Saturday, April 19, 2014

Geological Legacies of the Paris Basin: Part I – Plaster of Paris, the Windmills of Montmartre, the Park of Buttes-Chaumont and a new Artistic Creativity

In March, I escaped from the frigid grip of the Polar Vortex that enveloped New England and found climatic, cultural and culinary refuge in Paris and London. Not expecting to encounter any geological discoveries worthy of a post, I found precisely the opposite. Herein is the first of two posts on the Geological Legacies of the Paris Basin, and later, a few worthy geo-gems I found in London. 

WHAT'S IN A NAME?
The Romans called their settlement on the south bank of the Seine River Lutetia Parisiorum or Lutetia of the Parisi, after the Gallic people who settled in the area in the third century BC. Lutetia (Lutece in French) is thought to have been derived from a Celtic root-word luteuo- meaning "marsh" or "swamp." Lutum is also the Latin word for "mud."  

The settlement also lent its name to the Lutetian Age of the Eocene Epoch that occurred 41.3 to 47.8 million years ago. It was a time when the Paris Basin was invaded by a shallow, warm tropical sea from the north of Europe. It was also a time of marine sedimentation, when Lutetian gypsums and limestones formed. They would eventually help to construct the buildings, monuments and churches of the glorious city of Paris. 




The official international reference point (GSSP) for the Lutetian is located in the limestone strata of the quarries below the streets of Paris at a water-well that bears the name Bain de pieds des carriers or the Quarrymen's Footbath. The descent to the footbath cuts through the Lower Lutetian limestone allowing the age's precise identification. We'll visit the footbath on post Part II, when we investigate the subterranean catacombs of Paris.

MOULIN DE LA GALETTE - THE MILL OF GALETTE
Perched high above Paris on "La Butte" of Montmartre stands a windmill called le Moulin de la Galette or the Mill of Galette. More precisely a cluster of windmills that any one in in particular, it was built in 1717. The name is derived from a “galette” - a flat crusty tart baked by the Debray family, the mill’s nineteenth century owners and millers.

Along with le Moulin de Radet down the street and Moulin a Poivre nearby, they were the last of perhaps thirty (the numbers vary in the literature) that once dominated the heights of Montmartre, a once pastoral village dotted with vineyards on the northern outskirts of Paris and now a heavily touristed, upscale residential district of the city.

The windmill was also known as the Blute-Fin - from the French verb “bluter” which means to sift flour. In addition to grinding corn and grains, and crushing grapes and flowers, many of the mills crushed gypsum into a fine powder for the making of plaster of Paris.




The Mill of Montmartre
In the first quarter of the nineteenth century, bucolic Montmartre
was a picturesque Paris suburb of windmills and vineyards.
Georges Michel, oil on canvas, ca. 1820


Moulin de la Galette and Moulin de Radet on Rue Lepic near the end of the nineteenth century
Public Domain

According to French history, four Debray family men were involved in defending Montmartre and Paris against the invading Cossacks in 1814. Three were killed and one was quartered and nailed to the blades of the windmill. So the legend goes. The surviving fourth transformed the windmill into the Blute-Fin. The family is buried in the butte's small cemetery with small red windmills marking their graves, a fitting memorial to their nationalistic pride. 

As we shall see, the Impressionist artists turned their attention to the windmills of Montmartre, joining the tradition of a cadre of great masters in celebrating an iconic image of Bohemian Paris. Today, the windmill stands as a French national monument with a great story to tell - one where history, politics, philosophy, art and even geology come together.


Moulin de Radet, a few doors down Rue Lepic from Moulin de la Galette


THE GYPSUM OF MONTMARTRE
The country village of Montmartre arose on a 420-foot butte above Paris, which served to isolate it from Paris - for a time. Its core contained extensive deposits of layered gypsum - "gypse" in French - derived during the Lutetian Age that played into the history of the region. The word gypsum is a contraction of two Greek words, "ge" for earth and "epsun" meaning to concoct. The soft mineral was sought after throughout Europe and across the Atlantic in the 18th and 19th centuries. For it was gypsum that was processed into plaster of Paris. 


Entrance to a quarry at the foot of Montmartre in 1832
Artist unknown
 
Photograph of visitors to a Montmartre quarry
The "room and pillar" mining method (piliers tournes), by excavating the deposits into a cathedral-like vault, reinforced the ceiling with a supportive buttress. Given gypsum's fragility, due to its water-solubility and mechanically weak nature, street and house collapses were common. A famous accident occurred in 1778 where horses, wagons and people were engulfed. Regulations and edicts followed with the establishment of the position of Inspector of the Quarries by King Louis XVI, who's responsibility was to map and reinforce the quarries. Note the stratification of the gypsum, marl and sand in the quarry walls, referred to as "masses" in the geological French literature. The average mass of gypsum was about 5 to 20 meters thick. Limestone is buried below the gypsum and is prominent in Paris.
 
The gypsum quarries of Montmartre on the Right Bank (and as we shall see later, the limestone quarries of the Left Bank) literally riddle the depths of Paris. Since the time of the Romans, Montmartre has been heavily quarried. Mechanically weak and highly soluble, gypsum offers no resistance to cave-ins and is a great impediment to construction. Even over a century after the mines closed, many areas remained unbuildable.



Cathedral-like vault in a Montmartre gypsum quarry with wooden shorings to prevent collapse


When visitors approach Paris from a distance, one of the most conspicuous buildings they see is the Basilica of Sacre Cour, dedicated to the Sacred Heart of Jesus, on the summit of Montmartre built between 1875 and 1914. The absence of large surrounding structures isn't because developers desired to maintain Montmartre's rustic ambiance. It's because the undermined, gypsum terrain is unsuitable to withstand the weight. To overcome the obstacle, the travertine of Sacre Cour required specially deep foundations during its construction to secure it from collapse.



Seen from the top of the Eiffel Tower, the Basilique du Sacre-Cour towers over the Butte Montmartre. By the way, Montmartre is thought to have derived its name either from the Romans, who called it Mont de Mars (in French), or the early Christians, who called it Mont des Martyrs for Saint Denis who was arrested and beheaded at the top of the hill in the third century. On the site before the construction of the basilica, the Abbey of Montmartre built in 1113 used the early windmills of Montmartre to crush grapes for winemaking that were grown in the vineyards that covered the hill in the 16th century. 


FROM MINE TO MARKET
After removal from the quarries, gypsum was heated in kilns at 300ยบ F to drive off water and brought up the road on wagons pulled by donkeys or oxen to the mills for grinding. Romantic and colorful images of the early mining and milling days of Montmartre were created by a cadre of impressionist artists that gravitated to the area not only to paint but make residence. They document the pastoral nature of Montmartre, its windmills on the heights and the quarries below.




Early Windmills and Montmartre Quarry
Artist and source unknown


Montmartre the Quarry and Windmills
Vincent van Gogh, oil on canvas, 1886 


After milling, the calcined ground gypsum was bagged and sent downhill by wagon on its way to global markets via the River Seine. At the foot of Montmartre, it passed through the Barriere Blanche or White Barrier, a gate built for the collection of taxes for goods such as plaster coming into the city of Paris and named for the white powder that spilled from the wagons on the facades of buildings and the roadway.

Later, the gate became the Place Blanche or White Plaza. Even the Paris Metro train station is called Blanche. Francophiles will recognize the plaza as the location of the Moulin de la Galette-inspired Moulin Rouge or Red Mill. The faux-mill was a fashionable cabaret that opened at the foot of the Montmartre hill in the red-light district in the late nineteenth century and home of the anatomy-revealing can-can dance. And nearby at the top of the Rue Lepic on Montmartre, the historic Moulin de la Galette is still open for business as a restaurant.



At the Moulin Rouge, the Dance
Henri de Toulouse-Latrec, oil on canvas, 1880 


The impact of geology on the evolution of Parisian history acted in both subtle and obvious ways - the butte location of Montmartre (which has also served as a strategic military location), its gypsum-grinding windmills, and the establishment of Montmartre's artistic heritage based on its geographic and political location and isolation.     

PLASTER OF PARIS, FRANCE
When water is re-added to heat-calcined gypsum, it forms a hard setting paste - a calcium sulphate hemi-hydrate or plaster of Paris. The compound is a non-combustible, natural fire retardant and insulator that absorbs heat and only releases water vapor in a fire. It was not only used on building facades but as a stone mortar by the Romans in the first century. It was also a sculpting material and used for decorative architectural purposes on tiles and frescoes dating back as far as the ancient Egyptians and Mesopotamian cultures.


Paris escaped devastating urban fires since the late Middle Ages, in part because of plaster on interior and exterior walls. One year after the Great Fire of London in 1666, French King Louis XIV decreed that timber-framed structures were to be covered with plaster. That put Montmartre and its gypsum deposits on the map, but it was Louis-Napoleon Bonaparte, later to become Emperor Napoleon III and the nephew of Napoleon Bonaparte, that took the city of Paris and Montmartre in a completely different direction.



In this 1820 view of the butte of Montmartre, urbanization has already begun, yet the gypsum quarries, both open and underground, were still present. Off to the left you can make out two windmills. Mining would change under the reign of Napoleon III.


QUEST TO BUILD A MODERN METROPOLIS OUT OF A MEDIEVAL CITY
In 1848, Louis-Napoleon arrived in Paris from London at forty years of age. After a family exile of thirty-three years, he brought back his architectural experience of Europe's grand cities and envisioned the same for Paris. After becoming the first president of France in 1853, Napoleon and his appointed Prefect of the Seine, Georges-Eugene Haussmann, initiated a seventeen year plan of radical demolition and extensive reconstruction of the city of Paris. Napoleon's quest to build a modern European French capitol had begun, and its buildings and monuments would rise out of the limestone buried beneath the city.


Percement de l'avenue de l'Opera in Paris awaits demolition
Photograph by Charles Marville, Napoleon III's official photographer of Paris beginning in 1862 to document the "Haussmannization" of Paris. Marville excelled at architectural photographs and poetic urban views, capturing everything from Paris's oldest quarters, narrow streets, buildings, monuments and gardens to lampposts and urinals. Marville captured the transition from the Old Paris to the New. The emptiness of the streets is very misleading, because in all likelihood, it was filled with people and vehicles. The long exposure times necessary to capture the image on a negative failed to preserve any transient passersby.

The "Old" Paris of crowded, dangerous, filthy, disease-infested, narrow labyrinthine streets was razed and transformed into a modern "New" Paris of broadly radiating boulevards, elegant parks, public buildings, private palaces, apartment complexes, ornate fountains, decorated bridges, reliable water, sewer systems, facade-standardized buildings, railroads, gas street lamps and even public urinals for men - essentially the modern Paris of today.  

"Paris is an immense workshop of putrefaction, where misery, pestilence
and sickness work in concert, where sunlight and air rarely penetrate.
Paris is a terrible place where plants shrivel and perish, and where,
of seven small infants, four die during the course of the year."
Considerant, French social reformer, 1845




Paris Street, Rainy Day
This 1877 oil of Gustave Caillebotte is a snapshot of Haussmann's elegantly rebuilt Paris with its exaggerated, plunging perspective and flat colors. Notice the broad avenues lined by monumental canyons of facade-alike buildings topped by mansard roofs and anonymous, well-to-do (notice the pearl earring) Parisians strolling along in the rain (called flaneur, a stroller with rich connotations). Caillebotte was a member of the upper class and an Impressionist, although his short brushstrokes are barely visible. About the "new" Paris, historians believe that an additional motivation for the new street design was to facilitate the movement of troops and make the city revolution-proof. What renovation surely did was to displace the working class to outlying villages such as Montmartre, an event that, in part, facilitated the advancement of impressionistic art on the Parisian scene. Although the razing of Paris in a sense brought the impressionists together in Montmartre, they were detached by the social upheaval and physical destruction of Paris. Napoleon eventually fired Haussmann in 1870, who was criticized for the immense cost of the project.


THE GEOGRAPHIC ISOLATION OF LA BUTTE DE MONTMARTRE
Reminiscent of Greenwich Village, a former bohemian haven and now upper-class neighborhood in New York City, Montmartre's autonomy as a country village has survived, in part, by virtue of its isolated geography having been a train ride or one hour walk from center Paris up the heights, as well as having escaped Haussmann's radical renovation.

Montmartre was outside the Mur des Fermiers generaux (the Wall of the Farmers-General), a 28 km long, physical and fiscal barrier that surrounded Paris built by King Louis XVI between 1784 and 1791. Rather than acting as a defensive barrier against invasion, unpopular entry tolls were extracted and duties were levied on goods entering the city (called "octroi") at various point along the wall. The wall contained 47 gates and 16 tollhouses, many with architectural merit. Interestingly, some portions of the wall still exist as an elevated roadway and four tollhouses remain. We'll enter one in my Post II at the Barriere d'Enfer on the Left Bank and descend into the limestone quarries beneath the streets of Paris. 


Map of Paris (pink) and environs (tan) in 1841, sliced in two by the west flowing River Seine. 
The larger, outer 33 km enclosure (red) is the defensive Thiers Wall constructed between 1841 and 1844, whereas the inner enclosure is the Wall of the Farmers-General constructed between 1784 and 1791. The two arrows mark the locations of gypsum quarries in the villages of Montmartre and Bellville outside the Farmers-General wall. The majority of the toll barriers were destroyed during Napoleon III's expansion of Paris in 1860. Notice the meandering course of the river within the sedimentary basin of Paris (Bassin de Paris).


WORKING CLASS EXODUS
Unable or unwilling to pay the entry taxes and displaced by Haussmann's city-wide renovation, thousands of the less well-healed working class of laborers, farmers, seamstresses, milliners, students and artists departed from Paris. Outside the customs barriers and the taxman's reach, Montmartre's quiet streets and low rents made it a melting pot for free-thinking bohemians, dissident politicians and the young avant-garde.

As for the fourteen windmills on the hill, they had less to grind. The gypsum quarries closed in 1860, the same year that Montmartre was annexed to Paris with the destruction of its walled enclosure. Today, Montmartre is within the 18th arrondissement - Paris's clockwise spiral of municipal districts - yet still retains its medieval, narrow maze of streets in contrast to the "new" Paris in the flats below the butte.


Looking down a steep Montmartre street from Rue Lepic toward the flat terrain of Paris, the Moulin de Radet is directly behind. The gold dome in the distance is L'Hotel National des Invalides across the Seine. The complex was a hospital and retirement home for disabled war veterans built by King Louis XIV in 1670. Today, it's a military museum and burial site for Napoleon Bonaparte. Out of view, the Eiffel Tower is off to the right. 


A TALE OF TWO CITIES - ONE A MODERN METROPOLIS AND THE OTHER A STRONGHOLD OF CREATIVITY
As for the Moulin de la Galette, it was repurposed by the Debray family into a "guinguette," after a sour local white wine called "ginguet". Guinguettes were colorful, outdoor, raucous establishments for eating, drinking, laughing and enjoying life and nightlife. It was where bourgeois (middle class) patrons from Paris could rub elbows with prostitutes. It was where dancing was allowed where you could touch your partner!

Furthermore, it had an even greater impact as a place where Paris's displaced intellectuals, artists, writers, poets, musicians, sculptors and architects gathered. The impressionist paintings of carefree Parisians enjoying Montmartre by artists such as Renoir, van Gogh, Degas, Picasso, Modigliani, Utrillo, Toulouse-Lautrec and others documented the evolution of the two cities and even their geological histories.



Bal (dance) du Moulin de la Galette
Renoir depicted cheerful and carefree, middle-class Parisians wearing their Sunday best, enjoying life in the guinguette of Moulin de la Gallette. With music played by a ten-man band, not only modest quadrilles were danced where only hand-touching was allowed, but patrons danced the Viennese waltz with real bodily contact. He was the first artist to transfer a scene of everyday life to a large canvas with brushstrokes that could be seen in the style of the impressionists. Classical artists before this time painted only biblical, mythological and heroic events of times gone by.
Pierre-Auguste Renoir, oil on canvas, 1876.


LES GYPSE ET CALCAIRE DES CARRIERES DE PARIS - THE GYPSUM AND LIMESTONE QUARRIES OF PARIS
Sedimentary deposits of gypsum were generally located in the north and northeast quarters of Paris, mainly in the neighborhoods of Montmartre, Buttes-Chaumont, Charonne and Menilmontant. Gypsum is present in South Paris across the river but in thinner deposits. On the map (below) of the "Old Quarries of Paris," the two main quarries of gypsum (green shaded) are identified by arrows in the villages of Montmartre on the left and Belleville on the right, both on the Right Bank (north side) of the River Seine.




Stratigraphic Map of Paris
In 1811, Georges Cuvier's (early nineteenth century founder of vertebrate paleontology) and Alexandre Brongniart's (scientist and mining engineer) stratigraphic portrayal of the Paris Basin in the region of Paris. With colors, they identified layers of limestone (craie and calcaire), gypsum (gypse) and marine marls (marnes). Their discoveries proved that the stratal formations in the Paris Basin had been deposited in alternating fresh and saltwater conditions, implying the existence of inland seas at various times in the remote history of the region. Although Cuvier's concepts of evolution were catastrophic with new species forming after Noah's Flood, his concepts of biostratigraphy were ground breaking (pun intended).

The gypsum that was quarried in Paris's northern tier was called ludium gypsum in strata separate and above that of limestone in the southern tier called lutetian limestone. Before the initiation of limestone formation, 50 million years ago, deformation elevated the southern portion of the Paris Basin. The sea repeatedly transgressed and regressed over the region forming carbonate banks. Once elevated, a crustal fold confined sea water to lagunas that formed evaporites of gypsum in layers. The geological fold - called the Ypresian fold - acted as a dam on the upper plateau south of Paris. The contemporary result was high concentrations of gypsum in the subsurface and limestone to the south near the surface (20 to 30 m).


In French, the four masses of gypsum found in the northern tier of Paris
Gypsum has a high solubility, but its presence was protected from dissolution by a thick overburden of clay. Each of the four deposits received a colorful name by the quarrymen: les fleurs (the flowers), le gros cul (the big ass), les foies de cochon (pig livers) and les pots a beure (butter pot) or les crottes d'anes (donkey droppings).
From exploration.urban,free,fr
 

ANCIENNES CARRIERES DE PARIS - OLD QUARRIES OF PARIS
Across the River Seine from Montmartre that slices Paris into its two famous banks, the Left Bank was open-pit mined for its "coarse" limestone (calcaire grossiersince Gallo-Roman times. In the 17th and 18th centuries, mining went underground, which honeycombed the depths of Paris even more than Montmartre with miles of subterranean (souterraines) quarries. As with gypsum, the deposits of limestone and their quarries have affected the historical, political, cultural and creative evolution of the city of Paris.


Ancient Gypsum and Limestone Quarries of Paris in 1908
The River Seine follows the trough of the Paris Basin to the Atlantic Ocean. In so doing, it divides Paris into an “elegant” Right Bank (Rive Droite) and a “bohemian” Left Bank (Rive Gauche). Green shading on the Right Bank indicates the underground mines of "gypse" or gypsum clustered at Montmartre (left arrow) and the village of Belleville (right arrow). The red shading, largely on the Left Bank, indicates the mining of "calcaire grossier" or coarse limestone. Modified from Wikipedia.


LE BASSIN DE PARIS - THE PARIS BASIN
More than just the immediate lowland around its namesake, the Paris Basin covers a vast portion of northern France – over 140,000 square kilometers - and measures 500 by 300 km. The basin extends northwestward below the English Channel into the London Basin and connects to the Belgium Basin to the north - summarily referred to as the Anglo-Paris Basin.

Simplified Geologic Map of Europe Showing the Main Orogenic Systems and Sedimentary Basins
From Geology of Europe by Franz Neubauer


The 776 km Seine River and its tributaries drain the basin and slice Paris into its two famous banks – Left and Right for south and north. The basin recharges along its eastern border and discharges to the English Channel’s seafloor at Le Havre, Normandy.








ORIGIN AND EVOLUTION OF THE PARIS BASIN
Geologically, the Paris Basin is an intracratonic (intraplate) sedimentary trough of flat valleys and low plateaus built on a collapsed Variscan collisional belt. The depocenter resides on an extended continental shelf (epicontinental) that has been periodically invaded by marine high seas. It's built on a Cadomian-Variscan crystalline foundation
surrounded by crystalline highs of late Paleozoic age. Its tectono-sedimentary evolution is related to the paleogeography of the Variscan orogeny and the geometry of the resulting structural pattern. How did the complex geology of the Paris Basin originate in France?


Topographic Satellite Image of France
The upper central portion of the satellite photo is dominated by the Paris Basin and the Seine River and its tributaries. Paris is located at the red dot.
NASA Visible Earth Image Courtesy of Shuttle Radar Topography Mission Team


The Paris Basin's genesis is tectonically challenging to grasp with many aspects that are strongly debated. For clarity (I hope), I arbitrarily divided the events into the following stages: (1) Acquisition of Cadomian basement; (2) Avalonia-type terranes accrete to Laurentia; (3) Cadomia-type terranes accrete to Laurussia; (4) Variscan orogeny forms Gondwana Europe within Pangaea; (5) Post-Variscan extension creates epicontinental depocenters; (6) Pangaean fragmentation sends many peri-Gondwanan terranes adrift as high seas repeatedly flood Europe; (7) Crush of the Alpine orgogeny.

(1) Acquisition of Cadomian basement rocks
The break-up of the supercontinent of Rodinia in the latest Proterozoic to Early Cambrian (ca. 0.75 Ga) resulted in the formation of three large mega-continents, numerous diminutive landmasses and a plethora of microterranes. The big three (below) were: Laurentia and Baltica located equatorially and massive Gondwana sprawling australly. An elongate assemblage of island-arc, microterranes of Rodinian ancestry attached to the northern margin of West Gondwana during the Cadomian orogeny. The ribbon of amalgamated terranes is also called a superterrane named for their ultimate destinations.






Late Proterozoic Reconstruction of the Southern Hemisphere
In the latest Proterozoic (550 Ma), Rodinia has fragmented apart forming Laurentia (North America), Baltica (northern Europe) and Gondwana (mostly our South Hemispheric continents) with the opening of the Iapetus Ocean. The peri-Gondwanan terranes of Avalonia, Armorica and others have assembled on the northern Gondwana margin from the craton of Amazonia to West Africa. Many aspects of these paleographic reconstructions are subject to intense debate and ongoing investigation.
Modified from Cocks and Torvik, 2006.

Facing the newly opened Iapetus Ocean (more so as Baltica drifts to the north), these “peri-Gondwanan” terranes are categorized as largely Avalonian-type and Cadomian-type, which designates their future accretionary destiny after separating, rifting and drifting from Gondwana. One author's interpretation (below) adds the Serindia-type terrane for regions of North China. The Cadomian terranes eventually formed a portion of France's basement carrying its earlier Rodinia rocks in transit. Typical of tectonic processes, plate collisions transport, reimprint and rework their crust.


Early Ordovician (490 Ma) South Hemispheric Reconstruction of the North Margin of West Gondwana
This ambitious reconstruction depicts a ribbon-like superterrane, that throughout the Paleozoic beginning in the Devonian, will rift from the northern margin of West Gondwana (at the Amazonia craton of South America and the West Africa craton) and collide with Laurentia and Baltica. Avalonia will depart first closing the Iapetus Ocean and Cadomia second, closing the Rheic Ocean along with the remaining mass of Gondwana. Note that based on paleomagnetic and paleontological data, Armorica (which will form western France) is placed on Gondwana, which appears to remain attached before the Early Devonian. See the paper referenced below for the complete terrane legend in the diagram.
Modified from Stampfli et al, 2002.


(2) Avalon-type terranes accrete to Laurentia
Although this stage is not germane to the formation of the Paris Basin, my explanation would be incomplete without commenting on the Avalonia terrane. Throughout Paleozoic time in what's called the "supercontinental cycle," the Gondwana-derived basement blocks sequentially reassembled to form the supercontinent of Pangaea. During the Acadian-Caledonian orogeny (Ordovician to Early Devonian), the Avalonian-type terranes rifted from Gondawana, drifted across the Iapetus Ocean as it closed, and accreted to eastern Laurentia (early or proto-North America). Following the Silurian closure of the Iapetus Ocean, mountains were built from northeastern Laurentia into Scandinavia and parts of north-central Europe. The black outline of the modern continents can be differentiated on the map. At this time, the Cadomia-type terranes remained attached to Gondwana.

Jumping ahead briefly, when Pangaea later fragmented apart (just as Rodinia previously did), the Avalonia terranes would separate between North America and Europe across the Atlantic Ocean. As a result, we occasionally use the terms of West Avalonia (for the Canadian Maritimes and down the east coast of North America) and East Avalonia (for southern Britain and the Brabant Massif into parts of northern Germany). When new landmasses (and even ocean basins) form and reform, geologists use new names to identify them in time - similar to new countries that are renamed by their new political leaders.


Latest Ordovician Reconstruction of the Southern Hemisphere
In the latest Ordovician-Earliest Silurian (440 Ma), Avalonia (both West and East reside at left arrow) has previously rifted from the northern margin of Gondwana, drifted across the closing Iapetus Ocean and is about to collide with Baltica and Laurentia during the Acadian-Caledonide orogeny. The main body of South Polar Gondwana is in the process of traversing a diminishing Rheic Ocean. The Cadomian-type terranes (right arrow) are still docked on the margin of Gondwana.
Modified from Cocks and Torsvik, 2006.

(3) Cadomia-type terranes accrete to Laurussia - France's basement!
By the Permian, the main mass of Gondwana collided with Laurussia (Laurentia + Baltica + Avalonia) in the Ouachita-Alleghenian-Variscan orogeny and assembled the supercontinent of Pangaea. The resulting mountain belt was the largest collisional orogen of the Paleozoic. In Europe, it produced a suture from Germany (Mid-German Crystalline zone) through southern Britain (Lizard ophiolite) through France to southern Iberia (Pulo do Lobo unit). Hence, the Rheic suture separates the Cadomian terranes of western and central Europe from the terranes derived from East Avalonia in Britain.

The closure of the intervening Rheic Ocean (recall that the Iapetus Ocean closed with the Avalonia collision!) brought the Cadomian-type terranes of Gondwana into contact with Laurussia (red arrow) during the Variscan orogeny (formerly Hercynian). The Variscan and Alleghenian orogenies were contemporaneous and more-or-less physically contiguous. The collision of a Gondwana-derived Europe was forming on Laurussian soil! France was never before so close to French Canada!




Mississippian Reconstruction of the Southern Hemisphere
In this Mississippian view (340 Ma), the Cadomian-type terranes (arrow) have rifted from the main body of Gondwana and will collide with Laurussia along with Gondwana (to follow) during the Ouachita-Alleghenian-Variscan orogeny. Gondwana's collision formed Pangaea at the expense of the Rheic Ocean. The basement terranes of Europe have now formed - a Gondwana Europe. The only thing left to do is get them across the Atlantic Ocean, which will soon form.
Modified from Cocks and Torsvik, 2006.


(4) Variscan orogeny froms Gondwana Europe wihtin Pangaea
The Variscan orogeny is building a Gondwana European basement within Pangaea. Its formation left Variscan orogenic remnants and a montage of Cadomian terranes in France and central Europe. As with East Avalonia in southern Britain, Europe's Cadomian basement ended up across the Atlantic when Pangaea fragmented apart.

Early Permian (280 Ma) Timeslice of Pangaea and Ouachita-Alleghenian-Varsican Orogeny
Pangaea has fully formed with the collision of Gondwana and Laurentia (actually Laurussia). The Cadomian terranes terranes have accreted in the Variscan orogeny to Laurussia. The Ouachita-Alleghenian-Variscan orogeny is fully underway building the Appalachian Mountain chain in North America. The collision will distribute remnants of the Variscan orogen in France and Europe, and around the Paris Basin, which is about to form in a fore-arc, extensional regime.
Modified from Ron Blakey and Colorado Plateau Geosystems, Inc.
 
The Paris Basin has tectonically-acquired its Cadomian-Variscan crystalline basement. Europe's cratonic platform is comprised of a montage of terranes and fault-bounded blocks of continental crust with Avalonian and Cadomian ancestry - a Gondwanan-derived Europe of recycled Precambrian and Cambrian crust. The principal ones that now form Europe are Avalonia, the Rheno-Hercynian Terrane, the Armorican Terrane assemblage, Perunica, Apulia, Adria, the Hellenic terrane and Moesia - all peri-Gondwanan terranes with the exception of Baltica-derived Scandinavia.

A European Collage of Amalgamated Gondwana-derived, Avalonia and Cadomia-type Terranes
This map demonstrates the complex accretion history of Europe. For reference, Paris is at the red dot.
Modified from Ballevre et al, 2008.


(5) Post-Variscan extension creates epicontinental depocenters - and the Paris Basin!
Following the Permian consolidation of Pangaea, the supercontinent began to fragment apart. The re-activation of pre-exisiting Variscan compressional faults formed new, extensional back-arc rifts in late Permian through Triassic times. In the Triassic, extension led to the opening of oceanic marginal basins. This allowed the development of numerous European sedimentary basins including the Paris Basin in Gondwana Europe. Europe has not yet formed and will not be called as such, geologically, until Pangaea fragments aparts and sends parts of the Avalonia terrane and the entirety of the Cadomia terrane across the Atlantic Ocean.

Early Jurassic Timeslice (200 Ma)
The Varsican orogen has left remnants in what will become France and central Europe. Extension within the Variscan's fore-arc regime has already begun to flood with waters from the newly opening North Atlantic Ocean. As the mid-Atlantic Ridge widens and Pangaea continues to fragment apart, Europe and Africa will reside on their own tectonic plates and France will have acquired its Paris Basin.
Modified from Ron Blakey and Colorado Plateau Geosystems, Inc.


(6) Pangaea rifts apart sending select peri-Gondwanan terranes across the Atlantic as high seas repeatedly flood Europe
As Pangaea's break up progressed, the Eurasian-North American plates drifted apart sending East Avalonia and the Cadomian terranes across the Atlantic. At the same time while in tectonic-transport, crustal extension continued across Europe with the establishment of a broad, open shelf that occupied much of southern Germany, the North Sea and the Paris Basin. Most of the Paris Basin became emergent near the end of Jurassic time, a relict appendage of the large Triassic German basin.

Late Cretaceous Timeslice (75 Ma)
The nascent Atlantic Ocean has begun to separate in the north at the Mid-Atlantic Ridge. The tectonic plates of North America and Eurasia are separating. Europe and Africa have formed but are submerged by global high seas. The region of the epicontinental Anglo-Paris Basin is fully submerged,one of many eustatic events that will contirbute to sediment deposition into the many basins of Europe. Notice the various Variscan orogenic remnants distributed about western Europe - France, Spain and Portugal in particular.
Modified from Ron Blakey and Colorado Plateau Geosystems, Inc.

Today, the Paris Basin is surrounded by outcrops of four Variscan massifs, relics of the Variscan mountain chain: the Armorican Massif in the west, the Central Massif in the south, the Vosges in the east, and the Ardennes in the northeast.

Paris within the Paris Basin Surrounded by Remnants of the Variscan Orogen
From CNAM / MNHN: SGF "The Parisian basement: quarries, underground projects and the Grand Paris"
by J.-P. Gely, 2013


(7) Marine seas repeatedly flood epicontinental Europe
The opening of the Atlantic Ocean, beginning in the Cenozoic, had a profound affect on the neighboring North America and Eurasian plates. The main process was a general extensional stretching that produced numerous marginal basins and grabens. Large quantities of clastic materials were deposited in repeated transgression-regressions of the sea within the many depocenters that trended pre-existing structural directions.

In France within the Paris Basin, during the Late Triassic, siliciclastics were deposited; Jurassic Liassic-time organic-rich black shales, Dogger carbonates and Malm-time clays. The return of the sea in Cretaceous time deposited chalk. Basin sedimentation continued into the Tertiary. With particular interest to this post is the Lutetian age of the Eocene (Tertiaire on the map below and diagram below) with a shallow-water environment conducive to the formation of limestone and evaporite deposits of gypsum.

Simplified Map of France and the Paris Basin
 
Geologic Cross Section through the Paris Basin
Modified from Beccaletto et al, 2011.

(8) Alpine orgogeny shapes and confines the Paris Basin
The Paris Basin took on its present shape following uplift of the surrounding basement blocks during the Alpine orogeny. The collision occurred between the Africa and Eurasia plates and included the subduction of the intervening Tethyan Ocean. The Alpine orogeny is considered the third major collision to define the geology of Europe in the Late Cretaceous through Recent, along with the previously discussed Caledonian and Variscan orogenies. In addition to creating Alpine mountain plate across Europe and into Asia, it regionally caused northwest-southeast compression of the Paris Basin and formed anticlines along genetically-related, basement fault systems. The widespread uplift inverted many basins and served to isolate the Paris Basin. The uplift also profoundly effected the fluvial systems with drainage lines occurring along structural elements. 

THE PARK OF BUTTES-CHAUMONT - A GREEN SPACE UNLIKE ANY OTHER
We have one more important gypsum-mining area to discuss located about two miles east of the Montmartre quarries. Like Montmartre, the quarry is inactive and unrecognizable. Inaugurated in 1867 and coinciding with the opening of the World's Fair in Paris, les Parc des Buttes-Chaumont occupies the site between the villages of Belleville and La Villette (right arrow above) in the 19th arrondissement.

Butte is French for “mound,” and Chaumont is a 9th century contraction of “chauve” meaning bald and “mont” meaning mount. The "Bald Mount" acquired its name from its lack of vegetation due to an abundance of clay and gypsum in the soil.


View of Park of Buttes-Chaumont from the promenade looking north toward the lake and the temple. The residential quarter of La Villette is in the background.


"URBAN NATURE"
In spite of its most austere beginnings, today the park is a major local attraction replete with a rocky island topped by a romantic shrine in the middle of a picturesque artificial lake. Evocative of the Alps, it occupies 25 hectares and is the fifth largest park in Paris. Its grounds are overflowing with ornamental trees, waterbirds, and within the lake, an abundance of fish. From a bleak gypsum quarry to an iconic urban park, the history of its metamorphosis is beyond anything imaginable. 


The Temple of Sibylle in the Park of the Buttes-Chaumont
A tonemapped, High Dynamic Range Photo 

A LUNAR LANDSCAPE WITH A SINISTER AND MOST PUTRID REPUTATION
The area of the park, being just outside the limits of the toll barrier wall, was mined for gypsum for centuries as was the Butte Montmartre. It was close to the site of the Gibet of Montfaucon, a notorious and malodorous place where 80 condemned men and women could be executed at the gallows simultaneously and their bodies left to dangle on display as a deterrent to crime well after their executions. Later, the desolate quarry became a public waste refuse and sewage dump, and even an abattoir (slaughterhouse) for horses where the remains were left to decompose. The quarry also had an unsavory reputation for harboring thieves and as a shelter for the destitute. It took a tremendous imagination to envision a park on this impoverished site. 


Photo of the America Quarries by Charles Marville along Rue de Mexico before 1877
 So much gypsum was shipped to Louisiana that the quarry was called the America Quarry. According to urban legend, the quarry provided gypsum to the United States for building the White House, but in fact it was used for domestic construction. When Marville made this photograph, the quarry was still in operation, but it closed by the 1880's. Notice the buildings of La Villette virtually next to the quarry off to the right. Once again, the only people visible are those that are stationary for the long exposure.
 
The quarry photographed by Henri le Secq in 1863 showed a desolate, pockmarked lunar-landscape sandwiched between the villages of Belleville and La Villette.
 

The site "spread infectious emanations not only to the neighboring areas, but, following the direction of the wind, over the entire city" (Alphand). Amazingly, this most desolate wasteland was transformed into a spectacular garden park as part of the new Paris of the Second Empire.


Left: Gibet de Montfaucon, 1811.                                    Right: 1811 Rendering horses
From an article by Francois Choay in the Urban Park magazine, 29, 1975.


"A DELICIOUS OASIS" (GUIDE DU PROMENEUR, 1867)
This not so promising site, to say the least, was envisioned by Napoleon III as a romantic garden showcase befitting a capital. Chosen and conceived by his prefect, Baron Haussmann, it was to be the site of a park for the recreation and pleasure of the rapidly growing population of the 19th and 20th arrondissement - the working class of the petit bourgeoisie. Jean-Charles Adolphe Alphand was the chosen landscape engineer to 
personally execute the remarkable transformation.


A plan of the Parc des Buttes-Chaumont
Note the promenades, belvedere, restaurants, artificial lake, central island and its rotunda. A railroad (left) was constructed to bring in soil and supplies. The grotto is at the top center. 


When Napolean III became emperor in 1852, Paris had only four public parks, all in the center of the city. His vision changed parks such as the Buttes-Chaumont that were not longer the preserve of aristocratic or royal landowners but were open to the public at large. Through their collaboration, what resulted was one of the crowning achievements of the Second Empire as part of the radical renovation that swept through Paris.


The quarry cliffs likely photographed by Charles Marville around 1865. The key features of the park are beginning to emerge -the gorge-spanning brick bridge and a section of the quarry above what is to be the lake.


GLAMOUR FROM DECAY
Beginning in 1864, two years were spent in terracing the land. Railroad tracks were laid to bring in 200,000 cubic meters of topsoil. A thousand workers renovated the landscape, digging a lake and contouring the grounds with rambling lawns, gently sloping hillsides, splendid vistas and shaded strolling paths.


The plan of the park created by Alphand and photographed by Marville. Again, notice the promenades, the carefully landscaped terrain, a restaurant, the supply railroad, the lake, island and temple at the summit.


NATURE TECHNOLOGICALLY REINVENTED FOR THE PETITE BOURGEOISIE
Explosives were used to sculpt the gypsum buttes and former quarry into a small mountain 50 meters high on a rocky island surrounded by cliffs. In a corner of the park, a spacious grotto was fashioned with a cathedral-like vault remniscent of the interiors of gypsum quarries seen at Montmartre. Its ceiling was decorated with artifical stalactites. Even a hydraulically-pumped waterfall cascaded into a stepping-stone lined pool that flowed out of the grottoes second opening. And everywhere, mosses and vines hung its walls.


Outside view of the grotto from the walking path

Engineered Nature
View of the inside of the grotto with its contrived waterfall, reflecting pool and faux stalactites

The ceiling of the grotto with its faux stalactites and skylight. No bats in this place!

Even the stone railings that line the paths of the park are faux bois or fake wood intricately stylized with cut branches, bark, leaves and knots, all cast in recently-perfected concrete almost 150 years ago.

The Roman temple at the top of the promontory was modelled after the Temple of Vesta in Tivoli, Italy


Two bridges reach the center island - a 63 meter-long, red metal suspension bridge by Gustave Eiffel, the designer of the Eiffel Tower, and a twelve meter-long masonry bridge, known as the "suicide bridge." Unnoticed by most passersby, the alternating layers of gypsum, marl and sandstone are on display on the excavated quarry-flanks of the mountain.  




IN CONCLUSION
It comes as no surprise, certainly amongst geologists who are acutely aware of these things, that geology has a profound affect on the evolution of civilizations, cultures and societies. We have seen on our brief visit to Paris how its geography and deposits of gypsum have shaped the history of politics, philosophy and art within the city and around the world.

In my next post Part II on the Geological Legacies of the Paris Basin, we will see the affect that deposits of limestone had on the city of Paris. We'll also descend into the dimly-lit catacombs beneath the streets of Paris and explore the infamous ossuaries where 6,000,000 exhumed skeletons from the eighteenth century are interred.

HELPFUL RESOURCES
European Geography in a Global Context from the Vendian to the End of the Paleozoic by Cocks and Torsvik, 2006.
Impressionism - 50 Paintings You Should Know by Ines Janet Engelman, 2010.
Middle Lutetian Climate in the Paris Basin: Implications for a Marine Hotspot of Paleodiversity by D. Huyghe et al, 2012 (on-line). 
Neoproterozoic-Early Cambrian Evolution of Peri-Gondwanan Terranes: Implications for Laurentia-Gondwana Connections by Murphy et al, 2003.
Paleography of Europe, DVD Collection, Ron Blakey, Colorado Plateau Geosystems, Arizona, USA.
Paleozoic Evolution of the Pre-Variscan Terranes: From Gondwana to the Variscan Collision by Stampfli et al, 2002.
Paleozoic History of the Armorican Massif by Michel Ballevre et al, 2008.
Paris Reborn - Napoleon III, Baron Haussmann and the Quest to Build a Modern City, by Stephane Kirkland, 2013.
The Formation of Pangaea bt G.M. Stampfli et al, 2013.
The Rheic Ocean: Origin, Evolution, and Significance by R. Damian Nance, 2008 (on-line).
Urban Design and Civic Spaces: Nature at the Parc des Buttes-Chaumont in Paris by Ulf Strohmayer, 2006 (on-line).
Vinvent van Gogh - Moulin de la Galette by Simon C. Dickinson, 1023 (PDF on-line).