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UNIVERSITY OF GOTHENBURG Department of Earth Sciences Geovetarcentrum/Earth Science Centre Petrography and sedimentary facies of the lower Cambrian succession at the Kinnekulle table mountain, south-central Sweden - Implications for the late Precambrian peneplainization and early Cambrian transgression Anders Eurenius ISSN 1400-3821 B974 Master of Science (120 credits) thesis Göteborg 2017 Mailing address Address Telephone Telefax Geovetarcentrum Geovetarcentrum Geovetarcentrum 031-786 19 56 031-786 19 86 Göteborg University S 405 30 Göteborg Guldhedsgatan 5A S-405 30 Göteborg SWEDEN Abstract Kinnekulle, in south-central Sweden, is located in a region of table mountains where weathered Proterozoic gneiss is overlain by early Paleozoic strata, which have been preserved by Permian dolerite intrusions. The early and middle Cambrian (Stage 4 and 5) succession at Kinnekulle is here studied in a new drill core containing strata from the File Haidar (Mickwitzia Sandstone and Lingulid Sandstone members) and Alum Shale Formation. A stratigraphic log, together with petrographic descriptions and field observations from localities at Råbäcks hamn and Lugnås, form the basis for this study. Results show that, in addition to the weathered gneissic basement, seven distinctly different sedimentary lithofacies can be recognized. These include: 1 – Massive polymict conglomerate, characterized by poorly sorted, sub-angular to rounded, fine to pebble-sized quartz and distinctly weathered feldspar; 2 – Interbedded sandstone and mudstone, characterized by cross-laminated and normally graded, fine-grained sand and bioturbated mud; 3 – Thickly bedded sandstone, characterized by cross-laminated or massive, fine to coarse-grained sandstone; 4 – Disrupted sand and mudstone, characterized by fine-grained sand and mudstone constituting homogenized zones, remnant original bedding, mudstone clasts and vertical tubes; 5 – Massive sandstone, characterized by very fine-grained, homogenous sandstone with thin, interspersed, silty and micaceous lamina; 6 – Sandstone-pebble conglomerate, characterized by internally sorted and vaguely imbricated sandstone-pebble clasts and fine-grained quartz matrix; and 7 – Black shale, characterized by laminated black shale interspersed with thin layers of limestone or fine-grained quartz-rich sand. Together, lithofacies 1 – 7 represent different types of deposition occurring in terrestrial and marine environments. They record a variety of processes related to marine storm and fair- weather sedimentation, fluvial currents, chemical weathering, cementation, bioturbation, and possibly eolian abrasion and soft-sediment deformation. The basement rock is characterized by distinct textures associated with Precambrian weathering. The lower Mickwitzia Sandstone Member includes a basal conglomerate that consist of sediment derived from different local sources and was reworked in a terrestrial environment. Reworking also occurred during the early Cambrian transgression, after which the conglomerate was chemically weathered and cemented. The conglomerate is followed by deposits of sandstone and mudstone that show an upward increase of storm-influenced facies associated with the lower shoreface. The overlying Lingulid Sandstone Member record deposition of overall homogenous and more bioturbated sands, possibly indicating relatively calm conditions. The early Cambrian sediment was lithified, indicating substantial burial. An erosion surface at the topmost Lingulid Sandstone Member marks the region-wide Hawke Bay unconformity, which was followed by an intra-basin conglomerate that developed during sub-aerial exposure and fluvial processes. The environment then changed rapidly from terrestrial to marine, represented by deposition of black shale that belong to the Alum Shale Formation. Key words: Early Cambrian, File Haidar Formation, Kinnekulle, Cambrian transgression, peneplainization, stratigraphy, sedimentary facies, petrography Table of contents 1. Introduction ........................................................................................................................................................ 1 1.1. Background .................................................................................................................................................. 1 1.2. Aim and purpose .......................................................................................................................................... 1 1.3. Study area .................................................................................................................................................... 1 1.4. Geologic setting and stratigraphic framework ............................................................................................ 2 Baltica and surrounding paleo continents of the late Precambrian to early Cambrian ................................. 2 Lithotectonic units and peneplainization of the Baltic shield ........................................................................ 3 Precambrian and early Cambrian basins and sediment ................................................................................. 5 The early Cambrian shelf and highlands ........................................................................................................ 5 Regional extent of the lower Paleozoic cover rocks ....................................................................................... 6 Sequence stratigraphy of the early Cambrian ................................................................................................ 6 Clastic supply over the course of the early Cambrian .................................................................................... 6 The File Haidar Formation .............................................................................................................................. 7 2. Material and methods ......................................................................................................................................... 9 2.1. Drill core....................................................................................................................................................... 9 2.2. Localities .................................................................................................................................................... 10 2.3. Petrography ............................................................................................................................................... 11 2.4. Terminology ............................................................................................................................................... 12 3. Results and interpretation ................................................................................................................................ 13 3.1. Stratigraphic log ......................................................................................................................................... 13 3.2. Gneissic basement ..................................................................................................................................... 22 3.3. Sedimentary facies ..................................................................................................................................... 24 Lithofacies 1: Massive polymict conglomerate ............................................................................................ 24 Lithofacies 2: Interbedded sandstone and mudstone .................................................................................. 29 Lithofacies 3: Thickly bedded sandstone ...................................................................................................... 34 Lithofacies 4: Disrupted sandstone and mudstone ...................................................................................... 37 Lithofacies 5: Massive sandstone ................................................................................................................. 41 Lithofacies 6: Sandstone-pebble conglomerate ........................................................................................... 43 Lithofacies 7: Black shale .............................................................................................................................. 45 4. Discussion .......................................................................................................................................................... 46 4.1. Peneplainization and the development of the basal conglomerate .......................................................... 47 4.2. Marine environments represented by the Mickwitzia Sandstone Member.............................................. 51 4.3. Marine environments represented by the Lingulid Sandstone Member .................................................. 53 4.4. Development of the sandstone-pebble conglomerate and the following transgression .......................... 55 5. Conclusions ....................................................................................................................................................... 57 6. Acknowledgements ........................................................................................................................................... 58 7. References ......................................................................................................................................................... 59 1. Introduction 1.1.