The document details a high precision zircon dating project focusing on tuffs within the Sydney-Gunnedah Basin, utilizing advanced isotopic analysis techniques to obtain dating and sedimentation rates. It describes the project's progress, including the collection and analysis of 526 samples with preliminary dating results for many, as well as ongoing efforts to enhance chronostratigraphic correlations within coal basins. Future work includes redefining stratigraphic nomenclature and updating related geological publications.

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