Paul D Taylor (UK)
Nouvelle-Aquitaine (New Aquitaine) is a vast region of southwest France covering more than 30,000 square miles. Between 1154 and the end of the Hundred Years War in 1453, much of the region was under British control. Links with Britain are still strong today, both through tourism and the large ex-patriate British population, particularly in the Dordogne, known jokingly to locals as ‘Dordogneshire’.
The geology of Aquitaine is diverse, with sedimentary rocks of Mesozoic and Cenozoic especially well represented. Indeed, Nouvelle-Aquitaine contains the historical type sections of several international stratigraphical divisions, including the Coniacian (Cognac), Santonian (Saintes) and Campanian (Aubeterre–Royan) stages of the Late Cretaceous, and the Aquitanian and Burdigalian stages of the early Miocene.
A good sense of the local geology can be gained by studying the building stones of the remarkable Romanesque churches (Église) that occur in profusion throughout Aquitaine. The bonus is that many of these churches are hidden architectural gems. And anyone with even a passing interest in Medieval stone carvings is in for a treat: mythical griffins and zoomorphic creatures abound.
The churches featured in this article are all in the area at the borders between four Departments – Charente, Charente Maritime, Dordogne and Gironde – and are located to the west or north of Bordeaux, and to the east of Bergerac. Many have somewhat stark interiors with little or no decoration; the main interest lies in their exteriors, which is just as well as the smaller churches are frequently locked and impossible to enter.
The churches are usually constructed of cream- to golden-coloured limestones, either of Late Cretaceous or early Oligocene age, depending on which rocks were closer to hand. Counterintuitively, the younger Oligocene limestones tend to be harder than the older Cretaceous limestones. There are two possible reasons for this:
(1) The Oligocene limestones are generally coarser, their greater porosity allowing the passage of fluids from which carbonate cements could be precipitated; and
(2) Fewer molluscs with aragonitic shells were present on the Late Cretaceous seabed and it is the dissolution of such aragonitic shells that provides much of the carbonate cement in these limestones.
Aubeterre-sur-Dronne, Charente (Fig. 1)
Popular with British tourists, the picturesque small town of Aubeterre has geological significance in being one of the principal sites used by Henri Coquand when he proposed the Campanian, the penultimate stage of the Cretaceous Period. The name Campanian derives from the ‘Grand Champagne’ hills to the northwest of Aubeterre. Confusingly, although these hills are carpeted by vineyards, the grapes are not used for champagne production but mostly for making brandy (Cognac).
Fossiliferous limestone is evident evident throughout the town and it can take a lot of self-control not to be tempted to prise the oysters, bryozoans and other fossils from the crumbling limestones facing several of the buildings. Natural outcrops are also evident, for example, behind the lower carpark where the Barbezieux Formation may be studied, and adjacent to the upper entrance gates of the chateau showing the overlying Aubeterre Formation.
There are two equally striking churches in Aubeterre. The first is the underground church of St Jean. Hewn into the rock beneath the chateau, this huge excavation almost twenty metres tall was begun in the seventh century and enlarged in the twelfth century. Constructed within the church is a reliquary. Bands of rock packed with the Gryphaea-like oyster, Pycnodonte vesiculare, are visible on the walls of the cavern and can be seen in natural outcrops around the entrance. The surfaces of the shells are covered with circular borings made by sponges, constituting the trace fossil Entobia cretacea.
Although now a diminished vestige of its former glory, the twelfth century church of St Jacques at the other end of the town is notable for its magnificent façade, ornamented by stone carvings.
Some depict everyday Medieval scenes but others show mythical creatures such as griffins, which, incidentally, are believed by some to have been based on fossils of the dinosaur Protoceratops, discovered in the Gobi Desert. The columns supporting the three arches contain moulds of dome-shaped solitary corals in chaotic orientations, probably as a result of burrowing animals churning the lime sediment, as at the church in nearby St Aulaye.
St Aulaye, Dordogne (Fig. 2)
Located a few miles southwest of Aubeterre, the Bastide town of St Aulaye contains the fine Romanesque Église St Eulalie, dating from the twelfth century. The main building stones are Campanian limestones. Several different facies are visible on the western façade, where the slightly green, glauconitic limestones have suffered extreme weathering, bringing the fossils to prominence. These include fragments of branching and foliaceous (that is, resembling leaves) bryozoan colonies.
St-Félix, Charente (Fig. 3)
The eponymous twelfth century church in this small village is constructed from Campanian limestone containing age-diagnostic fossils, such as onychocellid bryozoans. Aside from the fossils, the church boasts a range of animals and anthropomorphic carvings in the capitals on either side of the entrance arch and the two smaller flanking arches. The low height of the capitals means that the carvings are more easily seen than is often the case in the Aquitanian Romanesque churches.
Talmont, Charente Maritime (Fig. 4)
On a clifftop promontory at Talmont is the small but imposing Église St Radegonde, a well-known tourist attraction. This twelfth century church has suffered periodic damage from violent storms but is now restored to its full glory. Alas roped off and no longer accessible, the cliffs below the church consist of limestones of the Late Campanian Barbezieux Formation and it is likely that stone from this formation was used in the construction of the church. Some of the limestone blocks are richly fossiliferous, the fossils accentuated by weathering in this exposed location overlooking the broad estuary of the Gironde.
St Émilion, Gironde (Fig. 5)
St Émilion is world famous for the prestigious red Bordeaux wines produced from the numerous vineyards surrounding the town. Once an ecclesiastical centre with monasteries and convents, and now a UNESCO World Heritage Site, St Émilion contains two major churches built from the local Oligocene Calcaire à Astéries (‘starfish limestone’): the twelfth century collegiate church, and the monolithic church whose tower is topped by a fifteenth century spire that overlies catacombs excavated into the limestone beneath. The masonry at the base of the tower contains spectacular examples of honeycomb weathering. It is unclear exactly how this formed, but it seems possible that bands of well-cemented limestone alternated with bands of softer limestone, the activities of vertically burrowing animals complicating the pattern of cementation. Blocks of cross-bedded calcarenite can be seen in the walls of the collegiate church.
Petit-Palais-et-Cornemps, Gironde (Fig. 6)
Rebuilt in the sixteenth century, the Église St Pierre at Petit-Palais-et-Cornemps, near Coutras, dates back to the thirteenth century and is almost certainly constructed from Oligocene Calcaire à Astéries. In places, this shelly calcarenite is cross-bedded. Some blocks have not survived well and are deeply weathered, the weathering picking out burrows probably made by crustaceans. Fragments of bivalve molluscs and bryozoans occur in profusion, but the preservation of the fossils is poor. Architecturally, the highlight of the church is the western facade with its three polylobate arches; the central arch over the entrance doorway is flanked by two smaller blind arches. Above these incised arches are a pair of carved lions associated with two human figures, a kneeling woman and a man removing a thorn from his foot, who is thought to represent the apostle St Paul.
Sauve-Majeure Abbey, Gironde (Fig. 7)
About 15 miles east of Bordeaux is the ruined abbey of Sauve-Majeure, another UNESCO World Heritage Site. The Benedictines constructed the abbey between the eleventh and thirteenth centuries and it served as a stopover for pilgrims on their way to Santiago de Compostela in northern Spain. Like many of the older buildings in Bordeaux, the abbey was built from limestone of the Calcaire à Astéries. Some of the limestone employed is moderately coarse, with recognisable fragments of bivalves, bryozoans and serpulid worm tubes. Most remarkable are the carved capitals depicting a range of real and imaginary animals, mermaids and centaurs.
The small number of churches mentioned here represent the tip of the iceberg as far as Aquitanian ‘geoarchitectural’ treasures are concerned. If ever you have the opportunity to visit this scenic and culturally rich area of southwest France, take an opportunity to look at the local churches. You may be surprised by the unexpected, and unheralded, geological interest they hold.