Title: Results of laser fusion 40Ar-39Ar dating of alkali feldspar crystals from two pumice clasts in a tuff of Member III,
Author: Ian McDougall
Last saved by: Charlotte Skelton
Company: ANU

Supplementary Table 7. Results of laser fusion ^40Ar-^39Ar dating of alkali feldspar crystals from three pumice clasts in the Lokochot (=A) Tuff of the Nkalabong Formation, below the Kibish Formation, west flanks, Harpoon Hill, Kibish, Ethiopia, 5°24.54'N, 35°55.54'E

Sample

^36Ar/^39Ar
x 10^-3

^37Ar/^39Ar
x 10^-3

^40Ar/^39Ar

K/Ca

^40Ar*/^39Ar_K
± c.v.

% ^40Ar*

^39Ar
10^-15 mol

Calculated age
Ma ± 1 s.d.

02-013A pumice, 16 g; J = 1.251E-04 ± 0.45%; level 4, ANU 98
–1 | 11.298 ±  0.94% | – | 19.29 ± 0.23% | – | 15.89 ± 0.35% | 82.4 | 1.6 | 3.583 ± 0.020
–2 (3) | 10.406 ±  0.84% | – | 19.16 ± 0.22% | – | 16.02 ± 0.30% | 83.6 | 2.5 | 3.613 ± 0.020
–3 (3) | 123.410 ±  0.88% | – | 52.70 ± 0.47% | – | 16.18 ± 2.51% | 30.7 | 2.5 | 3.647 ± 0.093
–4 (3) | 18.396 ±  0.99% | 41.28 ±  3.78% | 21.52 ± 0.29% | 13 | 16.03 ± 0.51% | 74.5 | 3.5 | 3.615 ± 0.025
–5 (3) | 33.045 ±  1.06% | – | 25.89 ± 0.28% | – | 16.07 ± 0.78% | 62.1 | 2.8 | 3.623 ± 0.033
–6 (3) | 2.467 ±  6.82% | – | 16.46 ± 0.28% | – | 15.68 ± 0.43% | 95.2 | 1.8 | 3.535 ± 0.022
–7 (3) | 2.483 ±  6.19% | – | 16.90 ± 0.32% | – | 16.11 ± 0.44% | 95.3 | 2.1 | 3.633 ± 0.023
–8 (3) | 2.313 ±  2.53% | – | 16.83 ± 0.30% | – | 16.09 ± 0.33% | 95.6 | 2.3 | 3.628 ± 0.020
–9 (4) | 3.810 ±  1.82% | – | 17.03 ± 0.23% | – | 15.84 ± 0.28% | 93.0 | 2.2 | 3.572 ± 0.019
–10 (4) | 5.147 ±  1.23% | 2.566 ± 38.09% | 17.49 ± 0.26% | 205 | 15.91 ± 0.31% | 91.0 | 2.3 | 3.587 ± 0.020
| | | | | Arithmetic mean age (n = 10) Weighted mean age (n = 10) | 3.604 ± 0.034 3.595 ± 0.017
02-013B pumice, 36 g; J = 1.255E-04 ± 0.75%; level 6, ANU 98
–1 | 14.578 ±  0.90% | 3.148 ±  6.87% | 20.09 ± 0.17% | 167 | 15.73 ± 0.33% | 78.3 | 3.5 | 3.559 ± 0.029
–2 | 5.733 ±  2.16% | – | 17.50 ± 0.21% | – | 15.75 ± 0.33% | 90.0 | 4.5 | 3.563 ± 0.029
–3 | 34.618 ±  0.74% | – | 26.19 ± 0.15% | – | 15.90 ± 0.54% | 60.7 | 5.2 | 3.598 ± 0.033
–4 | 1.495 ±  9.07% | 0.863 ± 99.11% | 16.35 ± 0.33% | 610 | 15.85 ± 0.42% | 97.0 | 1.5 | 3.586 ± 0.031
–5 | 20.843 ±  1.07% | – | 22.06 ± 0.18% | – | 15.84 ± 0.49% | 71.8 | 4.2 | 3.585 ± 0.032
–6 | 2.842 ±  2.70% | – | 16.72 ± 0.53% | – | 15.82 ± 0.58% | 94.6 | 2.7 | 3.578 ± 0.034
–7 | 4.025 ±  4.30% | 2.454 ± 89.49% | 17.22 ± 0.27% | 214 | 15.97 ± 0.43% | 92.7 | 2.3 | 3.613 ± 0.031
–8 | 6.293 ±  1.87% | – | 17.85 ± 0.43% | – | 15.93 ± 0.53% | 89.2 | 3.1 | 3.603 ± 0.033
–9 | 4.914 ±  1.88% | – | 17.32 ± 0.29% | – | 15.81 ± 0.36% | 91.3 | 2.8 | 3.577 ± 0.030
–10 | 9.725 ±  2.31% | – | 18.63 ± 0.45% | – | 15.70 ± 0.68% | 84.3 | 3.0 | 3.551 ± 0.036
–11 | 2.851 ±  1.33% | – | 16.64 ± 0.20% | – | 15.74 ± 0.23% | 94.6 | 3.8 | 3.560 ± 0.028
–13 | 6.069 ±  1.41% | 2.636 ± 60.49% | 17.62 ± 0.22% | 200 | 15.77 ± 0.30% | 89.5 | 3.2 | 3.567 ± 0.029
–15 | 5.667 ±  2.33% | 10.011 ± 23.92% | 17.30 ± 0.39% | 53 | 15.57 ± 0.50% | 90.0 | 1.3 | 3.522 ± 0.032
| Arithmetic mean K/Ca (n = 5) | 249 ± 212 | Arithmetic mean age (n = 13) Weighted mean age (n = 13) | 3.574 ± 0.024 3.571 ± 0.027
02-014 pumice, 20 g; J = 1.249E-04 ± 0.75%; level 7, ANU 98
–2 | 4.230 ±  1.68% | 4.375 ±  8.95% | 17.70 ± 0.20% | 120 | 16.39 ± 0.25% | 92.6 | 6.4 | 3.717 ± 0.029
–3 | 2.478 ±  2.12% | 1.404 ± 33.29% | 16.77 ± 0.17% | 375 | 15.98 ± 0.21% | 95.3 | 8.8 | 3.624 ± 0.028
–6 | 11.532 ±  2.62% | – | 19.10 ± 0.21% | – | 15.63 ± 0.63% | 81.8 | 2.4 | 3.545 ± 0.035
–9 | 14.364 ±  2.06% | – | 20.09 ± 0.25% | – | 15.79 ± 0.64% | 78.6 | 1.7 | 3.580 ± 0.035
–12 | 6.425 ±  2.80% | - | 17.64 ± 0.27% | - | 15.68 ± 0.46% | 88.9 | 1.8 | 3.557 ± 0.031
–13 | 8.932 ±  1.45% | 14.414 ± 58.79% | 18.49 ± 0.48% | 36 | 15.79 ± 0.61% | 85.4 | 1.4 | 3.581 ± 0.035
–15 | 4.573 ±  1.24% | 6.165 ± 31.49% | 17.86 ± 0.29% | 85 | 16.45 ± 0.33% | 92.1 | 4.2 | 3.731 ± 0.031
–17 | 2.682 ± 10.95% | – | 16.74 ± 0.42% | – | 15.89 ± 0.70% | 94.9 | 1.2 | 3.603 ± 0.037
–18 | 4.678 ±  7.10% | – | 17.42 ± 0.27% | – | 15.98 ± 0.68% | 91.7 | 1.0 | 3.623 ± 0.037
| Arithmetic mean K/Ca (n = 4) | 154 ± 151 | Arithmetic mean age (n = 9) Weighted mean age (n = 9) | 3.618 ± 0.066 3.647 ± 0.028

λ = 5.543 x 10^-10 a^-1		  Sensitivity 2.5 (± ~15%) x 10^-17 mol/mV	
(^36Ar/^37Ar)_Ca = 3.50 x 10^-4; (^39Ar/^37Ar)_Ca = 7.86 x 10^-4; (^40Ar/^39Ar)_K = 0.055 to 0.059
^40Ar* - radiogenic ^40Ar;	^39Ar_K – K-derived ^39Ar.	Irradiation for 6 hours in X33 or X34, HIFAR reactor
Number of crystals fused is indicated in parentheses in first column; absence of parentheses indicates a single crystal fused 
Mass of alkali feldspar used in each experiment generally 0.5 to 3 mg
Fluence monitor: Fish Canyon Tuff sanidine 92-176 of reference age 28.1 Ma
All errors are one standard deviation. Uncertainty on the ^40Ar*/^39Ar_K ratio is the analytical error. This error is combined quadratically with the estimated error of J to yield the quoted error for each age