![]() | Eastern Mojave Geology -- A Botanist's View |
Tom Schweich |
![]() Topics in this Article: Rock Units Geomorphology Economic Geology Literature Cited |
Try as I might, I am unable to ignore the substrate for the plants I study. Over the years, notes about rock units, sand dunes, and mines have accumulated at such a rate as to present the alarming possibility that I might be nearly as interested in the geology as the botany. My intention for this page is to present those notes as a very brief review of the geology immediate to Lobo Point and the Mid Hills. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Literature Cited:
Locations: Lobo Point. Mid Hills. |
IntroductionThese notes comprise readily accessible data about the rock units, the common geomorphic features and the economic geology of the eastern Mojave. There are many other sources of information. The Reynolds and Reynolds (1995) volume and the web sites prepared by the U. S. G. S. are also excellent starting places for additional information.Both the National Park Service and the United States Geological Survey have web pages about the geology of Mojave National Preserve. You can find them at:
|
Other articles:
This article is one of three geology articles on my web site. The other two pages are: Death Valley Geology and Inyo-White Geology.
|
|
| Geologic Time Scale.The University of California Museum of Paleontology has a excellent Geologic Time Scale.
|
| Rock Units
|
In this chapter, rock units are presented in time sequence from oldest rocks to youngest rocks.
|
|
| PrecambrianPrecambrian metamorphic gneiss and schist crop out just north of the North Wild Horse Mesa and Lobo Point.
|
| Hadean
|
| Archaean
|
Large volumes of continental crust were produced over a short period of time in the Archean, when the planet was probably too hot for modern plate tectonics to operate. Under the higher thermal gradient of the Archean, it is likely that metamorphism of subducted oceanic crust proceeded via a different P-T path than followed by present day subducted oceanic crust. In particular, the higher temperatures at shallower depths quickly dehydrated subducting oceanic crust metamorphosing it through the lower pressure greenschist to amphibolite to granulite facies, as opposed to the higher-pressure blueschist to eclogite facies of modern day subduction.
|
|
Literature Cited:
Other articles:
Bjørnerud and Austrheim (2004) studied an outcrop of partly eclogitized mafic granulite facies in Holsnøy, western Norway, in which reaction process to eclogite from granulite was limited by the availability of water. Such dehydrated but uneclogitized mafic crust could have been very strong and too buoyant to sink into the mantle, and it may have formed the substrate for the first continental lithosphere.
|
|
Literature Cited:
… emergence of the aerobic biosphere during the Archean-Proterozoic transition …
|
|
| Proterozoic EonThe period of Earth's history that began 2.5 billion years ago and ended 542.0 million years ago is known as the Proterozoic, which is subdivided into three eras: the Paleoproterozoic (2.5 to 1.6 billion years ago), Mesoproterozoic (1.6 to 1 billion years ago), and Neoproterozoic (1 billion to 542.0 million years ago).
|
| Paleoproterozoic EraSpans the time period from 2,500 to 1,600 million years ago (2.5–1.6 Ga), is the first of the three sub-divisions (eras) of the Proterozoic Eon. It was during this era that the continents first stabilized.Paleontological evidence suggests that the Earth's rotational rate during this era resulted in 20 hour days ~1.8 billion years ago, implying a total of ~450 days per year.
|
| MesoproterozoicThe Mesoproterozoic Era is a geologic era that occurred from 1,600 to 1,000 million years ago. The Mesoproterozoic was the first period of Earth's history of which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic), but little is known about them. The continental masses of the Mesoproterozoic were more or less the same ones that exist today
|
| NeoproterozoicThe Neoproterozoic Era is the unit of geologic time from 1,000 to 541 million years ago.It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran Periods. It is preceded by the Mesoproterozoic era and succeeded by the Paleozoic era. The most severe glaciation known in the geologic record occurred during the Cryogenian, when ice sheets reached the equator and formed a possible "Snowball Earth". The earliest fossils of multicellular life are found in the Ediacaran, including the Ediacarans, which were the earliest animals. According to Rino and co-workers, the sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust
|
Literature Cited:
The succession of Precambrian-Cambrian rock units from the southeast near Las Vegas to the northwest in the Inyo-White mountain ranges show facies changes from continental deposits through shallow water or continental margin deposits in the death Valley area to deep water deposits in the Inyo-White Mountains.
|
|
Literature Cited:
Locations: Marble Mountains.
In the Mojave this succession was studied by Fedo and Cooper (1990).
|
|
Literature Cited:
Locations: Marble Mountains.
|
|
Other articles:
Locations: Pahrump.
| Pahrump Group
|
| Crystal Spring Formation
|
| Beck Spring Dolomite
|
| Kingston Peak Formation
|
| Paleozoic
|
Locations: New York Mountains. Providence Mountains.
The Paleozoic is represented by the shales and limestones of the Providence and New York Mountains.
|
|
Literature Cited:
| Prospect Mountain QuartziteThis is an abandoned term in most of the Mojave Desert. This sequence of quartzite is now attributed to, in ascending order, the Johnnie, Stirling, Wood Canyon and Zabriskie Formations (DeCourten, 1979)
|
Literature Cited:
Other articles:
Locations: Latham's Cabin.
| Latham ShaleThe Latham Shale is a Lower Cambrian, fossiliferous, greenish-gray platy shale, ranging between 55 and 75 feet in thickness. With a type locality of Latham's Cabin, northern Providence Mountains, the Latham Shale is common in the Providence and Marble Mountains, and east-central Mojave Desert. It is considered a part of the Carrara Formation (DeCourten, 1979).
|
Literature Cited:
Hazzard (1954) describes the Latham Shale as a fossiliferous greenish gray platy shale which weathers to platy and paper-thin fragments. Thin, buff-weathering sandy limestone layers are present.
|
|
Locations:
Summit Spring.
The Latham Shale is exposed at several places around the periphery of the Providence Mountains. One of the most accessible locations is found near Summit Spring at the north end of the Providence Mountains.
|
|
Literature Cited:
Locations: Chambless. Marble Mountains.
| Chambless LimestoneThe Chambless limestone is a Lower Cambrian massive to thick-bedded, light to gray limestone with abundant oncolites, including a platy, fossiliferous zone yeilding brachiopods and trilobites. It commonly about 200 feet thick. The type locality is 2 miles north of Chambless in an old quarry in the Marble Mountains. The Chambless Limestone is found in the Providence and Marble Mountains, and is considered a part of the Carrara Formation (DeCourten, 1979).
|
Literature Cited:
Hazzard (1954) describes the Chambless Limestone as a massive weathering, light to dark limestone in beds 1 to 10 feet thick, with algal nodules throughout. Locally a 10 to 15-foot zone of platy, fossiliferous limestone occurs a little above the middle.
|
|
Literature Cited:
Locations: Cadiz. Marble Mountains.
| Cadiz FormationThe Cadiz Formation is a Lower and Middle Cambrian sequence of shale, arenaceous limestone, nodular limestone, and argillaceous limestone; commonly fossiliferous and locally cross-bedded, from 400 to 600 feet thick. The type locality is in the Marble Mountains, 3 miles north of Cadiz. The Cadiz Formation is well exposed in the east-central Mojave Desert region, particularly in the Providence - Marble Mountains area. Some authors now consider the Cadiz Formation to be part of the Carrara Formation (DeCourten, 1979).
|
Literature Cited:
Hazzard (1954) describes the Cadiz Formation as a buff and gray muddy limestone, purplish and reddish shale; greenish gray shale, and platy quartzite.
|
|
Literature Cited:
Other articles:
Locations: Providence Mountains.
| Bonanza King FormationThe Bonanza King Formation is a Middle and Upper Cambrian, non-fossiliferous, light gray domomite and dolomitic limestone commonly displaying algal laminae and containing chert nodules. It is 1900 to 2000 feet thick. The type locality is the east flank of the Providence Mountains. The distribution of the Bonanza King Formation includes the Providence Mountains and several adjacent ranges of the eastern Mojave desert, also much of the southwestern Basin and Range province in California (DeCourten, 1979).
|
Literature Cited:
In the Providence Mountains, the Bonanza king Formation has been divided into three units.
The lower unit is a dark smoky gray dolomite and partially dolomitized limestone, locally cherty and sandy with intraformational pebble and cobble conglomerates, in individual beds 6 inches to 3 feet thick (Hazzard, 1954).
|
|
Literature Cited:
| Silver King DolomiteThe Silver King dolomite is the middle unit of the Bonanza King Formation and is a very dark smoky gray to nearly black dolomite (Hazzard, 1954).
|
The upper unit of the Bonanza King Formation is a light creamy gray dolomite.
|
|
Literature Cited:
Other articles:
Locations: Goodsprings. Sheep Mountain.
| Goodsprings DolomiteThe Goodsprings dolomite was named and described by Hewett (1931), who assigned a Cambrian-Devonian age based on sparse fossils and stratigraphic position between known Cambrian and Devonian strata. In its type section at Sheep Mountain, the Goodsprings is 2,475 ft (750 m) thick and lies between the Middle Cambrian Bright Angel Shale (= Carrara Formation) and the Middle Devonian Sultan Formation (Cooper, 1987).
|
Locations:
Kokoweef Peak.
The peak of Kokoweef Peak is formed of Goodsprings Dolomite.
The outcrop is bounded by the Clark Mountain Fault and extends to the southeast into the Ivanpah Valley. Flanking the north and west of Kokoweef Peak is a series of progressively younger rocks, beginning with the Sultan Limestone and ending with the Aztec Sandstone.
|
|
Literature Cited:
The Goodsprings Dolomite is not identified in the Providence Mountains by Hazzard (1954).
Instead he describes 750 feet of dolomite, containing an unconformity, that has been formerly named the Cornfield Springs Formation.
On the basis of the materials I have, it appears that relationship between the Bonanza King and Goodsprings Formations is unclear and requires additional work.
|
|
Literature Cited:
Locations: Sultan Mine.
| Sultan LimestoneThe Sultan limestone is a Middle Devonian massive, finely crystalline limestone, crystalline dolomite, thin bedded bleached linestone, and chert. It is locally fossiliferous. The type locality is near the Sultan Mine, Goodsprings District, Nevada. The Sultan limestone is common in many eastern Mojave Desert ranges; Providence Mountains -- Devil's Playground area (DeCourten, 1979).
|
Literature Cited:
Locations: Ironside Mine.
| Ironside(?) dolomiteThe Ironside Dolomite member of the Sultan limestone is a Middle and Upper Devonian dark gray to black dolomite, up to 150 feet thick, and sparsely fossiliferous. The type area is near the Ironside mine, west side of the Spring Mountains, Goodsprings quadrangle, Nevada. The Ironside dolomite is common wherever the Sultan limestone is present in the eastern Mojave Desert region; Providence Mountains (DeCourten, 1979).
|
Literature Cited:
Locations: Valentine Mine.
| Valentine limestoneThe Valentine Limestone Member of the Sultan Limestone is a Devonian dolomite, limestone, and dolomitic limestone, up to 700 feet in total thickness. The type locality is east of the Valentine mine, Clark County, Nevada. The Valentine Limestone is recognized wherever the Sultan Limestone is present in the east-central Mojave Desert, in the Providence -- Marble Mountains region (DeCourten, 1979).
|
Literature Cited:
Locations: Crystal Pass.
| Crystal Pass LimestoneThe Crystal Pass Limestone member of the Sultan Limestone is a thick-bedded light gray limestone with subordinate dolomite and white to brown dolomitic limestone; up to 300 feet thick. The type locality is in the Crystal Pass area, Clark County, Nevada. The Crystal Pass Limestone is found in the east-central Mojave Desert region; Providence and Old Dad Mountains (DeCourten, 1979).
|
Literature Cited:
Other articles:
I think somewhere about here, the latest Devonian -- Early Mississippian Antler orogeny fits in.
|
|
Literature Cited:
Other articles:
Locations: Monte Cristo Mine. Old Dad Mountain.
| Monte Cristo Formation
|
Literature Cited:
The lowest unit of the Monte Cristo Formation is a white to brownish-weathering vitreous quartzite and sandstone with local cross-bedding (Hazzard, 1954).
|
|
Literature Cited:
Other articles:
Omya (California) operates the Amboy Limestone quarry located 6 miles east of Amboy, California, in the southern Bristol Mountains. The Amboy Limestone deposit, a very high purity, high brightness (white) crystalline limestone deposit is of such high purity it is suitable for pharmaceutical and food grade limestone applications, and can be utilized in products for human consumption. The limstone is mined from an extensive dip slope of Mississippian age Monte Cristo Limestone, Bullion Member, up to 300 feet thick, and 1500 feet long. Current mine life is 55 years, plus reclamation phases for a total operation life of 70 years. The current Phase 1 quarry development occurs in an area of about 10 acres. The ultimate quary will cover approximately 50 acres.
|
|
Literature Cited:
Locations: Dawn Mine.
| Dawn limestoneThe Dawn Limestone Member of the Monte Cristo Formation is a Lower Mississippian fossiliferous, dark blue-gray, massive to thick-bedded limestone and crystalline dolomite with locally abundant lenses of chert, 100-300 feet thick. The type locality is near the Dawn Mine, in the Goodsprings Mining District of southern Nevada. The Dawn Limestone is found in the Providence - New York Mountains area (DeCourten, 1979).
|
Literature Cited:
Hazzard (1954) describes the Dawn Limestone as a light and dark limestone in massive beds up to 20 feet thick separated by platy beds. The upper part is characterized by much chert in irregular discontinuous beds up to 3 inches in thickness.
|
|
Locations: Pahranagat Range.
The Dawn Limestone, as exposed in the Arrow Canyon Range, plays a part in understanding significant changes in carbon and oxygen isotope of the Lower Mississippian.
Deposited in the foreland basin on the craton-side of the Antler orogenic system, Saltzman (2002) compared carbon and oxygen isotopes in the Dawn Limestone with those found in Limestone X from the Pahranagat and and the Henderson Canyon Formation (limestone) from southeast Idaho in an attempt to understand the cause of increased 13C.
While Saltzman was able to show synchronicity in the isotope changes, his data does not show whether the cause was burial of organic carbon in deep-marine basins associated with subsidence during the Antler orogeny, or eustatic lowering of sea level due to glaciation.
|
|
Literature Cited:
Other articles:
Locations: Anchor Mine.
| Anchor LimestoneThe Anchor Limestone Member (of the Monte Cristo Limestone) is a Mississippian pale gray, platy, crinoidal limestone containing irregular-shaped brown chert nodules, which ranges from 100 to 150 feet in thickness in the eastern Mojave Desert. The type locality is the Anchor Mine, Goodsprings quadrangle, Nevada. In the Mojave Desert, the Anchor Limestone is found in the Providence Mountains (DeCourten, 1979).
|
Literature Cited:
Hazzard (1954) describes the Anchor Limestone as a light gray, platy-weathering crinoidal limestone with much brown chert in irregular nodules and sheets along bedding planes.
|
|
Literature Cited:
Locations: Bullion Mine.
| Bullion LimestoneAlso known as the Bullion Dolomite Member (of the Monte Cristo Formation) is a Lower Mississippian massive, commonly cliff-forming, coarsely crustalline crinoidal dolomite. The type locality is near the Bullion Mine, in the Goodsprings Quadrangle of southern Nevada. The Bullion Limestone is common in the east-centeral Mojave, particularly in the Providence Mountains - Devil's Playground area (DeCourten, 1979).
|
Literature Cited:
Hazzard (1954) describes the Bullion Limestone as a light gray to cream-colored crinoidal imestone with very obscure bedding; commonly cliff forming.
|
|
Literature Cited:
Locations: Yellowpine Mine.
| Yellowpine limestoneThe Yellowpine Limestone member (of the Monte Cristo Limestone) is an Upper Missippian dark gray limestone, massive to thin-bedded, fossiliferous; 75-125 feet thick in the Providence Mountains. The type locality is near the Yellowpine Mine, Goodsprings region, Nevada. The Yellowpine Limestone is found in the Providence Mountains region, of the east-central Mojave (DeCourten, 1979).
|
Literature Cited:
Hazzard (1954) describes the Yellowpine Limestone as a very dark gray limestone, generally massive but locally thinly bedded.
|
|
Literature Cited:
Other articles:
Locations: Bird Spring Range.
| Bird Spring Formation
|
Literature Cited:
The lower unit of the Bird Spring Formation in the Providence Mountains is a very dark to light creamy gray limestone, that is locally domomitized.
The lower half of the unit comprises massive weathering beds up to 30 feet in thickness separated by platy, commonly cherty and fossiliferous layers.
Minor amounts of sandstone, sandy limestone, and shale occur.
The outcrop surface commonly develops a cliff-bench slope (Hazzard, 1954).
|
|
Literature Cited:
In the Providence Mountains, the upper unit contains both sandstone and limestone.
At the base is 20-foot some of locally cross-bedded sandy limestone and limy sandstone with black chert pebbles.
About 75 feet above is a massive 70-foot light gray limestone.
As a unit the lower 750 feet of beds consists of dark and light limestone in beds up to 10 feet thick.
Platy to shaly, in part sandy, fossiliferous, chert rich zones separate some of the massive beds.
The upper 1380 feet of the section is medium to light gray, sparingly fossiliferous limestone in beds up to 5 feet thick. Minor chert and sandstone occur (Hazzard, 1954).
|
|
Literature Cited:
Other articles:
Somewhere around here the Late Permian -- earliest Triassic Sonoma orogeny fits in.
|
|
| Mesozoic
|
At the beginning of the Mesozoic, the continents of the Earth formed a supercontinent called Pangea. The western or northwestern coast of the supercontinent was the Panthalassa Ocean.
|
|
Literature Cited:
Other articles:
Locations: Aztec Tank. Mescal Range.
| Aztec Sandstone
|
![]()
The Mesozoic era is represented in the Mid Hills by the Mid Hills adamellite and other granitic intrusive rocks.
|
|
Locations: Little Thorne Mountains. Lobo Point.
Washes at Lobo Point contain grus from the
Mesozoic granite of Little Thorn Mountains to the north.
|
|
Literature Cited:
Other articles:
This outcrop of tectonic breccia alongside Wild Horse Canyon Road contains Mid Hills adamellite with tumbled blocks of Precambrian gneiss (Reynolds and Reynolds, 1995).
|
|
| Cenozoic
|
| Tertiary
|
The Sevier Thrust Belt is found in southeastern California, southeastern Nevada, western Utah, southwestern Wyoming, eastern Idaho, and western Montana,
|
|
Literature Cited:
Locations: Wah Wah Mountains.
In Utah the Sevier Thrust Belt is found in the Wah Wah Mountains.
|
|
| Miocene
|
Literature Cited:
Other articles:
Rocks at Lobo Point and North Wild Horse Mesa are Miocene rhyolitic
pyroclastic flows interbedded with lacustrine sedimentary rocks
(McCurry, 1985).
|
|
Other articles:
| Peach Spring Tuff
|
Literature Cited:
Other articles:
A single welded rhyolite tuff containing conspicuous chatoyant sanidine phenocrysts occurs in the Tertiary section in many mountain ranges in western Arizona and the Mojave Desert.
The tuff is exposed is continuously in a region stretching from Barstow, California to the Colorado Plateau at Peach Springs, Arizona.
In most ranges it is the only welded tuff in the Tertiary section.
These scattered outcrops represent part of a single enormous early Miocene outflow sheet (Glazner et al., 1986)
|
|
Literature Cited:
The tuff was originally recognized over an area of about 500 km2 between Kingman and Peach Springs, where it was named.
Mapping in the Colorado River trough extended the correlation westward into tilted Miocene sections on both sides of the Colorado River.
In the eastern Mojave Desert, the tuff has been found in the Providence Mountains (Goldfarb et al., 1986), the Mid Hills at Wild Horse Mesa and Pinto Mountain, and the New York Mountains (Miller et al., 1986). Petrographically identical tuff occurs in most of the desert ranges of the central Mojave Desert, such as the Bristol Mountains, Bullion Mountains, Cady Mountains, and Old Dad Mountains.
|
|
Other articles:
Correlation of the tuff makes it a exceptionally valuable stratigraphic and tectonic marker horizon because of (1) its presence in otherwise difficult-to-correlate local stratigraphic sections, (2) its deposition during a time of regional extension, and (3) its wide geographic distribution across Neogene tectonic-province boundaries.
|
|
Literature Cited:
Other articles:
Locations: Peach Springs.
The Peach Springs Tuff and its Mojave Desert equivalent are characterized by discrepant K-Ar ages.
Ages determined on sanidine, the mineral most often used for dating, range from 16.2 to 20.0 Ma; the mean is 18.2 Ma.
|
|
The tuff lacks a known source; however, trends in outcrop thickness suggest
the source was somewhere in the Colorado River trough area,
near the southern tip of Nevada.
|
|
Literature Cited:
Other articles:
Approximately coeval with the welded tuffs of the eastern Mojave Desert are the ignimbrites of the Sierra Madre Occidental.
Peculiar to these ignimbrites is eruption from large fissures rather than calderas as we look for in the Mojave Desert.
As described by Aguirre-Diaz and Labarthe-Hernandez (2003), the fissures have the same general trend of Basin and Range faults.
The authors propose a model in which batholith-sized magma chambers reached shallow crustal levels and erupted their contents when they reached Basin and Range normal faults.
|
|
Other articles:
Outcrop at Columbus/Gem mine, in Daggett Ridge.
|
|
Other articles:
Locations:
Daggett Ridge.
|
|
Other articles:
|
|
Other articles:
| Winkler Formation
| |