Book contents
- Frontmatter
- Contents
- List of contributors
- Preface
- Acknowledgements
- 1 Geodynamic controls on glaciation in Earth history
- 2 Glacial-marine facies in a continental rift environment: Neoproterozoic rocks of the western United States Cordillera
- 3 The Neoproterozoic Konnarock Formation, southwestern Virginia, USA: glaciolacustrine facies in a continental rift
- 4 Glaciogenic deposits of the Permo-Carboniferous Dwyka Group in the eastern region of the Karoo Basin, South Africa
- 5 Itararé Group: Gondwanan Carboniferous-Permian of the Paraná Basin, Brazil
- 6 The interpretation of massive rain-out and debris-flow diamictites from the glacial marine environment
- 7 Neoproterozoic tillite and tilloid in the Aksu area, Tarim Basin, Uygur Xinjiang Autonomous Region, Northwest China
- 8 Lithology, sedimentology and genesis of the Zhengmuguan Formation of Ningxia, China
- 9 Architectural styles of glacially influenced marine deposits on tectonically active and passive margins
- 10 Marine to non-marine sequence architecture of an intracratonic glacially related basin. Late Proterozoic of the West African platform in western Mali
- 11 The enigmatic Late Proterozoic glacial climate: an Australian perspective
- 12 Isotopic signatures of carbonates associated with Sturtian (Neoproterozoic) glacial facies, central Flinders Ranges, South Australia
- 13 Reactive carbonate in glacial systems: a preliminary synthesis of its creation, dissolution and reincarnation
- 14 A Permian argillaceous syn- to post-glacial foreland sequence in the Karoo Basin, South Africa
- 15 A palaeoenvironmental study of black mudrock in the glacigenic Dwyka Group from the Boshof-Hertzogville region, northern part of the Karoo Basin, South Africa
- 16 Late Paleozoic post-glacial inland sea filled by fine-grained turbidites: Mackellar Formation, Central Transantarctic Mountains
- 17 Ice scouring structures in Late Paleozoic rhythmites, Paraná Basin, Brazil
- 18 Soft-sediment striated surfaces and massive diamicton facies produced by floating ice
- 19 Environmental evolution during the early phase of Late Proterozoic glaciation, Hunan, China
15 - A palaeoenvironmental study of black mudrock in the glacigenic Dwyka Group from the Boshof-Hertzogville region, northern part of the Karoo Basin, South Africa
Published online by Cambridge University Press: 06 July 2010
- Frontmatter
- Contents
- List of contributors
- Preface
- Acknowledgements
- 1 Geodynamic controls on glaciation in Earth history
- 2 Glacial-marine facies in a continental rift environment: Neoproterozoic rocks of the western United States Cordillera
- 3 The Neoproterozoic Konnarock Formation, southwestern Virginia, USA: glaciolacustrine facies in a continental rift
- 4 Glaciogenic deposits of the Permo-Carboniferous Dwyka Group in the eastern region of the Karoo Basin, South Africa
- 5 Itararé Group: Gondwanan Carboniferous-Permian of the Paraná Basin, Brazil
- 6 The interpretation of massive rain-out and debris-flow diamictites from the glacial marine environment
- 7 Neoproterozoic tillite and tilloid in the Aksu area, Tarim Basin, Uygur Xinjiang Autonomous Region, Northwest China
- 8 Lithology, sedimentology and genesis of the Zhengmuguan Formation of Ningxia, China
- 9 Architectural styles of glacially influenced marine deposits on tectonically active and passive margins
- 10 Marine to non-marine sequence architecture of an intracratonic glacially related basin. Late Proterozoic of the West African platform in western Mali
- 11 The enigmatic Late Proterozoic glacial climate: an Australian perspective
- 12 Isotopic signatures of carbonates associated with Sturtian (Neoproterozoic) glacial facies, central Flinders Ranges, South Australia
- 13 Reactive carbonate in glacial systems: a preliminary synthesis of its creation, dissolution and reincarnation
- 14 A Permian argillaceous syn- to post-glacial foreland sequence in the Karoo Basin, South Africa
- 15 A palaeoenvironmental study of black mudrock in the glacigenic Dwyka Group from the Boshof-Hertzogville region, northern part of the Karoo Basin, South Africa
- 16 Late Paleozoic post-glacial inland sea filled by fine-grained turbidites: Mackellar Formation, Central Transantarctic Mountains
- 17 Ice scouring structures in Late Paleozoic rhythmites, Paraná Basin, Brazil
- 18 Soft-sediment striated surfaces and massive diamicton facies produced by floating ice
- 19 Environmental evolution during the early phase of Late Proterozoic glaciation, Hunan, China
Summary
Abstract
Thin horizons (< 0.5 m) of black mudrock are present in the Dwyka Group (< 25 m thick), which overlies the floor of a palaeovalley near the northern margin of the Karoo Basin, South Africa. This palaeovalley was excavated by southward-moving glaciers from the mid-Namurian until the late Sakmarian. The Dwyka Group was deposited during deglaciation (late Sakmarian–early Artinskian), when a tidewater glacier retreated northwards up the valley.
The black mudrock forms a minor component of an argillaceous sequence up to 10 m thick that was deposited in the northern part of the palaeovalley in a subaqueous proglacial environment proximal to the glacier ice-front. The underlying lithofacies are dominated by diamictite that represent debris flow and minor debris rain deposits. Overlying strata comprise sandstone (± 2 m thick), which is attributed to sedimentation on an ice-proximal, prograding, subaqueous outwash fan, and a thin (< 0.3 m) conglomerate-diamictite couplet that represents sediment gravity flows associated with failure of unstable material, when rapid glacial melting caused a sudden rise in water-level.
Presence of Botryococcus braunii in the black mudrock indicates freshwater that was derived from the nearby melting glacier and also small icebergs. The marine setting of the Karoo Basin during the Dwyka glaciation implies a brackish-water environment in the palaeovalley due to mixing with freshwater near the glacier ice-front.
- Type
- Chapter
- Information
- Earth's Glacial Record , pp. 204 - 214Publisher: Cambridge University PressPrint publication year: 1994
- 3
- Cited by