Geological investigations in the northwestern Springbergs lead to an improved understanding of the regional significance of contractile structures in the. The Fermo-Triassic thrust belt ends in the Cottonwood Mountains to the north or continues into central Nevada. Extension within the extended domain of the Death Valley obscures the relationship between the Fermo-Triassic thrust belt in the Cottonwood Mountains and the Central Nevada thrust belt.
CHAPTER 2
Our results suggest that various Ediacaran faunas postdate the youngest major Neoproterozoic ice age by tens of thousands of years. In one consideration, a diverse Ediacaran fauna appeared tens of thousands of years after the youngest Neoproterozoic ice age (Grotzinger and others, 1995). Only simple Ediacaran slices are present below glacial diamictite of the Ice Brook Formation (Hofmann and others, 1990).
MACKENZIE MOUNTAINS
Levy and others (1994) suggested that incised valleys in the uppermost Caddy Canyon Formation of Idaho and Utah resulted from a major regional base-level change. Idaho and Utah Formations: GC, Geertsen Canyon Quartzite; BH, Brown's Hole Fm.; M, Mutual Fm.; CC, Caddy Canyon quartzite; KC, Kelley Canyon Fm.; MC, Maple Canyon Fm.; PC, Perry Canyon Fm. Nevada and California Formation Names: WC, Wood Canyon Fm.; SQ, Stirling quartzite; JO, Johnnie Fm.; ND, noon dolomite; KP, Kingston Peak Fm.; BS, Beck Spring Dolomite; CS, Crystal Spring Fm.
NEVADA
Geographic distribution of the Johnnie Formation in southern Nevada and southeastern California, and measured sections described in the text. Measured sections of the upper part of the Johnnie Formation in the Resting Spring Range. Lateral outcrop of the conglomeratic section in the northwestern Spring Mountains is obscured by structural complexity and alluvial cover.
NW Spring NW Spring
Hill 1152T Hill 1314T
The Caddy Canyon valleys and the Johnnie valleys are larger than any other incised valleys within the post-diamictite Neoproterozoic section in the western part. Ranges containing incised valleys in the upper Caddy Canyon Formation (Idaho and Utah) and the upper Johnnie Formation (southern Nevada and southeastern California). Geographic distribution of incised valleys in the upper Caddy Canyon Formation of Levy and others (1994).
N CANADA t
Red dots indicate carbon isotope values that may be secondary (see text and Figure 2-11), and blue dots indicate carbon isotope values that are likely primary.
NOPAH RANGE, CA
Negative carbon isotope values in the middle Johnnie Formation may be primary or secondary. Carbon isotope values are uniformly negative in the Noonday Dolomite and lowermost 50 m of the Johnnie Formation in the Nopah Range of southeastern California. As in the Nopah Range, carbon isotope values in the Bannock Range change from negative to positive upsection.
BANNOCK RANGE, ID
Contains 30% light red (lOR 6/2); weathered light yellow brown (lOYR 6/2); stringers and blebs of micritic limestone with blebs of siltstone. Also contains pale red (SR 6/2), brown-black (SR 211) to medium brown (SYR 4/4) weathered fine-grained dolomite.
TOTAL THICKNESS OF MEASURED
Quartzite, very pale orange (lOYR 8/2) to yellowish gray (SY 8/1); the same weather; very coarse grains, cemented with. Quartzite, medium reddish brown (IOR 4/6); the same weather; moderately decomposing, becoming much more decomposing within feet S of Stirling contact; very fine quartz sand with silt -20%. Phyllitic stone, gray olive (lOY 4/2); weather is same plus light brown (SYR S/6); silver neckline on the flag; breaks down.
Layered sandstone and shale, olive gray (SY 411) to light brown (SYR S/6); the same thing again; Sandstone shapes. Phyllitic siltstone; greenish gray (SY 6/1) alternating with light greenish gray (SY 8/1) and dark brown (SYR 2/2).
Conglomerate contains granule to pebble sizes up to 20 mm, including vein-quartz lithics (feldspathic granitic rocks), jasper, and large purple shale rip-up clasts (less common higher in . section).
TOTAL MEASURED THICKNESS
One hundred and six core samples were collected from the Noonday Dolomite, Johnnie Formation, and basal Stirling Quartzite in the southern Nopah Range, California. Samples were collected at five to ten meter intervals throughout the nine hundred and thirty three meter section. These samples were collected in the informally defined algal dolomite member of the Noonday Formation (Hazzard, 1937).
This negative interval is overlapped by an interval of 128 m of generally positive values which range from -0.57%0 to +2.89%0. The stratigraphically lowest positive value in this interval occurs 72.5 meters below the oolite marker bed in the Rainstorm Member and the stratigraphically highest positive value occurs 55 meters above the marker bed. The mostly positive interval near the top of the Johnnie Formation is overlain by a very negative interval which begins about lOm below the Johnnie-Stirling contact and includes at least the lower 75 m of the Stirling Quartzite.
Values in the Noonday Formation typically increase from about -7.9%0 at the bottom to -5.5%0 about 75m below the top. Values decrease in the overlying rocks to a minimum of about -9.5%0 about 60 m above the base of the Johnnie Formation. In the remainder of the Johnnie Formation, values range from -11.05 to -2.71 with stratigraphically adjacent values varying up to 5% o.
Near the Stirling-Johnnie contact, 3180 values become markedly negative, correlate strongly with 813c (r=.94), and reach the minimum value for the traverse in the lower Stirling quartzite.
CHAPTER 3
The stratigraphy of the northwestern Spring Mountains was described by Burchfiel (1964) and Burchfiel and others (1974), and is shown in Figure 3-1. The base of the upper Johnnie Formation is emplaced at the base of a distinctive grayish-orange oolitic limestone bed. The quartzite contrasts sharply with the underlying brown and light green siltstones of the upper Johnnie Formation.
The upper part of the formation comprises very light gray quartzite which has a yellowish tinge in places. The lower part of the formation includes dolostone two meters thick, as well as small amounts of quartzite. Abundant fossil fragments in carbonates from the upper part of the formation allow them to be easily distinguished from non-fossil carbonates in the lower part.
In the study area, a 2-m-long layer of skolithos piperock marks the base of the formation. In this study, the top of the formation was placed at the base of the first thick limestone interval in the Bonanza King Formation. In general, the Stirling quartzite in the hanging wall of the Diebert fault is upright and generally dips between 19 and 33°.
In the area of this map, the Hill 1348T anticline is defined by folding of the Diebert fault.
J Zjm
Map showing the Niavi fault and transverse structures in the north-central part of the study area. Map showing the Niavi fault and transverse structures in the northwestern part of the study area. The Niavi Hanging Wall passes through an additional section in the northwesternmost part of the study area ('Highway 95 section', northern part of Figure 3.7).
To the southeast, the mapped continuation of the Gold Spring fault is complex and apparently schematic. Two chains of the Gold Spring fault probably cut the Point of Rocks fault beneath the debris. A smaller western part of the fault was also mapped east of the main set.
The fault consists of a number of anastomosing strings in the central part of the map area. To the southeast in plate 2, the fault faces the upper part of the Carrara Formation. The fault dips to the southeast on the Geologic Map of the Spring Mountains, Nevada (Burchfiel et al., 1974).
Previous work - Burchfiel (1965) mapped the Jaybird Fault in the northern part of the study area.
The axial plane of the hanging wall anticline dips more shallowly (30°) than other folds in the Johnnie Formation to the north. An unconformity at or below the base of the Stirling Quartzite may remove a significant portion of the upper Johnnie Formation at Hill 1321 T. In the southern part of the study area, the Jaybird fault includes just over 200 m of structural relief at the base of the Stirling Quartzite .
The upper Johnnie Formation in the hanging wall of the fault is tectonically thickened by tight folds with a wavelength on the order of 5 meters. The Johnnie Formation north of the folds dips 9-39° with dip directions ranging from north-northwest to north-northeast. A VIRIS image (top) and a geologic map (bottom) of folds within the Johnnie Formation in the northeastern part of the study area.
Of the three folds in the northern part of the study area, only the inverted anticline can be traced to the south. Geologic map showing folds within the Johnnie Formation in the northeastern part of the study area. Burchfiel (1965) noted two other small-scale folds in the Johnnie Formation within the central part of the study area.
Geological map of fold trains in the hanging wall of the Paddy's fault in the southern part of the study area.
Alluvium
Stirling Quartzite
In the quartzite interval, for example, the dip changes from 34° W to 74° E over a strike distance of about 50 m. Like the syncline described in the previous section, the fold has a steep axial surface that dips ca. 60° and an amplitude of approx. 100 m. Fold in the middle of the Johnnie Formation is similar in wavelength and amplitude to folds in the same part of the Johnnie Formation in the hanging wall.
Earlier work - Burchfiel (1965) and Burchfiel et al (1983) schematically indicate an overturned syncline in the Johnnie Formation in the footwall of the Paddy fault. During thesis work, Ivosevic (1976) recognized the complexity of folding in the Johnnie Wash area, but did not characterize the fold geometry in detail. This Study - Folding within the footwall Johnnie Formation was investigated in detail in the southern part of the study area using an A VIRIS image (Figure 3-20).
Folding is discordant and the highest fold amplitude occurs in the upper part of the middle Johnnie Formation. The Johnnie Formation is rifted throughout the field and this rifting was studied in detail near the folds in the footwall of Paddy's fault. The absence of low rift-bedding angles, and the relationships between rift-bedding angle and fold geometry, suggest the presence of a single early-formed rift in the Johnnie Formation.
A VIRIS image and geological map of folds in the footwall of the Paddys Fault in the southern part of the study area.
