozoic zircons are subhedral, implying a different Laurentide source through the Humber valley. Euhedral-subhedral unzoned zircons yielded two groups of Cretaceous dates: ∼105 Ma from the Cree Member, and ∼120 Ma from the Missisauga Formation. [ABSTRACT FROM AUTHOR]

Facies analysis in outcrops on land is strongly dependent on the lateral variability of lithofacies. Interpretation of conventional core in wells relies principally on the vertical succession of lithofacies. To better understand depositional environments and reservoir sandstone connectivity, the lithofacies of reservoir sandstones sampled in conventional core were correlated laterally through two sets of closely spaced wells in the Scotian Basin: in the Barremian-Albian succession around the Panuke-Cohasset field and in the Late Jurassic succession west of the Venture field. Regional correlation by gamma logs is confirmed by lithologically similar transgressive units including shelly mudstones or coals. A standard scheme of lithofacies and recognition of three types of parasequences were used for comparisons between wells. Some transgressive surfaces are of limited extent and may represent delta distributary switching and subsidence rather than regional changes in sea level. Major sandstone packets extend at least 10-30 km laterally, but commonly show lateral changes in lithofacies, and some are bounded by the margins of incised valleys. Such packages show poor correlation of lithofacies with porosity and permeability, probably because of the variable effects of diagenesis. Lateral transitions from tidal estuary sandstones in Panuke B-90 to thick-bedded river-mouth turbidites in Lawrence D-14, over a distance of 15 km, demonstrates the scale of delta lobes and confirms that sharp-based sandstone beds are turbidites related to river floods, not storm deposits. Similar lateral transitions in the Venture field are on a similar scale and pass distally into prodeltaic muddy landslide deposits. [ABSTRACT FROM AUTHOR]

The tectonic and geomorphological evolution of the Scotian margin and its hinterland is poorly known between Late Triassic rifting and the Early Cretaceous progradation of major deltas. This study determined sedimentary provenance of Middle Jurassic Mohican Formation sandstones from three wells using heavy minerals and mineral chemistry. Indicator minerals such as xenotime, altered ilmenite, and varietal types of garnet and tourmaline are similar to those in Hauterivian-Barremian sandstones in the western Scotian Basin, which are almost exclusively derived from the Meguma terrane. The wells adjacent to the Canso Ridge have more zircon and less ilmenite, indicating a greater contribution of polycyclic reworking, but with an ultimate source in the Meguma terrane. Zircon and ilmenite were likely derived in part from Carboniferous sandstones in eastern mainland Nova Scotia and Cape Breton Island. Any river drainage from the inboard terranes of the Appalachians either was diverted through the Fundy Basin or entered the easternmost Scotian Basin, where the Mohican Formation is 5.5 km thick, along the linear continuation of the southwest Grand Banks transform. Such sediment did not reach the Canso Ridge, suggesting that the Cobequid-Chedabucto fault zone in Orpheus graben was not a significant physiographic feature. This tectonically controlled paleogeography in the Middle Jurassic is quite different from that during active rifting in the Late Triassic - Early Jurassic. Middle Jurassic quiescence was followed in the Tithonian - Early Cretaceous by renewed tectonic uplift associated with rifting of Grand Banks from Iberia and Labrador from Greenland. [ABSTRACT FROM AUTHOR]

Geochronology of detrital muscovite from the Lower Cretaceous of the central Scotian Basin has shown predominant supply of Meguma terrane detritus, including muscovite with Alleghanian (mid-Carboniferous to Permian) ages from the inner Scotian Shelf. In this study, 87 detrital muscovite grains from five wells in the eastern Scotian Basin, representing depositional ages from Tithonian to Early Albian, were dated by single-grain 40Ar/39Ar techniques. Previous work shows that the provenance of this sediment was different from wells in the central Scotian Basin. Compared with the central Scotian Basin, the muscovite age populations from the eastern Scotian Basin have more (20% versus 7%) pre-Devonian ages, derived from inboard terranes of the Appalachians. In both the central and eastern Scotian Basin, most old grains are found in the Tithonian and the Aptian-Albian, with fewer in the Valanginian and almost none in the Kimmeridgian and the Hauterivian-Barremian. These data suggest rapid unroofing of the Meguma terrane in the Kimmeridgian and Hauterivian-Barremian and greater supply of sediment from Newfoundland to the eastern Scotian Basin in the Tithonian and Aptian-Albian. Compared with the central Scotian Basin, which has most ages in the range 340-300 Ma, the muscovite age populations from the eastern Scotian Basin have a higher proportion of 420-340 Ma and in particular 300-260 Ma ages. Such late Alleghanian overprinting of argon ages is very rare on land in Nova Scotia, but in the Maritimes Basin, this was the time of uplift and erosion of strata. [ABSTRACT FROM AUTHOR]

The ∼51 Ma Montagnais impact crater on the outer Scotian Shelf is well known, but the potential effects from the impact event on the slope and rise seaward of the crater have, until now, remained poorly understood. Through detailed seismic stratigraphic correlation and ties to available wells, we define a threefold seismic stratigraphic subdivision for Upper Cretaceous to Eocene strata on the shelf and slope, calibrated to the most recent biostratigraphic results. Using this framework, we identify a number of depositional and erosional products that are temporally consistent with a late Ypresian impact event (within the limits of seismic and biostratigraphic resolution). We link a series of prominent failure scarps on the outer shelf and upper slope to a single widespread mass-transport deposit (MTD) on the lower continental slope, rise, and abyssal plain. Failed material amassed in a large debris field referred to here as the 'Montagnais MTD'. It covers an area of ∼93 000 km2 and travelled up to 580 km from the impact site where its distal termination onlaps the New England Seamounts, making it one of the largest known debris avalanches on Earth. We interpret these deposits, and the associated pattern of erosion landward of them, as products of widespread margin collapse caused by a combination of ground shaking and ensuing tsunamis triggered by the Montagnais impact event. This study provides insight into the potential effects of outer-shelf marine impact events immediately downslope from impact sites, and their diminished effects with increasing distance along the margin. [ABSTRACT FROM AUTHOR]

There are two allochthonous salt canopies within the central Scotian margin, one on the shelf and another in deeper waters on the Scotian slope. The Sable Shelf Canopy trends southwest-northeast and covers an area approximately 650 km2. Salt thickness within this canopy is generally <1000 m. Reloading of the salt has welded out the margins of the canopy, significantly reducing its extent. Salt tectonics related to this canopy produced many of the exploration targets drilled on the shelf. The Sable Slope Canopy is 50 km basinward on the Scotian slope. This canopy is significantly larger, covering 12 700 km2, and the allochthonous salt is as thick as 3500 m. Although the two canopies are separated by a significant distance, a common detachment surface connects them in multiple locations. Extensional systems detach in the Sable Shelf Canopy, displace strata downdip, and expel salt into the Sable Slope Canopy. The outer shelf and slope region separating these two canopies is dominated by detachment systems. One term, the Sable Canopy Complex, was developed to describe both salt canopies and the zone of detachment that separates them. Interpretation of two-dimensional and three-dimensional seismic data throughout the Sable Canopy Complex has resulted in a detailed allochthonous salt map and all related components including welded systems, salt stocks, faults, sutures, and minibasins. Four distinct expulsion styles are observed to contribute volumes of salt to the canopies: salt-based detachments, counterregional systems, hybrids, and salt stocks. Potential explanations for the variations in expulsion style range from varying volumes of sediment input to paleogeographic positions on the margin to salt sheet length. [ABSTRACT FROM AUTHOR]