Tyrrhenian Basin
   HOME

TheInfoList



OR:

The Tyrrhenian Basin is a
sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock They form when long-term subsidence ...
located in the western
Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...
under the
Tyrrhenian Sea The Tyrrhenian Sea (, ; or ) , , , , is part of the Mediterranean Sea off the western coast of Italy. It is named for the Tyrrhenians, Tyrrhenian people identified with the Etruscans of Italy. Geography The sea is bounded by the islands of C ...
. It covers a 231,000 km2 area that is bounded by
Sardinia Sardinia ( ; ; ) is the Mediterranean islands#By area, second-largest island in the Mediterranean Sea, after Sicily, and one of the Regions of Italy, twenty regions of Italy. It is located west of the Italian Peninsula, north of Tunisia an ...
to the west,
Corsica Corsica ( , , ; ; ) is an island in the Mediterranean Sea and one of the Regions of France, 18 regions of France. It is the List of islands in the Mediterranean#By area, fourth-largest island in the Mediterranean and lies southeast of the Metro ...
to the northwest,
Sicily Sicily (Italian language, Italian and ), officially the Sicilian Region (), is an island in the central Mediterranean Sea, south of the Italian Peninsula in continental Europe and is one of the 20 regions of Italy, regions of Italy. With 4. ...
to the southeast, and peninsular
Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...
to the northeast. The Tyrrhenian basin displays an irregular seafloor marked by several seamounts and two distinct sub-basins - the Vavilov and Marsili basins. The Vavilov deep plain contains the deepest point of the Tyrrhenian basin at approximately 3785 meters. The basin trends roughly northwest–southeast with the spreading axis trending northeast–southwest.


Regional geologic setting

The Tyrrhenian basin is located in a geologically complex portion of the Mediterranean Sea. The basin is partially encircled by several orogenic belts, including the
Apennines The Apennines or Apennine Mountains ( ; or Ἀπέννινον ὄρος; or – a singular with plural meaning; )Latin ''Apenninus'' (Greek or ) has the form of an adjective, which would be segmented ''Apenn-inus'', often used with nouns s ...
to the northeast, the
Alps The Alps () are some of the highest and most extensive mountain ranges in Europe, stretching approximately across eight Alpine countries (from west to east): Monaco, France, Switzerland, Italy, Liechtenstein, Germany, Austria and Slovenia. ...
to the north, and the
Atlas Mountains The Atlas Mountains are a mountain range in the Maghreb in North Africa. They separate the Sahara Desert from the Mediterranean Sea and the Atlantic Ocean; the name "Atlantic" is derived from the mountain range, which stretches around through M ...
to the southwest. It is also bounded by a
convergent boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...
and associated trench to the southeast. Deep reflection seismic lines near the trench clearly show
oceanic lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time sc ...
from the African plate flexing beneath
Calabria Calabria is a Regions of Italy, region in Southern Italy. It is a peninsula bordered by the region Basilicata to the north, the Ionian Sea to the east, the Strait of Messina to the southwest, which separates it from Sicily, and the Tyrrhenian S ...
to join a seismogenic slab that extends down to 500 km beneath the Tyrrhenian basin. Between the upper slope of the trench and Calabria are a number of small fore-arc basins that developed through extensional listric faulting during the
Tortonian The Tortonian is in the geologic time scale an age or stage of the late Miocene that spans the time between 11.608 ± 0.005 Ma and 7.246 ± 0.005 Ma (million years ago). It follows the Serravallian and is followed by the Messinian. The Tort ...
. These basins subsequently subsided between the late
Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 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), as well as the current and most recent of the twelve periods of the ...
and are now infilled with
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 con ...
. The
Aeolian Islands The Aeolian Islands ( ; ; ), sometimes referred to as the Lipari Islands or Lipari group ( , ) after their largest island, are a volcanic archipelago in the Tyrrhenian Sea north of Sicily, said to be named after Aeolus, the mythical ruler of ...
north of Calabria and Sicily represent the
volcanic arc A volcanic arc (also known as a magmatic arc) is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc ...
of the convergent system. The volcanism associated with these islands occurs at the northeast closure of the downgoing slab and began approximately during the late Pliocene to early Pleistocene (1.5–1.7 Ma). The Tyrrhenian basin lies to the northwest of the Aeolian Islands and represents a
back-arc basin A back-arc basin is a type of geologic Structural basin, basin, found at some convergent boundary, convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found ...
formed from tensional forces associated with the northwest subduction of the African Plate beneath the Eurasian Plate. Similar to other back-arc basins, the Tyrrhenian basin displays a shallowing of the
Moho discontinuity Moho may refer to: Birds * Moho (genus), ''Moho'' (genus), an extinct genus of birds in the family Mohoidae * The Hawaiian name of the Hawaiian rail, an extinct species * The Māori name of the North Island takahē, an extinct species * A local na ...
towards the central part of the basin, a Wadati Benioff zone, abnormally high
heat flow Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...
(exceeding 200 mW/m2 in some places), and an active
volcanic belt A volcanic belt is a large volcanically active region. Other terms are used for smaller areas of activity, such as volcanic fields or volcanic systems. Volcanic belts are found above zones of unusually high temperature () where magma is created ...
on the arc-ward edge of the basin.


Basement structure

Tyrrhenian basement rocks consist of late
Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...
granites derived from the Hercynian orogeny. Basement rocks in the southeastern portion of the basin were reactivated during the
Alpine orogeny The Alpine orogeny, sometimes referred to as the Alpide orogeny, is an orogenic phase in the Late Mesozoic and the current Cenozoic which has formed the mountain ranges of the Alpide belt. Cause The Alpine orogeny was caused by the African c ...
while those to the northwest were undisturbed.


Stratigraphy


Upper Sardinia Margin

The Upper Sardinia Margin is a fault-bounded
passive margin A passive margin is the transition between Lithosphere#Oceanic lithosphere, oceanic and Lithosphere#Continental lithosphere, continental lithosphere that is not an active plate continental margin, margin. A passive margin forms by sedimentatio ...
located northwest of the Vavilov Basin. Seismic reflection surveys across the Upper Sardinia Margin exhibit a stratigraphic geometry suggestive of pre-rift, syn-rift, and post-rift sequences. Drill cores penetrating to the base of the syn-rift sediments identified a transgressive sequence related to
subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...
of the
continental crust Continental crust is the layer of igneous, metamorphic, and sedimentary rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as '' continental shelves''. This layer is sometimes called '' si ...
during the rifting stage of the Tyrrhenian Basin opening. At the base of the syn-rift sequence are 60 meters of
Tortonian The Tortonian is in the geologic time scale an age or stage of the late Miocene that spans the time between 11.608 ± 0.005 Ma and 7.246 ± 0.005 Ma (million years ago). It follows the Serravallian and is followed by the Messinian. The Tort ...
conglomerate with subrounded clasts derived from metamorphosed carbonate and quartzitic basement. It is inferred that this conglomerate formation was deposited in a high-energy subaerial environment like an alluvial fan. Overlying the conglomerate formation are oyster-bearing glauconitic sandstones deposited in a nearshore environment. Late Tortonian to Early
Messinian The Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 Ma and 5.333 ± 0.005 Ma (million years ago). It follows the Tortonian and is followed by the Zanclean, the fir ...
calcareous ooze and claystone with
benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...
foram assemblages overlays the sandstone formation; this indicates that water depth increased, perhaps due to subsidence at the end of the syn-rift period. The boundary between the syn-rift and post-rift periods is believed to be located in a 50-meter section of late Messinian
gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...
that overlays the calcareous ooze and claystone formations. At the top of the
stratigraphic section A stratigraphic section is a sequence of layers of rocks in the order they were deposited. It is based on the principle of original horizontality, which states that layers of sediment are originally deposited horizontally under the action of ...
are 243 meters of
Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
post-rift sediment containing calcareous mud with occasional terrigenous clastics and
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, produced during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to r ...
.


Lower Sardinia Margin

The Lower Sardinia Margin lies near the transition between continental and
oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramaf ...
. This is the easternmost point on the margin where pre-rift, syn-rift, and post-rift sediments can be clearly discerned on seismic reflection profiles. A drill core to the base of the syn-rift sediments revealed 533 meters of thinly-bedded, calcareous, siltstone and sandstone with dispersed detrital gypsum grains and
anhydrite Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the ...
nodules. The entire sequence is reversely magnetized, which when placed in the context of the adjacent stratigraphy, suggests that it was deposited during the reversed polarity event of the Gilbert epoch (between 4.79 and 5.41 Ma). The environment of deposition for this section is uncertain; however, due to the presence of thin, well-graded layers and a lack of marine fossils, it is possible that the formation was deposited in a closed lacustrine setting. Overlaying the syn-rift sediments are 200 meters of Pliocene to Pleistocene hemipelagic
marine sediment Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor. These particles either have their origins in soil and Rock (geology), rocks and have been Sediment transport, ...
with intermittent volcanic glass. This sediment layer is believed to be deposited after the end of rifting due to its subhorizontal seismic reflection profile.


Vavilov Sub-Basin

The basement rock in the Vavilov Basin consists of strongly serpentinized
peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high pr ...
with both high and low-temperature phases of deformation. The peridotite is overlain by 120 meters of tholeiitic
pillow basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron ( mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% o ...
containing carbonate-filled veins. Nannofossils and planktonic foraminifera within the carbonate veins constrain the age of emplacement between 3.1 and 3.6 Ma. Immediately above the basalt is a 100-meter-thick section of Pleistocene sedimentary cover, consisting primarily of nannofossil-rich mud with occasional reworked
volcano A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most oft ...
genic debris.


Marsili Sub-Basin

The basement rock of the Marsili Basin is vesicular basalt. Due to the abundance (10–30% of rock volume) and size (up to 3 or 4 mm) of the vesicles, it is likely that the basalt was emplaced as a flow rather than a sill. Overlaying the basement is 250 meters of calcareous mud and ooze with interbedded volcanoclastic layers. Benthic foraminifera and magnetic anomaly data from the base of this section constrain the terminus of rifting between 1.67 and 1.87 Ma. At the top of the stratigraphic section are 350 meters of volcanoclastic
turbidites A turbidite is the geologic Deposition (geology), deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing ...
.


Basin tectonics and evolution


Temporal onset of rifting

It is widely agreed that extension in the Tyrrhenian basin began in the late
Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...
, as shown by the recognition in seismic reflection profiles of pre-evaporitic (i.e. pre-Messinian) sediments in the western Tyrrhenian and by age estimates based on the overall lithospheric thickness, basement relief, and heat flow. K-Ar dating of peripheral oceanic basalts, drilled at the southeast edge of the Vavilov plain, estimates the beginning of extension to be 7.3 ± 1.3 Ma. Basalts recovered near the spreading center, in middle of the Vavilov plain, yielded ages of 3.4–3.6 Ma. This means that back-arc extension in this part of the basin occurred approximately between the late Tortonian and the middle Pliocene. However, in the Marsili plain, the oldest basaltic crust was found to be 2.1 Ma. This lower age limit, along with the presence of a saddle containing continental crust (the "Issel bridge") between the Vavilov and Marsili plains, implies that there were two distinct episodes of back-arc extension.


Mechanism of development

Between the Tortonian and middle Pliocene, W-E directed extension opened the Vavilov plain and Sardinia margin in the northwest portion of the present day basin. By the end of the Pliocene, extension rapidly turned to NW-SE and was limited to the southeastern Marsili plain. This rapid shift in the direction and spatial location of extension may be due to how the relative velocities of interacting
tectonic plates Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...
change over time. For example, if the horizontal velocity of the overriding Eurasian plate exceeds the velocity of slab rollback and trench retreat in the underthrusting African plate, then extension should not occur in the back-arc region. However, if the velocity of slab rollback and trench retreat exceeds that of the overriding plate, then back-arc extension will occur. The Pliocene-Pleistocene changes in Tyrrhenian back-arc extension may have also been influenced by the adjacent Adriatic and Sicilian forelands. These sectors were not thinned by rifting and are characterized by normal continental lithosphere. During its southeastward migration, the passively retreating oceanic slab had to adjust and deform in relation the large and buoyant continental sectors. Post-Pliocene migration was eventually driven through the narrow corridor (250 km) represented by the present Ionian Sea and thus separated the Adriatic and Sicilian sectors. Changes in lithospheric composition may have also contributed to differences in subduction geometry. For instance, during the first episode of subduction, thinned continental lithosphere underlying the Apenninic margin subducted beneath the Eurasian plate. However, in the second episode of subduction, it was instead Ionian oceanic lithosphere that was involved in subduction. A transition from continental to oceanic lithosphere subduction could explain the late onset of arc volcanism (2-1.5 Ma) as well as the lack of arc volcanism in the central Tyrrhenian basin.


Rates of extension and subsidence

The full spreading rate of the Tyrrhenian basin has been estimated to be 3–5 cm/yr based on kinematic reconstructions and magnetostratigraphy. This is a relatively slow spreading rate when compared to spreading rates in other back-arc basins like the East Scotia basin (5–7 cm/yr) and the Manus basin (13 cm/yr). The ratio between the initial crustal thickness and final crustal thickness, also known as the beta factor, is estimated to be 3.3 for the Tyrrhenian basin.


Petroleum resources

Although there are numerous petroleum plays in mainland Italy and the northern
Ionian Sea The Ionian Sea (, ; or , ; , ) is an elongated bay of the Mediterranean Sea. It is connected to the Adriatic Sea to the north, and is bounded by Southern Italy, including Basilicata, Calabria, Sicily, and the Salento peninsula to the west, ...
, the potential for
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...
accumulation in most of the Tyrrhenian basin is very poor. This is primarily due to the basin's high
geothermal gradient Geothermal gradient is the rate of change in temperature with respect to increasing depth in Earth's interior. As a general rule, the crust temperature rises with depth due to the heat flow from the much hotter mantle; away from tectonic plat ...
which pushes the oil window to very shallow depths where structural and stratigraphic traps are uncommon. There is, however, active
hydrocarbon exploration Hydrocarbon exploration (or oil and gas exploration) is the search by petroleum geologists and geophysicists for hydrocarbon deposits, particularly petroleum and natural gas, in the Earth's crust using petroleum geology. Exploration methods ...
on the south edge of the basin near the
Sicily Channel Sicily (Italian language, Italian and ), officially the Sicilian Region (), is an island in the central Mediterranean Sea, south of the Italian Peninsula in continental Europe and is one of the 20 regions of Italy, regions of Italy. With 4. ...
. Here, the small Narciso and Nilde fields produce sulphur-rich, light to medium-grade
crude oil Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring u ...
(
API gravity The American Petroleum Institute gravity, or API gravity, is a measure of how heavy or light a petroleum liquid is compared to water: if its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks ...
ranging between 21 and 39). The primary reservoirs in these fields are Miocene
karstic Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. There is some eviden ...
limestones Limestone is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Limestone forms when these ...
that are sealed by Pliocene
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
s. The source of the hydrocarbons is unknown but is inferred to be
Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...
limestone. Traps are structural in nature and are primarily thrust faults related to the Tunisian Atlas thrust belt.


References

{{coord, 39, 56, N, 12, 14, E, dim:1000000_region:IT, display=title Sedimentary basins of Europe Landforms of the Tyrrhenian Sea