Mareuil Anticline
Encyclopedia
The Mareuil Anticline, also called Mareuil-Meyssac Anticline, is a structural high within the sedimentary sequence
of the northeastern Aquitaine Basin. The northwest-southeast trending anticline
was caused by tectonic movements probably starting in the Upper Cretaceous
.
, a small town in the northwestern Dordogne
, France
. The centre of the structure is near Sainte-Croix-de-Mareuil
, somewhat farther to the northwest. In plan view the anticline has the shape of an elongated pear with its long axis aligned NW-SE and reaching about 5 km in length (the Cenomanian
/Turonian
boundary serving as a reference horizon). The short axis is only 2 km in length. The structure is doubly asymmetric, with steeper dipping northeastern and northwestern limbs. It is accompanied on its northeastern side by the Mareuil Fault, which starts at La Rochebeaucourt
and continues to the north of Brantôme
. Along this fault the northeastern side of the anticline was pushed up by about 30 m.
On the southeastern side of the anticline, there are several smaller cross-cutting faults locally disturbing the angle of dip. These cross faults are all following Riedel
directions, either the R- or the R'-position, hinting at an underlying shear zone
.
, at a distance of about 15 km. The sedimentary cover reaches a thickness of altogether 400 m in the anticline. In the syncline on the northeast (the Combiers-Saint-Crépin-de-Richemont Syncline), the sediments are 500 m thick. In the adjoining syncline on the southwestern side (the Gout-Rossignol-Léguillac Syncline), the sediments reach 700 m in thickness. This is followed 8 km to the southwest by another anticlinal ridge, the La Tour-Blanche Anticline
. In this second anticlinal ridge, the sediments already show a thickness of 1000 m.
The Mareuil Anticline is a large-scale structure. To the northwest it changes into a fault zone that can be traced from Angoulême
to Isle de Yeu. To the southeast it also changes into a fault zone running from Terrasson
to Meyssac
. It possibly continues into the Lacassagne Fault or even into the Souillac flexure.
(Kimmeridgian
) strata are exposed — thinly bedded, cryptocrystalline, fossiliferous limestone
s (micrite
s). After a long hiatus follow 8–20 m of transgressive
Cenomanian
consisting of green, glauconitic
marl
s rich in oyster
s and sandy, alveoline-bearing limestones. The Cenomanian is concordantly overlain by 55–65 m of Turonian
strata divided into the nodular, chalky limestones of the Ligérian
and the rudist-bearing limestones of the Angoumian
. This is followed by 50–65 m of Coniacian
— mainly hard, fossiliferous limestones. The sequence finishes with 45–60 m of chalk
y, glauconitic Santonian
, in places rich in oyster debris.
The strata below the 120 m thick Kimmeridgian do not outcrop, but the presence of 210 m of underlying Oxfordian, Bajocian
and Bathonian
strata is known from drilling results in the vicinity. Whether thin Lias
underlies the Dogger
cannot be ascertained.
and during the Maastrichtian
(end-Campanian-Maastrichtian event). But there is also a good possibility that the main orogenic
event during the Eocene
/Oligocene
in the Pyrenees
is somehow involved in the formation of the anticline. Like the Pyrenees, the Mareuil Anticline was created under compressive forces
, maybe even under transpression
. It is known that compressive forces responsible for the Pyrenean orogeny likewise affected the northeastern edge of the Massif Central (i.e. upthrusts within the Dogger can be seen in the quarry of Saint-Martial-de-Valette
).
narrowing to a spacing of 8 km and following a WNW-ESE direction.
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
of the northeastern Aquitaine Basin. The northwest-southeast trending anticline
Anticline
In structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships In structural geology, an anticline is a fold that is...
was caused by tectonic movements probably starting in the Upper Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
.
Description of the structure
The anticline was named after MareuilMareuil
Mareuil is the name or part of the name of the following communes in France:* Mareuil, Charente, in the Charente department* Mareuil, Dordogne, in the Dordogne department* Mareuil-Caubert, in the Somme department* Mareuil-en-Brie, in the Marne department...
, a small town in the northwestern Dordogne
Dordogne
Dordogne is a départment in south-west France. The départment is located in the region of Aquitaine, between the Loire valley and the High Pyrénées named after the great river Dordogne that runs through it...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. The centre of the structure is near Sainte-Croix-de-Mareuil
Sainte-Croix-de-Mareuil
Sainte-Croix-de-Mareuil is a commune in the Dordogne department in Aquitaine in southwestern France.-Population:-References:*...
, somewhat farther to the northwest. In plan view the anticline has the shape of an elongated pear with its long axis aligned NW-SE and reaching about 5 km in length (the Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...
/Turonian
Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous epoch, or a stage in the Upper Cretaceous series. It spans the time between 93.5 ± 0.8 Ma and 89.3 ± 1 Ma...
boundary serving as a reference horizon). The short axis is only 2 km in length. The structure is doubly asymmetric, with steeper dipping northeastern and northwestern limbs. It is accompanied on its northeastern side by the Mareuil Fault, which starts at La Rochebeaucourt
La Rochebeaucourt-et-Argentine
La Rochebeaucourt-et-Argentine is a commune in the Dordogne department in Aquitaine in southwestern France.-Population:-References:*...
and continues to the north of Brantôme
Brantôme
Brantôme may refer to:*Brantôme, Dordogne, a commune in the Dordogne département in central France*Pierre de Bourdeille, seigneur de Brantôme , French soldier and historian*Brantôme , champion French racehorse...
. Along this fault the northeastern side of the anticline was pushed up by about 30 m.
On the southeastern side of the anticline, there are several smaller cross-cutting faults locally disturbing the angle of dip. These cross faults are all following Riedel
Riedel
Riedel l), is a manufacturer of high-quality crystal wine glasses and related glass products based in Kufstein, Austria.Originally established in Bohemia in 1756, the company has been owned by the same family for more than 250 years...
directions, either the R- or the R'-position, hinting at an underlying shear zone
Shear zone
A shear zone is a very important structural discontinuity surface in the Earth's crust and upper mantle. It forms as a response to inhomogeneous deformation partitioning strain into planar or curviplanar high-strain zones. Intervening blocks stay relatively unaffected by the deformation...
.
Regional geology
Seen from the edge of the northeastern Aquitaine Basin, the Mareuil Anticline forms the first structural high within the sedimentary cover. It runs more or less parallel with the edge of the Massif CentralMassif Central (geology)
The Massif Central forms together with the Armorican Massif one of the two big basement massifs in France. Its geological evolution started in the late Neoproterozoic and continues to this day. It has been shaped mainly by the Caledonian orogeny and the Variscan orogeny. The Alpine orogeny has...
, at a distance of about 15 km. The sedimentary cover reaches a thickness of altogether 400 m in the anticline. In the syncline on the northeast (the Combiers-Saint-Crépin-de-Richemont Syncline), the sediments are 500 m thick. In the adjoining syncline on the southwestern side (the Gout-Rossignol-Léguillac Syncline), the sediments reach 700 m in thickness. This is followed 8 km to the southwest by another anticlinal ridge, the La Tour-Blanche Anticline
La Tour-Blanche Anticline
The La Tour-Blanche Anticline, also called Chapdeuil Anticline or Chapdeuil-La Tour-Blanche Anticline, is a tectonically caused, dome-like upwarp in the sedimentary succession of the northeastern Aquitaine Basin in France...
. In this second anticlinal ridge, the sediments already show a thickness of 1000 m.
The Mareuil Anticline is a large-scale structure. To the northwest it changes into a fault zone that can be traced from Angoulême
Angoulême
-Main sights:In place of its ancient fortifications, Angoulême is encircled by boulevards above the old city walls, known as the Remparts, from which fine views may be obtained in all directions. Within the town the streets are often narrow. Apart from the cathedral and the hôtel de ville, the...
to Isle de Yeu. To the southeast it also changes into a fault zone running from Terrasson
Terrasson-Lavilledieu
Terrasson-Lavilledieu is a commune in the Dordogne department in Aquitaine in southwestern France.The Gardens of the Imagination —classified as a remarkable garden by the French Ministry of Culture—are situated in Terrasson...
to Meyssac
Meyssac
Meyssac is a commune in the Corrèze department in central France.-Population:...
. It possibly continues into the Lacassagne Fault or even into the Souillac flexure.
Stratigraphy of the sedimentary sequence
In the core of the anticline the top 20 m of Upper JurassicJurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
(Kimmeridgian
Kimmeridgian
In the geologic timescale, the Kimmeridgian is an age or stage in the Late or Upper Jurassic epoch or series. It spans the time between 155.7 ± 4 Ma and 150.8 ± 4 Ma . The Kimmeridgian follows the Oxfordian and precedes the Tithonian....
) strata are exposed — thinly bedded, cryptocrystalline, fossiliferous limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
s (micrite
Micrite
Micrite is a limestone constituent formed of calcareous particles ranging in diameter up to 4 μm formed by the recrystallization of lime mud.The term was coined in 1959 by Robert Folk for his carbonate rock classification system...
s). After a long hiatus follow 8–20 m of transgressive
Transgression
Transgression may be:*a Biblical transgression, violation of God's ten commandments; sin *a legal transgression, a crime usually created by a social or economic boundary*a social transgression, violating a norm...
Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...
consisting of green, glauconitic
Glauconite
Glauconite is an iron potassium phyllosilicate mineral of characteristic green color with very low weathering resistance and very friable.It crystallizes with a monoclinic geometry...
marl
Marl
Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...
s rich in oyster
Oyster
The word oyster is used as a common name for a number of distinct groups of bivalve molluscs which live in marine or brackish habitats. The valves are highly calcified....
s and sandy, alveoline-bearing limestones. The Cenomanian is concordantly overlain by 55–65 m of Turonian
Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous epoch, or a stage in the Upper Cretaceous series. It spans the time between 93.5 ± 0.8 Ma and 89.3 ± 1 Ma...
strata divided into the nodular, chalky limestones of the Ligérian
Ligérian
The Ligérian is a regional geological substage of the Turonian. It designates sediments of the Lower Turonian in western France.- Etymology :The name Ligérian, in French Ligérien, is derived from the Latin Ligera, which stands for the Loire River....
and the rudist-bearing limestones of the Angoumian
Angoumian
The Angoumian is a geological group restricted to the northern Aquitaine Basin. The group consists of two fossiliferous limestone formations deposited during the Turonian.- Etymology :...
. This is followed by 50–65 m of Coniacian
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 89.3 ± 1 Ma and 85.8 ± 0.7 Ma...
— mainly hard, fossiliferous limestones. The sequence finishes with 45–60 m of chalk
Chalk
Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....
y, glauconitic Santonian
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 85.8 ± 0.7 mya and 83.5 ± 0.7 mya...
, in places rich in oyster debris.
The strata below the 120 m thick Kimmeridgian do not outcrop, but the presence of 210 m of underlying Oxfordian, Bajocian
Bajocian
In the geologic timescale, the Bajocian is an age or stage in the Middle Jurassic. It lasted from approximately 171.6 Ma to around 167.7 Ma . The Bajocian age succeeds the Aalenian age and precedes the Bathonian age....
and Bathonian
Bathonian
In the geologic timescale the Bathonian is an age or stage of the Middle Jurassic. It lasted from approximately 167.7 Ma to around 164.7 Ma...
strata is known from drilling results in the vicinity. Whether thin Lias
Lias Group
The Lias Group or Lias is a lithostratigraphic unit found in a large area of western Europe, including the British Isles, the North Sea, the low countries and the north of Germany...
underlies the Dogger
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
cannot be ascertained.
Age of movements
The first movements in the region of the Mareuil Anticline must have occurred in the Lower Cretaceous because of the transgressive nature of the Cenomanian. But these movements were not specific to the anticline; they affected the entire northeastern Aquitaine Basin. Synsedimentary slumps in the Turonian strata near the anticline are a good indicator that the first tectonic stirrings had happened in the anticline. Yet the major event responsible for the creation of the structure clearly must have taken place after the Santonian, because the entire sedimentary sequence has been deformed by it. This major event is thought to have occurred at the end of the CampanianCampanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
and during the Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
(end-Campanian-Maastrichtian event). But there is also a good possibility that the main orogenic
Orogeny
Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
event during the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
/Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
in the Pyrenees
Geology of the Pyrenees
The Pyrenees form part of the huge alpine orogenic system. This 430 kilometre long, roughly east-west striking, intracontinental mountain chain divides France, Spain, and Andorra. It has an extended, polycyclic geological evolution dating back to the Precambrian...
is somehow involved in the formation of the anticline. Like the Pyrenees, the Mareuil Anticline was created under compressive forces
Compression (geology)
In geology the term compression refers to a set of stresses directed toward the center of a rock mass. Compressive strength refers to the maximum compressive stress that can be applied to a material before failure occurs. When the maximum compressive stress is in a horizontal orientation, thrust...
, maybe even under transpression
Transpression
Transpression is a geological term used to describe a region of the Earth's crust that experiences strike-slip shear and a component of shortening, resulting in oblique shear. Transpression typically occurs at a regional scale, such as plate boundaries that have an oblique convergence. More...
. It is known that compressive forces responsible for the Pyrenean orogeny likewise affected the northeastern edge of the Massif Central (i.e. upthrusts within the Dogger can be seen in the quarry of Saint-Martial-de-Valette
Saint-Martial-de-Valette
Saint-Martial-de-Valette is a commune in the Dordogne department in Aquitaine in southwestern France.-Population:-External links:* *...
).
Structural observations
The Mareuil Anticline forms part of the anticlinal ridges within the northern Aquitaine Basin. These ridges follow a more or less northwesterly-southeasterly direction and run parallel to the South Armorican Shear Zone. Their age of formation is thought to be end-Campanian/Maastrichtian. Possibly they have a transpressive component and share with the South Armorican Shear Zone (SASZ) the same dextral sense of movement. Importantly they have a parallel alignment and a rather uniform spacing of 15–20 km. A local exception in this scheme is the La Tour-Blanche AnticlineLa Tour-Blanche Anticline
The La Tour-Blanche Anticline, also called Chapdeuil Anticline or Chapdeuil-La Tour-Blanche Anticline, is a tectonically caused, dome-like upwarp in the sedimentary succession of the northeastern Aquitaine Basin in France...
narrowing to a spacing of 8 km and following a WNW-ESE direction.