Offshore Eastern Canada Research Articles

Paleoenvironmental and chemostratigraphic implications of variations in geochemical proxies across the Upper Jurassic–Lower cretaceous boundary: a case study from the Flemish Pass Basin

The Jurassic–Cretaceous boundary is the only Phanerozoic period-level boundary that lacks a golden spike on the geological timescale despite significant global geological and environmental change during this time related to the opening of the Atlantic Ocean. Paleoenvironmental proxy profiles (total organic carbon, δ34S, δ15N, Fe, Mn, Ce/Ce*, Th/U, δ13Corg, P, Ni, Zn, Cu, and B/Ga) for core 3 of the Baccalieu I-78 well in the Flemish Pass Basin, offshore eastern Canada, exhibit a geochemical anomaly between 3288.5 and 3289 m, overlapping with the biostratigraphic placement of the Jurassic–Cretaceous boundary. Collectively the geochemical analyses are interpreted to indicate that the anomaly is associated with a fall in relative sea level, followed by a rise, which led to restricted circulation, stratification, and widespread anoxia. This anoxia, coupled with an arid climate, further resulted in reduced weathering, limited nutrient supply, and an overall reduction in primary productivity. The results of this study, in conjunction with previous biostratigraphic studies on core 3, suggest that the Jurassic–Cretaceous boundary in Baccalieu I-78 likely falls within the geochemical anomaly, specifically between 3228.5 and 3288.85 m. Furthermore, the paleoenvironmental interpretations derived in this study agree with published reports on global sea level and climate trends around the Jurassic–Cretaceous boundary, implying the influence of global, rather than regional, factors on deposition. This suggests that geochemical proxies may be useful in providing additional paleoenvironmental insights and helping to constrain stratigraphic boundaries, particularly in intervals that lack significant lithological or biological change.

Re-evaluation of the Mesozoic–Cenozoic biostratigraphy of the Laurentian Subbasin of the Scotian Basin, offshore eastern Canada

We use new and existing nannofossil, palynological, and microfossil biostratigraphic data in conjunction with lithologic and geophysical logs from four wells to establish a series of sequence-stratigraphic events in the Mesozoic–Cenozoic of the Laurentian Subbasin of offshore Newfoundland, eastern Canada. Well biostratigraphic events are integrated with reflection seismic in the area to correlate regional seismic stratigraphic surfaces. The four wells are: Bandol-1, Emerillon C-56, East Wolverine G-37, and Heron H-73. We extend the event stratigraphic scheme previously developed for the Scotian Margin, offshore Nova Scotia, into new areas to the east along the southern Grand Banks, where we recognize four new well-log sequence stratigraphic events, and we modify the definition of a previously recognized regional surface. The new and modified regional surfaces are the Early Albian Unconformity, the Late Bathonian Maximum Flooding Surface (MFS), the Late Bajocian MFS (renamed from Bathonian/Bajocian MFS), the ?Bajocian/Toarcian Unconformity, and the Late Pliensbachian MFS. We recognize the "Avalon Unconformity" and "Base-Tertiary Unconformity" of previous studies as amalgamations of multiple smaller-scale unconformities and refine their age in the studied wells. A major improvement over our earlier Scotian Margin event schemes is the extension of the event stratigraphy into the Early Jurassic using a suite of marine biostratigraphic markers. We compare the Early Jurassic event scheme to Deep Sea Drilling Project Site 547B on the conjugate Moroccan Margin to better constrain potential source rock intervals and the early history of the central Atlantic Ocean.

An integrated clinoform trajectory and sequence stratigraphic model for the Labrador margin, offshore eastern Canada

The passive margin offshore Labrador began forming during rifting in the Early Cretaceous, with seafloor spreading starting in the Maastrichtian and ending near the Eocene–Oligocene boundary. A foundational understanding of the associated stratigraphy of this margin has been developed through previous studies of the lithostratigraphy, biostratigraphy, and seismic stratigraphy, but the significance of clinoforms, stratal boundaries, and transgressive and regressive events has never been fully explored. In this study, we identify a series of clinoform successions from the Late Cretaceous through Pleistocene and apply a second-order sequence stratigraphic model to refine the geological framework for the margin. We focus on the Hopedale Basin where there is sufficient well and reflection seismic data, with substantial new seismic data collected over the last decade. Seismic interpretation is combined with paleoenvironmental and biostratigraphic data from the wells to map clinothem packages along the margin including: seven shoreline, five subaqueous delta, one shelf-edge, and three shelf-edge deltas, with illustration of these on seismic profiles and paleogeographic maps representing several time slices. Trajectory analysis of these clinothems permits the delineation of eight second-order sequences, with systems tracts and sequence stratigraphic surfaces identified. Broader implications of our results include a revised lithostratigraphic column for the Labrador margin. We further demonstrate regional trends during rifting and opening in term of controlling factors on clinoform development through comparison with adjacent and conjugate margins. Tectonism dominated as a controlling factor in the Cretaceous and dwindled near the end of the Paleocene. Eustasy and climate also influenced clinoform development in the Late Cretaceous, but became major factors during the Cenozoic, enhancing relative sea level fall and sediment supply, with similarities to other clinoform successions developed during Greenhouse and Icehouse conditions. Impacts to petroleum prospectivity in the region are also discussed, and our overall seismic and stratigraphic framework provide a basis for future study.

Heating Up in Icy Waters

It was an area once thought to be the last untapped jewel in the hunt for hydrocarbons in the Great White North—a frontier of equal parts promise and peril. The lure of massive oil deposits lurking miles below its icy waters had operators taking a hard look at offshore Eastern Canada as far back as the late 1960s; however initial production from the area—Cohasset-Panuke off Nova Scotia—did not begin until 1992. Logistical challenges related to the remote area and the lack of existing infrastructure made bringing on new production in the region an expensive proposition. The discovered fields would need to be sizable to warrant the required investment. After decades of fits and starts, offshore Eastern Canada has yielded just a handful of major developments, with the best of those facing their own sets of challenges. Newfoundland and Labrador’s Terra Nova, the first development in North America to use floating production, storage, and offloading (FPSO) technology in a harsh-weather environment featuring sea ice and icebergs, came on line in 2002, but has been suspended for the past 3 years due to issues with the vessel. White Rose, another FPSO-based development, came on stream in late 2005 via subsea wells tied back to the SeaRose vessel. After successful completion of one expansion project in the 2010s, a further expansion—West White Rose—was planned but halted in 2020 due to unfavorable oil markets caused by the COVID-19 pandemic. The project envisaged a wellhead platform supported by a concrete gravity structure (CGS) and topsides. The platform will produce back to the SeaRose FPSO. Cenovus approved the restart of the project in May 2022. The West White Rose project is expected to increase the production life of the field by 14 years. Newfoundland and Labrador’s landmark oil production platform Hibernia became the first to produce oil in the province just over 25 years ago. As of August 2022, the project has produced more than 1.2 billion bbl of oil from the field, with almost 580 million bbl remaining proven and possible reserves. The region’s newest producer is the ExxonMobil-operated Hebron. First oil from the field was produced in November 2017—37 years after the field’s discovery by former operator Chevron. Plans to develop the field were shelved in the early 2000s only to be revived later in the decade. As a result of production interruptions and project delays, overall production trends in the region have been on the decline since the end of 2019 (Fig. 1). Off Nova Scotia, both ExxonMobil’s Sable Offshore Energy Project and Ovintiv’s (formerly Encana) Deep Panuke produced commercially for a combined 24 years (19 and 5, respectively) before each was abandoned and decommissioned in 2018. However, the outlook for offshore Eastern Canada today is somewhat brighter.

The development of the eastern Orpheus rift basin, offshore eastern Canada: A case study of the interplay between rift-related faulting and salt deposition and flow

The salt-rich Orpheus rift basin, part of the eastern North American (ENAM) rift system, formed during the Late Triassic to Early Jurassic prior to opening of the Atlantic Ocean. Using a dense grid of 2D seismic-reflection lines, data from nearby wells, and information from adjacent ENAM rift basins, we have established a tectonostratigraphic framework, identified key structural elements, and reconstructed the deformation history for the eastern part of the basin. Our work shows that a series of E-striking, S-dipping faults with normal separation bound the basin on the north. Deformation within the basin is complex with forced folds above deep-seated intrabasin faults, detachment folds, detached thrust faults, and salt diapirs. The synrift evaporite sequence consists of an older massive salt unit that underlies a younger unit with two distinct interfingering facies. Facies A, consisting of salt and interbedded sedimentary rocks (likely shales), developed near the border-fault system and its relay ramps. Facies B, consisting of massive salt with few interbedded sedimentary rocks, developed toward the basin center. The youngest synrift unit accumulated exclusively within minibasins near the northern border-fault system. Based on location, this youngest synrift unit likely consists of coarse-grained and poorly sorted alluvial-fan or talus-slope deposits shed from the footwall. All synrift units are intruded by igneous sheets likely associated with the Central Atlantic Magmatic Province and, thus, are mostly Late Triassic in age (or possibly older). The border-fault system profoundly affected deposition within the eastern Orpheus rift basin by providing pathways for clastic sediment input into the salt-rich basin. These depositional patterns subsequently influenced deformation associated with lateral salt flow during minibasin formation. In regions with interbedded salt, detachment folds and thrust faults developed, whereas salt walls and stocks developed in regions with more massive salt.

E&P Notes (August 2021)

E&P Notes (August 2021)

A Probability-Based Daytime Algorithm for Sea Fog Detection Using GOES-16 Imagery

Fog is a hazardous weather event that can endanger navigation, aviation, and transportation. While human has several limitations in detecting and forecasting offshore fog, satellite remote sensing offers cost-effective images. In this study, a probability-based daytime sea fog detection algorithm, applied to geostationary operational environmental satellite (GOES) 16 satellite data over the Grand Banks offshore Eastern Canada, is presented and compared with the National Oceanographic and Atmospheric Administration (NOAA)'s Low Instrument Flight Rules (LIFR) probability map. Initially, clear-sky and ice cloud classes were delineated in the GOES-16 image and then the remaining pixels were assigned a fog probability by conducting small droplet proxy, spatial homogeneity, and temperature difference tests. Moreover, a green band was linearly interpolated using the first three bands of GOES-16 images to generate pseudotrue color composites. The resulting maps were evaluated both during an extended sea fog event and using several statistical measures. The average detection probability for the observed advection fog events was 66% for the proposed method, while that for NOAA's LIFR map was 38%. Furthermore, by thresholding the generated maps at the probability of 60%, the false alarm rate, probability of detection, hit rate, and Hanssen–Kuiper skill score were 0.09, 0.77, 0.83, and 0.68, respectively. The proposed method is operationally being used in this region to detect and monitor sea fog, facilitating safe navigation and aviation. This is the first study that uses GOES-16 for daytime fog detection and discusses a satellite-based solution for fog modeling in Grand Banks, NL.

First-cycle sand supply and the evolution of the eastern Canadian continental margin: Insights from Pb isotopes in the Mesozoic Scotian Basin

Abstract Provenance analysis provides a powerful means to understand, connect, and reconstruct source-to-sink systems and Earth surface processes, if reliable toolkits can be developed, refined, and applied. Deciphering sediment routing to the Scotian Basin, offshore eastern Canada, is marred by sedimentary recycling but is critical to understanding the evolution of the Canadian margin in response to the evolving Labrador rift. In this study, Pb isotopes in detrital K-feldspars were fingerprinted in 13 wells across the Scotian Basin to track first-cycle sand supply. Unlike previous approaches, which utilized less labile proxies such as zircon, detrital K-feldspars are unlikely to survive multiple sedimentary cycles. The Pb-isotopic data reveal a dynamic seesaw effect between hinterland sources across the Jurassic-Cretaceous boundary, reflecting the complex interplay between the northward propagation of uplift along the rising Labrador rift flank and the reactivation of fault systems in the lower drainage basin. Pb isotopes in K-feldspar record progressively increasing long-distance supply from eastern Labrador, as early as the Callovian in the central basin, alongside diminishing but persistent local sourcing from adjacent Appalachian terranes. Comparison with more resilient mineral proxies, notably zircon, appears to confirm recycling in the lower drainage basin and highlights the limitations of using a single mineral proxy in isolation. This case study serves as an example of the growing potential of multiproxy provenance toolkits not only to decipher sediment-routing corridors in paleodrainage systems, but to better define and connect the drivers, mechanisms, and spatial and temporal ranges of Earth surface processes and tectonic events.

New species of the dinoflagellate cyst genus <i>Svalbardella</i> Manum, 1960, emend. from the Paleogene and Neogene of the northern high to middle latitudes

Abstract. Species of the fusiform peridiniacean dinoflagellate cyst genera Svalbardella Manum, 1960, emend. (Eocene–Oligocene) and Palaeocystodinium Alberti, 1961 (Late Cretaceous–Miocene), have been examined from the high to middle latitudes of the Northern Hemisphere: Spitsbergen, Norwegian-Greenland Sea, Labrador Sea, western North Atlantic, and the North Sea basin. The genus Svalbardella is emended to comprise species with smooth or finely ornamented surfaces and for which one or both horns are bluntly rounded. Svalbardella clausii sp. nov. has a narrow range restricted to the lowermost Chattian (close to the NP24–NP25 boundary and within Chron C9n), and it therefore appears a useful stratigraphical marker. This species has a wide distribution across the North Atlantic, having been reported from the North Sea basin, western North Atlantic, and the Labrador Sea. Svalbardella clausii sp. nov. overlaps stratigraphically with the reoccurrence interval of Svalbardella cooksoniae Manum, 1960, and spans the Oi-2b cooling maximum. Its presence may therefore be related to the establishment of cooler surface waters at this time. Svalbardella kareniae sp. nov. has a discordant occurrence: Lower Oligocene and Lower Miocene of the Norwegian Sea at Deep Sea Drilling Project Site 338 and Ocean Drilling Program Site 643, respectively, and mid-Oligocene of the North Sea. Its distribution suggests that Svalbardella kareniae sp. nov. favours more open marine conditions. Palaeocystodinium obesum Fensome et al., 2009, described from offshore eastern Canada where it has a highest occurrence in the Lower Oligocene, is emended to include specimens with a finely ornamented periphragm and traces of tabulation in addition to the archeopyle.

Are submarine landslides an underestimated hazard on the western North Atlantic passive margin?

AbstractThe western North Atlantic passive margin is considered relatively stable, with few slope instabilities recognized during the Holocene. However, new multibeam bathymetry mapping and sediment core acquisition off eastern Canada indicate that previously unidentified, large, submarine landslide events occurred during the Late Holocene, between 4 and 1.5 ka. The recognition of these new gravitational events, in addition to the well-known C.E. 1929 Grand Banks earthquake-induced landslide, indicates that approximately one large landslide event per 1000 years has occurred offshore eastern Canada within the past 4000 years, a much shorter recurrence interval than hitherto reported. This Late Holocene recurrence rate is also similar to active margins around the world and is likely due to the under-consolidation and resultant instability of Scotian Slope sediments attributable to high glacial sedimentation rates. The discovery of these new Late Holocene landslides was made possible through detailed examination of cores recovered from the lower slope. These results demonstrate that submarine landslide hazard has been underestimated on the western North Atlantic margin—home to significant submarine infrastructure and proximal to a large coastal population.

Obstructed minibasins on a salt‐detached slope: An example from above the Sigsbee canopy, northern Gulf of Mexico

AbstractSalt‐detached gravity gliding/spreading systems having a rugose base‐of‐salt display complex strain patterns. However, little was previously known about how welding of supra‐salt minibasins to the sub‐salt may influence both the downslope translation of minibasins on salt‐detached slopes and the regional pattern of supra‐salt strain. Using a regional 3D seismic reflection data set, we examine a large salt‐stock canopy system with a rugose base on the northern Gulf of Mexico slope, on which minibasins both subside and translate downslope. Some minibasins are welded at their bases and others are not. We suggest that basal welds obstruct downslope translation of minibasins and control regional patterns of supra‐canopy strain. The distribution of strain above the canopy is complex and variable. Each minibasin that becomes obstructed modifies the local strain field, typically developing a zone of shortening immediately updip and an extensional breakaway zone immediately downdip of the obstructed minibasin. This finding is corroborated by observations from a physical sandbox model of minibasin obstruction. We also find in our natural example that minibasins can be obstructed to different degrees, ranging from severe (e.g., caught in a feeder) to mild (e.g., welded to a flat or gently dipping base‐of‐salt). By mapping both the presence of obstructed minibasins and the relative degree of minibasin obstruction, we provide an explanation for the origin of complex 3‐D strain fields on a salt‐detached slope and, potentially, a mechanism that explains differential downslope translation of minibasins. In minibasin‐rich salt‐detached slope settings, our results may aid: i) structural restorations and regional strain analyses; ii) prediction of subsalt relief in areas of poor seismic imaging; and iii) prediction of stress fields and borehole stability. Our example is detached on allochthonous salt and where the base‐of‐salt is rugose, with the findings applicable to other such systems worldwide (e.g., Gulf of Mexico; Scotian Margin, offshore eastern Canada). However, our findings are also applicable to systems where the salt is autochthonous but has significant local basal relief (e.g., Santos Basin, Brazil; Kwanza Basin, Angola).

The influence of turbidity currents and contour currents on the distribution of deep‐water sediment waves offshore eastern Canada

AbstractSediment waves are commonly observed on the sea floor and often vary in morphology and geometry according to factors such as seabed slope, density and discharge of turbidity currents, and the presence of persistent contour currents. This paper documents the morphology, internal geometry and distribution of deep‐water (4000 to 5000 m) bedforms observed on the sea floor offshore eastern Canada using high‐resolution multibeam bathymetry data and seismic stratigraphy. The bedforms have wavelengths of >1 km but fundamentally vary in terms of morphology and internal stratigraphy, and are distinguished into three main types. The first type, characterized by their long‐wavelength crescentic shape, is interpreted as net‐erosional cyclic steps. These cyclic steps were formed by turbidity currents flowing through canyons and overtopping and breaching levées. The second type, characterized by their linear shape and presence on levées, is interpreted as net‐depositional cyclic steps. These upslope migrating bedforms are strongly aggradational, indicating high sediment deposition from turbidity currents. The third type, characterized by their obliqueness to canyons, is observed on an open slope and is interpreted as antidunes. These antidunes were formed by the deflection of the upper dilute, low‐density parts of turbidity currents by contour currents. The modelling of the behaviour of these different types of turbidity currents reveals that fast‐flowing flows form cyclic steps while their upper parts overspill and are entrained westward by contour currents. The interaction between turbidity currents and contour currents results in flow thickening and reduced sediment concentration, which leads to lower flow velocities. Lower velocities, in turn, allow the formation of antidunes instead of cyclic steps because the densiometric Froude number (Fr′) decreases. Therefore, this study shows that both net‐erosional and net‐depositional cyclic steps are distributed along channels where turbidity currents prevail whereas antidunes form on open slopes, in a mixed turbidite/contourite system. This study provides insights into the influence of turbidity currents versus contour currents on the morphology, geometry and distribution of bedforms in a mixed turbidite–contourite system.

Seafloor pockmarks and gas seepages, northwestern Bay of Fundy, New Brunswick, Canada

Bathymetric images of linear and circular pockmark depressions on the Bay of Fundy seafloor, offshore eastern Canada, are interpreted to have been caused by escaping gas from underlying sediment or bedrock. Shallow interstitial gas within marine sediments restricts seismic reflection imaging (acoustic masking) of sub-bottom units resulting in obscured reflections within seismic profiles, confirming that interstitial gas is present in the underlying units. Pockmark fields are frequent in several bays and shallow coastal areas along the northern coast of the Bay of Fundy. The largest field containing over 10 000 pockmarks occurs in Passamaquoddy Bay, an estuary underlain by igneous and metamorphic bedrock. These features are interpreted to be caused by generation of biogenic methane from the microbial breakdown of organic matter buried within Holocene-age sediments and along the underlying Pleistocene/Holocene unconformity. The unconformity is recorded as a distinctive horizon that represents a time when glacier recession resulted in exposure of parts of the bay to sub-aerial erosion and growth of terrestrial vegetation at locations subsequently submerged by post-glacial transgression. Three areas of potential thermogenic gas occurrence were identified in seismic profiles collected south and east of The Wolves islands, New Brunswick. The underlying bedrock has not yet been precisely mapped, although outliers of Carboniferous-age bedrock that is the major petroleum source in New Brunswick may extend into this area of the Bay of Fundy.

Singing through winter nights: Seasonal and diel occurrence of humpback whale (Megaptera novaeangliae) calls in and around the Gully MPA, offshore eastern Canada

AbstractHumpback whale use of areas off eastern Canada is poorly understood, a knowledge gap that could impact future conservation efforts. We describe the acoustic occurrence of humpback whales in and around the Gully Marine Protected Area (MPA), an eastern Scotian Shelf submarine canyon. Near‐continuous acoustic recordings sampling at 16 kHz were collected from the MPA and nearby slope areas from October 2012 to September 2014 using near‐bottom recorders. In an offshore region where humpbacks were thought to be rare, we observed calls from October to June with a peak in song and nonsong calls in December and January. This suggests that some individuals occur in Canadian waters in winter and the Gully region may be a North Atlantic humpback whale migratory corridor. Calls were predominantly songs indicating potential mating activities. Song and nonsong calls occurred more at sunset and during hours of darkness than during daylight. This study improves our understanding of the seasonal occurrence of humpback whales on the Scotian Slope and, more specifically, their use of an offshore protected area.

The planktonic foraminifera of the Jurassic. Part II: Stratigraphy, palaeoecology and palaeobiogeography

The stratigraphy, palaeoecology and palaeobiogeography are outlined for two genera and ten species of Jurassic planktonic foraminifera described in Gradstein et al. (Swiss J Palaeontol 2017. doi: 10.1007/s13358-017-0131-z). The two genera are Globuligerina and Conoglobigerina. Globuligerina probably appeared in late Toarcian (late Early Jurassic) and Conoglobigerina first occurred in Middle Oxfordian (early Late Jurassic). Within the two genera ten species are defined, including from older to younger: Globuligerina dagestanica (Morozova), G. avariformis (Kasimova), G. balakhmatovae (Morozova), G. oxfordiana (Grigelis), G. bathoniana (Pazdrowa), G. jurassica (Hofman), G. oxfordiana (Grigelis) calloviensis Kuznetsova emended, G. tojeiraensis Gradstein, Conoglobigerina helvetojurassica (Haeusler), C. grigelisi Gradstein and C. gulekhensis (Gorbachik and Poroshina). Globuligerina balakhmatovae, G. oxfordiana and G. bathoniana are longer ranging, although there are subtle evolutionary trends in these taxa that may refine stratigraphic usage. Other taxa have shorter stratigraphic ranges. Using stratigraphic trends, test morphology and wall texture changes, the species are tentatively assembled in four evolutionary groups, termed A–D, and in six zones from Late Toarcian through Tithonian. The greater species diversity and possibly also specimen abundance took place in the Kimmeridgian, a time of high global sea level and greenhouse palaeoclimatic conditions. Jurassic planktonic foraminifera preferred marine continental margin conditions instead of the distal open ocean and spread from offshore Eastern Canada to offshore Western Australia along the margins of the Tethys Ocean. The group did not venture into austral or boreal realms, likely reasons why migration probably failed to the west coasts of South and North America.

Diagenetic F-rich ferroan calcite and zircon in the offshore Scotian Basin, eastern Canada: Significance for understanding thermal evolution of the basin

In the Scotian Basin, offshore eastern Canada, an unusual combination of high heat flow in the Cretaceous and the abundance of halite has resulted in unusual diagenetic minerals such as sphalerite. The Newburn H-23 well is the most distal well in the basin with good core samples and has two previously unknown diagenetic mineral occurrences: fluorine-rich ferroan calcite and diagenetic zircon. This study uses SEM backscattered electron images and EDS analyses, EMP WDS mineral analyses and Raman spectroscopy to determine mineral chemistry and textures to investigate the diagenetic and thermal significance of these minerals. Late diagenetic Fe-calcite contains 1–2.5 wt% fluorine, mostly from adsorption, but rarely as small fluorite crystals. Fluoride is also adsorbed on the surfaces of some framework minerals and chlorite. Fluoride was transported in highly saline formation brines derived from the Argo salt Formation. Zircon grains, 20–40 μm in size, have crystal outlines that are straight adjacent to pores, partially lobate filling porosity, and cross cutting other grains: these may be diagenetic. Some zoned detrital zircon grains show 1–3 μm wide diagenetic outgrowths. Neoformation of diagenetic zircon requires temperatures of >250 °C. Transport of zirconium is favored by ligands in low-pH solution, principally fluoride and phosphate anions, with zirconium mobilized during the alteration of metamict detrital zircon under low-grade metamorphic conditions. The presence of diagenetic sphalerite and the documented mid-Cretaceous thermal event in the Scotian Basin indicate conditions that could have been suitable for the formation of diagenetic zircon in this well. Suitable geological conditions for such diagenetic formation of zircon will be found in a subsiding rift basin with early evaporites that are affected by a subsequent phase of volcanism due to new rifting or subduction.

North Atlantic climatic events recorded in Aptian Naskapi Member cores, Scotian Basin

Early Aptian black laminated organic mudstones, including the Selli Level, are recognized over large areas of Tethys and western European basins. This interval was investigated in a 75 m-thick continuously cored section of varicoloured shale in the lower Naskapi Member from the Panuke B-90 well in the Scotian Basin, offshore eastern Canada. This study complements the palaeogeographic range of correlatable Selli black shales and provides information on their relationship to sea-level change and palaeoclimate. Total organic carbon (TOC) was measured on 127 discrete samples, chemical environmental proxies (Th/K, Mn/Ti, K/Ti, Th/Ti, V/Ti) were measured with a portable X-ray fluorescence (pXRF) spectrometer, and colour parameters L*a*b* were measured by spectrophotometer. Several black shale levels are recognized and correlated with similar shales in Europe between the Barremian–Aptian boundary and the Selli Level. The Th/K ratio proxy for hinterland humid or arid climate conditions shows no systematic variation with black shale levels. Several sea-level lowstands are inferred from condensed sandy intervals with some brackish water biota and tidal sedimentary structures. Black shale intervals are found in highstand intervals, with no systematic relationship to inferred transgressions. The formation of black shales is related to palaeoceanographic changes that may be driven by conditions remote from the Scotian Basin.

How sandstone porosity and permeability vary with diagenetic minerals in the Scotian Basin, offshore eastern Canada: Implications for reservoir quality

The Scotian Basin is an under-explored offshore basin that has produced gas and minor oil from Jurassic–Cretaceous deltaic sandstones. Reservoir quality is an important exploration risk in the basin. This study evaluates whether there are systematic stratigraphic or geographic variations in diagenetic mineral assemblage control of reservoir porosity and permeability. Three data sets are used: a compilation of all available core-plug porosity and permeability measurements (3271 in total), a subset of 577 corresponding to thin sections with lithofacies assignments, and a subset of 35 thin sections principally from reservoir sandstones, in which modal abundance of diagenetic minerals has been determined by image analysis of scanning electron microscope backscattered electron images. Abundances above a 4% threshold of diagenetic kaolinite, calcite and ankerite correlate inversely with permeability, but chlorite and possibly siderite correlate positively. Diagenetic assemblages show no systematic variation with stratigraphy or geography, both of which may involve variable detrital supply. Permeability shows the well-known variation with grain size and depth of burial, but after correcting for these effects it is greatest in estuarine channel and river-mouth turbidite sandstones. This is because these facies preferentially develop chlorite rims on detrital quartz grains and are also the sites of enhanced flow of late basinal fluids resulting in secondary porosity. Local effects such as facies distribution, architecture of channel sandstones, fluid pathways related to complex salt tectonics, and the effects of overpressure are more important than predictable basin-wide effects in controlling sandstone reservoir quality.

Erratum to: Petrology and tectonic significance of seamounts within transitional crust east of Orphan Knoll, offshore eastern Canada

The Early Cretaceous separation of Newfoundland from Iberia–Ireland is a classic example of a magma-poor continental margin with hyperextension and with widespread minor magmatism resulting in seamounts. This study defines the distribution of seamounts east of Orphan Knoll, and documents and interprets the geochemical character of the one recovered lava sample. Video imagery of lava outcrops, and the sample, were obtained by ROV from Orphan seamount, one of a linear series of small seamounts overlying transitional thinned continental crust on the seaward side of Orphan Knoll. New multibeam bathymetry and legacy seismic data show several seamounts that extend irregularly along the fault-bound NE margin of Orphan Knoll. Whole rock geochemistry shows the sample to be highly alkaline basanite or possibly tephrite. Diopside–hedenbergite, kaersutite and K-feldspar phenocrysts were analyzed by electron microprobe and scanning electron microscope, and alteration minerals including kaolinite were identified by X-ray diffraction. The highly alkaline character of the basanite is similar only to Early Cretaceous volcanic and sub-volcanic rocks erupted through thick continental crust of the Mesoproterozoic Grenville Orogeny. The location of the linear set of seamounts is related to margin-parallel faults on the seaward side of Orphan Knoll that provided a pathway for magma, although ENE-trending lineaments in individual seamounts or seamount groups suggest the influence of oceanic fracture zones. A lower gradient crest to Orphan seamount above 2,200 m suggests subaerial erosion, consistent with the presence of kaolinite as an alteration product and the absence of lava pillows at and above this depth.

Late Quaternary history of contourite drifts and variations in Labrador Current flow, Flemish Pass, offshore eastern Canada

Contourite drifts of alternating sand and mud, shaped by the Labrador Current, formed during the late Quaternary in Flemish Pass seaward of the Grand Banks of Newfoundland, Canada. The drifts preserve a record of Labrador Current flow variations through the last glacial maximum. A high-resolution seismic profile and a transect of four cores were collected across Beothuk drift on the southeast side of Flemish Pass. Downcore and lateral trends in grain size and sedimentation rate provide evidence that, between 16 and 13 ka, sediment was partitioned across Beothuk drift and the adjacent Flemish Pass floor by a strong current flow but, from 29 to 16 ka, sedimentation was more of a blanketing style, represented by draped reflections interpreted as being due to a weaker current. The data poorly resolve the low sedimentation rates since 13 ka, but the modern Labrador Current in Flemish Pass is the strongest it has been in at least the past 29 ka. Pre-29 ka current flow is interpreted based on reflection architecture in seismic profiles. A prominent drift on the southwestern side of Flemish Pass formed above a mid-Miocene erosion surface, but was buried by a mass-transport deposit after the penultimate glacial maximum and after drift deposition switched to eastern Flemish Pass. These findings illustrate the temporal complexity of drift sedimentation and provide the first detailed proxy for Labrador Current flow since the last glacial maximum.