TABLE 1. Comparison of the chemical composition of glass of the Marker Tuff Bed in the Horned Toad Hills with that of the 4.83-Ma Lawlor Tuff (type locality) in the San Francisco Bay area. Analysis by elecron microprobe (JEOL 8600), at the U.S. Geological Survey, Menlo Park, Calif. Charles Meyer, James Walker, David Wahl, and Elmira Wan, analysts (1982-2006). Analyses recalculated to a 100% fluid-free base to compensate for differences in hydration of glass. Sample HTH-5, obtained from Member 3, playa sediments, may be partly leached of Fe2O3. Composition of the tephra layer underlying the Marker Tuff Bed, HTH-3, is shown for comparison.
 
 

 

SiO2

Al2O3

Fe2O3

MgO

MnO

CaO

TiO2

Na2O

K2O

Total,R

 

Marker Tuff Bed at Horned Toad Hills, Mojave Desert (HTH-1, western part of study area; HTH-4, central part; HTH-5, eastern part)

 

HTH-1, T43-2

73.41

14.46

2.15

0.08

0.05

0.84

0.17

5.05

3.78

99.99

 

HTH-4, T546-2

74.02

14.19

2.11

0.10

0.04

0.85

0.19

4.62

3.88

100.00

 

HTH-5, T546-3

74.08

14.20

1.99

0.09

0.04

0.88

0.17

4.93

3.63

100.01

 

 

 

 

 

 

 

 

 

 

 

 

 

Lawlor Tuff, type locality in Lawlor Ravine, Los Medanos Hills, eastern San Francisco Bay area. LAWLOR-1, fall pumice; LAWLOR-2, ash-flow tuff

 

LAWLOR-1 T325-9

73.20

14.29

2.15

0.09

0.04

0.84

0.18

4.83

4.37

99.99

 

LAWLOR-1 T530-7

73.78

14.07

2.13

0.10

0.05

0.85

0.18

4.66

4.19

100.01

 

LAWLOR-2 T325-10

73.10

14.32

2.21

0.10

0.04

0.86

0.17

4.79

4.41

100.00

 

 

 

 

 

 

 

 

 

 

 

 

 

Statistics for the Lawlor Tuff, ash/pumice fall and ash-flow, from 43 localities in California, Nevada, and Arizona

 

Lawlor Tuff, Mean, 43 samples

73.79

14.23

2.16

0.10

0.04

0.88

0.17

4.44

4.18

100.00

 

Standard Deviation (1)

0.61

0.27

0.05

0.01

0.01

0.03

0.01

0.46

0.53

0.01

 

Range

2.83

1.32

0.24

0.04

0.05

0.12

0.06

2.38

3.01

0.04

 

Minimum

72.95

13.49

2.03

0.08

0.02

0.83

0.14

2.98

2.29

99.98

 

Maximum

75.78

14.81

2.27

0.12

0.07

0.95

0.20

5.36

5.30

100.02

 

 

 

 

 

 

 

 

 

 

 

 

 

Tephra Layer HTH-3, underlying the Marker tuff Bed with ~14 m separation, at the Horned Toad Hills

 

HTH-3, T546-1 (all shards)

64.75

15.42

5.68

1.65

0.09

3.94

1.00

4.15

3.32

100.00

 

HTH-3, T546-1 (high Ca, Fe)

61.65

16.05

6.95

2.30

0.10

5.00

1.07

4.15

2.74

100.01

 

HTH-3, T546-1 (med, Ca, Fe)

65.94

15.08

5.21

1.37

0.08

3.55

1.00

4.22

3.56

100.01

 

HTH-3, T546-1 (low Ca, Fe)

69.19

14.77

3.82

0.82

0.07

2.38

0.87

3.96

4.12

100.00

 

 

 

 

 

 

 

 

 

 

 

 

 

MSE 202 (1) T75-1

65.53

15.17

5.34

1.57

0.13

3.83

0.99

3.86

3.59

100.01

 

TWN-L-2.235B

66.00

15.48

5.05

1.49

ND

4.02

1.04

4.19

2.72

99.99

 

T2023M.12MTB;2, T187-2

65.15

16.06

5.11

1.70

0.09

3.93

0.93

4.40

2.63

100.00

 

 

 

 

 

 

 

 

 

 

 

 

 

Samples of the Pinole Tuff, eastern San Francisco Bay area

 

758-190B, T1-7, P

63.55

16.15

6.98

1.07

0.15

3.27

0.92

6.13

1.97

100.01

 

758-181A. T1-9. P

61.57

16.36

5.32

2.27

0.09

4.60

0.96

4.11

4.71

99.99

 

758-178B, T1-13. P

71.27

14.39

3.56

0.09

0.08

1.09

0.23

5.79

3.49

99.99