Transcript Lecture 12B / Geology of the Grand Canyon

Geology of the
Grand Canyon
GLG 101 - Physical Geology
Bob Leighty
These notes and web links are your primary “lecture” content in this class.
Additionally, various articles are assigned each week to supplement this “lecture”
information. I believe you’ll have enough information to reference without having
to purchase a costly textbook.
These lecture notes are very similar to the ones I use in my traditional classes.
You’ll find they are loaded with imagery and streamlined text that highlight the
most essential terms and concepts. The notes provide a framework for learning
and, by themselves, are not meant to be a comprehensive source of information.
To take advantage of the global knowledge base known as the Internet, I have
included numerous hyperlinks to external web sites (like the Wikipedia, USGS,
NASA, etc.). Follow the links and scan them for relevant info. The information
from linked web sites is meant to supplement and reinforce the lecture notes –
you won’t be responsible for knowing everything contained in them.
As a distance learning student, you need to explore and understand the content
more independently than in a traditional class. As always, I will help guide you
through this learning adventure. Remember, email Dr. Bob if you have any
questions about today’s lecture ([email protected]).
Leave no questions behind!
Explore and have fun!
Grand
Canyon
Physiography
Location Map
Grand
Canyon
Physiography
Lees Ferry
Uinkaret
volcanic field
Phantom
Ranch
Desert
View
Diamond
Creek
WESTERN
EASTERN
Digital relief map of the Grand Canyon region
(dark green are lower elevations, light green are higher elevations)
Grand
Canyon
Physiography
 In arid climates, sedimentary rock types that are resistant to
weathering (e.g., limestone & sandstone) form cliffs . . .
. . . and ones that are NOT resistant to weathering
(e.g., mudstone) form slopes
limestone
sandstone
mudstone
Grand
Canyon
Geologic Time
Paleozoic
sedimentary rocks
Grand Canyon Supergroup
missing
missing
missing
missing
Yavapai Supergroup + Intrusives
missing
missing
Grand
Canyon
Stratigraphy
 Proterozoic igneous & metamorphic rocks underlie
nearly flat-lying Paleozoic sedimentary rocks
Grand
Canyon
Early Proterozoic Rocks
Yavapai Supergroup
(~1750 Ma)
 Metamorphic rocks (Xm) exposed in the Inner Gorge
>
Vishnu Schist (Xms; metasedimentary)
>
Rama Schist & Gneiss (Xmv; felsic metavolcanics)
>
Brahma Schist (Xmv; mafic metavolcanics)
Xmv
Xms
Grand
Canyon
Early Proterozoic Rocks
Intrusive Igneous Rocks
(1840-1660 Ma)
 Mostly granitic-dioritic rocks
exposed in the Inner Gorge
>
Elves Chasm Granodiorite
Xgd
(Xgd; 1840 Ma = oldest in AZ)
>
Zoroaster Granite, etc.
(Xg; 1740-1660 Ma)
Xg
Grand
Canyon
Early Proterozoic Rocks
Intrusive Igneous Rocks
(1840-1660 Ma)
Xg
Granitic intrusions in the Inner Gorge
Xg
Grand
Canyon
Middle & Late Proterozoic Rocks
Grand Canyon Supergroup
(1250-800 Ma)
 Mostly sedimentary rocks and basaltic flows & sills
Ys
Ys
Grand
Canyon
Middle & Late Proterozoic Rocks
Grand Canyon Supergroup
(1250-800 Ma)
Unkar Group
(1250-1070 Ma)
 Bass Limestone, Hakatai Shale, Shinumo Quartzite, Dox
Sandstone (Ys)
 Basaltic lava flows, diabase sills & dikes (Yd; ~1100 Ma)
Ys
Grand
Canyon
Middle & Late Proterozoic Rocks
Grand Canyon Supergroup
(1250-800 Ma)
Unkar Group
(1250-1070 Ma)
Ys
Yd
Cardenas mafic dike intrudes reddish Hakatai Shale at Hance Rapids
Grand
Canyon
Middle & Late Proterozoic Rocks
Grand Canyon Supergroup
(1250-800 Ma)
Chuar Group
(~900-825 Ma)
 Organic-rich shallow marine mudstones (Zs)
Zs
Grand
Canyon
Paleozoic Rocks
 All sedimentary rocks
Grand
Canyon
Paleozoic Rocks
Tapeats Sandstone
(Cambrian)
 Cliff-forming nearshore shallow marine sandstone (Ct)
Grand
Canyon
Paleozoic Rocks
Tapeats Sandstone
(Cambrian)
Plateau
Point
Ct
Xg & Xm
Ct
View west from Skeleton Point of Pipe Creek and Plateau Point
Grand
Canyon
Paleozoic Rocks
Bright Angel Shale
(Cambrian)
 Slope-forming shallow to deep marine mudstone (Cba)
Cba
Grand
Canyon
Paleozoic Rocks
Bright Angel Shale
(Cambrian)
Cba
Bright Angel Shale exposed along the Bright Angel Trail near Indian Gardens
Grand
Canyon
Paleozoic Rocks
Muav Limestone
(Cambrian)
 Cliff-forming shallow to deep marine limestone (Cm)
Cm
Grand
Canyon
Paleozoic Rocks
Muav Limestone
(Cambrian)
Cm
Muav Limestone exposed along the Bright Angel Trail near Indian Gardens
Grand
Canyon
Paleozoic Rocks
 “Islands” of Precambrian rock (Y) in the Cambrian sea
Y
C
C
“Cheops Bay” across from Plateau Point.
The older rocks (Y) were higher when the younger rocks (Є) were deposited in a shallow ocean.
Grand
Canyon
Paleozoic Rocks
Temple Butte Limestone
(Devonian)
 Stream channel-filling limestone (Dtb)
Mr
Dtb channel
Cm
Temple Butte channel in Marble Canyon
Grand
Canyon
Paleozoic Rocks
Redwall Limestone
(Mississippian)
 Cliff-forming shallow marine limestone (Mr)
Mr
Grand
Canyon
Paleozoic Rocks
Redwall Limestone
(Mississippian)
Mr
Redwall alcove above Stephen Aisle
Grand
Canyon
Paleozoic Rocks
Supai Group
(Pennsylvanian-Permian)
 Cliff & slope-forming river delta, flood plain, desert dune,
& shallow marine sediments (PPs)
PPs
Grand
Canyon
Paleozoic Rocks
Supai Group
(Pennsylvanian-Permian)
PPs
Supai Group rocks exposed below Zoroaster Temple
Grand
Canyon
Paleozoic Rocks
Hermit Shale
(Permian)
 Slope-forming river delta & flood plain mudstone (Ph)
Ph
Grand
Canyon
Paleozoic Rocks
Hermit Shale
(Permian)
Ph
Hermit Shale exposed in Marble Canyon
Grand
Canyon
Paleozoic Rocks
Coconino Sandstone
(Permian)
 Cliff-forming eolian (wind-deposited) sandstone (Pc)
Pc
Grand
Canyon
Paleozoic Rocks
Coconino Sandstone
(Permian)
Pc
Sheer cliffs of Coconino Sandstone below Mather Point
Grand
Canyon
Paleozoic Rocks
Toroweap Formation
(Permian)
 Slope-forming unit composed of sandstone, dolomite, etc. (Pt)
Pt
Grand
Canyon
Paleozoic Rocks
Toroweap Formation
(Permian)
Ptw = Woods Ranch Member
Ptb = Brady Canyon Member
Pts = Seligman Member
Ptw
Ptb
Pts
Three members of the Toroweap Formation below Mather Point
Grand
Canyon
Paleozoic Rocks
Kaibab Formation
(Permian)
 Cliff-forming shallow marine dolomite & limestone (Pk)
Pk
Grand
Canyon
Paleozoic Rocks
Kaibab Formation
(Permian)
Pk
The Kaibab Formation at Mather Point
Grand
Canyon
Mesozoic Rocks
Moenkopi & Chinle Formations
(Triassic)
 Sedimentary rocks locally exposed as erosional remnants
Tc
Tm
Moenkopi and Chinle exposed at Cedar Mountain east of Desert View
Grand
Canyon
Cenozoic Rocks
Uinkaret volcanic field
(Plio-Pleistocene; 4 to <1 Ma)
 Tby, QTb - Basaltic cones and flows
 Lava dams created large lakes
Qb
Vulcans Throne
Recreation of the one of the
highest lava-dam lakes
Grand
Canyon
Cenozoic Rocks
Uinkaret volcanic field
(Plio-Pleistocene; 4 to <1 Ma)
Qb
Qb
Lava-filled stream channel at Whitmore Wash
Lava cascades at Vulcans Throne
Grand
Canyon
Cenozoic Rocks
Landslides & Rockfalls
(Pleistocene to Recent; <2 Ma)
Qls
Qt
Qt
Qls
Rockfall talus in Marble Canyon
Surprise Valley landslide at Deer Creek
Grand
Canyon
Proterozoic Tectonics
Yavapai Orogeny
(1710-1700 Ma)
 Subduction-related compression, with metamorphism, faulting,
and folding
Grand
Canyon
Phanerozoic Tectonics
Laramide Orogeny
(Late Cretaceous to Early Tertiary)
 Late Mesozoic/Early Cenozoic compression
due to low-angle subduction
 Reverse faulting forms monoclines across the
Colorado Plateau
Grand
Canyon
Phanerozoic Tectonics
Regional Uplift & Extension
(Late Tertiary)
 Late Tertiary extension creates high-angle normal faults
 <6 Ma, regional uplift causes stream downcutting & forms the
Canyon
Grand
Canyon
WWW Links in this Lecture
> Grand Canyon - http://en.wikipedia.org/wiki/Grand_Canyon
> Geologic time - http://www.stratigraphy.org/geowhen/timelinestages.html
> Grand Canyon Stratigraphy - http://3dparks.wr.usgs.gov/coloradoplateau/grandcanyon_strat.htm
> Basin and Range - http://en.wikipedia.org/wiki/Basin_and_Range_Province
> Colorado Plateau - http://en.wikipedia.org/wiki/Colorado_Plateau