Mareuil Anticline

The Mareuil- anticline, also Mareuil- Meyssac anticline, is a tectonic upheaval in the sedimentary layers of the Northeastern Association of Aquitaine basin. The structure follows a northwest - southeast direction. The first movements of her are probably already occurs in the Turonian.

Description of the structure

The anticline was named in the northwest of the department of Dordogne after the small town of Mareuil. The actual center of the structure, however, lies a little further northwest at Sainte- Croix -de- Mareuil. The anticline shows in plan a stretched, pear-shaped figure, the NW-SE trending axis reaches 5 km (border Cenomanian / Turonian as a reference horizon). The width dimension is just 2 kilometers. The structure is double asymmetric, with a steeper incident north-east and north-west flank. It is also accompanied along the northeast flank of a fault, the Mareuil- disorder that affects La Rochebeaucourt to the north of Brantome. In this disorder the northeast flank of the anticline has been dragged, the offset is approximately 30 meters.

At the southeast end of the anticline at Mareuil cross multiple transverse fractures, which led to local tilting of the layers Association. What is striking is their arrangement as so-called Riedel ( in R and R ' position) and who therefore may indicate a shear zone in the deeper subsoil.

Regional context

The Mareuil anticline is seen from the edge of the first high zone in the northeastern Aquitanian basin. It is about 15 kilometers away from the pool edge. The sedimentary cover is in the anticline approximately 400 meters. In the northeast offshore syncline ( Combiers -Saint -Crépin -de- Richemont syncline ) sedimentary thickness already reached 500 meters. It follows then southwest Gout - Rossignol - Léguillac - syncline with about 700 meters of sediment thickness. The next, running approximately parallel Antiklinalzug, the La Tour- Blanche anticline follows the Mareuil- anticline 8 km to the southwest. The sedimentary cover is grown here already to almost 1000 meters in thickness.

The Mareuil anticline is a large-scale structure that can be pursued to the Isle de Yeu to the northwest as a fault zone on Angoulême addition. To the southeast it also proceeds in a fault zone, which continues through Terrasson after Meyssac. Maybe they can be brought into connection with the Lacassagne disorder and the Souillac - flexure.

Stratigraphy of the constituent layer packet

At the core of Antiklinals at Sainte- Croix -de- Mareuil occurs Upper Jurassic ( Kimmeridgian ) to days - dünngebankte, cryptocrystalline limestones ( micrites ) - of which only the top 20 meters are open. After a major hiatus follows 8-20 meters powerful, transgressive Cenomanian consisting of green marls, which are rich in oysters, and sandy, Alveolinenführenden limestones. The concordant subsequent 55 - 65 meters thick Turonian builds up from nodular, chalky limestones of Ligérien and Rudistenkalken of Angoumien. The 50 - 65 meter thick Coniacian consists mainly of hard Fossilkalken. At the conclusion follows 45 - 60 meters powerful, chalky, partly glaukonithaltiges Santonian, which is sometimes rich in oysters Schill.

Not exposed in the anticline are below the 120 meters thick expectant Kimmeridgiums the layers of the Oxfordian and Dogger ( Bajocian and Bathonian, with a total of 210 meters width). It is not known whether including even thinner Lias is present.

Timeframe

The first movements in the field of Mareuil- anticline must have already been carried out in the Lower Cretaceous, since follows the Cenomanian with an erosional the Kimmeridgian. These movements, however, were not only bound to the anticline, but of regional importance. Synsedimentary Rutschungsvorgänge (English Slumps ) in layers of Turoniums leave to movements in Mareuil- anticline during this period close. The main phase of movement is, however, clearly takes place after the Santonian, since the entire coating was deformed. For the emergence of Antiklinalrücken assumes a endcampanischen - maastrichtischen phase at the end of the Cretaceous. Perhaps this is the main phase but also with the movements in the Pyrenees during the Eocene / Oligocene (Pyrenees main phase ) in context. As in the Pyrenees were also made to the Mareuil- anticline constricting, if not transpression movements. As is known, captured the constricting movements during the Pyrenäenorogenese even the northern edge of the Aquitaine basin (good to see thrusting, for example, in the quarry of Saint-Martial -de- Valette ).

Importance

The Mareuil anticline forms part of the northern Antiklinalrücken Aquitanian basin, which essentially follow the Armorican direction NW-SE and thus run parallel to Südarmorikanischen shear zone. Very likely they share with the latter also the same, dextral sense of movement. Also remarkable is the parallel staggered back with almost identical intervals in Deka km range (15 to 20 km ). An exception to this scheme is the La Tour- Blanche anticline, which is a local constriction ( 8 km).