Geology of Tunisia

Last updated

The geology of Tunisia is defined by the tectonics of North Africa, with large highlands like the Atlas Mountains as well as basins such as the Tunisian Trough. Geologists have identified rock units in the country as much as a quarter-billion years old, although most units date to the Mesozoic and Cenozoic, in the past 250 million years. Tunisia has a small but active mining industry and a significant oil and natural gas sector.

Contents

Structural Geology & Tectonics

The Tunisian Atlas mountains are a fold and thrust belt between the Rifo-Tellian chain, in the northwest (a part of the Alpine chain) and the Saharan platform in southern Tunisia. The Rifo-Tellian chain is separated from the Atlas Mountains in northern Tunisia by the Tunisian Trough. [1] Sedimentary units in the Tunisian Atlas mountains are divided by three regional faults: the Kasserine Fault, Gafsa Fault and Kaala-Djerda-Sbiba Fault. [2]

Stratigraphy & Geologic History

The oldest strata in Tunisia date to the Permian and are located beneath the Jeffara in Jebel Tebaga, in southeastern Tunisia. They are claystone and sandstone, interbedded with limestone containing foraminifera, corals and brachiopod fossils.

Mesozoic (251-66 million years ago)

The Triassic period is well preserved and known from outcrops in southern Tunisia and oil well drilling. The lower Triassic is defined by argillite and sandy fluvial, river sequences, overlain by a carbonate unit with palynomorphs indicating a Ladinian, Middle Triassic age. The Upper Triassic is marked by the Messaoudi dolomite, evidence of marine transgression. Lower and Middle Jurassic units are mainly calcareous and marl sediments, although some from the Late Jurassic preserve a deep ocean environment with the fossils of radiolarians.

Southwest of Jebel Zaghouan, Jurassic strata are for the most part limestones, while to the north and south dolomite sequences shift into Late Cretaceous argillites. [3] Paleosols and beds rich in plant fossils are common in Cretaceous units, which are also well preserved along with the Triassic.

Several thousand meters of clay from the Cretaceous fill the Tunisian Trough, laden with ammonite fossils and calpionellids, an extinct species of single celled organisms, as well as sand and calcareous deposits. In central Tunisia, the Meloussi Formation is made up of marine sandstone and carbonates. The Boudinar Formation comprises fluvial sandstones with poor sorting and the Gafsa Group contains clay, sand and carbonation sequences.

As in other places in Africa, southern Tunisia's Early Cretaceous rocks are part of the Continental Intercalation—which sometimes hold dinosaur bones. Other Cretaceous units include the Zebbaq Formation, with argillite and gypsum units, the Aleg Formation, with clay, marl and limestone, the El Haria Formation and Metlaoui Formation.

Cenozoic (66 million years ago-present)

The Souar Formation dates to the end of the Eocene and is made up of marine clay, marl, sand and gypsum. The Fortuna Formation in the Cap Bon area records the Oligocene with sandy limestone and marls, overlain by coarse sandstones and quartz pebbles, although it fades out in southern Tunisia. Other Cenozoic units include the Ain Grab Group and Oum Domil Formation. [2]

Quaternary stratigraphy, from the last 2.5 million years, includes quartz sands, rich in bivalves, as well as oolitic sands.

Natural resource geology

Mining is not a significant industry in Tunisia. The country has a modest amount of phosphate mining and fertilizer production, along with aluminum fluoride, cement and gypsum. The state-owned Compagnie des Phosphates de Gafsa (CPG) runs all phosphate mining and processing for Tunisia, out of eight open-pit mines near Sehib and Gafsa. Bougrine and Faj-Lahdoum (فج الهدوم) in northwestern Tunisia both have mining for lead and zinc. [4]

Oil and gas production is the main form of extraction in Tunisia, although proven reserves continue to decline. Most gas is sourced from the El Borma field offshore. Ezzaiua gas field is located off the coast of the tourist area of Djerba Island while the Abiod Formation contains the Maamoura oil field in the Gulf of Hammamet. [5]

Related Research Articles

North German basin Passive-active rift basin in central and west Europe

The North German Basin is a passive-active rift basin located in central and west Europe, lying within the southeasternmost portions of the North Sea and the southwestern Baltic Sea and across terrestrial portions of northern Germany, Netherlands, and Poland. The North German Basin is a sub-basin of the Southern Permian Basin, that accounts for a composite of intra-continental basins composed of Permian to Cenozoic sediments, which have accumulated to thicknesses around 10–12 kilometres (6–7.5 mi). The complex evolution of the basin takes place from the Permian to the Cenozoic, and is largely influenced by multiple stages of rifting, subsidence, and salt tectonic events. The North German Basin also accounts for a significant amount of Western Europe's natural gas resources, including one of the world's largest natural gas reservoir, the Groningen gas field.

Geology of Lebanon

The geology of Lebanon remains poorly studied prior to the Jurassic. The country is heavily dominated by limestone, sandstone, other sedimentary rocks, and basalt, defined by its tectonic history. In Lebanon, 70% of exposed rocks are limestone karst.

The geology of Somalia is built on more than 700 million year old igneous and metamorphic crystalline basement rock, which outcrops at some places in northern Somalia. These ancient units are covered in thick layers of sedimentary rock formed in the last 200 million years and influenced by the rifting apart of the Somali Plate and the Arabian Plate. The geology of Somaliland, the de facto independent country recognized as part of Somalia, is to some degree better studied than that of Somalia as a whole. Instability related to the Somali Civil War and previous political upheaval has limited geologic research in places while heightening the importance of groundwater resources for vulnerable populations.

Geology of Tanzania

The geology of Tanzania began to form in the Precambrian, in the Archean and Proterozoic eons, in some cases more than 2.5 billion years ago. Igneous and metamorphic crystalline basement rock forms the Archean Tanzania Craton, which is surrounded by the Proterozoic Ubendian belt, Mozambique Belt and Karagwe-Ankole Belt. The region experienced downwarping of the crust during the Paleozoic and Mesozoic, as the massive Karoo Supergroup deposited. Within the past 100 million years, Tanzania has experienced marine sedimentary rock deposition along the coast and rift formation inland, which has produced large rift lakes. Tanzania has extensive, but poorly explored and exploited natural resources, including coal, gold, diamonds, graphite and clays.

The geology of Morocco formed beginning up to two billion years ago, in the Paleoproterozoic and potentially even earlier. It was affected by the Pan-African orogeny, although the later Hercynian orogeny produced fewer changes and left the Maseta Domain, a large area of remnant Paleozoic massifs. During the Paleozoic, extensive sedimentary deposits preserved marine fossils. Throughout the Mesozoic, the rifting apart of Pangaea to form the Atlantic Ocean created basins and fault blocks, which were blanketed in terrestrial and marine sediments—particularly as a major marine transgression flooded much of the region. In the Cenozoic, a microcontinent covered in sedimentary rocks from the Triassic and Cretaceous collided with northern Morocco, forming the Rif region. Morocco has extensive phosphate and salt reserves, as well as resources such as lead, zinc, copper and silver.

The geology of Libya formed on top of deep and poorly understood Precambrian igneous and metamorphic crystalline basement rock. Most of the country is intra-craton basins, filled with thick layers of sediment. The region experienced long-running subsidence and terrestrial sedimentation during the Paleozoic, followed by phases of volcanism and intense folding in some areas, and widespread flooding in the Mesozoic and Cenozoic due to a long marine transgression. Libya has the largest hydrocarbon reserves in Africa, as well as deposits of evaporites.

The geology of Georgia is the study of rocks, minerals, water, landforms and geologic history in Georgia. The country is dominated by the Caucasus Mountains at the junction of the Eurasian Plate and the Afro-Arabian Plate, and rock units from the Mesozoic and Cenozoic are particularly prevalent. For much of its geologic history, until the uplift of the Caucasus, Georgia was submerged by marine transgression events. Geologic research for 150 years by Georgian and Russian geologists has shed significant light on the region and since the 1970s has been augmented with the understanding of plate tectonics.

Geology of Bosnia and Herzegovina

The geology of Bosnia & Herzegovina is the study of rocks, minerals, water, landforms and geologic history in the country. The oldest rocks exposed at or near the surface date to the Paleozoic and the Precambrian geologic history of the region remains poorly understood. Complex assemblages of flysch, ophiolite, mélange and igneous plutons together with thick sedimentary units are a defining characteristic of the Dinaric Alps, also known as the Dinaride Mountains, which dominate much of the country's landscape.

Geology of Moldova

The geology of Moldova encompasses basement rocks from the Precambrian dating back more than 2.5 billion years, overlain by thick sequences of Proterozoic, Paleozoic, Mesozoic and Cenozoic sedimentary rocks.

The geology of Mississippi includes some deep igneous and metamorphic crystalline basement rocks from the Precambrian known only from boreholes in the north, as well as sedimentary sequences from the Paleozoic. The region long experienced shallow marine conditions during the tectonic evolutions of the Mesozoic and Cenozoic, as coastal plain sediments accumulated up to 45,000 feet thick, including limestone, dolomite, marl, anhydrite and sandstone layers, with some oil and gas occurrences and the remnants of Cretaceous volcanic activity in some locations.

The geology of Utah includes rocks formed at the edge of the proto-North American continent during the Precambrian. A shallow marine sedimentary environment covered the region for much of the Paleozoic and Mesozoic, followed by dryland conditions, volcanism and the formation of the basin and range terrain in the Cenozoic. Utah is a state in the western United States.

The geology of Kuwait includes extremely thick, oil and gas-bearing sedimentary sequences from the Mesozoic and Cenozoic. Kuwait is a country in Western Asia, situated in the northern edge of Eastern Arabia at the tip of the Persian Gulf.

The geology of Afghanistan includes nearly one billion year old rocks from the Precambrian. The region experienced widespread marine transgressions and deposition during the Paleozoic and Mesozoic, that continued into the Cenozoic with the uplift of the Hindu Kush mountains.

Geology of Uzbekistan

The geology of Uzbekistan consists of two microcontinents and the remnants of oceanic crust, which fused together into a tectonically complex but resource rich land mass during the Paleozoic, before becoming draped in thick, primarily marine sedimentary units.

Geology of Bulgaria

The geology of Bulgaria consists of two major structural features. The Rhodope Massif in southern Bulgaria is made up of Archean, Proterozoic and Cambrian rocks and is a sub-province of the Thracian-Anatolian polymetallic province. It has dropped down, faulted basins filled with Cenozoic sediments and volcanic rocks. The Moesian Platform to the north extends into Romania and has Paleozoic rocks covered by rocks from the Mesozoic, typically buried by thick Danube River valley Quaternary sediments. In places, the Moesian Platform has small oil and gas fields. Bulgaria is a country in southeastern Europe. It is bordered by Romania to the north, Serbia and North Macedonia to the west, Greece and Turkey to the south, and the Black Sea to the east.

The geology of Lithuania consists of ancient Proterozoic basement rock overlain by thick sequences of Paleozoic, Mesozoic and Cenozoic marine sedimentary rocks, with some oil reserves, abundant limestone, dolomite, phosphorite and glauconite. Lithuania is a country in the Baltic region of northern-eastern Europe.

The geology of Greece is highly structurally complex due to its position at the junction between the European and African tectonic plates.

The geology of Denmark includes 12 kilometers of unmetamorphosed sediments lie atop the Precambrian Fennoscandian Shield, the Norwegian-Scottish Caledonides and buried North German-Polish Caledonides. The stable Fennoscandian Shield formed from 1.45 billion years ago to 850 million years ago in the Proterozoic. The Fennoscandian Border Zone is a large fault, bounding the deep basement rock of the Danish Basin—a trough between the Border Zone and the Ringkobing-Fyn High. The Sorgenfrei-Tornquist Zone is a fault-bounded area displaying Cretaceous-Cenozoic inversion.

The geology of Israel includes igneous and metamorphic crystalline basement rocks from the Precambrian overlain by a lengthy sequence of sedimentary rocks extending up to the Pleistocene and overlain with alluvium, sand dunes and playa deposits.

The geology of the United Arab Emirates includes very thick Paleozoic, Mesozoic and Cenozoic marine and continental sedimentary rocks overlying deeply buried Precambrian. The region has extensive oil and gas resources and was deformed during the last several million years by more distant tectonic events.

References

  1. Schlüter, Thomas (2008). Geological Atlas of Africa. Springer. p. 259.
  2. 1 2 Schlüter 2008, p. 260.
  3. Schlüter 2008, p. 259.
  4. Taib, Mowafa (2017). The Mineral Industry of Tunisia (PDF). USGS.
  5. Schlüter 2008, p. 261.