by

           Habte Giorgis Churnet

* Th 2000 trip is correct for 2000, and serves as the format for future trips.
 
 

Trip is between April 29 through May 9

Trip visits Arizona, Utah, Nevada, and California.

Cmping areas:

Day 1.   April 29.  Depart from Atlanta/Nashville  and arrive in Las Vegas.  Night at Lake Mead.
Day 2.   April 30.  Night at Panamint Range Warm Springs.
Day 3.   May 1    Deat Valley-
Day 4     May 2.   Night at lake Mead or LAS VEGAS
Day 5     May3    Night at Joseph City
Day 6     May 4        Night at the South Rim of the Grand Canyon
Day 7    May 5        Night at the South Rim of the Grand Canyon
Day 8    May 6        Night at Capitol Reef
Day 9    May 7        Night at Capitol Reef
Day 10    May 8       Night at Las vegas
Day 11    May 9     Night at Chattanooga

Important Stops include:

1)  Valley of Fire: Basalt: Thrust belts, Red Rock Canyon: Thrust belts; Pyroclastics
2) Death valley - Amargossa chaos, Turtlebacks, Badwater, Skarn at Panament Range, Phreatomagmatic domes at center of valley, sand dunes, Ubehebe Crater, Marble Canyon.
2) Lake Mead structure: Normal and strike slip fauts
3) Meteor Crater
4) Petrified forest and Painted Forest
5) SP Mountain
6) Grand Canyon
7) Bryce and Zion canyons
8) Volcanics at St. George's.
 

The following is a synopsis of the geology of Basin and Range Province, and is mostly abstracted from Werenkie (1988).  For gold deposits, check this.
 

BASIN AND RANGE

Morphologically, the Basin Range Province is bounded by the Colorado Plateau in the east and the Sierra Nevada in the west.  A median high, centered around Spring Mountains and Sheep Range, separates two low lying areas of the Colorado River Trough/Lake Mead area on the east and the Death Valley on the West (Fig. 04).  These low lying areas are highly extended regions, while the median high is less extended.

Being in the rainshadow of the Sierra Nevada, lying at low latitudes, and composed mostly of limestone which crops out well in a desert provide the necessary conditions for excellent exposures.  The Cordillera miogeocline is exposed across the entire width of the Province at the latitude of Las Vegas and shall be the area to be visited in this trip.
 

Basement, Proterozoic Basin, and Miogeoclinal Wedge.
 

Precambrian sedimentary rocks (Y) consist of the 1.4 to 1.7 Ga. old Pahrump Group.  This group uncomfortably overlies Precambrian crystalline basement and pinches out to the West beneath an unconformity (Fig. 0 3). Other Precambrian Clastic Wedge (Z) is conformably overlain by Paleozoic strata and thickens to the West. The clastic wedge thickens from less than 100 meters on the craton to the east, to  more than 5000 meters in western areas where most of the sequence lies below basal Cambrian beds. Overlying this lithological clastic sequence is the dominantly carbonate sequence of Middle Cambrian (Bonanza King or Mauve Limestone) and younger strata .

The Paleozoic is entirely marine to marginal marine except for some Permian strata which are none marine.  Westward thickening of the carbonate succession occurs in part by thickening of individual units and in part by the pinching in of Ordovician, Silurian and Devonian disconformity (effect of the Antler Orogeny). On the craton, Upper Devonian (Temple Butte Limestone) strata lie disconformably on Upper Cambrian and are in turn disconformably overlain by Carboniferous sequences.  To the West, they lie on progressively younger strata until a fully developed Ordovician, Silurian, and Devonian section is present. In sections in the transition zone between craton and miogeocline, the highest Paleozoic strata present on the craton, include the Kaibab and Torweap Formations, which pinch out westward beneath the basal Mesozoic unconformity (The effect of Sonoman Orogeny).  The youngest strata in the region are Triassic and are overlain in eastern areas by non marine clastics locally as young as Cretaceous, and in western areas by Cenozoic volcanics and alluvium.

Interpretation:  based on lateral facies changes and unconformities.

a) The Precambrian Z and Cambrian clastic wedge changes from dominantly quartzarenite and siltstone in the east to dominantly shale and carbonate in the west, and indicates westward transition from shelf to slope-and-rise facies.  {However, because the Paleozoic shelf orientation was different from later ones, Early Paleozoic slope-and-rise facies are not present  east of the Sierra Batholith at the Las Vegas Latitude (Fig. 02).}  This is similar to an eastward transition from the dominantly quartzarenitic Chilhawee Group to the dominantly shaley sequences of the Precambrian Ocoee Series in southeastern Tennessee. Overlying the clastic wedge in Tennessee is the Middle Cambrian and Cambrian Shady Dolomite, Rome Formation,  Conasauga Group, and Cambro-Ordovician Knox Group and represent the Sauk transgressive sequence.  Likewise, in the Basin and Range Province, the Upper Precambrian clastics overlain by Tapeats Sandstone the Bright Angle Shale and Mauv Limestone or Bonanza King are Sauk Transgressive unites.

The Sauk transgression in Tennessee was interrupted by the Post-Knox Unconformity, which marks  the docking of a micrcontinent on the eastern part of the American craton during the Taconian Orogeny.  In the foreland, that orogeny was associated with an unconformity bounded sedimentary package, consisting of dark Middle Ordovician  Sevier Shale at the bottom, gray Middle Ordovician limestones at the middle, and  red beds of uppermost Ordovician Sequatchie and Silurian Rockwood Formation at the top.  However, in the Basin and Range Province no such Tipecanoe sedimentary package is found.  Instead there apparently was a continued  period of erosion or sedimentary bypassing as a distant island arc, the Klamath was migrating toward the continent above a cratonward subducting zone.  The Tipecanoe sequence is missing in the Basin and Range

The Klamath island arc docked on the west side of the American craton in the Devonian and it thrust -transported slope-and-rise facies and placed them on top of miogeoclinal facies sequences in northern Nevada (Fig. 02).   The Antler Orogeny in the west must have been active through at least the Mississippian, although it began in the Devonian.  In the south though ,and farthest landward, the record of the Antler Orogeny is marked by the sporadically preserved Devonian Temple Butte Limestone, and the overlying shallow marine, marginal marine, and occasional coastal deposits.  There is an unconformity above the Missisipppian.  Whether that marked the end of the Antler sedimentary sequence or whether that sequence extended to Kaibab limestone is unclear.  Most of sedimentary package is shallow to marginal marine with occasional estuarian and eoline deposits.

The Sonama Orogeny began in the Permian and continued through part of the Triassic.
 
 

Mesozoic Thrust and Fold Belt

Mesozoic structures (thrusts and folds) are generally east vergent.  In the north, thrust faults are within the miogeocline wedge and often have ramp-thrust geometries.  They strike NNE-SSW, parallel to the paleoslope and isopach thickness.  In the south, the thrust belt changes trend to NE-SW, parallel to the eastern boundary of the Sierra Batholith, and cuts across the miogeoclinal wedge (Fig. 02,204).  These thrusts loose ramp-thrust geometries and steeply cut across the cratonal package and involve the basement.  The thrust stratigraphic sections thin as  they are traced southward and out of the miogeocline.  In the Spring and Clark mountains block (Fig. 01), the thrusts tend to converge upon one another in the south.

Throughout most of the region , exposures of pre-Tertiary rocks are separated by alluvial valleys.  Yet, the nature of the thrust plates (Fig. 04-05) can be deduced across three to four thrust plates.  As such thrusts represent useful markers for the reconstruction of Cenozoic tectonism  (Werenkie, 1988).

Description of principal characteristics of Mesozoic thrusts.
 

The major  thrust plates from west (Eastern-Sierran) to the east (Keystone) are (Fig.  04-05)

East-Sierran// Last Chance// Marble canyon// Clery// Wheeler Pass//  Keystone.

Note:
1) The thrusts do not young eastwards.
2) Las Vegas is east of the Keystone thrust plate.
3) South of the Garlock tear fault, Eastern-Sierran thrust is placed above Keystone- major telescoping effect.
4) The wheeler Pass thrust is equivalent to the Panamint Thrust.
5)  All the thrust plates are displayed in the corridor between the two strike slip faults, the Hunter Valley Fault zone and the Northern Death Valley Furnace Creek fault zone.

Description of principal characteristics of Cenozoic Extensional faults.

East and west of the median high at the Spring Mountain-Sheep Range, the region is highly extended by denudation normal faults and strike slip faults.

** Strike-slip faults.  These have two trends.  NE-SW trending faults, such the lake Mead fault zone are left lateral.  The NW-SE trending faults such as the Las Vegas Valley Fault Zone (LVVZ) are right-later.  The effect of these faults is to more or less make the crust maintain its thickness by a North-South compressional component to the generally west vergent, listric normal faults which brought about the Basin and Range structures.

Right lateral displacement on the LVVZ is 50 km.

The Death valley, bounded by the Black Mountain and the Panament is also considered to be a pull apart basin, which formed between the North Death Valley Furnace Creek Fault Zone and the South Death Valley fault Zone.

Room problem associated with listric normal faults is solved by rollover anticlines.  Thus, west vergent listric normal faults will produce east dipping strata on the west side of valleys.  Another and complimentary method of solving the room problem is isostatic rebounding and the lateral migration of rollover anticlines.   Both the Black Mountains and the Panament Range were close to Spring Mountain in the Cenozoic.  Their current position is a consequence of listric normal faulting in association with isostatic rebounding.