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Michael J. Jercinovic - One of the best experts on this subject based on the ideXlab platform.

  • th u total pb geochronology of authigenic monazite in the adelaide rift complex south australia and implications for the age of the type sturtian and marinoan Glacial Deposits
    Earth and Planetary Science Letters, 2010
    Co-Authors: Kevin H. Mahan, Brian P. Wernicke, Michael J. Jercinovic
    Abstract:

    The Adelaide rift complex in South Australia contains the type sections for Sturtian and Marinoan Glacial Deposits. The litho- and chemo-stratigraphy of these Deposits play a central role in evaluating global Neoproterozoic ice age hypotheses and Rodinia supercontinent reconstructions, but reliable depositional age constraints have been extremely limited. We report results of in situ Th–U–total Pb (electron microprobe) dating of detrital and authigenic monazite in two samples from the Umberatana Group (Sturtian Holowilena Ironstone and pre-Marinoan Enorama Shale) in the Central Flinders Ranges. Several texturally and chemically distinct detrital and authigenic populations are recognized. Detrital dates range from 1600 Ma to 760 Ma and most relate to well-known orogenic or igneous events in surrounding cratonic regions. Authigenic monazite grew in three or more pulses ranging from 680 Ma to 500 Ma. The date of 680 ± 23 Ma (2σ) for the earliest generation of authigenic monazite in sandstone from the Enorama Shale (1) provides an estimate for the age of the base of the Trezona carbon isotopic anomaly just beneath the Marinoan Glacial Deposits, (2) provides an absolute minimum age constraint on the underlying Sturtian Glacial Deposits, and (3) supports proposed correlations between type Marinoan Deposits and precisely dated Glacial Deposits in Namibia and China, which bracket the presumed Marinoan equivalents between 655 and 635 Ma. This age is inconsistent with a Re–Os isochron age of 643 ± 2.4 Ma (2σ) on shales near the bottom of the Sturtian–Marinoan interGlacial succession, stratigraphically > 3000 m below the Enorama Shale sample, and militate against the hypothesis that the type Marinoan is correlative with the 580 Ma Gaskiers glaciation. Monazite growth near 600 Ma and again at about 500 Ma probably represent hydrothermal fluid-flow events, the latter of which also corresponds to the well-known Delamerian Orogeny during which the Adelaide sediments were folded into their present structural pattern.

  • Th–U–total Pb geochronology of authigenic monazite in the Adelaide rift complex, South Australia, and implications for the age of the type Sturtian and Marinoan Glacial Deposits
    Earth and Planetary Science Letters, 2009
    Co-Authors: Kevin H. Mahan, Brian P. Wernicke, Michael J. Jercinovic
    Abstract:

    The Adelaide rift complex in South Australia contains the type sections for Sturtian and Marinoan Glacial Deposits. The litho- and chemo-stratigraphy of these Deposits play a central role in evaluating global Neoproterozoic ice age hypotheses and Rodinia supercontinent reconstructions, but reliable depositional age constraints have been extremely limited. We report results of in situ Th–U–total Pb (electron microprobe) dating of detrital and authigenic monazite in two samples from the Umberatana Group (Sturtian Holowilena Ironstone and pre-Marinoan Enorama Shale) in the Central Flinders Ranges. Several texturally and chemically distinct detrital and authigenic populations are recognized. Detrital dates range from 1600 Ma to 760 Ma and most relate to well-known orogenic or igneous events in surrounding cratonic regions. Authigenic monazite grew in three or more pulses ranging from 680 Ma to 500 Ma. The date of 680 ± 23 Ma (2σ) for the earliest generation of authigenic monazite in sandstone from the Enorama Shale (1) provides an estimate for the age of the base of the Trezona carbon isotopic anomaly just beneath the Marinoan Glacial Deposits, (2) provides an absolute minimum age constraint on the underlying Sturtian Glacial Deposits, and (3) supports proposed correlations between type Marinoan Deposits and precisely dated Glacial Deposits in Namibia and China, which bracket the presumed Marinoan equivalents between 655 and 635 Ma. This age is inconsistent with a Re–Os isochron age of 643 ± 2.4 Ma (2σ) on shales near the bottom of the Sturtian–Marinoan interGlacial succession, stratigraphically > 3000 m below the Enorama Shale sample, and militate against the hypothesis that the type Marinoan is correlative with the 580 Ma Gaskiers glaciation. Monazite growth near 600 Ma and again at about 500 Ma probably represent hydrothermal fluid-flow events, the latter of which also corresponds to the well-known Delamerian Orogeny during which the Adelaide sediments were folded into their present structural pattern.

Riko Noormets - One of the best experts on this subject based on the ideXlab platform.

  • Glacial Deposits and Late Weichselian ice-sheet dynamics in the northeastern Baltic Sea
    Boreas, 2008
    Co-Authors: Riko Noormets, Tom Flodén
    Abstract:

    Glacial Deposits and landforms, interpreted from the continuous seismic reflection data, have been used to reconstruct the Late Weichselian ice-sheet dynamics and the sedimentary environments in the northeastern Baltic Sea. The bedrock geology and topography played an important role in the Glacial dynamics and subGlacial meltwater drainage in the area. Drumlins suggest a south-southeasterly flow direction of the last ice sheet on the Ordovician Plateau. Eskers demonstrate that subGlacial meltwater flow was focused mostly within bedrock valleys. The eskers have locally been overlain by a thin layer of till. Thick proximal outwash Deposits occupy elongated depressions in the substratum, which often occur along the sides of esker ridges. Ice-marginal grounding-line deposit in the southern part of the area has a continuation on the adjacent Island of Saaremaa. Therefore, we assume that its formation took place during Palivere Stadial of the last deglaciation, whereas the moraine bank extending southwestward from the Serve Peninsula is tentatively correlated with the Pandivere Stadial. The wedge-shaped ice-marginal grounding-line deposit was locally fed by subGlacial meltwater streams during a standstill or slight readvance of the ice margin. The thickness of the glacier at the grounding-line was estimated to reach approximately 180 m. In the western part of the area, terrace-like morphology of the ice-marginal deposit and series of small retreat moraines 10–20 km north of it suggest stepwise retreat of the ice margin. Therefore, a rather thin and mobile ice stream was probably covering the northeastern Baltic Sea during the last deglaciation.

  • Glacial Deposits and ice-sheet dynamics in the north-central Baltic Sea during the last deglaciation
    Boreas, 2008
    Co-Authors: Riko Noormets, Tom Flodén
    Abstract:

    Nine seismic stratigraphic units were distinguished, and their distribution mapped, in an 80 × 130 km submeridionally oriented area in the north-central Baltic Sea, east of Gotska Sandon and Faro. Analysis of these units revealed a great influence of the bedrock topography on the structure and distribution of the Glacial Deposits. Major Glacially eroded valleys in the Baltic Clint, connecting the Faro Deep and the North Central Baltic Basin (Harff & Winterhalter 1996) across a narrow sill, form an extensive submeridional bedrock depression. The concentration of ice flow into this depression is reflected in the drumlinized surface of the till near the Baltic Clint. Large eskers in the elongated bedrock depressions and on the Ordovician Plateau mark the locations of former subGlacial meltwater conduits. Termination of the eskers with extensive glacio fluvial outwash fans at the northern limit of the Faro Deep, the presence of subaquatic melt-out till in the bottom of it, and wedge-shaped ice-marginal grounding-line deposit on the Silurian Plateau suggest floating ice margin conditions in the low-lying areas and a local ice shelf confined to the Fro Deep during the deglaciation.

  • Glacial Deposits, sedimentary environments and ice sheet dynamics in the northern Baltic Sea and Lake Peipsi during the Late Weichselian
    2001
    Co-Authors: Riko Noormets
    Abstract:

    Glacial Deposits, sedimentary environments and ice sheet dynamics in the northern Baltic Sea and Lake Peipsi during the Late Weichselian

Kevin H. Mahan - One of the best experts on this subject based on the ideXlab platform.

  • th u total pb geochronology of authigenic monazite in the adelaide rift complex south australia and implications for the age of the type sturtian and marinoan Glacial Deposits
    Earth and Planetary Science Letters, 2010
    Co-Authors: Kevin H. Mahan, Brian P. Wernicke, Michael J. Jercinovic
    Abstract:

    The Adelaide rift complex in South Australia contains the type sections for Sturtian and Marinoan Glacial Deposits. The litho- and chemo-stratigraphy of these Deposits play a central role in evaluating global Neoproterozoic ice age hypotheses and Rodinia supercontinent reconstructions, but reliable depositional age constraints have been extremely limited. We report results of in situ Th–U–total Pb (electron microprobe) dating of detrital and authigenic monazite in two samples from the Umberatana Group (Sturtian Holowilena Ironstone and pre-Marinoan Enorama Shale) in the Central Flinders Ranges. Several texturally and chemically distinct detrital and authigenic populations are recognized. Detrital dates range from 1600 Ma to 760 Ma and most relate to well-known orogenic or igneous events in surrounding cratonic regions. Authigenic monazite grew in three or more pulses ranging from 680 Ma to 500 Ma. The date of 680 ± 23 Ma (2σ) for the earliest generation of authigenic monazite in sandstone from the Enorama Shale (1) provides an estimate for the age of the base of the Trezona carbon isotopic anomaly just beneath the Marinoan Glacial Deposits, (2) provides an absolute minimum age constraint on the underlying Sturtian Glacial Deposits, and (3) supports proposed correlations between type Marinoan Deposits and precisely dated Glacial Deposits in Namibia and China, which bracket the presumed Marinoan equivalents between 655 and 635 Ma. This age is inconsistent with a Re–Os isochron age of 643 ± 2.4 Ma (2σ) on shales near the bottom of the Sturtian–Marinoan interGlacial succession, stratigraphically > 3000 m below the Enorama Shale sample, and militate against the hypothesis that the type Marinoan is correlative with the 580 Ma Gaskiers glaciation. Monazite growth near 600 Ma and again at about 500 Ma probably represent hydrothermal fluid-flow events, the latter of which also corresponds to the well-known Delamerian Orogeny during which the Adelaide sediments were folded into their present structural pattern.

  • Th–U–total Pb geochronology of authigenic monazite in the Adelaide rift complex, South Australia, and implications for the age of the type Sturtian and Marinoan Glacial Deposits
    Earth and Planetary Science Letters, 2009
    Co-Authors: Kevin H. Mahan, Brian P. Wernicke, Michael J. Jercinovic
    Abstract:

    The Adelaide rift complex in South Australia contains the type sections for Sturtian and Marinoan Glacial Deposits. The litho- and chemo-stratigraphy of these Deposits play a central role in evaluating global Neoproterozoic ice age hypotheses and Rodinia supercontinent reconstructions, but reliable depositional age constraints have been extremely limited. We report results of in situ Th–U–total Pb (electron microprobe) dating of detrital and authigenic monazite in two samples from the Umberatana Group (Sturtian Holowilena Ironstone and pre-Marinoan Enorama Shale) in the Central Flinders Ranges. Several texturally and chemically distinct detrital and authigenic populations are recognized. Detrital dates range from 1600 Ma to 760 Ma and most relate to well-known orogenic or igneous events in surrounding cratonic regions. Authigenic monazite grew in three or more pulses ranging from 680 Ma to 500 Ma. The date of 680 ± 23 Ma (2σ) for the earliest generation of authigenic monazite in sandstone from the Enorama Shale (1) provides an estimate for the age of the base of the Trezona carbon isotopic anomaly just beneath the Marinoan Glacial Deposits, (2) provides an absolute minimum age constraint on the underlying Sturtian Glacial Deposits, and (3) supports proposed correlations between type Marinoan Deposits and precisely dated Glacial Deposits in Namibia and China, which bracket the presumed Marinoan equivalents between 655 and 635 Ma. This age is inconsistent with a Re–Os isochron age of 643 ± 2.4 Ma (2σ) on shales near the bottom of the Sturtian–Marinoan interGlacial succession, stratigraphically > 3000 m below the Enorama Shale sample, and militate against the hypothesis that the type Marinoan is correlative with the 580 Ma Gaskiers glaciation. Monazite growth near 600 Ma and again at about 500 Ma probably represent hydrothermal fluid-flow events, the latter of which also corresponds to the well-known Delamerian Orogeny during which the Adelaide sediments were folded into their present structural pattern.

Tom Flodén - One of the best experts on this subject based on the ideXlab platform.

  • Glacial Deposits and ice-sheet dynamics in the north-central Baltic Sea during the last deglaciation
    Boreas, 2008
    Co-Authors: Riko Noormets, Tom Flodén
    Abstract:

    Nine seismic stratigraphic units were distinguished, and their distribution mapped, in an 80 × 130 km submeridionally oriented area in the north-central Baltic Sea, east of Gotska Sandon and Faro. Analysis of these units revealed a great influence of the bedrock topography on the structure and distribution of the Glacial Deposits. Major Glacially eroded valleys in the Baltic Clint, connecting the Faro Deep and the North Central Baltic Basin (Harff & Winterhalter 1996) across a narrow sill, form an extensive submeridional bedrock depression. The concentration of ice flow into this depression is reflected in the drumlinized surface of the till near the Baltic Clint. Large eskers in the elongated bedrock depressions and on the Ordovician Plateau mark the locations of former subGlacial meltwater conduits. Termination of the eskers with extensive glacio fluvial outwash fans at the northern limit of the Faro Deep, the presence of subaquatic melt-out till in the bottom of it, and wedge-shaped ice-marginal grounding-line deposit on the Silurian Plateau suggest floating ice margin conditions in the low-lying areas and a local ice shelf confined to the Fro Deep during the deglaciation.

  • Glacial Deposits and Late Weichselian ice-sheet dynamics in the northeastern Baltic Sea
    Boreas, 2008
    Co-Authors: Riko Noormets, Tom Flodén
    Abstract:

    Glacial Deposits and landforms, interpreted from the continuous seismic reflection data, have been used to reconstruct the Late Weichselian ice-sheet dynamics and the sedimentary environments in the northeastern Baltic Sea. The bedrock geology and topography played an important role in the Glacial dynamics and subGlacial meltwater drainage in the area. Drumlins suggest a south-southeasterly flow direction of the last ice sheet on the Ordovician Plateau. Eskers demonstrate that subGlacial meltwater flow was focused mostly within bedrock valleys. The eskers have locally been overlain by a thin layer of till. Thick proximal outwash Deposits occupy elongated depressions in the substratum, which often occur along the sides of esker ridges. Ice-marginal grounding-line deposit in the southern part of the area has a continuation on the adjacent Island of Saaremaa. Therefore, we assume that its formation took place during Palivere Stadial of the last deglaciation, whereas the moraine bank extending southwestward from the Serve Peninsula is tentatively correlated with the Pandivere Stadial. The wedge-shaped ice-marginal grounding-line deposit was locally fed by subGlacial meltwater streams during a standstill or slight readvance of the ice margin. The thickness of the glacier at the grounding-line was estimated to reach approximately 180 m. In the western part of the area, terrace-like morphology of the ice-marginal deposit and series of small retreat moraines 10–20 km north of it suggest stepwise retreat of the ice margin. Therefore, a rather thin and mobile ice stream was probably covering the northeastern Baltic Sea during the last deglaciation.

Brian P. Wernicke - One of the best experts on this subject based on the ideXlab platform.

  • th u total pb geochronology of authigenic monazite in the adelaide rift complex south australia and implications for the age of the type sturtian and marinoan Glacial Deposits
    Earth and Planetary Science Letters, 2010
    Co-Authors: Kevin H. Mahan, Brian P. Wernicke, Michael J. Jercinovic
    Abstract:

    The Adelaide rift complex in South Australia contains the type sections for Sturtian and Marinoan Glacial Deposits. The litho- and chemo-stratigraphy of these Deposits play a central role in evaluating global Neoproterozoic ice age hypotheses and Rodinia supercontinent reconstructions, but reliable depositional age constraints have been extremely limited. We report results of in situ Th–U–total Pb (electron microprobe) dating of detrital and authigenic monazite in two samples from the Umberatana Group (Sturtian Holowilena Ironstone and pre-Marinoan Enorama Shale) in the Central Flinders Ranges. Several texturally and chemically distinct detrital and authigenic populations are recognized. Detrital dates range from 1600 Ma to 760 Ma and most relate to well-known orogenic or igneous events in surrounding cratonic regions. Authigenic monazite grew in three or more pulses ranging from 680 Ma to 500 Ma. The date of 680 ± 23 Ma (2σ) for the earliest generation of authigenic monazite in sandstone from the Enorama Shale (1) provides an estimate for the age of the base of the Trezona carbon isotopic anomaly just beneath the Marinoan Glacial Deposits, (2) provides an absolute minimum age constraint on the underlying Sturtian Glacial Deposits, and (3) supports proposed correlations between type Marinoan Deposits and precisely dated Glacial Deposits in Namibia and China, which bracket the presumed Marinoan equivalents between 655 and 635 Ma. This age is inconsistent with a Re–Os isochron age of 643 ± 2.4 Ma (2σ) on shales near the bottom of the Sturtian–Marinoan interGlacial succession, stratigraphically > 3000 m below the Enorama Shale sample, and militate against the hypothesis that the type Marinoan is correlative with the 580 Ma Gaskiers glaciation. Monazite growth near 600 Ma and again at about 500 Ma probably represent hydrothermal fluid-flow events, the latter of which also corresponds to the well-known Delamerian Orogeny during which the Adelaide sediments were folded into their present structural pattern.

  • Th–U–total Pb geochronology of authigenic monazite in the Adelaide rift complex, South Australia, and implications for the age of the type Sturtian and Marinoan Glacial Deposits
    Earth and Planetary Science Letters, 2009
    Co-Authors: Kevin H. Mahan, Brian P. Wernicke, Michael J. Jercinovic
    Abstract:

    The Adelaide rift complex in South Australia contains the type sections for Sturtian and Marinoan Glacial Deposits. The litho- and chemo-stratigraphy of these Deposits play a central role in evaluating global Neoproterozoic ice age hypotheses and Rodinia supercontinent reconstructions, but reliable depositional age constraints have been extremely limited. We report results of in situ Th–U–total Pb (electron microprobe) dating of detrital and authigenic monazite in two samples from the Umberatana Group (Sturtian Holowilena Ironstone and pre-Marinoan Enorama Shale) in the Central Flinders Ranges. Several texturally and chemically distinct detrital and authigenic populations are recognized. Detrital dates range from 1600 Ma to 760 Ma and most relate to well-known orogenic or igneous events in surrounding cratonic regions. Authigenic monazite grew in three or more pulses ranging from 680 Ma to 500 Ma. The date of 680 ± 23 Ma (2σ) for the earliest generation of authigenic monazite in sandstone from the Enorama Shale (1) provides an estimate for the age of the base of the Trezona carbon isotopic anomaly just beneath the Marinoan Glacial Deposits, (2) provides an absolute minimum age constraint on the underlying Sturtian Glacial Deposits, and (3) supports proposed correlations between type Marinoan Deposits and precisely dated Glacial Deposits in Namibia and China, which bracket the presumed Marinoan equivalents between 655 and 635 Ma. This age is inconsistent with a Re–Os isochron age of 643 ± 2.4 Ma (2σ) on shales near the bottom of the Sturtian–Marinoan interGlacial succession, stratigraphically > 3000 m below the Enorama Shale sample, and militate against the hypothesis that the type Marinoan is correlative with the 580 Ma Gaskiers glaciation. Monazite growth near 600 Ma and again at about 500 Ma probably represent hydrothermal fluid-flow events, the latter of which also corresponds to the well-known Delamerian Orogeny during which the Adelaide sediments were folded into their present structural pattern.