1. The Global Detrital Zircon Database: An Update
Peter Voice
Michał Kowalewski
Ken Eriksson

2. Basic Detrital Zircon Methodology

3. Minimum Sample Size Constraints
What is the minimum sample size necessary to have a sample that represents every “major” age fraction potentially present ?
Several studies have attempted some variant of this
What is the minimum sample size necessary to best estimate the age of the host sediment using detrital zircon geochronology?
The goal of this study

4. Previous Sample Size Approaches
Dodson et al. (1988) used:
P = (1-f)n
P = probability
f = fraction of grains representing a subpopulation within the population
n = sample size
If f is set to 0.05 and P to 0.05, then n ≈ 60

5. Previous Sample Size Approaches
Vermeesch (2004) used:
Using this equation, Vermeesch (2004) shows that at least 117 grains need to be sampled in order to be 95% confident that any fraction of the population greater than 0.05% is not missed.

6. Our Approach
The Previous sample size approaches are based on theoretical statistics; Our approach is based on empirical data from a very large database
Defined a metric: the offset between the maximum age of the host sediment and the age of the youngest grain in the sample
Calculated the offset for all samples in the GDZDb
Averaged the offsets as a function of sample size for different filters

7. The Offset Host Sediment Time (Ma) Offset
Time
(Ma)
Offset
Youngest Detrital Zircon Age
Minimum Host Sediment Age
Maximum Host Sediment Age
Host Sediment Ages Independent of Detrital Zircon Data

8. The Global Detrital Zircon Database Structure
1,248 studies compiled
5,529 Age Frequency Distributions
281,239 individually dated detrital zircons
Samples from modern sediments, sedimentary rocks, and meta-sediments
78 variables (78 *281,239 = 21,936,642 cells)
Variables include: host sediment lithology and metamorphic grade; minimum and maximum age constraints on host sediment; host sediment tectonic setting, etc.

10. Global Age Frequency distribution
1000
2000
3000
4000
n = 199,358
n = 118,682
n = 100,445
Geologic Age (Ma)
Frequency of Dated Detrital Zircon Grains I.
II.
III.
IV. V.
Global Age Frequency distribution

11. Frequency of Dated Detrital Zircon Grains North America Europe Africa
1000
2000
3000
n = 43,160
n = 7,344
n = 7,153
n = 12,774
n = 5,094
n = 20,461
500
4000
n = 2,493
Geologic Age (Ma)
Frequency of Dated Detrital Zircon Grains
North America
Europe
Africa
Antarctica
South America
Asia
Australia

12. Sample Size Results

13. Full Database
n = 4,885

14. -
200
100
300
400
500
600 20 40 60 80
120
140
Passive Margins
Active Margins
Rift Basins
Binned n
Average Offset between youngest grain age and Maximum estimate of host sediment age (Ma)
Full Database

15. ≤ ±5% discordant data
n = 3,890

16. ≤ ±5% discordant data Binned n-
100
200
300
400
500
600 20 40 60 80
120
140
Passive Margins
Active Margins
Rift Basins
Binned n
Average Offset between youngest grain age and Maximum estimate of host sediment age (Ma)
≤ ±5% discordant data

17. Modern River Samples
n = 435

18. Modern River Samples Binned n
500
1000
1500
2000
2500 20 40 60 80
100
120
140
Passive Margins
Active Margins
Rift Basins
Binned n
Average Offset between youngest grain age and Maximum estimate of host sediment age (Ma)
Modern River Samples

19. Sample Size Recommendations
Recommended n
Filter
passive margins
active margins
rift basins
Full Database 80 40 30
5% discordance filter 70 50
Phanerozoic
Modern Sediment
Average n = 51 grains

20. Conclusions
Regardless of filter or Tectonic setting a conservative estimate of the sample size necessary to best estimate the host sediment age stabilize at approximately 50 grains
minimum offset at n = 50 is Ma
Individual samples may be heavily influenced by source sediment age, local basin conditions, etc.