Old Earth Ministries Online Earth History Curriculum
Presented by Old Earth Ministries (We Believe in an Old Earth...and God!)
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Chapter 13 - The Neogene Period
Lesson 65: The Grand Canyon, Part 1
The Grand Canyon has fascinated visitors for many years, and has drawn the attention of many Christians, as they wonder how this geologic feature was made, and if it had anything to do with Noah's Flood. In this lesson, we will examine the making of the rocks that comprise the canyon, and in the next lesson, we will examine how the canyon was formed.
The Grand Canyon is a steep-sided canyon carved by the Colorado River in the United States in the state of Arizona. It is largely contained within the Grand Canyon National Park, one of the first national parks in the United States. President Theodore Roosevelt was a major proponent of preservation of the Grand Canyon area, and visited it on numerous occasions to hunt and enjoy the scenery.
Chapter 13: The Neogene Period
Click picture to enlarge (Picture Source)
The Grand Canyon is 277 miles (446 km) long, up to 18 miles (29 km) wide and attains a depth of over a mile (1.83 km) (6000 feet). Nearly two billion years of the Earth's
The geology of the Grand Canyon area exposes one of the most complete and studied sequences of rock on the planet. The nearly 40 major sedimentary rock layers exposed in
Uplift of the region started about 75 million years ago in the Laramide orogeny; a mountain-building event that is largely responsible for creating the Rocky Mountains to the east. In total the Colorado Plateau was uplifted an estimated 2 miles (3.2 km). The adjacent Basin and Range province to the west started to form about 18 million years ago as the result of crustal stretching. A drainage system that flowed through what is today the eastern Grand Canyon emptied into the now lower Basin and Range province. Opening of the Gulf of California around 6 million years ago enabled a large river to cut its way northeast from the gulf. The new river captured the older drainage to form the ancestral Colorado River, which in turn started to form the Grand Canyon.
Wetter climates brought upon by ice ages starting 2 million years ago greatly increased excavation of the Grand Canyon, which was nearly as deep as it is now by 1.2 million years ago. Volcanic activity deposited lava over the area 1.8 million to 500,000 years ago. At least 13 lava dams blocked the Colorado River, forming lakes that were up to 2,000 feet (610 m) deep. The end of the ice age and subsequent human activity has greatly reduced the ability of the Colorado River to excavate the canyon. Dams in particular have upset patterns of sediment transport and deposition. Controlled floods from Glen Canyon Dam upstream have been conducted to see if they have a restorative effect. Earthquakes and mass wasting erosive events still affect the region.
Metamorphic and Igneous Basement
The Granite Gorge Metamorphic Suite consists of the metasedimentary Vishnu Schist and the metavolcanic Brahma and Rama Schists. All were formed 1.75 billion to 1.73 billion years ago in Precambrian time when thousands of feet of volcanic ash, mud, sand, and silt were laid down in a shallow backarc basin similar to the modern Sea of Japan. The basin was between an early form of North America called Laurentia and an orogenic belt of mountains and volcanoes in an island arc similar to modern Japan.
From 1.8 to 1.6 billion years ago at least two island arcs collided with the proto-North
As the volcanic islands collided with the mainland around 1.7 billion years ago, blobs of magma rose from the subduction zone and intruded the Granite Gorge Metamorphic Suite. These plutons slowly cooled to form the Zoroaster Granite; part of which would later be metamorphosed into gneiss. This rock unit can be seen as light-colored bands in the darker garnet-studded Vishnu Schist (see 1b in Figure 1). The intrusion of the granite occurred in three phases: two during the initial Vishnu metamorphism period, and a third around 1.4 billion years ago. The third phase was accompanied by large-scale faulting, particularly along north—south faults, leading to a partial rifting of the continent. The collision expanded the continent from the Wyoming–Colorado border into Mexico and almost doubled the crust's thickness in the Grand Canyon region. Part of this thickening created the 5-to-6-mile (8 to 10 km) high ancestral Mazatzal Mountains.
Subsequent erosion lasting 300 million years stripped much of the exposed sediments and the mountains away. This reduced the very high mountains to small hills a few tens to hundreds of feet (tens of meters) high. Geologist John Wesley Powell called this major gap in the geologic record, which is also seen in other parts of the world, the Great Unconformity. Other sediments may have been added but, if they ever existed, were completely removed by erosion. Such gaps in the geologic record are called unconformities by geologists. The Great Unconformity is one of the best examples of an exposed nonconformity, which is a type of unconformity that has bedded rock units above igneous or metamorphic rocks.
Deposition of Sedimentary Layers
Grand Canyon Supergroup
In late Precambrian time, extension from a large tectonic plate or smaller plates moving away from Laurentia thinned its continental crust, forming large rift basins that would ultimately fail to split the continent. Eventually, this sunken region of Laurentia was flooded with a shallow seaway that extended from at least present-day Lake Superior to Glacier National Park in Montana to the Grand Canyon and the Uinta Mountains. The resulting Grand Canyon Supergroup of sedimentary units formed by this shallow seaway is composed of nine varied geologic formations that were laid down from 1.2 billion and 740 million years ago in this sea. Good exposures of the supergroup can be seen in eastern Grand Canyon in the Inner Gorge and from Desert View, Lipan Point and Moran point.
The oldest section of the supergroup is the Unkar Group. It was laid down in an offshore environment. The first formation to be laid down in the Unkar Group was the Bass Limestone. The Bass Limestone was deposited in a shallow sea near the coast as a mix of limestone, sandstone, and shale. It is 120 to 340 feet (37 to 100 m) thick and grayish in color. Averaging 1250 million years old, this is the oldest layer exposed in the Grand Canyon that contains fossils—stromatolites. The next layer is the Hakatai Shale. It is made of thin beds of marginal-marine-derived mudstones, sandstones, and shale that, together, are 445 to 985 feet (136 to 300 m) thick. This formation indicates a short-lived regression (retreat) of the seashore in the area that left mud flats. Today it is very bright orange-red and gives the Red Canyon its name. Shinumo Quartzite was a resistant marine sandstone that later formed islands in Cambrian time. Those islands withstood wave action long enough to become re-buried by other sediments in the Cambrian Period. It was later metamorphosed into quartzite. Dox Sandstone is over 3,000 feet (910 m) thick and is made of ocean-derived sandstone with some interbedded shale beds and mudstone. Ripple marks and other features indicate it was close to the shore. Outcrops of this red to orange formation can be seen in the eastern parts of the canyon. Fossils of stromatolites and algae are found in this layer. At 1070 ± 70 million years old, the Cardenas Lava is the youngest formation in the Unkar Group. It is made of layers of dark brown basaltic rocks that flowed as lava up to 1,000 feet (300 m) thick.
Nankoweap Formation is around 1050 million years old and is not part of a group. This rock unit is made of coarse-grained sandstone, and was deposited in a shallow sea on top of the eroded surface of the Cardenas Lava. The Nankoweap is only exposed in the eastern part of the canyon. A gap in the geologic record, an unconformity, follows the Nankoweap.
All formations in the Chuar Group were deposited in coastal and shallow sea
About 800 million years ago the supergroup was tilted 15° and block faulted in the Grand Canyon Orogeny. Some of the block units moved down and others moved up while fault movement created north—south-trending fault-block mountain ranges. About 100 million years of erosion took place that washed most of the Chuar Group away along with part of the Unkar Group (exposing the Shinumo Quartzite as previously explained). The mountain ranges were reduced to hills, and in some places, the whole 12,000 feet (3,700 m) of the supergroup were removed entirely, exposing the basement rocks below. Any rocks that were deposited on top of the Grand Canyon Supergroup in the Precambrian were completely removed. This created a major unconformity that represents 460 million years of lost geologic history in the area.
During the Paleozoic era, the western part of what would become North America was near the equator and on a passive margin. The Cambrian Explosion of life took place over about 15 million years in this part of the world. Climate was warm and invertebrates, such as the trilobites, were abundant. An ocean started to return to the Grand Canyon area from the west about 550 million years ago. As its shoreline moved east, the ocean began to concurrently deposit the three formations of the Tonto Group.
These three formations were laid down over a period of 30 million years from early to
Temple Butte, Redwall, and Surprise Canyon
The next two periods of geologic history, the Ordovician and the Silurian, are missing from the Grand Canyon sequence. Geologists do not know if sediments were deposited in these periods and were later removed by erosion or if they were never deposited in the first place. Either way, this break in the geologic history of the area spans about 165 million years. A type of unconformity called a disconformity was formed. Disconformities show erosional features such as valleys, hills and cliffs that are later covered by younger sediments.
An unconformity of 15 to 20 million years separates the Supai Group from the previously deposited Redwall Formation. Supai Group was deposited in late Mississippian, through the Pennsylvanian and into the early Permian time, some 320 million to 270 million years ago. Both marine and non-marine deposits of mud, silt, sand and calcareous sediments were laid down on a broad coastal plain similar to the Texas Gulf Coast of today. Around this time, the Ancestral Rocky Mountains rose in Colorado and New Mexico and streams brought eroded sediment from them to the Grand Canyon area.
Supai Group formations in the western part of the canyon contain limestone, indicative of a warm, shallow sea, while the eastern part was likely a muddy river delta. This formation consists of red siltstones and shale capped by tan-colored sandstone beds that together reach a thickness of 600 to 700 feet (200 to 200 m). Shale in the early Permian formations in this group were oxidized to a bright red color. Fossils of amphibian footprints, reptiles, and plentiful plant material are found in the eastern part and increasing numbers of marine fossils are found in the western part.
Formations of the Supai Group are from oldest to youngest (an unconformity is present at the top of each): Watahomigi is a slope-forming gray limestone with some red chert bands, sandstone, and purple siltstone that is 100 to 300 feet (30 to 90 m) thick. Manakacha is a cliff- and slope-forming pale red sandstone and red shale that averages 300 feet (90 m) thick in Grand Canyon. Wescogame is a ledge- and slope-forming pale red sandstone and siltstone that is 100 to 200 feet (30 to 60 m) thick. Esplanade is a ledge- and cliff-forming pale red sandstone and siltstone that is 200 to 800 feet (60 to 200 m) thick. An unconformity marks the top of the Supai Group.
Hermit, Coconino, Toroweap, and Kaibab
Uplift marked the start of the Mesozoic and streams started to incise the newly dry land. Streams flowing through broad low valleys in Triassic time deposited sediment eroded from nearby uplands, creating the once 1,000-foot (300 m)-thick Moenkopi Formation. The formation is made from sandstone and shale with gypsum layers in between. Moenkopi outcrops are found along the Colorado River in Marble Canyon, on Cedar Mountain (a mesa near the southeastern park border), and in Red Butte (located south of Grand Canyon Village). Remnants of the Shinarump Conglomerate, itself a member of the Chinle Formation, are above the Moenkopi Formation near the top of Red Butte but below a much younger lava flow.
Formations totaling over 4,000 to 5,000 feet (1,200 to 1,500 m) in thickness were deposited in the region in the Mesozoic and Cenozoic but were almost entirely removed from the Grand Canyon sequence by subsequent erosion. The geology of the Zion and Kolob canyons area and the geology of the Bryce Canyon area records some of these formations. All these rock units together form a super sequence of rock known as the Grand Staircase.
What is Missing From the Grand Canyon?
When examining the rocks of the canyon, young earth creationists see rock layers that were laid down by the global flood of Noah. Thus, the rocks of the Grand Canyon should contain fossils of dinosaurs killed during the flood. However, dinosaurs are missing from the rocks of the canyon. This is because the oldest rock unit, the Kaibab Limestone, was formed 270 million years ago, which is about 50 million years prior to the time of the dinosaurs. All evidence for dinosaurs, including bones, nesting sites, eggs, footprints, etc., are post-flood. This problem is usually ignored by young earth creationists.
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