The Ventersdorp contact reef; final phase of the Witwatersrand Basin, independent formation, or precursor to the Ventersdorp Supergroup?
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The Ventersdorp Contact Reef (VCR) is an Archaean conglomeratic gold placer, mined in the Carletonville, West Rand, and Klerksdorp goldfields of the Republic of South Africa. It belongs to a lithostratigraphic formation, the Venterspost Conglomerate Formation (VCF), which is considered to be stratigraphically independent of the underlying Witwatersrand Supergroup sediments and overlying Ventersdorp Supergroup volcanics. In this paper, the present formal stratigraphic placement of the Formation is compared with its alternative stratigraphic assignment to either of the underlying Witwatersrand or overlying Ventersdorp Supergroups. Evidence for a basin-wide, angular unconformity separating the VCF from Witwatersrand rocks, which were regionally lithified prior to deposition of the Formation, indicates that it is stratigraphically divorced from the Witwatersrand Supergroup. While similar angular, internal unconformities are present within the Witwatersrand Supergroup, a significant difference between these and the VCF unconformity is that the internal Witwatersrand unconformities are asserted to have basinward extents only to the tectonic hinge between continuous deposition and contemporaneous (Witwatersrand) foreland basin destruction. A genetic difference between the VCR and typical Witwatersrand placers is reflected by their differing mineralogical content and metamorphic grade. These differences, by implication, also reflect a substantial time gap separating their deposition. The fact that the conglomerates and sandstones of the VCF are locally interbedded with lava flows that are geochemically similar to the lava of the basal Westonaria Formation of the Ventersdorp Supergroup, indicates lithologic and genetic links to this Supergroup. These relationships are further supported by the presence of tuffaceous sandstone beds within the VCF. The occurrence of deformational load structures at the contact between the formation and the basal lava flows of the overlying Ventersdorp Supergroup indicates an unconsolidated, probably water-saturated state of the VCF sediments at the time of their envelopment by the lava, and implies a conformable relationship with the lower formations of the Supergroup. In conclusion, it is proposed that the VCF be stratigraphically assigned to the Ventersdrop Supergroup.Keywords:
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Research Article| March 01, 2014 The Old Fort Point Formation: Redefinition and formal subdivision of a distinctive stratigraphic marker in the Neoproterozoic Windermere Supergroup, southern Canadian Cordillera M.D. Smith; M.D. Smith Department of Earth Sciences, University of Ottawa, Marion Hall, 140 Louis Pasteur, Ottawa, ON K1N 6N5, Canada Search for other works by this author on: GSW Google Scholar R.W.C. Arnott; R.W.C. Arnott Department of Earth Sciences, University of Ottawa, Marion Hall, 140 Louis Pasteur, Ottawa, ON K1N 6N5, Canada Search for other works by this author on: GSW Google Scholar G.M. Ross G.M. Ross Kupa'a Farm, P.O.Box 458, Kula, HI 96790, USA Search for other works by this author on: GSW Google Scholar Author and Article Information M.D. Smith Department of Earth Sciences, University of Ottawa, Marion Hall, 140 Louis Pasteur, Ottawa, ON K1N 6N5, Canada R.W.C. Arnott Department of Earth Sciences, University of Ottawa, Marion Hall, 140 Louis Pasteur, Ottawa, ON K1N 6N5, Canada G.M. Ross Kupa'a Farm, P.O.Box 458, Kula, HI 96790, USA Publisher: Canadian Energy Geoscience Association Received: 04 Mar 2013 Accepted: 11 Feb 2014 First Online: 13 Jul 2017 Online ISSN: 2368-0261 Print ISSN: 0007-4802 © the Society of Canadian Petroleum Geologists Bulletin of Canadian Petroleum Geology (2014) 62 (1): 1–13. https://doi.org/10.2113/gscpgbull.62.1.1 Article history Received: 04 Mar 2013 Accepted: 11 Feb 2014 First Online: 13 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation M.D. Smith, R.W.C. Arnott, G.M. Ross; The Old Fort Point Formation: Redefinition and formal subdivision of a distinctive stratigraphic marker in the Neoproterozoic Windermere Supergroup, southern Canadian Cordillera. Bulletin of Canadian Petroleum Geology 2014;; 62 (1): 1–13. doi: https://doi.org/10.2113/gscpgbull.62.1.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract The southern Canadian Cordillera strata of the Neoproterozoic Windermere Supergroup form an areally extensive outcrop belt of deep-marine sedimentary rocks. Within this generally monotonous pile of siliciclastic and minor carbonate rocks, the Old Fort Point Formation forms a lithologically and geochemically distinctive unit that serves as a key regional stratigraphic marker. New sedimentologic and stratigraphic work demonstrates that it is lithologically distinctive, mappable and correlatable on a regional scale and deserves formal recognition.The Old Fort Point Formation comprises three lithostratigraphic members that have a consistent stratigraphic relationship across the basin and can easily be distinguished from lithofacies in the enveloping strata of the Windermere Supergroup. The basal Temple Lake Member is composed primarily of siltstone to mudstone that grades upward into rhythmically interstratified limestone-siltstone. The middle Geikie Siding Member is a thin, organic-rich mudstone-pelite. The Whitehorn Mountain Member is the uppermost unit and varies locally and regionally in thickness and lithology, including diamictite, breccia to conglomerate, mudstone to siltstone, subarkose, quartzarenite, calcareous arenite, arenaceous limestone, and limestone.This unique lithostratigraphic unit is here formally named the Old Fort Point Formation and other site-specific names should be discontinued. The use of the name Old Fort Point Formation is an attempt to simplify part of a complicated and informally defined stratigraphic nomenclature currently in use for rocks in the Neoproterozoic Windermere Supergroup, southern Canadian Cordillera. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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Abstract Fossiliferous Cretaceous rocks in western Raukumara Peninsula occur as a narrow band along the southern margin of underlying Torlesse Supergroup greywacke rocks and beneath a cover of Tertiary rocks, or as infaulted or erosional outliers within Torlesse Supergroup. A major regional angular unconformity representing the Rangitata Orogeny and subsequent peneplanation of variable duration, separates complexly folded and faulted, mostly steeply dipping, virtually unfossiliferous, indurated greywacke rocks of Torlesse Supergroup from less indurated, open folded, fossiliferous Cretaceous shelf sediments. Cretaceous sequences commence with basal transgressive sandstone and conglomerate ranging in age from Korangan Stage (Aptian) to Haumurian Stage (Maastrichtian). Other unconforrnities, mostly local, are present in Cretaceous sequences, and a second regional unconformity occurs below a Haumurian, and locally Piripauan, transgressive succession. The geographic and stratigraphic distribution of lithofacies, unconformities and the thickness of units during the Cretaceous suggest complex patterns of deposition and erosion possibly in response to faulting and folding in the Torlesse basement.
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Abstract The Neoproterozoic Windermere Supergroup (WSG) is exposed over an area of 35 000 km 2 in the southern Canadian Cordillera, and consists primarily of deep-marine meta-sedimentary rocks interpreted to have been deposited during rifting and subsequent post-rift thermal relaxation. The main exposures of the WSG occur within thrust panels and structural culminations of the eastern Cordilleran orogen. Within the thick stratigraphic succession ( c. 9 km) are three units of glaciogenic affinity: Toby, Vreeland and Old Fort Point (OFP) formations. The Toby Formation (Fm.) is composed of up to 2500 m of diamictite, interbedded with conglomerate, sandstone, mudstone, carbonate and mafic volcanic rocks. The Vreeland Formation ranges from 350 m to 2000 m in thickness and consists of diamictite, interbedded with mudstone, sandstone and conglomerate. The OFP ranges from 60 to 450 m in thickness and consists of a distinctive threefold stratigraphic package of basal siltstone grading upward into limestone–siltstone rhythmite, organic-rich mudstone and an overlying heterolithic unit of diamictite, breccia, conglomerate, sandstone, siltstone to mudstone and limestone. A locally prominent unconformity marks the base of the OFP upper member. Both the Toby and Vreeland formations represent remobilized glacially derived marine sediments deposited by sediment-gravity flows. Deposition of the Toby Fm. was fault-controlled during an active tectonic phase (rifting), whereas the Vreeland Fm. accumulated during the subsequent quiescent phase (post-rift) with limited structural control. The OFP is interpreted to be a regionally extensive deep-marine post-glacial marker temporally associated with the glaciogenic Vreeland Fm. Although direct geochronological ages for WSG units in southwestern Canada are generally absent, high-precision radiometric ages of underlying and overlying igneous events constrain the relative maximum and minimum timing of deposition from c. 740–728 Ma to c. 569 Ma. At the base of the WSG succession, the Toby Fm. may be as young as c. 685 Ma based on ages obtained from potential stratigraphic correlatives in the USA. There is no direct age constraint for the deposition of the Vreeland Fm.; its minimum timing is based on its stratigraphic relationship with the post-glacial OFP. The middle member of the OFP was precisely dated at 607.8±4.7 Ma using the Re–Os method, placing it in the Ediacaran Period. Published geochemical and stable isotopic data are similarly limited for all three units with only some δ 34 S py values available from one section of the OFP. Recent work has focused on detailed sedimentological and stratigraphic studies of the Toby and OFP formations with future efforts being directed towards integrated geochemical and isotopic research. Additional geochronological constraints are needed to refine palaeogeographical models and strengthen regional correlations with other North American Cordilleran glaciogenic units.
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Breccia
Subaerial
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Alluvial fan
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The Meguma Supergroup of southern mainland Nova Scotia is an Early Cambrian to Early Ordovician deep-water peri-Gondwanan succession. The base is not seen, but isotopic and geochronologic evidence suggest broadly ‘Avalonian’ basement. The lower part of the succession (Goldenville Group) comprises relatively quartz-rich, thickly bedded turbidites and interbedded green slates. Abundant turbidite structures indicate sedimentation continuously below wavebase, and the great thickness of the succession attests to major subsidence. The trace fossil Oldhamia indicates Early Cambrian age. At the top of the group the stratigraphy is more diverse; alternating finer and coarser units show enrichment in manganese and spectacular bioturbation. A rare trilobite-bearing horizon indicates Middle Cambrian age. A unit of manganiferous laminated slate marks the transition into the overlying Halifax Group. The overlying Cunard Formation comprises rustyweathering black pyrite-rich slate, siltstone, and sandstone with turbidite structures. Higher parts of the group possibly show a transition to shallower water conditions, with more abundant trace fossils, and rare Tremadocian graptoloids. The group is overlain with angular unconformity by the Early Silurian White Rock Formation. The succession in the Harlech Dome in North Wales is also an Early Cambrian to Early Ordovician deep-water peri-Gondwanan succession. Underlying basement is not seen but drilling has revealed ‘Avalonian’ volcanics in the subsurface. The lowest part of the Harlech Grits Group comprises Early Cambrian cross-bedded, probably deltaic sandstones which pass up into fully marine slates. The overlying Rhinog Formation consists of relatively quartzose thickly bedded turbidites and green slates. Abundant turbidite structures indicate sedimentation continuously below wavebase, suggesting significant subsidence. At the top of the group the stratigraphy is more diverse; alternating finer and coarser units show enrichment in manganese and spectacular bioturbation. Rare trilobite fragments indicate Middle Cambrian age. A unit of carbonaceous laminated slate marks the base of the overlying Mawddach Group. The overlying Maentwrog Formation comprises rusty-weathering black pyrite-rich slate, siltstone, and sandstone with turbidite structures. Trilobites indicate Late Cambrian age. Higher parts of the group show a clear transition to shallower water conditions above wavebase, with linguloid brachiopods and trilobites indicating Tremadocian age. The group is unconformably overlain by the Early Ordovician Rhobell and Aran volcanic groups. Lithological and chronological analogies between the two successions are striking. However, significant differences include: (1) the greater thickness of the Meguma succession; (2) the presence of shallow marine to non-marine strata at the base and top of the Harlech succession; (3) the possible presence of an unconformity between the two groups in Harlech; and (4) the presence of volcanics near the base and top of the Welsh succession. Nonetheless, the similarities indicate closely similar evolution for the two basins, and would be consistent with deposition in connected parts of a peri-Gondwanan rift system.
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A 4800 m-thick composite reference profile was measured for the Mozaan Group of the Pongola Sequence in the Hartland area of northern Natal. In broad lithostratigraphic terms the sequence consists of a basal quartzite successively overlain by a thick shale unit with interbeds of iron-formation, magnetic mudstone and quartzite, a central quartzite and shale sequence, an upper shale unit with a lava interbed and an uppermost quartzite-rich unit with an interbed of shale and volcaniclastics. Several modifications are proposed for the formally recognized subdivision of the sequence. The sequence comprises marine shelf shales and shallow marine shelf orthoquartzites interbedded with fluvial braidplain quartzites. In the area mapped, tidalites are rare to absent
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Trough (economics)
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Siliciclastic
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Arenite
Placer deposit
Ladinian
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