Title: Supplementary Table 21
Author: myself
Last saved by: Charlotte Skelton
Company: ANU

Supplementary Table 21. Results of ^40Ar/^39Ar step heating experiment on feldspar from pumice in Topernawi Tuff, Lonyumun Member, Nachukui Formation, Lomekwi Laga, west of Lake Turkana, northern Kenya

Step
No.

Temp.
°C

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

^37Ar/^39Ar
x 10^-2

^40Ar/^39Ar

^40Ar*/^39Ar_K
± c.v.

% ^40Ar*

^39Ar
10^-15 mol

% Cum.
    ^39Ar

Calculated age
   Ma ± 1 s.d.

93-1066 anorthoclase; J = 5.637E-4 ± 0.35%; level 3, ANU 53, 0.0146 g
1 | 550 | 2782.3     ± 12.24% | 827.710 ± 69.17% | 980.360 ± 11.56% | 160.05 ± 94.8% | 16.2 | 0.01 | 0.01 | 155.8  ± 141.5
2 | 650 | 37.07   ±  4.99% | 7.781 ± 99.95% | 20.454 ±  0.63% | 9.479 ± 5.92% | 46.3 | 0.23 | 0.17 | 9.613 ± 0.568
3 | 750 | 29.49   ±  2.52% | 1.707 ± 64.68% | 14.795 ±  0.20% | 6.053 ± 3.65% | 40.9 | 0.97 | 0.87 | 6.145 ± 0.224
4 | 800 | 7.271 ±  5.53% | 7.577 ± 19.40% | 6.724 ±  0.24% | 4.555 ± 2.63% | 67.7 | 1.24 | 1.77 | 4.626 ± 0.122
5 | 850 | 7.984 ±  2.23% | 3.262 ± 37.92% | 6.527 ±  0.21% | 4.142 ± 1.31% | 63.5 | 1.96 | 3.19 | 4.207 ± 0.055
6 | 900 | 4.638 ±  3.74% | 5.594 ± 27.76% | 5.425 ±  0.24% | 4.032 ± 1.31% | 74.3 | 3.27 | 5.56 | 4.095 ± 0.054
7 | 950 | 4.153 ±  2.40% | 0.775 ± 80.28% | 5.162 ±  0.25% | 3.907 ± 0.82% | 75.7 | 4.90 | 9.12 | 3.969 ± 0.032
8 | 990 | 4.177 ±  2.36% | 0.320 ± 88.65% | 5.237 ±  0.20% | 3.974 ± 0.78% | 75.9 | 5.88 | 13.38 | 4.036 ± 0.031
9 | 1020 | 4.937 ±  1.52% | 1.945 ± 22.92% | 5.398 ±  0.21% | 3.912 ± 0.63% | 72.5 | 6.16 | 17.85 | 3.973 ± 0.025
10 | 1050 | .300 ±  1.69% | – | 5.008 ±  0.16% | 4.004 ± 0.46% | 79.9 | 6.80 | 22.79 | 4.067 ± 0.019
11 | 1070 | 4.351 ±  0.92% | 3.251 ± 23.83% | 5.187 ±  0.20% | 3.876 ± 0.41% | 74.7 | 6.59 | 27.57 | 3.937 ± 0.016
12 | 1090 | 4.894 ±  1.42% | 0.821 ± 49.07% | 5.390 ±  0.14% | 3.916 ± 0.56% | 72.6 | 6.74 | 32.46 | 3.977 ± 0.022
13 | 1105 | 6.214 ±  0.88% | 0.210 ± 99.95% | 5.802 ±  0.13% | 3.937 ± 0.45% | 67.9 | 6.58 | 37.23 | 3.999 ± 0.018
14 | 1115 | 8.172 ±  0.76% | 0.936 ± 26.88% | 6.424 ±  0.13% | 3.981 ± 0.51% | 62.0 | 5.68 | 41.35 | 4.044 ± 0.020
15 | 1125 | 9.465 ±  1.77% | 1.177 ± 99.95% | 6.765 ±  0.20% | 3.940 ± 1.31% | 58.2 | 5.56 | 45.39 | 4.002 ± 0.052
16 | 1140 | 10.882 ±  1.17% | 1.783 ± 19.56% | 7.146 ±  0.20% | 3.903 ± 1.03% | 54.6 | 5.77 | 49.58 | 3.965 ± 0.041
17 | 1160 | 12.504 ±  0.97% | 1.249 ± 42.51% | 7.570 ±  0.14% | 3.847 ± 0.97% | 50.8 | 6.17 | 54.05 | 3.908 ± 0.038
18 | 1180 | 15.277 ±  0.97% | 0.842 ± 28.11% | 8.416 ±  0.21% | 3.874 ± 1.22% | 46.0 | 6.31 | 58.63 | 3.935 ± 0.048
19 | 1200 | 17.133 ±  0.86% | 0.863 ± 45.97% | 8.978 ±  0.16% | 3.887 ± 1.18% | 43.3 | 6.39 | 63.27 | 3.948 ± 0.046
20 | 1220 | 9.295 ±  1.19% | – | 6.664 ±  0.27% | 3.888 ± 0.96% | 58.3 | 8.51 | 69.44 | 3.949 ± 0.038
21 | 1240 | 11.736 ±  1.06% | 1.769 ± 16.59% | 7.395 ±  0.17% | 3.900 ± 0.99% | 52.7 | 8.80 | 75.83 | 3.961 ± 0.039
22 | 1260 | 10.310 ±  0.65% | 0.785 ± 27.47% | 6.973 ±  0.14% | 3.898 ± 0.57% | 55.9 | 11.53 | 84.19 | 3.959 ± 0.022
23 | 1275 | 14.144 ±  0.88% | 0.527 ± 99.95% | 8.124 ±  0.19% | 3.916 ± 1.02% | 48.2 | 9.51 | 91.09 | 3.977 ± 0.040
24 | 1290 | 27.334 ±  0.51% | 0.318 ± 99.90% | 11.980 ±  0.25% | 3.874 ± 1.23% | 32.3 | 6.23 | 95.61 | 3.935 ± 0.048
25 | 1310 | 63.209 ±  0.73% | 2.435 ± 25.05% | 22.627 ±  0.19% | 3.922 ± 3.65% | 17.3 | 3.32 | 98.02 | 3.984 ± 0.145
26 | 1340 | 165.290 ±  0.61% | 1.063 ± 99.95% | 52.405 ±  0.25% | 3.533 ± 9.17% | 6.7 | 1.72 | 99.27 | 3.589 ± 0.329
27 | 1370 | 370.270 ±  0.59% | 0.441 ± 99.90% | 113.480 ±  0.31% | 4.033 ± 18.3% | 3.6 | 1.01 | 100.00 | 4.097 ± 0.748

λ = 5.543 x 10^-10 a^-1	       Sensitivity 3 (± ~15%) x 10^-17 mol/mV            ^40Ar* – radiogenic argon	 
^39Ar_K — K-derived ^39Ar     Error on age reflects analytical uncertainty only; error in J is not included
(^36Ar/^37Ar)_Ca = 3.50 x 10^-4; (^39Ar/^37Ar)_Ca = 7.86 x 10^-4; (^40Ar/^39Ar)_K = 0.0289
Irradiation for 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
All errors are one standard deviation