Athabasca Oil Sands Research Articles

Treatment of naphthenic acids in oil sands process-affected waters with a surface flow treatment wetland: mass removal, half-life, and toxicity-reduction

This study is the first to investigate the removal of naphthenic acids in a full-scale constructed wetland within the Alberta Oil Sands region. The average mass-removal efficiency for all O2-naphthenic acids measured in three separate deployments in the wetland ranged from 7.5% to 68.9% and appeared sensitive to physicochemical properties of the naphthenic acids, environmental conditions, and water quality. Treatment efficiency of individual naphthenic acids was found to increase with increasing carbon number and decreasing number of double bond equivalents in the molecule. Treatment efficiency was also found to increase with both higher initial turbidity in OSPW entering the wetland, and warmer average OSPW temperatures during wetland operation. Half-life times of naphthenic acids in the treatment wetland ranged between 8.9 and 39 days and were substantially lower than those in tailings ponds (i.e., 12.9–13.6 years) and laboratory studies focussed on bench-scale aerobic microbial biodegradation (i.e., 44–315 days). Using published dose-response data, biomimetic extraction measurements using solid phase microextraction fibers indicate that 14 days of wetland treatment resulted in a reduction in (4 d) deformity of Danio rerio from 50 to 16%, while exhibiting less than 1% toxic response for less sensitive toxic endpoints. The study concludes that wetland treatment is a feasible and productive treatment method for naphthenic acids in oil sands process-affected water due to a combination of sorption and biodegradation.

Vegetation Changes in Alberta Oil Sands, Canada, Based on Remotely Sensed Data from 1995 to 2020

There are rich oil and gas resources in Alberta oil sand mining area in Canada. In the 1960s, the Canadian government decided to increase the mining intensity. However, the exploitation will bring many adverse effects. In recent years, more people pay attention to the environmental protection and ecological restoration of mining areas, such as issues related to changes in vegetated lands. Thus, the authors used the Landsat-5 TM and Landsat-8 OLI remote sensing images as the basic data sources, and obtained the land cover classification maps from 1995 to 2020 by ENVI. Based on the NDVI, NDMI and RVI, three images in each period are processed and output to explore the long-term impact of exploitation. The results show that from 1995 to 2020, the proportion of vegetation around mining areas decreased sharply, the scale of construction land in the mining area increased, and the vegetated land was changed to land types such as tailings ponds, oil sand mines and other land types. In addition, three vegetation indexes decreased from 1995 to 2020. Although the exploitation of oil sand mining areas brings great economic benefits, the environmental protection (especially vegetation) in oil sand mining areas should be paid more attention.

Rich solvent - Steam assisted gravity drainage (RS-SAGD): An option for clean oil sands recovery processes

The impact of steam generation on Steam-Assisted Gravity Drainage (SAGD) process economics and environmental impacts have led to various modifications of SAGD including solvent co-injection with steam. One example is the Expanding Solvent Steam-Assisted Gravity Drainage (ES-SAGD) process where 1–5 vol% solvent is injected with the steam into the reservoir. The solvent travels with the steam to the edge of depletion chamber dissolving into the oil thereby mobilizing the oil more than would have been achieved with heating alone. This means lower steam-to-oil ratio and thus, greater thermal efficiency, lower emissions intensity, and water consumption intensity. However, processes where the majority of the fluid injected is steam are still overly emissive and expensive to operate. There is a need to develop carbon-neutral bitumen production processes. Rich Solvent-SAGD (RS-SAGD) aims at injecting mostly solvent into the reservoir with small amounts of steam to achieve radically lower emissions and water consumption intensities than that of SAGD. Here, a RS-SAGD process is investigated where the solvent content is >60 vol% by using detailed thermal-solvent reservoir simulation in an Athabasca oil sands reservoir. The results reveal that RS-SAGD yields higher oil rate than that of SAGD and the process has significantly higher energy efficiency, up to 96% lower emissions and water consumption intensities than that of SAGD. Given the performance of RS-SAGD processes, oil sands operators should consider such processes for future operations.

Carbon and Nutrient Stoichiometric Relationships in the Soil–Plant Systems of Disturbed Boreal Forest Peatlands within Athabasca Oil Sands Region, Canada

Peatlands store carbon (C), nitrogen (N), and phosphorus (P), and the stoichiometric relationship among them may be modified by ecosystem disturbances, with major implications for boreal peatland ecosystem functions. To understand the potential impact of landscape fragmentation on peatland nutrient stoichiometry, we characterize the stoichiometric ratios of C, N and P in the soil–plant systems of disturbed boreal forest peatlands and also assessed relationships among site conditions, nutrient availability, stoichiometric ratios (C:N:P) and C storage in four sites that represent the forms of disturbed peatlands in the Athabasca oil sands region. Our results showed that nutrient stoichiometric balance differed across and within these peatlands, among plants, peat, and groundwater. Ratios of C:N and C:P in peat is a function of nutrient and moisture conditions, increasing from nutrient-rich (C:N = 28; C:P = 86) to nutrient-poor fens (C:N = 82; C:P = 1061), and were lower in moist hollows relative to drier hummock microforms. In groundwater, the drier nutrient-rich fen had higher N:P ratios relative to the nutrient-poor fen, reflecting interactions between dominant hydrologic conditions and stoichiometric relationships. The N:P ratio of plants was more similar to those of peat than groundwater pools, especially in the most recently disturbed nutrient-poor fen, where plant C:N:P ratios were greater compared to older disturbed sites in the region. These findings suggest that disturbances that modify moisture and nutrient regimes could potentially upset the C:N:P stoichiometric balance of boreal forest peatlands. It also provides valuable insights and essential baseline data to inform our understanding of how peatland C:N:P stoichiometry would respond to disturbance and restoration interventions in a boreal forest region at the tipping point of environmental change.

Review on Microwave Application in Petroleum processing

Microwave energy is becoming the most diverse form of energy transfer, used in the petroleum industry for inspecting coiled tubing and line Pipe, measuring multiphase flow, and the mobilization of asphaltic crude oil. Depletion of conventional crude oil reserves creates economic Demand for various fuels; in Canada, efforts have intensified to develop microwave technology for in-situ enhanced oil recovery of heavy oil/Bitumen; about 26 of the estimated 30 billion barrels of heavy oil are considered unrecoverable using current technology. Specific objectives included Studying microwave process conditions affecting upgrading of heavy oil/bitumen to synthetic crude and achieve up to 50% desulphurization. This review provides a general overview of microwave applications in oil sands bitumen or shale oil pro-Duction in petroleum upgrading. The vast oil reserves in the oil sands of Alberta will become a major source of petroleum products in the near future and a number of alternative technologies have been explored for the production and upgrading of oil sands and heavy oil.

In situ stress field in the Athabasca oil sands deposits: Field measurement, stress-field modeling, and engineering implications

In situ stress is one of the key engineering parameters that ensures caprock integrity in steam-assisted gravity drainage (SAGD) operations. Massive steam injections during an SAGD operation leads to significant changes in the pore pressure, temperature, stress, and volumetric strain in the rock formations. These changes trigger deformation and stress redistribution in the overburdened strata, which could lead to a containment breach of the caprock through shear or tensile failure. To ensure subsurface steam containment, both to satisfy public safety considerations and instill confidence that the steam containment will continue over the necessary timescales, the Alberta government requires every SAGD operator to measure the in situ stress conditions in the oil sands reservoir and its caprock. Minifrac test is a suggested method that can measure the minimum principal stress with high confidence. A safety factor (SF) of 80% is used to determine the maximum operation pressure (MOP) for safe SAGD operations; in other words, MOP = 80%*σmin, where σmin is the minimum principal stress at the base of the caprock. In most cases, this 80% SF safeguards the SAGD injection pressure to always remain lower than the σmin at the base of the caprock, ensuring that no tensile fractures are initiated at the caprock.In this study, we compiled a database containing in excess of 100 minifrac datasets across the Athabasca oil sands region and constructed an in situ stress map. Based on our in situ stress dataset, we developed a quantitative risk model to analyze the effects of uncertainties on the probability of exceedance (i.e., the probability that the MOP exceeds the fracture pressure at the base of the caprock). The risk model involves defining probability distributions to quantify the uncertainties at the shallowest depth and minimum stress gradient. The output of the risk model was a set of predictions of exceedance probabilities, which were computed using Monte Carlo simulations. Through a statistical analysis of this in situ database and risk-based simulation analysis, this study demonstrates the reliability of a SF of 80%.

Migrations of Devonian brine up-section and the origin of calcite-cemented sand in the Lower Cretaceous McMurray Formation, Athabasca Oil Sands

Calcite-cemented sand intervals are widely distributed in the lower interval of the McMurray Formation of the Lower Cretaceous Athabasca Oil Sands deposit, northeastern Alberta. Flows of Devonian brine were driven up-section upon mixture with meteoric-charged groundwater that came in contact with the Prairie Evaporite Formation only 200 m below. Voluminous migrations of carbonate-saturated Devonian formation water during lower McMurray Formation deposition account for the distribution of decimetre to multimetre thick calcite-cemented sand intervals and giant concretions within the syndepositional fill of the Bitumount Trough, a 100 km long salt dissolution–collapse structure that floored the northern Athabasca Oil Sands deposit. Precipitations of calcite cement concurrent with deposition of the lower McMurray Formation provide insight into the eventual disposition of the voluminous brine that would have resulted from the dissolution of as much as 130 m of Middle Devonian salt section below the Bitumount Trough in contrast to deep basin storage elsewhere. Breccia pipes developed in Middle–Upper Devonian carbonate beds flooring the Bitumount Trough provided migration pathways up-section for the carbonate-saturated Devonian brines. Giant concretions of calcite-cemented sand, 1–2 m across, developed in homogeneous sands proximal to collapse-breccia pipes that vent along the Trough floor, whereas brine flows directed along heterogeneous sands resulted in tabular calcite-cemented beds. Similar but volumetrically less significant Quaternary brine migrations diluted with glacial meltwater were discharged at the surface as saline springs along the modern river valleys, resulting in geochemical trends characterized by concentration of total dissolved solids but without associated precipitations of calcite cement.

Groundwater monitoring near oil sands development: Insights from regional water quality datasets in the Alberta Oil Sands Region (AOSR)

Study regionThis study is carried out across a 142,000 km2 area within the Alberta Oil Sands Region (AOSR), Alberta, Canada. Study focusGroundwater quality data for the AOSR are compiled and interpreted to provide information on regional water quality to inform groundwater monitoring and land use planning. A database of 546 water quality parameters measured between 1958 and 2015 from 5118 water wells is compiled, cleaned, and analyzed by hydrostratigraphic unit (HSU). New hydrologic insights for the regionBaseline water quality conditions were found to vary in the 12 main HSU’s, with wide ranges in total dissolved solids and geochemical facies, reflecting variable lithology and geochemical processes. Median concentrations for multiple parameters exceeded “interim trigger values” under consideration by government regulators. Statistically significant temporal changes in water quality were detected in the 2000’s in isolated areas of Surficial Sands aquifer, the Cretaceous and Devonian formations in the North Athabasca Oil Sands, and in Quaternary aquifers in the South Athabasca Oil Sands and Cold Lake Beaver River. Temporal anomalies occur in areas with enhanced vertical connectivity due to the presence of buried channels, incised rivers, or where the Colorado Group is thin or completely absent. The compiled dataset highlights the role of geochemical data in identifying aquifer connectivity and monitoring priority. Lack of publicly available data for key aquifers near some mining areas are noted.

Spatial patterns and mass balance of sodium in near-surface peat of a constructed fen

At the Nikanotee Fen Watershed, a pioneering reclamation project in the Athabasca Oil Sands Region, elevated sodium (Na+) in the porewater of mine-waste materials has been shown to migrate to the fen through groundwater, likely influencing fen vegetation health. Given the potential of Na+ to steer the ecological development of the fen, the goal of this research is to quantify the spatial distribution of Na+ and to characterize the Na+ mass balance of the surface and shallow subsurface of the fen. For a given time, the highest Na+ concentrations were generally found in the wettest part of the fen in the southwestern corner, and the lowest in the relatively dry northeast corner near the drainage outlet. Na+ concentrations in ponded surface water were responsive to rainfall-induced dilution and evapoconcentration, whereas porewater salinity in shallow groundwater was insensitive to meteorological conditions. Surface discharge controlled the mass efflux of Na+ from the system at an estimated average rate of 4 kg∙day−1 between June and August. Given the relatively small proportion of salt being flushed annually, and the greater rate of mass inflow relative to export, elevated salinity will likely be sustained for several decades. Since elevated Na+ concentrations are impacting the rooting zone of vegetation and have exceeded the salinity stress-threshold of mosses, targeting salt-tolerant vegetation will be important to maintain carbon accumulation in constructed systems.

A temporal snapshot of ecosystem functionality during the initial stages of reclamation of an upland-fen complex

Study regionAthabasca River Watershed, Athabasca Oil Sands Region (AOSR), Alberta, Canada. Study focusAOSR pre-disturbance landscape consists of a mosaic of upland-peatland complexes, dominated by fens, which have become the focus of recent mandatory reclamation efforts. Quantifiable metrics for evaluating reclamation project trajectories and long-term sustainability are required. Here, the initial performance of a constructed upland-peatland complex (Nikanotee Fen Watershed) is evaluated through a functional-based, ecosystem-scale approach focused on carbon dynamics and water use efficiency (WUE). Initial seven years (2013–2019) post-construction were monitored using eddy covariance and multispectral imagery to capture ecosystem evolution. New hydrological insights for the regionResults indicate the fen quickly evolved from a bare-ground, carbon source (2013) to a sedge-dominated (Carex aquatilis), carbon sink (2015). Slower growth rate of trees (Pinus banksiana, Populus balsamifera) and dry edaphic upland conditions initially resulted in net carbon losses. However, as upland vegetation became established, plant CO2 uptake increased. After 2015, fen WUE remained relatively stable despite fluctuations in seasonal rainfall. Stable WUE reflects a well-connected groundwater network between the two landscape units that supports hydrological self-regulation sufficient to maintain adequate plant function. Because of this groundwater supply, fen plants were no longer dependent solely on precipitation – increasing resilience to intervals of periodic water stress. Overall, carbon and water dynamics during early-development suggests the system is evolving towards a self-sustaining, carbon-accumulating, functional ecosystem.

Algorithm for estimating SARA fraction properties and its application in predicting the densities of heavy oils, bitumen and diluted bitumen with solvents

Using aromatic ring index (ARI) and the densities of saturates, aromatics, resins and asphaltenes (SARA) at any temperature, an algorithm was developed to iteratively estimate the molecular weights and specific gravities (60 °F) of the SARA fractions. The algorithm circumvents molecular weight measurements in reporting SARA fractions properties. Then, using the corresponding state principles the critical properties and acentric factor of the fractions were estimated using the correlations available in literature. Further, applying regular solution theory the densities of heavy oils, bitumen, and five diluted Athabasca bitumen with 5 solvents were predicted from Hankinson-Thomson and a compressed liquid density correlation. The average absolute deviation (AAD) in predicting the densities was found to be 1.33% for 1524 points with temperature range from 288 K to 463 K and pressure from 0.1 to 10 MPa. The method exhibits predictive ability and can be used satisfactorily for any heavy oil/bitumen/solvent system. In order to improve the accuracy of the calculated densities, a constant density translation method can also be applied to the bitumen/oil mixtures. When the translation method was used, the AAD of mixtures was improved to 0.69%. The proposed method was found to be better or comparable to other models in predicting densities.

Microsatellite mutation frequencies in river otters (Lontra Canadensis) from the Athabasca Oil Sands region are correlated to polycyclic aromatic compound tissue burden.

Mining activities in the Athabasca oil sands region (AOSR) have contributed to an increase of polycyclic aromatic compounds (PACs) locally. However, many PACs found in the AOSR, and the combined effects of PAC mixtures have not been evaluated for genotoxicity in wildlife. Here, we examine whether mutation frequencies in AOSR river otters are correlated to PAC tissue burdens. We used single-molecule polymerase chain reaction (SM-PCR) to measure the mutant frequency of unstable DNA microsatellite loci in the bone marrow of wild river otters (n=11) from the AOSR. Microsatellite mutation frequencies were regressed against liver PAC burden (total, low/high molecular weight [LMW/HMW], and parent/alkylated PACs), and to the distances from where the samples were collected to nearby bitumen upgraders. We found that microsatellite mutation frequency was positively correlated with total liver PAC burden. LMW and alkylated PACs were detected at higher levels and had a stronger positive relationship with mutation frequency than HMW (alkylated and parent) PACs. There were no significant relationships detected between mutation frequency and LMW parent PACs or the distance from bitumen upgraders. Furthermore, pyrogenic and petrogenic signatures suggest PACs in animals with high mutation frequencies were associated with combustion processes; although further investigation is warranted, due to limitations of diagnostic ratio determination with biotic models. Our findings support the hypothesis that PACs found in the AOSR increase mutation frequency in wildlife. Further investigation is required to determine if the elevated PAC levels associated with higher mutation frequency are due to natural exposure or elevated human activity.

Fish assemblage monitoring in Alberta’s Ells River: Baseline fish and habitat variability prior to major development

The collection of sentinel fish species for Environmental Effects Monitoring (EEM) has provided ancillary fish assemblage surveys on several tributaries in the Athabasca Oil Sands Region (AOSR) of Alberta, Canada over the last decade. Using available, comparable data we investigated baseline fish assemblage variability along the Ells River, a tributary of the Athabasca River experiencing increasing proximity to natural bitumen deposits and proposed mining development as it approaches confluence with the mainstem Athabasca. Transect-based electrofishing data from four sites surveyed in September 2013, 2014 and 2018 showed significant spatiotemporal variability in assemblages, where spatial variability was greatest in 2013 and temporal variability was observed in assemblages both upstream (2013–2014) and downstream (2014–2018) of proposed development. Habitat assessments in 2018 revealed significant relationships among pH, algae cover and site slope with fish assemblages of the same year. Due to the complementary nature of assemblage surveys, data challenges (changing methodologies, sampling effort, and limited ancillary physiochemical data) have presented limitations to the multivariate approach applied in the study. Moving forward, employing consistent methods for fish collections and fine-scale habitat assessments will improve the ability to correlate assemblage variability with changes in the physical environment. Ultimately, this will aid in developing potential triggers of change that may be attributed to or confound adjacent, expanding Oil Sands activities. These findings will also inform monitoring programs on the use of fish assemblages as indicators of change, potentially providing an alternative to existing biomonitoring approaches in small streams with small fish populations.

Technology, technology, technology: An integrated assessment of deep decarbonization pathways for the Canadian oil sands

As a party to the Paris Agreement, Canada has an ambitious climate target of net-zero emissions by 2050. The country also holds the world's third largest oil reserves in the Alberta oil sands. Given increasing emissions from the oil sands sector, achieving Canada's net-zero target requires significant oil sands decarbonization. If, while phasing out fossil fuels, there is still a demand for Canadian oil sands, then the decarbonization of the resource production process becomes crucial. In this study, we use an enhanced version of the Global Change Analysis Model (GCAM) with a detailed unconventional oil sector for Canada, including mining and in situ resources. We ask, what is the future of the oil sands sector in deeply decarbonized global and Canadian economies? We address this question under four mitigation scenarios with varying global net-zero GHG emissions constraints, three additional representative lower carbon extraction technologies available for the oil sands sector, as well as global direct air capture (DAC) deployment. We find that lower carbon technology deployment allows a 20%–44% increase in oil sands production by 2050 for scenarios with net-zero GHG emissions in 2100 or 2075. DAC helps maintain oil sands production in the most ambitious global decarbonization scenario (net-zero GHG by 2050), without which low international oil demand makes Canadian oil sands production uncompetitive. Canadian oil sands production thus depends highly on the availability of lower carbon extraction technologies and international oil demand, which to a certain extent relies on the availability and global deployment of negative emissions technologies.

Process model correlating Athabasca bitumen thermally cracked at edge of coking induction zone

Abstract Athabasca bitumen is an abundant resource that has successfully been upgraded using delayed coking that typically operates at 499 °C (∼930 °F), 207 kPa (∼37 psig), 1–2 min residence time on this type of crude. With society’s desire to reduce industry environmental impact while still providing energy to earth’s growing population, lower energy intensive (and thus lower greenhouse gas emissions) bitumen conversion approaches have been researched and are moving towards commercialization. The paper reviews a correlative model developed on a novel thermal cracking process, operated at lower temperatures (395–405 °C (743–761 °F)), lower pressures (<69 kPa (∼<10 psig) and up to 1 h residence time versus delayed coking, that takes various lab and pilot data, both batch and continuous, as inputs into developing the model. The purpose of the model is for use in industrial operations to provide guidance to operations for representative thermal cracker performance. The model is based on the Arrhenius equation using first order reaction kinetics for easy comprehension and use in an operational environment. Data for developing the model has been taken from various literature sources in the area of study, notably by researchers, Dr. W. Svrcek, Dr. Wiehe, Dr. Mehrotra, and Dr. Yarranton. The public data is used to create a viable range of performance that includes proprietary developments with the novel thermal cracking process. The model is configured on a mass basis so that mass balance closure can be readily calculated. A range of kinetic coefficients are provided that can be used to fit commercial plant performance based on the expected range of product outputs noted in the paper.

The effect of biodegradation on bound aromatic hydrocarbons released from intermediate-temperature gold-tube pyrolysis of severely biodegraded Athabasca bitumen

Polycyclic aromatic hydrocarbons (PAHs) from two severely biodegraded Athabasca oil sand bitumens released by gold-tube pyrolysis at 300–525 °C with 2 °C/h heating rate were characterized by gas chromatography-mass spectrometry. Alkylnaphthalenes, alkylphenanthrenes and alkyldibenzothiophenes were fully removed by biodegradation from the free phase aromatic hydrocarbon fraction in raw bitumens, while tetracyclic aromatics were partially attacked. Sample A has suffered less extensive biodegradation influence than sample B due to different oil-water-contact situations. Pronounced changes were observed in the distribution of various compound classes after pyrolysis due to thermal cracking, aromatization and condensation. PAHs released from occluded phase at intermediate–temperature (< 425 °C) exhibit clear biodegradation impact. The proportion of alkylnaphthalenes released in initial pyrolysates is much lower than those highly fused aromatics, reflecting more biodegradation influence on lower ring number aromatic hydrocarbons. Within alkylnaphthalenes, naphthalene and methylnaphthalenes with less substituents are largely depleted in the pyrolysates, indicating preferential removal of less alkylated homologues from the occluded phase by biodegradation. Isomer selectivity from the occluded aromatic hydrocarbons follows the same sequences as those observed from the free phase, resulting in poor correlation between isomerization based maturity parameters and heating temperatures. PAHs released from extremely biodegraded bitumens in intermediate–temperature pyrolysates might differ totally from those in the non-degraded oils. Caution should be taken when molecular parameters derived from occluded phase are applied for organic source input and maturity assessment.

The effects of oil sands process-affected water naphthenic acid fraction components on GDF15 secretion in extravillous trophoblast cells

Exposure to compounds present in petroleum and wastewaters from oil and gas extraction sites in the Alberta Oil Sands Region can impair reproductive health. It has been established that acid extractable organics found in oil sands process-affected water (OSPW) such as naphthenic acids (NA-fraction components; NAFC) can adversely affect reproductive outcomes. We have shown that NAFC exposure results in a significant upregulation of GDF15 in placental trophoblasts, a cellular stress marker known to be involved in human embryonic development and necessary for the maintenance of pregnancy. However, little is known regarding the mechanism(s) underlying NAFC-induced increases in GDF15 production during early placentation. The goal of this study was to examine the effects of NAFC exposure on the regulation of critical transcription factors of GDF15 in extravillous trophoblast cells. Of these transcription factors, inflammatory mediators including prostaglandins have been reported to inhibit proliferation and migration of trophoblast cells in vitro. Hence, the secondary goal of this study was to determine whether inflammation mediated through prostaglandin production is critical to GDF15 secretion. HTR-8/SVneo cells were exposed to an NAFC for 6 and 24 h to assess the expression of key transcriptional regulators, GDF15 secretion, and prostaglandin (PGE2) output. Treatment with NAFC (125 mg/L only) significantly increased GDF15 expression and secretion in association with upregulation of the transcription factors KLF4, EGR1, ATF3 and TP53. Similarly, PTGS2 (i.e. COX2) expression and PGE2 output were significantly increased at the same concentration. However, co-treatment with a COX2 selective antagonist (SC236) only partially blocked the NAFC-induced increase in PGE2 output and did not block GDF15 expression or secretion. These findings suggest that while NAFC may affect GDF15 production, it is not exclusively a result of prostaglandin-mediated inflammation. This study provides new insights into the mechanisms by which NAFC may adversely affect placental trophoblast cell function in mammals.

Carbon dissolution effects on pH changes of RAMP lakes in northeastern Alberta, Canada

Study regionThis study focuses on boreal lakes in the Athabasca Oil Sands Region (AOSR), Alberta, Canada between latitude 55.68°N and 59.72°N and longitude 110.02°W and 115.46°W. Study focusThis study focuses on interpretation of hydrochemistry from 50 lakes thought to be acid sensitive, and so monitored by the Regional Aquatic Monitoring Program (RAMP) over the last two decades. This study uses basic statistics, principal component analysis, lithological evidence, CO2 saturation estimates, mineral equilibria and δ13CDIC measurements to describe and assess controls on pH and to investigate causal factors of observed pH increase in the lakes. New hydrological insights for the regionOur assessment provides evidence of two main geochemical processes that control pH increase, namely carbonate dissolution and organic matter uptake, the latter a particularly important component of alkalinity in low pH lakes. Lakes in all subregions show strong evidence of dissolution of marine carbonates of undetermined source, and lake water appears to be trending from CO2 super-saturation towards atmospheric CO2 equilibrium. This supports the hypothesis of carbonate input due to permafrost thaw via surface or groundwater pathways, but also reveals likely influence from CO2 dissolution mechanisms related to climatic influence on ice cover duration.

Salt dissolution tectonism and origin of lacustrine carbonate beds: Mn‐Fe‐calcite and Mn‐siderite micro‐spherulite fabrics of the Lower Cretaceous McMurray Formation, Athabasca Oil Sands deposit, western Canada

AbstractSeveral lacustrine carbonate beds, each a metre‐thick interval of densely packed Mn‐rich sideritic micro‐spherulites or Mn‐rich ferroan calcite micro‐spherulites, are recorded for the first time within strata of the Lower Cretaceous McMurray Formation of the northern Athabasca Oil Sands deposit, western Canada. A lower McMurray lacustrine carbonate deposit is characterised by a metre‐thick bed fabric of Mn‐rich siderite micro‐spherulites. The middle and upper interval McMurray beds developed fabrics of Mn2+‐rich ferroan calcite micro‐spherulites. These carbonate beds represent saline lacustrine depositional environments that resulted from the lake bottom sediments ingressed from below by Mn2+‐Fe2+‐rich carbonate‐saturated brines. These up‐section migrations of Devonian formation water were sourced from dissolution trends developed in limestone and halite‐anhydrite beds of the underlying Devonian Prairie Evaporite during Cordilleran deformation of the Alberta Basin foreland. These brines ascended to the overlying McMurray Formation sediments along dissolution‐collapse structures such as breccia pipes, sinkholes and margins of differentially subsided Upper Devonian fault blocks. The up‐section migration of a sulphate‐saturated Fe2+ and Mn2+‐rich brine resulted in the ingress of a lower McMurray lacustrine bottom sediment at a site associated with the development of a peat mire terrain. Microbial redox of the lake bottom sediment resulted in a carbonate bed of micro‐spherulitic fabrics of Mn‐rich siderite interwoven with pyrite laminae. Subsequent salt dissolution events and up‐section migrations of Devonian brine during deposition of the middle and upper McMurray intervals resulted in similar carbonate‐saturated but sulphate‐poor chemistry. These saline flows also ingressed lacustrine bottom sediments below, and resulted in limestone beds of densely packed spherulitic fabrics of Mn‐ferroan calcite, not siderite. These deposits provide insight into largely unknown dispositions of voluminous brine resulting from salt dissolution trends below the Athabasca Oil Sands and further our understanding of controversial McMurray depositional processes.

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

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