The geology of

Turkmenistan Turkmenistan ( or ; tk, Türkmenistan / Түркменистан, ) is a country located in Central Asia, bordered by Kazakhstan to the northwest, Uzbekistan to the north, east and northeast, Afghanistan to the southeast, Iran to the sout ...

includes two different geological provinces: the Karakum, or South Turan Platform, and the Alpine Orogen.

Geologic History, Stratigraphy & Tectonics

Basement rock is only exposed at the surface in three places on the Turkmenistan plain. Shale with lenses of

spilite Spilite (from el, σπιλάς) is a fine-grained igneous rock, resulting particularly from alteration of oceanic basalt. The term was introduced into the geological literature by Alexandre Brongniart in 1827.Manfred Schidlowski: ''Spilite and ...

, jasper-like rocks and silicified limestone outcrops in the center of the Tuarkyr elevation. Together with

gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is che ...

, serpentinized

pyroxenite Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite, diopside, hypersthene, bronzite or enstatite. Pyroxenites are classified into clinopyroxenites, orthopyroxenites, and the websteri ...

and

diabase Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-graine ...

and numerous

radiolarian The Radiolaria, also called Radiozoa, are protozoa of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ectoplasm. The elab ...

fossils, they form an

ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is found i ...

mélange In geology, a mélange is a large-scale breccia, a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all sizes, contained in a fine-grained deformed matrix. The mélange typically cons ...

from the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

, overlain by four kilometers of sandstone, clay, tuff and conglomerate. Late Paleozoic igneous rocks are exposed on the Krasnovodsk Peninsula, including granite, gabbro and acid volcanic rocks dating to 450 to 350 million years ago. The third exposure is on the left bank of the Amudarriya River, where 285 to 280 million year old

cataclastic A cataclastic rock is a type of fault rock that has been wholly or partly formed by the progressive fracturing and comminution of existing rocks, a process known as ''cataclasis''. Cataclasis involves the granulation, crushing, or milling of the ori ...

granite intrudes

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

clay and carbonate sediments.

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...

amphibolite Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flaky ...

and

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...

, Middle Paleozoic granite, gabbroid, metamorphosed volcano-sedimentary rocks and Late Paleozoic intrusives are known through drillholes in the South Turan Platform. Geologists divide the platform basement into Precambrian massif and fold zones related to the

Hercynian orogeny The Variscan or Hercynian orogeny was a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea. Nomenclature The name ''Variscan'', comes f ...

Mesozoic (251-66 million years ago)

Sedimentary rocks formed during the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

and

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

overlie the South Turan Platform. In the Murgab depression and Cis-Kopetdag, they reach up to eight to 10 kilometers thick, although average thickness is one to two kilometers. Turkmenistan has tectonically complex uplands, often separated by shallow deeps. Rhaetic and Liassic age Alpine cover rocks on the South Turan Platform lies unconformably atop folded basement rocks. These are mainly sand and clay layers deposited in a nearshore environment, often with coal layers. Late Jurassic deposits include a 60-meter clay and marl unit, an 800-meter carbonaceous unit and an upper 1.2-kilometer salt-bearing sequence. Jurassic sediments are up to three kilometers thick in the South Turkmenistan subsidence system.

Cenozoic (66 million years ago-present)

In the

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...

and the

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

, the North Mesotethys Ocean closed, forming the Shachrud-Nishapoor thrusted-folded arc and the Eastern Iran transverse folded system. This led to the incorporation of Turkmenistan, Iran and Afghanistan into the larger Eurasian Plate. As Gondwana moved northward and interacted with Eurasia in the

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

, subduction began south of the current Zagros Mountains in northern Iraq and Iran. As the North Mesotethys Ocean basin was subducted, it kicked off calc-alkaline volcanism in Iran in the Eocene. The Badkhys volcanic rocks and Great Balkhan bentonites on the Turan Plate in Turkmenistan are remnants of the inland extent of this subduction and volcanism. The collisions uplifted a large area across Eurasia as the Alpine-Asiatic mobile belt. Regionally, this uplift resulted in the Turkmen-Khorasan and Afghan-Tien Shan folded regions. The Southern Turkmen sutural zone, a linear area with wrench-dislocations is forming in the southwest along the Turkmen-Khorasan fold system. Throughout the

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

deep troughs filled with

molasse __NOTOC__ The term "molasse" () refers to sandstones, shales and conglomerates that form as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse deposits accumulate in a foreland basin, especially on top of flys ...

deposits two kilometers to as much as eight kilometers thick (in the case of the West Turkmenian Basin). During the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

, the level of the

Caspian Sea The Caspian Sea is the world's largest inland body of water, often described as the world's largest lake or a full-fledged sea. An endorheic basin, it lies between Europe and Asia; east of the Caucasus, west of the broad steppe of Central Asia ...

has varied widely. In fact the level of the Caspian basins dropped up to 500 meters. This has tended to deep paleo-valleys as downcutting took place. Turkmenistan is highly seismically active, especially around the Kopetdag-Balkhan deep fault zone.

Natural resource geology

Oil and gas are the dominant natural resources in Turkmenistan, with over 50 deposits discovered before the end of the 20th century. The West Turkmen Depression, also known as the Transcaspian Depression, is the main oil-producing area primarily from

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58mirabilite Mirabilite, also known as Glauber's salt, is a hydrous sodium sulfate mineral with the chemical formula Na2SO4·10H2O. It is a vitreous, colorless to white monoclinic mineral that forms as an evaporite from sodium sulfate-bearing brines. It is fo ...

and sodium sulfate. The eastern region of Guardak-Kugitang has abundant potassium salt, halite and sulfur, while the Oglanly deposit in Great Balkhan in Eocene sediments is a major supply of

bentonite Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-mon ...

. Keramsite and other material is mined for construction.

Hydrogeology

Oases supply the cities of Cis-Kopetdag and Tedzhen-Murgab with drinking water and groundwater is widely extracted for use in the arid oil fields, particularly the Yaschan freshwater aquifer at Uzboy. Turkmenistan has mineral water springs at Archman, Ashkhabad and Bayram-Ali.

References

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