Aquitaine Basin
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The Aquitaine Basin is the second largest
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 ...
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 ...
in
France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
after the
Paris Basin The Paris Basin () is one of the major geological regions of France. It developed since the Triassic over remnant uplands of the Variscan orogeny (Hercynian orogeny). The sedimentary basin, no longer a single drainage basin, is a large sag in ...
, occupying a large part of the country's southwestern quadrant. Its surface area covers 66,000 km2 onshore. It formed on
Variscan The Variscan orogeny, 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 ...
basement which was peneplained during the
Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...
and then started subsiding in the early
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 ...
. The basement is covered in the Parentis Basin and in the Subpyrenean Basin—both sub-basins of the main Aquitaine Basin—by 11,000 m of sediment.


Geography

The Aquitaine Basin, named after the French
region In geography, regions, otherwise referred to as areas, zones, lands or territories, are portions of the Earth's surface that are broadly divided by physical characteristics (physical geography), human impact characteristics (human geography), and ...
Aquitaine Aquitaine (, ; ; ; ; Poitevin-Saintongeais: ''Aguiéne''), archaic Guyenne or Guienne (), is a historical region of southwestern France and a former Regions of France, administrative region. Since 1 January 2016 it has been part of the administ ...
, is roughly funnel-shaped with its opening pointing towards 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 ...
. Here it meets for 330 km the straight, more or less north–south-trending Atlantic coastline but continues offshore to the
continental slope 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 margi ...
. To the south, it is delimitated for 350 km by the west-northwest–east-southeast trending
Pyrenees The Pyrenees are a mountain range straddling the border of France and Spain. They extend nearly from their union with the Cantabrian Mountains to Cap de Creus on the Mediterranean coast, reaching a maximum elevation of at the peak of Aneto. ...
. In the southeast, the basin reaches the Seuil de Naurouze (also called ''Seuil du Lauragais'') between the
Montagne Noire The Montagne Noire (; , known as the 'Black Mountain' in English) is a mountain range in central southern France. It is located at the southwestern end of the Massif Central at the juncture of the Tarn, Hérault and Aude departments. Its highe ...
on its northern side and the Mouthoumet range in the south. Just west of
Narbonne Narbonne ( , , ; ; ; Late Latin:) is a commune in Southern France in the Occitanie region. It lies from Paris in the Aude department, of which it is a sub-prefecture. It is located about from the shores of the Mediterranean Sea and was ...
, the basin is overridden by Pyrenean thrusts. The northeastern boundary of the basin is formed by the arcuate basement outcrops of the Massif Central. Via the 100 km wide Seuil du Poitou in the northeast, the basin is connected to the
Paris Basin The Paris Basin () is one of the major geological regions of France. It developed since the Triassic over remnant uplands of the Variscan orogeny (Hercynian orogeny). The sedimentary basin, no longer a single drainage basin, is a large sag in ...
. In the far north, the basin abuts the east–west-oriented Variscan basement of the
Vendée Vendée () is a department in the Pays de la Loire region in Western France, on the Atlantic coast. In 2019, it had a population of 685,442.Armorican Massif The Armorican Massif (, ) is a geologic massif that covers a large area in the northwest of France, including Brittany, the western part of Normandy and the Pays de la Loire. It is important because it is connected to Dover on the British side o ...
.


Basin structure

The Aquitaine Basin is a very asymmetric
foreland basin A foreland basin is a structural basin that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithospher ...
. It reaches its deepest part of 11 km just in front of the North Pyrenean Thrust. The 2,000 m
isobath A bathymetric chart is a type of isarithmic map that depicts the submerged bathymetry and physiographic features of ocean and sea bottoms. Their primary purpose is to provide detailed depth contours of ocean topography as well as provide the si ...
follows more or less the course of the
Garonne The Garonne ( , ; Catalan language, Catalan, Basque language, Basque and , ; or ) is a river that flows in southwest France and northern Spain. It flows from the central Spanish Pyrenees to the Gironde estuary at the French port of Bordeaux †...
River and divides the basin into a relatively shallow northern platform, the so-called ''Aquitaine Plateau'', and into a much deeper, tightly folded, southern region. The tabular platform in the north contains only a much reduced sedimentary succession that is gently undulating and occasionally faulted. The folding intensity in the southern region increases steadily towards the south, the structures being further complicated by superimposed salt
diapirism A diapir (; , ) is a type of intrusion in which a more mobile and ductilely deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–Taylor ...
. This somewhat simplified structural subdivision gets complicated by the Parentis Basin which extends out into the Atlantic. The Parentis Basin is situated in the Golfe de Gascogne and also reaches 11 km depth; it is a symmetrical basin oriented east–west and comes ashore near
Arcachon Arcachon (; ) is a commune in the southwestern French department of Gironde. It is a popular seaside resort on the Atlantic coast southwest of Bordeaux, in the Landes forest. It has a sandy beach and a mild climate said to be favourable for p ...
. This sub-basin is underlain on its far western side by
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 ...
dated at 100–95 million years BP (
Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...
). It is bounded by dextral wrench faults (possible
transform fault A transform fault or transform boundary, is a fault (geology), fault along a plate boundary where the motion (physics), motion is predominantly Horizontal plane, horizontal. It ends abruptly where it connects to another plate boundary, either an ...
s) and probably represents a
pull-apart basin In geology, a basin is a region where subsidence generates accommodation space for the deposition of sediments. A pull-apart basin is a structural basin where two overlapping (en echelon) strike-slip faults or a fault bend create an area of crust ...
.


Stratigraphy

(Note: Permo-Triassic basins like the Brive Basin and the GrĂ©signe Basin are considered to belong to the basement of the Massif Central.) Structural and sedimentological investigations of the basin have been carried out in over 70 drilled wells that encountered the Variscan basement sometimes below 6,000 m of sedimentary cover. The sedimentary evolution in the Aquitaine Basin begins in the
Lower Triassic The Early Triassic is the first of three epoch (geology), epochs of the Triassic Period (geology), Period of the geologic timescale. It spans the time between 251.9 annum, Ma and Ma (million years ago). Rocks from this epoch are collectively kno ...
close to the North Pyrenean Thrust. From here, it slowly started spreading farther north.


Triassic

Sedimentation started in the very south of the Aquitaine Basin during the Lower Triassic with coloured
sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
s and
mudstone 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.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...
s, followed during the Middle Triassic by dolomitic
limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
s,
evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...
strata In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...
and coloured mudstones. During the Upper Triassic evaporites continued being precipitated, crowned by ophitic
lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...
flows (
dolerite 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-grain ...
s and
tholeiite The tholeiitic magma series () is one of two main magma series in subalkaline igneous rocks, the other being the Calc-alkaline magma series, calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes ...
s). The evaporites were later activated as
diapir A diapir (; , ) is a type of intrusion in which a more mobile and ductilely deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–Taylor ...
s during the Pyrenean orogeny and the mudstones served as decollement horizons along which Triassic sediments were squeezed northwards to the line Arcachon–
Toulouse Toulouse (, ; ; ) is a city in southern France, the Prefectures in France, prefecture of the Haute-Garonne department and of the Occitania (administrative region), Occitania region. The city is on the banks of the Garonne, River Garonne, from ...
. The sediments are typically ''germanotype'' in character, i.e. very similar to the Triassic succession in
Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
. In the north of the Aquitanian plateau, only a continental Upper Triassic is preserved. In the south, the sediments are marine and show their full development. The Triassic marine transgression probably invaded the southern Aquitaine Basin from the southeast or from the south (from the Tethys) via the then still immersed Pyrenean region. The sediments indicate a restricted shallow marine environment with drying-up periods that created evaporites. The Triassic sediments can attain a maximum thickness of 1,000 m and reach as far north as the line Garonne estuary – Brive.


Jurassic

The entirely marine Jurassic cycle can be subdivided into seven second-order sequences bounded by
unconformities An unconformity is a buried erosion surface, erosional or non-depositional surface separating two Rock (geology), rock masses or Stratum, strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer ...
, three in the Lias, two in the Dogger and two in the Malm: * Hettangian-Sinemurian sequence. * Lotharingian-Carixian-Domerian sequence (Upper Sinemurian–Pliensbachian). * Toarcian-Aalenian sequence. * Bajocian–Lower Bathonian sequence. * Middle Bathonian–Callovian sequence. * Oxfordian–Sequanian sequence (Oxfordian–Lower Kimmeridgian). * Kimmeridgian–Portlandian sequence (Kimmeridgian-Tithonian). The complete Jurassic cycle is only preserved in the
Quercy Quercy (; , locally ) is a former province of France located in the country's southwest, bounded on the north by Limousin, on the west by Périgord and Agenais, on the south by Gascony and Languedoc, and on the east by Rouergue and Auverg ...
; farther south, e.g. in the Subpyrenean Basin, the cycle has many gaps.


Lias

The basal
Hettangian The Hettangian is the earliest age and lowest stage of the Jurassic Period of the geologic timescale. It spans the time between 201.3 ± 0.2 Ma and 199.3 ± 0.3 Ma (million years ago). The Hettangian follows the Rhaetian (part of the Triass ...
-Sinemurian sequence is fully transgressive over basement rocks or Permo-Triassic sediments. At that time, the first open-marine sediments (yet rather poor in fossils) were being deposited in the Aquitaine Basin. The ''Lias Transgression'', as it is also called, started to encroach on the entire Aquitaine during the
Sinemurian In the geologic timescale, the Sinemurian is an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series. It spans the time between 199.5 ±0.3 annu ...
, characterised by calcareous-dolomitic, partially oolitic sediments. Despite smaller regressions during the
Pliensbachian The Pliensbachian is an age of the geologic timescale and stage in the stratigraphic column. It is part of the Early or Lower Jurassic Epoch or Series and spans the time between 192.9 ±0.3 Ma and 184.2 ±0.3 Ma (million years ago). The Plie ...
towards the end of the Lias and at the beginning of the Dogger the sea had onlapped the basement rocks of the Massif Central and the western VendĂ©e (reaching today's limits) by 30 km. On the Aquitaine Plateau in the north, an interior shelf was constructed as far south as the line
La Rochelle La Rochelle (, , ; Poitevin-Saintongeais: ''La Rochéle'') is a city on the west coast of France and a seaport on the Bay of Biscay, a part of the Atlantic Ocean. It is the capital of the Charente-Maritime Departments of France, department. Wi ...
-
AngoulĂȘme AngoulĂȘme (; Poitevin-Saintongeais: ''Engoulaeme''; ) is a small city in the southwestern French Departments of France, department of Charente, of which it is the Prefectures of France, prefecture. Located on a plateau overlooking a meander of ...
-
Périgueux Périgueux (, ; or ) is a commune in the Dordogne department, in the administrative region of Nouvelle-Aquitaine, southwestern France. Périgueux is the prefecture of Dordogne, and the capital city of Périgord. It is also the seat of ...
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Figeac Figeac (; ) is a Communes of France, commune in the southwestern French Departments of France, department of Lot (department), Lot. Figeac is a Subprefectures in France, sub-prefecture of the department. Geography Figeac is on the via Podiensis ...
. On this shelf the generally detritic transgression sediments of the Hettangian normally comprise a base conglomerate,
arkose Arkose () or arkosic sandstone is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose. Components ...
s, and fairly thick layers of sand- and mud-stones rich in plant material. The rest of the Hettangian is made up of marine sediments deposited in a restricted environment (
lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...
al) evolving towards a lacustrine facies (green shales, coloured marls, dolomitic limestones and platy limestones rich in dwarf fossils, and evaporitic interlayers). The sediments of the Sinemurian are again fully marine and carry a pelagic fauna (soft banded limestones and hard lithographic limestones). At the end of the Sinemurian, a sudden regression occurred, forming
hardgrounds Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor (Wilson and Palmer, 1992). A hardground is essentially, then, a lithified seafloor. Ancient hardgrounds are found in limestone ...
. The second sequence of the Lias again is marine-transgressive and commences during the ''Lotharingian''/Lower ''Carixian''. The sediments can be well dated by
ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...
s—( Arietites, Oxynoticeras, Deroceras, and '' Uptonia jamesoni''). They are mainly calcareous and rich in quartz grains and pebbles of reworked Sinemurian. The Upper Carixian consists of very fossiliferous ('' Aegoceras capricornu'') marly limestone layers interlayered with grey marls. These are followed by ammonite-bearing ('' Amaltheus margaritatus'') and
oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but no ...
-bearing ('' Gryphaea cymbium'') marls indicating a shelf environment open to the spreading Atlantic Ocean. During the Lower Domerian, a connection to the Paris Basin is breached for the first time via the Seuil du Poitou and also to the Jurassic sea of southeastern France via the Détroit de Rodez and the Détroit de Carcassonne. During the Upper Domerian, another regression sets in leaving sandy limestones very rich in fossils ('' Pleuroceras spinatum'', '' Pecten aequivalvis''). These
littoral The littoral zone, also called litoral or nearshore, is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely i ...
facies rocks can change into iron-rich oolites along their margins. The sequence finishes again with hardgrounds. The third and last sequence of the Lias sets in during the Lower Toarcian without any detrital deposits at its base, the sediments being black ammonite-bearing marls (with '' Harpoceras falciferum'' and '' Hildoceras bifrons''). Towards the end of the Toarcian and the beginning of the Aalenian, the sediments turn into sandy limestones indicating another regression. Interlayered with these sandy limestones are oyster beds, iron oolite and
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 ...
layers; they contain ammonites like '' Pleydellia aalensis'' and '' Leioceras opalinum''. The sequence ends with an erosional unconformity. In the southern part of the Aquitanian basin, the evaporite deposition (including layers of
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 ...
) begun in the Triassic carries on right through the Lias; it reaches a thickness of up to 500 m.


Dogger

The Dogger attains a maximum thickness of about 300 m along a north–south-trending zone running from AngoulĂȘme to
Tarbes Tarbes (; Gascon language, Gascon: ''Tarba'') is a Communes of France, commune in the Hautes-Pyrénées Departments of France, department in the Occitania (administrative region), Occitanie Regions of France, region of southwestern France. It is ...
. Along this zone
reef A reef is a ridge or shoal of rock, coral, or similar relatively stable material lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic (non-living) processes such as deposition (geol ...
s began to grow, splitting the Aquitaine Basin into two major facies domains. Prominent reef complexes are situated east of AngoulĂȘme, northwest of PĂ©rigueux and east of Pau. The reefs are associated with calcareous oolites and mark a high-energy zone. On the shallow shelf-domain east of the reefs, neritic limestones were deposited in the north and dolomites in the south; in the Quercy, even supratidal
lignite Lignite (derived from Latin ''lignum'' meaning 'wood'), often referred to as brown coal, is a soft, brown, combustible sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35% and is considered the lowest ...
-bearing limestones were formed. In the western domain open towards the Atlantic, the pelagic sediments comprise ammonite-bearing limy marls very rich in filamentous microfossils ( bryozoans). The first sequence in the Dogger (note: sequences are only distinguished in the eastern shelf-domain) starts transgressing in a restricted environment during the
Bajocian In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.9 ±0.8 Ma to around 168.2 ±1.2 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonia ...
with dolomite. In places, Aalenian is reworked. The
Bathonian In the geologic timescale the Bathonian is an age (geology), age and stage (stratigraphy), stage of the Middle Jurassic. It lasted from approximately 168.2 ±1.2 annum, Ma to around 165.3 ±1.1 Ma (million years ago). The Bathonian Age succeeds ...
is calcareous in the northeast, whereas in the southeast it keeps its dolomitic character. The end of the sequence in the Lower Bathonian shows regressive tendencies with lignites,
breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...
s, and lacustrine fossils in the Quercy. No ammonites are found in the eastern domain right up to the Kimmeridgian—a great handicap for correct dating purposes. The Pyrenean realm meanwhile is characterised by a long hiatus. The second sequence in the Dogger begins in the Middle Bathonian with lacustrine limestones and in places with breccia-bearing detritus. This is followed by neritic limestones precipitated in calm conditions. Yet in the south, dolomites continue to be deposited. The sequence finishes in the
Callovian In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 165.3 ± 1.1 Ma (million years ago) and 161.5 ± 1.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the ...
with littoral border-facies deposits.


Malm

The facies dividing reef-zone persists into the Malm. In the western domain, initially ammonite-bearing
marl Marl is an earthy material rich in carbonate minerals, Clay minerals, clays, and silt. When Lithification, hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. M ...
s and limestones were deposited, whereas in the eastern domain the sediments are calcareous dolomites. The retreat of the Jurassic sea became noticeable during the late
Tithonian In the geological timescale, the Tithonian is the latest age (geology), age of the Late Jurassic Epoch and the uppermost stage (stratigraphy), stage of the Upper Jurassic Series. It spans the time between 149.2 ±0.7 annum, Ma and 143.1 ±0.6 (mi ...
with dolomites and breccias in the Adour Basin, evaporites in the
Charente Charente (; Saintongese: ''Chérente''; ) is a department in the administrative region of Nouvelle-Aquitaine, southwestern France. It is named after the river Charente, the most important and longest river in the department, and also the r ...
, extremely littoral sediments in the Quercy, lacustrine limestones in the Parentis Basin, and anhydrites in the
Gers Gers (; or , ) is a departments of France, department in the regions of France, region of Occitania (administrative region), Occitania, Southwestern France. Gers is bordered by the departments of Hautes-Pyrénées and Pyrénées-Atlantiques to ...
. The seaways that had opened in the Lias closed again and a single reef persisted in the
Périgord Périgord ( , ; ; or ) is a natural region and former province of France, which corresponds roughly to the current Dordogne department, now forming the northern part of the administrative region of Nouvelle-Aquitaine. It is divided into f ...
at La Tour-Blanche. In the end, the sea withdrew south of the Garonne River. In the Lower Oxfordian, the first sequence of the Malm seems to follow the Callovian without a distinctive break. Yet cellular limestones and breccias indicate sediment reworking (this was certainly the case in the
Grands Causses The Causses () are a group of limestone plateaux (700–1,200 m) in the Massif Central. They are bordered to the north-west by the Limousin and the PĂ©rigord uplands, and to the east by the Aubrac and the CĂ©vennes. Large river gorges cut throug ...
farther east). During the Middle and the Upper Oxfordian, marine limestones are laid down which incorporate occasional reefs. The Lower Kimmeridgian sediments are sedimented close to the shore, they bear oysters, urchins, and
ripple marks In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water ( current or waves) or directly by wind. Defining ripple cross-laminae and asymmetric ripples * ''Current ripple ...
. The second sequence of the Malm starts in the Upper Kimmeridgian, only in places does it show regressive traits, nevertheless the sedimentary character changes. Laid down are breccias and the sediments also show synsedimentary reworkings; periodically interbedded limestones and marls carrying lignite horizons begin to form. The sediments can be dated by the ammonites Aulacostephanus and '' Aspidoceras orthocera''. This strongly disturbed depositional environment with a coexistence of open marine facies and muds deposited under reducing conditions in a restrictive setting seems to coincide with a first sedimentary individualisation of the Pyrenean realm. The event has received its name ''Virgulian'' from the oyster '' Exogyra virgula''. During the Tithonian, the shrinkage of the basin became even more evident, only to end in a nearly complete withdrawal of the sea from the Aquitaine Plateau before the close of the Tithonian (the south is not affected by this). During the Tithonian, iron-bearing calcareous oolites interbedded with marls, as well as dolomite and border facies deposits develop—dated by '' Gravesia portlandicum''.


Lower Cretaceous

In comparison with the Jurassic, the
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 ...
has less pronounced sequences. The Lower Cretaceous sediments are restricted to close to the Pyrenees. Most likely the exchange of ocean water masses was better towards the Tethyan realm than towards the Atlantic. Sedimentation increased again after a longer hiatus in the Lower Cretaceous, but only in two locales—the Parentis Basin and the Adour Basin. Both sub-basins manifest a huge
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 ...
. During the Lower Cretaceous the Parentis Basin received 2,000 m of sediment and the Adour Basin 4,000 m. The remainder of the Aquitaine Basin is meanwhile subjected to strong erosion. The
Angeac-Charente bonebed The Angeac-Charente bonebed is a fossil deposit located near Angeac-Charente in western France. It dates to the Berriasian stage of the Early Cretaceous, and is coeval with the Purbeck Group of Southern England. It has amongst the most diverse asse ...
is a major fossil deposit in the Aquitane Basin, dating to the
Berriasian In the geological timescale, the Berriasian is an age/ stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 143.1 ±0.6 Ma and 137.05 ± 0.2 (million years ago) ...
.Ronan Allain, Romain Vullo, Lee Rozada, Jérémy Anquetin, Renaud Bourgeais, et al.
Vertebrate paleobiodiversity of the Early Cretaceous (Berriasian) Angeac-Charente LagerstÀtte (southwestern France): implications for continental faunal turnover at the J/K boundary
Geodiversitas, Museum National d’Histoire Naturelle Paris, In press. ffhal-03264773f
The first deposits in the two sub-basins were littoral sediments in Wealden facies, mainly sandstones and shales. During the
Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 125.77 Ma (million years ago) and 121.4 ± 1.0 Ma (Historically, this stage was placed at 129.4 million to approximately 125 million years ago) It is a ...
, marine shallow-water carbonates were precipitated, changing to detritic sediments in the northern Parentis Basin. Near
Lacq Lacq (; ) is a commune in the Pyrénées-Atlantiques department in southwestern France. On 1 January 2024, the former commune of UrdÚs was merged into Lacq. It lies just northwest of the prefecture (department capital) Pau. Economy In mo ...
, they change to lagoonal anhydrites. In the Upper Aptian, the reef-forming Urgonian facies became established in both sub-basins—fossiliferous limestones composed of
algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...
, coralline polyps, and
rudist Rudists are a group of extinct box-, tube- or ring-shaped marine heterodont bivalves belonging to the order Hippuritida that arose during the Late Jurassic and became so diverse during the Cretaceous that they were major reef-building organis ...
s. The Urgonian facies completely surrounds the Parentis Basin and persists into the Albian. Since the onset of the
Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...
, strong halokinetic movements affect the southern Aquitaine Basin and in turn profoundly influence sedimentation patterns. As a result, breccias, thick conglomerates, and
turbidite 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 ...
s are shed. In the Parentis Basin, a distinct
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 ...
develops. At the same time, the sediments on the Aquitaine Plateau farther north are folded into gentle wavetrains following the Hercynian strike (northwest-southeast). All these movements are correlated with the first tectonic stirrings in the Western Pyrenees. Towards the end of the Albian, the sea level is rising and the Urgonian calcareous reefs are consequently draped by muds.


Upper Cretaceous

The transgression that began in the late Albian spread rapidly northward during the
Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...
. In the northern part of the Aquitanian Basin, the Cenomanian sea reclaimed nearly the same areas that had been occupied by the Jurassic sea; in the east, however, it only reached the line Brive-
Cahors Cahors (; ) is a Communes of France, commune in the western part of Southern France. It is the smallest prefecture among the 13 departments that constitute the Occitania (administrative region), Occitanie Region. The capital and main city of t ...
-Agen- Muret-Carcassonne. The region of the later formed North Pyrenean Thrust is a decisive facies boundary at this time: to the north, shelf sedimentation continued but to the south rapidly subsiding basins developed into which
flysch Flysch () is a sequence of sedimentary rock layers that progress from deep-water and turbidity flow deposits to shallow-water shales and sandstones. It is deposited when a deep basin forms rapidly on the continental side of a mountain building ep ...
sediments (and partially also ''wildflysch breccias'') from the Pyrenean realm were shed. Near Saint-Gaudens, the flysch sediments are even accompanied by volcanic rocks—
trachyte Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanite, aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava (or shallow intrus ...
s, and ultrabasic lavas. The sedimentation in the flysch basins during the
Turonian The Turonian is, in the International Commission on Stratigraphy, ICS' geologic timescale, the second age (geology), age in the Late Cretaceous epoch (geology), Epoch, or a stage (stratigraphy), stage in the Upper Cretaceous series (stratigraphy), ...
and during the
Coniacian The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by ...
is very unsettled. The flysch sedimentation then continues right through the Upper Cretaceous, mainly interbedded sandstones and shales with some carbonaceous layers were laid down. Towards the end of the Upper Cretaceous, there are signs of the start of a regression and the sea then actually retreats before the K/T boundary. In the Subpyrenean Basin near the Petits Pyrénées, the sea lingers on till the lowermost
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), ...
(
Danian The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Cretac ...
). In the remainder of the Aquitaine Basin, mainly pelagic limestones (
chalk Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Ch ...
facies) are sedimented during the Upper Cretaceous, including the type localities for the
Coniacian The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by ...
,
Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya ( million years ago) and 83.6 ± 0.7 m ...
, and
Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...
in the Charente. At the northern edge of the basin, more differentiated coastal facies develop. In the north, the Cenomanian is made up of three sedimentary cycles (from young to old): * An upper cycle with regressive tendencies. In the northwest, sandy rudist-bearing limestones and oyster-bearing marly shales were deposited; in the northeast, very shallow marine gypsum-bearing shales and sands. * A generally deeper marine middle-cycle with marls. These sediments spread into the Quercy. In the PĂ©rigord, littoral facies and lignites accumulated near paleohighs. * A shallow marine lower-cycle with rudist reefs in the northwest and continent-derived lignites in the northeast. The Turonian reflects a transgressive period with the sea spreading into the Lot. At this point, the Upper Cretaceous sea had reached its highstand. This also coincides with a climatic optimum with global average sea-water temperatures around 24 Â°C compared to today's 13 Â°C. The Turonian can be subdivided into two parts: * The so-called ''Angoumian'' (named after
AngoulĂȘme AngoulĂȘme (; Poitevin-Saintongeais: ''Engoulaeme''; ) is a small city in the southwestern French Departments of France, department of Charente, of which it is the Prefectures of France, prefecture. Located on a plateau overlooking a meander of ...
) on the top. It consists of massive, partially brecciated rudist limestones at its base followed by ocre calcareous sands. The resistant Angoumian formed extensive cliffs. * The so-called ''Ligerian'' (Latin name for the Massif Central) at the base—wavy chalky marls. Towards the end of the Turonian, the Massif Central experienced uplift which is reflected in the sediments of the northeastern Aquitaine Basin as a strong input of detritus, mainly sands in the upper part of the Angoumian. The Coniacian and the Santonian are expressed as typical chalky limestones in the north, but both stages take on a more sandy character east of PĂ©rigueux. The
Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...
follows after a pronounced unconformity. The southern flysch basins began to expand northward. Near Pau before the onset of the flysch sedimentation, a very strong erosion removed the entire Lower Cretaceous, the entire Jurassic and sometimes even cut right down to the basement. North of Pau, the Campanian is a marly facies called ''Aturian''. In the northern Aquitaine Basin, the sediments become more homogenised and settle out as fully marine
flint Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Historically, flint was widely used to make stone tools and start ...
-bearing calcareous
micrite Micrite is a limestone constituent formed of calcareous particles ranging in diameter up to four ÎŒm formed by the recrystallization of lime mud. FlĂŒgel, Erik, ''Microfacies of Carbonate Rocks: Analysis, Interpretation and Application,'' Springe ...
s. During the
Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...
, a regression commences. After the initial deposition of bioclastic rudist-bearing limestones and the formation of some reef complexes composed of rudists and single corals, the sea level started dropping. Northern Aquitaine became emersed and the sea withdrew in stages southward to the line Arcachon-Toulouse. At the same time, the northern edge of the basin experienced another folding episode with low-amplitude folds striking northwest–southeast.


Cenozoic


Paleogene

During 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), ...
, the coastline roughly followed the line Arcachon-Toulouse. In the ''North Aquitaine Zone'' north of this line, the sediments possess continental character – red mudstones, sands, and lacustrine limestones. The sea made a short-lived advance into this domain and left echinid-bearing limestones behind. In the ''Central Aquitaine Zone'' (northern half of the southern basin), a shelf built out to the line
Audignon Audignon (; ) is a commune of the Landes department in Nouvelle-Aquitaine in southwestern France. Population See also *Communes of the Landes department The following is a list of the 327 communes of the Landes department of France ...
-Carcassonne. Farther south in the ''South Aquitaine Zone'', deep water conditions prevailed in the west, shallowing out towards the east. The sediments in the ''Aturian Gulf'' (Golfe Aturién) in the west are pelagic limestones containing globigerinids, operculinids, and alveolinids. Near the Petits Pyrénées, the sediments change into shallow-water facies rich in madreporians, echinids, and operculinids. Farther east in the AriÚge and in the
CorbiĂšres Massif The CorbiĂšres Massif ( ; ; ) is a mountain range in the Pre-Pyrenees. It is the only true foothill of the Pyrenees on their northern side. Geography The CorbiĂšres are a mountain region in the Languedoc-Roussillon in southeastern France, loc ...
, the sediments become totally continental and lacustrine. In the Lower Eocene (
Ypresian In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...
), another transgressive period saw the sea advance north into the Médoc and south of
Oléron The Isle of Oléron or Oléron Island (, ; Saintongese dialect, Saintongese: ''ilùte d'Olerun''; , ) is an island off the Atlantic coast of France (due west of Rochefort, Charente-Maritime, Rochefort), on the southern side of the Pertuis d'Antio ...
; in the southeast it even reached the Montagne Noire. In the Aturian Gulf, Globorotalia-bearing marls were deposited, while farther east
turritella ''Turritella'' is a genus of medium-sized sea snails with an operculum, marine gastropod mollusks in the family Turritellidae.Vos, C.; Gofas, S. (2013). Turritella Lamarck, 1799. Accessed through: World Register of Marine Species at http://www. ...
-rich marls and limestones were formed. The newly inundated areas receive sands and limestones rich in alveolinids and nummulites. Meanwhile, iron-rich sands (in the Charente) and
molasse __NOTOC__ In geology, "molasse" () are 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 ...
s (in the Libournais and in the
Agenais Agenais (), or Agenois (), was an ancient region that became a county (Old French: ''conté'' or ''cunté'') of France, south of Périgord.Mish, Frederick C., Editor in Chief. "Agenais". ''Webster's Dictionary#The Collegiate Dictionary, Webster's N ...
) were sedimented in the continental north and northeast. The provenance area of these continental deposits up to Middle Ypresian times was mainly the Massif Central. The sea-level kept rising during the Middle Eocene (
Lutetian The Lutetian is, in the geologic timescale, a stage (stratigraphy), stage or age (geology), age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it ...
and
Bartonian The Bartonian is, in the International Commission on Stratigraphy's (ICS) geologic time scale, a stage or age in the middle of the Eocene Epoch or Series. The Bartonian Age spans the time between . It is preceded by the Lutetian and is follow ...
). The area covered by alveolinid- and nummulite-bearing limestones increased, northward to
Blaye Blaye (; ) is a commune and subprefecture in the Gironde department in Nouvelle-Aquitaine in southwestern France. For centuries, Blaye was a particularly convenient crossing point for those who came from the north and went to Bordeaux or fur ...
and Saint-Palais and eastward into the Agenais. The Subpyrenean Basin deepened and was simultaneously being filled by conglomerates brought in from the east, the so-called Poudingues de Palassou. This marked the ''beginning of uplift in the Pyrenean orogen'' and a switch-over in detritus provenance from the Massif Central in the north to the Pyrenees in the south. Coalescing
alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to Semi-arid climate, semiar ...
s built out north into the Castrais. On the northern flank of the fans, lakes formed, precipitating lacustrine limestones. The detrital sediments with provenance from the meanwhile strongly eroded Massif Central (muds, sands, gravels) then affected only a small fringe zone in the northeast. In the PĂ©rigord and in the Quercy, the SidĂ©rolithique accumulated—iron-rich sediments that resemble
laterite Laterite is a soil type rich in iron and aluminium and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by intensive and prolo ...
s indicating a subtropical climate. During the Upper Eocene (
Priabonian The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene Epoch or Series. It spans the time between . The Priabonian is preceded by the Bartonian and is followed by the Rupelian, the lowest stage ...
), a regression set in. The Subpyrenean Basin became completely filled with the erosional debris of the rising Pyrenees. In the Médoc, nummulite-bearing marls and limestones were still being laid down, but east of Bordeaux already continental molasses appeared that change farther south into gypsum-bearing formations. During the
Lower Oligocene The Rupelian is, in the geologic timescale, the older of two ages or the lower of two stages of the Oligocene Epoch/Series. It spans the time between . It is preceded by the Priabonian Stage (part of the Eocene) and is followed by the Chattia ...
(
Rupelian The Rupelian is, in the geologic timescale, the older of two age (geology), ages or the lower of two stage (stratigraphy), stages of the Oligocene epoch (geology), Epoch/series (stratigraphy), Series. It spans the time between . It is preceded b ...
), a permanently marine environment persists in the south with marls and sands rich in nummulites,
lamellibranch Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...
s, and echinids. The anomiid-bearing limestones of the southern Médoc are lagoonal deposits. After a short-lived advance at the beginning of the
Chattian The Chattian is, in the geologic timescale, the younger of two ages or upper of two stages of the Oligocene Epoch/Series. It spans the time between . The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage ...
with seastar-bearing limestones in the northern Médoc and in the Libournais and with mammal-bearing molasses in the Agenais, the sea made a big retreat at the end of the Oligocene. This retreat was accompanied by tectonic movements creating trains of deeper-seated anticlines in the central and northern Aquitaine Basin. The debris-carrying alluvial fans issuing from the rising Pyrenees reached into the
Agenais Agenais (), or Agenois (), was an ancient region that became a county (Old French: ''conté'' or ''cunté'') of France, south of Périgord.Mish, Frederick C., Editor in Chief. "Agenais". ''Webster's Dictionary#The Collegiate Dictionary, Webster's N ...
and attained their largest extent. They pushed the surrounding belt of lakes ahead of them (in northerly directions) thereby spreading lacustrine limestones well into the Quercy, onto the
Causses The Causses () are a group of limestone plateaux (700–1,200 m) in the Massif Central. They are bordered to the north-west by the Limousin (rĂ©gion), Limousin and the PĂ©rigord uplands, and to the east by the Aubrac and the CĂ©vennes. Large river ...
, and even onto the Massif Central.


Neogene

Following its retreat in the southwestern Landes, the sea began transgressing towards the north and the east during the
Lower Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages: the Aquitanian age, Aquitanian and Burdigalian stages. The sub-epoch lasted from 23.03 ± 0.05 annum, Ma to ...
( Aquitanian). Marine, littoral, and lacustrine facies interchange. During a minor regression, a huge lake formed near
Condom A condom is a sheath-shaped Barrier contraception, barrier device used during sexual intercourse to reduce the probability of pregnancy or a Sexually transmitted disease, sexually transmitted infection (STI). There are both external condo ...
, the ''Lac de Saucats'', in which grey lacustrine-limestones precipitated, the so-called Calcaire gris de l'Agenais. Shortly thereafter the sea attained its highstand. It was rimmed completely by continental deposits whose thickness increased towards the southeast. For the first time, the alluvial fans along the Pyrenean front receded, the reason being increased subsidence in front of the orogen; yet they still stretched as far north as the Agenais. The retreat of the alluvial fans also continued during the Middle Miocene (
Langhian The Langhian is, in the ICS geologic timescale, an age or stage in the middle Miocene Epoch/Series. It spans the time between 15.97 ± 0.05 Ma and 13.65 ± 0.05 Ma (million years ago) during the Middle Miocene.GeoWhen (2007) The Langhian was ...
and
Serravallian The Serravallian is, in the geologic timescale, an List of time periods, age or a stage (stratigraphy), stage in the middle Miocene epoch (geology), Epoch/series (stratigraphy), Series, which spans the time between 13.82 annum, Ma and 11.63 Ma (m ...
). Consequently, the lacustrine band reached as far south as the
Armagnac Armagnac (, ) is a distinctive kind of brandy produced in the Armagnac (region), Armagnac region in Gascony, southwest France. It is distilled from wine usually made from a blend of grapes including Baco 22A, Colombard, Folle blanche and Ugni ...
. The Upper Miocene (
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 ...
and
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 ...
) witnessed a drastic withdrawal of the sea to the west. This process started first in the Bordelais and in the Bazadais, ending with a nearly complete withdrawal from the basin. In areas left behind by the sea in the Armagnac, unfossiliferous sands and muds were deposited. At the same time in the north and in the east, today's river network draining the Massif Central was already being beginning to form. During the
Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Zanclean The Zanclean is the lowest stage or earliest age on the geologic time scale of the Pliocene. It spans the time between 5.332 ± 0.005 Ma (million years ago) and 3.6 ± 0.005 Ma. It is preceded by the Messinian Age of the Miocene Epoch, and f ...
), the sea occupied merely a small strip near the Arcachon Basin south of Soustons. Sandy shales very rich in a
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". ...
microfauna were deposited. In the rest of the Aquitaine Basin, continental sands were laid down, the so-called Sables fauves. The alluvial fans restricted their activity to the immediate vicinity of the Pyrenean mountain front and created the alluvial fans of Ger, Orignac- Cieutat, and
Lannemezan Lannemezan (; Gascon Occitan ''Lanamesa'', "heath of the middle") is a commune in the Hautes-Pyrénées department and the Occitanie region in south-western France. The inhabitants are called Lannemezanais. Lannemezan is the largest city i ...
. The drainage system of the Garonne already resembled more or less today's pattern, the river avoiding the Miocene gravel accumulations as much as possible and then following between Toulouse, Agen and Bordeaux a weekly subsiding graben. The progressive landfall of the Aquitaine Basin proceeded from the northeast and was coupled with an important subaerial erosion. As a consequence several peneplanations were carved out from the detrital alluvial plains: * an eocene peneplain. * an aquitanian, strongly silicified peneplain. This is very well developed in the Périgord, in the Agenais, and in the Quercy. * a pliocene (zanclean) peneplain, characterised by gravel-bearing clays in the Bordelais and in the Landes. On the pliocene peneplain, today's drainage system was firmly established.


Quaternary

The three last
Pleistocene 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 ...
ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...
s— Mindel, Riss, and
WĂŒrm Wurm or WĂŒrm may refer to: Places * Wurm (Rur), a river in North Rhine-Westphalia in western Germany * WĂŒrm (Amper), a river in Bavaria, southeastern Germany ** WĂŒrm glaciation, an Alpine ice age, named after the Bavarian river * WĂŒrm (Nagold ...
—are also documented in the Aquitaine Basin, mainly by different levels of river terraces. Additionally amongst glacial phenomena the following can be cited: * cave infills. These are very important for dating
archeological Archaeology or archeology is the study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscapes. Archaeology ...
finds. * aeolian deposits. They cover more than a third of the Aquitaine region and can be found mainly in the MĂ©doc and in the Landes. They were deposited during the last two cold stages of the WĂŒrm glaciation. The dune belt parallel to the Atlantic shoreline formed during the
Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
. It contains
Europe's Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
largest dune, The Great Dune of Pyla. * colluvium masking hillsides and hilltops. * creeping cryoclastic debris. The development of the
Gironde Gironde ( , US usually , ; , ) is the largest department in the southwestern French region of Nouvelle-Aquitaine. Named after the Gironde estuary, a major waterway, its prefecture is Bordeaux. In 2019, it had a population of 1,623,749.
estuary goes back about 20,000 years into the late WĂŒrm. Finally, the rich
prehistoric Prehistory, also called pre-literary history, is the period of human history between the first known use of stone tools by hominins  million years ago and the beginning of recorded history with the invention of writing systems. The use o ...
finds and their sites in the Aquitaine Basin merit mentioning, especially in the Département
Dordogne Dordogne ( , or ; ; ) is a large rural departments of France, department in south west France, with its Prefectures in France, prefecture in Périgueux. Located in the Nouvelle-Aquitaine region roughly half-way between the Loire Valley and ...
.


Structural organisation and tectonics

Structurally the Aquitaine Basin can be divided into two provinces separated by a prominent fault zone, the so-called ''North Aquitaine Flexure''. This fault zone extends from Arcachon to Carcassonne and represents the continuation of the continental slope onshore. The ''Northern Province'' or ''Aquitaine Plateau'' forms a typical continental shelf region with reduced sedimentation and several periods of emersion (during the entire Lower Cretaceous and during parts of the Upper Cretaceous and the Cenozoic). The basement is rarely encountered deeper than 2,000 m. Triassic and Jurassic together have an accumulated sediment thickness of 1,000–1,700 m. The Lower Cretaceous is completely missing and the Upper Cretaceous only reaches a thickness of several hundred metres. The
Paleogene The Paleogene Period ( ; also spelled Palaeogene or PalĂŠogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...
is, if present, very thin in the north but increases in thickness towards the south where it is overlain by thin
Neogene The Neogene ( ,) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period million years ago. It is the second period of th ...
. In the eastern section, one can discern several low-amplitude structures that are parallel to the Pyrenees farther south and strike west-northwest-east-southeast: * Quercy synform. *
Tarn-et-Garonne Tarn-et-Garonne (; ) is a Departments of France, department in the Occitania (administrative region), Occitania Regions of France, region in Southern France. It is traversed by the rivers Tarn (river), Tarn and Garonne, from which it takes its n ...
antiform. *
Castres Castres (; ''Castras'' in the Languedocian dialect, Languedocian dialect of Occitan language, Occitan) is the sole Subprefectures in France, subprefecture of the Tarn (department), Tarn Departments of France, department in the Occitania (adminis ...
graben structure. * Toulouse antiform. Generally the Northern Province is characterised by rather simple structures (syn- and antiforms, low-amplitude fold trains, faults) that follow hercynian, armorican and variscan strike directions. The structures were formed during several tectonic phases: * Jurassic phase. The resulting structures are mainly of synsedimentary origin and follow variscan strike directions. They profoundly influenced facies distributions and transgressive style during the Upper Cretaceous. * Late Campanian-Maastrichtian phase. This phase enhanced the structures already formed in the Jurassic phase. The following anticlinal ridges, which run more or less parallel to the northeastern basin margin and can be traced for more than 200 km, were being generated (from north to south): ** The Mareuil-Meyssac Anticline. This structure is an asymmetric anticline near Mareuil, becoming a high-offset normal fault between Terrasson and Meyssac. ** The PĂ©rigueux anticline. This structure can be followed from
Cognac Cognac ( , also , ) is a variety of brandy named after the Communes of France, commune of Cognac, France. It is produced in the surrounding wine-growing region in the Departments of France, departments of Charente and Charente-Maritime. Cogn ...
via La Tour-Blanche to Périgueux and Saint-Cyprien. It forms a typical anticline near La Tour-Blanche. Near Saint-Cyprien, it is mainly a normal fault. ** The Oléron-
Jonzac Jonzac (; ) is a commune of the Charente-Maritime department, Nouvelle-Aquitaine, southwestern France. The historian Jean GlĂ©nisson (1921–2010) was born in Jonzac as well as the philosopher Jean Hyppolite (1907–1968). Geography The r ...
- Ribérac- Sauveterre-la-Lemance anticline. This structure is an anticline near Jonzac and Sauveterre.
Between the anticlines are synforms near Saintes and Sarlat. * Eocene-Oligocene phase. More anticlines at a deeper level that are not detectable at the surface were created: ** Northeast-southwest-striking domal upwarps near Listrac, near Blaye and near CouquĂšques. ** The northwest–southeast-striking upwarp of Sainte-HĂ©lĂšne-
Carcans Carcans (; , ) is a commune in the Gironde department, administrative region of Nouvelle-Aquitaine (before 2015: Aquitaine), France. Carcans is one of the 14 members of the Community of Communes of Médoc Atlantique. Geography Location Sit ...
. ** The Bordeaux syncline. ** The east–west-striking anticline of La Teste- Villagrains- Landiras-Miramont in the
Guyenne Guyenne or Guienne ( , ; ) was an old French province which corresponded roughly to the Roman province of '' Aquitania Secunda'' and the Catholic archdiocese of Bordeaux. Name The name "Guyenne" comes from ''Aguyenne'', a popular transform ...
. The ''Southern Province'' is characterised by the deep Parentis and Adour sub-basins with the
Mimizan Mimizan (; ) is a commune in the Landes department in Nouvelle-Aquitaine in south-western France. There are two separate districts of the town: Mimizan-Bourg (town center) and Mimizan-Plage (resort). Geography Mimizan is a seaside resort on t ...
high ground in between. Compared with the Northern Province its sediments show a pronounced increase in thickness (  altogether). The Triassic and the Jurassic combined reach 2,000–3,000 , the Lower Cretaceous 500–1,500 m. The Upper Cretaceous can vary between 500 and 3,000 m and even the Neogene still attains a thickness of nearly 1,000 m. The tectonic movements were much more complicated in the Southern Province, having superimposed on them very strong halokinetic motions (salt diapirism). A large part of the formed structures is concealed under Plio-Quaternary detritus. The many exploration wells drilled for hydrocarbons and groundwater helped immensely in unravelling these structures. Similar to the Northern Province, the major structures are again trains of parallel anticlines whose wavelength steadily diminishes approaching the Pyrenean front. Inversely the effects of the salt movements become stronger towards the south. The anticlines were formed during the uplift of the Pyrenees during the Eocene/Oligocene. The structures were set in place by Miocene times. The following anticlines can be distinguished (from north to south): * Parentis- Bouglon-Agen. * Mimizan-
Roquefort Roquefort () is a sheep milk blue cheese from southern France. Though similar cheeses are produced elsewhere, European Union law, EU law dictates that only those cheeses aged in the natural Combalou caves of Roquefort-sur-Soulzon may bear the na ...
- Créon- Cezans- Lavardens. * Boos-Audignan-
Nogaro Nogaro (; Gascon: ''NogarĂČu'') is a commune in the Gers department, Southwestern France. It is the site of a distillery of Armagnac brandy. Geography The commune is bordered by six other communes: Caupenne-d'Armagnac to the northwest, ...
. * Saubrigues- Biarotte- Bastennes- Garlin. * Peyrehorade- Sainte-Suzanne-
Lacq Lacq (; ) is a commune in the Pyrénées-Atlantiques department in southwestern France. On 1 January 2024, the former commune of UrdÚs was merged into Lacq. It lies just northwest of the prefecture (department capital) Pau. Economy In mo ...
-Pau- Meilhon. Isostatic movements during the Plio-Quaternary at the northeastern edge of the Aquitaine basin lead to an uplift and rejuvenation of the peneplained basement in the Massif Central. In the Aquitaine basin itself, these movements follow already existing basement structures and entrain the tilting of some of the pliocene peneplains. This in turn has a strong effect upon the hydrographic network, for example in the
drainage basin A drainage basin is an area of land in which all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, ...
s of the Garonne and Adour, the rivers' courses were changed or entirely abandoned. Tectonic movements are still at work in the Aquitaine Basin today—strong earthquakes in the Pyrenees (with destroyed villages and churches) and somewhat milder tremors near the island of OlĂ©ron keep reminding us of that fact.


Tectono-metamorphic organisation of the basement

According to
geophysical Geophysics () is a subject of natural science concerned with the physical processes and properties of Earth and its surrounding space environment, and the use of quantitative methods for their analysis. Geophysicists conduct investigations acros ...
explorations the Variscan basement hidden under the sediments of the Aquitaine Basin can be subdivided into several northwest–southeast-striking tectono-metamorphic zones (from north to south): * Ligero-arvernian Zone. The zone is limited on the south by the line
Niort Niort (; Poitevin: ''NiĂ u''; ; ) is a commune in the Deux-SĂšvres department, western France. It is the prefecture of Deux-SĂšvres. The population of Niort is 58,707 (2017) and more than 177,000 people live in the urban area. Geography T ...
-AngoulĂȘme- Fumel-
Montauban Montauban (, ; ) is a commune in the southern French department of Tarn-et-Garonne. It is the capital of the department and lies north of Toulouse. Montauban is the most populated town in Tarn-et-Garonne, and the sixth most populated of Oc ...
running parallel to the South Armorican Shear Zone farther north. It forms the polymetamorphic core region of the Variscan orogen in Europe. * South Armorican Zone. The zone is bounded on the south by the line La Rochelle-Saintes- Chalais and pinches out near Bergerac. It is composed of southward-thrust basement nappes of
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
/
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 ...
age. * North Aquitaine Zone. Its southern boundary is identical with the ''South Variscan Thrust Front'' (and also the North Aquitaine Flexure) and follows the line Arcachon-Agen-Toulouse. It is made up of nappes of the orogen's external zone which were thrust southward during the Pennsylvanian. * ''Aquitaine block'', also called microcontinent
Aquitania Gallia Aquitania (, ), also known as Aquitaine or Aquitaine Gaul, was a province of the Roman Empire. It lies in present-day southwest France and the comarca of Val d'Aran in northeast Spain, where it gives its name to the modern region of Aquit ...
. It is bounded in the south by the North Pyrenean Thrust Front and is equivalent to the Southern Province. This continental foreland block already belonged to
Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...
's northern edge.


Depths of the Mohorovicic Discontinuity

The maximum depth of the Mohorovicic Discontinuity in the Aquitanian Basin is 36 km, following more or less the path of the Garonne River. Towards the Massif Central in the northeast, the discontinuity flattens out to 30 km. The same holds for approaching the northern edge of the Pyrenees, here the discontinuity is also at 30 km depth. In the oceanic part of the Parentis Basin, it is already encountered at 20 km depth. This implies a significant stretching 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 ...
and the beginning of oceanisation. As a comparison, underneath the Central Pyrenees the continental crust is 50 km thick.


Geodynamic setting

For a better understanding of the geological successions and structures in the Aquitaine Basin, it is important to consider the greater geodynamic setting. Two geodynamic developments are of primordial importance for the basin: * The break-up of
Pangaea Pangaea or Pangea ( ) was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous period approximately 335 mi ...
and the opening history of the Northern Atlantic (and hence the
Bay of Biscay The Bay of Biscay ( ) is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Point Penmarc'h to the Spanish border, and along the northern coast of Spain, extending westward ...
). * The movements of the microcontinent
Iberia The Iberian Peninsula ( ), also known as Iberia, is a peninsula in south-western Europe. Mostly separated from the rest of the European landmass by the Pyrenees, it includes the territories of peninsular Spain and Continental Portugal, compri ...
. In the Upper Triassic (
Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...
) about 230 million years ago, the supercontinent Pangaea started slowly to break up. In the Atlantic domain, the disintegration began in the area of the ''Central Atlantic''. Already in the Lower Jurassic, the initial rifting process had given way to the marine drifting stage. In the
Toarcian The Toarcian is, in the International Commission on Stratigraphy, ICS' geologic timescale, an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic. It spans the time between 184.2 Megaannum, Ma (million ...
about 180 million years ago, the Central Atlantic was spreading and
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
,
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
and
Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...
were separating. By
Callovian In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 165.3 ± 1.1 Ma (million years ago) and 161.5 ± 1.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the ...
times, the Central Atlantic was fully marine. Spreading continued and gradually also began to affect the Northern Atlantic domain. During the
Tithonian In the geological timescale, the Tithonian is the latest age (geology), age of the Late Jurassic Epoch and the uppermost stage (stratigraphy), stage of the Upper Jurassic Series. It spans the time between 149.2 ±0.7 annum, Ma and 143.1 ±0.6 (mi ...
about 150 million years ago, a rift arm infiltrated along today's continental margin of northwestern France. Consequently, Iberia, so far being positioned right below the Armorican Massif (
Brittany Brittany ( ) is a peninsula, historical country and cultural area in the north-west of modern France, covering the western part of what was known as Armorica in Roman Gaul. It became an Kingdom of Brittany, independent kingdom and then a Duch ...
), was wedged southward. This gave the Atlantic the chance to directly reach the Aquitaine Basin for the first time. In the wake of the southward drifting Iberia during the Lower Cretaceous, the Bay of Biscay opened up. The microcontinent Iberia underwent in addition to its southward drifting motion a counterclockwise rotational movement that eventually brought it in close contact with southern France (reflected in first tectonic movements in the Pyrenees during the
Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...
; also documented by metamorphism in the Pyrenees dated between 108 and 93 million years ago and by the transgression of the
Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...
sea). The final collision happened during the
Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
/
Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...
uplifting the mountain chain and subjecting it to severe erosion at the same time. The main phase of uplift ended with the close of the Aquitanian, followed mainly by isostatic movements lasting to this day.


Megasequences

By taking as a reference point the onset of rifting in the Bay of Biscay during the Tithonian the geodynamic evolution of the Aquitaine Basin can be subdivided into four megasequences (somewhat simplified): * Prerift megasequence. Triassic till Upper Jurassic. Mainly clastic sediments and carbonates followed by thick evaporites during the Triassic; shelf carbonates during the Jurassic. * Synrift megasequence. Lower Cretaceous (Tithonian till Albian). The Bay of Biscay opened and became partially underlain by
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 ...
. During the Neocomian nonmarine and shallow-marine clastics and carbonates formed, followed by thick shelf carbonates during the Aptian and Albian. The megasequence ends in the Cenomanian with inversion tectonics along preexisting tensional faults. * Postrift megasequence. Cenomanian till Paleocene. Sinistral motions of Iberia relative to France created several transtensional sub-basins (pull-apart structures). Turbidite sedimentation in the south. * Foreland basin megasequence. Eocene till recent. The collision of Iberia with France in the Eocene terminated the transtensional tectonics. The rising orogen of the Pyrenees shed flysch sediments during the Eocene and molasses during the Miocene into the foreland basin.


Resources


Hydrocarbons

Amongst the many resources in the Aquitaine Basin, the
hydrocarbons 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 hydrophobic; their odor is usually faint, and may b ...
oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) and lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturate ...
and
gas Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure gas'' is made up of individual atoms (e.g. a noble gas like neon) or molecules of either a single type of atom ( elements such as ...
are without doubt of prime importance for the French economy. Major sources are found in the following sub-basins of Lower Cretaceous age: * In the Parentis Basin. Oil is found in Parentis,
Cazaux Cazaux () is a commune of the AriĂšge department in southwestern France. Population See also *Communes of the AriĂšge department The following is a list of the 325 communes of the AriĂšge department of France France, officia ...
and Lavergne. The Parentis Basin contains most oil reserves of continental France. * In the Adour Basin. Gas is found in Lacq gas field, Meillon, and Saint-Marcet. With its 220 billion cubic meters of gas, the Adour Basin stocks practically all the gas reserves of France. Source/host rocks are Jurassic (Kimmeridgian) and Lower Cretaceous limestones and dolomites. Lower Aptian shales function as seals.


Groundwater aquifers

Classic
groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...
aquifer An aquifer is an underground layer of water-bearing material, consisting of permeability (Earth sciences), permeable or fractured rock, or of unconsolidated materials (gravel, sand, or silt). Aquifers vary greatly in their characteristics. The s ...
s are found in Upper Cretaceous and Cenozoic rocks of the Bordelais. Recently a gigantic aquifer has been discovered in Eocene sands near Lussagnet—of great importance for the region Pau-Toulouse.


Other resources

Further notable resources include: *
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 and
mudstone 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.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...
s. They are the raw material for innumerable
tile Tiles are usually thin, square or rectangular coverings manufactured from hard-wearing material such as ceramic, Rock (geology), stone, metal, baked clay, or even glass. They are generally fixed in place in an array to cover roofs, floors, wal ...
and brick factories (manufacture of tiles, bricks, terracotta, etc.). Horizons are found mainly in the Toarcian, in the Eocene (Lutetian), in the Oligocene, and in the Miocene (Aquitanian, Burdigalian,
Langhian The Langhian is, in the ICS geologic timescale, an age or stage in the middle Miocene Epoch/Series. It spans the time between 15.97 ± 0.05 Ma and 13.65 ± 0.05 Ma (million years ago) during the Middle Miocene.GeoWhen (2007) The Langhian was ...
, and
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 ...
). *
Kaolinite Kaolinite ( ; also called kaolin) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral sheet of alumina () ...
. This is the raw material for the manufacture of
china China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
. Mainly found in residual pockets of Eocene age filling depressions and caves in Upper Cretaceous
karst Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and Dolomite (rock), dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. Ther ...
developments. For example, near
Les Eyzies Les Eyzies (; ) is a commune in the Dordogne department in Nouvelle-Aquitaine in southwestern France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and terri ...
. *
Peat Peat is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. ''Sphagnum'' moss, also called peat moss, is one of the most ...
.
Pleistocene 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 ...
and
Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
horizons in the Médoc (Gironde estuary). *
Lignite Lignite (derived from Latin ''lignum'' meaning 'wood'), often referred to as brown coal, is a soft, brown, combustible sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35% and is considered the lowest ...
. In the Cenomanian of the Sarladais; Upper Miocene/Pliocene deposits in the Landes are strip-mined near Arjuzanx. *
Bauxite Bauxite () is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (), boehmite (γ-AlO(OH)), and diaspore (α-AlO(OH) ...
. In Jurassic karst pockets between Pech and
Lavelanet Lavelanet (; ''L'Avelhanet'' in the Languedocian dialect of Occitan language, Occitan) is a Communes of France, commune in the AriĂšge (department), AriĂšge Departments of France, department in the Occitania (administrative region), Occitanie ...
. Economically not viable. *
Iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
. Contained within the Eocene age Sidérolithique, mainly in the Périgord and in the Quercy. Economically no longer viable. *
Metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...
s. Mainly
lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...
-
zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...
mineralisations occurring in the basal Sinemurian. Found in the Charente and near Figeac, yet economically no longer viable. *
Wood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...
. Large forests in the Landes and in the Dordogne form the basis for a diversified industry (firewood for power stations and private use,
charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, ca ...
, palettes, timber, furniture industry, etc.). *
Fruits In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...
.
Plum A plum is a fruit of some species in Prunus subg. Prunus, ''Prunus'' subg. ''Prunus'.'' Dried plums are often called prunes, though in the United States they may be labeled as 'dried plums', especially during the 21st century. Plums are ...
s in the Agenais (''Pruneau d'Agen''). *
Wine Wine is an alcoholic drink made from Fermentation in winemaking, fermented fruit. Yeast in winemaking, Yeast consumes the sugar in the fruit and converts it to ethanol and carbon dioxide, releasing heat in the process. Wine is most often made f ...
. World-famous wines like the Cognac, Bordeaux, Armagnac, Chalosse, and
Béarn Béarn (; ; or ''Biarn''; or ''Biarno''; or ''Bearnia'') is one of the traditional provinces of France, located in the Pyrenees mountains and in the plain at their feet, in Southwestern France. Along with the three Northern Basque Country, ...
are grown in the Aquitaine Basin.


Conclusions

The structural and hence sedimentary organisation in the Aquitaine Basin was ultimately influenced by two principal factors: * By structural inheritance from the Variscan basement. * By the evolution of the Pyrenean orogen. The strong ''northwest-southeast-striking tectono-metamorphic zonation'' in the basement has profoundly influenced the structural and the sedimentary evolution of the Aquitaine Basin. The same ''hercynian'' direction is also followed by the continental edge of northwestern France which formed during the evolution of the Bay of Biscay. The ''continental edge'' finds its prolongation in the superdeep Subpyrenean Basin. The system of ''anticlinal ridges'' affecting the sedimentary cover is also arranged in this direction. The prominent South Armorican Shear Zone farther north also strikes northwest–southeast, but additionally has a distinct dextral wrenching movement. Like the South Armorican Shear Zone, the anticlinal ridges too are affected by similar shearing movements and are not purely compressional in origin. Even the
Paris Basin The Paris Basin () is one of the major geological regions of France. It developed since the Triassic over remnant uplands of the Variscan orogeny (Hercynian orogeny). The sedimentary basin, no longer a single drainage basin, is a large sag in ...
is bounded by these transtensional dextral shear zones and can hence be interpreted as an east–west-oriented pull-apart basin. Within the context of the opening of the Bay of Biscay, the Parentis Basin can furthermore be regarded as a failed attempt of the Atlantic to wedge into the continent's interior. The reason for this is the counterclockwise rotational motion of Iberia blocked further rifting. Since the Cenomanian, the Aquitaine Basin is under the influence of the Pyrenean orogeny with its west-northwest-east-southeast-striking structural grain. The Pyrenean orogen likewise has not merely a compressional origin but also a strong, in this case, sinistral transtensional component. The Pyrenean orogen exerted a very profound influence upon the Aquitaine Basin up to this day, subjecting it not only to more or less north–south-directed compression but also to transtension. The effects were of a penetrative nature—tectonic repercussions of the Pyrenean orogeny can even be seen at the northeastern basin margin in the immediate vicinity of the Massif Central.


References

* Chantraine J, Autran A, Cavelier C, et al. ''Carte géologique de la France à l'échelle du millionÚme.'' (1996). BRGM. . * GÚze B & Cavaillé A. (1977). ''Aquitaine orientale.'' Guides géologiques régionaux. Masson. . * Vigneaux M. (1975). ''Aquitaine occidentale.'' Guides géologiques régionaux. Masson. . * Winnock E. (1996). Bassin d'Aquitaine. Contribution in the ''Encyclopaedia Universalis''. . {{Authority control Sedimentary basins of Europe Foreland basins Geology of France