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Rasthof Formation

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Series: Geological Society, London, Special Publications
Published: 01 January 2015
DOI: 10.1144/SP418.7
EISBN: 9781862397163
... Abstract The Rasthof Formation is a mid-Cryogenian cap carbonate succession deposited in Namibia following the Sturtian glaciation. It includes a microbial member, typically >100 m thick. This member exhibits contorted intervals, and is divisible into two informally defined units. The lower...
FIGURES | View All (8)
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Geological map of the Rasthof Formation showing the fossiliferous localities. Inset map of Namibia in southern Africa shows mapped area in the north. Geological map shows the four localities: Ombepera  =  A, South Ombepera  =  B, Okaaru  =  C, and Ongongo  =  D. Stratigraphic names used in this paper are provided below the key. Modified from P. Hoffman and Pruss et al. (2010).
Published: 01 February 2013
FIGURE 1— Geological map of the Rasthof Formation showing the fossiliferous localities. Inset map of Namibia in southern Africa shows mapped area in the north. Geological map shows the four localities: Ombepera  =  A, South Ombepera  =  B, Okaaru  =  C, and Ongongo  =  D. Stratigraphic names used
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Stratigraphic columns of the Rasthof Formation at the four localities. Colored dots at Ombepera and South Ombepera mark the stratigraphic positions of fossiliferous and unfossiliferous samples, respectively. Fossiliferous samples from Ongongo and Okaaru described in Bosak et al. (2011a, 2012) are shown at the appropriate stratigraphic horizons.
Published: 01 February 2013
FIGURE 2— Stratigraphic columns of the Rasthof Formation at the four localities. Colored dots at Ombepera and South Ombepera mark the stratigraphic positions of fossiliferous and unfossiliferous samples, respectively. Fossiliferous samples from Ongongo and Okaaru described in Bosak et al. (2011a
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Representative morphologies of tubular tests from Rasthof Formation (Namibia). All images are scanning electron micrographs. A−E: Tubular tests with transverse constrictions (t) and folds (f). F: Aperture of B showing small mineral grains on exterior and in lumen (arrows). G: Aperture of C showing small mineral grains coating lumen and exterior (arrows). H: Upper terminus of E exposing wall thickness and lumen (arrow). I: Detail of D showing sinuous ridges (r) and larger mineral grains (arrows). J: Tapering end of D (detail) showing transverse constrictions (t). K: Detail of J outlined by white rectangle exposing wall thickness and hollow interior (arrow). Platy mineral grains are visible on surface. Scale bar in E (in μm): 100 in A–E; 25 in F; 8 in G; 30 in H; 20 in I; 14 in J; 6.7 in K.
Published: 01 January 2012
Figure 2. Representative morphologies of tubular tests from Rasthof Formation (Namibia). All images are scanning electron micrographs. A−E: Tubular tests with transverse constrictions ( t ) and folds ( f ). F: Aperture of B showing small mineral grains on exterior and in lumen (arrows). G
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...
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Journal Article
Journal: PALAIOS
Published: 01 February 2013
PALAIOS (2013) 28 (2): 67–79.
...FIGURE 1— Geological map of the Rasthof Formation showing the fossiliferous localities. Inset map of Namibia in southern Africa shows mapped area in the north. Geological map shows the four localities: Ombepera  =  A, South Ombepera  =  B, Okaaru  =  C, and Ongongo  =  D. Stratigraphic names used...
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Journal Article
Journal: Geology
Published: 21 October 2020
Geology (2021) 49 (3): 263–267.
...) contains abundant dropstone-bearing intervals and striated clasts. It is capped by the Rasthof Formation, composed of laminites in its lower portion and microbial carbonates above. These laminites are locally found to contain pebble- and granule-sized lonestones in abundance. At the Omutirapo outcrop...
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Journal Article
Journal: Geology
Published: 01 January 2012
Geology (2012) 40 (1): 67–70.
...Figure 2. Representative morphologies of tubular tests from Rasthof Formation (Namibia). All images are scanning electron micrographs. A−E: Tubular tests with transverse constrictions ( t ) and folds ( f ). F: Aperture of B showing small mineral grains on exterior and in lumen (arrows). G...
FIGURES
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Field images from the syn-glacial half graben on Toekoms farm. (A) View looking southward across the basin from the base of columnar section R (Fig. 19). The prominent hill, 3 km distant, center is an Early Cretaceous flood-basalt outlier (unit Ke), at the base of which the thin black band is the Rasthof Formation (unit Ar) cap limestone. (B) Parallel-laminated silty argillite in the upper part of columnar section N. (C) Ice-rafted dropstones of granodiorite (G) and quartz-arenite (Q) in parallel-laminated silty argillite from the upper part of columnar section N. (D) Graded turbidite beds of quartz arenite in silty argillite in the middle part of columnar section P. (E) Sandy conglomerate from the basal part of columnar section M. (F) Sharp conformable base of the Rasthof Formation cap limestone (unit c) at the top of columnar section Q. Lithologic units: a—basement-clast diamictite with detrital dolomite matrix; b—basement-derived feldspathic greywacke; c—dark-gray micritic limestone; d—quartz-pebble conglomerate interbed. Stratigraphic conformity is implied by the persistence of a thin basement-clast diamictite beneath the Rasthof Formation in sections K–R inclusive.
Published: 01 June 2017
black band is the Rasthof Formation (unit Ar) cap limestone. (B) Parallel-laminated silty argillite in the upper part of columnar section N. (C) Ice-rafted dropstones of granodiorite (G) and quartz-arenite (Q) in parallel-laminated silty argillite from the upper part of columnar section N. (D) Graded
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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
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.
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Composite boron and carbon (B, C) isotope record and paleo-pH reconstruction across Neoproterozoic Chuos and Ghaub glacials and subsequent greenhouse transitions on southern Congo craton in northern Namibia. Rasthof cap carbonate of Chuos glacial includes two separate sections, Fransfontein (closed circles) and Entrance (open circles). Ombaatjie Formation is from eponymous type locality. Keilberg-Maieberg Formation cap sequence of Ghaub glacial and overlying Elandshoek Formation is from Fransfontein section. Gray area marks average B isotope composition and ocean pH conditions of inferred Neoproterozoic climatic normalcy. Arrow indicates inferred transient ocean acidification event. Note that the stratigraphic interval between top of Rasthof Formation and base of Ombaatjie Formation at Fransfontein and at Entrance was not sampled; stratigraphic thicknesses are 14 m and 283 m, respectively. cc—carbonate carbon.
Published: 01 September 2010
of inferred Neoproterozoic climatic normalcy. Arrow indicates inferred transient ocean acidification event. Note that the stratigraphic interval between top of Rasthof Formation and base of Ombaatjie Formation at Fransfontein and at Entrance was not sampled; stratigraphic thicknesses are 14 m and 283 m
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North wall of the Omutirapo paleovalley, viewed from the south. Chuos Formation (unit Ac) thickens southward from 65 to 450 m in the field of view, incised into the Okakuyu (unit Ok) and Devede (unit Od) Formations. Beesvlakte Formation is unit Ob; Rasthof Formation is unit Ar. Note the onlap of Chuos glacial and associated strata against the steep valley wall (half arrow).
Published: 01 June 2017
Figure 7. North wall of the Omutirapo paleovalley, viewed from the south. Chuos Formation (unit Ac) thickens southward from 65 to 450 m in the field of view, incised into the Okakuyu (unit Ok) and Devede (unit Od) Formations. Beesvlakte Formation is unit Ob; Rasthof Formation is unit Ar. Note
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Inclined satellite view looking westward at the north-facing south wall of the Omutirapo paleovalley (see Figs. 4 and 5 for location). Magenta arrow indicates where the Chuos Formation (unit Ac) cuts down steeply across the Okakuyu (unit Ok) and upper Devede (Od) Formations (between columns 2 and 4, Figs. 5, 9). Other units: Ar—Rasthof Formation; Ag—Gruis Formation; Ab—Ombaatjie Formation.
Published: 01 June 2017
columns 2 and 4, Figs. 5 , 9 ). Other units: Ar—Rasthof Formation; Ag—Gruis Formation; Ab—Ombaatjie Formation.
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Fig. 6.
Published: 19 January 2016
of the Rasthof Formation at location a is tentatively interpreted as a lateral ramp. [Colour online.]
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Photomicrographs of walled tests in thin sections of microbialaminites from basal Rasthof Formation at Okaaru (Namibia). Widths (10–15 μm) and lengths (110–400 μm) of tubular structures visible in thin sections are comparable to dimensions of smaller extracted tubular microfossils. A, B: Tubular microfossils are rare. C: Oval walled structures are abundant; hundreds of these morphologies have been extracted from Okaaru locality (Bosak et al., 2011). Scale bars: 100 μm.
Published: 01 January 2012
Figure 1. Photomicrographs of walled tests in thin sections of microbialaminites from basal Rasthof Formation at Okaaru (Namibia). Widths (10–15 μm) and lengths (110–400 μm) of tubular structures visible in thin sections are comparable to dimensions of smaller extracted tubular microfossils. A, B
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Inclined satellite view of the incised Sturtian paleovalley at Omutirapo springs, looking toward the WNW. Magenta arrows indicate the paleovalley walls, 4.3 km apart, defined by the erosive base of the glacigenic Chuos Formation (unit Ac). Wavy line is an intra–Ombombo Subgroup (Tonian) growth fault, which may have localized Sturtian incision. Chuos Formation is 500 m thick in the paleovalley axis (Fig. 7), 10× thicker than outside the paleovalley. Units above the Rasthof Formation (Fig. 4) are not shown for simplicity. Numbered light-blue lines are the measured sections of Figure 6. Unit Qt—Quaternary travertine as in Figure 4.
Published: 01 June 2017
) growth fault, which may have localized Sturtian incision. Chuos Formation is 500 m thick in the paleovalley axis ( Fig. 7 ), 10× thicker than outside the paleovalley. Units above the Rasthof Formation ( Fig. 4 ) are not shown for simplicity. Numbered light-blue lines are the measured sections of Figure
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(A) Outcrop view of section at Rasthof Farm (Namibia), showing vertically inclined strata that young toward the left side. Position of the profile in Figure 2 is shown; i.e., location of the lonestone-bearing strata in the Rasthof Formation. Field of view in foreground is ∼50 m. (B) Dololaminites with abundant lonestones, many of which show evidence for impact structures, with punctured underlying laminations and undisturbed, draping laminations. Note also the presence of a “clast cluster” at the bottom right-hand corner of image. Evidence for normal faults with millimeter-scale offset, capped by undisturbed laminations, is seen throughout the section. (C,D) Quartz granule in disturbed laminations; note also the presence of pyrite (Pyr) throughout. (E) Two examples of completely isolated lonestones within dololaminites, each showing impact structures. Coin diameter is 24 mm. (F) Thin-section image. Upper part is largely undeformed, with evidence for impact structures beneath lonestones and undisturbed, draping laminations. Bottom part of image shows multiple lines of evidence for soft-sediment deformation, including normal fault and intralaminar folds. These features are interpreted as products of early compaction.
Published: 21 October 2020
Figure 4. (A) Outcrop view of section at Rasthof Farm (Namibia), showing vertically inclined strata that young toward the left side. Position of the profile in Figure 2 is shown; i.e., location of the lonestone-bearing strata in the Rasthof Formation. Field of view in foreground is ∼50 m. (B
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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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Autochthonous columnar sections of the Abenab and basal Tsumeb Subgroups on Bethanis farm and across the asynchronous Soutput growth fault and Toekoms border fault (see Fig. 17 for locations). Vertical datum (0 m) is the base of the Keilberg Member (Karibib Formation, Tsumeb Subgroup), also the base of the Ediacaran Period. Soutput fault slip ended by middle Ghaub Formation time, and Toekoms by Rasthof Formation time. Soutput fault was not structurally inverted, likely because its strike nearly parallels the direction of Damaran shortening. Note localized thickening of the Marinoan Ghaub Formation on Bethanis farm. Lack of incision suggests that Ghaub thickening represents a positive topographic feature, unrelated to the Soutput growth fault. Field number for each section is shown beneath each column.
Published: 01 June 2017
), also the base of the Ediacaran Period. Soutput fault slip ended by middle Ghaub Formation time, and Toekoms by Rasthof Formation time. Soutput fault was not structurally inverted, likely because its strike nearly parallels the direction of Damaran shortening. Note localized thickening of the Marinoan
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Stratigraphic relationships and lonestone-bearing strata at Omutirapo, Namibia. (A) Stratigraphic contact between sheared diamictites of the Chuos Formation (below the hammer) and dololaminites of the basal Rasthof Formation (above the hammer). Hammer is ∼30 cm long. (B) Tripartite interval consisting of dololaminites at the base, normally graded packstone-grainstone in the middle, and dololaminites at the top. (C) Approximately 1-m-thick floatstone interval sandwiched between dololaminites. This floatstone interval is the lateral equivalent of the normally graded packstone-grainstone shown in B. (D) Detail of floatstone bed with subrounded to rounded clasts. Coin diameter is 24 mm. (E) Sheared and attenuated clasts at the bottom of the floatstone interval in C (next to the head of the hammer in C).
Published: 21 October 2020
Figure 3. Stratigraphic relationships and lonestone-bearing strata at Omutirapo, Namibia. (A) Stratigraphic contact between sheared diamictites of the Chuos Formation (below the hammer) and dololaminites of the basal Rasthof Formation (above the hammer). Hammer is ∼30 cm long. (B) Tripartite