Geology of the Grand Canyon area

The geology of the Grand Canyon is characterized primarily by one of the most comprehensive ergeschichtlich rock sequences on our planet. In the steep walls of the Grand Canyon about 1.5 billion years of geological development of this part of North America are disclosed. For the most part, these are to sedimentary rocks. These are approximately 1200 and 250 million years old and thus comprise a period of almost one billion years. If the metamorphic, supracrustal rocks of the majority of Vishnu Basement Rocks ( " Vishnu - basement " ) taken with added, then the geological tradition reaches back even to 1750 Ma BP. Most sediments were deposited in warm shelf seas, mostly near the coast. Host rocks of marine origin but are also terrestrial deposits, including dune sediments of a former desert landscape.

In the course of lara mix orogeny that began before 75 million years, much further to the east located Rockies were forced to steeply dipping faults in the air, but also in the vicinity of the Grand Canyon, there was a wide -scale uplift. 17 million years ago ( Miocene ) was further accelerated the lifting process and it created the Colorado Plateau that frame the Grand Canyon. Overall, the Grand Canyon may have been pushed up by approximately 3000 meters; this allowed the forerunner of the present Colorado River, is to mill in the resulting plateau landscape. The actual canyon was but only a 5.3 million years ago when the Gulf of California opened and thus reduced the erosion base of Colorado at sea.

With the onset of ice ages before 2.5 million years ago, there was an increase in rainfall and thus to a much greater erosive power of the Colorado; as approximately the current base level was reached before 1.2 million years. The 2 million years ago onset of volcanism in Uinkaret volcanic field lavas and ashes brought to the deposition. At least 13 lava flows dammed the Colorado River and formed huge lakes that were up to 600 meters deep and 160 miles long.

With nearly 40 designated rock formations and unconformities 14 ( hiatuses ), the Grand Canyon one of the most studied rock consequences of the world dar.

• 2.1 uplift and nearby crustal strain
• 2.2 The newly emerged Colorado River begins its erosion work
• 2.3 volcanic activity dams the river in the new Canyon

Stratigraphic sequence

Polymetamorphes basement - Vishnu Basement Rocks

The beginnings of the Vishnu Basement Rocks ( unit 1a in the adjacent figure ) go back to the Paleoproterozoic. In a backarc basin similar to the Sea of ​​Japan, a thick sedimentary package had in the period 1750 to 1740 million years BP deposited consisting of Volcanic ash, clay, silt and sand. The former sedimentary basin was located between the further north-west continent of Laurentia, the precursor of the current North American continent, and a southeast offshore volcanic island arc, which probably resembled the present-day Japan.

However Oldest radiometrically dated rocks of the Vishnu Basement Rocks is the Elves Chasm gneiss, a metamorphosed orthogneiss with a crystallization age of 1840 Ma BP. It shows affinities to continental Mojave Terran and made ​​perhaps the abutment of the sediment pile.

From 1740 Ma BP, the aforementioned island arc of the Yavapai province began with the Wyoming craton in the north and colliding the Mojave Terran in the West. This collision caused plattentektonisch compressed the intervening marine sediment pile and pushed him onto the continental margin of Laurentia. The highlight of the Dynamo metamorphosis was achieved 1706-1697 Ma BP, the Akkretionsvorgang, however, held a total of more to 1650 Ma BP, which continued with the Mazatzal province still be added joined a second island arc to the southeast.

The by the collision of tectonic highly stressed and metamorphosed sediments are now in the Inner Gorge at the bottom of the canyon. These are the dark, garnet- leading and generally northeast-southwest - trending shale rocks of the Vishnu Basement Rocks, belong to the Vishnu Schist of, the Brahma Schist and the Rama Schist. You are fossil empty, but from time to time contain marble lenses, which are possibly due to primitive algae colonies.

From 1740 Ma BP the Vishnu Basement Rocks were penetrated by ascending magma that came from a southeast offshore subduction zone. It gradually solidified at this Zoroaster Granite and several other plutons - bright layers in the Vishnu Schist ( unit 1b ). During these intrusions but did not stop the tectonic movements and so the granitic intrusions were converted in places later gneiss.

The granite intrusions took place in several phases: three during the metamorphosis process of Vishnu basement Rocks 1740-1660 Ma BP and the last before about 1400 Ma BP. This last phase was accompanied by large disturbances on north trending faults there were grave -like fractures and perhaps even to a partial re- breaking ( rifting ) of the emergent continent.

In the rocks of the Vishnu Basement Rocks can the traces of two mountain -building events and reading - in the Yavapai orogeny followed by the Mazatzal Mountain formation. The case deferred mountain ranges are likely to have nachgestanden the height dimensions of today's Himalayas in nothing. With the decay of the orogenic movements then began the erosion and reduced in the next 400 million years, the former high mountains to a low hill country. This left an enormous angular unconformity above the ablated mountain stump

Meso - and Neoproterozoic sediments - the Grand Canyon Supergroup

In Mesoproterozoikum there was a thinning of the continental crust caused by the wegdriftende of Laurentia movement of a larger plate (or several small plates). At this elongation process that should eventually lead to 1100 Ma BP to Midcontinent Rift System, Laurentia was nearly broken - it created large intercontinental grave breach basin along which penetrated the sea. In Laurentia, a shallow sea that extended from the area of Lake Superior over the Glacier National Park in Montana up to the Grand Canyon and the Uinta Mountains formed.

The while these marine incursion in the period 1200-825 Ma BP deposited sediments form the Grand Canyon Supergroup ( unit 2 ), which in turn is divided into two large groups and is composed of nine very different formations. Your total thickness of sediments and volcanic lava exceeds 3000 meters. She is open-minded places in the Inner Gorge and in some of the deeper side canyons.

The deepest portion of the supergroup forms the open marine Unkar Group ( the geological term group comprises two or more formations that are interconnected in a special way ). It begins with the

• Bass lineup, one about 1,250 million years old gray colored dolomite formation. The lowermost Hotauta Conglomerate Member of the Bass Formation is the base conglomerate of the engagement from the west marine transgression over the ablated basement stump, its pebbles were swept along by the surging waves of slowly invading sea. The subsequent actual bass formation is a shallow coastal marine sediment near, which consists of alternating dolomite, sandstone and shale. Its thickness is between 35 and 100 meters. Also first fossils already occur in it - stromatolites.
• It follows the approximately 1.2 billion years old Hakatai Shale. It is composed of thin-layer shales, sandstones and shales of marine origin not. The Hakatai Shale was deposited during a short-term regression of Küstensaums. His orange to red color gave the Red Canyon its name.
• With the Shinumo Quartzite is established again fully marine conditions. It is an extremely resistant sandstone, which should protrude during the Cambrian island-like from the Cambrian sea. These islands resisted in the surf for a long time; they were covered until much later sedimentary, the sandstone was thereby converted to quartzite.
• The Dox Sandstone is about 1,190 million years old and is up to 985 meters thick. He is shallow marine origin and contain intermediate claystone and Schiefertonlagen. The occurrence of ripple marks and other structures reveals its coastal depositional environments. Outcrops of red to orange Formation are located in the eastern sections of the canyon. When fossils are found stromatolites and algae.
• About the previously accumulated sediments then poured the Cardenas Lava, the uppermost formation of the Unkar Group. the dark brown lava was extruded superficial, it has basaltic composition and was dated from 1103 to 1070 Ma BP. It consists of 10 to 12 individual lava flows and reaches a thickness of 300 meters. In genetic connection with the Cardenas Lava likely basaltic sills and passages are that enforce the lower layer Unkar members of the Group.

It follows that some 1050 million years old Nankoweap formation that does not belong to the two groups. It consists of coarse-grained sandstone shallow marine origin, was deposited along a Transgressionsdiskordanz on the Cardenas lava. The Nankoweap lineup is open only in the eastern part of the canyon. it ends with a hiatus, a geological layer gap.

The formations of the Neoproterozoic Chuar Group were formed in the period 1000-825 Ma BP. The deposition conditions were generally flat coastal and marine.

• The Chuar Group begins with the green colored Galeros Formation, which consists of an alternation of sandstone, limestone and shale. Some of Schiefertonlagen are brightly colored, the colors vary from red to violet. In the Galeros lineup also occur stromatolites.
• The auflagernde Kwagunt lineup consists of black shales and red to purple colored shales, limestones are subordinate. Chance switched red sandstone pockets, on the Carbon Butte. Also in the lineup Kwagunt occur stromatolites.
• In conclusion then follows the Sixtymile lineup. It consists largely of brown sandstone, which contains little to shale.

In order to approximately 800 Ma BP held Grand Canyon orogeny the Grand Canyon Supergroup was adjusted to 15 ° and broken into individual floes. This faulting was mainly on north-south trending faults and produced a fraction Scholl Mountains. In the next 100 -million-year interval was pulled back most of the Chuar Group and part of the Unkar Group, the erosion reached locally up to Shinumo Quartzite down ( see above). The fracture Scholl chains were leveled, sometimes even the entire Grand Canyon Supergroup has been eroded away, so that the underlying Vishnu Basement Rocks reappear.

John Wesley Powell described this phenomenon as the Great Unconformity - one of the world's best examples of an angular unconformity on an enormous scale. In it, a total of 250 million years were lost to regional geological history.

The Great Canyon Supergroup and the Great Unconformity are well appreciated in the eastern part of the Inner Gorge.

Cambrian - Tonto Group

At the turn of the Neoproterozoic / Cambrian at 550 Ma BP the sea returned again from the west in the area of the Grand Canyon and began with the sedimentation of the three formations of the Tonto Group:

• At the bottom of the approximately 545 million years old Tapeats Sandstone. This dark brown and thin-layer sandstone formation consists of medium-to coarse-grained sands and conglomerates, which are taken from the surf zone ( unit 3a ). In the upper layer members are often found ripple marks, fossil receive the Tapeats Sandstone are brachiopods and trilobites of the leakage paths. The formation reaches a thickness of 75 to 90 meters, it is resistant to weathering and therefore forms cliffs in the Grand Canyon.
• On the transgressive base unit of the Tapeats Sandstone follows the approximately 530 million years old Bright Angel Shale, a shale, are embedded in the subordinate sandstone, marl and thin dolomite layers. He had been deposited as mud near the coast and contains brachiopods, trilobites and worming ( unit 3b). The Bright Angel Shale reaches a thickness of 100 to 120 meters, is usually greenish colored with brown and gray liners. He weathered very light and therefore forms over the steep walls of the Tapeats Sandstone gently inclined slopes.
• Finally, the approximately 515 million years old Muav Limestone ( unit 3c ), which consists of gray, dünngebankten limestones. He came in deeper, more remote coastal areas deposit and is relatively poor in fossils, only occasionally be found brachiopods and trilobites. Its thickness varies greatly ( 250-375 meters ), in the western part of the Grand Canyon, he falls much more powerful than in the eastern part. The Muav Limestone also forms steep walls.

The three formations of the Tonto Group were deposited over a period of around 30 million years ago ( Cambrian - Middle Cambrian ). Trilobites and Wurmbauten are relatively common in these sediments. The sedimentological sequence documents a gradual transgression taking place from the west to the Transcontinental Arch, the southern slopes of the former North American continent. The Tonto Group today forms the so-called Tonto Platform above the Colorado River. In contrast to the Grand Canyon Supergroup their layer limbs are horizontal and in their original position. The slope -forming Bright Angel Shale in the Tonto Platform is a good impermeable bedrock, groundwater remains in the overlying Muav Limestone and occurs at several sources in the Inner Gorge from again - essential for survival in this arid landscape.

Lower Devonian to Upper Carboniferous - Temple Butte Formation, Redwall Limestone and Surprise Canyon Formation

The next two periods of the geologic time scale, the Ordovician and Silurian, leaving no deposits in the Grand Canyon. It is not clear whether during this period sediments came to the sales and were then eroded away again or whether it was ever come to sedimentation. Anyway, the hiatus lasted approximately 165 million years.

It is certain that during this period, deep channels were incised into the surface of Muav Limestone. The reason for this is most likely flow erosion, as well as submarine currents are possible. From around 350 Ma BP, these wells were then filled again in the Middle Devonian. It formed the

• Temple Butte Formation ( also called Temple Butte Limestone - Unit 4a ) whose total thickness varies between 80 and 120 meters. The violet -colored fillings are made of a gutter Süßwasserkalk and are good to see in the located in the eastern part of the National Park Marble Canyon. In the western part of the park, the lime goes into a very resistant gray to cream-colored dolomite, which forms steep walls. It vertebrate remains have been found in the eastern part of the bone plates of freshwater fish in the west part, however many marine fish. The Temple Butte Formation ends with an unconformity.
• The next formation in the sedimentary sequence of the Grand Canyon is 140 to 160 meters thick Redwall Limestone ( unit 4b ). It consists of fairly dense, dark brown to blue-gray limestones and dolomites with intercalated chert nodules. The Redwall Limestone formed approximately 335 million years ago (Lower to Middle Carboniferous ) in a receding tropical sea near the equator. It contains fossilized crinoids, brachiopods, bryozoans, horn corals, nautiloids, and sponges, as well as trilobites and other marine organisms. The limestone or dolomite rock is quite solid, formed partly overhanging cliffs, rock arches and caves. After deposition of the Redwall Limestone, the area of the Grand Canyon was slowly raised so that the upper parts were removed in places, again during the Upper Carboniferous. The red color of the rock is of a purely cosmetic nature, it comes from the overlying red beds of the Supai Group and Hermit Shale.
• The Surprise Canyon Formation consists of reddish-purple shales that are pending in incoherent layer packets over the Redwall Limestone ( unit 4c). Their formation was carried out in the tidal area of estuaries during the very late Lower Carboniferous, possibly even during the very early Upper Carboniferous. In isolated sediment lenses it reaches a thickness of up to 12 meters. The Surprise Canyon Formation was first discovered in the 1980s and can be approached only by helicopter. Above it is an unconformity that removed most of their former association layer and has the underlying Redwall Limestone exposed again.

Upper Carboniferous to Lower Permian - Supai Group

The Supai Group is predominantly siliciclastic origin and was deposited during the Upper Carboniferous and Permian of in swamps and floodplains, their average age is 285 million years BP. In the western part of the national park limestones occur - an indication of a warm shallow sea. Sedimentation in the eastern part may have been a muddy river delta. It consists essentially of red siltstones and shales, which are overlain by brownish sandstones. Your total thickness varies 180-210 meters. The Permian Schiefertonlagen were oxidized to a bright red color. In the eastern part of the park fossil footprints of amphibians are preserved geblienen, there are also fossils of reptiles and plants (very often ). In the western part, however, outweigh fossils of marine origin. The Supai Group consists of the following individual formations together (from old to youngest ):

• Watahomigi Formation ( unit 5a ): A hang -forming gray limestone formation, are turned into the chert bands, sandstone layers and a violet Silsteinschicht. It is 30 to 50 meters thick.
• Manakacha Formation ( unit 5b ): it consists of pale red resistant sandstone and red slope -forming shale, their thickness varies between 60 and 85 meters.
• Wescogame Formation ( unit 5c ): A pale red resistant sandstone which alternates with a pale red slope -forming siltstone, thickness is between 30 and 70 meters. At the top finally follows the
• Esplanade Formation ( Unit 5d): In their sedimentological structure, it is a repetition of Wescogame lineup, only twice as powerful ( 70 to 90 meters).

Each of these formations will be completed by an unconformity.

Perm - Hermit Shale, Coconino Sandstone, Toroweap Formation and Kaibab Limestone

• Like the Supai Group was previously also in the means 265 million years old Hermit Shale deposited in swampy environment ( unit 6a ). He builds up from dünnbankigen, iron oxide -containing alternating layers of shale and siltstone, the sediments were transported by rivers in a semi-arid basin. The deep red, 49-53 meters thick sediment package is very soft and therefore forms the canyon slopes. The headward erosion in the Hermit Shale often undermines this overlying layer associations, so that house large blocks detach from their association and come crashing down on the Tonto Platform. The Hermit Shale contains fossils - wing insects, cone-bearing plants and ferns have been found. The formation also concludes with an unconformity.
• The following Coconino Sandstone ( unit 6b ) reflects continental, desert-like environment. The sandstone originated about 260 million years ago, when gradually penetrated from pure quartz sand dunes in expanding existing wilderness areas. The thickness of the sandstone formation varies 115-200 meters and forms white to off-white cliffs below the canyon rim. In the former petrified sand dunes can be seen aeolian ( generated by the wind ) oblique stratifications, the dunes body itself are composed of myriads of opaque, rounded and well-sorted sand grains. They also contain fossilized tracks of arthropods and reptiles as well as their first buildings. Here follows an unconformity.
• Above it is the 60 to 75 meters thick and about 250 million years old Toroweap Formation ( unit 6c). It is composed of red and yellow-colored sandstone and gray marly limestone containing gypsum layers together. The carbonate sediments are taken from a warm shallow sea, they reflect oscillating sea levels and generally the slow return to marine conditions. Fossil content are brachiopods, corals, mollusks and various land plants. The Toroweap Formation comprises the layer members ( oldest to young):
• Seligman Member: A hang -forming yellowish to reddish sand - or siltstone.
• Brady Canyon Member: A resistant, steep wall forming gray limestone with intercalated chert lenses.
• Wood Ranch Member: A slope -forming pale red and gray colored siltstones and dolomitic sandstone. An unconformity completed the lineup.
• At the canyon rim then finally the massive, steep wall-forming, 80 to 110 meters thick Kaibab Limestone ( 6d ). This off-white to gray-white limestone formation was about 225 million years ago ( Middle Permian) in the deeper areas of warm shallow seas that had already transgrediert during the Toroweap formation, emerged. Usually follows the Kaibab Limestone on a basal sandstone layer a sandy limestone, which can be peeled off in places in the upper part also of sandstone and shale, however. On fossil shark teeth and numerous marine invertebrates such as were Brachiopods, corals, mollusks, sea lilies and worms found. The Kaibab Limestone covers large parts of the north of the Grand Canyon located Kaibab Plateau and the immediate southern Coconino Plateau. Also, this formation is included by an unconformity.

Mesozoic

With the beginning of the Mesozoic era began in the area of the Grand Canyon uplift the fallen dry landscape was re- crossed by rivers. Sediment from the nearby hinterland was settled during the Triassic in broad, low-lying valleys and created up to 300 meters thick Moenkopi formation. It consists of sandstone and shale with intervening layers of plaster. The formation is weathering very unstable and therefore only occurs very sporadically. Open-minded, it is along the Colorado River in Marble Canyon, at Cedar Mountain, a mesa in the southeast part of the National Park and the Red Butte south of Grand Canyon Village. About the Moenkopi Formation to follow at Red Butte then remains of the Shinarump Conglomerate, a conglomerate which is part of the Chinle Formation, and a much younger lava flow.

During the Mesozoic and Cenozoic of the mighty rock formations were sedimented in the region of the Grand Canyon over 1500 meters, but were eliminated again by the then taking place in this sector mostly erosion (see following section). More details can also be found under Geology of Zion National Park and Bryce Canyon geology of. These lost in the Grand Canyon layer sequences, however, are more preserved in the north of the so-called Grand Staircase and perfectly exposed.

Formation of the Grand Canyon

Uplift and nearby crustal strain

The Lara mixer orogeny recorded the entire western North America and therefore contributed to the formation of the Rocky Mountains and the American Cordillera at. The orogenic movements put an end to the Mesozoic to 72 Ma BP and continued until the earliest Tertiary, ie to the Paleogene. A second uplift phase occurred before 17 million years in the Lower Miocene and created the Colorado Plateau ( the Colorado Plateau north of the Grand Canyon, the Kaibab, Kanab and Shivits Plateau and south include the Cococino Plateau ). Strangely enough, the layer remained Association in Colorado Plateau relatively undisturbed during these two enhancement processes and also retained its original horizontal storage conditions, although he was raised up to 2700 meters. An attempt to explain makes do a made ​​clockwise rotation of the plateau - crustal blocks that made allegedly maintain its stability. Before raising the Plateau was only about 300 meters above sea level and was surrounded by high mountain ranges in the south and west.

In about the same time as the second uplift phase occurred about 20 Ma BP to strong crustal strain, old existing disorders were revived it and created new fractures. This process was accompanied by relatively moderate volcanic activity. Further west, however, the effects of crustal strain were enormous: it was the Basin and Range Province - a grave breach system of north-south oriented elongated fault zones in left standing clumps ( the present mountain ranges ) and bagged trenches ( the present basins ) differentiated and thereby a crust break of more than 100% enabled. The Grand Wash Fault in the west end of the Grand Canyon National Park already belongs to the sphere of influence of the Basin and Range Province.

The newly emerged Colorado River begins its erosion work

Continuous tectonic movements in the area of the Colorado Plateau generated in the outer layers spacious Monoklinalfalten and led to a significant height gain, which could rise sharply in the region of the gradient flow of the waters. The primeval Colorado River had been until about 5.3 million years ago an inland river without access to the sea. He ended up back in large inland lakes - in the early Tertiary still within the Colorado Plateau and the Middle Tertiary then in the Basin and Range Province. The large Monoklinalfalte of the Kaibab Arch gradually began herauszuwölben six million years ago. According to a hypothesis of this obstacle was overcome in the course of the Colorado River by both an east and a west canyon coming from the same back border eroded and then combined. The other possibility is of course that the antecedent of the river acted against the slowly ascending obstacle.

The opening of an arm of the Gulf of California 5.3 million years ago changed the direction of flow of the surrounding waters toward the sinking and collapsing Riftgraben. The uplift of the basin at the headwaters and the reduction of the lower reaches at the opening into the Gulf of California rivers led to an overall stronger gradient and increased erosion, so that the rivers could dig faster in the countryside. By headward erosion of the catchment areas of several rivers have been merged into a main drain then in geologically short period of time, now the Colorado River. The most important stage came when a separate older river that drained by the San Andreas Fault in the Gulf of California, to the then ending as a single Colorado River took possession. The cutting of the eastern part of the Colorado River had indeed begun earlier, but had been then greatly accelerated and extended to the west.

With the onset of ice ages before 2.5 million years BP in the Pleistocene the climate in the region was much cooler and wetter. The additional rainfall resulted in a higher runoff and erosion increased by higher spring snowmelt and flash floods in the summer. Due to the higher volume, the steeper gradient and by the lower base level of erosion, the river from two million years BP performed significantly faster with the landscape, reaching about 1.2 million years ago almost its present depth.

Volcanic activity dams the river in the new Canyon

During the Quaternary years ago around 725 000 BP to basaltic lava poured out in the western Grand Canyon. She came to the entry into eruption of the cinder cones Uinkaret volcanic field. In the period 725000-100000 years BP, the river was dammed several times. The duration of these huge reservoirs is controversial, often 20,000 years it will be accepted, other researchers, however, doubt this and believe that the volcanic dams of not too long duration were triggered catastrophic floods and in her surrender. The extent of the lava itself is remarkable, from river mile 178 to follow on the 121 km course of the Colorado River!

Actuogeology, anthropogenic influence and the future

With the end of the Ice Age in the Pleistocene and the beginning of the Holocene, the shift from a cold, damp climate began to the current drier conditions. The erosive action of the river fell due to lower rainfall and the rocks of the Inner Gorge is more resilient with today's flow rates. Mass movements such as Rockslides won so with regard to the erosion of meaning. This steeper sidewalls and the Grand Canyon created with its tributaries widened.

At the present time leads to the construction of dams, such as the Glen Canyon Dam, to a further reduction of erosion. Dams reduce the flow rate, at the same time the water flows through the canyon more evenly. The reduced sediment load to the river eroding its abrasive effect is also lost. The additional withdrawal of water for drinking water supply and irrigation causes the Colorado River no longer reaches its delta in the Gulf of California in dry years.

The dam has also changed the properties of the river water. Was the water before muddy and rather warm and so offered fish at the bottom of the water body habitat, the river is now more clear and cold, making the trout used a livelihood was created. This had an impact on the migration behavior of the bald eagle, which was originally the canyon as a stopover on the way to the fishing grounds downstream took advantage, but in the meantime visit the Canyon as a food source.

During the 1990s occurred at the Grand Canyon and its surroundings about 45 earthquakes, five of which reached an intensity that was lying on the Richter scale between 5.0 and 6.0. Dozens of faults cross the canyon and many of them are in the last hundred years have been seismically active.

The slope of the Colorado River is strong enough to allow another 400 to 600 meters of erosion work. Here, a further raising of the environment in the geological future has not been considered. The influence of man is more likely retarding effect on the erosive power of the Colorado River.