Lithofacies association F-1 is a dark to black colored organic-rich, dolomitic siltstone. The grain-size is primarily composed of coarse-silt with thin laminae of fine-silt. The fine-silt laminae are preserved as horizontal to wavy lamination (Figure 11(A)). The thickness of individual fine-silt lamina within Lithofacies F-1 is approximately 2 mm to 3 mm. Thin-section petrography of samples obtained from Lithofacies association F-1 confirm the nature of silt composition and further show that the grains are subangualar to subrounded (Figure 11(D)), and well sorted (Figures 11(E)-(G)). SEM analysis shows that the organic rich siltstone of Lithofacies F-1 is composed of dolomite, mica, and clay minerals (Figure 11(B) and Figure 11(C)). Trace fossils are not present in Lithofacies F-1. The basal contact between Lithofacies F-1 and Lithofacies F-2 is abrupt.

The dark color organic rich content (~2 wt% TOC) of Lithofacies F-1 is related to high nutrient rich sediment source and rapid sedimentation, which enhanced the preservation of organic matter [47] in oxygen-poor depositional environment [47] - [55] , where density or temperature stratified water column form, typically below wave-base [47] . Oxygen poor environments can be characteristic of a distal offshore setting [51] [53] [54] . The organic matter and high TOC of Lithofacies F-1 is associated with the clay mineral. [56] study the relationship between organic matter and shale in modern sediments and found that adsorption of carbon compounds onto clay mineral surfaces played a fundamental role in the burial and preservation of total organic carbon in the sediment. Organic matter is an economically important source of hydrocarbons, minerals, and metals [56] . Organic carbon is derived mostly from photosynthesis by plants and algae, which are atoms of carbon buried in sediments [57] . Lithofacies F-1 is mainly composed of coarse silt-sized grains. Silt and very fine-grained sediment is the product of weathering, and subsequently transported by fluvial or aeolian mechanisms. [58] used depositional model (Figure 12) to show sediment source and various ways of sediments transport to environment of deposition. Particularly, [58] shows that the deposition of silt and very fine-grained sediments are related to mobilization of fines across-shelf, or transported through processes, which may include sediments deposition from hyperpycnal plumes [59] [60] . As hyperpycnal flow gradually loses part of its suspended load progressively seaward, the finer-grained silt-sized particles are deposited in distal offshore environments [61] , where changes in bottom water anoxia and sediments settling from suspension mostly dominate [62] .

Preserved horizontal to wavy lamination in lithofacies F-1 developed during sedimentation when finer-grains settle from suspension under gravity influence in a decelerating flow regime as experimented by [63] . The outershelf (distal offshore setting) environment is a locus for such decelerated bottom flow regime [64] . The sluggish flow regime enhances the development of lamination, characterized by very distinct, abrupt laminae surfaces of less than 1 mm thick, which contains finer-grained particles than the surrounding deposit [65] . The absence of soft-sediment deformation structures and convolute bedding in Lithofacies F-1 imply that wave loading, episodic, or seismically triggered deposition were not at play in the depositional process of Lithofacies F-1.

The subangular to subrounded grains of Lithofacies F-1 have implications for the sediment source, transport mechanism and duration of entrainment [66] [67] . Generally, grain roundness is a fundamental physical property of sediment particles, affecting their entrainment, transport, deposition, and, therefore provides clues about the sediment provenance, transport history and depositional conditions [68] [69] . Subangular to subrounded grainsizes of Lithofacies F-1 infers relatively short distance of transport from sediment source-rock prior to initial entrainment into suspension [70] [71] . The well sorted textural characteristics of Lithofacies F-1 implies the evenness of the mass of particles with the total amount of material that are within the same grain-size distribution as seen under microscopy. Mineralogical composition of Lithofacies F-1 includes silt-sized quartz, dolomite, mica, and clay. The silt size grains in Lithofacies F-1 derived its origin from the mechanical and chemical breakdown of quartz [72] [73] [74] [75] [76] . In support of weathering as a mechanism of disintegration of quartz into silt sized particles, an account of structural defects in quartz crystals was experimentally presented by [75] [76] , and their findings suggest that silts may be released directly from bedrock during weathering [75] [76] . Furthermore, production of silt is associated with fracturing of coarser quartz grains during weathering and pedogenesis [77] . The depositions of silty sediments into distal setting are significantly related to flocculation of fines due to the affinity of mica as a major component of siliciclastic sediments [27] . Suspended sediments are well known to be transported primarily as flocculated material [78] . Flocs are composed of a complex matrix of organic particles, inorganic particles (e.g. clays and silts) and substantial interfloc spaces (pores) that allows for the retention, sustenance and flow through water [78] .

The profound plume experimental work of [57] shows bedload transport of mud by floccule. In [57] [78] [79] show that floccule is associated with bedload transport in a thin layer of floccule-carrying clay in suspension within boundary-layer of higher concentration and interpreted the phenomenon as a direct analogue to the heavy fluid layer in sand transport. As a result of flocculation, significant alterations of the constituent particles in a hydrodynamic flow modifies grain-size and their shape, thereby enhancing effective transport of sediment [78] .

Thin-section petrography shows that the dolomite in Lithifacies F-1 is detrital. The detrital nature of the dolomite in some thin-sections show sigmoidal morphorlogy resembling ripple lamination, suggesting that the dolomite fragments may have been shed from carbonate apron as debris. The scattered, detrital dolomite nature seen in thin-section petrography could be interpreted as postdepositional in origin, rather than in-situ.

The absence of bioturbation in Lithofacies F-1 imply stressed and disaerobic conditions [54] [58] [80] [81] . Thus, Lithofacies F-1 deposition may be related to pelagic processes [82] . Pelagic depositional process is supported by the absence of depositional features characteristic of shoreface, such as storm or wave generated primary sedimentary structures (cross bedding, or hummocky cross stratification). The absence of trace fossils in lithofacies F-1 may be due to dysaerobic or oxygenation stress [34] [54] [82] [83] .

Dysoxic conditions prevailed for most of the Permian-Triassic (P-T) boundary that caused mass extinction, which ravaged biotic communities, the most severe in Earth’s history [15] [84] - [97] , due to unequalled decline in the amount of dissolved oxygen in the world’s oceans [75] - [88] . The anoxic conditions extended intermittently into shallow marine (proximal shelf) depositional settings [4] [51] [89] , which have been reported to be associated with global anoxic conditions that subsequently caused a prolonged faunal recovery in the aftermath of Permian-Triassic biota crises [85] [90] . The protracted fauna recovery continued into the Lower and Middle Triassic time [4] , thereby delaying fauna revitalization for several millions of years following the fauna mass extinction [51] [91] - [96] . The harsh environmental conditions post P-T fauna environmental crises may have implications for the non-fossiliferous, or the non-evidence of fauna traces in Lithofacies association F-1. Based on the above sedimentological characteristics of Lithofacies association F-1 (organic rich siltstone), it is interpreted herein as a deposition in a distal offshore (outershelf) to ramp setting (Figure 12). A shelfal environment has been interpreted for similar siltstone facies [64] [98] , or outershelf to continental slope bathymetry [64] [98] . This interpretation is in line with previously reported depositional environment for the Lower Triassic Montney Formation by [4] [9] [23] [98] [99] .

Lithofacies association F-2 is composed of interbedded, laminated, very fine-grained sandstone and siltstone (Figure 13(A), Figure 14, and Figure 15(C)). The ratio of sand to silt in Lithofacies F-2 is approximately 3:1 (Figure 15(C)) in some successions, and ~2:1 ratio in some beds (Figure 13(B), Figure 13(C), and Figure 13(D)). Thin-section analysis of Lithofacies association F-2 confirms that the lithology is siliceous, and the grain-size ranges from very fine-grained sandstone to coarse siltstone grade (Figure 17(D)). Petrographic examination of Lithofacies F-2 further shows that the grains

sorting are variable, from moderately well sorted to poorly sorted (Figure 17), and texturally matured, but mineralogically submature as evidenced by the present of feldspar and clay (Figure 17(D)). In addition, thin-section petrography shows that the mineral composition of Lithofacies F-2 comprises quartz, mica, pyrite, and detrital dolomite (Figure 17). SEM analysis further shows that some of the quartz in lithofacies F-2 has developed authigenic quartz overgrowth (Figure 16(G)).

Lithofacies F-2 have well-preserved plane parallel laminae (Figure 13, Figure 14, Figure 18, and Figure 19). The sand laminae exhibit fractures along sandstone bedding planes (Figure 15(B)). Depositional features in Lithofacies F-2 comprise dewatering sedimentary structures, soft sediment deformation structures, convolute bedding/ lamination (Figure 14(C); Figure 18(C)), and small-scale current ripples (Figure 15(A), Figure 19). The current ripples are dominantly straight-crested, and rarely bifurcating (Figure 16(A), Figure 16(D)). Body fossils are not present in Lithofacies F-2. The basal contact of Lithofacies F-2 with Lithofacies F-3 is sharp, and abruptly ungradational.

Lithofacies association F-2 is composed of interbedded, laminated, and very fine- grained sandy-siltstone. [100] originally defined laminae (Figure 14(A) and Figure 15(A)) as sedimentary strata that are less than 10 mm thick. The present of preserved interbedded sandy-siltstone, and thinly laminated layers (approximately <10 mm) in Lithofacies association F-2 reflect variation in sediment texture between grain-size during sedimentation. The formation of laminae involves transcurrent migration of grains due to low relief in topography, and bed waves [101] [102] . Low relief and bed waves migration of sediments are characteristic of the lower shoreface through proximal offshore environment [103] [104] . Thinly laminated silt and very fine-grained sand in lithofacies F-2 may be related to deposition resulting from gravity influenced sedimentation in lower shoreface environment, where fair weather processes are dominant.

Silt and very fine-grained textural characteristics of Lithofacies F-2 suggests that the sediments may have been initially deposited on the shelf as fine-grained sediments, and subsequently transported either via suspension or near-bed migration to lower shoreface―proximal offshore settings [103] . This interpretation is supported by the absence of sedimentary structures characteristic of upper shoreface environment, where higher energy dominate [104] , such as hummocky cross stratification, wave or oscillatory ripples, which are primarily a response to high-energy currents and waves [105] . Thus, quiescent sedimentation processes may have dominated during the deposition of very fine-grained sandstone interbedded with siltstone of Lithofacies F-2. Silt and very fine-grained sand in Lithofacies F-2, in part suggest the possibility of input from aeolian sediment source. Evidence supporting aridity in Western Canada Sedimentary Basin (WCSB) during the Triassic time was reported by [24] in the study of paleogeographic, paleolatitude and paleomagnetic analyses. Fauna record [12] and paleolatitude study shows that paleoclimate may have ranged from sub-tropical to temperate [11] [12] [24] during the Triassic period of WCSB, and has been interpreted to be arid, and

was dominated by winds from the west [24] [106] . Paleoclimate of 30˚N as the location of the WCSB in Triassic time is consistent with arid climate and desert conditions, in which aeolian depositional processes can thrive. Evidence that supported seasonal aridity during the Triassic was established by [106] through the measurement of paleocurrent on aeolian sandstone beds, which indicated a wind flow direction from northeast in a southwest direction. The southwest directional wind transport of sediments is believed to have released seasonal offshore silt and very fine-grained sands into marine surface water [23] . The north to south longshore sediment transport affected Montney sedimentation [23] .

The siliceous characteristics of Lithofacies F-2 imply quartz dominant amongst the sandstone mineralogical composition. The variable grain sorting (moderately well sorted to poorly sorted) of Lithofacies F-2 is related to the interbedded sandy-siltstone (Figure 17(A) and Figure 17(D)), and is interpreted as texturally matured, but mineralogically submature. The sedimentological manifest of small-scale current ripples (Figure 15(A), Figure 15(D); Figure 18(A)) form a continuum of Lithofacies F-2 interpretation. Current ripple probably correspond to waning flow conditions [107] . Current ripples readily form in shallow water, but can also form in deepwater setting due to ocean-bottom currents [108] . However, the current ripple reported in Lithofacies F-2 may have formed in lower shoreface or proximal offshore environment. The proximal offshore setting has relatively low topographic gradient, which provides an excellent platform for the formation of ripples under deceleration of currents, as sand and silt fall from suspension during low energy coupled with dominance of sand that are reworked on the beds into ripples [108] . Deformation structures in Lithofacies F-2 (Figure 13(D); Figure 14(C); Figure 18(C); Figure 19(A)) is a result of wave loading commonly due to storm or high-energy deposit [109] . Soft sediment deformation

structures in Lithofacies F-2 are formed due to processes occurring during a deformational event at or near the contemporary surface of unconsolidated sediments either before, or soon after burial [110] . Deformation structure are produced due to mechanical forces causing plasticity, commonly related to gravity acting upon weak sediment, usually silts or sands, prior to or soon after, or at deposition along the sediment surface [110] . Soft sediment deformation structures can develop only in the presence of susceptible sediments, with appropriate forces that can trigger deformation mechanism [111] [112] . Liquefaction or fluidization is the most important agent for the development of sediment deformation structures in water-saturated and cohesionless sediments [111] . Liquefaction or fluidization in unconsolidated sediments may be triggered by several processes such as seismic shocks, or aftershocks, wave loading or overloading, groundwater movements, and effect of storm waves [113] . The contrasting grain-sizes (very fine-grained sand and silt) of Lithofacies F-2 characterized by alternating grain sizes, overlying homogeneous sediments makes deformation structure possible.

The analysis of soft-sediment deformation structures can unravel the driving force, deformation mechanism, timing of deformation relative to sedimentation, and the triggering agent [113] . Sediment deformation structures in Lithofacies F-2 may be related to the Triassic tectonic activity. [114] [115] [116] [117] interpreted sediments loading, deformed beddings, slumping structures and small-scale faults as indicators of tectonically driven factors that influenced the deposition of Triassic succession. Other workers [117] [118] have interpreted some of the deformation structures in the Montney Formation to be related to initial terrain collision in the British Columbia/Yukon as part of a regional tectonism of Early to Middle Triassic. Other possibilities for the formation of deformation structures in Lithofacies F-2 include seismicity, current turbulence associated with the onset of sediment-laden hypopycnal plumes could trigger deformation of laminae [118] [119] [120] , and hydrostatic pressure effects associated with upwelling [121] [122] .

Convolute bedding [101] , and convolute lamination [123] [124] in Lithofacies F-2 are associated with fluid escape, and their formation is related to grain-size and deformation mechanism. The convolute lamination/bedding structures involve folding of lamination into cuspate upright form with a sharp anticline and a relatively gentle syncline (Figure 14(C)), and they are formed as a result of plastic deformation of partially liquefied sediment usually occurring shortly after deposition [108] . Convolute lamination may also be the product of seismically triggered event that results in rapid deposition. The present of soft sediment deformation and convolute lamination in Lithofacies F-2 (Figure 14(C); Figure 16(C)) are evidence of penecontemporaneous event, or small-scale local episodic deposition.

The observed bedding plane fractures in Lithofacies association F-2 formed as a result of grain-size gradations and internal layering of parallel lamination and depositional fabric [125] . Natural fractures are important features that can help deliver hydrocarbons from tight rock matrix of a formation to the wellbore [126] . The natural bedding plane fractures in Lithofacies F-2 have the potential to serve as both initial permeability conduit [9] and can also hydraulically enhanced permeability conduits for hydrocarbon flow from tight rock reservoir [126] [127] . Mineralogical composition of Lithofacies F-2 comprises quartz, dolomite, feldspar, mica, illite clay and pyrite. Quartz is the most abundant mineral in sandstone and serves as an indicator of textural and compositional maturity [68] . Quartz rich sediments have implication for porosity, particularly, effective porosity―the result of interconnectivity of pores in a siliciclastic matrix. Based on SEM analysis, the quartz in Lithofacies F-2 shows evidence of quartz overgrowth (Figure 16(G)). Although quartz overgrowth within a dolomitic fabric insinuates complex relationships between quartz and carbonate, however, textural and mineralogical evidence from SEM (Figure 16(E) and Figure 16(G)) suggests that at least two different phases of cementation may have taken place during authigenic modification of quartz. The dolomitic nature of the Montney Formation siltstone within the study area implies that carbonate cements may have been precipitated subsequent to, or post-dated an early quartz cement, and may have peripherally replaced the cement of overgrowth and detrital grain surfaces [128] . The present of feldspar in Lithofacies F-2 is diagnostic of provenance, and useful in the estimation of paleoclimatotogical conditions [129] , which can be derived from unstable minerals, particularly, the present of feldspar group in a siliciclastic deposit [130] . Plagioclase feldspar tends to be unstable during weathering, which limits its use to rocks that were deposited under tectonic conditions and favorable for rapid deposition [129] . The instability of plagioclase feldspar is useful in the interpretation of provenance and sediment history because any sandstone containing appreciable amounts of plagioclase feldspar would probably be first-cycle, and therefore, do not lead to erroneous interpretation on multi-cycle material [129] . Second-cycle feldspar grains are not common, because feldspar is not resistant to weathering. In general, most plagioclase feldspar in sedimentary rocks are sourced from igneous or gneiss [68] [72] . The interpretation for the present of feldspar in Lithofacies F-2 indicate that the sediments are compositionally immature and have not undergone multiple cycles of sedimentation and redeposition.

Pyrite in Lithofacies F-2 (Figure 16(A); Figure 17(A)) is interpreted as post-deposi- tional emplacement due to diagenesis. The pyrite in Lithofacies F-2 (Figure 18(A)) appears as detrital pyrite aggregate within a dolomitic, very fine-grained, siltstone matrix (Figure 16(A); Figure 17(A)). Aggregated pyrite has been defined by [131] [132] as “a texture seen under the microscope, under reflected light microscopy appearing as small pyrite crystals that are aggregated into irregularly rounded ‘clots’ that are partly coalescent with one another and partly separated by non-reflective clay and carbonate”. Aggregate pyrite in Lithofacies F-2 is interpreted to have formed in-situ during diagenesis. Pyrite is an important diagenetic mineral and can help define the diagenetic history of sediments [131] . Thus, the present of pyrite in Lithofacies F-2 is an indication of diagenesis in the Montney Formation.

Detrital dolomite in Lithofacies F-2 appears to have been shed-off from carbonate apron as debris (Figure 17(B)). The present of detrital dolomite has been interpreted by [133] as post-depositional in origin. Based on the aforementioned lithological description, petrographic examination, scanning electron microscopy, and depositional characteristics of Lithofacies association F-2, it is interpreted herein as a deposition in the lower shoreface through proximal offshore depositional environment, occurring just below fair-weather wave base (Figure 12).

Lithofacies F-3 is primarily composed of very fine-grained sandstone and coarse siltstone grade. Based on trace fossil assemblage, lithofacies F-3 is subdivided into: Lithofacies F-3A (Skolithos ichnofacies) and lithofacies F-3B (Cruziana ichnofacies). The typical assemblage of the Skolithos ichnofacies and Cruziana ichnofacies is presented as a model in Figure 20. Although the model show ichnofauna diversity and abundance, the recorded trace fossils within the study interval of the Montney Formation in British Columbia does not have abundance and diversity of either the Skolithos ichnofacies, or the Cruziana ichnofacies. The description of lithofacies association F-3A and F-3B are discussed below. The recorded infauna traces in cores from the study area are defined morphologically in Table 1.

Lithofacies F-3-A is composed of bioturbated, very fine-grained sandy-siltstone (Figure 21). The trace fossils in Lithofacies F-3A comprises Planolites, Phycosiphon, Cruziana, Skolithos, Teichichnus, and Palaephycus. Lithofacies F-3A has preserved wavy to parallel lamination (~10 mm to 15 mm in thickness), wave ripples, sediment deformation, and escape structures such as fugichnia (Figure 22(C), Figure 23). Thin-section analysis of lithofacies F-3A shows Phycosiphon trace fossil (Figure 24(A) and Figure 24(B)), and vuggy porosity resulting from bioturbation (Figure 24(D)). Thin-section examination of Lithofacies F-3A shows that the grain-sizes are moderately well sorted (Figure 24(C)) admix dolomite and pyrite (Figure 24(C), Figure 24(E)).

Lithofacies F-3A comprises trace fossils characteristic of a diverse ichnological assemblage, which is typical of the Skolithos ichnofacies. Such trace fossils suite characterizes fine-grained siltstones and mudstones with diverse suites [134] . The trace fossils within Lithofacies F-3A are Skolithos, Planolites, Phycosiphon, Cruziana, Teichichnus, and Paleaeophycos. The Skolithos ichnofacies is indicative of relatively high-energy environment [134] such as the shoreface. They are associated with wave, current energy and typically developed in slightly muddy to clean, moderately sorted sediments [34] . The Skolithos ichnofacies can also develop in a loose or shifting particulate (sand-prone) substrates in marine environments [34] [134] . The present of escape traces in Lithofacies F-3A correspond to disturbances made by organisms entrained in, or buried by the event bed during sedimentation.

Thin-section analysis shows that the porosity observed in Lithofacies F-3A is associated with biogenic modification or reorganization of sediment fabric due to burrows

by organisms, coupled with heterogeneous distribution of cements (Figure 25). Such observation in thin-sections signifies that petrography should not be overlooked as a useful technique in assessing reservoir quality in sediments; although, due to over reliance on wire-line log analysis and other large-scale methods of reservoir evaluation, petrography seems to be overlooked [135] . Evidently, petrography offers a microscopic opportunity to assess reservoir characteristics, albeit, not possible by large-scale assessment methods [135] .

Based on the present of Skolithos ichnofacies in Lithofacies F-3A, the depositional characteristics corresponds to the lower shoreface depositional environment [34] . Thus, the bioturbated very fine-grained sandy-siltstone of Lithofacies of F-3A is assigned to the Skolithos ichnofacies and interpreted herein as a deposit in the lower shoreface environment.

Lithofacies F-3B is composed of bioturbated siltstone dominated by Cruziana ichnofacies. The trace fossils recorded in Lithofacies F-3B are rare Zoophycos? Planolites, Phycosiphon, Chondrites, Thalassinoides, Cruziana, Skolithos, Teichichnus, and Palaephycos (Figure 20). In some cores, these traces are not well preserved, but appeared as cryptic bioturbation. The grain-size of lithofacies F-3B is moderately well sorted. Sedimentary structures in lithofacies F-3B include sediment deformation and fugichnia- escape structures.

Trace fossils such as Planolites, Thalassinoides, Cruziana, and Palaeophycus are ichnocoenosis of the Cruziana ichnofacies [34] . The generalized ichnogenera attributed to the Cruziana ichnofacies is shown in Figure 20 and Figure 21. The Cruziana ichnofacies is commonly characterized by a high diversity of trace fossils (Figure 20) associated with a variety of ichnofauna [136] [137] . Cruziana expressions of distal proximal offshore environment are transitional between distal expression of the Skolithos ichnofacies and the archetypal Cruziana ichnofacies [34] . Distal expressions of the Cruziana ichnofacies are associated with muddy siltstone, silty mudstone, reflecting a soft, cohesive

substrate under persistent quiescent fully marine condition [44] , which is the case in Lithofacies F-3B. Lithofacies F-3B shows an increased proportion of Phycosiphon, Planolites, Thalassinoides, Chondrites and rare Zoophycos? which reflects a basinward ichnofacies. Thus, the present of these trace fossils in Lithofacies F-3B are indicative of distal offshore setting. Facies associated with rapid deposition rates are usually characterized by reduction in bioturbation intensity [34] [138] . Ichnofauna associated with such deposits are those showing escape behavior structure such as fugichnia (Figure 23(C)), and simple feeding structures, persistently high rate of deposition or event sedimentation results in low biodiversity and sparse ichnological imprint. Indications of rapid, episodic, or seismically generated tempestites (small scale = cm) in Lithofacies F-3B are suggested by the presence of finer-grained sand overlying siltstone, fluid escape structures, and soft sediment deformation. Such episodic or event deposition typically results in reduced or non-bioturbation due to insufficient time for endobenthic fauna to recolonize the tempestite substrate [34] . Commonly known Cruziana ichnofacies are those with deeply penetrating dwelling structures (e.g. Thalassinoides, Ophiomorpha) and rapidly adjusting structures (e.g. Diplocraterion, Teichichnus), intrabasinal feeding structures (e.g. Planolites, Macaronichnus) and escape structures tend to be the most common elements in the suites characteristic to rapid sedimentation [34] . The dwelling structures trace fossils, feeding structures traces, and rapidly adjusting structures occur as mono-specific ichnogenera with poor diversity in Lithofacies F-3B.

Based on the above sedimentological and ichnofacies characteristics of Lithofacies F-3B, it is interpreted as a deposition in a distal offshore setting (Figure 12).

Lithofacies F-4 consists of dolomitic, thin beds (≤1 m) of very fine-grained sandstone reoccurring as facies association throughout the entire successions in the logged cores (Figures 8-10). Thin-section petrography confirms that Lithofacies F-4 is quartz rich, moderately well sorted and dolomitic. Bioturbation and sedimentary structures are not present in lithofacies association F-4. In general, Lithofacies F-4 succession shows a coarsening upward trend. The basal contact of lithofacies F-4 with Lithofacies F-5 is sharp and grades into coarse siltstone grade.

The coarsening-upward trend in Lithofacies F-4 is interpreted as basinward shoreline shift, which often characterizes a progradational trend [139] [140] . The coarsening upward succession of Lithofacies F-4 is likely to have accumulated in deepening water, particularly in areas that are not adjacent to the shoreline [141] [142] , and are characteristic of facies that prograded basinward during a falling stage of regression [139] . Based on depositional characteristics of Lithofacies F-4, it is interpreted herein as a deposition in proximal offshore depositional environment (Figure 12). The proximal offshore is characterized by storm wave base, immediately seaward of the lower limit of minimum fairweather wave base, where offshore processes operate continually.

Lithofacies F-5 is composed of dolomitic dark grey to black colored, organic rich, pyritized, massive siltstone (Figure 26). Petrographic examination of Lithofacies F-5 confirm the present of dolomite, quartz grains that are sub-angular to sub-rounded, and pyrite (Figures 27(A)-(D)). The texture of pyrite in Lithofacies F-5 under reflected light microscopy appears as irregularly rounded “clots” that partly coalesce with one another and partly separated by non-reflective dolomite (Figure 27(B)). SEM analysis of Lithofacies F-5 further shows that mineralogy comprises clay (smectite, illite, dickite, and palygorskite), and detrital dolomite (Figure 27(E) and Figure 27(F)). The observed palygorskite only occur in one sample and more analysis will help to establish how widely distributed palygorskite is in Lithofacies F-5. X-ray diffraction (XRD) analysis shows a spectrum and arrays of major and accessory minerals in Lithofacies F-5, which further confirm the present of dolomite, pyrite, and in addition, shows mica, and Albite. Bioturbation are not present in Lithofacies F-5. The basal contact of Lithofacies F-5 with Lithofacies F-4 is sharp. The upper contact of Lithofacies F-5 in some succession is sharp and erosionally demarcated from the overlying Doig Formation by an erosional lag deposit (Figure 26(D)).

The dark grey to black colored, organic carbon content of Lithofacies F-5 is a result of high nutrient rich sediment source and rapid sedimentation, which enhanced the preservation of organic matter [47] , in oxygen-poor depositional environment [47] [48] [52] [54] [142] , where density or temperature stratified water column form, typically below wave-base [47] . Oxygen-depleted environment is characteristic of a distal offshore setting [52] [54] [55] . The organic carbon richness of Lithofacies F-5 implies that F-5 is a potential hydrocarbon source rock.

Pyrite in Lithofacies F-5 is related to post-depositional emplacement caused by the dissolution of organic matter due to diagenesis (Figure 27(D)). Pyrite is commonly associated with organic rich sediments, such as black shales, and has been interpreted as

concretionary in origin [143] . Localized pyrite concentrations in sediments are formed under fully anoxic conditions, due to an excess of H2S in the sediment from iron that was released from terrigenous grains, thereby causing precipitation in the form of disseminated tiny iron sulfide grains [143] . Accumulation of localized pyrite is related to anoxic organic-rich sediments, which is typically in a non-sulfidic surface layer [144] . In such environmental settings, iron oxyhydroxide coatings on terrigenous grains of the surface sediment readily source and solubilized iron that keeps pore waters free of H2S via pyrite formation [144] [145] . Contemporaneously, bacterial decay of organic matter becomes a mechanism of diffusing oxygen from the pore waters [143] . Under the ensuing combination of anoxic and non-sulfidic conditions, [143] argued that iron should be able to migrate through the sediment, making possible the localized accumulation of pyrite. This phenomenon produces various kinds of pyrite aggregates commonly present in organic rich black shales [143] . Morphologically, pyrites can be described as pyrite nodules, pyrite laminae, pyritized burrows, pyritized fossils [143] , or nucleated pyrite [142] . Pyrite is an important diagenetic mineral and their present in a sample can help define the diagenetic history of sediments [131] . Therefore, the occurrence of pyrite in Lithofacies F-5 is a strong evidence of post depositional changes, and interpreted herein to have formed in-situ during diagenesis. Similarly, the present of detrital dolomite in Lithofacies F-5 is interpreted as post-depositional in origin, rather than in-situ [133] . Clay mineral in Lithofaciesis F-5 is associated with the organic carbon richness. [56] study the relationship between organic matter and shale in modern sediments and found that adsorption of carbon compounds onto clay mineral surfaces played a fundamental role in the burial and preservation of total organic carbon in the sediment. This evidence proved that organic matter are within the smectite interlayers of clay, which implies that hydrocarbon prone source rock may be closely related to clay mineralogy [56] . The depositional mechanism of the silt-sized grains and clay in lithofacies F-5 may be related to flocculation of fines due to the affinity of mica mineral as a major component of siliciclastics sediments, which is particularly more associated with silts and very fine-grained sediments [27] .

[145] observed that the distance of transport of clay rich sediments affects clay mineral composition, thus they differ from one depositional environment to another (e.g., coastal clay mineral differs from continental slope clay mineral). The observation of [145] shows that chlorite proportion of clay mineral increase from the lower slope to upper slope, corresponding with a decrease in the proportion of smectite. The illite component of clay reaches its maximum on the middle slope [145] . Differential proportion of clay in the different depositional environment may be due to different mineral grain-sizes that characterize different depositional settings, and the different affinities to flocculation effects associated with deposition of hemipelagic [145] . The illitic/ palygorskite clay in lithofacies F-5 (Figure 27(E) and Figure 27(F)) has significant interpretation in relation to petrogenesis of the Montney Formation. [145] stated that kaolinite tends to flocculate near the river mouths, whereas illite (Figure 27(E) and Figure 27(F)) and montmorillonite (smectite) are transported further offshore, thus, supporting a distal depositional environment interpretation for Lithofacies F-5. [146] [147] [148] have reported similar depositional environment based on clay mineralogy. The X-ray diffraction response of illite (clay mineral) coupled with SEM image is an indication of the diagenesis, and low-grade metamorphic history of a sedimentary rock [149] [150] [151] [152] . Kaolinite is transformed to illite during diagenesis, typically at temperatures of 212˚ - 230˚F (100˚C - 110˚C) [153] [154] . The transformation of illite clay to dickite, and further transformation to palygorskite clay (Figure 27(E) and Figure 27(F)), supports the interpretation of diagenesis in lithofacies F-5. The clay associated with lithofacies F-5 is interpreted as post depositional in origin based on the diagenetic transformation of illite clay to palygorskite clay (Figure 27(E) and Figure 27(F)). [154] have reported that post-depositional origin is one of the ways clay minerals in sediments are derived, or by diagenetic modification. The absent of bioturbation in Lithofacies F-5 imply stressed and anaerobic conditions in restricted or oxygen poor environment [54] [55] [56] [57] [58] [80] [82] . Thus, lithofacies F-5 deposition may be related to pelagic processes. Pelagic depositional process is supported by the absence of depositional features characteristic of shoreface environment, such as storm or wave generated primary sedimentary structures (cross bedding, or hummocky cross stratification). The absence of trace fossils in lithofacies F-5 may be due to dysaerobic or oxygenation stress [33] [34] [49] [84] [85] .

The upper contact of lithofacies F-5 of the Montney Formation with the overlying Doig Formation is reminiscent of erosional lag deposit characterized by a Glossifungites-Trypanites surface [19] [20] [83] . The mechanics of the deposition of rip-up clast of pebble sized to very coarse-grained sandstone, erosional disconformity that mark the boundary between the Montney and Lower Doig formations is interpreted to be akin to upper flow regime. The deposition of massive siltstone of Lithofacies F-5 may be related to transport and deposition from suspension, principally enhanced by the influence of waves mobilization of sediment by hyperpycnal mechanisms [58] [59] [60] [61] . As hyperpycnal flow gradually loses competence, part of its suspended load progressively settle from suspension seaward, the finer-grained silt-sized particles are deposited in distal offshore environments [64] , where changes in bottom-water anoxia and suspension sediments settling from buoyant plumes mostly dominate [62] . The initial entrainment of sediments into suspension in the surf zone is due to turbulence, convection and eddy currents [155] [156] . As sediments goes beyond shoreface environment, energy start to dwindle and coarser grain-size begin to fall off from suspension and are deposited, while finer grains (silt-size) particles continue in suspension basinward. [155] [156] reported that gravity waves contribute significantly to the entrainment and transport of sediment, by enhancing near-bed velocities. [157] [158] proved with field measurement that turbulence are significantly responsible for sediments suspension in hydrodynamic flows. Siltstone deposit commonly occurs in a variety of depositional settings where energy and hydrodynamic processes are subtle and quiescent. Lithofacies F-5 massive siltstone was deposited by hydrodynamic processes related to settling of silt size particles through the water column. The organic rich nature of Lithofacies F-5 suggests pelagic or hemipelagic processes commonly associated with distal settings. Based on the sedimentological and mineralogical characteristics of Lithofacies F-5 as described above, it is interpreted herein, as a deposition in a distal offshore (outer shelf) depositional environment to ramp setting.