Thick Salt Research Articles

Prediction of Favorable Carbonate Reservoirs under Extremely Thick Salts via Poststack Facies-Controlled and Prestack Zoeppritz Equation Inversions in the Santos Basin of Brazil

Subsalt carbonate rocks in Brazil’s deepwater region have broad prospects for oil and gas exploration and development. Due to the low-frequency bandwidth of the seismic data and the poor signal quality for this kind of reservoir target, there is a demand for accurate seismic prediction methods. We employ the facies-controlled inversion using a low-pass filter matrix to ensure the accuracy of the low frequency and to improve the robustness of the inversion results. We integrated the concept of adaptive regularization constraint of the Zoeppritz equation into the generalized linear inversion theory framework, which overcomes the shortcomings of the approximate equation. Making full use of the large angle prestack seismic information, Zoeppritz equation inversion improves the accuracy of the inversion results. The application of this method in carbonate reservoirs under extremely thick salts in the Santos Basin of Brazil indicates the feasibility and practicality of the proposed integrated prediction method.

Topographic and Tectonic Evolution of Mountain Belts Controlled by Salt Thickness and Rift Architecture

AbstractThe role of the heterogeneous rheological architecture of rifted margins in the building of mountain belts has challenged our view of how a collisional orogen formed. We show, using two‐dimensional numerical experiments of collision built by the inversion of rifted margins, that a weak pre‐extensional evaporitic layer delays the growth of topography and the onset of syn‐orogenic sedimentary record in foreland basins. In tectonic models lacking a weak décollement layer, the orogen grows by progressive accretion of basement thrusts. With a 2‐km‐thick salt layer, the orogen develops an antiformal stack in the deep crust that is kinematically connected to a shallow thin‐skin thrust belt in the foreland as observed in many orogens. A 5‐km‐thick weak layer leads to the quasi‐absence of topography and widespread salt tectonics and obliterates thrusts propagation while promoting crust and mantle underthrusting. During convergence, the preservation of a marine seaway emphasizes that collision may involve a significant period of submarine continental accretion, which duration is controlled by the thickness of the weak décollement layer. From these experiments we infer that the thicker the salt layer, the longer the delay between the onset of far‐field shortening and the formation of the orogen. Our study explains first‐order features recognized in many orogens controlled by variable salt thickness and extension.

Structural setup of Gara Marine area as deduced from 3D seismic interpretation and gravity-magnetic modelling, Gulf of Suez, Egypt

ABSTRACT An integrated interpretation utilising seismic data and inverse modelling is executed to more-reveal the subsurface complexity in Gara Marine area. The shallow features are identified by doing the seismic analyses on tops of Miocene formations. The deeper structures are deduced through constructing two gravity-magnetic models constrained by seismic and well data. The seismic results indicate that upper-Miocene rocks are characterised by a thick salt section (~2Km), which rarely cut by faults. South Gharib exhibits a structural closure at the centre due to a salt dome with dipping limbs towards the east and west. Belayim and Kareem are thinner in thickness, uniform distribution and steeply dipping to the southwest. Rudeis seems thicker westward, deposited in the downthrown side of a master block-fault. The uncertainty in seismic interpretation due to Miocene salts is estimated on tops of different horizons (±70 m static). The models indicate that Pre-Miocene sediments were deposited on a rough basement surface, with southwest regional dip-regime. The basement is deformed by the cross-faults (NW and NE) which vanish within Miocene section, with no evidences support presence of magmatic materials. The dip-reversal along flanks of Miocene salt structure, and limbs of pre-Miocene uplift, are the most potential traps.

Domínios Estruturais Relacionados à Tectônica do Sal na Região Sul da Bacia do Espírito Santo

The offshore portion of the drift section of the Espirito Santo basin is known for its stratigraphic and structural complexity related to the post-breakup salt tectonics. The movement of the salt deformed the sedimentary record of the drifte phase in the Domos de Sal Province, southern region of the basin, area of study of this work. In this research, structural domains related to salt tectonics were delineated according to the patterns and character of the structures present in the study area. The analyzes were performed using seismic data from 39 2D seismic sections and geophysical and geological data from wells drilled by the oil and gas industry. The stratigraphic-structural styles identified were: nucleated faults nucleated from the zones of detachment, carbonate rafts of albian age, turtle hull structures, domes, diapers, tongues and salt sheets. From the interpretation of structures related to salt tectonics, it was possible to delimit four structural domains. The first domain, present in the proximal region, is marked by the absence or small thickness of salt, structured with lithic faults and well defined zone of detachment; the second domain, in the intermediate portion, presents the association of small saline domes with the turbulent hull-like albian sedimentary section; the third domain displays well- -developed salt walls and walls; while the fourth domain, located in the most distal portion of the study area, presents the diameters with a subtle vergence to the east and salt tongues. With the seismic interpretation of the top of the salt, a structural contour map was generated in seismic time (TWT) that aided the delimitation of these four structural domains, as well as the observation of the alignment of the salt structures, with direction NNW-SSE. From the analysis of the structures present in the first three domains, it is suggested that they are under a distensive tectonic regime, whereas in the fourth domain it is inferred that they are resulting from compressive local conditions. The development of local tectonic regimes related to saline tectonics, which evolve from distensive to compressive in the WE direction, downdip, is explained by the salt displacement to the east caused by the slope geomorphological slope in the Espirito Santo basin and by the overload of subsequent on the platform from the Paleogene.

Salt tectonics in the Eastern Mediterranean Sea: Where a giant delta meets a salt giant

AbstractThe circum-Nile deformation belt (CNDB) demonstrates the interaction between a giant delta and a giant salt body. The semi-radial shape of the CNDB is commonly interpreted as the product of salt squeezing out from under the Nile Delta. We demonstrate, however, that this is not the dominant process, because the delta and its deep-sea fan do not reach the deep-basin salt. The distal part of the deep-sea fan overlies the edge of the salt giant, but squeezing this edge (<150 m thickness) should have had only little effect on the regional salt tectonics. Only on the easternmost side of the deep-sea fan, toward the Levant Basin, does the squeeze-out model work. Here, the delta front reaches the thick salt layer and differential loading promotes basinward salt flow, even upslope. On the western side of the delta, downslope gliding of the sediment-salt sequence toward the Herodotus Basin is driven by the elevation gradient toward the deepest part of the basin. Our analysis shows that salt squeezing by differential loading was previously overestimated in the Eastern Mediterranean and raises the need to carefully map the boundary of salt basins prior to any interpretation. This conclusion is especially relevant in young basins where deltas and shelves have not propagated far enough into the basin.

The demise of a ‘salt giant’ driven by uplift and thermal dissolution

The development of giant salt basins and eventual cessation of rapid salt deposition is founded on a delicate balance of salinity and heat fluxes within the water body governed by tectonic, climatic and eustatic change. The onset of salt deposition in such basins is widely accepted to be initiated by basin restriction. However, the processes that lead to the termination of salt deposition are comparatively unclear. Here we use an array of 2D and 3D seismic surveys to reveal that the truncation surface at the top of a thick salt sequence in the Eastern Mediterranean is far more extensive than previously thought. We show that uplift of the salt driven by deformation and thermal dissolution initiated the demise of the ‘salt giant’, even prior to the final dilution and emplacement of brackish Lago Mare and fluvial deposits. Progressive uplift of the salt through the thermocline and into the under-saturated epilimnion led to dissolution. We argue that dissolved salt was recycled and re-precipitation from the hypolimnion in the deepest sections of the basin contemporaneous with dissolution of halite from the shallower epilimnion. These findings explain how rapid basinwide salt deposition was brought to an end in the Eastern Mediterranean and present a novel process for sculpting the final architecture of a ‘salt giant’.

Evolution of a structural basin: Numerical modelling applied to the Dehdasht Basin, Central Zagros, Iran

The Dehdasht Basin, a small structural basin located in the southeast of the Dezful Embayment in the Zagros fold-and-thrust belt, has a complex tectonic structure characterized by both compressional and halokinetic features. 2D numerical models are used to test how geometrical and rheological parameters affected the Miocene-Pliocene evolution of this deep basin. The analysed parameters include rates of syntectonic sedimentation and erosion, thickness and viscosity of the lower detachment (Hormuz salt) and of the upper detachment (Gachsaran evaporites) developing diapiric salt walls, salt extrusions and minibasins-growth synclines that characterize the internal structure of the Dehdasht Basin. Assuming reasonable dimensions and rheologies (0.5 km Hormuz basal detachment with moderate viscosity of 1019 Pa·s, and Gachsaran upper detachment with a minimum original thickness of 1.5 km and viscosity between 5 · 1018 and 1019 Pa·s), our models reveals that an almost intermediate ratio between the rates of surface processes and deformation well approximate the geological and geophysical observations. A local decrease in the thickness of the Hormuz salt below the Dehdasht Basin with respect to surrounding regions was of great importance for its structural evolution. We suggest that the large volume of Gachsaran evaporites presently filling the basin was partly due to their gravitational flow from the emerging surrounding anticlines into the basin. The numerical experiments also demonstrate that in a compressional setting, shortening is the main factor for the rapid initial growth of the diapirs, although, with increasing syntectonic sedimentation the effect of shortening diminishes.

Pore pressure estimation in salt-sealed formations

Abstract Many conventional methods for pore pressure estimation are challenged by conditions below salt, and this is especially true in isolated sediments. However, for Gulf of Mexico salt allochthons – and potentially for other settings where sediments were sealed by salt early in their burial histories – a simple consideration of seal capacity provides useful insight into possible pressures. Data from several such confined settings are presented here and compared to two simple sealing models. The resulting observations are also compared to regional mudrock trends and intra-salt data to evaluate the potential implications. Together, the data suggest the salt seal fails at a constant pressure below the base-salt minimum confining stress, and pressure in sediments below that point increases at a constant gradient. The field data shown here indicate a consistent behavior over a large area of the Gulf of Mexico, despite substantial variability in salt thickness, water depth, etc. The proposed model provides estimates that agree with observed pressures within salt, at base salt, and through salt-sealed sediments below salt. A simplified version of the model can also provide a map of pressure or effective stress across base salt; while not fully accounting for sub-salt structure, such maps can be valuable in assessing relative drill-site risk to guide more detailed site-specific work.

Observational Constraints on the Formation of Cl2 From the Reactive Uptake of ClNO2 on Aerosols in the Polluted Marine Boundary Layer

AbstractWe use observations from the 2015 Wintertime Investigation of Transport, Emissions, and Reactivity (WINTER) aircraft campaign to constrain the proposed mechanism of Cl2 production from ClNO2 reaction in acidic particles. To reproduce Cl2 concentrations observed during WINTER with a chemical box model that includes ClNO2 reactive uptake to form Cl2, the model required the ClNO2 reaction probability, γ (ClNO2), to range from 6 × 10−6 to 7 × 10−5, with a mean value of 2.3 × 10−5 (±1.8 × 10−5). These field‐determined γ (ClNO2) are more than an order of magnitude lower than those determined in previous laboratory experiments on acidic surfaces, even when calculated particle pH is ≤2. We hypothesize this is because thick salt films in the laboratory enhanced the reactive uptake ClNO2 compared to that which would occur in submicron aerosol particles. Using the reacto‐diffusive length‐scale framework, we show that the field and laboratory observations can be reconciled if the net aqueous‐phase reaction rate constant for ClNO2 (aq) + Cl‐(aq) in acidic particles is on the order of 104 s−1. We show that wet particle diameter and particulate chloride mass together explain 90% of the observed variance in the box model‐derived γ (ClNO2), implying that the availability of chloride and particle volume limit the efficiency of the reaction. Despite a much lower conversion of ClNO2 into Cl2, this mechanism can still be responsible for the nocturnal formation of 10–20 pptv of Cl2 in polluted regions, yielding an atmospherically relevant concentration of Cl atoms the following morning.

3D kinematics of a thick salt layer during gravity-driven deformation

Abstract We present the results of an interpretation of 2D and 3D seismic from offshore Lebanon in which we identify a suite of 5 linearly distributed trails of fluid escape pipes with pockmarks at their upper terminus. These features transect the thick Messinian evaporites and root within prominent NE-SW oriented pre-salt folds. The pipe trails are oriented orthogonal to the strike of the pre-salt folds, with a synchronous initial expulsion episode in each trail dated at 1.7 Ma (±0.3 Ma), approximately coeval with the onset of salt-detached growth faulting along the basin margin. Each expulsion episode has been systematically offset to the NW away from the pre-salt fold by the flow of the salt, resulting in deformation of the fluid escape pipes in the salt. The orientation of the pipe trails thus provides a direct kinematic indicator for the flow direction of the salt layer during early stages of gravity-driven deformation of the salt and overburden, concomitant with basin margin uplift and tilting. The unidirectional NW oriented flow is recorded over a region of some 50 km width within the translational domain of the salt tectonic deformation. Synchronicity in the onset of fluid expulsion from overpressured reservoirs within the pre-salt succession evidenced by these pipe trails and growth fault development at the basin margins implies that the pipe trails record the kinematics of the deforming salt layer throughout its post-Messinian phase of deformation. The deformed pipe trails demonstrate a Couette flow regime for the salt layer and document subtle changes in cumulative strain and velocity (2–4 mm/yr; ±0.3 mm/yr) over distances of a few km. It is proposed that this novel method of using fluid flow features as natural markers for the kinematics of deforming salt layers could be utilized in other parts of Eastern Mediterranean, as well as other salt basins on Earth.

Base‐salt relief controls salt‐tectonic structural style, São Paulo Plateau, Santos Basin, Brazil

AbstractBase‐salt relief influences salt flow, producing three‐dimensionally complex strains and multiphase deformation within the salt and its overburden. Understanding how base‐salt relief influences salt‐related deformation is important to correctly interpret salt basin kinematics and distribution of structural domains, which have important implications to understand the development of key petroleum system elements. The São Paulo Plateau, Santos Basin, Brazil is characterized by a >2 km thick, mechanically layered Aptian salt layer deposited above prominent base‐salt relief. We use 3D seismic reflection data, and physical and conceptual kinematic models to investigate how gravity‐driven translation above thick salt, underlain by complex base‐salt relief, generated a complex framework of salt structures and minibasins. We show that ramp‐syncline basins developed above and downdip of the main pre‐salt highs record c. 30 km of Late Cretaceous‐Paleocene basinward translation. As salt and overburden translated downdip, salt flux variations caused by the base‐salt relief resulted in non‐uniform motion of the cover, and the simultaneous development of extensional and contractional structures. Contraction preferentially occurred where salt flow locally decelerated, above landward‐dipping base‐salt and downdip of basinward‐dipping ramps. Extension occurred at the top of basinward‐dipping ramps and base‐salt plateaus, where salt flow locally accelerated. Where the base of the salt layer was broadly flat, structures evolved primarily by load‐driven passive diapirism. At the edge of or around smaller base‐salt highs, salt structures were affected by plan‐view rotation, shearing and divergent flow. The magnitude of translation (c. 30 km) and the style of salt‐related deformation observed on the São Paulo Plateau afford an improved kinematic model for the enigmatic Albian Gap, suggesting this structure formed by a combination of basinward salt expulsion and regional extension. These observations contribute to the long‐lived debate regarding the mechanisms of salt tectonics on the São Paulo Plateau, ultimately improving our general understanding of the effects of base‐salt relief on salt tectonics in other basins.

Structure and kinematics of the Central Sivas Basin (Turkey): salt deposition and tectonics in an evolving fold-and-thrust belt

Abstract The Sivas Basin in central-eastern Anatolia is a north-verging salt-bearing fold-and-thrust belt including synorogenic salt tectonics. It formed between the northern leading edge of the Taurides platform and the Kırşehir block since Late Cretaceous time. We have constructed five regional cross-sections supported by field data and 2D seismic to constrain the structure of the basin and its evolution. The area is divided into three tectonic domains from south to north: (1) a Maastrichtian to Eocene north-verging fold-and-thrust belt, which terminates by a regional Eocene evaporitic level; (2) an Oligo-Miocene salt domain which contains two generations of minibasins separated by a salt canopy, forming a salt-and-thrust belt; and (3) a late Miocene to present day foreland basin. The cross-sections show the along-strike variations and the increasing shortening in the fold-and-thrust belt from west ( c. 15 km) to east ( c. 25 km). The thick salt allows for the intracutaneous propagation of the fold-and-thrust belt below a domain of salt withdrawal minibasins, decoupled as the initial salt thickness increases. In that case, the salt domain is thrusted both frontward and backward. Efficient exhumation followed by erosion of the fold-and-thrust resulted in synorogenic salt tectonics in the foreland and thus increased the mechanical resistance between them.

Composition and origin of molecular compounds in the condensate oils of the Dabei gas field, Tarim Basin, NW China

Abstract The Dabei gas field in the Kuqa Depression of the Tarim Basin is the most complex and deep continental condensate gas field in China. Comprehensive two-dimensional gas chromatography-time of flight mass spectrometer (GC×GC-TOFMS) analysis was conducted on five condensate oil samples from this field. The results show that the samples have n-alkane series in complete preservation and rich adamantanes. According to the methyladamantane index, the condensate oil is the product of the source rock with vitrinite reflectance (Ro) of 1.3%–1.6%. According to the gas maturity calculated through carbon isotope and vitrinite reflectance, the natural gas is corresponding to Ro of 1.3%–1.7%, reflecting that the natural gas and condensate oil are basically formed during the same period at the high maturity stage of source rock. The Dabei gas field has favorable geological conditions for hydrocarbon accumulation: thick salt rock in the Paleogene acts as a regional high-quality caprock directly overlying the high-quality sandstone reservoir of the Cretaceous, the coal source rocks have high hydrocarbon generation intensity and provide continuous oil and gas, and the subsalt thrust structures develop in rows with rich faults, providing migration pathways for oil and gas migration. These factors together controlled the formation of the Dabei gas field.

Petroleum generation potentials and kinetics of coaly source rocks in the Kuqa Depression of Tarim Basin, northwest China

Confined pyrolysis experiments (gold capsules) were performed to determine the yields and kinetic features for petroleum formation for seven coal samples with hydrogen index (HI) ranging from 57 to 278 mg HC/g TOC and maturities of 0.58–0.74 %Ro from coal pits within Triassic–Jurassic strata in the Kuqa Depression, China. Gases and liquid yields were measured at regular intervals as the sealed tubes were heated at 2 and 20 °C/h and total thermal stress calculated as a vitrinte reflectance equivalent (%Re) using Easy%Ro. The total confined pyrolysate yields of oil and gaseous hydrocarbons at 1.19–1.50 %Re only account for a portion (38–53%) of the releasable moieties in measured by Rock-Eval (open) pyrolysis, suggesting that a substantial portion of (47–62%) of these moieties was rearranged and incorporated into polyaromatic residual solids. At maturities >1.87 %Re, the solid residues of the seven coals have very similar gas generative potentials (ΣC1–5), which are substantially higher than their quality index (QI = (S1 + S2)/TOC) with differences ranging from 20 to 40 mg/g TOC. This result can be mainly ascribed to the differences both in methane formation mechanisms and final thermal stress levels between open (2.25 %Re) and confined pyrolysis (4.44 %Re). Only a minor portion of gaseous hydrocarbons (∼32% and 44% for the Jurassic and Triassic coals, respectively) was generated up to 2.19 %Re while the major portion was generated at higher maturities. Under a heating rate of 5 °C/My, the Jurassic and Triassic coals are modeled to become effective gas source rocks with gas yield (ΣC1–5) > 20 mg/g TOC at maturities of >1.76 %Re and 1.59 %Re, respectively. The abundant gaseous hydrocarbons found in the Kuqa Depression can be mainly ascribed to the high maturities of coal source rocks (>2.0 %Ro), in combination with excellent seal of thick salt and gypsum for the gas reservoirs.

Thermobaric depth settings of sedimentary rock basins and their fluid dynamics: Communication 3. Superhigh pressures in the stratisphere and salt diapirs

The article discusses the patterns of location and the conditions for the formation of salt diapirs. Their formation is associated with thick salt cjmpleses in which phase transformations within closed physicochemical systems form ultrahigh pressures. The latter are the cause of the flow of salts and their penetration through tectonic cracks and fractures to the earth's surface. The similarity of the formation of salt diapirs and mud volcanoes is emphasized. The possibility of the influence of ultrahigh pressures on the autonomous folding of the sedimentary cover is assumed.

Protection of concrete structures under sulfate environments by using calcifying bacteria

Abstract Application of microbial induced calcium carbonate precipitation (MICP) via biomineralization process has been considered as a novel method in improving durability properties of concrete. This bio-based treatment had been extensively targeted to improve the overall performance of concrete at lab scale experiments. Durability of microbial treated concrete under aggressive environments is still unexplored. In the current study, the durability properties of microbial treated concrete structures were studied after exposure to chemical and physical sulfate salt solutions (5% Na2SO4 and 5% MgSO4). It has been observed that sulfate attack damaged the untreated concrete specimens causing ultimate failure due to expansion under both exposure regimes. Thick salt efflorescence and severe surface scaling was observed in untreated mortar during physical sulfate attack. However, specimens treated with bacteria (Bacillus sp. CT5) significantly improved the resistance towards sulfate ingress. The experimental results indicate the extensive reduced expansion rate, salt efflorescence and surface scaling in bacterial treated concrete in sulfate exposure. The present study results indicates the potential of this technology in the overall improved resistance of microbial concrete against sulfate environment.

Salt thickness and composition influence rift structural style, northern North Sea, offshore Norway

Abstract“Salt” giants are typically halite‐dominated, although they invariably contain other evaporite (e.g. anhydrite, bittern salts) and non‐evaporite (e.g. carbonate, clastic) rocks. Rheological differences between these rocks mean they impact or respond to rift‐related, upper crustal deformation in different ways. Our understanding of basin‐scale lithology variations in ancient salt giants, what controls this and how this impacts later rift‐related deformation, is poor, principally due to a lack of subsurface datasets of sufficiently regional extent. Here we use 2D seismic reflection and borehole data from offshore Norway to map compositional variations within the Zechstein Supergroup (ZSG) (Lopingian), relating this to the structural styles developed during Middle Jurassic‐to‐Early Cretaceous rifting. Based on the proportion of halite, we identify and map four intrasalt depositional zones (sensu Clark et al., Journal of the Geological Society, 1998, 155, 663) offshore Norway. We show that, at the basin margins, the ZSG is carbonate‐dominated, whereas towards the basin centre, it becomes increasingly halite‐dominated, a trend observed in the UK sector of the North Sea Basin and in other ancient salt giants. However, we also document abrupt, large magnitude compositional and thickness variations adjacent to large, intra‐basin normal faults; for example, thin, carbonate‐dominated successions occur on fault‐bounded footwall highs, whereas thick, halite‐dominated successions occur only a few kilometres away in adjacent depocentres. It is presently unclear if this variability reflects variations in syn‐depositional relief related to flooding of an underfilled presalt (Early Permian) rift or syn‐depositional (Lopingian) rift‐related faulting. Irrespective of the underlying controls, variations in salt composition and thickness influenced the Middle Jurassic‐to‐Early Cretaceous rift structural style, with diapirism characterising hangingwall basins where autochthonous salt was thick and halite‐rich and salt‐detached normal faulting occurring on the basin margins and on intra‐basin structural highs where the salt was too thin and/or halite‐poor to undergo diapirism. This variability is currently not captured by existing tectono‐stratigraphic models largely based on observations from salt‐free rifts and, we argue, mapping of suprasalt structural styles may provide insights into salt composition and thickness in areas where boreholes are lacking or seismic imaging is poor.

Weld kinematics of syn-rift salt during basement-involved extension and subsequent inversion: Results from analog models

Scaled analog models based on extensional basins with synrift salt show how basement topography exerts a control factor on weld kinematics during the extension and inversion phases. In the case of basement-involved extension, syn-rift salt thickness differences may lead to variable degrees of extensional decoupling between basement topography and overburden, which in turn have a strong impact on the development of salt structures. With ongoing extension and after welding, the basin kinematics evolves toward a coupled deformation style. The basin architecture of our experimental results record the halokinetic activity related to growing diapirs and the timing of weld formationduring extension. Moreover, the structures that result from anysubsequent inversion of these basins strongly depends on the inherited welds and salt structures. While those basins are uplifted,the main contractional deformation during inversion is absorbed by the pre-existing salt structures, whose are squeezed developing secondary welds that often evolve into thrust welds. The analysis of our analog models shows that shortening of diapirs is favored by: i) basement topography changes that induce reactivation of primary welds as thrust welds; ii) reactivation of the salt unit as a contractional detachment and iii) synkinematic sedimentation during basin inversion. Finally, in this article, we also compare two natural examples from the southern North Sea that highlight deformation patterns very similar to those observed in our analog models.

Petroleum that has migrated into an outcropping of the Jurassic Ayad Salt Dome of Shabwah depression, Yemen

Two oil seep samples were collected from outcropping Jurassic Ayad Salt Dome of Shabwah depression. The results of this study have been used to provide information of the origin of the oil seeps and the type of organic matter and maturity of their potential source rock in the basin. Although these are surface oil seeps, their high saturated hydrocarbon content indicates that they are non-degraded oils, probably due to an arid environment of the thick salt sediments. The analyzed oil seep samples are characterized by full complement of n-alkanes, a very high component of phytane, relatively low CPIs of less than unity, and an unusually high content of aliphatic HCs. These features suggest that the analyzed oil seeps are generated from an algal marine organic matter in the source rock that deposited under highly anoxic hypersaline conditions and indicate a moderately low level of maturity. The geochemical characteristics of the analyzed oil seeps in this study are similar and consistent with the source rock characteristics of the Safer Member in the Sabatayn Basin.

Salt tectonism and distribution of brackish-water trace fossils in the Cretaceous McMurray Formation, Athabasca Oil Sands, Alberta Foreland Basin

A proposed salt tectonism-saline seep model provides a novel alternative to the two widely accepted but irreconcilable depositional models for middle McMurray Formation strata of the Lower Cretaceous Athabasca Oil Sands deposit. Established interpretations of a fluvial axial channel belt along the eastern Alberta Foreland Basin contrast with a hundreds-of-kilometres long estuarine marine–fluvial transition zone setting that was characterized by brackish-water trace fossil laden beds. The architecture of a highly sinuous fluvial meander channel belt with bank-full depths of 30–40 m furthermore is not compatible with an estuary having a tens-of-metres thick salt wedge extending hundreds-of-kilometres upstream. This new model proposes that the removal of the underlying 100 m thick Middle Devonian salt section occurred across thousands of square kilometres and resulted in voluminous saline seeps up-section into river channel fills of the middle McMurray Formation. Southward transgression by a Boreal Sea tongue terminated fluvial lower McMurray Formation deposition, and transported brackish-water larvae inland along the tide-impacted backwater length. This zoology was sustained along the fluvial channel belt by the saline seeps that elevated salinity levels in channel muds as the fluvial system dominance reasserted. Brackish-water macroinvertebrates rapidly adapted to new terrestrial food sources in these fluvial channels, precluding the necessity for a salt wedge to have extended inland for hundreds of kilometres. This research presents the first quantitative analysis of the McMurray Formation trace fossil distribution patterns. Quaternary saline surface seep trends are proposed to represent intermittent seepage up-section since the Early Cretaceous.