exploration in the house 2015: high precision zircon dating of tuffs in the sydney-gunnedah basin by...
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High Precision Zircon Dating of Tuffs in the Sydney-Gunnedah Basin
Dr Kevin Ruming
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TUFFS
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NOBBYS TUFF
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TUFFS
CHARBON COLLIERY BOX CUT
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CA-IDTIMS Chemical Abrasion Isotope Dilution Thermal
Ionisation Mass Spectrometry Process • Extract zircons • Select primary magmatic zircons • Zircons are individually thermally annealed and
chemically abraded • U - Pb isotope concentrations • Age of each zircon calculated, and a weighted mean
age for each tuff sample is determined
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The Project
Progress – Overall Project • 526 Samples collected from
Australia • 87 Dates, 154 Samples in progress
or with preliminary dates
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The Project – NSW NSW Project • Enhanced correlation within &
between coal basins • High resolution estimates of
sedimentation rates • Modelling depositional evolution of
NSW coal basins Progress – NSW Project • 391 Samples collected from NSW to
date • 59 Dates • 100 Samples in progress or with
preliminary dates • 38 Samples had no zircons
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Correlations Ulan Seam F Ply
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Regional Chronostratigraphic Correlations - Ulan Seam F Ply & Fairford
WESTERN COALFIELD Ulan Coal F Ply 257.24 ± 0.14 257.46 ± 0.22 (Prelim)
HUNTER COALFIELD Fairford Claystone 257.04 ± 0.15 257.43 ± 0.09 Mount Arthur Amoco Wybong 1
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Correlations
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Chronostratigraphic v’s Lithostratigraphic Units
SCALE
Ma GROUP AGE AGE GROUP
252.50252.75253.00254.50254.75 254.82 ± 0.04 254.88 ± 0.19 (P)255.00255.25 255.26 ± 0.14255.50 255.37 ± 0.17255.75256.00256.25
NEWCASTLE COALFIELD
Malabar Formation to Milbrodale Fm
Althorpe FormationMount Leonard Fm
SUBGROUP/FORMATION SUBGROUP/FORMATION
Narrabeen Group
Lambton Subgroup
Nobbys Tuff
Moon Island Beach Adamstown Subgroup
Newcastle Coal
Measures
Waratah Sandstone / Dempsey Formation
Moon Island Beach to Adamstown Subgroup
Tomago Coal Measures
Nobbys TuffWatts Sandstone / Denman Formation
Wittingham Coal
Measures
HUNTER COALFIELD
Narrabeen Group
Newcastle Coal
Measures
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Hunter Coalfield Gunnedah Basin
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Ulan Seam – Western Coalfield
Depositional Rate: C Marker to F Ply = 6.94m/my (On compacted sediment, does not account for post-depositional compaction)
ULAN COAL CA-IDTIMS DATES B Parting: 255.97 ± 0.14 C Ply: 256.19 ± 0.05, 256.37 ± 0.21 E31 Ply: 258.58 ± 0.24 (Prelim. Date) F Ply: 257.24 ± 0.14, 257.46 ± 0.22 (Prelim) Tuffaceous Units below F Ply: 257.17 ± 0.09, 257.84 ± 0.16, 258.77 ± 0.22
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Biostratigraphy • Palynological
samples are being taken in conjunction with CA-IDTIMS samples (where possible)
• Calibrating endemic Australian biozonation against the established global timescale
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Finding the P-T Boundary – Southern Coalfield
P-T Boundary = Historically been placed above the Bulli Coal
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Finding the P-T Boundary • P-T Boundary = Between 251.941 ±
0.037 and 251.880 ± 0.031 • Bulli Coal = 252.60 ± 0.04Ma • Gap of ~700,000 Years
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Future Work • Redefining stratigraphic nomenclature of major NSW basins/coalfields • Possible redefining type holes/sections • Updating Departmental publications
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Basin Scale Fence Diagram
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Acknowledgements
• Bob Nicoll, John Laurie – Geoscience Australia • Ian Metcalfe - University of New England • Erin Holmes - GSNSW • Research School of Earth Sciences – ANU • Isotope Geology Laboratory – BSU