Abstract ........................................................ 1
Introduction and previous work .................................. 2
Early studies of the Chemehuevi Formation .................... 2
Groundwater and paleoseismic studies ......................... 5
Geologic mapping and geochronology ........................... 6
Need for a formal definition of the Chemehuevi Formation ..... 9
Methods ......................................................... 9
Distribution of the Chemehuevi Formation ....................... 10
Geographic distribution ..................................... 10
Longitudinal distribution ................................... 10
Sedimentology .................................................. 13
Mud facies .................................................. 13
Sand facies ................................................. 14
Rhythmite facies ............................................ 15
Tributary facies ............................................ 21
Valley margin facies ........................................ 26
Structural deformation ......................................... 26
Members and marker horizons .................................... 26
Basal gravel member ......................................... 26
Tephra layers ............................................... 30
Boundaries ..................................................... 31
Base of the formation ....................................... 31
Top of the formation and overlying terrace gravel
sequence .................................................... 33
No regional internal unconformities ......................... 37
Previous age control ........................................... 37
Tephra correlations and age constraints ........................ 42
Correlation among tephra layers in the formation ............ 42
Mammoth Mountain source area ................................ 42
Stratigraphic context of chemically similar tephra layers
elsewhere ................................................... 44
Summary of age control ...................................... 44
Interpretations and discussion ................................. 47
Interpretation of depositional environments ................. 47
Mudfacies ................................................ 47
Sand facies .............................................. 48
Rhythmite facies ......................................... 48
Tributary facies ......................................... 49
Regional stratigraphic architecture and the sand-over-mud
contact ..................................................... 49
Origin of the Chemehuevi Formation .......................... 50
Designation as a lithostratigraphic unit ....................... 51
Category and rank ........................................... 51
Selection and derivation of name ............................ 52
Stratotypes and reference sections .......................... 52
Type section-Loaf Rock hill .............................. 52
Reference section-Katherine Landing near Loaf Rock ....... 53
Reference section-Old Callville outcrop described by
Longwell (1936) .......................................... 53
Conclusions .................................................... 53
Acknowledgments ................................................ 66
References Cited ............................................... 66
Figures
1 Photograph of a typical Chemehuevi Formation outcrop ......... 3
2 Maps of study area showing surveyed outcrops and place
names ........................................................ 4
3 Reproduction of Newberry's sketch of Elephant Hill ........... 5
4 Pre-Lake Mead aerial photograph .............................. 6
5 Comparitive stratigraphy ..................................... 7
6 Models of the stratigraphic architecture of the Chemehuevi
Formation .................................................... 8
7 Longitudinal profile of the Chemehuevi Formation and
pre-Hoover Dam valley ....................................... 11
8 Relative thicknesses of sand, silt and clay in selected
outcrops .................................................... 12
9 Particle size distributions of samples ...................... 14
10 Mud facies photographs ...................................... 16
11 Sand facies photographs ..................................... 18
12 Deposits mapped by Longwell (1936) in Lake Mead area ........ 21
13 Rhythmite facies photographs ................................ 22
14 Tributary facies photographs ................................ 25
15 Valley margin facies photograph ............................. 27
16 Gradients of longitudinal profiles and tephra horizon ....... 28
17 Basal gravel photograph ..................................... 32
18 Monkey Rock tephra photographs .............................. 34
19 Other tephra photographs .................................... 35
20 Upper stratigraphic boundary of the Chemehuevi Formation .... 38
21 Tephra correlation diagram .................................. 43
22 Map of volcanic source area and sites of related tephra
layers ...................................................... 46
23 Maps of type locality ....................................... 54
24 Photographs of type locality and type section ............... 56
25 Simplified type section ..................................... 57
26 Photograph—interfingering of mud and sand near type
section ..................................................... 58
27 Photograph and reference section of partly submerged
exposure near Lake Mohave, Katherine Landing, Ariz .......... 59
28 Reference section at Old Callville .......................... 65
Tables
1 Grain-size proportions by thickness described from the
Chemehuevi Formation ........................................ 13
2 Possible locations of basal gravel member ................... 29
3 Geochemistry and stratigraphic context of four tephra
layers in the Chemehuevi Formation .......................... 36
4 Previous age control for the Chemehuevi Formation ........... 39
5 Correlation matrix for Chemehuevi Formation tephra
layers ...................................................... 40
6 Geochemistry of closest chemical matches to Mammoth
Mountain proximal pumice samples ............................ 45
7 Proposed type section of the Chemehuevi Formation at Loaf
Rock hill ................................................... 60
Appendixes
Appendix 1 Elevation and stratigraphic context of surveyed
Chemehuevi Formation localities .................... 72
Appendix 2 Particle size distributions from samples of mud
and sand facies .................................... 84
Appendix 3 List of outcrops mapped by Longwell (1936),
including minimum and maximum elevation ............ 85
Appendix 4 Old Callville section (from Longwell, 1936) ........ 87
Appendix 5 Sandy Point section (from Longwell, 1936) .......... 88
Appendix 6 Pearce Ferry sections (from Longwell, 1936) ........ 89
Appendix 7 Lithologic log of well LCRP-15 near Blythe
(from Metzger and others, 1973) .................... 90
Appendix 8 Detailed measured section surrounding the Monkey
Rock tephra layer .................................. 93
Appendix 9 Detailed measured section near Lake Mohave,
Katherine Landing, Ariz ............................ 94
|
