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The Stratigraphic Record and Processes of Turbidity Current Transformation Across Deep-Marine Lobes

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The Stratigraphic Record and Processes of Turbidity Current Transformation Across Deep-Marine Lobes This is a repository copy of The stratigraphic record and processes of turbidity current transformation across deep-marine lobes. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/107528/ Version: Accepted Version Article: Kane, IA, Ponten, A, Vangdal, B et al. (3 more authors) (2017) The stratigraphic record and processes of turbidity current transformation across deep-marine lobes. Sedimentology, 64 (5). pp. 1236-1273. ISSN 0037-0746 https://doi.org/10.1111/sed.12346 © 2016 The Authors. Sedimentology © 2016 International Association of Sedimentologists. This is an Accepted Article that has been peer-reviewed and approved for publication in the Sedimentology, but has yet to undergo copy-editing and proof correction. 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[email protected] https://eprints.whiterose.ac.uk/ Page 1 of 65 Sedimentology 1 2 3 4 1 The stratigraphic record and processes of turbidity current transformation across deep- 5 6 2 marine lobes 7 8 3 9 10 1* 2 3 4 5 11 4 Ian Kane , Anna Pontén , Brita Vangdal , Joris Eggenhuisen , David M. Hodgson , Yvonne T. 12 5,4 13 5 Spychala 14 15 6 1Statoil ASA, Exploration, NO-1364, Oslo, Norway 16 2 17 7 Statoil ASA, Research Centre Rotvoll, NO- 005 Trondheim, Norway 18 3 8 Statoil ASA, Research Centre Bergen, NO-5020, Bergen, Norway 19 20 9 4Faculty of Geosciences, ,trecht ,niversity, PO Box .0021, 350.TA ,trecht, The Netherlands 21 5 22 10 School of Earth and Environment, ,niversity of /eeds, /S2 01T, ,nited 2ingdom 23 11 3Present address4 School of Earth, Atmospheric and Environmental Sciences, ,niversity of 24 25 12 5anchester, Oxford Road, 5anchester 513 0P/, ,nited 2ingdom 26 27 28 13 Abstract 29 30 14 Sedimentary facies in the distal parts of deep-marine lo,es can diverge significantly from those 31 32 15 predicted ,y classical tur,idite models, and sedimentological processes in these environments are 33 16 poorly understood. This gap may ,e ,ridged using outcrop studies and theoretical models. In the 34 35 17 S-oorsteen,erg .m., a downstream transition from thic-ly-,edded tur,idite sandstones to 36 37 18 argillaceous, internally layered hy,rid ,eds is o,served. The hy,rid ,eds have a characteristic 38 19 stratigraphic and spatial distri,ution, ,eing associated with ,ed successions which generally coarsen- 39 40 20 and thic-en-upwards reflecting deposition on the fringes of lo,es in a dominantly progradational 41 42 21 system. 0sing a detailed characterisation of ,ed types, including grain si1e, grain fa,ric and 43 22 mineralogical analyses, a process-model for flow evolution is developed. This is e2plored using a 44 45 23 numerical suspension capacity model for radially spreading and decelerating tur,idity currents. The 46 47 24 new model shows how decelerating sediment suspensions can reach a critical suspension capacity 48 25 threshold ,eyond which grains are not supported ,y fluid tur,ulence. Sand and silt particles, settling 49 50 26 together with flocculated clay, may form low yield-strength cohesive flows3 development of these 51 52 27 higher concentration lower ,oundary layer flows inhi,its transfer of tur,ulent -inetic energy into the 53 28 upper parts of the flow ultimately resulting in catastrophic loss of tur,ulence and collapse of the 54 55 29 upper part of the flow. Advection distances of the now transitional to laminar flow are relatively 56 57 30 long 4several -m5 suggesting relatively slow dewatering 4several hours5 of the low yield strength 58 59 60 1 Sedimentology Page 2 of 65 1 2 3 4 31 flows. The catastrophic loss of tur,ulence accounts for the presence of such ,eds in other fine- 5 6 32 grained systems without invo-ing e2ternal controls or large-scale flow partitioning, and also 7 8 33 e2plains the a,rupt pinch-out of all divisions of these sandstones. Estimation of the point of flow 9 34 transformation is a useful tool in the prediction of heterogeneity distri,ution in su,surface systems. 10 11 12 35 2eywords4 6ybrid beds, transitional flow deposits, flow transformation, deep-marine channels and 13 36 lobes, reservoir 8uality, flow capacity, 2aroo 14 15 16 37 17 18 38 Introduction 19 20 21 39 O,servation and interpretation of sedimentary facies from deep-marine lo,e deposits has ,een 22 40 strongly influenced ,y models developed from relatively small and coarse-grained ,asins, for 23 24 41 e2ample the Annot su,-,asins 4Bouma, 17825 and the Californian Borderlands 4Lowe, 17825. 25 26 42 owever, today’s ultra-deep-water su,surface e2ploration targets are typically associated with 27 43 sedimentary systems that are up to orders of magnitude larger, drained much larger areas, and are 28 29 44 significantly finer grained 4e.g. the Wilco2 .m. of the Gulf of Me2ico, Zarra et al., 200A5. The 30 31 45 sedimentary environments and facies distri,utions of these systems are understudied as they 32 46 commonly develop on passive margins and may overlie transitional or oceanic crust, and as such are 33 34 47 prone to su,duction. Numerous studies have documented these systems from remote sensing-,ased 35 36 48 o,servations and slightly more limited core data from the modern and olocene stratigraphy 4an 37 49 e2cellent e2ample ,eing the Mississippi .an, see summary in Twichell et al., 20075. Due to the 38 39 50 paucity of outcrops revealing such systems, it may ,e appropriate to use fine-grained systems in 40 41 51 smaller ,asins as process analogues to larger systems 4e.g. Martinsen et al., 20003 Sullivan et al., 42 52 20005. In these fine-grained systems, complicated facies and facies distri,utions, which diverge 43 44 53 significantly from classical tur,idite models, are reported from medial and distal lo,e settings 45 46 54 4 aughton et al., 200C, 20073 Sylvester D Lowe, 20043 Talling et al., 2004, 20123 Amy D Talling, 47 55 20083 Ito, 20083 Bar-er et al., 20083 Davies et al., 20073 odgson, 20073 Kane D Pontén, 20123 48 49 56 Pyles D Jennette, 20123 Talling, 201C3 GrundvEg et al., 20143 Terla-y D Arnott, 20143 .onnesu et 50 51 57 al., 20153 Southern et al., 2015, 20183 Spychala et al., in revision5. Such ,eds have ,een termed 52 58 hy,rid event ,eds ,y aughton et al. 420075, which emphasises that an individual ,ed represents the 53 54 59 deposits of different types of flow within the same event. Typically, this is a ,asal tur,idite and an 55 56 60 upper de,rite3 the term has, however, ,een adopted to cover a wide range of deposit and process 57 61 types which com,ine to form a single Fhy,rid’ ,ed 4e.g., odgson, 20073 Talling, 201C3 .onnesu et 58 59 60 2 Page 3 of 65 Sedimentology 1 2 3 4 62 al., 20155. The stratigraphic and spatial comple2ity of these ,ed types means that deep-marine fan 5 6 63 systems represent significant challenges for reservoir prediction at ,oth e2ploration and development 7 8 64 scales 4Porten et al., in press5. The Paleogene Wilco2 .m. e2emplifies these challenges: it is 9 65 characterised ,y e2tremely large volumes of sandstone, ,ut often occurring as mud-rich sandstones 10 11 66 with marginal reservoir Huality 4i.e., low porosity and permea,ility values5, with stratigraphically 12 13 67 and spatially isolated higher-Huality reservoir sandstones 4Zarra, 200A3 Kane and Pontén, 20125. 14 15 68 In this contri,ution, the spatial and stratigraphic distri,ution of the various sedimentary facies 16 17 69 associated with pro2imal, medial and distal deep-marine lo,e environments of .an C, 18 70 S-oorsteen,erg .m., TanHua Karoo, are presented and characterised, with particular emphasis on 19 20 71 hy,rid ,eds. The paper comprises two interlin-ed sections, with the main focus ,eing 15 to 21 22 72 characterise fine-grained hy,rid ,eds, and 25 to develop a process ,ased numerical model for their 23 73 o,served occurrence. In the first part, we use outcrop and petrological o,servations to infer 24 25 74 sedimentological flow processes. In the second part, a numerical model is introduced to investigate 26 27 75 the inferred processes. The model uses a suspension-capacity model 4Eggenhuisen et al., 20185, and 28 76 applies it to radially spreading decelerating flows. Integrating the detailed ,ed characterisation and 29 30 77 the numerical model, we propose that these types of hy,rid ,eds form due to the loss of tur,ulence 31 32 78 due to flow deceleration, the development of internal stratification and eventual catastrophic loss of 33 79 tur,ulence in the flow. 0nderstanding of the process sedimentology of these deposits and their 34 35 80 stratigraphic and spatial distri,ution can ,e applied to systems of similar grain-si1e range to 36 37 81 significantly reduce su,surface uncertainty and to improve prediction.
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