Supplementary Table 11. Results of laser fusion 40Ar/39Ar dating of single crystals of alkali feldspar from feldspar concentrates 
from tuff D-3-2, Member D, Shungura Formation, Section 11, NE of American Camp, about 505’N, 3601’E, Ethiopia (03-040),
 and from tuff B-10-1 (03-039) from about 80 m above base of Member B, Shungura Formation type area, about 503.6’N,
 3601.7’E

									
Sample	36Ar/39Ar
x 10-3	37Ar/39Ar
x 10-3	40Ar/39Ar	K/Ca	40Ar*/39ArK
± c.v.	% 40Ar*
	39Ar
10-15 mol	Calculated age
Ma ± 1 s.d.	
									
03-040 (780 –Ei; tuff D-3-2); J = 5.325E-04 ± 0.35%; level 6, ANU 106	
 –1	1.413  12.85%	1.918  23.36%	2.939  0.33%	274	 2.492  2.19%	84.8	3.0	2.393  0.053	
 –2	1.158  16.09%	2.019  24.45%	2.814  0.35%	261	 2.443  2.29%	86.8	2.9	2.345  0.054	
 –3 	2.262   1.92%	1.602  10.04%	3.255  0.35%	328	 2.557  0.67%	78.6	4.4	2.455  0.019	
 –4 	4.044   1.67%	35.270   1.66%	3.765  0.33%	  15	 2.544  0.93%	67.6	3.6	2.442  0.024	
 –5 	1.660   2.24%	0.856  40.01%	3.087  0.33%	615	 2.567  0.59%	83.2	4.8	2.464  0.017	
 –6	1.177   2.56%	9.188   3.10%	2.978  0.30%	  57	 2.602  0.49%	87.4	6.3	2.497  0.015	
 –7 	2.380   1.35%	9.403   2.13%	3.351  0.33%	  56	 2.620  0.56%	78.2	7.1	2.515  0.017	
 –8 	1.462   4.18%	1.561  11.86%	2.972  0.32%	337	 2.511  0.82%	84.5	6.8	2.411  0.021	
 –9 	1.714   1.89%	23.225   2.83%	3.117  0.33%	  23	 2.583  0.54%	82.9	5.9	2.480  0.016	
 –10	1.723   2.75%	2.394   4.24%	3.083  0.31%	220	 2.544  0.67%	82.5	9.0	2.442  0.018	
 –11	2.036   2.18%	18.065   2.01%	3.159  0.32%	 29	 2.530  0.65%	80.1	7.9	2.429  0.018	
                                                    Arithmetic mean K/Ca (n = 11)      201  188       Arithmetic mean age (n = 11)       2.443  0.048  	
                                                                                                                                     Weighted mean age (n = 11)       2.466  0.010	
	
03-039 (tuff B-10-1); J = 5.289E-04 ± 0.35%; level 4, ANU 106	
 –1	0.598   7.93%	4.458   2.50%	3.313  0.32%	118	 3.107  0.57%	93.8	9.1	2.962  0.020	
[–2	1.676   6.92%	11.270   1.74%	3.680  0.31%	 47	 3.157  1.14%	85.8	7.3	3.010  0.036]	
 –3 	0.852   4.76%	2.105   2.96%	3.382  0.32%	250	 3.101  0.52%	91.7	11.4	2.956  0.018	
[–4 	9.685   1.20%	10.975   4.19%	6.081  0.30%	 48	 3.190  1.21%	52.5	8.5	3.042  0.038]	
[–5	56.180   0.96%	9.465   4.04%	19.853  0.33%	 56	 3.223  5.35%	16.2	6.7	3.073  0.164]	
 –6	0.232  15.42%	6.601   1.21%	3.223  0.32%	 80	 3.126  0.47%	97.0	10.4	2.980  0.017	
[-7	43.616   0.95%	9.726   3.67%	16.154  0.29%	 54	 3.237  4.05%	20.0	9.0	3.086  0.125]	
 –8	2.857   1.83%	7.004   3.26%	3.986  0.29%	 75	 3.113  0.62%	78.1	9.5	2.968  0.021	
 –9	0.427  12.62%	20.515   0.80%	3.262  0.32%	 26	 3.109  0.61%	95.3	8.6	2.964  0.021	
 –10	0.293   5.63%	13.177   1.60%	3.213  0.32%	 40	 3.098  0.37%	96.4	8.1	2.954  0.015	
 –11	3.049   1.79%	10.677   3.10%	4.026  0.30%	 49	 3.097  0.65%	76.9	9.7	2.953  0.022	
 –12	0.139  32.96%	12.770   1.83%	3.190  0.32%	 41	 3.121  0.54%	97.8	8.9	2.975  0.019	
 –13	0.095  88.33%	25.176   3.45%	3.172  0.37%	 21	 3.117  0.88%	98.3	4.8	2.972  0.028	
 –14	0.211  24.60%	6.806   2.93%	3.176  0.30%	 77	 3.085  0.59%	97.1	7.4	2.941  0.020	
 –15	0.124  29.85%	7.888   4.13%	3.200  0.33%	 67	 3.134  0.49%	98.0	5.9	2.988  0.018	
                                                        Arithmetic mean K/Ca (n = 11)   77  64          Arithmetic mean age(n = 11)        2.965  0.014	
                                                                                                                                     Weighted mean age (n = 11)       2.965  0.011	

l = 5.543 x 10-10 a-1      Sensitivity 2.5 ( ~15%) x 10-17 mol/mV        Bracketed results excluded from mean age calculation	
(36Ar/37Ar)Ca = 3.50 x 10-4;	 (39Ar/37Ar)Ca = 7.86 x 10-4; 	(40Ar/39Ar)K = 0.0295
40Ar* - radiogenic 40Ar;	39ArK – K-derived 39Ar;	
Mass of alkali feldspar used in each experiment generally 0.5 to 1.8 mg
Irradiation for 24 hours in X33 or X34, HIFAR reactor
Fluence monitor: Fish Canyon Tuff sanidine 92-176 of reference age 28.1 Ma
All errors are one standard deviation. Uncertainty on the 40Ar*/39ArK ratio is the analytical error. This error is combined quadratically with the estimated error of J to yield the quoted error for each age