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Regional map of the Western Canadian Sedimentary Basin (WCSB) with contours showing approximate thickness (km) of Phanerozoic rocks and Precambrian structural features (modified from Wendte et al., 1992; Burwash et al., 1994; Ross and Eaton, 1999). Faults shown in blue are the STZ-Snowbird Tectonic Zone and GSLSZ-Great Slave Lake Shear Zone. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
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Given the recent induced seismic activity in Alberta, identification of subsurface faults and areas of structural complexity has become increasingly important in improving our understanding of the controls on induced seismic events. Using a 3D geological model supplemented with 2D and 3D reflection seismic data, several basement-bounded and basemen...
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... summary review of the literature relevant to the WCSB and then more specifically the west-central Alberta study area and the Swan Hills Formation is presented where faults have been inferred using deposi- tional or diagenetic patterns ( Figs. 1 and ...
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... is known about structural features within deep sedimentary strata in the WCSB. Furthermore, beyond an understanding of the broad tectonic provinces within Precambrian basement rocks, less is known of the structure therein. Much of the structural data from the subsurface in Alberta was collected using aeromagnetic, gravity, electrical conduc- tivity, and the 1994 Canadian Lithoprobe program seismic data (Wright et al., 1994;Ross et al., 1994;Eaton, 1995;Eaton et al., 1999;Hope and Eaton, 2002). Thinning and onlap of sedimentary strata are used to infer the presence of putative paleotopographic highs that may be re- lated to structural offsets, and to estimate the length of time that they remained emergent. There are several large, regional scale sub-Devon- ian structural features that have continued to influence depositional pat- terns in the WCSB throughout its history. The most prominent base- ment features were identified early on in the history of petroleum ex- ploration within the Alberta portion of the basin as paleotopographic highs, some that would have remained emergent through a significant part of the Paleozoic. The Tathlina Uplift, a basement high located just north of the Alberta and Northwest Territories border, was emer- gent until the Early to Middle Devonian ( Fig. 1; Norris, 1965, Belyea, 1971, Meijer Drees, 1989. The Peace River Arch (PRA) is another prominent paleotopographic high that was present at least as early as the Cambrian and emergent throughout much of the Devonian, then eventually collapsed and was inundated by the beginning of the Car- boniferous ( Fig. 1 ;Cant, 1988;O'Connell et al., 1990;Eaton, 1995). Fig. 2. Study Area and fault compilation map overlain on the subsurface Swan Hills Formation reef complexes (modified from Schultz et al., 2016; Swan Hills Formation outline -mod- ified from Wendte and Uyeno, 2005) with an accompanying table of the subsurface rock formations in the west-central area of Alberta, Canada (Table of Formations modified from Alberta Geological Survey, 2015). Formation names are in the coloured boxes and formation members are denoted here in italic text. Blue color represents carbonates, grey = shales, pink = evaporites, yellow and orange = sandstone and conglomerate, respectively. Abbreviations: AB = Alberta; O/S = Ordovician and Silurian; Lx Gp. = Lynx Group; BHL Gp. = Beaver- hill Lake Group; Wrbn Gp. = Winterburn Group; Wbm Gp. = Wabamun Group; Penn. = Pennsylvanian; Perm. = Permian; Trias. = Triassic; 2WS = Second White Specks unit; 1WS = First White Specks unit; LP = Lea Park Formation. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this ...
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... is known about structural features within deep sedimentary strata in the WCSB. Furthermore, beyond an understanding of the broad tectonic provinces within Precambrian basement rocks, less is known of the structure therein. Much of the structural data from the subsurface in Alberta was collected using aeromagnetic, gravity, electrical conduc- tivity, and the 1994 Canadian Lithoprobe program seismic data (Wright et al., 1994;Ross et al., 1994;Eaton, 1995;Eaton et al., 1999;Hope and Eaton, 2002). Thinning and onlap of sedimentary strata are used to infer the presence of putative paleotopographic highs that may be re- lated to structural offsets, and to estimate the length of time that they remained emergent. There are several large, regional scale sub-Devon- ian structural features that have continued to influence depositional pat- terns in the WCSB throughout its history. The most prominent base- ment features were identified early on in the history of petroleum ex- ploration within the Alberta portion of the basin as paleotopographic highs, some that would have remained emergent through a significant part of the Paleozoic. The Tathlina Uplift, a basement high located just north of the Alberta and Northwest Territories border, was emer- gent until the Early to Middle Devonian ( Fig. 1; Norris, 1965, Belyea, 1971, Meijer Drees, 1989. The Peace River Arch (PRA) is another prominent paleotopographic high that was present at least as early as the Cambrian and emergent throughout much of the Devonian, then eventually collapsed and was inundated by the beginning of the Car- boniferous ( Fig. 1 ;Cant, 1988;O'Connell et al., 1990;Eaton, 1995). Fig. 2. Study Area and fault compilation map overlain on the subsurface Swan Hills Formation reef complexes (modified from Schultz et al., 2016; Swan Hills Formation outline -mod- ified from Wendte and Uyeno, 2005) with an accompanying table of the subsurface rock formations in the west-central area of Alberta, Canada (Table of Formations modified from Alberta Geological Survey, 2015). Formation names are in the coloured boxes and formation members are denoted here in italic text. Blue color represents carbonates, grey = shales, pink = evaporites, yellow and orange = sandstone and conglomerate, respectively. Abbreviations: AB = Alberta; O/S = Ordovician and Silurian; Lx Gp. = Lynx Group; BHL Gp. = Beaver- hill Lake Group; Wrbn Gp. = Winterburn Group; Wbm Gp. = Wabamun Group; Penn. = Pennsylvanian; Perm. = Permian; Trias. = Triassic; 2WS = Second White Specks unit; 1WS = First White Specks unit; LP = Lea Park Formation. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this ...
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... West Alberta Ridge (WAR), a feature that borders the Alberta Basin in the west, is recognized by thinning of Devonian carbonate rocks that onlap the high ( Fig. 1; Cecile et al., 1997;Wendte et al., 1992). Fi- nally, the Sweetgrass Arch (SA) is a large N-S striking structural feature in southeastern Alberta that divides the WCSB into the Alberta Basin and the Williston Basin, the latter being an intracratonic basin to the east-southeast of the SA arch ( Kent and Christopher, 1994;Baird et al., 1995). These sub-Devonian highs are acknowledged as having influ- enced relative sea level changes and subsequent depositional patterns in the WCSB (Mountjoy, 1980;Wendte et al., 1992;Hope et al., ...
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... many theories exist concerning the dominant control on De- vonian carbonate buildup distribution and morphology in the WCSB, there is general consensus that reef buildups form on paleotopographic highs of varying magnitude and origin such as monadnocks, shoals, or faults (e.g. Andrichuk, 1958;Cook et al., 1972;Mountjoy, 1980). Much of the early work in the WCSB on large carbonate platforms suggested faults or large structural highs as the major controlling factor on deter- mining the location of their inception (Goodman, 1956;Layer, 1958;Sikabonyi and Rodgers, 1959;Andrichuk, 1961;Martin, 1967;Keith, 1970;Klovan, 1974;Mountjoy, 1980;Viau and Oldershaw, 1984;Viau, 1987). These studies utilized spatial relationships, reef morphologies, depositional patterns, offset analysis using structural cross sections, and distributions of diagenetic cements and overprinting to infer a struc- tural origin of reef inception. Martin (1967) reviewed the morphologi- cal characteristics of Devonian reefs in Alberta, specifically the conspic- uous linear trends, angularity of the reef outlines, sharp changes in the direction of the reef margins, and the straight sides of many of the De- vonian carbonate platforms (e.g., Keg River, Swan Hills, and Leduc for- mations), which were attributed to underlying deep-seated faults. In an overview paper on Devonian reefs of the WCSB, Mountjoy (1980) cites the underlying NE tectonic grain associated with planes of weakness in the Churchill Province (Precambrian basement) as a dominant con- trol on carbonate platform inception and localization. When palinspas- tically restored, the Devonian carbonate platforms in southern and cen- tral parts of Alberta have a NE trend, in similar alignment with the ob- vious trend present in the Rimby-Meadowbrook Leduc reef chain ( Fig. 1 in Mountjoy, 1980). Mid-to Upper Frasnian-aged Leduc Formation reefs that fringe the Peace River Arch display abrupt changes (up to 90°) in reef margin orientations that coincide with faults and underlying northwest-southeast Precambrian lineaments, suggesting that there may have been a structural control on the Leduc margin (Dix, 1990). Pinna- cle reefs in the Nisku Formation, which is the final sequence of major reef building during the Devonian in the WCSB, have also been influ- enced by structure in the Brazeau area (Fig. 2) and in the Front Ranges of the Rocky Mountains display a structural control (Villeger, 1997). In the northern part of the province, Chen et al. (2005) cite a NE alignment of the Rainbow area reefs of the Keg River Formation that follow ther- mal anomalies in the Precambrian basement along the Great Slave Lake Shear Zone. In southern Alberta, lithoprobe transectsrecognized low-re- lief Precambrian basement highs associated with onlapped Cambrian strata, differential compaction of shales in the East Shale Basin, and a collocation with the southern Alberta Leduc shelf margin (Edwards and Brown, ...
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... are areas of the WCSB where basement faults have been ob- served and inferred to have influenced patterns of reef growth, such as the Peace River Arch, where faulted paleotopography clearly pro- vided antecedent highs for the inception of fringing reefs ( Fig. 1 ;Cant, 1988;Gosselin et al., 1989;O'Connell et al., 1990;Dix, 1990;Keith, 1990). Despite this, and numerous modern analogues, there is contin- ued debate as to whether faults or underlying structure has controlled the inception of large reef complexes in the WCSB, in areas where faults have not been directly interpreted from reflection seismic (Andrichuk, 1961;Jones, 1980;Mountjoy, 1980;Viau, 1987;Wendte and Uyeno, 2005). Other fault proxies include localized, fault-related dolomitiza- tion in some carbonate successions, which provide evidence for the presence of deep-seated faults that acted as conduits for upward trans- mission of dolomitizing fluids derived from deeper in the stratigraphy Wendte et al., 1992;Burwash et al., 1994;Ross and Eaton, 1999). Faults shown in blue are the STZ -Snowbird Tectonic Zone and GSLSZ -Great Slave Lake Shear Zone. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.) (Mountjoy et al., 1999;Davies and Smith, 2006). More recently, the dis- covery that all of the induced seismic events recorded in Alberta's his- tory have a statistically significant correlation to occurring within 10 km outside and 20 km inside of the edge of the Swan Hills Formation car- bonate platform in west-central Alberta ( Fig. 2; Schultz et al., 2016) im- plies that critically stressed faults are located in close proximity to the Swan Hills platform edge. Previous studies have used the depths of the hypocentres of seismic events, relocated through double difference tech- niques on local arrays, to indicate that these faults are within the basal sedimentary strata ( Schultz et al., 2017;Bao and Eaton, 2016). Faults are confirmed, as part of this study, in the vicinity of the Swan Hills plat- form edge through the interpretation of 2D and 3D seismic, along with the type of faulting observed. The mere presence of faults in the vicin- ity of the platform edge cannot definitively answer the historic question of fault-reef coupling in the WCSB; however, in consideration of previ- ous evidence and new data to indicate that the relationship exists, our understanding of the nature of faults in this region can be improved through examining present day and past fault-reef ...
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Citations
... For example, the correlation between high wastewater injection rates and induced earthquakes is not conclusive, as seismic events can also occur in proximity to wells with lower injection rates (Shah & Keller, 2017). Specifically, the locations of earthquakes may be highly correlated with specific geological conditions, and key factors such as porosity, permeability, and fault zone structures can all affect the diffusion of fluids in the subsurface (Cappa et al., 2022;Corlett et al., 2018;Foulger et al., 2018;Green & Mountjoy, 2005;Guglielmi, Cappa, et al., 2015;B. Q. Li et al., 2019;Shah & Keller, 2017;Stokes et al., 2023). ...
The distribution of hydraulic‐fracturing‐related seismicity is largely controlled by subsurface structures, yet the physical process that governs the redistribution of injected fluids and stress heterogeneity remains underexplored due to a lack of observational constraints. In this study, we monitored an active hydraulic fracturing (HF) well for two months with a surface nodal array of 60 three‐component stations. We built a high‐resolution catalog comprised of 1369 events (−1.1<M<2.3 ; Mc = −0.2). Their associated seismogenic structures are resolved by seismic reflection data and a 3D velocity model obtained from ambient noise imaging. Earthquakes concentrate near the transition zone between high and low‐velocity structures, with the majority (∼70%) occurring on the high‐velocity side, accompanied by abrupt variations in seismic attributes from reflection data. Particularly, relatively large (ML> 1.0) earthquakes terminate near the edge of the high‐velocity zone. This distinct interface may represent a geological boundary or strong material property contrast that acts as a physical barrier to rupture propagation and migration of seismic sequence. Locally, two key nearby clusters exhibit distinct characteristics in spatial concentration, focal mechanisms and statistical features. We suggest that variations of structural dimension (i.e., fractures vs. faults) within a complex fault system can dominate the clustering behaviors. Overall, our integrated analysis provides new constraints on mechanical interactions among seismicity, local geological structure, and fluid migration during HF operations.
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Differentially dolomitized carbonate strata in the Western Canada Sedimentary Basin (WCSB) are increasingly targeted for carbon capture, utilization, and storage (CCUS), yet few studies have evaluated the petrophysical characteristics of these conventional hydrocarbon reservoirs for this purpose. To address this, this study uses drill-core analysis (sedimentology, diagenesis, pore morphology, and distribution), together with core-plug and production data, to evaluate the properties of five depleted oil and gas fields in the Middle to Upper Devonian Swan Hills Formation, Leduc Formation and Wabamun Group.
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... The Fox Creek area is in the West-Central Plains domain in Alberta (AGS, 2019). Corlett et al. (2018) and AGS (2019). ...
... In the Fox Creek area, the Phanerozoic sedimentary package over the Precambrian basement is around 4 to 4.5 km thick, and the succession thickens westward. The base of the preserved succession is progressively younger easterly with the youngest basal sediments over the Precambrian basement being Early Devonian in the area northeast of the Fox Creek area (Corlett et al., 2018;AGS, 2019), this results from an easterly-directed, Paleozoic marine onlapping over an irregular topography on top of the Precambrian basement. The succession in the Fox Creek area can be divided into two broad stratigraphic assemblages. ...
Abstract
The shallow aquifer in the Fox Creek area is hosted by the Paleocene Paskapoo Formation. The formation consists of fluvial deposits with channel-filled high-energy sandstone cutting through finegrained, low energy overbank sediments. Three internal members are recognized, these members define
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We use machine learning and cross-correlation techniques to enhance earthquake detectability by two magnitude units for the earthquake sequence near Musreau Lake, Alberta, which is induced by wastewater disposal. This deep catalogue reveals a series of en echelon ∼N-S oriented strike-slip faults that are favorably oriented for reactivation. These faults require only ∼0.6 MPa overpressure for triggering to occur. Earthquake activity occurs in bursts, or episodes; episodes restricted to the largest fault tend to have earthquakes starting near the southern end (distant from injectors) and progressing northwards (towards the injectors). While most events are concentrated along these ∼N-S oriented faults, we also delineate smaller faults. Together, these findings suggest pore pressure as the triggering mechanism, where a time-dependent increase in pore pressure likely caused these faults to progressively reawaken. Analysis of the “next record-breaking event”, a statistical model that forecasts the sequencing of earthquake magnitudes, suggests that the next largest event would be ML ∼4.3. The seismically illuminated length of the largest fault indicates potential magnitudes as large as Mw 5.3.
... Such faults could provide a plausible means for channelized pore pressure migration from the basal Paleozoic injection interval (1.9 km) into the basement (<2.4 km). The deposition of basal carbonate reef formations, like the injected Leduc Formation, have (arguably) been influenced by faulting/tectonic structures (Corlett et al., 2018). Depth differentials of ∼2-4 km between the sedimentary injection interval and basement induced earthquakes have been documented before (McGarr & Barbour, 2017;Schultz et al., 2014;Skoumal et al., 2020). ...
Plain Language Summary
Earthquakes can be caused by underground fluid injection; cases of M5 induced events have caused damage and harm. One of the largest recorded earthquakes in Alberta (ML 5.6) occurred in a region of underground oil sand development. Here, ground shaking and deformation information are combined into an interpreted result: that ancient faults were reactivated with reverse slip. The fault slip is largely within the crystalline basement, with a small portion extending into basal sediments. Nearby injection operations dispose of petroleum‐related wastewater in these basal sediments. This earthquake was likely triggered by the injection process: injection increases pore pressure, which diffuses laterally along permeable sediments, until encountering fractured rock, which channelizes flow into the crystalline basement—the increase of pore pressure within the fault continues until reaching a critical point for slip initiation. This event likely being induced will have important implications for future operations.
... The long-term seismic quiescence is previously attributed to the unfavorable orientation of the preexisting structures and/or the limited level of stress perturbations caused by fluid injections . Although fault structures in the study area have not been investigated as thoroughly as in the nearby Fox Creek area (e.g., Chopra et al., 2017;Corlett et al., 2018;Weir et al., 2018), it has been suggested that they correspond to widespread basement-rooted faults distributed along the Devonian reef margin . Recently, a series of 187 small-sized and moderate-sized earthquakes (local magnitude, M L , ranging 1.3-3.9) ...
Riedel shear structures (RSS) are often observed in the embryonic stage of strike‐slip fault development, which can be depicted in the field through outcrops and coseismic surface ruptures. It is a critical concept linking the geomechanical behavior of individual earthquakes to structural geology at both local and regional scales. However, the influence of long‐term fluid injections on the developing process of RSS, as manifested by the common occurrences of injection‐induced earthquakes, has been rarely addressed. Here we document for the first‐time subsurface RSS expedited by long‐term wastewater disposal injections in western Canada. We study an earthquake sequence consisting of 187 events (ML ranging 1.3–3.9) between 1 January 2018 and 15 July 2021 in an area without any previous seismic history. According to 31 well‐constrained focal mechanism solutions, the injection‐related earthquake sequence exhibits various faulting types with the vast majority (87%) being compatible with the background stress regime (SHmax azimuth = N38°E). The orientation of derived nodal planes collectively indicates a model of RSS that consists of four primary strike‐slip structures striking 19° (R′), 79° (R), 94° (PDZ), and 109° (P), respectively. Moreover, six fault segments delineated from the relocated local seismicity are parallel to the substructures of RSS. Mohr‐Coulomb failure analysis further suggests a cumulative stress perturbation of up to 10.0 MPa. Our observations suggest that long‐term fluid injection can expedite the development of local fault systems. Therefore, it is probably important to consider the dimension of local/regional RSS in the assessment of the overall seismic hazard due to fluid injections.
... The long-term seismic quiescence is previously attributed to the unfavorable orientation of the preexisting structures and/or the limited level of stress perturbations caused by fluid injections . Although fault structures in the study area have not been investigated as thoroughly as in the nearby Fox Creek area (e.g., Chopra et al., 2017;Corlett et al., 2018;Weir et al., 2018), it has been suggested that they correspond to widespread basement-rooted faults distributed along the Devonian reef margin . Recently, a series of 187 small-sized and moderate-sized earthquakes (local magnitude, M L , ranging 1.3-3.9) ...
... The most pronounced of these dissolution features occurs along the shelf edge bordering the La Crete sub-basin (Fig. 12a). The coincidence of this karstification and the edge of the Keg River shelf along the PRA is suggestive of possible fault systems, responsible for both buildup location and later evaporite removal (see Corlett et al., 2018). Faulting is well-known in the Precambrian basement within this location (Anderson et al., 1988) and farther westwards towards the apex of the PRA (O'Connell, 1994). ...
Lithostratigraphic correlation and mapping of formations and units within the Upper Elk Point subgroup provide updated information on their extent and distribution within the province of Alberta. Together with detailed bed-scale evaporite mapping of three evaporite minerals — halite, anhydrite, and gypsum — within evaporitic successions for net-thickness maps, these data allow new representations of the paleogeography of these units across the province. Paleogeographic maps of the Keg River, Prairie Evaporite and Muskeg formations reveal new details on the location of the La Crete sub-basin in northern Alberta, and the distribution and nature of Keg River Formation buildups and the overlying evaporite strata within this depositional realm. Net-evaporite mapping gives a robust picture of the distribution of Upper Elk Point subgroup evaporites, and allows for a detailed characterization of heterogeneities, halite dissolution, and sulphate karstification. Mapping of gypsum reveals that rehydration of anhydrite to gypsum (gypsification) through meteoric inflow is most pronounced within the La Crete sub-basin in northeastern Alberta, particularly where thick anhydrite deposits are associated with interbuildup basinal areas east of the Prairie Evaporite halite dissolution scarp. This association provides an explanation for the location of where active gypsification, dissolution and associated karstification is occurring and where it can be expected to occur. The process of gypsification, and ultimately sulphate dissolution, is requisite for the formation of porous dedolomite zones within the carbonates of the Prairie Evaporite Formation. Dedolomitized beds are recognized as aquifer units that are known to have contributed to Devonian-sourced, high-salinity water inflows to mine pits in the mineable oil sands area. Evidence is provided for a top-down advancement of halite and sulphate dissolution in all evaporites in northeastern Alberta. Circular, chain-like karst lakes are likely surficial expressions of the meteoric conduits for top-down karstification of sulphates east of the Prairie Evaporite halite dissolution scarp, similar to that observed in the well-documented sulphate karst district of Wood Buffalo National Park.
... A viable explanation could be due to the different injection depths, as well #460875 targets the deeper Middle-Upper Devonian aquifer at ∼4.4 km while the other two wells (∼4 km) aim at the Upper Devonian aquifer. Given that our study area is located at the northwest margin of the Swan Hills reef complexes (Figure 1a; Corlett et al., 2018), fluid injected into the Middle-Upper Devonian aquifer may access the underlying ancient Devonian reef system more easily than that into the shallower aquifers ( Figure 2d). ...
Plain Language Summary
Earthquakes can be triggered during the injections of both hydraulic fracturing and wastewater disposal. In the Western Canadian Sedimentary Basin, the latter injection type appears to have caused much fewer earthquakes than the former. Recently, a sequence of 43 small‐to‐moderate‐sized earthquakes occurred in a seismically quiet area, where injections have been safely operated for more than two decades prior to becoming intensive in 2018. The refined earthquake distribution confirms that these earthquakes are related to disposal injections. The inception of local seismicity implies that long‐term injections probably have loaded nearby fault structures to rupture. Among the four active wells, the one with a deeper injection depth caused more earthquakes than other shallower wells. As the injection of the deeper well is close to the ancient reef system, horizontal fluid migration is facilitated and more likely to reach nearby faults. Fluid migration along subvertical faults can cause deeper earthquakes in the basement and aseismic creep in the overlying shale formation. The induced aseismic slip can further load the adjacent fault segment and foster earthquakes at shallow depths. The fact that stress released by individual earthquakes varies widely between 0.8 and 230 MPa also hints the existence of aseismic creep.
... Despite the apparent features revealed in the crustal-scale seismic reflection profiles, there is little clear evidence for any large-scale tectonic reactivation within the Precambrian basement. Nevertheless, numerous studies (see recent review in Corlett et al. [2018]) have used various lines of evidence suggesting that the modest fault displacements of the basement may have influenced the deposition of the Paleozoic strata. If fault-related displacements of the basement exist in the study area, they remain below the limit of seismic resolution (Ross & Eaton, 1999). ...
... In other locales, faults have not been explicitly imaged. However, their existence has been inferred from various attributes (e.g., Chopra et al., 2017;Corlett et al., 2018;Ekpo et al., 2017;Weir et al., 2018). Sedimentation patterns and accommodation trends within the basin could also be indicative of differential vertical displacements. ...
