Porcupine Basin
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The Porcupine Seabight or Porcupine Basin is a deep-water
oceanic basin In hydrology, an oceanic basin (or ocean basin) is anywhere on Earth that is covered by seawater. Geologically, most of the ocean basins are large Structural basin, geologic basins that are below sea level. Most commonly the ocea ...
located on the
continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental marg ...
in the northeastern portion of the
Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...
. It can be found in the southwestern offshore portion of
Ireland Ireland (, ; ; Ulster Scots dialect, Ulster-Scots: ) is an island in the North Atlantic Ocean, in Northwestern Europe. Geopolitically, the island is divided between the Republic of Ireland (officially Names of the Irish state, named Irelan ...
and is part of a series of interconnected basins linked to a failed
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-graben ...
structure associated with the opening of the Northern
Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...
. The basin extends in a North-South direction and was formed during numerous
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 ...
and rifting periods between the Late
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
and Late
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
. It is bordered by the * Goban Spur to the south * Slyne Ridge to the north *
Porcupine Bank Porcupine Bank is a raised area on the Irish shelf, approximately west of Ireland. It is 200 m below sea level at its highest.Shannon, P, Haughton, P, Corcoran D, (2001) The Petroleum Exploration of Ireland's Offshore Basins, Geological Society ...
to the west *
Porcupine Abyssal Plain The Porcupine Abyssal Plain (PAP) is located in international waters, adjacent to the Irish continental margin. The PAP lies beyond the Porcupine Bank's deepest point and is southwest of it. It has a muddy seabed, with scattered abyssal hill ...
to the southwest Due to subsidence, water depths range from 3000 m in the south near its mouth to 400 m in the north. The Porcupine Basin lies on the Caledonian
metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...
basement and preserves up to 12 km of sedimentary strata from Late
Palaeozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three 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 at the start of ...
to
Quaternary 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 ...
which includes significant hydrocarbon reservoirs. Sediment was likely sourced from the uplifted Caledonian metamorphic rocks of the Porcupine Median Ridge. The basin lent its name to Operation Seabight, an Irish drug-bust of November 2008.


Geologic history

The basin was formed during numerous subsidence and rifting periods between the Late
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
and Late
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
. Repeated stages of uplift and subsidence were responsible for sediment input, the formation of accommodation space and the creation of steep basin margins: # Initial rifting occurred in the
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
, with a series of minor rifting episodes. # Main rifting developed in the Mid to Late
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 143.1 Mya. ...
, and lasted around 20 to 30 million years. # Major thermal subsidence, or uplift. # Minor rifting in the Early
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
. # Irregular subsidence in the
Tertiary Tertiary (from Latin, meaning 'third' or 'of the third degree/order..') may refer to: * Tertiary period, an obsolete geologic period spanning from 66 to 2.6 million years ago * Tertiary (chemistry), a term describing bonding patterns in organic ch ...
, from possible lithospheric stretching by rifting or mantle plume. Extreme stretching of the
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 ...
has been documented in the Porcupine Basin. This stretching is especially found in the southern part of the basin as a result of rotation of the Porcupine Ridge away from the Irish shelf. * Crustal thickness in this area was found to be 7.5 ± 2.5 km. * Lithospheric stretching of β>6. There are a number of unconformities found within the basin. Folding, uplift and related erosion during the Jurassic to Cretaceous produced the regional Base Cretaceous Unconformity in the northern section. Accommodation for the Early Cretaceous succession was not only generated by thermal
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 ...
following the Late Jurassic crustal extension, but also by compressional deformation during the latest Jurassic–earliest Cretaceous. Inverted structures found in the basin formed may be related to the initial closure of the Alpine Tethys. The latest Jurassic to Cretaceous uplift, inversion and erosion observed in many basins in Western Europe may also be associated with this event.


Ecology

A large number and variety of sea life and
cetacean Cetacea (; , ) is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively c ...
s migrate through the area, which is regarded as a prominent habitat for them. This includes many
fin whale The fin whale (''Balaenoptera physalus''), also known as the finback whale or common rorqual, is a species of baleen whale and the second-longest cetacean after the blue whale. The biggest individual reportedly measured in length, wi ...
s and
blue whale The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known ever to have existed. The blue whale's long and slender body can ...
s, the first confirmed sighting of the latter in Irish waters being made here as recently as 2008.


Carbonate mounds

The Porcupine Seabight contains some of the most well investigated deep-water carbonate mounds in the world. Carbonate mounds, which can reach heights of up to 600 m, are formed from the accumulation of
cold-water coral The habitat of deep-water corals, also known as cold-water corals, extends to deeper, darker parts of the oceans than tropical corals, ranging from near the surface to the abyss, beyond where water temperatures may be as cold as . Deep-water co ...
s that trap fine-grained sediment. These mounds can be found at depths of 500 to 1000 m over areas of a few square kilometers. Three distinct mound provinces are located in the Porcupine Seabight: # Belgica Mound Province (eastern slope) # Hovland Mound Province (central northern portion) # Magellan Mound Province (northern portion). More than a thousand mounds have been identified in the Porcupine Seabight. The mounds are most common in the northern section, near the Hovland and Magellan Provinces. These carbonate mounds are still not fully understood. Their formation and growth patterns have been hotly debated and multiple hypotheses have been proposed. One hypothesis connects their formation to the seepage of hydrocarbons, either along faults or from former gas-hydrate layers, as a response to glacial-interglacial changes in current patterns and sea levels. Another hypothesis relates their distribution to nutrient fluxes driven by specific oceanic conditions, notably the interaction of internal waves, formed at the boundary between different water masses, with the continental slope.


Hydrocarbon exploration

* 31 wells drilled in total since 1977 by **
Amoco Amoco ( ) is a brand of filling station, fuel stations operating in the United States and owned by British conglomerate BP since 1998. The Amoco Corporation was an American chemical and petroleum, oil company, founded by Standard Oil Company i ...
, BP,
Chevron Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * '' Eulithis testata'', a moth * Chevron (geology), a fold in rock la ...
,
ExxonMobil Exxon Mobil Corporation ( ) is an American multinational List of oil exploration and production companies, oil and gas corporation headquartered in Spring, Texas, a suburb of Houston. Founded as the Successors of Standard Oil, largest direct s ...
,
Marathon Oil Marathon Oil Corporation was an American company engaged in hydrocarbon exploration. In November 2024, it was acquired by ConocoPhillips and absorbed into the company. Marathon was founded in Lima, Ohio, as the Ohio Oil Company. In 1899, the ...
and
Royal Dutch Shell Shell plc is a British multinational oil and gas company, headquartered in London, England. Shell is a public limited company with a primary listing on the London Stock Exchange (LSE) and secondary listings on Euronext Amsterdam and the New ...
* Three prospective wells flowed hydrocarbons, these being ** Burren, Connemara and Spanish Point * Drilling has met with no commercial success * Just one well (Dunquin) has been drilled since 2003. Modelling of hydrocarbon generation shows that the main Jurassic source rocks in the Porcupine Basin are mature to overmature.
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 ...
generation started in Late Cretaceous times for the deepest Jurassic sequences, and is still ongoing today along the edges of the basin. The carbonate mounds found in the basin may in fact be surface expressions of an underlying active petroleum system. There are likely to be multiple potential fluid migration pathways within the basin. The presence of oil shown at different levels of the stratigraphy attests to the ability of fluids to move from deep to shallower levels in the
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 ...
and
Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...
. Major
igneous Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...
activity, of Early Cretaceous and Palaeogene times, is also likely to have produced fluid circulation patterns and some additional fluid transport channels along the flanks of volcanic centres, through associated dyke systems and compaction-associated faults above the volcanic centres. The overall
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...
of the basin, shallowing towards the margins and towards the northern section, is likely to have facilitated fluid migration in Cenozoic times towards these shallower regions. All of these point towards the movement of mantle-derived fluids within the basin, directed towards the basin margins.


See also

* List of abyssal plains and oceanic basins * List of oceanic landforms *
Solid Earth Solid earth refers to "the earth beneath our feet" or '' terra firma'', the planet's solid surface and its interior. It excludes the Earth's fluid envelopes, the atmosphere and hydrosphere (but includes the ocean basin), as well as the biosphere ...


References


External links


Global Solid Earth Topography
{{physical oceanography, expanded=other Physical oceanography Marine geology