Sedimentologic and Petrographic Evidence Of
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SEDIMENTOLOGIC AND PETROGRAPHIC EVIDENCE OF FLOW CONFINEMENT IN A PASSIVE CONTINENTAL MARGIN SLOPE CHANNEL COMPLEX, ISAAC FORMATION, WINDERMERE SUPERGROUP, BRITISH COLUMBIA, CANADA Tyler Billington Thesis submitted to the Faculty of Graduate and Postdoctoral Studies in partial fulfillment of the requirements for the M.Sc. degree in Earth Sciences Ottawa-Carleton Geoscience Centre Faculty of Science University of Ottawa © Tyler Billington, Ottawa, Canada, 2019 University of Ottawa Abstract At the Castle Creek study area in east-central British Columbia a well-exposed section about 450 m wide and 30 m thick in the (Neoproterozoic) Isaac Formation was analyzed to document vertical and lateral changes in a succession of distinctively heterolithic strata. Strata are interpreted to have been deposited on a deep-marine levee that was sandwiched between its genetically related channel on one side and an erosional escarpment sculpted by an older (underlying) channel on the other. Flows that overspilled the channel (incident flow) eventually encountered the escarpment, which then set up a return flow oriented more or less opposite to the incident (from the channel) flow. This created an area of complex flow that became manifested in the sedimentary record as a highly tabular succession of intricately interstratified sand and mud overlain by an anomalously thick, plane-parallel interlaminated sand-mud unit capped finally by a claystone. ii Résumé Dans la zone d’étude de Castle Creek, situé au centre-est de la Colombie-Britannique, se trouve une section exposée de 30 m d’épaisseur et de 450 m de large dans la formation Isaac (Neoprotérozoique). Cette formation à été analysée afin de documenter les changements verticaux et latéraux d’une succession de strates hétérolithiques. Il est suggéré que ces strates se sont déposé lors d’une transgression marine. Les sédiments sont alors en étau entre leur chenal et un escarpement dû a l’érosion, sculpté par un ancien chenal (sous-jacent). L’écoulement dépassant ce chenal atteint éventuellement l’escarpement, ce qui causera un retour de ce courant, en sens inverse de l’incident. La déposition des sédiments sera alors le reflet de la complexité de ce courant, se manifestant sous forme d’une succession de lits de sable et de boue finement interstratifiés, suivi par une unité parallèle au plan de sable-boue interlaminée anormalement épaisse, le tout recouvert par de l’argilite. iii Extended Abstract Along the base of passive continental margins, like the Canadian east coast, extensive deep- water clastic turbidite systems are present. Through the 21st century these systems have been increasingly recognized as prolific petroleum reservoirs and currently represent about 20-30% of global production. In spite of their excellent resource potential, deep-marine turbidite systems also come with many uncertainties and substantial drilling costs. In order to reduce economic risk and improve exploration success, petroleum geologists have turned to the ancient deep-marine sedimentary record to find meaningful analogues to describe passive margin deep-water turbidite systems. These deposits are often classified using the Bouma turbidite model; a generally upward- fining succession composed of five sharply bounded layers, each exhibiting a unique assemblage of predictable sedimentary structures and textures. In the Windermere Supergroup, however, in addition to classical turbidites, another type of strata, which superficially resemble turbidites, are observed. Where fully developed these strata consist of a basal massive or structured sandstone (F1) overlain sharply by structured, interstratified clayey sandstone and mudstone (F2). This layer is then overlain gradationally by distinctively rhythmically interstratified, sandy claystone capped sharply by structureless claystone (F3). The study area crops out for over 450 metres laterally and can be subdivided into two parts. The first part consists of a basal amalgamated unit overlain by a heterolithic unit capped sharply by a thick succession of fine-grained, thin-bedded classical turbidites. The basal amalgamated unit is 15 metres thick, composed of amalgamated coarse-grained sandstone to pebble conglomerate, and interpreted to be a channel complex. The second part occurs at the same stratigraphic level, but 250 metres to the northwest. Here strata consist of a thick succession of rhythmically interlaminated, well-sorted, very fine-grained sandstone overlain sharply by mudstone that iv distinctively lack traction transport structures and are intercalated with thin- to very thin-bedded turbidites (F4). Although the contact between the two parts is covered, such a dramatic lithological change over only a few hundred metres suggests that the channel complex scoured these fine- grained strata (F4) and then became partly filled with the amalgamated unit. These strata grade upward over about one metre into the heterolithic unit that forms a 13 metre-thick succession that comprises 2-5 metre-thick bedsets comprising F1 to F3. Collectively, the lithological difference between strata in the heterolithic unit and classical turbidites is interpreted to be a consequence of flow confinement. Here two-way confinement was provided by the escarpment that had previously been sculpted by the channel complex in the fine- grained unit to the northwest, and growth of a levee associated with a younger, but out-of-the- plane-of-the-outcrop channel located to the southeast. Flows overspilled the new channel and over the developing levee where it eventually encountered the escarpment resulting in a return flow orientated in the opposite direction. The interaction of the incident (from the channel) and return flow (from the escarpment) created a local area of complex flow and depositional conditions, which here is manifested as the heterolithic unit. With continued deposition, relief of the escarpment was reduced and, in turn the strength of the return flow diminished. Later the development of an even younger channel further to the southeast, and the flattening of the local sea floor, allowed overspill flows to move unobstructed and unconfined and deposit the thin- bedded turbidites that cap the study area. The ability to recognize the distinctive lithological characteristics of these heterolithic strata, but equally, appreciate and understand their interpretive significance, will aid in modelling these sub-seismic features, which also may be important in predicting reservoir v compartmentalization and fluid flow pathways in hydrocarbon reservoirs hosted in submarine channel complexes. vi "If I have seen further it is by standing on the shoulders of Giants." – Isaac Newton (1675) nanos gigantum humeris insidentes vii Acknowledgements My journey through this thesis project over the past few years would not be possible without the guidance, aid, and support of countless individuals along the way. First and foremost, I would like to thank my supervisor Bill Arnott for his guidance, knowledge, and wisdom he offered throughout this project. I came into this project with little knowledge of the deep-marine, however, Bill quickly sparked my interest in the topic the first time I talked with him on the phone as his enthusiasm and knowledge of the material intrigued me. My fascination with deep-marine sedimentology, and its often-enigmatic processes continued throughout my time in Ottawa during team meetings and lectures with Bill. His willingness to drop whatever he is doing to discuss geology, especially topics focussed on the deep-marine, or help with any issues being faced at the time was always much appreciated. I would like to thank Quentin Gall and Don Cummings for taking the time to serve on my defense committee and their insightful feedback on how to improve this thesis. This project was supported by the Windermere Consortium, which is an industry-, government-, and academia-funded research initiative directed by Bill. I would like to thank the following partners for their continued intellectual and financial support: Anadarko Petroleum Corporation, Apache Corporation, Equinor, Husky Energy, Natural Sciences and Engineering Research Council of Canada (NSERC), and the University of Ottawa. Scholarships and financial aid were also greatly appreciated from the Canadian Society of Petroleum Geologists (2017 CSPG Regional Graduate Scholarship – Ontario region), American Association of Petroleum Geologists (2018 AAPG Grants-in-Aid – Martin D. Hewitt Named Grant), and the University of Ottawa (CUPE financial aid). viii Special thanks to Lilian Navarro for her countless hours of great conversation and guidance regarding geology, grad school, and life in general. She got me started off on the right track the first summer in the field and helped at any point along the way including aiding in cutting samples, preparing samples for analysis, and the many analytical techniques she helped me understand and utilize. Lilian did not hesitate to answer any questions I had and was always willing to discuss or refine ideas. Thanks for your numerous edits and help in deciphering Bill’s cryptic written text when I had troubles reading it. Thank you to the rest of the Windermere research group: Curran Wearmouth, Dylan Cochrane, Anika Bergen, Omar Al-Mufti, Celeste Cunningham, Derrick Midwinter, Sean Ludzki, and Gabriella Milczarek. Your comments and feedback in the field, during team meetings, or just casually in the hall helped improve this thesis greatly. Although not officially part of the Windermere