![Gulf of Corinth regional map](https://upload.wikimedia.org/wikipedia/commons/3/37/Gulf_of_Corinth_regional_map.jpg)
The Gulf of Corinth basin, or Corinth rift, is an active extensional marine sedimentary basin thought to have started deforming during 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 ...
–
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...
epoch. The dimensions of the Gulf of Corinth are approximately 105 km long and 30 km wide with a basement depth of 3 km at its center. This
half-graben basin is formed by a N100°E-oriented
rift
In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics.
Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...
which separates the
Peloponnese peninsula from the continental mainland of
Greece
Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders ...
.
Currently the Corinth rift is opening at rate of 10–15 mm/yr, with respect to the
Eurasia Plate
The Eurasian Plate is a tectonic plate that includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent and ...
.
The basin is bounded by the Peloponnese highlands to the south and the westward-moving Anatolian
Fault to the north. Major and minor fault planes make up the north and south margins, and its north-south extension is due to activity along an E-W to NW-SE oriented coastal southern margin.
The basin's active and inactive faults create associated syn-rift sediment fill. These aspects provide a unique opportunity for scientists to study the tectonic and stratigraphic development of a rift, while further understanding how a basin is actually made.
It is postulated that crustal extension is related to a combination of factors: westward movement of the
North Anatolian Fault
The North Anatolian Fault (NAF) ( tr, Kuzey Anadolu Fay Hattı) is an active right-lateral strike-slip fault in northern Anatolia, and is the transform boundary between the Eurasian Plate and the Anatolian Plate. The fault extends westward fro ...
,
gravitational collapse of the thickened Hellenide orogenic crust,
subduction, and slab roll back of the
African Plate
The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plate ...
at the Hellenic trench.
As
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
subducts beneath the
Aegean Sea Plate
The Aegean Sea Plate (also called the Hellenic Plate or Aegean Plate) is a small tectonic plate located in the eastern Mediterranean Sea under southern Greece and western Turkey. Its southern edge is the Hellenic subduction zone south of Crete, ...
the slab essentially pulls the over-riding plate with it, inducing extension.
Rifting
In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics.
Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben wi ...
occurs as the plate stretches weakening the thickened crust causing its collapse upon itself, creating the basin.
Stratigraphy/sedimentation
Deposition in the Gulf of Corinth occurred in at least two phases, separated by a widespread
unconformity
An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...
. Deposition before 400 ka marks the first phase, likely open to the east, was filled with continental and shallow-water deposits with subsidence rates slightly exceeding sedimentation rates.
Average uplift rates during the late
Quaternary are estimated between 1–1.5 mm/yr on the southern margin increasing during the Holocene at 1.3–2.2 mm/yr.
The high uplift rates expose many
marine terraces and other continental to marine deposits.
Infilling of the basin began in the Pliocene, depositing continental and shallow-water lacustrine facies followed by marine sediments in the middle Pliocene.
This phase can be called proto-Gulf of Corinth as it was a different size and fill than the present day basin and had two different 20–50 km wide
depocenter
A depocenter or depocentre in geology is the part of a sedimentary basin where a particular rock unit has its maximum thickness. Depending on the controls on subsidence and the sedimentary environment the location of basin depocenters may vary wit ...
s.
These depocenters, controlled by north and south dipping faults, crop out near the south margin on the Peloponnese inland.
Subsidence is linked to the fault systems bordering the depocenters, which have quickly developed in the basins relatively short 1–2 Ma existence.
Sedimentation can be subdivided into
transgressive and regressive trends.
The lower transgressive sediments are based with alluvial
fanglomerate
Conglomerate () is a clastic rock, clastic sedimentary rock that is composed of a substantial fraction of rounded to subangular gravel-size clasts. A conglomerate typically contains a matrix (geology), matrix of finer-grained sediments, such as ...
s followed by
alluvial plain conglomerate rocks. On top of this is seasonally flooded forest deposits indicated by organic rich
mudstones
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' ...
containing leaves of ''
Acer'' cf. ''
viminalis'' and ''
Platanus
''Platanus'' is a genus consisting of a small number of tree species native to the Northern Hemisphere. They are the sole living members of the family Platanaceae.
All mature members of ''Platanus'' are tall, reaching in height. All except ...
s.'' Tabular bodied transgressive beach deposits are interbedded with fine-grained sediments and
lignite, alluding to fresh-water
lacustrine
A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...
like environment. Animal life fossilized in lacustrine
marls
Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae.
Marl makes up the lower part o ...
consist of few
Oligocene ostracods
Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typical ...
and
mollusks – indicative of fresh or shallow
brackish water
Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...
– suggesting the basin had very shallow waters even in its most open condition.
Overlying these are regressive beach type deposits, displaying large-scale
foresets A foreset bed is one of the main parts of a river delta. It is the inclined part of a delta that is found at the end of the stream channel as the delta sediment
Sediment is a naturally occurring material that is broken down by processes of wea ...
and a coarsening upward sequence. Passing from open-water the
facies change to nearshore and alluvial deposits. A 1000 m basinwide fanglomeratic unit overlies these deposits.
The second
sedimentary
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
phase is marked by a dramatic increase in subsidence, unmatched by sedimentation. This phase has a complex history and is composed of deep sea deposits and Gilbert-type deltas sitting unconformably on the fanglomeratic unit.
A fault group with a displacement of ~ 600 m created the basis for the deepwater Gilbert-type deposits. These older
Evrostini Gilbert-type delta deposits were then uplifted to 800–600 m above sea level, and the younger Ilias Gilbert-type delta formed. This fan delta is approximately 400–300 m above sea level, putting the Evrostini deposits 1200–600 m above sea level. Present day Gilbert-type deltas form on the basin margin as the result of transfer faults perpendicular to the main extension. The present Gulf of Corinth delta deposits crop out along the rim supplying
turbidite
A turbidite is the geologic 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
Turbidites wer ...
deposits which are the basins current main fill.
Active faults
Western Gulf of Corinth (Aigion to Akrata)
The north and south
Eratini faults offshore the western gulf are 15 km in length overlapping completely, uplifting a notable basement
horst. The south dipping West Channel Fault controls the western draining axial channel which widens eastward as the northern margin becomes controlled by the south dipping East Channel Fault. The East and West
Eliki
Eliki ( el, Ελίκη, before 1917: Ζευγολατιό - ''Zevgolatio''), is a village in the municipal unit of Diakopto, Achaea, Greece. It was named after the nearby ancient town Helike. Eliki is located near the river Selinountas and the ...
and Aigion faults control the coastline on the southern margin, the
Akrata fault may be part of the East Eliki fault. A group of south coast landward inactive faults (
Mamoussia – Pirgaki to
Kalavrita) are thought to have contributed to extension in an earlier phase of the rifts evolution.
Central Gulf of Corinth (Akrata to Xylokastro)
The northward dipping 30–40 km Corinth fault lies along the southern margin boundary between Akrata and
Xylokastro
Xylokastro ( el, Ξυλόκαστρο) is a seaside town or village and a former municipality in Corinthia in the Peloponnese, Greece. Since the 2011 local government reform it is part of the municipality Xylokastro-Evrostina, of which it is a un ...
. This fault, once thought to be just a single fault, is supported as being split into two segments, the western segment is the Derveni Fault and the eastern segment is the Likoporia fault. The northern margin boundary is the eastern extension of the East Channel fault and the south dipping Western Antikyra fault. In adjunct with these active faults there are a few inactive faults, such as the onshore Xylokastro presently located in the footwall of the offshore Likoporia fault.
Eastern Gulf of Corinth (Xylokastro to Perachora peninsula)
The northern basin margin is defined by minor fault segments such as the southward dipping Eastern
Antikyra
Antikyra or Anticyra ( el, Αντίκυρα) is a port on the west coast of the Gulf of Antikyra named after it. That gulf is a north-coast bay of the Gulf of Corinth. The settlement was made basically on a floor and beach fringing the northeas ...
fault. Several inactive buried faults (N. and S. Corinth) produce localized subsidence. The eastern southern margin is controlled by two 12-km-long northwestward dipping Perachora faults and the northward dipping Xylokastro fault.
Alkyonides Gulf
Significant faults are the offshore north dipping West and East Alkyonides fault and the onshore north dipping Pisia and skinos faults. Both Pisia and skinos faults mentioned are major structures controlling the topography.
The West and East Alkyonides are not connected at the surface and they seem to overlap. These faults control the uplifted Strava
graben and uplifted Alkyonides islands.
On the northern shore, south dipping faults are much less notable. In 1981 a sequence of
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...
s reactivated the Kaparelli fault which has since then had low and infrequent slip rates.
----
Earthquakes
Under the north
Peloponnese is a 5.5–10 km well defined seismogenic zone that deepens to 12 km under the northern shore of the gulf.
This is responsible for major earthquakes like the
Mw 6.2 15 June 1995 event, and a large number of small to moderate earthquakes. For instance, in the summer of 1993, 232 earthquakes were recorded
Due to such active seismicity, many earthquakes activate new fault planes.
It is hypothesized that extensional slip on E-W striking, 20°-40° north-dipping planes are caused by earthquakes beneath the northern shore. However, in the Aigion area, fault planes like the
Helike
Helike (; el, , pronounced , modern ) was an ancient Greek polis (city-state) that was submerged by a tsunami in the winter of 373 BC. It was located in the regional unit of Achaea, northern Peloponnesos, two kilometres (12 stadia) from the ...
Fault have much steeper dips of 55°-70° that can be observed.
This difference leaves the connection between outcropping faults and the seismogenic zone open for debate. Other hypotheses include: steeply dipping faults abut at a low-angle seismically active detachment,
or they undergo a progressive down-dip curvature and merge into low-angle detachments.
The seismic activity of the Corinth rift is monitored by the Corinth Rift Laboratory, an international observatory belonging the European Plate Observing System
References
External links
{{commonscat-inline, Gulf of Corinth
Geology of Greece
Basins
Cenozoic rifts and grabens
Gulf of Corinth