Title: Table R
Author: RSES
Last saved by: Charlotte Skelton
Company: ANU

Supplementary Table 19. Results of laser fusion ^40Ar/^39Ar dating of anorthoclase from two pumice clasts from the Kangaki Tuff, upper part of Kalochoro Member, Nachukui Formation. Kangaki Laga, west of Lake Turkana, 3˚59.15’N, 35˚47.1’E, northern Kenya. Sample 00-296B was collected as field number K89-3433

Sample

^36Ar/^39Ar
x 10^-4

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

^40Ar/^39Ar

K/Ca

^40Ar*/^39Ar_K
± c.v.

% ^40Ar*

^39Ar
10^-14mol

Calculated age
Ma ± 1 s.d.

98-328 anorthoclase; J = 4.253E-4 ± 0.50%; level 12, ANU45
1 | 3.300 ±  8.72% | - | 2.818 ± 0.25% | - | 2.662 ± 0.42% | 94.5 | 0.58 | 2.041 ± 0.013
2 | 6.582 ±  9.68% | 9.275 ± 19.43% | 2.908 ± 0.22% | 57 | 2.656 ± 0.75% | 91.3 | 0.72 | 2.034 ± 0.018
3 | 1.716 ± 30.93% | 17.255 ± 49.19% | 2.754 ± 0.27% | 31 | 2.646 ± 0.66% | 96.1 | 0.61 | 2.029 ± 0.017
4 | 2.062 ± 19.89% | 4.912 ± 31.82% | 2.769 ± 0.29% | 107 | 2.649 ± 0.55% | 95.7 | 0.80 | 2.032 ± 0.015
5 | 0.893 ± 35.29% | 4.564 ± 48.59% | 2.755 ± 0.23% | 115 | 2.670 ± 0.42% | 96.9 | 0.82 | 2.048 ± 0.013
6 | 2.499 ±  7.63% | 16.267 ± 14.03% | 2.794 ± 0.25% | 32 | 2.663 ± 0.34% | 95.3 | 0.72 | 2.042 ± 0.012
7 | 5.186 ± 10.51% | - | 2.835 ± 0.39% | - | 2.623 ± 0.74% | 92.5 | 0.15 | 2.011 ± 0.018
| Arithmetic mean K/Ca (n = 5) | 68 ± 41 | Arithmetic mean age (n = 7) Weighted mean age (n =  7) | 2.034 ± 0.012 2.038 ± 0.011
00-296B anorthoclase; J = 4.097E-4 ± 0.30%; level 7, ANU69
1 | 5.513 ± 16.57% | 12.497 ±  2.76% | 2.926 ± 0.27% | 42 | 2.722 ± 1.03% | 93.0 | 1.12 | 2.011 ± 0.022
2 | 1.213 ± 61.56% | 19.542 ±  3.31% | 2.870 ± 0.29% | 27 | 2.795 ± 0.85% | 97.4 | 0.87 | 2.064 ± 0.018
[3 | 3.326 ±  8.62% | 36.765 ±  1.04% | 6.714 ± 0.25% | 14 | 6.578 ± 0.28% | 98.0 | 1.14 | 4.855 ± 0.020]
4 | 20.317 ± 1.75% | 15.344 ±  0.91% | 3.510 ± 0.25% | 34 | 2.869 ± 0.48% | 81.7 | 1.71 | 2.119 ± 0.012
[5 | 3.033 ±  4.24% | 10.927 ±  2.62% | 6.744 ± 0.27% | 48 | 6.613 ± 0.28% | 98.1 | 0.98 | 4.881 ± 0.020]
6 | 62.565 ±  1.12% | 32.280 ±  0.78% | 4.721 ± 0.29% | 16 | 2.833 ± 0.87% | 60.0 | 1.04 | 2.093 ± 0.019
7 | 7.081 ±  4.25% | 30.645 ±  1.00% | 3.003 ± 0.26% | 17 | 2.755 ± 0.43% | 91.7 | 1.15 | 2.035 ± 0.011
8 | 5.411 ± 12.58% | 46.850 ±  0.57% | 2.979 ± 0.30% | 11 | 2.782 ± 0.79% | 93.4 | 0.70 | 2.054 ± 0.017
9 | 141.16   ±  1.05% | 12.495 ±  1.26% | 7.048 ± 0.28% | 42 | 2.836 ± 1.69% | 40.2 | 0.85 | 2.094 ± 0.036
10 | 12.465 ±  4.53% | 34.586 ±  0.92% | 3.137 ± 0.27% | 15 | 2.730 ± 0.69% | 87.0 | 0.58 | 2.017 ± 0.015
11 | 115.48   ±  0.95% | 12.510 ±  2.08% | 6.306 ± 0.26% | 42 | 2.853 ± 1.27% | 45.2 | 0.64 | 2.107 ± 0.027
12 | 16.354 ±  2.24% | 11.907 ±  3.62% | 3.353 ± 0.26% | 44 | 2.829 ± 0.49% | 84.4 | 0.79 | 2.090 ± 0.012
13 | 4.103 ± 18.99% | 19.240 ±  3.06% | 2.907 ± 0.32% | 27 | 2.746 ± 0.90% | 94.5 | 0.62 | 2.028 ± 0.019
14 | 4.270 ± 12.94% | 38.871 ±  2.42% | 2.919 ± 0.20% | 14 | 2.757 ± 0.63% | 94.4 | 0.86 | 2.036 ± 0.014
15 | 3.389 ± 15.68% | 6.978 ± 10.64% | 2.880 ± 0.17% | 75 | 2.740 ± 0.60% | 95.2 | 0.60 | 2.024 ± 0.014
16 | 7.931 ±  3.09% | 15.326 ±  4.23% | 3.031 ± 0.22% | 34 | 2.758 ± 0.36% | 91.0 | 0.48 | 2.037 ± 0.009
17 | 2.097 ± 13.81% | 25.778 ±  1.89% | 2.878 ± 0.18% | 20 | 2.779 ± 0.36% | 96.5 | 0.61 | 2.052 ± 0.010
18 | 1.547 ± 31.02% | 17.402 ±  1.63% | 2.860 ± 0.20% | 30 | 2.776 ± 0.55% | 97.1 | 0.89 | 2.051 ± 0.013
19 | 5.140 ± 10.70% | 16.098 ±  5.92% | 2.939 ± 0.21% | 33 | 2.749 ± 0.63% | 93.5 | 0.70 | 2.031 ± 0.014
20 | 10.074 ±  2.24% | 36.100 ±  1.35% | 3.102 ± 0.20% | 15 | 2.768 ± 0.33% | 89.2 | 0.72 | 2.045 ± 0.009
21 | 48.991 ± 21.32% | 12.640 ±  4.19% | 4.242 ± 0.20% | 42 | 2.756 ± 0.80% | 65.0 | 0.81 | 2.036 ± 0.017
22 | 2.983 | 24.965 ±  3.16% | 2.902 ± 0.15% | 21 | 2.777 ± 0.70% | 95.7 | 0.89 | 2.051 ± 0.016
| Arithmetic mean K/Ca (n = 20) | 30 ± 16 | Arithmetic mean age (n = 20) Weighted mean age (n = 20) | 2.054 ± 0.031 2.051 ± 0.007

λ = 5.543 x 10^-10 a^-1        Sensitivity 2.7 (±~15%) x 10^-17 mol/mV	 Bracketed results excluded from mean age calculations
(^36Ar/^37Ar)_Ca = 3.50 x 10^-4	(^39Ar/^37Ar)_Ca = 7.86 x 10^-4	(^40Ar/^39Ar)_K = 0.059 for 98-328; 0.042 for 00-296B
^40Ar* – radiogenic ^40Ar	^39Ar_K – K derived ^39Ar	
Mass of alkali feldspar used in each analysis in range:  98-328 – 0.3 to 1.6 mg; 00-296B – 0.7 to 2.7 mg
Irradiated 24 hours in X33 or X34, HIFAR reactor
Fluence monitor: 92-176 sanidine from Fish Canyon Tuff; K-Ar reference age utilized: 28.1 Ma
For sample 98-328 each analysis was done on a single crystal
For sample 00-296B, analyses 1 to 16 were done on single crystals, analyses 17 to 22 were made on 2 or 3 crystals
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