Geological Eras
The Precambrian Eon
The Precambrian Eon refers to almost 90% of the entire history of the earth. It involves the formation of the earth's crust. It has been divided into three eras: the Hadean, the Archean, and the Proterozoic. Each has its unique characteristics.
The Hadean Earth (Hades-like)
This era began with the formation of the earth from dust and gas orbiting the Sun about 4.6 billion years ago. The Earth was a place of molten rock, boiling sulphur, and volcanoes. Many asteroids were bombarding the Earth at this time.
The Archean Earth (Ancient or Primitive)
During this ancient or primitive era about a billion years after the formation time, things have cooled down. Even though there is still volcanic action, the lava has cooled sufficiently to form an ocean floor creating a global ocean. The air is mostly nitrogen and the sky is filled with clouds and rain. There are still many volcanoes and numerous small islands are forming. Evidence of blue-green algae was floating in this ocean. Geologists find that the Archean era is the age of the oldest rocks on earth.
The Proterozoic Earth (Early Life)
This era dates approximately 700 million years ago. There is considerably less volcanic action; however, the earth's plates are in motion now and a super continent, Pangaea, has been formed. Eukaryotic (multi-celled) organisms are found along with the bacteria and algae. The atmosphere is still mostly nitrogen with little water vapor and carbon dioxide, but some free oxygen is released by the floating algae. Now extremely cold, the earth is partially covered with huge, bluish glacial ice sheets visible across the super continent.
Paleozoic Era
The Paleozoic (Ancient Life) Era is the first of three geologic eras squeezed into the last 10% of the Earth's geologic history. It is also called the Phanerozoic Eon or the eon of "evident life." This era lasted 325 million years. Included in this era are several periods including: Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Carboniferous, and Permian. Plate tectonics continues to be the moving force and the land is locked into two super-continents called Gondwanaland and Laurasia. The composition of the atmosphere changed slowly, with the increase of oxygen produced by plants.
Local Precambrian Events, 1.8 Billion Years Ago
More than 1.8 billion years ago, this area was covered by a vast, shallow sea. The sediments accumulated until they reached 40,000 feet. With time, chemical concretion, and pressure, they became sedimentary rock. Then during a period of orogeny (mountain-building), metamorphic rocks were formed. These rocks are called the Idaho Springs Formation and are located nearby in Idaho Springs, Colorado.
One billion years ago, in another period episode of orogeny, a huge batholith (a gigantic igneous rock) was forced upward from deep below the Earth's surface. This batholith is what is referred to locally as the Pikes Peak batholith and the rock is Pikes Peak granite. It is now exposed over an area of hundreds of square miles.
Lipalian Interval
At the end of the Precambrian time, the entire earth was geologically quiet. Locally, the ancestral Rockies began to erode and finally became a flat, slightly undulating terrain called a peneplane.
Cambrian Period
In this period, the atmosphere rapidly evolved into a more oxygen-rich environment. Many cratons and shields formed all over the world. Stromatolite becomes diverse and widespread as well as dolomite and other microfossils. The mobile belts and major cratonic structures of North America formed during the Paleozoic Era.
Local Cambrian History, 600—500 Million Years Ago
The local events of this period (600-500 million years ago) include the formation of Pikes Peak Granite and the Idaho Springs metamorphics. As erosion continued throughout early and middle Cambrian time, the sea gradually transgressed from both the west and the southeast. Late in Cambrian time, perhaps 530 million years ago, the seas met in the Colorado Sag. The beaches transgressed, thus forming the Sawatch Sandstone. The sandstone underwent a gradual transition into the red and greenish carbonate rock of the Peerless Formation. These were deposited after the sea transgressed and formed either limestone or dolomite. Dolomite is a calcium-magnesium carbonate which is more resistant to chemical weathering than limestone.
Ordovician Period
Early in the Ordovician period, which covers 425 to 500 million years ago, a huge mobile belt, the Appalachian craton, was encroached by the Sauk Sea. Carbonate deposition dominated the land on the craton as the Sauk Sea transgressed during this early Ordovician period. As the Sauk Sea regressed, it revealed a landscape of low relief; predominately limestone. The large continent of Laurentia was moving northward, but was still located within tropical latitudes. Most of the North American craton was covered with a warm epeiric sea. In the present day Great lakes, basins were surrounded by large reefs. The first fish appeared during this time.
Local Ordovician History, 425—500 Million Years Ago
During the early Ordovician Period, gentle uplift and erosion removed a large amount of the Peerless Formation in this area. The sea deepened again, and a period of intense carbonate deposition began. The Manitou Formation was deposited consisting of nearly 200 feet of dolomite and limestone. Today, this formation is red or buff-gray. Fossils, such as trilobites, can be found in the Manitou and remaining Peerless formations. The sea retreated in the middle of the Ordovician period, but again transgressed later in the period. This resulted in the sandstone and shale Harding Formation and the carbonates of the Fremont Limestone. Unfortunately, both of these formations were almost entirely eroded locally, but can be seen to the south near Cañon City, Colorado.
Devonian Period
The two super-continents, Laurentia and Baltica, collided along a convergent plate boundary to form the larger continent, Laurasia, in the late Silurian and early Devonian period. As a result of this collision, the Acadian Orogeny occurred on the eastern margin of Laurasia. The later erosion of these highlands provided huge amounts of reddish, fluvial sediments that covered large areas of northern Europe and eastern North America. Other tectonic events during this period involved the collision of Laurentia and the Baltica, resulting in the Antler Orogeny and the Ellesmere Orogeny. These were mountains in the Uralian mobile belt of eastern Baltica. The distribution of reefs, evaporites and red beds, as well as the floras throughout the world, suggests a uniform global climate. There was still more diversity of fish during this period, and the appearance of the first amphibians and insects.
Local Devonian History, 345—405 Million Years Ago
According to some geologists, there was deposition in the entire Rocky Mountain area during this period. There is evidence of a shallow inland sea. However, erosion may be responsible for the lack of carbonates of this period with one significant exception: the Williams Canyon limestone was formed during the late Devonian period. All of these deposits contained layers of limestone and dolomite, as well as thin layers of sandstone and shale.
Silurian Period
The Silurian Period was characterized by organic reefs and evaporite facies. The Michigan basin was formed, as well as an alluvial plain on the east coast of North America. This was a result of another inland sea, Tippecanoe, gradually regressing from the craton thus creating this thick deposition of sediments; nearly half of them being halite and anhydrite. This alluvial plain was nearly 1,500 meters thick. The world was still basically two large continents. Present day North America was still near the equator and temperatures were high. There was a diversity of jawless fish, later followed by the first jawed fish. Vascular plants and arthropods also appeared during this period.
Local Silurian History, 405—425 Million Years Ago
Locally, the Silurian Period was a rather quiet time and the main factor during this period was erosion. Most of the "beach" sandstone (Harding Formation) and the carbonates (Fremont Limestone) were eroded away during this period.
The Carboniferous Period, Including the Mississippian and Pennsylvanian Periods
During the Carboniferous Period, southern Gondwanaland moved over the South Pole, resulting in continental glaciation. The advance and retreat of these glaciers produced changes in the sea level globally. This in turn affected sedimentation patterns on the cratons. Gondwanaland continued moving northward and finally collided with Laurasia during the early Carboniferous Period. As a result of this collision, several mountain belts were formed, such as the Ouachita Mountains in (present-day) Oklahoma. At the end of the Carboniferous Period, the continental landmasses were close together and the super-continent of Pangaea began to form. There were Carboniferous coal basins in eastern North America, western Europe, and the Ukraine since at that period, they were near the equator. The fossil plants found in the coals of Siberia and China indicate well-developed seasonal growth rings, which occur in areas with abundant rainfall and distinct seasons. The biological life of this period included extensive forests of vascular plants, the first seed plants, and the origin of reptiles. Reptiles and amphibians were the dominant animal life.
Local Mississippian History, 310—345 Million Years Ago
After a brief period of non-deposition in the late Devonian period, the land gently subsided and the sea once more covered this area. Late Devonian and early Mississippian periods found the deposition of the Williams Canyon Limestone and the Hardscrabble and Beulah formation. All of these deposits contained layers of both limestone and dolomite, as well as thin layers of sandstone and shale. Shale is a sedimentary rock formed from very fine-grained particles of mud and silt and will often contain oil deposits. In the latter Mississippian time, the land rose again, and erosion was the main force. Much of the Hardscrabble and Beulah formation was eroded away. Another name for the remaining Hardscrabble formation is Madison Limestone. All of the depositions in this period have been grouped together and are known as the Leadville Limestone. The most significant development (for the Cave of the Winds) was the formation of caverns occurring in the latter part of the Mississippian Period. In a fairly humid climate with abundant rainfall and carbonate surface rock, the rain water can dissolve the rock and form many sinkholes, caverns, and tunnels in the land. This type of landscape is called karst topography. The many caves in Williams Canyon are more recent developments.
Permian Period
An enormous single ocean, Panthalassa, surrounded Pangaea and spanned the earth from pole to pole. The water temperature was consistently equal. The formation of a single large landmass had climatic consequences for the terrestrial environment as well. Sediments of this period indicate arid and semi-arid conditions widespread over Pangaea. There were dry conditions in North America and Europe. Permian coals, indicative of abundant rainfall, were limited to the northern temperate belts. The last remains of the Carboniferous ice sheets retreated to the mountainous regions of eastern Australia. During the latter portion of this period, the central and southern parts of the Appalachian mobile belt (from New York to Alabama) were folded and thrust toward the craton. This is referred to as the Alleghenian Orogeny. This was the beginning of the Appalachian and Allegheny Mountains. Significant biological events were the radiation of reptiles, the origins of mammal-like reptiles and modern orders of insects, and the extinction of many marine invertebrates.
Local Permian History, 230—280 Million Years Ago
Now the Ancestral Rockies were considerably worn down and formed a peneplane. A Sahara-like arid climate prevailed and dune sands developed in the region. These dunes developed into a sandstone formation known as the Lyons Sandstone. These quite clearly indicate the cross-bedding typical of windblown sand. This rusty-colored sandstone is in the Garden of the Gods. As the Paleozoic Era came to a close, the eastern sea again returned and the sand, shales and thin limestone layers of the Lykin Formation were deposited. These formations are difficult to date due to the lack of fossils.
Mesozoic Era
The major geologic event of the Mesozoic Era was the break-up of Pangaea, which affected oceanic and climatic circulation patterns. This era was known as the Age of Reptiles, but it was also the time which birds, mammals, and angiosperms (flowering plants) first evolved.
Triassic Period
There were areas of great tectonic activity during this period due to the break-up of Pangaea. There was deposition of Triassic evaporites, red bed and desert dunes in the low and middle latitudes of North and South America, Europe and Africa, indicating a dry climate. Coal deposits were formed mainly in the high latitudes, indicating humid conditions. The global temperature increased in the Northern Hemisphere continents. Fault blocking and igneous activity began in the Appalachian region as North America and Africa separated. The newly formed Gulf of Mexico experienced extensive evaporite deposition. Cone-bearing plants (gymnosperms) dominated the landscape, and the first dinosaurs, mammals and birds appeared on the scene.
Local Triassic History, 180—230 Million Years Ago
Hardly anything of significance occurred during this period except the continuation of the Lykin Formation during the early portion.
Jurassic Period
This was the age of the dinosaurs. These included many sizes, shapes and species, from flying to swimming. The giant sauropod walked the Earth. Most of the landscape was jungle-like and the climate was generally mild. Fragmentation of Pangaea continues. There is, however, a close connection among all continents. Invertebrates, such as ammonites and cephalopods, increase in diversity, and coral reefs are common.
Local Jurassic History, 135—180 Million Years Ago
The eastern seas retreated from this area. No evidence of any more deposition for the next 50 million years is apparent. The local landscape consisted of swampy lowlands and meandering streams connecting numerous fresh water lakes. Clay, silts, shales and carbonates accumulated the most extensive and famous formation of the Rocky Mountain area—the Morrison Formation. Many dinosaurs lived in this area and the fossil remains of the Stegosaurus came from the shales of the Morrison Formation north of Cañon City. In the Garden of the Gods, a layer of gypsum is located at the base of the Morrison Formation.
Cretaceous Period
The further fragmentation of Pangaea has occurred with South America and Africa being separated. Australia separated from South America, but remains connected to Antarctica. The North Atlantic Ocean continues to open. The north-south zonation of climates is more marked, but remain equable. Climate becomes more seasonal and cooler at the end of this period. The most dramatic event is the extinction of dinosaurs, flying reptiles and marine reptiles. Theory states that a huge meteor collided with the earth near the present day Yucatan peninsula, creating a huge dust cloud that enveloped the earth and was responsible for the widespread extinction. Placental and marsupial mammals diverge and there is a continued diversification of ammonites. Near the end of the Cretaceous period, the ammonites, rudists and most planktonic forminifera become extinct.
Local Cretaceous History, 70—135 Million Years Ago
The swamp lowland condition continues into the early Cretaceous Period. The Purgatoire Formation (seen on Gold Camp Road near Section 16) shows a gradual transition from the lowland conditions to a marine environment. The great Cretaceous seas covered this area during most of the remainder of the period. The Purgatoire Formation consists of two members: the lower Lytle Sandstone and the upper Glen Cairn Shale. The Lytle Sandstone is nearly white, contains very coarse grains and is sometimes considered a conglomerate. With the accelerated subsidence of the land, beach sands accumulate along the shore of the sea that advanced from the northeast. These sands formed the buff-colored Dakota Sandstone. This formation is rich in preserved ripple marks and iron-stone concretions. These concretions are round little balls of darker brick, colored by iron oxide. The Purgatoire and the Dakota Formations are referred to as the Dakota Group. As the shallow seas advanced to cover the beaches, the deposition changed from sand to shale to limestone. The resulting formations form the Benton Group. They comprise approximately 500 feet of strata and include Graneros Shale, Greenhorn Limestone and Carlisle Shale. A possible nonconformity exists between the Benton Group and the next formation. This represents a period of alternating erosion and deposition, leaving no stratigraphic evidence. The land subsided once more and the sea deepened, leaving a very thick layer of dense, gray limestone, called the Fort Hays Limestone. The next deposition in this sea (Pierre Seaway) was the Pierre Shale. This is the thickest of all the local sedimentary strata; approximately 5,000 feet of coarse gray limestone. This formation is very rich in fossils, including baculites, clams, mosasaurs, extinct crabs, horsetail ferns, cycads, and other plants. Near the end of the period, the last of the great inland seas retreated to the northeast. The receding shoreline resulted in the Fox Hills Sandstone which is two to three hundred feet in thickness. Also at this time, the lagoons and swamps provided the dense vegetation that later became the coal beds of the Laramie Formation. To the north of Colorado Springs is the Denver Formation, a sandstone-shale formation resulting from the retreating sea.
Cenozoic Era
The Cenozoic, or Recent Life, Era is the last of the three geologic eras in the Phanerozoic Eon. This is the "Age of Mammals" in which the whales were dominant in the ocean and the saber-tooth tiger cohabited with elephants and giant sloths. Finally, humans dominated the earth. The global climate turned somewhat colder, and the giant glaciers and ice caps returned to North America, Eurasia, and Antarctica.
Tertiary Period
This era includes the Paleocene, Eocene, Oligocene, Miocene, and the Pliocene Epoch. The breakup of Pangaea and the drift of its various fragments account for the present geographic distribution of continents and oceans. Various oceanic rifts are occurring during this period; the East African Rift system, the rift in the Red Sea and the rift in the Gullet of Adem. The Arabian plate has separated from Africa and caused the Dead Sea fault. The collision of plates resulted in orogeny that uplifted the Himalayas and is still continuing today. The Andes of South America are formed as a result of convergence of the Nazca and South American plates. The origin of the land connection between North and South America is a result of the Pacific plate subducted at the Cuban and Puerto Rican trenches. The Laramide Orogeny occurred during this period, resulting in volcanism and mountains from eastern Washington state through Nevada, Utah, and Colorado. Much volcanism and fault formations occurred during this time. The present distinctive topography of the Appalachian Mountains is the result of Tertiary period uplift and erosion. Biological events include the major radiation of mammals, birds, pollinating insects, the origin of many primate groups, and the appearance of ape-like ancestors of humans.
Local Tertiary History, 1—63 Million Years Ago
The Laramide Orogeny was experienced locally as gentle uplift that caused the retreat of the Cretaceous Sea (Pierre Seaway). More intense uplift gradually progressed, resulting in a huge block of crustal material thrust upward 10,000 to 15,000 feet by a series of uplifts. These uplifts were most intense during the Paleocene Epoch, and started to diminish through the Eocene and Oligocene Epochs. Great faults occurred where the blocks broke away from the surrounding rock, and the ancient Pikes Peak Granite was lifted into contact with Mesozoic and tertiary sedimentary strata. The fault that begins in the Garden of the Gods and runs north for about thirty miles is the Rampart Range Fault. The fault that runs south of Cheyenne Mountain westward through Ute Pass is the Ute Pass Fault. The Ute Pass Fault is the result of a huge piece of the exposed Pikes Peak Batholith being thrust upward and outward over the sedimentary strata to the east. In the northern part of the area, and under much of the Air Force Academy and Black Forest, is a stratum called Dawson Arkose, which is coarse sandstone and conglomerate deposited during the erosion of the rapidly rising Front Range. A number of volcanoes were known to have erupted in this area during the Laramide Orogeny. The Cripple Creek gold mines are located in the caldera of an extinct volcano, as well as the 39-Mile Volcanics. The Florissant Fossil Beds were formed when volcanic ash covered a fresh water lake in that area, preserving many plants and insects. The Castle Rock Conglomerate also was formed in this period.
Quaternary Period
This period was characterized by the Ice Ages. The Quaternary period is divided into two epochs, the Pleistocene and Holocene (Recent). The onset of the glacial conditions began about 40 million years ago when the surface ocean waters at high southern latitudes rapidly cooled, and the water in the deep-ocean basin soon cooled to about 10°C colder than previously. While the Pleistocene Epoch is best known for glaciation, it was also a time of tectonic unrest. Folding, faulting and uplift were common in western North America. These resulted from Pacific and North American plate interaction along the San Andreas fault system. There were at least 20 major warm-cold cycles in which the world's mean temperature ranged from 6°C to 10°C. Stratigraphic evidence indicates that there were at least four major episodes of Pleistocene glaciation in North America and seven major glacial advances and retreats in Europe. Humans appeared in this period.
Local Quaternary History, The Last Million Years
The local area was too far south for continental glaciation, but in the Rocky Mountains, alpine-type glaciers grew and spread down to an elevation of approximately 9,500 feet. The ice carved bowls (called cirques) out of the mountain faces. When the ice moved down the valleys, great quantities were carried along the glacier, forming lateral and terminal moraines. The melted water carried enormous amounts of material from the mountain toward the plains. This material became unconsolidated and graded deposits known as quaternary alluvium. The Mesa gravels, which form the flat topped hills around Colorado Springs, represent the outwash from melting glaciers.
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