BACTRIAN MOUNTAIN

 

Bactrian Mountain is a double-hump, ENE-WSW trending extension of the southern Mt. Irish Range in southern Nevada, Great Basin, USA. It is northeast of America's Groom Lake Facility ("Area 51"), and accessed by gravel roads heading north from the Extraterrestrial Highway (formerly Rt. 375).

 

The section at Bactrian Mountain is a nice Devonian to Mississippian succession of mostly carbonates & siliciclastics.  The section has a well-constrained Frasnian-Famennian boundary (lower Upper Devonian-upper Upper Devonian boundary & mass extinction horizon).  The only known place on Earth having a Famennian-aged carbonate succession is right here in the Great Basin.  The stratigraphy here also records the Middle Paleozoic transition from a passive margin to an active margin along Laurentia's Cordilleran margin.  This passive-to-active margin transition was a result of the Antler Orogeny.

 

Above & below: Looking ~N.  The double-humped ridge in the foreground is the Bactrian Mountain section.  The rocks here are dipping westward.  The peak on the right contains Devonian sedimentary rocks.  The peak on the left contains Mississippian sedimentary rocks.  The Devonian-Mississippian boundary occurs somewhere near the western edge of the saddle between the two peaks.

 

Stratigraphy at Bactrian Mountain:

 

                     Joana Limestone

        _____________________________

 

                         Pilot Shale                        ~Dev.-Miss. bdy.

        _____________________________

 

                West Range Limestone

        _____________________________

                                                                    Frasnian-Famennian bdy.

                  Guilmette Formation

 


 

Above & below: Looking W.  This is the southern face of Bactrian Mountain.  The eastern hump is to the right.  The western hump is the cliff top at left-center.  The rocks in the slope at center & right are part of the Guilmette Formation (Upper Devonian), a heterolithic unit containing limestones, quartzites, & evaporites.  The steep cliff face in the distance is the Joana Limestone (Kinderhookian, lower Lower Mississippian).  The Pilot Shale (~uppermost Devonian to ~lowermost Mississippian) is the gray slope below the Joana cliffs.  The thin limestone cliffs below the Joana are part of the West Range Limestone (Famennian, upper Upper Devonian).

 


 

Above: Looking ~NW.  Southern slopes of Bactrian Mountains's eastern hump.  These beds are part of the Guilmette Formation.

 


 

BACTRIAN MOUNTAIN EAST

 

 

Above & below: Wonderful views of the Pahranagat Valley from the eastern hump of Bactrian Mountain, Mt. Irish Range, southern Nevada, USA.

 

 

Above: The Frasnian portion (lower Upper Devonian) of the Guilmette Formation's upper member.  The light gray rocks are limestones.  The dark brownish rocks are quartzites (well-cemented quartz sandstones).  Ernie Slucher for scale (Ohio Geological Survey).

 

Above: zebra evaporites in the Guilmette Formation's upper member (upper Frasnian Stage, lower Upper Devonian).

 

Above: geologists examining the Frasnian-Famennian boundary (= gray limestone bedding plane marked with stake, just below camera bag at center-left).  The Frasnian-Famennian boundary divides the Upper Devonian into two parts.  The F-F boundary marks one of the top five most significant mass extinction events in Earth history (others include the end-Ordovician m.e., the end-Permian m.e., the end-Triassic m.e., and the Cretaceous-Tertiary boundary).  The F-F boundary in the Bactrian Mountain East section occurs at the top of unit 4 of Morrow (1997, Courier Forschungsinstitut Senckenberg 219).

 

Above: Bedding plane view of the Frasnian-Famennian boundary, Guilmette Formation's upper member, mid-Upper Devonian.

 

Above: Ernie Slucher (Ohio Geological Survey) resting on the Frasnian-Famennian boundary.

 

 

Above & below: plants of the genus Yucca are moderately common in southwestern America's deserts.  The green leaves are extremely stiff & sharp-pointed.  They could easily serve as daggers.  Extreme care is advised when walking along & among Yucca plants.

 

 


 

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