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Paleoenvironmental interpretation and identification of the Norian-Rhaetian boundary in the Sinwa Formation… Lei, Jerry Zhen Xiao 2018-04

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  PALEOENVIRONMENTAL INTERPRETATION AND IDENTIFICATION OF THE NORIAN – RHAETIAN BOUNDARY IN THE SINWA FORMATION (MOUNT SINWA, BRITISH COLUMBIA) USING STABLE ISOTOPES AND CONODONTS by JERRY (Z.X.) LEI  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF BACHELOR OF SCIENCE (HONOURS) in THE FACULTY OF SCIENCE Department of Earth, Ocean, and Atmospheric Sciences  This thesis conforms to the required standard    ……………………………………………………………………………………………………… Advisor                                                Faculty Co-Advisor  THE UNIVERSITY OF BRITISH COLUMBIA April 2018 ii  Abstract   The Sinwa Formation is exposed at its type locality on Mt. Sinwa, located in the southern portion of the Whitehorse Trough in northwestern British Columbia. Composed of thick, fossiliferous Late Triassic carbonates, the formation is interpreted to have been deposited in the forearc basin between the Stikine Terrane (pre-accretion) and the North American Craton.   This study marks the first detailed stratigraphic investigation of the Sinwa Formation and has significant implications for understanding Late Triassic paleoenvironmental changes in the region and the location of the Norian-Rhaetian boundary in North America. It also contributes to ongoing research refining Late-Norian to Rhaetian conodont biostratigraphy. This was achieved by recording lithologies, δ13C, and conodonts across a 231.3 m thick section.  Carbonate facies progress up-section from rip-up clast rich mudstone, to coral fragment wackestone, to bivalve coral wackestone/packstone and intact coral boundstone, to a dark siliciclastic shale. This progression is interpreted as rising sea level caused by local tectonics. Petrographic thin sections show variation in depositional energy based on matrix texture.   Conodont species recovered include Mockina englandi, M. carinata, M. cf. spiculata, M. bidentata, and M. mosheri. Being exclusively Rhaetian (Carter and Orchard, 2007), the appearance of M. mosheri at 231 m places the Norian-Rhaetian boundary below it. The δ13C record shows 3 negative excursions. Comparable to the western Tethys section investigated by Zaffani et al. (2017), the stratigraphically highest iii  excursion starting at 230 m may coincides with the Norian-Rhaetian boundary.  In considering evidence from both conodont biostratigraphy and carbon isotopes the boundary is tentatively constrained between 230-231 m from the base of the Mt. Sinwa section. In a lithological context, this places the Norian-Rhaetian boundary 0.3-1.3 m below the transition between coral boundstone (Facies 3) and shale (Facies 4).                     iv  Table of Contents  Abstract .......................................................................................................................... ii Table of Contents ......................................................................................................... iv List of Figures .............................................................................................................. vi List of Tables .............................................................................................................. viii Acknowledgements ...................................................................................................... ix 1.0 Introduction ............................................................................................................. 1 2.0 Background and Past Research ............................................................................ 3 2.1 Global Trends in Oceanic Conditions During the Mesozoic .............................. 3 2.2 Regional Geology, the Canadian Cordillera ...................................................... 7 2.3 Local Geology, Late Triassic Carbonates in the Whitehorse Trough .............. 12 3.0 Methods ................................................................................................................. 17 3.1 Fieldwork......................................................................................................... 17 3.2 Thin Section Preparation................................................................................. 18 3.3 Conodont Preparation ..................................................................................... 18 3.4 Stable Isotope Ratio Mass Spectrometry ........................................................ 19 4.0 Data ........................................................................................................................ 21 4.1 Field Lithological ............................................................................................. 21 4.2 Petrographic Description of Thin Sections ...................................................... 30 4.3 Conodont Biostratigraphy ............................................................................... 40 4.4 Stable Isotope Geochemistry .......................................................................... 44  v  5.0 Analysis ................................................................................................................. 47 5.1 Lithological ...................................................................................................... 47 5.2 Geochemical and Paleontological ................................................................... 51 6.0 Conclusions ........................................................................................................... 53 References ................................................................................................................... 55 Appendices .................................................................................................................. 61 Appendix A ................................................................................................................ 61 Appendix B ................................................................................................................ 64                     vi  List of Figures  Fig. 2.1.1           Global tectonic arrangement during the Late Triassic ........................ 3 Fig. 2.1.2           (A) Preserved soft-tissue of the conodont animal (B) Conodont apparatuses ................................................................................................................. 5 Fig. 2.2              Geological map of British Columbia showing the configuration of Intermontane belt terranes ........................................................................................... 8 Fig. 2.3               Preliminary geology of the Sinwa Creek area ................................. 13 Fig. 3.1               Traverse route on Mt. Sinwa ........................................................... 18 Fig. 4.1.1            Stratigraphic column of the Sinwa Formation on Mt. Sinwa ............ 21 Fig. 4.1.2            Carbonate mud chips of Facies 1 ................................................... 27 Fig. 4.1.3            Convolute lamination or stromatolites of Facies 1 .......................... 27 Fig. 4.1.4            Bivalve wackestone of Facies 3 ...................................................... 29 Fig. 4.1.5            Coral boundstone of Facies 3 ......................................................... 30 Fig. 4.2.1            Thin section V-003818, potential bivalve geopetal structure ........... 33 Fig. 4.2.2            Thin section V-003826, crinoid columnal ........................................ 34 Fig. 4.2.3            Thin section V-003827, coral/bryozoan fragment ........................... 35 Fig. 4.2.4            Thin section V-003834, recrystallized large shelly fragment ........... 36 Fig. 4.2.5            Thin section V-003818, rectangular sparite cluster ......................... 37 Fig. 4.2.6            Thin section V-003821, irregularly shaped sparite cluster .............. 38 Fig. 4.2.7            Thin section V-003823, calcite veins crosscutting sparite clusters . 39 Fig. 4.3.1            Simplified stratigraphic column of the Sinwa Formation on Mt. Sinwa aligned with conodont biostratigraphy ........................................................................ 41 vii  Fig. 4.3.2            Conodont species recovered from the Sinwa Formation exposed on Mt. Sinwa ................................................................................................................... 42 Fig. 4.4.1            Simplified stratigraphic column of the Sinwa Formation on Mt. Sinwa aligned with δ18O and δ13C isotope records ............................................................... 44 Fig. 4.4.2            Cross-plot of δ18O and δ13C isotope systems in Sinwa Formation carbonate samples from Mt. Sinwa ............................................................................ 45 Fig. 4.4.3            Limestone-dolostone differentiated cross-plot of δ18O and δ13C isotope systems in Sinwa Formation carbonate samples from Mt. Sinwa ................. 45 Fig. 5.1.1            Reef zonation off the coast of the Lewes River Arc, with the depositional settings of Facies 1 through 4 ................................................................ 48 Fig. 5.1.2            Change in local sea level through the progression of Facies 1 through 4 ................................................................................................................... 49 Fig. 5.1.3            Sequence chronostratigraphy across the Triassic showing global sea level fluctuation .......................................................................................................... 50  viii  List of Tables  Table 4.2           Description of thin sections from Mt. Sinwa ..................................... 31 Table 4.3           Conodont recovery from the Mt. Sinwa section ............................... 40                       ix   Acknowledgements   I would like to thank my advisors Dr. Martyn Golding and Prof. Stuart Sutherland, to both of whom I owe a lot, for their incredible support and expertise. I couldn’t have asked for better advisors.   I would like to thank Prof. Jon Husson for all the guidance he provided in the field, and the geochemical expertise he shared afterwards.    I would like to thank Hillary Taylor and the Geological Survey of Canada, Vancouver for conducting and walking me through the laboratory procedures of conodont preparation.    I would like to thank Janet Gabites and the Pacific Centre for Isotopic and Geochemical Research, UBC for conducting the stable isotope mass spectrometry of so many samples.  I would like to thank Prof. Maya Kopylova for coordinating the theses and keeping us on track throughout the year. I would like to thank the Geological Survey of Canada and the GEM 2 program for providing the funding and facilities.  I would like to thank Vancouver Petrographic Ltd for the expedient creation of the thin sections.   I would like to thank Norm Graham, Paula Vera, and Discovery Helicopters, who always got us where we needed to be.   1  1.0 Introduction  The Late Triassic epoch was a time of rapid environmental and faunal change. Greatly differing from their Paleozoic counterparts, newly established ecosystems of dominantly modern fauna were just hitting their stride following the lengthy refractory period in the aftermath of the Permian-Triassic event (Sepkoski, 1981). Environmental change is associated with significant biotic reorganization across the multiple extinctions of the Late Triassic, leading up to the end-Triassic event (Sephton et al., 2002). The Sinwa Formation within the Whitehorse Trough was deposited during 1 of these periods of extinction for bivalves and ammonoids at the Norian-Rhaetian boundary (Sephton et al., 2002) recorded in other sections. The Whitehorse Trough is interpreted as being a forearc basin between the North American Craton and pre-accretionary Stikine Terrane. It records virtually continuous carbonate deposition and is known for having some of the best developed Late Triassic reef complexes in the North American Cordillera (Yarnell et al., 1999).   Localities of the Sinwa Formation have been provisionally mapped and described (Mihalynuk et al., 2017), but no sections have been analyzed in detail. The goal of this study is to interpret the paleoenvironment and paleontology across a stratigraphic section on Mt. Sinwa, the type-locality of the Sinwa Formation. Methods utilized to this end include facies analysis and interpretation of depositional environment, thin section analysis, systematic stable isotope geochemistry, and paleontological analysis (detailed for conodonts only). Techniques included field stratigraphic logging, transmitted reflected and scanning electron microscopy, stable isotope mass spectrometry, and 2  acetic acid conodont preparation. An improved resolution of the stratigraphic location of the Norian-Rhaetian boundary is attempted by using data gathered from both chemostratigraphical and biostratigraphical methods. From this, the boundary can be placed in the context of stratigraphy and associated facies of the Mount Sinwa section and may allow correlation to other localities of both the Sinwa Formation and the possibly coeval Aksala Formation in the Yukon (Lowey et al., 2009). The recovery of conodonts at Mt. Sinwa is also helping to improve conodont biostratigraphy, contributing to ongoing efforts to refine the Late-Norian to Rhaetian stratigraphy.                3  2.0 Background and Past Research  2.1 Global Trends in Oceanic Conditions During the Mesozoic The Late Triassic epoch was a time of great climatic change and faunal turnover, punctuated by a number of extinction and origination pulses, ultimately culminating in the end-Triassic mass extinction event (Simms & Ruffell, 1990).    Figure 2.1.1: Global tectonic arrangement during the Late Triassic. Approximate location of study area annotated. Modified from Golonka (2007). Simms & Ruffell (1990) discuss the impact of environmental change on various organism groups across this timeframe. The Norian-Rhaetian boundary that the study area spans is considered to be a time of rapid change in marine environments, following a period of relative stability throughout the Norian. Bivalves experienced a pronounced extinction spike (Hallam, 1981) and conodonts continued their steady decline, towards complete extinction during the end-Triassic event (Clark, 1983). Briggs et al. (1983) 4  describe conodonts as apatite microfossils interpreted to be the teeth of jawless agnathan chordates. Conodont elements are commonly utilized in biostratigraphy as they are relatively abundant microfossils through the Paleozoic and into the Triassic that evolved many species, many of which have stratigraphically useful ranges. Conodont apparatuses consisting of multiple elements and intact conodont animals containing multiple apparatuses are much more rarely found (Figure 2.1.2 – Briggs et al., 1983). The dominantly Scleractinian coral reefs that rose to prominence in the Norian experienced significant reorganization at this boundary (Simms & Ruffell, 1990), and the reef complexes of which were subsequently terminated in the end-Triassic extinction before recovering in the Middle Jurassic (Walker & James, 1992). 5   Figure 2.1.2: (A) Preserved soft-tissue of the conodont animal, image 16 mm in width. (B) Conodont apparatuses, image 2 mm in width. From Briggs et al., (1983).  Stable isotope systems are commonly used to interpret shifts in paleoenvironmental conditions. Both volcanic warming triggering the release of light 6  carbon methane clathrates, and biotic crisis inputting light carbon previously sequestered in organisms are associated with a negative excursion in the δ13C record, as organisms preferentially utilize light carbon over heavy carbon (Zaffani et al., 2017). Warming periods resulting in greater incorporation of melting ice into seawater are associated with a negative δ18O excursion, as light oxygen is preferentially evaporated in the hydrological cycle (Epstein & Mayeda, 1953). However, the δ18O system is easily affected by diagenesis and alteration, and values tend to decrease with age in carbonate rocks (Swart, 2015). Tethyan marine stratigraphic sections recorded in a variety of European localities show a δ13C negative excursion in the mid-Norian (Muttoni et al., 2014). Zaffani et al. (2017) recorded a negative organic carbon isotope excursion at the Norian-Rhaetian boundary in the Western Tethys, preceded by 2 additional negative excursions of lesser to equal magnitude in the mid to late-Norian. The study tentatively points towards volcanism associated with the late-Norian Angayucham large igneous province as the cause of the global Norian-Rhaetian excursion. Organic carbon and nitrogen isotope excursions recorded at the Norian-Rhaetian boundary in Northeast British Columbia, representative of a deep marine setting, are indicative of widespread ocean stagnation resulting in anoxic environments (Sephton et al., 2002). The study points to low degrees of latitudinal ocean temperature variation during the Triassic as support for this interpretation. Without a strong temperature gradient to drive circulation, ocean systems would be fragile and susceptible to stagnation during periods of climatic warming. All of this occurred against the tectonic backdrop of Pangea rifting with increasing intensity, as a precursor to its eventual breakup. This increase in volcanism 7  and associated climatic warming is described by Simms & Ruffell (1990) and is proposed to have potentially been the trigger for oceanic stagnation.  Jenkyns (1999, 2010) describes global ocean anoxic events in the Jurassic and Cretaceous periods. The onset of these events correlates with abrupt increases in global temperature, proposed to be resultant from increased volcanic carbon dioxide output, which triggered additional release of greenhouse gases through various climatic positive feedback mechanisms. The increased temperature accelerated the hydrological cycle, which resulted in increased weathering and nutrient input into marine environments. The increased organic productivity and organic carbon burial is proposed to create the positive δ13C excursion characteristic of these anoxic events. Oscillation in δ13C is explained by negative excursions caused by the release of methane from methane clathrates via feedback mechanisms, and resultant oxidation into carbon dioxide, introducing more light carbon (Jenkyns, 1999; Jenkyns, 2010).          2.2 Regional Geology, the Canadian Cordillera The Canadian Cordillera comprises of a series of exotic terranes (crustal blocks with distinct geological histories) which were accreted onto the North American continent (Laurentia), with the Intermontane Belt emplaced during the Mesozoic. A combination of faunal and paleomagnetic studies have been used to constrain the movement of these terranes and have concluded considerable latitudinal and longitudinal movement prior to accretion onto the North American Craton (Kent & Irving, 2010; Belasky et al., 2002). This has important implications for the interpretation of depositional paleoenvironments of pre-accretionary formations in the Cordillera. The Whitehorse Trough lies along the boundary of two such terranes within the 8  Intermontane belt, with the oceanic Cache Creek Terrane bounding the northeast, and the island arc Stikine Terrane bounding the southwest (Mihalynuk et al., 2017). This configuration is shown in Figure 2.2.  Figure 2.2: Geological map of British Columbia showing the configuration of Intermontane belt terranes and highlighting the Whitehorse Trough in particular. From English et al., 2005. An area of contention surrounds the relative placements of the Stikine, Cache Creek, and Quesnel terranes. The Cache Creek Terrane is interpreted as more exotic than the other two terranes, yet is enclosed by them on the west, east, and north sides. 9  One model proposed to explain this arrangement involves a rotational tectonic orocline (post-formational bending of an orogenic belt), with the Stikine Terrane having rotated counter clockwise, hinged by the Yukon-Tanana Terrane to its north. The Stikine Terrane to the west, Yukon-Tanana Terrane to the north, and Quesnel Terrane to the east would have formed a clothespin, with the Cache Creek Terrane being inserted before rotational closure in the mid-Jurassic (Mihalynuk et al., 1994). Wernicke & Klepacki (1988) offer an alternative ‘escape’ hypothesis. It is proposed that the absence of an island arc volcanic belt between the outermost Wrangellia Terrane to the west and North American Craton to the east in the Columbia embayment area suggests the Stikine Terrane had escaped northward to form the relationship seen today (Wernicke & Klepacki, 1988).      Hart (1997) interprets the Whitehorse Trough as the forearc basin to the Lewes River Arc (over Stikine Terrane basement). The evolution of this arc system in the Carnian is marked by basaltic volcanism and sedimentation. This arc building and subsequent erosion resulted in volcaniclastic material accumulation to the east of the arc (western margin of the trough), which formed a shallow marine shelf. During the Norian, Scleractinian corals first became dominant reef-builders, particularly in high energy, shallow water environments (Simms & Ruffell, 1990). The shallow shelf was host to extensive reef development and associated carbonate deposition. Alternating deposits of carbonate-dominant and volcaniclastic-dominant strata are possibly explained by a quiescent environment with short periods of high erosion caused by sea level fall (Hart, 1997). By the late Norian, carbonate depositional environments dominated throughout the trough, when deposition exceeded the rate of subsidence, 10  and resulting in carbonate buildup forming a very shallow marine environment (Hart, 1997).     English et al. (2005) describe the structure of the Central Whitehorse Trough as imbricated and shortened, caused by the accretion of the Cache Creek terrane during the mid-Jurassic, which also formed a southwest trending fold and thrust belt. The Central Whitehorse Trough is comprised of the Upper Triassic Stuhini Group, and the Jurassic Laberge Group. The mid-Norian to end-Norian Sinwa Formation is characterized by marine carbonates, and caps off the top of the Stuhini Group. It conformably overlays the dominantly volcanic Stuhini Group deposits towards the southwest, and dominantly siliciclastic Stuhini Group deposits in the northeast. The Inklin Formation marks the base of the Laberge Group. It is dominantly composed of sandstone, but also contains fine grained argillites. The Inklin Formation lies unconformably above the Sinwa Formation (English et al., 2005).  As the Whitehorse Trough extends through both British Columbia and the Yukon, alternate nomenclature has been attributed to possibly analogous and coeval formations. Lowey et al., (2009) provide an overview of the lithologies within the Late Triassic Lewes River Group. The 2000-meter-thick Late-Triassic Aksala Formation within the group possibly correlates with the Sinwa Formation. The Casca Member marks the bottom of the Aksala Formation, comprising of mudstone, sandstone, limestone, and a minor component of conglomerate. The Hancock Member above it comprises entirely of limestone. The Mandanna Member capping off the formation is comprised of sandstone, limestone, volcaniclastics, and a minor component of conglomerate. Analogous to the Inklin Formation, the early-Jurassic to mid-Jurassic 11  Tanglefoot and Richthofen Formations sit unconformably on top the Aksala Formation (Lowey et al., 2009).    Yarnell et al., (1999) examined Late Triassic reefs in the Stikine Terrane, and found them to be representative and typical of the other exotic terranes in the North American Cordillera. This indicates a certain amount of proximity between terranes during deposition and therefore prior to accretion, possibly supporting the two-stage accretion model proposed by Johnston and Borel (2007), describing an initial stage of offshore amalgamation. The Tethyan fauna found in the Stikine Terrane connects it to the Tethys region in Eurasia, supporting the concept of the terrane being far-travelled (Yarnell et al., 1999). Extensive reefs that developed along the margins of the Tethys Seaway have become the standard model of large reef formations in the Late Triassic (Stanley & Senowbari-Daryan, 1986).          English et al. (2005) also investigated the hydrocarbon potential of the Central Whitehorse Trough, particularly that of Sinwa Formation carbonates and Inklin Formation sandstones. In terms of source rock maturation, poor to fair areas are found throughout, with more mature and viable areas exclusive to the organic-rich units of the Inklin Formation. In terms of reservoir rocks, carbonates of the uppermost Sinwa Formation are highly porous due to extensive weathering and deformation from the Cache Creek terrane accretion. Inklin Formation sandstones and siltstones generally have low porosity due to pervasive diagenetic alteration, but higher porosity pathways can still readily be found via the alignment of porous strata in the succession. For caprocks, the shale and silt layers within the Inklin Formation can form local traps. The base of the Inklin Formation is dominantly siltstone and argillite, forming an extensive 12  trap above the Sinwa Formation. Ultimately, the study proposes the Inklin Formation to be most viable for a gas play, primarily due to high levels of source rock maturation towards the northeast of the trough (English et al., 2005).   2.3 Local Geology, Late Triassic Carbonates in the Whitehorse Trough The type locality of the Sinwa Formation is found at Mt. Sinwa (Souther, 1971). Mihalynuk et al. (2017) describe the formation at this locality as outcropping on ridges as light-grey weathering, massive, and at least 2 kilometers thick. Bedded sections were observed near the base and middle of the section, and extensive karst development was observed throughout. A colonial coral packstone layer was noted to form a distinct horizon, with the corals tentatively identified as Retiophyllia. This horizon was not specifically located by the study. Chert nodules were observed in localized zones. Two depositional cycles are proposed, with the first gradually grading up from dark siliciclastic rocks to slightly bioclastic limestone. The transition into the second cycle is marked by the return of siliciclastic deposition, alongside breccia zones, all of which is overlain by further limestone deposition (Mihalynuk et al., 2017). The geology of the Mt. Sinwa locality is shown in Figure 2.3. 13   Figure 2.3: Preliminary geology of the Sinwa Creek area, including Mt. Sinwa. Sinwa Formation is denoted with light blue. From Mihalynuk et al., 2017.    14            Figure 2.3: Continued. The Sinwa Formation as outcropping south to southeast of Atlin Lake, British Columbia is described by English et al. (2005) as pale grey, bioclastic, extensively calcite veined, mostly massive limestone of shallow marine origin. A rarer component of darker, silty, organic-rich limestone has also been described. Calcite veins are indicative of past permeability, perhaps linked to fracturing caused by the aforementioned 15  accretion of the Cache Creek terrane. Thickness of the Sinwa Formation ranges from 300 meters south of Atlin Lake, to 600 meters further south at Tulsequah (English et al., 2005). The Sinwa Formation as outcropping west of Dease Lake, British Columbia is described by Gabrielse (1998) as largely light grey, massive, recrystallized limestone with laminations, local bedding, and extensive jointing. Detrital quartz and poorly preserved corals are observed as minor constituents. Brecciation is observed with proximity to the King Salmon Fault, dolomitization is locally observed west of Kutcho Creek, and crinoid columnals are locally observed east of Kehlechoa River (Gabrielse, 1998). Yarnell et al. (1999) describe multiple sections of Late Triassic carbonate from the Aksala Formation in the Whitehorse region. The Pilot Mountain locality exposes massive and weakly silicified limestone outcrop. Fauna observed include corals, sponges, tabulozoans, and brachiopods. The Emerald Lake locality exposes massive, recrystallized limestones. Fauna observed include brachiopods, spongiomorphs, crinoids, corals, gastropods, sponges, and bivalves. The Grey Mountain locality exposes massive, light grey weathering but otherwise dark limestone. Fauna observed include bivalves, and small corals. The Cap Creek locality exposes dark grey, massive limestone. Laminated mudstone representative of a deeper marine environment can be found east of this limestone. Fauna observed include bivalves, sponges, spongiomorphs, corals, and gastropods. The well-studied Lime Peak locality exposes the thickest and most fossil-rich section of limestone in the Whitehorse Trough. The plethora of fauna observed in the massive, light brown limestone facies include 16  sponges, spongimorphs, tabulozoans, dishectoporids, sceractinian corals, algae, brachiopods, and molluscs (Yarnell et al., 1999). It is proposed that the reefs observed here have characteristics of Dachstein-type, which would make it a rare example of a Dachstein Reef in North America. Summarized by Stanley and Senowbari-Daryan (1986), Dachstein Reef Limestone outcrops in the Northern Limestone Alps, and are a subset of Tethyan reefs. Characteristics include thick, massive deposition, light colour, distinct associations between corals and other reef organisms, and infilled reef structures indicative of multiple cementation cycles (Stanley & Senowbari-Daryan, 1986). Characteristics observed in the Aksala Formation are relevant to the Sinwa Formation if they are indeed analogous.    Conodont biostratigraphy has been widely used to determine stratigraphic age in the region (Golding et al., 2017). Of particular interest to this study are a number of samples that were previously described as late-Norian and later revised to Rhaetian by Golding et al. (2017).               17  3.0 Methods  3.1 Fieldwork  Fieldwork for the purpose of sample collection and the production of a stratigraphic log was conducted over a period of 3 days on Mt. Sinwa in the Stikine Region, located in the northwest corner of British Columbia (Figure 3.1). Based out of Atlin, British Columbia, the mountain was accessed via helicopter drop-off and pickup. The first day (July 22, 2017) involved traversing the extent of the mountaintop and determining a path for stratigraphic logging. The second day (July 24, 2017) involved stratigraphic logging and sample collection from UTM zone 8V, easting 0597174, northing 6526076 to UTM zone 8V, easting 0597172, northing 6526185. The third day (July 25, 2017) continued stratigraphic logging and sample collection, finishing at UTM zone 8V, easting 0597233, northing 6526358. Stratigraphic logging was conducted with a Jacob’s Staff after measuring the dip of the bedding with a Brunton compass. Limestone petrology in the field was categorized using the scheme of Dunham (1962), taking note of the presence or absence of bedding, laminations, rip-up clasts and other sedimentary structures, dolomitization, silicification, and faunal content (bivalves, solitary corals, and colonial corals). Samples for stable isotope geochemistry were collected approximately every meter as outcrop allowed, avoiding veins, chert, and bioclasts if possible. Samples collected were approximately 4-5 cm across and labelled in multiple areas. Samples for conodont preparation and thin section production were collected in localities of particularly high bioclastic content.  18   Figure 3.1: Traverse route on Mt. Sinwa along which stratigraphy was recorded.  3.2 Thin Section Preparation For each locality conodonts were sampled, a lithologically representative sample was set aside for thin section production. The samples were cut into slabs, perpendicular to bedding (when visible), with a Marathon Electric water-cooled trim saw fitted with a 240 mm diameter continuous rim diamond blade. Thin section preparation was conducted by Vancouver Petrographics Ltd. The slabs were fixed to glass slides with epoxy, then cut and polished to be 30 microns thick. Cover slips were applied with epoxy. Thin section images were taken with a Leica DM750P microscope camera.   3.3 Conodont Preparation Samples for conodont preparation were processed by the Geological Survey of Canada Pacific in Vancouver, British Columbia. Individual samples were crushed into approximately 3 cm fragments, with batches weighing approximately 2 kg. Some samples were much lighter due to collection difficulty at particular horizons. Samples were weighed and sorted by locality into batches and dissolved in acetic acid for 10 – 19  14 days. Per 1 kg of samples, a solution of 6 L of water, 3.2 L of 10-15% acetic acid (to create a buffer), and 0.8-1 L of 99.5% glacial acetic acid was used. The residues that remained after treatment were then sieved to collect the 90 – 850 μm fraction. The isolated fraction was then rinsed, dried, and separated using sodium polytungstate (specific gravity of 2.85 kg/L) as a heavy liquid with the heavy fraction collected. Magnetic roller separation was conducted for samples too large for conodont picking and with red or green colouration indicating possibly high metallic content. Further heavy liquid separation with sodium polytungstate (specific gravity of 2.90 kg/L) was run if the sample remained too large. Conodonts were picked with a fine paintbrush under a binocular microscope and applied to a stub for scanning electron microscopy. Conodont images were taken with the Hitachi TM3000 scanning electron microscope at the Geological Survey of Canada.  3.4 Stable Isotope Ratio Mass Spectrometry       Using a Marathon Electric water-cooled trim saw fitted with a 240 mm diameter continuous rim diamond blade, stable isotope ratio-oriented limestone samples collected were cut into small slabs approximately 1.2 cm thick, perpendicular to bedding when visible, and maximizing surface area. Ideally, slabs were around 3 cm by 3 cm, but the small initial size of some samples, and the breaking apart of heavily jointed samples resulted in many slabs being much smaller. Powder for mass spectrometry was extracted from the cut faces of the slabs, while the remaining parts of samples were stored for possible future analysis. Water was applied to the slabs to better determine a location for powder extraction, preferring finer grained sections, and avoiding veins, bioclasts, sharpie markings, and edges. Powder was extracted with a 20  small Dremel drill press fitted with a fine tapered grinding bit, largely extracting material only along the cut surface to avoid unseen veins and bioclasts deeper in the slabs. Powder was carefully collected onto heavy paper and funneled into small labelled containers. Exact amounts of powder extracted varied with slab quality, but only 1 mg was required per sample and over approximately 10 mg was extracted consistently. A compressed air blower was used to clean the drill bit and stage between every sample to avoid contamination. Stable isotope ratio mass spectrometry was conducted by the Pacific Centre for Isotopic and Geochemical Research, University of British Columbia. A Delta PlusXL mass spectrometer with Finnigan Gas Bench attached was used for δ13C and δ18O analysis of carbonates. The powders were dissolved with 99% phosphoric acid in airtight glass exetainers filled with helium, producing CO2. Carried by helium, the CO2 was introduced into the mass spectrometer in a continuous flow. The gas produced by each sample was compared with reference CO2 of known composition. δ13C and δ18O results were corrected to VPDB. Both isotope systems were corrected for fractionation using repeat analyses of UBC internal carbonate standards BN 13, BN 83-2, and H6M, calibrated against NBS international standards NBS 18 & 19.            21  4.0 Data  4.1 Field Lithological  Figure 4.1.1: Stratigraphic column of the Sinwa Formation exposed on Mt. Sinwa. Limestone classification scheme of Dunham (1962) is used. 22   Figure 4.1.1: Continued.  23   Figure 4.1.1: Continued.   24   Figure 4.1.1: Continued.   25   Figure 4.1.1: Continued.  Facies 1 Facies 1 is characterized by pervasive carbonate mud (micrite) chip rip-up clasts (Figure 4.1.2). These are typically 1-3 mm across (but can be larger, see Figure 4.1.2), angular to sub-angular, and paler in colour than the grey limestone matrix. This facies extends from the base of the section to 75.5 m. The limestone is variably bedded (0.4-2.7 m) to massive in character. 1-2 mm thick laminations are common in the bedded 26  units and can be locally convolute (Figure 4.1.3). The localized nature of these structures indicates they were formed by soft sediment deformation (likely by sediment loading or dewatering) and are not structural tectonic features. It is also possible that some of these structures can also be stromatolites (organo-sedimentary structures) produced by mats of cyanobacteria. Several horizons of interbedded limestone and dolomite can be observed but are not extensive and are largely restricted to the lower half of Facies 1. The dolomite horizons tend to protrude, indicating higher weathering resistance than the surrounding limestone. These dolomite-limestone units extend vertically 1-3 m and demonstrate bedding 10-20 cm thick. Additional minor dolomite horizons occur higher in the stratigraphy, varying between 20-75 mm thick beds. Bivalve wackestone is common (13.0%), but bioclastic content is much lower than Facies 3 higher in the section. Intact shells are typically 25 mm across, while fragments can be much smaller. Bioclast distribution is variable even within a wackestone bed.    27    Figure 4.1.2: Pale grey carbonate mud chips 3-10 mm across (particularly large) surround by a darker grey micrite matrix, 30 m from base of section, Facies 1.  Figure 4.1.3: Convolute lamination or stromatolites, 34 m from base of section, Facies 1.  28  Facies 2  Facies 2 consists of limestone (mostly micrite dominated mudstone) ranging from massive to bedded (1.5-2.2 m); laminations are much more rarely observed than in Facies 1. Facies 2 is further characterized by a lack of the rip-up clasts that in part characterize Facies 1 and has much lower bioclastic wackestone content (12.2%) than Facies 3. This facies extends from 75.5 m to 105 m above the base of the section. Dolomitization is not observed in Facies 2. A 3.6 m thick horizon of solitary coral wackestone constitutes the only bioclastic content observed. The coral fragments are 1-10 mm across. Facies 3 Facies 3 is primarily bioclastic wackestone with a higher bioclastic content than the previous facies. This facies also exhibits silicification. Facies 3 ranges from 105 m to 231.3 m above the base of section. Bedding is present, but not as distinct as the prior facies. Between 163.8 m to 165.5 m above the base, minor interbedded limestone/dolomite can be observed. Beds in this horizon are 20-40 mm thick and produces an area that is of lower relief than the surrounding wackestone. At 171 m from base, a thin 10 mm horizon of darker grey limestone is observed containing both carbonate mud chips and bivalve bioclasts, the only such cooccurrence of these features in the section. The bivalve and solitary coral bioclasts (Figure 4.1.4) are more abundant in this facies and becomes progressively more so up-section. This culminates in the presence of in-situ colonial coral boundstone (Figure 4.1.5). Intact bivalves are typically 20-30 mm across, while fragments can be much smaller. Bivalves are not present in the colonial coral packstone. Coral fragments are highly variable in size but 29  rarely exceed 10 mm. Degree of silicification also increases up-section, observed as protruding dark-brown/grey weathering silicified bioclasts, chert layers 60-220 mm thick, and rounded chert nodules 140 mm to 0.5 m (Figure 4.1.4).    Figure 4.1.4: Bivalve wackestone with calcite veins and a chert nodule, 118 m from base, Facies 3. Fine stylolites are also present.   30   Figure 4.1.5: Coral boundstone with dark grey silicified coral weathering out of the carbonate matrix, 231 m from base, Facies 3. Facies 4 The top of Facies 3 ends abruptly at 231.3 m above the base of section and is succeeded by the dark organic-rich shales of Facies 4, sharply juxtaposing the carbonates.    4.2 Petrographic Description of Thin Sections Table 4.2: Description of thin sections from Mt. Sinwa. Dunham (1962) and Folk (1959) limestone classifications are used. 31   Thin SectionStratigraphic Height (m)Lithofacies (field)BioclasticsSparite ClustersMatrixVeinsOtherFolkDunhamV-0038180Massive mudstoneBivalves with sparite infill, sometimes micrite rim, 0.8-3mm length. 4%20% irregular (dismicrite), 20% rounded (clasts/crinoids), 60% elongate (bivalves), 0.1-0.5mm. 15% overall. Beige-grey. 50% micrite, 50% sparite mix. 78% overall.Minor calcite veins with coarse infill. 3%Largest sparite cluster rectangular, 2X8mm.BiospariteBioclastic wackestoneV-00382144Bedded mustone with mudchipsBivalves with micrite infill, 0.3-1.5mm in length. 2%Irregular (dismicrite), 0.2-4mm. 4% Beige-grey. 88% micrite, 12% sparite mix. 64% overall.Calcite veins with coarse infill, up to 3mm wide. 30% Very minor quartz veins.Sparite portions of matrix typically appear in close proximity to veins.MicriteMudstoneV-00382272Laminated massive mudstone with mudchipsNone.Rounded (clasts/crinoids), 0.2-0.5mm. 3% Beige-brown. 18% micrite, 82% sparite mix. 85% overall.Calcite veins with coarse infill. 12% Very minor quartz veins.Some sparite appears highly weathered, with finer matrix cutting.SpariteMudstoneV-00382392Massive mudstoneBivavle with micrite infill, 3mm in length. 1%Rounded (clasts/crinoids), 0.2-0.4mm. 1% Beige-grey. 94% micrite, 6% sparite mix. 83% overall.Calcite veins with coarse infill and stress jointing. 15%Rhombohedral dolomite crystal in sparite vein, 0.5mm.MicriteMudstoneV-003826114Silicified bedded bivalve coral wackestoneBivalves with sparite infill, 0.2-6mm, 15%. Crinoid with sparite infilled lumen, 0.7mm, 2%. Coral/bryozoan, 0.4mm, 1%. 18% overall.40% irregular (dismicrite), 10% rounded (clasts/crinoids), 50% elongate (bivalves), 0.2-0.6mm. 10% overall. Brown. 60% micrite, 40% sparite mix. 62% overall.Minor calcite veins. 3%Alignment of clasts indicate compaction. Large rounded sparite clusters with sparite infill and micrite core, 4mm. 7% BiomicriteBioclastic wackestoneV-003827118Silicified bedded bivalve coral wackestoneCorals/bryozoans, rounded 0.6-1.4mm, elongate 8mm in length. 7%75% irregular (dismicrite), 20% rounded (clasts/crinoids), 5% elongate (bivalves), 0.2-0.5mm mostly, some 1.4mm. 30% overall. Brown. 73% micrite, 27% sparite. 55% overall.Calcite veins, some with coarse infill. 7%Quartz clast with small calcite inclusions. Subangular, 0.5mm. 1%BiomicriteBioclastic wackestoneV-003834231Highly silicified bedded intact coral boundstoneBivalve with sparite infill and micrite rim, 4mm. 4%70% irregular (dismicrite), 15% rounded (clasts/crinoids), 15% elongate (bivalves), 0.3-4.5mm. 20% overall. Beige-brown and beige-grey. 25% micrite, 75% sparite mix. 60% overall.Large channel, lighter colour and finer grained than matrix, small inclusions of matrix. 15% Minor calcite veins. 1%Stress fractures at some micrite-sparite interfaces, quartz infilled.BiospariteBioclastic wackestone32  Thin sections were made from samples taken from Facies 1 through 3 and represent a variety of lithologies (Table 4.2). Lithologies include (under Folk (1959)): micrite, sparite, biomicrite, and biosparite, and (under Dunham (1962)): mudstone and bioclastic wackestone. All thin sections correspond to the location of a conodont sample (Table 4.4). Bioclasts are potentially present in all the thin sections, though some are recrystallized to the point of being unidentifiable. From the base of the stratigraphic column, bioclastic content is consistently low until V-003826, after which it decreases up-stratigraphy. Bivalves (Figure 4.2.1) are common throughout the section, while crinoids (Figure 4.2.2) and corals/bryozoans (Figure 4.2.3) are exclusive to higher in the stratigraphy.  The relative proportions of either micrite or spar matrix alternates through the section. However, the heavily bioclastic sections in the upper portion prior to the Facies 3 coral boundstones are exclusively micrite dominant (Figure 4.2.4). A dark brown matrix colouration is also distinct in these heavily bioclastic sections, contrasting the beige and grey seen lower in the column.   Clusters of sparite are observed in most thin sections, taking on a large variety of sizes and shapes. Rounded clusters could be replaced crinoids bioclasts or intraclasts. Elongate clusters (Figure 4.2.5) could be replaced bivalve bioclasts or intraclasts, with more curved elongate clusters more likely to be bioclastic. Irregular shaped clusters (Figure 4.2.6) are likely the product of recrystallized micrite (aggrading neomorphism). The prevalence of calcite veins (Figure 4.2.7) decreases with increased bioclastic content. 33   Figure 4.2.1: Thin section V-003818. 40 X magnification, 5 mm field of view, cross polarizing light. Potential bivalve geopetal structure. Micrite capped with sparite preserves the original sediment level within the fossil. Parts of the original internal shell lamination have been preserved while other areas have been recrystallized to calcite spar.  34   Figure 4.2.2: Thin section V-003826. 40 X magnification, 5 mm field of view, cross polarizing light. Calcite replaced, crinoid columnal with sparite infilled lumen. Possible recrystallized bivalve fragments of smaller size are also seen. Alignment of bioclasts may indicate compaction.  35   Figure 4.2.3: Thin section V-003827. 40 X magnification, 5 mm field of view, cross polarizing light, dimmed to accentuate bioclastic texture. Coral/bryozoan fragment surrounded by dark micrite and cross cut by calcite veins.   36   Figure 4.2.4: Thin section V-003834. 40 X magnification, 5 mm field of view, cross polarizing light. Recrystallized large shelly fragment surrounded by dark brown fine grained micrite.   37   Figure 4.2.5: Thin section V-003818. 40 X magnification, 5 mm field of view, cross polarizing light. Particularly large rectangular sparite cluster.  38   Figure 4.2.6: Thin section V-003821. 40 X magnification, 5 mm field of view, cross polarizing light. Large irregularly shaped sparite cluster as seen in an uncharacteristically sparite dominant portion of the thin section.  39   Figure 4.2.7: Thin section V-003823. 40 X magnification, 5 mm field of view, cross polarizing light. Calcite veins crosscutting sparite clusters.             40  4.3 Conodont Biostratigraphy Table 4.3: Conodont recovery of sampling sites from the Mt. Sinwa section.  Sample Stratigraphic Height (m) Conodont Species Found Sample AgeV-003818 0 Barren UnknownV-003819 5 M. englandi Late NorianV-003820 42 M. englandi, M. carinata Late NorianV-003821 44 Barren Late NorianV-003822 72 Barren Late NorianV-003823 92 Barren Late NorianV-003824 106 M. englandi, M. carinata, M. cf. spiculata Late NorianV-003825 112 M. englandi, M. carinata Late NorianV-003826 114 M. englandi, M. carinata Late NorianV-003827 118 Barren Late NorianV-003828 120 M. englandi, M. carinata, M. bidentata Late NorianV-003829 127 M. englandi, M.carinata Late NorianV-003830 164 M. englandi, M.carinata Late NorianV-003831 178 Barren Late NorianV-003832 179 Barren Late NorianV-003833 188 M. englandi, M. carinata Late NorianV-003834 231 M. englandi, M. carinata, M. mosheri Rhaetian41   Figure 4.3.1: Simplified stratigraphic column of the Sinwa Formation exposed on Mt. Sinwa aligned with conodont biostratigraphy. Constrained range of the Norian-Rhaetian boundary is indicated in red. 42   Figure 4.3.2: Conodont species recovered from the Sinwa Formation exposed on Mt. Sinwa. 1-2: Mockina bidentata (Carter & Orchard); sample V-003828. 3-4: M. carinata (Orchard); sample V-003833. 5-6: M. englandi (Carter & Orchard); sample V-003828. 7-8: M. mosheri (Carter & Orchard); sample V-003834. 9-10: M. cf. spiculata (Orchard); sample V-003824. Conodont species found on Mt. Sinwa include Mockina englandi, M. carinata, M. cf. spiculata, M. bidentata, and M. mosheri (Figure 4.3.2). Conodonts were recovered from most samples across the section, with the notable exception of consistently barren samples 44 m to 92 m from base, which spans a considerable portion of both Facies 1 and Facies 2. M. englandi ranges from late-Norian to Rhaetian (Carter & Orchard, 43  2007), is found from 5 m to 231 m in the section and is the most abundant species. M. carinata ranges from mid-Norian to late-Norian (Orchard, 1991), is found from 42 m to 231 m in the section and is quite abundant. M. cf. spiculata ranges from mid-Norian to late-Norian (Orchard, 1991) and is only found in the sample taken at 106 m. M. bidentata ranges from late-Norian to Rhaetian (Carter & Orchard, 2007) and is only found in the sample taken at 120 m. M. mosheri is exclusively Rhaetian (Carter & Orchard, 2007), and is only found in the sample taken at 231 m. The presence of M. mosheri indicates that the Norian-Rhaetian boundary lies somewhere in between the 188 m and 231 m sampling sites (Figure 4.3.1). Taxonomic notes for each species can be found in Appendix A.              44  4.4 Stable Isotope Geochemistry   Figure 4.4.1: Simplified stratigraphic column of the Sinwa Formation exposed on Mt. Sinwa aligned with δ18O and δ13C isotope records. Values are corrected to Vienna Pee Dee Belemnite. The 3 negative excursions in δ13C are highlighted.  45   Figure 4.4.2: Cross-plot of δ18O and δ13C isotope systems in Sinwa Formation carbonate samples from Mt. Sinwa.   Figure 4.4.3: Limestone-dolostone differentiated cross-plot of δ18O and δ13C isotope systems in Sinwa Formation carbonate samples from Mt. Sinwa. R² = 0.0625-1.500-1.000-0.5000.0000.5001.0001.5002.0002.5003.000-25 -20 -15 -10 -5 0δ13C VPDB (‰)δ18O VPDB (‰)δ13C vs δ18O-1.500-1.000-0.5000.0000.5001.0001.5002.0002.5003.000-25 -20 -15 -10 -5 0δ13C VPDB (‰)δ18O VPDB (‰)δ13C vs δ18OLimestoneDolostone46  The δ13C record of the Sinwa Formation exposed on Mt. Sinwa includes 3 pronounced negative excursions (Figure 4.4.1). The excursion spanning the stratigraphic heights of 32-39 m has a minimum value of -1.2 ‰. The excursion spanning the stratigraphic heights of 60-63 m has a minimum value of -1.2 ‰. The excursion spanning the stratigraphic heights of 230-231 m has a minimum value of -1.1 ‰. Excluding the 2 lower excursions, background variation range decreases from the base of the section to 125 m (standard deviation without excursions: 0.474), past which the variation range increases to the end of the section (standard deviation without excursion: 0.617). The δ18O record includes 2 minor negative excursions at 166 and 197 m, both of which coincide with minor negative excursions in δ13C. All 3 major δ13C excursions coincide with minor δ18O excursions, but the magnitudes are not very significant compared to background variation. δ13C values weakly correlate positively with δ18O, R2: 0.0625 (Figure 4.4.2). Dolomitic portions of the section tend to have greater δ18O values than limestone portions (Figure 4.4.3). The datasheets for both isotope systems can be found in Appendix B.         47  5.0 Analysis  5.1 Lithological Each of the facies described are indicative of a distinct depositional setting. The high rip-up clast content mudstone predominant in Facies 1 indicates shallow marine conditions, within the wave base that would permit nearby semi consolidated substrate to be eroded and deposited as mud chips during a high energy event, such as a storm. The variable sparite to micrite proportions across Facies 1 demonstrates that water depth was shallow enough for even minor changes in turbidity to affect the depositional energy, and therefore matrix grain size. These qualities suggest that Facies 1 may represent a shallow back reef lagoon. Facies 2 primarily differs from Facies 1 with the presence of solitary coral wackestone, indicating a depositional setting closer in proximity to the reef crest but potentially still in the back-reef lagoon. This would explain the presence of coral fragments, which in this scenario, may have broken off the reef crest. The higher bioclastic content, presence of in-situ life assemblages, and lack of rip-up clasts in Facies 3 places the depositional setting at the reef crest; despite the shallower sea level, the wave resistant coral framework prevents the substrate from being churned up. Fragmental bioclastic content generally increases up Facies 3, culminating in in-situ boundstone, indicating approach towards a maximum reef crest. However, minor oscillation of bioclastic proportions within the facies is observed, perhaps representing minor sea level fluctuations or heterogeneity of biotic density within the surrounding reef crest region. The dark thinly laminated shale of Facies 4 indicates an extremely low energy environment in a deeper, more distal marine setting. 48  These depositional environments are arranged from west to east in the context of the Lewes River Arc forearc basin (Figure 5.1.1).      Figure 5.1.1: Reef zonation off the coast of the Lewes River Arc, with the depositional settings of Facies 1 through 4 indicated. Diagram not to scale. The upward stratigraphic progression of depositional settings across back reef to reef crest indicates a progressive rise in local sea level across Facies 1 through 3 (transgression), with the reef migrating west to keep pace with optimal sea level for reef development. This compound aggrading reef pattern indicates intermediate magnitude and speed of sea level fluctuation, with reefs exhibiting keep-up, or less commonly catch-up growth strategies (Walker & James, 1992).  The sharp transition from reef crest deposition to distal indicates a cessation of reef production. This could be caused by rapid local sea level rise between Facies 3 49  and 4 (Figure 5.1.2). The Norian-Rhaetian boundary that this section spans is globally marked by sea level fall (Figure 5.1.3 - Haq et al., 1988). That is the opposite of what is observed on Mt. Sinwa, suggesting the sea level rise may have been produced by local causes. Local causes could include tectonic basin subsidence, sediment loading, and faulting.  Alternatively, the cessation of reef production could be more related to the Norian-Rhaetian Ocean Anoxic Event proposed by Sephton et al. (2002) than sea level change.    Figure 5.1.2: Schematic graph representing change in local sea level through the progression of Facies 1 through 4.   50          Figure 5.1.3: Sequence chronostratigraphy across the Triassic showing global sea level fluctuation. Modified from Haq et. al (1988).    51  5.2 Geochemical and Paleontological The location of the Norian-Rhaetian boundary is currently uncertain, with the formal designation of the Global Stratotype Section and Point still under consideration (Rigo et al., 2016). The first proposed section is the Steinbergkogel section in Austria, with the boundary marked by the appearance of conodont species Misikella hernsteini, or M. posthernsteini (Krystyn et al., 2007). An alternate proposed is the Pignola-Abriola section in Italy, with the boundary marked by the appearance of the conodont species M. posthernsteini, which coincides with a negative δ13C excursion (Rigo et al., 2016). U-Pb analysis of volcanic ash beds in the Aramachay Formation in Peru correlated with bivalve biostratigraphy dates the Norian-Rhaetian boundary to be at 205.50 ± 0.35 Ma, with the Rhaetian spanning 4.14 ± 0.39 m.y., and the Triassic-Jurassic boundary at 201.36 ± 0.17 Ma (Wotzlaw et al., 2014).       The conodont biostratigraphy observed on Mt. Sinwa indicates that the Norian-Rhaetian boundary lies somewhere in between the 188 m and 231 m sampling sites due to the presence of M. mosheri (Figure 4.3.1). The δ13C record observed on Mt. Sinwa resembles the record described by Zaffani et al. (2017) from sections in the Western Tethys: a negative excursion at the Norian-Rhaetian boundary preceded by 2 other negative excursions in the late-Norian. This, combined with how conodont biostratigraphy constrains the Norian-Rhaetian boundary to be between 188 m and 231 m (Figure 4.3.1), indicates the excursion highlighted in red coincides with the Norian-Rhaetian boundary (Figure 4.4.1). The 2 excursions in the late-Norian are highlighted in yellow (Figure 4.4.1). The chemostratigraphic record therefore refines the stratigraphic height of the Norian-Rhaetian boundary to be close in proximity to 230 m, where the 52  excursion starts. In a lithostratigraphic context, this places the boundary 0.3-1.3 m below the contact between the limestone of Facies 3 and the shale of Facies 4.  Given how recrystallized the limestone in the section often is, and how easily the δ18O system can be reset, the δ18O trend is likely induced by diagenesis and alteration. The lack of a major δ18O excursion at the Norian-Rhaetian boundary and weak correlation between the δ18O and δ13C records overall indicate the δ13C excursions aren’t related to diagenesis and alteration, as the 2 systems were not reset together. This is supported by how the δ13C value distribution does not vary significantly between dolomitic and limestone portions of the section, while δ18O values tend to be restricted to the higher end of the range in dolomitic portions. Given how the δ18O system is more resistant to equilibration in dolomite (Weber, 1965) compared to calcite, this trend can be interpreted as heating and deformation of the Sinwa Formation altering limestone portions to isotopically lighter values (representing higher temperatures), while dolomitic portions aren’t as strongly influenced.                      53  6.0 Conclusions   The Norian to Rhaetian carbonates of the Sinwa Formation outcropping on Mt. Sinwa display a variety of lithologies, progressing from the rip-up clast rich mudstone and bivalve wackestone of Facies 1, to the mudstone and coral fragment wackestone of Facies 2, to the bivalve-coral wackestone/packstone and coral boundstone of Facies 3, to the dark shale of Facies 4. This progression is consistent with a progressively rising sea level, followed by a rapid rise between Facies 3 and 4, likely caused by local tectonics given that global sea level was falling during this interval (Haq et al., 1998). Variation in thin section matrix texture indicates considerable fluctuation in depositional energy, even within facies (Table 4.2).  Conodonts recovered from the section include Mockina englandi, M. carinata, M. cf. spiculata, M. bidentata, and M. mosheri (Figure 4.3.2). The appearance of the exclusively Rhaetian species M. mosheri (Carter and Orchard, 2007) at 231 m from base indicates the Norian-Rhaetian boundary, based on conodonts, lies between the sampling sites of 188 m and 231 m (Figure 4.3.1).  The δ13C isotope record of the section includes 3 distinct negative excursions (Figure 4.4.1). These can be interpreted as drops in biotic productivity, associated with the multiple occurrences of biotic reorganization, instability characteristic of the Late Triassic (Sephton et al., 2002). Zaffani et al. (2017) observed a similar record in a section in the Western Tethys of the same age and interpreted the stratigraphically highest excursion as coinciding with the Norian-Rhaetian boundary. The stratigraphically highest negative excursion in the Sinwa Formation section very likely 54  represents the Norian-Rhaetian boundary, placing it above 230 m from base. This is supported in that this excursion lies within the range of the boundary predicted by conodont biostratigraphy, tightly constraining the boundary at 230-231 m from base, 0.3-1.3 m below the lithological transition between Facies 3 and 4. The δ18O record only weakly correlates with the δ13C, showing minor negative excursions at all 3 δ13C excursions, but not of significantly greater magnitude than background fluctuation (Figure 4.4.2). This indicates the δ13C excursions are not related to diagenesis/alteration, as the 2 systems were not reset together.  It is proposed that further investigation at Mt. Sinwa should focus on more intensive conodont sampling in the upper portion of the section to refine the biostratigraphically proposed Norian-Rhaetian boundary. Investigation of other Sinwa Formation localities, as well as possibly analogous Aksala Formation localities, would demonstrate the degree to which the stratigraphic trends observed on Mt. Sinwa can be correlated throughout the Whitehorse Trough. The facies transition between coral boundstone and dark shale at Mt. Sinwa is sharp and is located just above the Norian-Rhaetian boundary in this section; it may be possible to correlate this boundary in other sections of the Sinwa Formation using this facies change as a proxy, assuming that the facies change is synchronous.         55  References  • Belasky, P., Stevens, C.H. and Hanger, R.A. (2002). Early Permian location of western North American terranes based on brachiopod, fusulinid, and coral biogeography. 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Remarks: Although the anterior platform ornamentation of M. bidentata resembles that of M. englandi, elements of M. bidentata are overall shorter than M. englandi and have a much narrower posterior platform. Occurrence on Mt. Sinwa: Sample V-003828 (120 m).  Stratigraphic range: late-Norian to Rhaetian  Mockina carinata (Orchard, 1991) Description: Platform is wide and rounded. A single large denticle is present on one of the lateral margins at the anterior end of platform, whereas two large denticles are found on the other margin. Smaller denticles are present to the posterior of these large denticles. Basal pit is anterior shifted. Carina extends to the posterior end and has 3 denticles. Free blade is present. Remarks: This species can be distinguished from others of the genus by having 1 large denticle on 1 lateral margin of the platform and 2 large denticles on the other. 62  Occurrence on Mt. Sinwa: Samples V-003820 (42 m), V-003824 (106 m), V-003825 (112 m), V-003826 (114 m), V-003828 (120 m), V-003829 (127 m), V-003830 (164 m), V-003833 (188 m), and V-003834 (231 m). Stratigraphic range: mid-Norian to late-Norian  Mockina englandi (Carter & Orchard, 2007) Description: Platform is wide and rounded. A single pair of large denticles are found on the anterior end of the platform, with smaller denticles present to the posterior. Basal pit is shifted to the anterior. Carina extends to the posterior end and has 3 denticles. Free blade is present. Remarks: This species can be distinguished from others of the genus by the presence of only 1 pair of large denticles on the anterior end of the platform. Occurrence on Mt. Sinwa: Samples V-003819 (5 m), V-003820 (42 m), V-003824 (106 m), V-003825 (112 m), V-003826 (114 m), V-003828 (120 m), V-003829 (127 m), V-003830 (164 m), V-003833 (188 m), and V-003834 (231 m). Stratigraphic range: late-Norian to Rhaetian  Mockina mosheri (Carter & Orchard, 2007) Description: Platform is relatively long and rounded. A single pair of large denticles are found on the anterior end of the platform, with smaller denticles present to the posterior. Basal pit is shifted to the anterior. Carina extends to the posterior end of the element and consists of 4-5 denticles. 63  Remarks: This species can be distinguished from M. englandi by its relatively long and narrow platform, and the presence of 4-5 denticles in its carina, as opposed to the 3-4 denticles found in the carina of M. englandi.  Occurrence on Mt. Sinwa: Sample V-003834 (231 m). Stratigraphic range: Rhaetian  Mockina cf. spiculata (Orchard, 1991) Description: Platform is wide and rounded. A single pair of large denticles are found on the anterior end of the platform, with smaller denticles present to the posterior. The posterior platform margin is ornate, bearing as many as 3 denticles projecting beyond the end of the element. Basal pits are shifted to the anterior. Carina extends to the posterior end and has 3 denticles. Free blade is present. Remarks: This species can be distinguished by its 3-denticle posterior ornamentation. The specimens recovered from Mt. Sinwa are referred to M. cf. spiculata, as the anterior platform margin bears more denticles than is typically observed in the species.  Occurrence on Mt. Sinwa: Sample V-003824 (106 m) Stratigraphic range: mid-Norian to late-Norian       64  Appendix B  Geochemical Data  Stratgraphic Height (m) δ13C (VPDB) δ18O (VSMOW) Continued:0 1.393 17.165 53 2.223 22.2230 1.538 17.272 54 2.035 21.7861 1.471 18.026 55 1.463 21.8202.1 1.579 24.650 55 1.319 21.4672.1 1.939 24.555 56 1.190 23.8593 0.814 19.749 57 0.734 17.9204 1.597 17.987 58 1.372 15.5545 1.719 14.832 59 0.614 20.6846 0.323 19.170 60 -1.071 20.2577 1.818 24.047 60 -1.166 20.7018 2.658 19.882 61 -0.260 19.7608 2.680 19.931 62 -0.974 18.2719 1.936 24.972 63 -1.061 19.4849 1.864 24.607 64 0.218 16.84111.65 2.610 23.220 65.3 0.691 20.38613 2.034 24.714 66.1 1.596 23.68913 2.037 23.650 67 1.484 19.18313 2.016 24.216 67 1.616 19.97013.9 1.722 23.407 68 1.087 16.38815 1.648 24.214 69 2.619 20.16315 1.682 24.009 69.9 2.041 19.12315 1.634 24.126 69.9 2.112 19.01115 1.540 23.611 71 2.039 23.41816 1.004 17.426 72 1.408 19.12917 1.356 15.661 73 2.329 21.77518 0.504 17.916 74 2.291 23.99919 1.941 18.828 75 2.225 21.31120 1.747 18.089 76 1.660 22.19621 0.967 18.057 77 0.767 20.48222 1.236 18.183 78 1.450 23.24422.6 1.226 15.270 78 1.526 24.00022.6 1.049 15.828 79 1.891 21.28229.6 2.695 23.871 80 1.811 22.58231 1.234 21.655 80 1.875 23.09032 -0.819 21.292 81 1.859 22.19733 -1.152 17.346 82 1.771 20.66733 -1.159 18.303 83 1.006 21.38334 0.380 19.294 84 1.948 20.83235 -0.649 21.841 85 1.431 20.59935 -0.785 21.776 85 1.488 19.13136 0.199 21.197 86.2 2.160 19.11537.2 -0.590 20.497 87 1.886 19.70038 -0.695 20.446 89 1.570 20.04038 -0.637 20.780 90 0.678 19.65939 -0.055 19.702 91 0.993 21.23240 1.029 20.696 92.2 1.522 19.89741 0.581 19.749 92.2 1.630 19.75942 1.031 20.091 93 1.765 16.89043 2.067 21.308 94.2 1.838 17.93243 1.977 21.329 95 1.634 20.06944 2.172 20.333 95 1.745 20.10345 2.231 18.933 96 1.798 21.54745 2.123 18.519 97 1.741 22.43546 1.404 21.096 97 1.664 22.68946 1.320 20.031 98 1.576 21.72247 2.101 21.751 100 1.488 20.95448 2.077 22.490 101 1.755 21.50849 1.880 22.172 102 2.381 20.72950 1.579 20.601 103 1.554 19.07451 0.969 22.155 104 1.555 16.18452 1.224 21.716 104 1.334 16.54065        Continued: Continued:105 1.261 16.136 158 1.215 19.764106 1.322 16.676 159 1.182 17.158107 1.553 15.905 160 1.519 20.836108 1.930 16.254 161 1.872 20.143109 1.919 14.639 161 1.898 20.227110 1.545 15.933 162.1 1.055 21.293111 1.974 17.880 163 1.343 19.365112 1.892 17.118 165.9 0.348 9.430113 1.318 18.778 165.9 0.659 8.627114 1.274 17.979 165.9 0.533 8.920115 1.437 17.148 167 1.909 21.645116 1.375 17.946 168 1.355 20.288117 1.527 15.433 168 1.612 20.562117.1 1.637 19.687 169 1.311 15.189118 1.276 15.927 169 1.125 15.068119 0.999 19.178 170 1.028 17.374119 1.255 19.724 170 1.086 17.406120 1.661 20.209 170 0.966 17.934120 1.123 20.978 171 0.914 18.379121 1.358 19.410 172 1.125 14.151122 1.541 21.520 173 -0.234 17.116122 1.524 21.694 174 0.415 16.414123 1.906 22.270 175 0.135 17.908123 1.807 21.816 176 0.331 17.713123 1.622 21.763 178.1 0.591 16.479124 1.479 21.812 180 1.494 20.258125 1.733 21.408 181 2.606 20.737126 1.195 21.930 182.2 2.354 17.533127 0.682 16.584 183 2.064 20.049128 0.576 21.700 184 1.529 21.778129 1.646 23.141 185 1.897 20.376130 1.842 21.400 186 0.149 18.888131 0.556 19.184 187 0.232 21.056132 2.224 22.872 188 0.536 14.546133 1.286 22.521 189 1.283 21.945134 1.066 23.832 190 1.533 18.801135.1 1.307 16.693 192.3 1.461 14.271135.1 1.324 16.579 192.3 1.420 14.369136 1.020 18.609 192.3 1.389 14.981137 1.429 20.684 193 1.008 20.174138 2.439 19.673 194 0.375 20.652139 0.185 22.275 195 1.181 14.623140 2.435 21.031 195 1.188 15.386140 2.530 21.230 196 0.384 15.402141 1.806 20.658 197 0.139 11.580141 1.326 20.354 197 0.380 12.224143 1.132 19.965 198 1.854 20.391144.1 1.721 22.143 201 1.964 18.524145 1.190 19.345 204.5 1.711 18.953146 0.690 20.245 204.5 1.735 19.150147 0.592 20.447 207 1.224 20.649148 0.670 19.900 210 2.180 20.787149 1.077 20.701 221.1 2.101 21.760150 1.153 16.580 221.8 2.269 21.387151 0.978 21.429 227 1.382 18.411151 0.985 21.690 229 1.053 20.222152 1.181 22.250 230 -1.108 19.067153 0.926 17.233 231 -0.706 20.438154 1.383 19.264 240 0.625 20.623155 1.093 18.578 240 0.843 21.133157 1.480 17.655

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