Exploration in the House 2015: High Precision Zircon Dating of Tuffs in the Sydney-Gunnedah Basin by Dr Kevin Ruming

1. High Precision Zircon Dating of Tuffs
in the Sydney-Gunnedah Basin
Dr Kevin Ruming

2. TUFFS

3. NOBBYS TUFF

4. TUFFS
CHARBON COLLIERY BOX CUT

5. 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

6. The Project
Progress – Overall Project
• 526 Samples collected from
Australia
• 87 Dates, 154 Samples in progress
or with preliminary dates

7. 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

8. Correlations
Ulan Seam F Ply

9. 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

10. Correlations

11. Chronostratigraphic v’s Lithostratigraphic Units
SCALE
Ma GROUP AGE AGE GROUP
252.50
252.75
253.00
254.50
254.75 254.82 ± 0.04 254.88 ± 0.19 (P)
255.00
255.25 255.26 ± 0.14
255.50 255.37 ± 0.17
255.75
256.00
256.25
NEWCASTLE COALFIELD
Malabar Formation to Milbrodale
Fm
Althorpe Formation
Mount 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 Tuff
Watts Sandstone / Denman Formation
Wittingham
Coal
Measures
HUNTER COALFIELD
Narrabeen Group
Newcastle
Coal
Measures

12. Hunter Coalfield Gunnedah Basin

13. 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

14. Biostratigraphy
• Palynological
samples are being
taken in conjunction
with CA-IDTIMS
samples (where
possible)
• Calibrating endemic
Australian
biozonation against
the established
global timescale

15. Finding the P-T Boundary – Southern
Coalfield
P-T Boundary = Historically been placed above the Bulli Coal

16. 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

17. Future Work
• Redefining stratigraphic nomenclature of
major NSW basins/coalfields
• Possible redefining type holes/sections
• Updating Departmental publications

18. Basin Scale Fence Diagram

19. 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