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Chuos Formation

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Series: Geological Society, London, Special Publications
Published: 01 January 2019
DOI: 10.1144/SP475.2
EISBN: 9781786204141
... Fig. 7. Satellite image of the Chuos Formation near Orusewa ( Fig. 3a ) highlighting the variable thickness of the ferruginous facies (dark horizon). These lateral thickness changes are interpreted to be the result of increased accommodation space and preservation potential within...
Journal Article
Journal: Geosphere
Published: 01 June 2017
Geosphere (2017) 13 (3): 811–837.
... thickening are poorly known. We studied three local thickenings of the Sturtian Chuos Formation in northern Namibia by measuring closely spaced columnar sections, not only of the synglacial deposits but also of the bounding pre- and post-glacial strata. This enabled incised paleovalleys filled by glacial...
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Simple composite sedimentary log of the Chuos Formation in the Ghaub and Varianto Farm areas of northern Namibia (see Fig. 1B and C for location). The positions of both outcrop photographs (Fig. 6) and thin-section interpretations (Figs. 7, 8) are shown. From Busfield and Le Heron (2013).
Published: 29 May 2018
Fig. 5.— Simple composite sedimentary log of the Chuos Formation in the Ghaub and Varianto Farm areas of northern Namibia (see Fig. 1 B and C for location). The positions of both outcrop photographs ( Fig. 6 ) and thin-section interpretations ( Figs. 7 , 8 ) are shown. From Busfield and Le
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Thin-section photographs of Chuos Formation microstructures at Ghaub–Varianto (A–D) and Omutirapo (E–H). Stratigraphic context of photos A–D is shown in Figure 5. White bar is 1 mm. A) Sheared diamictite from the lower ductile zone showing arcuate grain alignments, S-C shear structures, and clast dispersion tails. B) Jig-saw fit pattern of fractured clasts in middle brittle zone. C, D) Sheared diamictite from the upper ductile zone showing asymmetric pressure shadows (C), sheared and attenuated clasts (D) and a well-developed unistrial plasmic fabric. E) Arcuate grain alignments around “core” stone. Note skelsepic plasmic fabric which wraps around the margins of the core skeleton grain. F) Bed-parallel boudinaged clast. G, H) Two principal plasmic fabric orientations are observed: the subhorizontal fabric interpreted as a product of glaciotectonic shearing, and the high-angle fabric interpreted as the micro-scale expression of the steeply dipping cleavage observed at outcrop.
Published: 29 May 2018
Fig. 8.— Thin-section photographs of Chuos Formation microstructures at Ghaub–Varianto (A–D) and Omutirapo (E–H). Stratigraphic context of photos A–D is shown in Figure 5. White bar is 1 mm. A) Sheared diamictite from the lower ductile zone showing arcuate grain alignments, S-C shear structures
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Outcrop expression of Chuos Formation diamictites in northern Namibia at Ghaub–Varianto (A–F) and Omutirapo (G, H). See Figure 5 for stratigraphic context. A) High-strain zone with attenuated clasts. B) Small, asymmetric fold with sense of shear indicated. C) Clast with asymmetric pressure shadow in stratified diamictite. D) Rotational deformation structure surrounding “core” stone. E) Highly attenuated, sheared diamictite with characteristic S-C structures. F) Sedimentary dike crosscutting sheared diamictite. Contains fragments of sheared diamictite set in carbonate matrix. G) Clast-poor stratified diamictite with orange carbonate pebbles to boulders adjacent to hammer. H) Bedding-cleavage relationships at Omutirapo. Pervasive slaty cleavage is well developed at this locality. Scales: coin is 20.5 mm in diameter, hammer is 279 mm long.
Published: 29 May 2018
Fig. 6.— Outcrop expression of Chuos Formation diamictites in northern Namibia at Ghaub–Varianto (A–F) and Omutirapo (G, H). See Figure 5 for stratigraphic context. A) High-strain zone with attenuated clasts. B) Small, asymmetric fold with sense of shear indicated. C) Clast with asymmetric
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Paired thin-section photograph and interpretation of Chuos Formation microstructures at Ghaub–Varianto (Parts A–C) and Omutirapo ( Part D). Refer to Figure 5 for stratigraphic context. A) Lower ductile zone: well developed subhorizontal fabric and abundant rotational deformation structures (turbate structures, asymmetric boudins, clast dispersion tails, and asymmetric pressure shadows). Microstructures support top-to-the-NW shear sense. B) Middle brittle zone: section characterized by fractured and crushed quartz grains (white) and magnetite crystals (black). Fractured surfaces can be traced between adjacent clasts, akin to a “jig-saw” pattern, indicating in situ clast breakage. Sense of deformation cannot be ascertained. C) Upper ductile zone: microstructures are highly attenuated, defined by the predominance of sheared clast boudins. These features, alongside asymmetrical pressure shadows and rare rotational turbates, support top-to-the-NW deformation. D) Thin section from Omutirapo showing much more poorly developed shearing, largely limited to pinching and swelling of grain bands and rare rotational deformation structures. Note cleavage crosscutting primary fabric at high angle.
Published: 29 May 2018
Fig. 7.— Paired thin-section photograph and interpretation of Chuos Formation microstructures at Ghaub–Varianto (Parts A–C) and Omutirapo ( Part D). Refer to Figure 5 for stratigraphic context. A) Lower ductile zone: well developed subhorizontal fabric and abundant rotational deformation
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Columnar sections of the Chuos Formation diamictite wedge in the southwestern half of the Vrede south dome (Fig. 10), showing its relations to the Ugab Subgroup, to the Rasthof and Narachaams Formations of the nonglacial Abenab Subgroup (Cryogenian), to the Marinoan glacial erosion surface at the base of the Tsumeb Subgroup, and to the erosional disconformity at the base of the syn-orogenic Kuiseb Formation (Mulden Group). Draping of the Tsumeb Subgroup over the Chuos wedge reflects differential compaction of the argillaceous Narachaams Formation. Decompaction would yield a flatter Marinoan glacial surface beneath the Tsumeb Subgroup. Vertical datum is the same as Figure 15. The apparent bilateral symmetry of the Chuos wedge is an artifact of the curved line of columns (Fig. 10). Field number for each section is shown near the column number.
Published: 01 June 2017
Figure 16. Columnar sections of the Chuos Formation diamictite wedge in the southwestern half of the Vrede south dome ( Fig. 10 ), showing its relations to the Ugab Subgroup, to the Rasthof and Narachaams Formations of the nonglacial Abenab Subgroup (Cryogenian), to the Marinoan glacial erosion
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Bar graph of syn-glacial Chuos Formation stratigraphic thicknesses in 88 columnar sections (including 38 from this study) measured by the authors in northern Namibia, in order of increasing thickness from left to right.
Published: 01 June 2017
Figure 1. Bar graph of syn-glacial Chuos Formation stratigraphic thicknesses in 88 columnar sections (including 38 from this study) measured by the authors in northern Namibia, in order of increasing thickness from left to right.
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Ferruginous facies of the Chuos Formation, Namibia. A: Lamination within cherty ironstone. Diameter of coin is 23 mm. B: Rare lonestone within laminated iron formation. Diameter of coin is 23 mm. C: Laminated iron formation beds overlain and underlain by massive diamictite. Hammer is 28 cm long. D: The Chuos Formation of Mitten fold, Damara Belt (20.6375°S, 15.1125°E); the ferruginous (Ferr.) facies occupy a depression on an erosional unconformity.
Published: 01 November 2016
Figure 2. Ferruginous facies of the Chuos Formation, Namibia. A: Lamination within cherty ironstone. Diameter of coin is 23 mm. B: Rare lonestone within laminated iron formation. Diameter of coin is 23 mm. C: Laminated iron formation beds overlain and underlain by massive diamictite. Hammer is 28
Journal Article
Published: 01 March 2011
South African Journal of Geology (2011) 114 (1): 57–76.
... with regional profiles in the southern Central Zone would indicate that it is hosted by the Etusis Formation (Fe-rich feldspar-quartz rocks) of the Nosib Group, in a condensed stratigraphic section of the supergroup, and not the Chuos Formation (diamictite, turbidite and thin iron-formation layers...
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Journal Article
Published: 29 May 2018
Journal of Sedimentary Research (2018) 88 (5): 659–677.
...Fig. 5.— Simple composite sedimentary log of the Chuos Formation in the Ghaub and Varianto Farm areas of northern Namibia (see Fig. 1 B and C for location). The positions of both outcrop photographs ( Fig. 6 ) and thin-section interpretations ( Figs. 7 , 8 ) are shown. From Busfield and Le...
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Journal Article
Journal: Geology
Published: 21 October 2020
Geology (2021) 49 (3): 263–267.
...D.P. Le Heron; M.E. Busfield; C. Kettler Abstract Dropstones of ice-rafted origin are typically cited as key cold-climate evidence in Cryogenian strata and, according to conventional wisdom, should not occur in postglacial, warm-water carbonates. In Namibia, the Chuos Formation (early Cryogenian...
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Columnar sections of the lower Naauwpoort(?) and Chuos Formations in the Toekoms syn-glacial half graben (see Fig. 17 and satellite view inset for locations). Vertical datum (0 m) is the base of the Rasthof Formation cap limestone. Note the thin glacigenic diamictite directly beneath the cap limestone in sections K–R inclusive. TBF is the Toekoms border fault, an inferred normal-sense growth-fault detachment. Heavy dotted lines divide the mini-basin into four approximately isochronous units: (1) basal conglomerate unit, (2) main diamictite-bearing unit, (3) siltstone with coarse-grained clastics, and (4) siltstone with turbidites, ferruginized (red dots) distally from the TBF, and dropstones (see satellite inset). Note the shift in the locus of maximum accumulation from TBF proximal to TBF distal over time (Fig. 21). Field number for each section is shown beneath each column. See Figure 17 for inset coordinates.
Published: 01 June 2017
Figure 19. Columnar sections of the lower Naauwpoort(?) and Chuos Formations in the Toekoms syn-glacial half graben (see Fig. 17 and satellite view inset for locations). Vertical datum (0 m) is the base of the Rasthof Formation cap limestone. Note the thin glacigenic diamictite directly beneath
Series: Geological Society, London, Special Publications
Published: 01 January 2007
DOI: 10.1144/SP286.7
EISBN: 9781862395343
... Abstract The lower cap carbonate (Rasthof Formation) overlies Neoproterozoic glacial deposits (Chuos Formation) and is exposed in the Khowarib-Warmquelle area in Northern Namibia. The basal 14.2 m part of the Rasthof Formation (total about 220 m) consists of the carbonate rhythmite...
Journal Article
Published: 01 June 2001
South African Journal of Geology (2001) 104 (2): 115–136.
... with thinned continental crust. In the Windhoek Rift Zone, terrestrial conditions prevailed and the newly deposited rift sequences were subjected to erosion. Succeeding the primary rifting was the Chuos Formation glacial/marine event, which produced thick deposits along the northern and western margins...
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Journal Article
Journal: Geology
Published: 01 January 2002
Geology (2002) 30 (1): 35–38.
...D.J. Condon; A.R. Prave; D.I. Benn Abstract Stratigraphically discrete glacigenic dropstone intervals have been identified within six separate Neoproterozoic glaciomarine successions: the ca. 720 Ma Chuos Formation (southwestern Congo craton) and Surprise Diamictite (southwestern Laurentia), the ca...
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Field images from the Omutirapo springs area. See Figures 5 and 6 for column locations. (A) Massive diamictite with clasts of dolomite, quartz arenite, and basement grantitoid; Chuos Formation, column 7. Pen (circled) is 15 cm long. Note the subrounded clasts, consistent with subglacial (not supraglacial) transport. (B) Sheared diamictite in which soft-sediment shear banding (S1) is transected by tectonic cleavage (S2); Chuos Formation, column 7. Hammer handle is 33 cm long. (C) Laminated siltstone with ice-rafted dropstones (arrows) of dolomite and quartz arenite; Chuos Formation, column 7. (D) Monomict breccia and conglomerate of stromatolitic dolomite from the directly underlying Devede Formation forms the basal meter of the Chuos Formation in the paleovalley; column 7. (E) Quartz-arenite cobble with multiple directions of glacial striae from a massive diamictite high in section; column 5. Coin is 2 cm in diameter. (F) Looking north toward the north wall of the paleovalley between columns 7 and 9. Dashed line is the incisement surface. Chuos Formation (unit Ac) in foreground is directly on strike with Devede Formation (unit Od) dolomite in background.
Published: 01 June 2017
Figure 8. Field images from the Omutirapo springs area. See Figures 5 and 6 for column locations. (A) Massive diamictite with clasts of dolomite, quartz arenite, and basement grantitoid; Chuos Formation, column 7. Pen (circled) is 15 cm long. Note the subrounded clasts, consistent
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Vertical satellite view of the south end of the Vrede south dome, showing thickening of Sturtian diamictite in the Chuos Formation (unit Ac) and the locations of columnar sections 2–5 and C–L. White dashed line indicates the thin Rasthof Formation (cap limestone) draping the Chuos Formation, which is truncated by the Ediacaran Karibib Formation (unit Tk) in columns E–G. Other units: Ut—marble tectonite; Uc—carbonate-facies Ugab Subgroup; An—Narachaams Formation (Figs. 11C–11D); Mk—syn-orogenic Kuiseb Formation. As drawn, unit Tk includes up to 5.5 m of Marinoan diamictite (Ghaub Formation) as in column F (Fig. 13). The pale band indicated by asterisks in the upper Chuos Formation corresponds to carbonate diamictite in columns F and G (Fig. 16).
Published: 01 June 2017
Figure 14. Vertical satellite view of the south end of the Vrede south dome, showing thickening of Sturtian diamictite in the Chuos Formation (unit Ac) and the locations of columnar sections 2–5 and C–L. White dashed line indicates the thin Rasthof Formation (cap limestone) draping the Chuos
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(A) Stratigraphy of the Otavi Group, Namibia. Maximum age constraint for the Chuos Formation, 747 ± 2 Ma, is based on U-Pb dating of Askevold Formation volcanics in the Ombombo Subgroup (Hoffmann et al., 2004). Upper glacial unit, Ghaub Formation, exhibits a 635 ± 1 Ma depositional age from U-Pb dating of ash beds (Hoffman et al., 1996). (B) Summary sedimentary logs of the uppermost part of the Chuos Formation (base not shown) and the lower part of the Rasthof Formation at both Omutirapo and Rasthof Farm. VC—very coarse.
Published: 21 October 2020
Figure 2. (A) Stratigraphy of the Otavi Group, Namibia. Maximum age constraint for the Chuos Formation, 747 ± 2 Ma, is based on U-Pb dating of Askevold Formation volcanics in the Ombombo Subgroup ( Hoffmann et al., 2004 ). Upper glacial unit, Ghaub Formation, exhibits a 635 ± 1 Ma depositional
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Columnar sections of the Ombombo Subgroup (Beesvlakte, Devede, and Okakuyu Formations) and Chuos Formation in the Omutirapo springs area, documenting incision of the Sturtian paleovalley. Vertical datum (0 m) is the base of the Rasthof Formation cap carbonate. (A) Chuos Formation sections (see Fig. 5 for locations) projected without vertical exaggeration onto a 003° azimuth, or normal to the pre-Chuos growth fault between sections 6 and 7 shown in B. (B) Sections positioned schematically along the SSW–NNE outcrop belt (Fig. 4) with 12.3× vertical exaggeration to show lithologic units (described in Supplemental Tables S2 [footnote 2] and S3 [footnote 3]). Field number for each section is shown beneath the column number. The white box in column 12 is undifferentiated dolostone. The orange band within the Devede Formation is a sandstone-conglomerate lithosome.
Published: 01 June 2017
Figure 6. Columnar sections of the Ombombo Subgroup (Beesvlakte, Devede, and Okakuyu Formations) and Chuos Formation in the Omutirapo springs area, documenting incision of the Sturtian paleovalley. Vertical datum (0 m) is the base of the Rasthof Formation cap carbonate. (A) Chuos Formation