Palynology of uppermost Proterozoic and lowermost Cambrian formations, central Mackenzie Mountains, northwestern Canada (original) (raw)
Related papers
Cambrian shelf deposits of the King Square Formation, Saint John Group, southern New Brunswick
Atlantic Geology, 1989
The upper Middle Cambrian to early Late Cambrian King Square Formation, Saint John Group, southern New Brunswick, is an approximately 380 m thick silicilastic sequence of interbedded fine-grained sandstones and siltstones and shales. On the basis of sandstone to shale/siltstone ratios, bed thickness and characteristics, sedimentary structures and degree of bioturbation three lithofacies are recognized. These are facies KS1, thin bedded sandstone and shale lithofacies; KS2, thick bedded sandstone lithofacies; and KS3, bioturbated shale and siltstone with interbedded sandstone lithofacies. These lithofacies are interpreted to have been deposited on a wave-and storm-influenced marine subtidal shelf. Facies KS 1 was deposited essentially below wave base though in its upper horizons, deposition may have occurred above storm wave base. Facies KS2 was essentially deposited in a shallower subtidal inner-to mid-shelf environment above storm wave base and facies KS3 initially above and latterly below storm wave base. The exact nature of the currents responsible for transportation and deposition of the storm-related sandstones (geostrophic flows or turbidity currents) is impossible to determine and therefore palaeocurrent data must be interpreted with caution. The stratigraphic arrangement of the lithofacies, with facies KS1 being the oldest and KS3 the youngest, suggests that the King Square Formation represents a regressive-transgressive sequence.
Canadian Journal of Earth Sciences, 2000
The youngest formations of the Neoproterozoic Windermere Supergroup in northwestern Canada (Gametrail, Blueflower, and Risky formations) record the transition from slope to shelf deposition on a prograding passive margin. Eleven facies associations are recognized, representing environments ranging from carbonate-and siliciclasticdominated continental slope to open carbonate shelf and siliciclastic shoreface. Seven simple sequences are recognized, which can be grouped into three composite sequences. Combination of the data presented here with previous work on underlying and overlying formations indicates that the sequence-stratigraphic record is least detailed in the deepestwater facies and most detailed in shelf facies, reflecting the relative inability of high-frequency relative sea-level oscillations to affect deposition in deep-water settings. Falling-stage deposits are especially common in the upper slope region. Several major sequence boundaries (unconformities) are clustered in the interval a short distance below the Precambrian-Cambrian boundary. The most significant of these occurs high in the Blueflower Formation, not at the top of the Risky Formation as commonly inferred. This interval containing several surfaces may reflect thermal uplift related to the rifting recorded in rocks of this age in the southern Canadian Cordillera. Renewed subsidence (thermal relaxation) commenced just prior to the Neoproterozoic-Cambrian boundary, giving rise to a thick succession of shelf to nonmarine basal-Cambrian deposits. Ediacaran body fossils previously reported from the studied units occur in a range of slope to shoreface environments, including some facies that were deposited below the photic zone. The most common taxa occur across a spectrum of facies and were apparently ecological generalists.
The Pre- Carboniferous rocks of the western Cobequid Hills, Avalon zone, Nova Scotia
Atlantic Geology, 1986
Pre-Carboniferous rocks of the western Cobequid Hills outcrop north of the Cobequid Fault, are cut by several major east-west faults, and are onlapped unconformably to the north by the Late Carboniferous Cumberland Group. The oldest rocks comprise the Late Hadrynian Jeffers Formation. In the south, this unit consists of mafic and felsic volcanic rocks, interbedded with mudstones and carbonates, that are overlain by turbidites. To the north, the Jeffers Formation consists of a thick sequence of felsic volcanogenic turbidites. This stratigraphic succession of volcanic rocks passing up into turbidites differs from some other Late Hadrynian Avalonian sequences in the predominance of sedimentary rocks, but does resemble the Georgeville Group of the Antigonish Highlands. Mafic dykes and sills, and associated porphyritic rhyolite intrusions, intruded the Jeffers Formation prior to the formation of a regional flat-lying cleavage. The Late Hadrynian Jeffers Brook Pluton, which postdates this cleavage, consists of diorite with marginal granitic phases that also occur as dyke-like intrusions beyond the main pluton. Several smaller intrusions petrographically similar to the Jeffers Brook Pluton also occur. At least two series of later dykes, probably pre-Silurian in age, cut the Jeffers Formation and the Late Hadrynian intrusions. The Silurian Wilson Brook Formation outcrops only at the extreme northern edge of the Cobequid Hills: it consists of fossiliferous fine-grained sandstones and shales which overlie thin rhyolites, basalts and red clastic sediments. This sequence is very similar to the lower part of the Arisaig Group north of the Antigonish Highlands to the east. It is overlain unconformably by the Devono-Carboniferous Fountain Lake Group of volcanic rocks and by Carboniferous sedimentary rocks which are significantly deformed only near the Cobequid Fault. Carboniferous granite plutons appear spatially related to the Kirkhill and Cobequid Faults. They are in places foliated and contain abundant mafic sills and dykes that appear to reflect continuing motion on the Cobequid Fault during emplacement and cooling of the granites. Dans l'Ouest des Monts Cobequid, les roches prAcarbonifAres affleurent au nord de la Faille de Cobequid. sont recoupAes par plusieurs failles majeures de direction est-ouest et sont recouvertes en discordance, au nord, par le Groupe de Cumberland d'age tardicarbonifAre. Les roches les plus vieilles englobent la Formation de Jeffers du Tardihadrynien. Au sud, cette demiAre se compose de volcanites mafiques et felsiques interlitAes avec des mudstones et des carbonates, le tout couronnA de turbidites. Vers le nord, la Formation de Jeffers renferrae une puissante assise de turbidites voleanogAnes felsiques. Cette succession stratigraphique de volcanites passant vers le haut A des turbidites diffAre certes de quelques autres sAquences tardihadryniennes avaloniennes par la prAdominance, en son sein, de roches sAdimentaires mais rappelle aussi le Groupe de Georgeville dans les Monts Antigonish. La mise en place de dykes et filons-couches mafiques, ainsi que des intrusifs de rhyolite qui leur sont associAs, eut lieu avant la formation d'un clivage rAgional horizontal. Le Pluton tardihadrynien de Jeffers Brook, qui est postArieur A ce clivage, est formA de diorite avec des phases granitiques marginales qui se prAsentent aussi au-delA du pluton principal sous forme d'intrusions ressemblant A des dykes. On rencontre aussi plusieurs intrusifs plus petits mais de pAtrographie similaire au Pluton de Jeffers Brook. Au moins deux ensembles de dykes plus tardifs, probablement d'age prAsilurien, recoupent la Formation de Jeffers et les intrusifs tardihadryniens. On n'observe la Formation silurienne de Wilson Brook qu'A la lisiAre la plus au nord des Monts Cobequid: elle englobe des grAs fins fossilifAres et des argilltes qui recouvrent, tous deux, de minces rhyolites, basaltes et sAdiments clastiques rouges. Cette sAquence rappelle fortement la partie infArieure du Groupe d'Arisaig au nord des Monts Antigonish plus A l'est. Elle est recouverte en discordance par le Groupe de volcanites dAvono-carbonifAres de Fountain Lake et par des roches sAdimentaires carbonifAres qui ne sont dAformAes de facon importante qu'auprAs de la Faille de Cobequid. Les plutons granitiques carbonifAres semblent rattachAs dans l'espace aux failles de Kirkhill et Cobequid. Ils sont foliAs par endroits et contiennent d'abondants filons-couches et dykes mafiques qui semblent traduire le jeu continu de la Faille de Cobequid durant la mise en place et le refroidissement des granites.
1982
Two measured sections of the upper Rabbitkettle Formation in the western District of Mackenzie are separated by a thrust fauh. These sections provide a record of silicified trilobite faunas across the Cambrian-Ordovician boundary in open marine carbonate rocks along the deeper portion of the shelf-a North American palaeogeographic setting not previously extensively sampled for macro fossils. A new biostratigraphy is proposed for the Trempealeauan to Lower Tremadocian interval in this setting. A Yukonaspis Zone with three divisions (in ascending order, Yukonaspis kindle i Fauna, Bowmania americana Fauna, and Elkanaspis corrugata Fauna) is based on eurekiine, entomaspid, and olenid trilobites. The Yukonaspis Zone is of Trempealeauan age and is considered equivalent to the Saukia Zone. AParabolinella Zone with three divisions (in ascending order, Missisquoia mackenziensis Fauna, Missisquoia depressa Subzone, and Apoplanias rejectus Fauna) is based on olenid, missisquoiid, and leiostegiid trilobites. The Parabolinella Zone is of Early Tremadocian age and is considered to be largely equivalent to the Missisquoia Zone. the top of the Rabbitkettle Formation, is a biogeographic boundary which separates the shelf-biogeographic region below from the slopebiogeographic region above. The extinction, immigration, speciation, and diversity patterns that define the Ptychaspid-"Hystricurid" Biomere boundary are explained with reference to the diversity-area relationships inherent in the equilibrium model of biogeography. Forty-six species of trilobites are described and illustrated. Four new genera are proposed {Larifugula , Kathleenella , Naustia, and Elkanaspis). Eleven species are new {Parabolinella panosa, Larifugula triangulata, ""Calvinella'' palpebra, Kathleenella subula, Kathleenella hamulata , Eurekia bacata , Naustia papilio , Elkanaspis futile, Elkanaspis corrugata, Missisquoia mackenziensis , and Tatonaspis diorbita. ''Acidaspis'" ulrichi Bassler is a junior synonym of Bowmania americana (Walcott), which is reassigned to the Entomaspidae. ""Leiobienvillia'' leonensis Winston and NichoUs is assigned to a new kingstoniid (?) genus, Larifugula. Liostracinoides Raymond and Kathleenella gen. no v. are assigned to the Euptychaspidinae. Yukonaspis Kobayashi is assigned to the Eurekiinae and Ptychopleurites Kobayashi to the Pagodiinae. Regional Setting and Stratigraphy Section K is located near the western margin of the Mackenzie Platform-a stable tectonic feature that received dominantly shallow-water sediments from the Helikian to the Late Devonian (Gabrielse, 1967). Flanking the Mackenzie Platform to the west is the epicontinental Selwyn Basin which is characterized by thick sequences of fine clastic rocks. The southwestern margin of the Selwyn Basin is bordered by the Pelly-Cassiar Platform which was initiated in the Late Cambrian as a site of andesitic volcanism and, in the Silurian and Devonian, was the locus of shallow-water carbonate sedimentation (Tempelman-Kluit, 1977). Tempelman-Kluit and Blusson (1977) and Tempelman-Kluit (1977) have provided evidence that, prior to mid-Cretaceous right-lateral movement on the Tintina Fault, the Pelly-Cassiar Platform was a narrow belt at the shelf-slope break at least 1000 km long. The Yukon Crystalline Terrane and its southern extension, the Omineca Crystalline Belt, comprise severely metamorphosed and tectionized sedimentary rocks that are probably in part equivalent to the unmetamorphosed Lower Palaeozoic sedimentary rocks on the shelf (Tempelman-Kluit, 1977: fig. 45.2). The relationship of these Lower Palaeozoic tectonic elements is shown in Fig. 2. Three carbonate formations of Late Cambrian and Early Ordovician age are exposed across the Mackenzie Platform between latitudes 62°N and 64°N. From east to west, these are the Franklin Mountain Formation in the Mackenzie River Valley, the Broken Skull Formation in the eastern and central Mackenzie Mountains, and the Rabbitkettle Formation in the western Mackenzie Mountains and the Selwyn Mountains (Aitken et al., 1973; Gabrielse et al., 1973; Norford and Macqueen, 1975). These formations are not well dated. The Franklin Mountain Formation contains brachiopods, molluscs, and trilobites of Dresbachian to middle Canadian age (Norford and Macqueen, 1975: 12; Aitken et al., 1973: 31). The Broken Skull Formation contains trilobite, brachiopod, and conodont faunas which range in age from late Franconian to late Canadian (Gabrielse et al., 1973: 49, Ludvigsen, 1975; Tipnis et al., 1979). Only a single fossil collection has been recovered from typical exposures of the Rabbitkettle Formation in the Selwyn Mountains. This is a trilobite collection of Franconian age (Gabrielse et al., 1973: 51). In the Howards Pass area, near Summit Lake, some 50 km southwest of Section K, the Rabbitkettle is conformably overlain by the Road River Formation which here contains early Arenigian graptolites near its base (Ludvigsen, 1975: 675). In other areas, the lower Road River Formation appears to be a facies equivalent of the Rabbitkettle Formation. The thick package of predominantly carbonate rocks of the Mackenzie Platform rests unconformably on Middle Cambrian and older formations. This is the "sub-Franconian unconformity" of Gabrielse et al. (1973) and the "sub-Dresbachian unconformity" of Aitken et al. (1973). The outcrop belts defined by the Franklin Mountain, Broken Skull, Rabbitkettle, and lowermost Road River formations are approximately parallel to one another and parallel to the western margm of the Mackenzie Platform. A generalized palaeoenvironment may be interpreted for each formation. Norford and Macqueen (1975) have presented a detailed discussion of the lithologic character and palaeoenvironment of the Franklin Mountain Formation at its type area in the Mackenzie River Valley. Here, the formation consists of laminated to Biostratigraphy Cambrian Winston and Nicholls (1967) proposed a four-fold subzonal division of the Saukia Zone for shallow-water carbonate rocks in central Texas which was based largely on saukiid and eurekiine trilobites. They named the upper three subzones and Longacre (1970) later named the lowest subzone. This biostratigraphic scheme has been applied, in part or in its entirety, to successions in Oklahoma (Stitt, 1971b, 1977), Alberta (Derby et al., 1972), and New York (Taylor and Halley, 1974). Biofacies differentiation among latest Cambrian trilobites hampers the utility of the four-fold subzonal division of the Saukia Zone outside the interior portions of the Middle Carbonate Beh of Palmer (1960a). These subzones cannot be recognized within the Inner Detrital Belt developed in the upper Mississippi Valley where the Saukia Zone and its divisions (Bell et al., 1956) are based largely on dikelocephalid and saukiid trilobites that have not been found in Texas and Oklahoma (Stitt, 1977: 15). Nor can the subzones be applied to coeval shelf-edge carbonate rocks carrying Hungaia associations in Newfoundland, Quebec, Vermont, and Alaska. In addition, the striking biofacies change at the Upper Cambrian shelf-slope break outlined by Taylor for western United States prevents the recognition of the Saukia Zone in autochthonous Trempealeauan Outer Detrital Belt sediments and Taylor (1976)
Early Cambrian braid-delta deposits, MacKenzie Mountains, north-western Canada
Sedimentology, 1997
Latest Neoproterozoic to earliest Cambrian strata in north-western Canada provide an example of a pre-vegetation braid-delta depositional system. Depositional environments represented in the succession include braided fluvial and braid-delta distributary channels, aeolian dune fields and interdistributary lagoons/bays, as well as mouth bar, beach to shoreface, and prodelta to distal shelf settings. Three formations have been investigated: the Ingta Formation formed in wave-dominated nearshore to offshore shelf environments with little or no apparent deltaic influence, whereas the overlying Backbone Ranges and Vampire formations contain an extensive record of braid-delta deposits ranging from braidplain to distal prodelta facies. On the braid-plain, river channels reached widths of up to several kilometres. Such channels terminated seaward in braid deltas that showed soke shoreline protuberance and were characterized by fluvial-dominated mouth-bar deposition with lesser wave influence; wave-dominated deltaic successions are rare in the succession. Interdeltaic areas were characterized by wave-dominated prograding shorelines. Interdistributary lagoons probably formed primarily in abandoned distributary channels. Deltafront/prodelta deposits are silt-rich and contain abundant soft-sediment deformation, including slumps. The deposits in these formations illustrate the significantly different nature of sedimentation prior to the advent of land plants. This is illustrated in the dominance of braided fluvial deposition and of silt-rich offshore facies that may have resulted from enhanced aeolian transport of loess. The non-actualistic effects of limited bioturbation and extensive microbial binding apparently exerted relatively little control on the distribution of facies. However, the absence of extensive bioturbation is manifest in pristine preservation of primary sedimentary structures, while the hypothesized latest Proterozoic-earliest Cambrian decline in microbial binding may be reflected in the upward increase in the abundance of sole marks in the succession.
2016
The Cambrian-Lower Ordovician Potsdam Group is a mostly siliciclastic unit that provides important insight into the paleoenvironmental, geologic and tectonic history of Early Paleozoic Laurentia. Nevertheless, in spite of 178 years of study the Potsdam in the Ottawa Embayment and Quebec Basin remains poorly understood. Also poorly understood is how the Potsdam relates with coeval strata regionally. In this work six siliciclastic paleoenvironments are recognized: (a) braided fluvial, (b) ephemeral fluvial, (c) aeolian, (d) coastal sabkha, (e) tide-dominated marine and (f) opencoast tidal flat. Fluvial strata were examined in particular detail and interpreted to consist of two end-member kinds. Braided fluvial deposits are dominated by low-relief bars formed in wide, shallow channels; however where basement structures limited the lateral growth of channels, flows were deeper and bar deposits thicker and higher angle. In contrast, ephemeral fluvial strata are dominated by sheetflood splay sedimentation with rare preservation of scour-filling supercritical bedform strataall later subjected to aeolian reworking. In the upper Potsdam, alternating ephemeral and braided fluvial strata provide a record of climate change, which, respectively, correlate with documented global cool (arid) and warm (humid) periods during the Late Cambrian and Early Ordovician. Three allounits are recognized in Potsdam strata, recording regional episodes of sedimentation and facilitating correlation with coeval strata throughout eastern North America. These correlations, aided with provenance data from detrital zircons, show that changes in the areal distribution of sediment supply, accommodation and deposition/erosion were principally controlled by episodic reactivation of the Neoproterozoic Ottawa graben, which then periodically modified the stratigraphic expression of the ongoing Sauk transgression. Specifically, episodes of tectonic reactivation occurred during late Early to Middle Cambrian (allounit 1), late Middle to early Late Cambrian (allounits 2-3 unconformity), and Earliest Ordovician (allounits 3-4 unconformity). The earliest episode is correlated to regional extension of southern Laurentia, whereas the latter two are linked to peri-Laurentian accretion events that triggered reactivation of the Ottawa graben via the Missisquoi oceanic fracture zone. iii Résumé Le Cambrien-Ordovicien précoce Groupe de Potsdam est une unité silicoclastique qui fournit des informations importantes sur le paléo-environnement, l'histoire géologique et tectonique du Paléozoïque Laurentia. Néanmoins, malgré 178 années d'études, le Potsdam dans la baie d'Ottawa et le bassin du Québec demeure mal comprise. La réaction régionale du Potsdam avec les strates contemporaines est aussi peu comprise. Dans ce travail six paléoenvironnements sont reconnus: (a) fluviatiles entrecroisés, (b) éphémère fluviatile, (c) éolien, (d) de sebkha côtière, (e) marine marémotrice et (f) ouvert de marée de la côte. Les strates fluviatiles ont été examinées en détails et interprétées comme étant constituées en deux types. I first and foremost wish to thank my thesis supervisor Bill Arnott for giving me the opportunity to pursue this project and for generously supporting me throughout my PhD tenure, particulalruy for supporting myself and my field assistants during my field seasons. Rental car and fuel costs add upon a montly basis they are more expensive than graduate students (yet, with the added cost you get greater efficiency). I'd also like to thank Bill for his patience, encouragement and motivation using both carrot and stick and for his uncommon attention to detail. Finally, Bill has been and continues to be a worthy role model for me and for others, given his integrity, honesty and positivity. I'd also like to thank all of my thesis reviewers, Quentin Gall, George Dix, Denis Lavoie and Rob Rainbird, for enduring this long-winded account of observations of sandstone and providing very fair criticism which have improved this thesis. Bruce Sanford is also worth of great thanks and praise for laying the foundation for this and more work to come in the future. Bruce also visited many outcrops with me and shared with me his passion and positivity. Bruce is always willing to chat, and we remain friendly in spite of some minor differences in our interpretation of the same rocks. Like Bill, he is a worthy role model. I'd also like to thank everyone who assisted me with my field work and other data collection including Gurvir Khosa, Chris Barnes, Ed Desantis, Lindsay Coffin, Mike Lowe, Megan Reardon and Jason Duff. Yes, even Chris Barnes managed to be helpful, in spite of losing his field notes twice, drawing cartoons in the margins of the notebooks and relentlessly beating be at Tock night after night. I am especially grateful to Lindsay and Gurvir whose French-speaking skills without which major parts of the thesis would be lacking data. I'd also like to acknowledge that the contributions of Lindsay, Mike, Megan and Jason were voluntary, so thank you for your time. Chris McFarlane and Crystal Laflamme deserve thanks for their help with the detrital zircon analyses in New Brunswick. James Conliffe read parts of this thesis to help me revise them for publication. From the Earth Sciences Department at U Ottawa I was greatly helped by Dave Schneider, George Mrazek and Helene De Gouffe. I'd also like to thank the members of the Windermere Group at U Ottawa for their thoughts and contributions, including Viktor Terlaky, Lillian Navaro, Mike Tilston, Shann Khan, Derrick Midwinter, Natasha Popovik, Katrina Angus and Gerry Dumachel. Special thanks also too to the many property owners that permitted us to look at rocks on their land and who took interest in my studies. There are too many people to list but the few names that come to mind include Brian Sloan, Mark Wilson, Tim Bresset and Bill Atwood. I was very lucky early on (in 2010) to join a "Potsdam Sandstone" field trip and meet the "New York crowd", including Bruce Selleck, Dave Franzi, Jeff Chiarenzelli and Mike Rygel, among others. I'd like to thank these individuals and also Lisa Amati for attending vii field trips that I've led on the Potsdam and for maintaining interest in my ongoing research and providing feedback. Special thanks to Dave Franzi who made me feel at home in Chazy, NY during the summers of 2011 and 2012, and helped me out with some of my field logistics and ideas. Thanks also to Al Donaldson for attending field trips with us, pointing out unusual features, and getting me involved in Lanark Country geoheritage. Al also introduced me to Chris Brett, a Lanark Country geological enthusiast who continues to update us with his discoveries in that area. In Quebec I was helped out and made feel at home by Mario Lacelle and Pierre Groulx. Both were more than accommodating and gave up their weekends to take us to various locations in the field. Pierre is especially deserving of thanks as he opened his home in Valleyfield to Chris Barnes and me. In Vermont I am grateful to Char Mehrtens for working with me on one of my field trips and inviting me to come to Vermont to present my research, meet their Department and to go look at rocks. Part way through my PhD I was forced to move to Nova Scotia, and so I'm grateful to Martin Gibling for introducing me to ideas about pre-vs. post-vegetated fluvial systems, giving me space to work at Dalhousie University and for connecting me with many great people at the Dalhousie University Earth Sciences Department. I would like to thank my family for encouraging me (or, at least not discouraging me) on this quest for esoteric knowledge that none of them really understand. Special thanks to my wife Megan (also unpaid field assistant) for putting up with the last .. How many years? My choice to do this PhD required you to make many sacrifices. At many points I felt as though this PhD process was too trivial a thing to have such an effect on our lives. Nevertheless, you unwaveringly encouraged me to continue. I assume Bill Arnott was paying you under the table, which might be why we have such a nice car-I wasn't getting enough over the table to afford that fancy Mazda. Seriously though, you recognized my convictions and long-term commitment to research and understanding the Earth, even when the shortterm circumstances made me forget. Thanks for your commitment to me; you're the best partner anyone could have. I'm very lucky. Finally, thank you (and good luck) to those who endeavor to read this thesis in its entirety. I am sure that there will realistically be no one to thank on that account. But if that's you, I truly appreciate it. viii