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P. F. Hoffman - One of the best experts on this subject based on the ideXlab platform.
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Chapter 36 Neoproterozoic glacial record in the Mackenzie Mountains, northern Canadian Cordillera
2016Co-Authors: P. F. Hoffman, G. P. HalversonAbstract:In the Mackenzie Mountains, an arcuate foreland thrust-fold belt of Late Cretaceous–Paleocene age in the northern Canadian Cordillera, two discrete glacial–periglacial sequences of Cryogenian age (the Rapitan Group and the Stelfox Member of the Ice Brook Fm.) are separated by c. 1.0 km of non-glacial strata. The older Rapitan Diamictite occurs in an amagmatic rift basin; the younger Stelfox Diamictite occurs on a passive-margin continental slope. The Rapitan Group consists of three formations. The lower Mount Berg Fm. is a complex of Diamictites and conglomerates of limited extent. The middle Sayunei Fm. is a thick sequence of maroon-coloured mudrocks hosting innumerable graded layers of silt- and fine-grained sandstone. It lacks wave- or traction current-generated bedforms, and is lightly sprinkled with granule aggregates (‘till pellets’) and lonestones of dolostone and rare extrabasinal granitoids. It is capped by a hematitic Fe-formation that was reworked into the disconformably overlying Shezal Diamictite. The Shezal Fm. is a complex of olive-green coloured boulder Diamictites with subordinate, dark-grey shales, siltstones and parallel-sided sandstones. Some of the boulders are faceted and striated, and include dolostone, quartzite, siltstone and gabbro in declining order of abundance. Diamictite terminates abruptly at the top of the Shezal Fm., which is sharply overlain by dark shales or by
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an ice grounding line wedge from the ghaub glaciation 635 ma on the distal foreslope of the otavi carbonate platform namibia and its bearing on the snowball earth hypothesis
Geological Society of America Bulletin, 2011Co-Authors: Eugene W Domack, P. F. HoffmanAbstract:Our detailed examination of the Ghaub Formation (possibly 635 Ma) on the distal foreslope of the Otavi carbonate platform is part of a regional study of the Congo paleocontinental margin in northwestern Namibia. Detrital carbonates of the Ghaub Formation disconformably overlie the Franni-aus Member of the Ombaatjie Formation, a coarsening-upward stack of carbonate turbidites and oolite-clast debris-flow breccias interpreted to be a glacioeustatic falling-stand wedge. Within the main Ghaub Formation, carbonate Diamictites are interleaved with mesoscale, laminated to cross-laminated (climbing rippled) grainstones and mudstones, and conglomeratic carbonates. Amalgamation of Diamictite units is observed where interleaved facies (grainstones/mudstones) are laterally discontinuous due to reactivation of erosion, followed by renewed deposition. The Diamictite package is progradational overall and 80 m thick on average. It is overlain by the 5–15-m-thick Bethanis Member, which is unique in its lateral continuity, composite fining-upward trend, and distinctive interbedding of turbidite grainstones, argillaceous siltstones, climbing-rippled mudstones, and meter-scale stromatolite dropstones. Dropstones are ubiquitous within the finer-grained (Ghaub) lithofacies, and their presence, along with the facies context for subglacial and near grounding-line deposition, indicates a glacigenic origin for the Ghaub Formation, despite its subtropical paleolatitude and distal foreslope setting. We infer a glacial maximum represented by the sub-Ghaub disconformity, followed by the main Ghaub interval when an ice grounding line on the distal foreslope experienced abrupt step backs and readvances of limited magnitude, terminated by the Bethanis episode of unusually widespread iceberg calving and slope instability. The Bethanis Member is overlain conformably by the Keilberg Member of the Maieberg Formation. Reconstruction of the foreslope places the Ghaub grounding-line wedge >1.3 km vertically below the rim of the platform, implying an enormous base-level change upon deglaciation, when the platform was drowned below wave base for a period far exceeding the time scale for isostatic adjustment. The magnitude of base-level change supports the pan-glacial hypothesis that dynamic (thick) ice sheets existed simultaneously on virtually all continents. The snowball hypothesis that the oceans were also covered by glacial ice (sea-glacier) provides a simple explanation for the main Ghaub-to-Bethanis transition—terminal deglaciation was triggered by collapse of the sea-glacier.
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chapter 36 neoproterozoic glacial record in the mackenzie mountains northern canadian cordillera
Geological Society London Memoirs, 2011Co-Authors: P. F. Hoffman, G. P. HalversonAbstract:Abstract In the Mackenzie Mountains, an arcuate foreland thrust-fold belt of Late Cretaceous–Paleocene age in the northern Canadian Cordillera, two discrete glacial–periglacial sequences of Cryogenian age (the Rapitan Group and the Stelfox Member of the Ice Brook Fm.) are separated by c. 1.0 km of non-glacial strata. The older Rapitan Diamictite occurs in an amagmatic rift basin; the younger Stelfox Diamictite occurs on a passive-margin continental slope. The Rapitan Group consists of three formations. The lower Mount Berg Fm. is a complex of Diamictites and conglomerates of limited extent. The middle Sayunei Fm. is a thick sequence of maroon-coloured mudrocks hosting innumerable graded layers of silt- and fine-grained sandstone. It lacks wave- or traction current-generated bedforms, and is lightly sprinkled with granule aggregates (‘till pellets’) and lonestones of dolostone and rare extrabasinal granitoids. It is capped by a hematitic Fe-formation that was reworked into the disconformably overlying Shezal Diamictite. The Shezal Fm. is a complex of olive-green coloured boulder Diamictites with subordinate, dark-grey shales, siltstones and parallel-sided sandstones. Some of the boulders are faceted and striated, and include dolostone, quartzite, siltstone and gabbro in declining order of abundance. Diamictite terminates abruptly at the top of the Shezal Fm., which is sharply overlain by dark shales or by 13 C-depleted limestone with graded bedding. The Stelfox Member is dominated by non-stratified, carbonate-clast Diamictite with faceted and striated clasts, locally associated with subordinate, well-laminated shales containing till pellets and ice-rafted dropstones. It is thin or absent on the palaeocontinental shelf, but thickens seaward (southwestward) on the palaeocontinental slope. A thin clay drape separates it from a laterally continuous post-glacial ‘cap’ dolostone, which is a very pale coloured, micro- to macropeloidal dolostone with low-angle cross-laminae, giant wave ripples and local bioherms of corrugated stomatolites. In the NW, the dolostone is followed by reddish and greenish marls, followed by black shale of the Sheepbed Fm. In the SE, the dolostone is overlain by pink or grey limestones with well-developed sea-floor cements pseudomorphic after aragonite. In this area, the top of the dolostone is ferruginous and contains digitate rosettes of sea-floor barite cement, variably calcitized. The dolostone–limestone contact is perfectly conformable, and synclinal structures previously intepreted as karst features are tectonic in origin. The grand mean palaeomagnetic pole for the well-studied Franklin Large Igneous Province ( c. 718 Ma) of Arctic Laurentia, coeval with the basal Rapitan Group in the Mount Harper area, Yukon Territory, places the Mackenzie Mountains firmly in the tropics, at 18±3°N palaeolatitude, at the onset of the Rapitan glaciation. Carbon (δ 13 C), oxygen (δ 18 O) and strontium ( 87 Sr/ 86 Sr) isotopes have been measured in carbonates bracketing the Rapitan and Stelfox Diamictites. Sulphur isotope data (δ 34 S) have been obtained from carbonate-associated sulphate and barite above the younger Diamictite, and calcium isotope data (δ 44 Ca) from the younger carbonate itself. The results are broadly consistent with data from other areas. Iron isotope (δ 57 Fe) and cerium anomaly (Ce/Ce*) values increase systematically upwards through the Sayunei Fe-formation, supporting an interpretation that deposition occurred within a redox chemocline through which the basin floor descended as a consequence of isostatic loading by the advancing Shezal ice sheet. Supplementary material: Data are available at http://www.geolsoc.org.uk/SUP18470.
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the marinoan glaciation neoproterozoic in northeast svalbard
Basin Research, 2004Co-Authors: G. P. Halverson, Adam C Maloof, P. F. HoffmanAbstract:Two separate and distinct Diamictite-rich units occur in the mixed carbonate- siliciclastic Polarisbreen Group, which comprises the top kilometer of47 km of Neoproterozoic strata in the northeast of the Svalbard archipelago.The platformal succession accumulated on the windward, tropical to subtropical margin of Laurentia.The older Petrovbreen Member is a thin glacimarine Diamictite that lacks a cap carbonate. It contains locally derived clasts and overlies a regional karstic disconformity that was directly preceded by a large (410% )n egatived 13 C anomaly in the underlying shallow-marine carbonates.This anomaly is homologous to anomalies in Australia, Canada and Namibia that precede the Marinoan glaciation.The younger and thicker Wilsonbreen Formation comprises terrestrial ice- contact deposits. It contains abundant extrabasinal clasts and is draped by a transgressive cap dolostone 3^18 m thick.The cap dolostone is replete with sedimentary features strongly associated with post-Marinoan caps globally, and its isotopic pro¢le is virtually identical to that of other Marinoan cap dolostones. From the inter-regional perspective, the two Diamictite-rich units in the Polarisbreen Group should represent the ¢rst and ¢nal phases of the Marinoan glaciation. Above the Petrovbreen Diamictite are 200 m of ¢nely laminated, dark olive- coloured rhythmites (MacDonaldryggen Member) interpreted here to represent suspension deposits beneath shorefast, multi-annual sea ice (sikussak). Above the suspension deposits and below the Wilsonbreen Diamictites is ao30-m-thick regressive sequence (Slangen Member) composed of dolomite grainstone and evaporitic supratidal microbialaminite.We interpret this sabkha-like lagoonal sequence as an oasis deposit that precipitated when local marine ice melted away under greenhouse forcing, but while the tropical ocean remained covered due to in£ow of sea glaciers from higher latitudes. It appears that the Polarisbreen Group presents an unusually complete record of the Marinoan snowball glaciation.
G. P. Halverson - One of the best experts on this subject based on the ideXlab platform.
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Chapter 36 Neoproterozoic glacial record in the Mackenzie Mountains, northern Canadian Cordillera
2016Co-Authors: P. F. Hoffman, G. P. HalversonAbstract:In the Mackenzie Mountains, an arcuate foreland thrust-fold belt of Late Cretaceous–Paleocene age in the northern Canadian Cordillera, two discrete glacial–periglacial sequences of Cryogenian age (the Rapitan Group and the Stelfox Member of the Ice Brook Fm.) are separated by c. 1.0 km of non-glacial strata. The older Rapitan Diamictite occurs in an amagmatic rift basin; the younger Stelfox Diamictite occurs on a passive-margin continental slope. The Rapitan Group consists of three formations. The lower Mount Berg Fm. is a complex of Diamictites and conglomerates of limited extent. The middle Sayunei Fm. is a thick sequence of maroon-coloured mudrocks hosting innumerable graded layers of silt- and fine-grained sandstone. It lacks wave- or traction current-generated bedforms, and is lightly sprinkled with granule aggregates (‘till pellets’) and lonestones of dolostone and rare extrabasinal granitoids. It is capped by a hematitic Fe-formation that was reworked into the disconformably overlying Shezal Diamictite. The Shezal Fm. is a complex of olive-green coloured boulder Diamictites with subordinate, dark-grey shales, siltstones and parallel-sided sandstones. Some of the boulders are faceted and striated, and include dolostone, quartzite, siltstone and gabbro in declining order of abundance. Diamictite terminates abruptly at the top of the Shezal Fm., which is sharply overlain by dark shales or by
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chapter 36 neoproterozoic glacial record in the mackenzie mountains northern canadian cordillera
Geological Society London Memoirs, 2011Co-Authors: P. F. Hoffman, G. P. HalversonAbstract:Abstract In the Mackenzie Mountains, an arcuate foreland thrust-fold belt of Late Cretaceous–Paleocene age in the northern Canadian Cordillera, two discrete glacial–periglacial sequences of Cryogenian age (the Rapitan Group and the Stelfox Member of the Ice Brook Fm.) are separated by c. 1.0 km of non-glacial strata. The older Rapitan Diamictite occurs in an amagmatic rift basin; the younger Stelfox Diamictite occurs on a passive-margin continental slope. The Rapitan Group consists of three formations. The lower Mount Berg Fm. is a complex of Diamictites and conglomerates of limited extent. The middle Sayunei Fm. is a thick sequence of maroon-coloured mudrocks hosting innumerable graded layers of silt- and fine-grained sandstone. It lacks wave- or traction current-generated bedforms, and is lightly sprinkled with granule aggregates (‘till pellets’) and lonestones of dolostone and rare extrabasinal granitoids. It is capped by a hematitic Fe-formation that was reworked into the disconformably overlying Shezal Diamictite. The Shezal Fm. is a complex of olive-green coloured boulder Diamictites with subordinate, dark-grey shales, siltstones and parallel-sided sandstones. Some of the boulders are faceted and striated, and include dolostone, quartzite, siltstone and gabbro in declining order of abundance. Diamictite terminates abruptly at the top of the Shezal Fm., which is sharply overlain by dark shales or by 13 C-depleted limestone with graded bedding. The Stelfox Member is dominated by non-stratified, carbonate-clast Diamictite with faceted and striated clasts, locally associated with subordinate, well-laminated shales containing till pellets and ice-rafted dropstones. It is thin or absent on the palaeocontinental shelf, but thickens seaward (southwestward) on the palaeocontinental slope. A thin clay drape separates it from a laterally continuous post-glacial ‘cap’ dolostone, which is a very pale coloured, micro- to macropeloidal dolostone with low-angle cross-laminae, giant wave ripples and local bioherms of corrugated stomatolites. In the NW, the dolostone is followed by reddish and greenish marls, followed by black shale of the Sheepbed Fm. In the SE, the dolostone is overlain by pink or grey limestones with well-developed sea-floor cements pseudomorphic after aragonite. In this area, the top of the dolostone is ferruginous and contains digitate rosettes of sea-floor barite cement, variably calcitized. The dolostone–limestone contact is perfectly conformable, and synclinal structures previously intepreted as karst features are tectonic in origin. The grand mean palaeomagnetic pole for the well-studied Franklin Large Igneous Province ( c. 718 Ma) of Arctic Laurentia, coeval with the basal Rapitan Group in the Mount Harper area, Yukon Territory, places the Mackenzie Mountains firmly in the tropics, at 18±3°N palaeolatitude, at the onset of the Rapitan glaciation. Carbon (δ 13 C), oxygen (δ 18 O) and strontium ( 87 Sr/ 86 Sr) isotopes have been measured in carbonates bracketing the Rapitan and Stelfox Diamictites. Sulphur isotope data (δ 34 S) have been obtained from carbonate-associated sulphate and barite above the younger Diamictite, and calcium isotope data (δ 44 Ca) from the younger carbonate itself. The results are broadly consistent with data from other areas. Iron isotope (δ 57 Fe) and cerium anomaly (Ce/Ce*) values increase systematically upwards through the Sayunei Fe-formation, supporting an interpretation that deposition occurred within a redox chemocline through which the basin floor descended as a consequence of isostatic loading by the advancing Shezal ice sheet. Supplementary material: Data are available at http://www.geolsoc.org.uk/SUP18470.
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cottons breccia of king island tasmania glacial or non glacial cryogenian or ediacaran
Precambrian Research, 2009Co-Authors: Paul Hoffman, Clive R Calver, G. P. HalversonAbstract:Abstract The Cottons Breccia of King Island, Tasmania, is a 100-m-thick carbonate-clast Diamictite traditionally interpreted as the product of a Cryogenian or Ediacaran glaciation. It was recently reinterpreted as a mass-flow deposit, unrelated to glaciation, within an active rift basin. We reaffirm the glacial–periglacial interpretation on the basis of sedimentary facies, internal facies relations, clast lithology and isotopic composition, clast fabric analysis, and consistent stratigraphic position beneath a typical post-glacial cap dolostone. The Cumberland Creek Dolostone closely resembles basal Ediacaran cap dolostones world-wide in terms of colour, texture, sedimentary structures and isotopic characteristics. Because it was deposited above storm wave-base, differences in δ 13 C between closely adjacent sections suggest diachronous deposition during post-glacial marine transgression of a basin with steep local topography. This is compatible with an active rift basin in which glacigenic Diamictites of the end-Cryogenian (Marinoan) pan-glacial episode were lodged.
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the marinoan glaciation neoproterozoic in northeast svalbard
Basin Research, 2004Co-Authors: G. P. Halverson, Adam C Maloof, P. F. HoffmanAbstract:Two separate and distinct Diamictite-rich units occur in the mixed carbonate- siliciclastic Polarisbreen Group, which comprises the top kilometer of47 km of Neoproterozoic strata in the northeast of the Svalbard archipelago.The platformal succession accumulated on the windward, tropical to subtropical margin of Laurentia.The older Petrovbreen Member is a thin glacimarine Diamictite that lacks a cap carbonate. It contains locally derived clasts and overlies a regional karstic disconformity that was directly preceded by a large (410% )n egatived 13 C anomaly in the underlying shallow-marine carbonates.This anomaly is homologous to anomalies in Australia, Canada and Namibia that precede the Marinoan glaciation.The younger and thicker Wilsonbreen Formation comprises terrestrial ice- contact deposits. It contains abundant extrabasinal clasts and is draped by a transgressive cap dolostone 3^18 m thick.The cap dolostone is replete with sedimentary features strongly associated with post-Marinoan caps globally, and its isotopic pro¢le is virtually identical to that of other Marinoan cap dolostones. From the inter-regional perspective, the two Diamictite-rich units in the Polarisbreen Group should represent the ¢rst and ¢nal phases of the Marinoan glaciation. Above the Petrovbreen Diamictite are 200 m of ¢nely laminated, dark olive- coloured rhythmites (MacDonaldryggen Member) interpreted here to represent suspension deposits beneath shorefast, multi-annual sea ice (sikussak). Above the suspension deposits and below the Wilsonbreen Diamictites is ao30-m-thick regressive sequence (Slangen Member) composed of dolomite grainstone and evaporitic supratidal microbialaminite.We interpret this sabkha-like lagoonal sequence as an oasis deposit that precipitated when local marine ice melted away under greenhouse forcing, but while the tropical ocean remained covered due to in£ow of sea glaciers from higher latitudes. It appears that the Polarisbreen Group presents an unusually complete record of the Marinoan snowball glaciation.
Vladimir I Davydov - One of the best experts on this subject based on the ideXlab platform.
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middle permian u pb zircon ages of the glacial deposits of the atkan formation ayan yuryakh anticlinorium magadan province ne russia their significance for global climatic interpretations
Gondwana Research, 2016Co-Authors: Mark D Schmitz, Vladimir I Davydov, A S Biakov, John L Isbell, James L Crowley, I L VedernikovAbstract:Abstract The Atkan Formation in the Ayan-Yuryakh anticlinorium, Magadan province, northeastern Russia, is of great interest because of the occurrence of deposits of apparent “dropstones” and “ice rafted debris” that have been previously interpreted as glacial. Two high-precision U–Pb zircon ages, one for an intercalated volcanic tuff (262.5 ± 0.2 Ma) and the other for a boulder clast (269.8 ± 0.1 Ma) within a Diamictite of the Atkan Formation, constrain the age of the Atkan Formation as Guadalupian (middle Permian). Sedimentologic study of the Atkan Formation casts doubt on the glacial nature of the Diamictites. Deposition of rocks of the Atkan Formation temporally correlates with the Capitanian interglacial event in the southern hemisphere that recently was calibrated with high precision CA-TIMS. The previously proposed climate proxy record based upon warm-water foraminifera, which corresponds closely to global climate fluctuations, is compared with the glacial record of eastern Australia and indicates that the Capitanian was a time of globally warm climate. The sedimentology of Atkan Formation, the record of diversification of both fusulinids and rugosa corals, global sea-water temperature, and sea-level fluctuations agree well with high latitude paleoclimate records in northeastern Russia and eastern Australia. Major components of the Atkan Formation, the volcanic rocks, are syngenetic with the sedimentation process. The volcanic activity in the nearby regions during middle–late Permian was quite extensive.
I L Vedernikov - One of the best experts on this subject based on the ideXlab platform.
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middle permian u pb zircon ages of the glacial deposits of the atkan formation ayan yuryakh anticlinorium magadan province ne russia their significance for global climatic interpretations
Gondwana Research, 2016Co-Authors: Mark D Schmitz, Vladimir I Davydov, A S Biakov, John L Isbell, James L Crowley, I L VedernikovAbstract:Abstract The Atkan Formation in the Ayan-Yuryakh anticlinorium, Magadan province, northeastern Russia, is of great interest because of the occurrence of deposits of apparent “dropstones” and “ice rafted debris” that have been previously interpreted as glacial. Two high-precision U–Pb zircon ages, one for an intercalated volcanic tuff (262.5 ± 0.2 Ma) and the other for a boulder clast (269.8 ± 0.1 Ma) within a Diamictite of the Atkan Formation, constrain the age of the Atkan Formation as Guadalupian (middle Permian). Sedimentologic study of the Atkan Formation casts doubt on the glacial nature of the Diamictites. Deposition of rocks of the Atkan Formation temporally correlates with the Capitanian interglacial event in the southern hemisphere that recently was calibrated with high precision CA-TIMS. The previously proposed climate proxy record based upon warm-water foraminifera, which corresponds closely to global climate fluctuations, is compared with the glacial record of eastern Australia and indicates that the Capitanian was a time of globally warm climate. The sedimentology of Atkan Formation, the record of diversification of both fusulinids and rugosa corals, global sea-water temperature, and sea-level fluctuations agree well with high latitude paleoclimate records in northeastern Russia and eastern Australia. Major components of the Atkan Formation, the volcanic rocks, are syngenetic with the sedimentation process. The volcanic activity in the nearby regions during middle–late Permian was quite extensive.
A S Biakov - One of the best experts on this subject based on the ideXlab platform.
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middle permian u pb zircon ages of the glacial deposits of the atkan formation ayan yuryakh anticlinorium magadan province ne russia their significance for global climatic interpretations
Gondwana Research, 2016Co-Authors: Mark D Schmitz, Vladimir I Davydov, A S Biakov, John L Isbell, James L Crowley, I L VedernikovAbstract:Abstract The Atkan Formation in the Ayan-Yuryakh anticlinorium, Magadan province, northeastern Russia, is of great interest because of the occurrence of deposits of apparent “dropstones” and “ice rafted debris” that have been previously interpreted as glacial. Two high-precision U–Pb zircon ages, one for an intercalated volcanic tuff (262.5 ± 0.2 Ma) and the other for a boulder clast (269.8 ± 0.1 Ma) within a Diamictite of the Atkan Formation, constrain the age of the Atkan Formation as Guadalupian (middle Permian). Sedimentologic study of the Atkan Formation casts doubt on the glacial nature of the Diamictites. Deposition of rocks of the Atkan Formation temporally correlates with the Capitanian interglacial event in the southern hemisphere that recently was calibrated with high precision CA-TIMS. The previously proposed climate proxy record based upon warm-water foraminifera, which corresponds closely to global climate fluctuations, is compared with the glacial record of eastern Australia and indicates that the Capitanian was a time of globally warm climate. The sedimentology of Atkan Formation, the record of diversification of both fusulinids and rugosa corals, global sea-water temperature, and sea-level fluctuations agree well with high latitude paleoclimate records in northeastern Russia and eastern Australia. Major components of the Atkan Formation, the volcanic rocks, are syngenetic with the sedimentation process. The volcanic activity in the nearby regions during middle–late Permian was quite extensive.