Geology Based Culture?
Civilization would not have developed without the availability and use of natural resources. Mineral resources generally correspond to underground resources. They form a concentration of naturally occurring solid, liquid, or gaseous materials in the earth’s crust or on the surface. Ancient people used hard rocks at first and made hunting aids from these rocks. Then they spread out all over the world carrying tequnique, how to make hunting aids, in their hands. West Asia has produced a variety of mineral resources abundantly and has supported to form civilization.
KeywordsSiliceous Sedimentation Pyrolysis Shale Cretaceous
The relationship between mineral resources and humans started when ancient people picked up suitably shaped stones for use as hunting aids. They discovered that siliceous nodules, chert, radiolarite, obsidian, and other hard rocks made the best knives and spear points. Native metals such as copper and gold were first used more than 20,000 years ago (Skinner et al. 2013). In ca. 5000 BC ancient people began to learn how to extract copper from certain minerals through a process known as smelting, which will be described in Chap. 8 in this volume. They found how to smelt minerals to produce lead, tin, zinc, silver, and other metals. The technique of mixing metals to create alloys was learned next, and bronze came into use by combining copper and tin. In this chapter, continental and regional topography and geological features of West Asia will be first described to discuss the relationship between the geology and the people.
2.1 Outline of West Asia
2.2 Plate Tectonics of West Asia
The outer layer of the earth is made of the firm, rigid lithosphere above the softer asthenosphere, where materials can easily flow. Much like a person slipping on a banana skin, the lithosphere easily glides over the asthenosphere. The lithosphere is divided into oceanic plates and continental plates moving in various directions to form three different types of boundaries. Convergent boundaries occur when plates collide. In such cases, the collision force can result in buckling of the two plates, or one plate may slide beneath the other. Divergent boundaries occur when the plates are pulled apart, and transform plate boundaries occur when two plates slide laterally against each other.
The Arabian and Iranian plates formed a collision zone. The collision caused orogenic movement and built up the Zagros Mountains.
The border of the Arabian and Eurasia plates formed a collision zone. Near Cyprus in the Mediterranean Sea, however, the convergence formed a subduction zone.
The border between the African and Arabian plates exhibits different characteristics throughout the region. Divergent and transform boundaries occur in the south and north regions, respectively.
2.3 Continental and Regional Topography of West Asia
2.3.1 General View of West Asian Topography
2.3.2 The Origin of the Desert
Type (a) desert is established in the subtropical high pressure belt where dry air of high temperature descends. In the case of no rotation of the Earth, air warmed in tropical zones rises and descends in the Polar region. This phenomenon is known as Hadley circulation. However, strong air currents flowing in the north and south directions caused by Earth’s rotation create a whirlpool effect. As a result, Hadley circulation occurs only in zones of low latitude where the influence of the rotation is very small. In zones of high latitude, however, where the influence of the rotation is large, Rossby circulation occurs. Atmospheric circulations in low and high latitudes are referred to as Ferrel and Polar cells, respectively. A subtropical high pressure belt lies between the border of the Hadley–Rossby circulation at about 20°–30° in latitude. Clouds do not appear over the land in this subtropical high pressure belt, and the precipitation is very small. This condition has created deserts such as the Sahara and Rub-al Khaliin the Arabian Peninsula.
Type (b) desert is produced by cold sea currents that flow from the polar regions toward the equator. Large quantities of heat occurring on land are cooled when contacting the cold sea currents. Because this cool and heavy air does not ascend, it does not form a rain cloud. Instead, it remains inland and forms deserts such as the Atacama and Namib.
In type (c) desert, air containing moisture meets and collides against high mountains along the shore, and precipitatesrain and snow. The remaining dry air across the mountains may accompany abnormal temperature rise to create desert conditions. This mechanism, known as the Föhn phenomenon, occurs unexpectedly and results in abnormally high temperatures. The Takla Makan desert was developed by this phenomenon.
2.3.3 Limestone Caves
Active limestone caves usually involve development of stalactites, which hang from the ceiling, and stalagmites, which are shaped like mushrooms on the floor. The dissolution of a limestone cave begins with groundwater flowing along cracks in a saturated water zone beneath the water table. The rain on the ground surface reaches the saturated water zone through underground cracks. The region between the ground surface and the saturation zone is known as a circulation water zone. The water flow channels migrate horizontally and vertically, and the duct of the saturated water zone gradually spreads laterally. Limestone is dissolved mostly in the shallow part of the saturated water zone in a semicircular shape, and stalactites are formed in the upper part of the cave space. When the water table drops, the dissolution finally stops, and the cave enters a stable stage.
As exemplified by the active Akiyoshido Cave in Japan, water generally plays a crucial role in developing the limestone caves. In the case of the Akiyoshido cave, there are three development stages according to the location level: high terrace (300 m asl), middle terrace (200 m asl), and low terrace (100 m asl). This situation indicates that the saturation water zone has decreased gradually. The caves on each terrace seem to have been formed 500,000–1 million years ago, 200,000–500,000 years ago, and 100,000–200,000 years ago, respectively.
In contrast to the East Asian Monsoon climate, the precipitation in West Asia is considerably lower. The monthly precipitation from November to April is between 20 mm and 80 mm in Shiraz, southern Iran. The precipitation is extremely low in this region, at 0 mm–7 mm from May to October. The formation of a limestone cave under such climate conditions seems impossible. However, the formation processes of limestone caves continue over tens of thousands of years, as exemplified by the Akiyoshido Cave. The limestone caves in southern Iran must also have been formed over thousand of years during which climatic conditions may have been quite different from those of the present day.
2.4 Geological Features of West Asia
2.4.1 General View
Sedimentary rocks, which are formed through consolidation of sediments, can be classified into two types. The first category is terrigenous clastics, which are formed by transportation and accumulation of terrigenous grains made of weathered and eroded surface rocks. The second includes carbonates, siliceous rocks, and chemical precipitates, which are formed by organisms or chemical deposition. Carbonate rocks which are the most representative rocks in West Asia will be described first. A discussion of the archaeologically important siliceous rock will follow it.
2.4.2 Carbonate Rock
18.104.22.168 Coral and Zooxanthellae
Carbonate rocks are considered to form through organic processes: some carbonates are directly related to structures such as coral reefs. Coral reefs are made of skeletons of coral polyp, a member of Coelenterata. The coral polyps grow by eating plankton, and develop their skeletons using calcium and bicarbonate ions dissolved in marine water. In addition, the coral polyps receive nourishment by photosynthesis from zooxanthellae living inside their tissue. Therefore, coral polyps may live as deep as they can photosynthesize; such a depth is known as the coral growth depth. The growth of coral depends on water temperature, salinity, photoenvironment, waves, and water flow.
22.214.171.124 Formation of Carbonate Rock Bodies
Carbonate rock is a generic term for sedimentary rocks with a ratio of carbonate minerals such as a calcite, aragonite and dolomite of more than half the volume. Carbonates are compounds in which part or all of the hydrogen of carbonic acid (H2CO3), a weak acid generated when carbon dioxide is dissolved in water, is replaced by metal.
The formation of carbonate sediments, which become carbonate rock through lithfication, depends on (1) organic production; (2) supply of terrigenous sediments; and (3) erosion, transportation, and sedimentation (Hoyanagi et al. 2004). Carbonate is produced by organisms in coral reefs, and the supply of the terrigenous sediments determines the production of the carbonate sediment. Carbonate minerals are also produced in subarctic and temperate climatic zones where the supply of the terrigenous clastics is poor.
Because particles constituting carbonate sediments are produced by organisms, its formation is affected by factors such as water temperature, light quantity, salinity, sedimentation rate, and the water circulation.
Reef corals are the main constituents of carbonate sediments in the tropic zone, whereas benthic foraminifera, bryozoans, and bivalves are the main producers in temperate and subarctic zones. However, reef coral is overwhelmingly predominant in the origin of carbonate mineral particles.
Rimmed continental shelf: This type occurs when a reef or the barrier of the carbonate sand body is formed on a remote continental shelf far from land. The Florida Peninsula and the Great Barrier Reef belong to this type.
Carbonate ramp: This type is formed in a continental shelf having a gentle slope, and it resembles a rimmed continental shelf. However, farther from land and at deeper depths, it does not form a reef or barrier on the continental shelf. The Gulfbelong to this type.
Epeiric platform: Different in size from the previous two types of carbonate platforms, this type extends hundreds and thousands of kilometers and was formed near the Gondwana Continent in the early Paleozoic. No example of this type exists in modern times.
Isolate platform: This type stands alone in the deep sea surrounded by straits. A coral reef develops in the periphery area, and its central part tends to be a depression or lagoon that forms an atoll. The Bahama Banks are a famous example, and seamounts and crest areas of fault scarp of the eastern Red Sea margin belong to this type.
The representative carbonate rock occurringon land is limestone. This rock is composed of brecciated sediment consisting of coral reef material formed in a shallow sea less than several hundred meters in depth.
2.4.3 Siliceous Rocks
Siliceous rocks are rich in silica (SiO2) and were very important for making lithic implements used by humans. Cenozoic siliceous shale and the Mesozoic/Paleozoic bedded chert are typical siliceous rocks occurring in the Japanese Islands.
Chert contains more than 90 % silica in the form of cryptocrystalline and microcrystalline quartz. It contains chert layers several centimeters to ten and several centimeters in thickness composed of siliceous remains such as radiolarian tests, which alternate with layers of mud several millimeters to tens of millimeters thick that do not contain abundant siliceous remains.
Periodical fluctuation of siliceous plankton
Secondary deposition of siliceous sediment (turbidite)
Of these, (a) explains the chert layer formed during blooming and rapid accumulation of radiolarians, whereas the mud layer formed during the period of low radiolarian production. (b) explains deposition from turbiditic flow sorted particle size into coarse radiolarian tests and fine clay particles. (c) attributes the siliceous layer to chemical accumulation of silica dissolved from mixed sediments of radiolarian tests and mud during diagenesis.
In addition, chert occurs in a nodular form, which archaeologists refer to as flint. It occurs as ball-like and irregular-shaped chert in carbonate rock, and it consists of microcrystalline quartz. This silica formed from radiolarian tests and sponge spicules and was crystallized as a result of a kind of segregation.
126.96.36.199 From the Formation of Basaltic Magma to Its Extrusion
In oceanic environments, basaltic magmas are usually generated underneath mid-oceanic ridges by partial melting of peridotites in the upper mantle. The melt separates from the partially moltenperidotite and accumulates to form magmas. The remaining rock after melt extraction is known as residual peridotite. When magmasform a magma reservoir in the crust, it begins to cool to form new oceanic crust. During the cooling, crystals that formed through crystallization in the magma chamber sink through it and accumulate at the bottom due to the density contrast between lighter magmas and heavier crystals. Rocks produced by this crystal settling process are known as cumulates. The rest of the magmas may continue to rise, and finally reach to the earth’s surface. Then, it is cooled rapidly by marine water and form pillow lavas of basaltic compositions.
188.8.131.52 Question About the Formation of Ophiolites
A large number of isolated ophiolite blocks are distributed over the fold belts in West Asia. It was believed that ophiolites represent structures of the oceanic lithospheres. However, as research on world ophiolites progressed, the chemical composition of its volcanic rocks were revealed to often have a similar composition to those formed in a subduction zone environment. Therefore, most ophiolites in West Asia are believed to have been developed in the so-called supra-subduction zone environment.
Ophiolites often accompany low-angle fault planes at its lowest boundary. When a continental landmass led by an oceanic plate reaches the subduction zone, the landmass cannot sink owing to its buoyancy. As a result, it is thought that the tip of a mantle wedge in the subduction zone thrust onto the landmass in a process known as obduction. It is often known that the formation age of igneous rocks in ophiolites and the age of arc magmatism intruded into the ophiolite are similar, which suggests that the formation sites of ophiolites are near island arcs or marginal seas where igneous activity was high (Arai 1988). Accordingly, because abundant ophiolites occur in the West Asia fold belt, numerous obduction events must have occurred in this region due to multiple crustal movements throughout the geological timescale.
2.4.5 History of Geological Feature in West Asia
Although Pangaea was a single huge continent, it underwent repeated breakup and collage. Tectonics in Pangaea are characterized by breakup along the northern edge of Gondwana and collage of small continents along the southern edge of Laurasia during several hundred million years. A typical example is the divergence and the convergence of Cimmerian Continent.
The Cimmerian Continent was a strip-shaped continent that was a collage of small continents from current West Asia to current Southeast Asia. The present-day Turkey, Sanandaj–Sirjan in the central part of Iran, south Tibet, and Sibumasu terrane extending from Myanmar to Sumatra through Thailand and Malaysia, were aligned to form this continent (Fig. 2.11b). This strip-shaped continent diverged from Gondwana, which produced a new ocean that separated from the old Tethys. This new ocean is known as the Neotethys, whereas the old ocean is known as the Paleotethys, to distinguish from the former Tethys Ocean. The expansion of the Neotethys was caused by the drift of the Cimmerian Continent to the north and accompanied consumption of the Paleotethys. The reduction and eventually the disappearance of the Paleotethys was caused by the subduction of the Paleotethys plate into the trench in front of Laurasia. Ultimately, the Cimmerian Continent combined with Laurasia during Triassic to Jurassic; the Alborz and other mountains were formed by this activity (Fig. 2.11c). In the Cenozoic era, the Arabian plate diverged from the African plate; thereafter, the Arabian plate drifted to the north and collided with the Eurasian (Iranian) plate. This collision formed the Zagros Mountains (Fig. 2.11d).
2.5 Richness of Mineral Deposits in West Asia
To say that West Asia is supported by abundant petroleum is not an exaggeration. Modern industry depends on petroleum; thus, West Asia has strongly affected the world’s economy. In this section, the reasons for the formation of such a huge petroleum field in West Asia are examined.
As for the origin of the petroleum, “origin hypothesis of Kerogen” is convincing. Kerogen is produced by high molecular compounds derived from organisms such as plankton, which are altered by terrestrial heat and pressure in a lengthy process known as pyrolysis. Rock containing more than 1 % gross weight of kerogen is known as petroleum source rock.
When we consider that the kerogen is derived from plankton, it appears that the sedimentation environment was the reductive with fine-grained sediments. Petroleum source rock is formed deep in a closed ocean basin such as the Black Sea. About half of the world’s petroleum source rock is the strata accumulated between the late Jurassic and the early Cretaceous eras. During this period, the temperature was highest in Earth’s history. The polar regions lacked ice, and oceanic general circulation might not have occurred. Therefore, the world ocean floor was reductive, which accelerated the formation of petroleum source rock (JOGMEC 2010).
The petroleum soaks into rocks with high porosity known as petroleum reservoir rock; 56 % of petroleum reservoir rocks in the world’s huge petroleum field are sandstones, and 44 % are carbonate rocks. Sandstone is composed of completely spherical grains, which represents the closest packing, has a porosity of 26 %. Porosity of 20 % and 15 % are considered to be very superior and good petroleum reservoir rocks, respectively; less than 5 % porosity is not considered a petroleum reservoir rock. The petroleum is produced in petroleum source rock and moves into the petroleum reservoir rock with high porosity during its primary movement. In its secondary movement, the petroleum is transmitted through the reservoir rock and moves to upper underground regions. The petroleum finally is stored in underground tanks known as traps, which form a petroleum field. Impermeable rock is necessary for forming these tanks because the petroleum must remain in place underground. This rock is also known as cap rock and is often composed of mudstone or halite. The buoyancy of petroleum results in high pressure applied to the upper level of the cap rock, and in some cases, petroleum penetrates the cap rock and seeps onto the ground surface. It is well-known that the ancient people of Baku near the Caspian Sea and the Tigris basin, Iraq, used such seeped petroleum for fuel and ointment (JOGMEC 2010).
As previously mentioned, the elements necessary for establishing West Asia as a petroleum field include petroleum source rock containing abundant kerogen, reservoir rocks such as sandstone and carbonate rock, and suitable tectonic movement such as a fold belt. In addition, the ex-equator belt provides a suitable zone because of the huge accumulation of petroleum reservoir rock and carbonate rock. Therefore, the reasons for the concentration of the large petroleum field in West Asia is explained by 1) the existence of the Zagros fold belt, 2) carbonate rock and sandstone sedimentation in the Tethys Ocean, and 3) abundant kerogen in the petroleum reservoir rock.
2.5.2 Metallic Minerals
In addition to petroleum, West Asia is a region of rich metallic minerals, particularly those useful for humans.
The Cimmerian Continent zone includes back-arc, magmatic arc, fore-arc, trench, ocean floor, and likely mid-ocean ridge tectonic settings formed in the Mesozoic that amalgamated through collision processes. This resulted in the formation of metallogenic zones along the orogenic belts. Jankovic and Petrascheck (1987) distinguished five groups of metallogenic zones and districts in the Alpine–Himalayan Belt related to late orogenic activation, subduction and collision, ocean floor spreading, rifting, and Alpidic remobilization.
As shown in Figs. 2.13, 2.14 and 2.15, metal deposition sites are concentrated in the UDMA and SSZ. Therefore, districts north of the Zagros Mountains are characteristically rich in metals compared with southern districts except for the Red Sea area.
2.5.3 Raw Materials for Stone Tools
Siliceous rocks were also important for the ancient people in West Asia. The raw materials used to make chipped stone implements included chert, obsidian, siliceous nodules, radiolarite, and other siliceous rock. Two famous obsidian sources are situated in Anatolia, and volcanic glass which has been traded throughout West Asia was used for making chipped implements, particularly during the Neolithic era. Other siliceous rocks such as chert and radiolarite have wider distributions and were indispensable materials for making chipped stone implements. I personally had a chance to study radiolarite of the Iranian Zagros Mountains, and have previously reported the general characteristics of siliceous rocks. Therefore, the present discussion is focused on radiolarite, particularly that from the Zagros region. Radiolarite has several advantages as a raw material for chipped stone implements such as homogeneity, hardness, and the capacity for splitting. These features are all crucial for making stone tools.
The question remains of how deep sediment such radiolarite can coexist with shallower rock such as limestones. The answer can be found in the geodynamics of the Zagros Mountains. The Zagros orogeny fundamentally reflects the collision tectonics between the Arabian plate and the Central Iran microcontinent that occurred during the Paleogene Period. The components of the Zagros Crushed Zone, SSZ, and UDMA were located between the plate and the microcontinent, and through collision tectonics, the components of these three zones were thrust over the Zagros Folded Zone on the Arabian plate. The Zagros Crushed Zone includes an ophiolite suite, which is an association of ultramafic rocks, coarse-grained gabbro, coarse-grained diabase, volcanic rocks, chert, and radiolarite. In short, the deeper radiolarite was thrust over the shallower limestone.
Biglari (2004) reported that radiolarite was used in present-day Kermanshah as a raw material for stone tools. Radiolarite occurs in the Zagros Mountains longitudinally and intermittently. Ancient people utilized radiolarite for stone implements and limestone caves for residences soon after arriving in the Zagros Mountains. They may have acquired skills and improved their technologies for making stone implements.
West Asia is known as the birthplace of ancient civilization, and the fertile nature of the locality has attracted attention. In addition, the huge petroleum region that became the base of modern industry spreads throughout West Asia with good reserves.
Concerning the plate tectonics, West Asia was formed as a node of three continents. This formation caused the geological complexities of West Asiawith the concentrations of stone and mineral resources along the plate boundaries, which were so significant for the development of lithic culture and metal use in human societies.
In the Paleolithic West Asia, the geology surrounding the Fertile Crescent provided an extremely attractive environment for humans including large limestone caves for their habitation and wonderful siliceous rocks such as chert and radiolarite for making chipped stone implements.
In the Neolithic era, species of plants and animals were domesticated. In addition, good geologic materials were available for building houses, such as limestone and basalt, and suitable siliceous rocks for making agricultural tools such as sickle elements. This also demonstrates that the geology of West Asia was extremely attractive for providing the basic requirements of humans.
After the Bronze Age, basic metallic materials such as copper, tin, and iron that were used to produce highly advanced tools existed in particular areas of West Asia. No other area in the world offers such metals in combination. These geologic requirements are prominent among areas of ancient civilization. It cannot be overemphasized that civilization occurred in West Asia as a result of these geologic requirements.
When we consider the role of petroleum in modern world, it is quite clear that petroleum has a special position in the world politics and economy. Siliceous rocks, metallic minerals including iron, and other important precious stones and their combinations had a special position in each era from the Paleolithic to the present world. This demonstrates that geological features became the basis of culture. Therefore, I answer the title of this paper with “Yes” without hesitation.
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