Monday, December 29, 2008

Deccan Traps: A Different Take

At the recent 2008 AGU meeting in San Francisco, a long simmering controversy reared its head again.  Paleontologists Gerta Keller and Sunil Bajpai and geophysicist Vincent Courtillot presented evidence that India’s Deccan Traps, and not the Chicxlub meteor in Mexico, created the unhealthful conditions that led to the extinction of the dinosaurs.  Their data is thought provoking but what attracted my attention was Dr. Keller’s comment that much of their data came from quarries in the basalt.  

Erupted 65 million years ago, the Deccan Traps covers an area as large as Texas.  Geologists have estimated the volume at 1.2 million cubic kilometers, with nearly half lost to erosion.  The depth of the layers is more than 3,500 meters thick.  At AGU, Keller observed that the viscous basalt spewed forth in as little as 10,000 years. 

Basalt Quarry: Photo from Gerta Keller

The quarries that interest Keller and her colleagues are found in flows that oozed 800 kilometers across India to Rajahmundry, on India’s east coast.  They are the longest lava flows on Earth.  Dozens of quarries pockmark the Rajahmundry traps of the Deccan plateau.  (Trap refers to any dark colored igneous rock though it is most commonly associated with basalt; trap comes from the Swiss word for step.)  According to Dr. Keller, families and extended clans work most of the quarry sites by hand, using hammers and explosives.  Men break up the stone and women carry it out on their heads.  And in some cases, trucks transport rock to people’s homes and dump the material in their backyards, where they work on it. 


Worker at basalt quarry: Photo from Gerta Keller

Because the Rajahmundry basalt resists weathering, much of it goes for roads and to make train beds.  It is shipped to Europe and perhaps to the United States.  Basalt from other flows in India have been used as a building stone, though Dr. Keller did not know if the Rajahmundry stone had gone into buildings. 

The quarries have played an important role in Dr. Keller’s research because they expose the rocks that she has wanted to study.  In the quarries is evidence for shallow marine deposition, where marine microfossils were preserved.  These fossils have been essential to narrowing the date of Deccan Trap deposition and allowing Dr. Keller to further elaborate on her thesis. I am not qualified to say whether her theory is right or wrong, but the work raises some interesting questions and if Dr. Keller is right, you may want to give a second thought to the road you travel on.  It may contain evidence for the dinosaur’s demise.

 

 

 

Tuesday, December 23, 2008

Airport Fossils

Trapped at SeaTac Airport in Seattle with nothing to do?  I am sure the people stranded there would rather be someplace else but the extra time will allow intrepid travelers to explore the many fossils found in the walls of the food court in concourse A.  The fossils make a captivating cast of characters that lived 155 million years ago in what became Germany.  During the Jurassic Period when dinosaurs roamed the land, a shallow sea covered much of Europe.  Many critters from that sea are now preserved in the tan to gray limestone cladding walls at SeaTac. 

155-million-year old ammonite - Good examples are in the pillars just past the security check, particularly the one nearest Ex-Officio.

The stone is known as the Treuchtlingen Marble, although it is not marble but limestone.  It was never metamorphosed.  As the animals died they settled to the bottom of the sea.  The most common fossils are sponges, bottom dwelling, filter feeders that formed small mounds.  They may be round, straight, or irregularly shaped and are darker than the surrounding limestone.  Also common are ammonites, coiled-shell animals that resemble a top down view of a cinnamon roll.  The biggest ones in the German limestone are about five-inches across, whereas the largest ones that ever lived were six feet wide.  Ammonites were prevalent marine predators in the Jurassic but went extinct at the end of the Cretaceous.  Their modern relatives include squids, chambered nautiluses, and octopi.  

You can also find another squid relative, belemnites, which look like a cigar.  They are dark brown and somewhat shiny.  Also seek out brachiopods, clam-shaped animals known as lampshells due to their resemblance to ancient oil lamps.  Unlike clams, brachiopods cannot move and feed by opening their shell and consuming bits that float by.  And finally, the white specks that look like oatmeal are single-celled sea dwellers called foraminifera. I hope this at least helps some people pass the time at SeaTac.

Saturday, December 20, 2008

The Comstock King and Brownstone

“San Francisco’s crown in the matter of private architecture has rested on the brow of the city’s famous Nob Hill for the past 10 years but the brightest jewel in the setting is receiving its finishing polish,” appeared on page 4 of the May 9, 1886 New York Times.  The short article was referring to the mansion of James C. Flood, best known as one of the Nevada Comstock Kings.  His home was reportedly the most expensive private residence in America.  The reason was understandable—Flood’s 42-room estate was made of sandstone shipped around Cape Horn from Connecticut.  Total cost was $1.5 million and included a $30,000 bronze fence, which was rumored to be polished by a man whose sole job was to do so. 


Flood chose the red sandstone, better known as brownstone, because it was the stone of the wealthy.  William Vanderbilt, J.P. Morgan, and George Pullman all lived in brownstone homes, and brownstone was called an “almost proverbial synonym for all that is elegant and desirable.”  Tons and tons of brownstone was shipped as ballast around Cape Horn.  The 107 foot by 127 foot edifice featured 14 solid stone columns, 13 feet tall by 22 inches square, and 23-foot-long sandstone steps.  The biggest blocks each weighed 18 tons.

I have long wanted to see Mr. Flood's brownstone.  Skipping out on a few sessions at AGU allowed me to reach this goal. The mansion is rather handsome and very out of place on its block surrounded by gargantuan and mostly granite buildings.  And it is clear that no one has polished the bronze fence in decades. 

The main brownstone quarries were in Portland, Connecticut.  First used for building in the 1650s, brownstone started to spread widely in the late 1700s and reached a peak by the last decade of the 19th century.  Following devastating floods, the quarries shut down around 1936, but not before the removal of 10 million cubic yards of rock. 

From a geologic point of view, brownstone has long attracted attention.  The red sands were part of an extensive series of sediments deposited in rift basins formed 200 million years ago by the separation of North America and Africa and the incipient opening of the Atlantic Ocean.  These sediments record more than 35 million years of time and stretch from South Carolina to Newfoundland.  The sediments also preserved the tracks of thousands of dinosaurs that roamed the wet sands near streams and lakes in the basins.  More than 20,000 of these tracks, including the legendary Noah’s Raven, are now displayed at the Amherst Museum of Natural History. 

James Flood’s residence was the lone mansion on Nob Hill to survive the 1906 earthquake.  It was, however, only a shell as fire had burned out the interior.  Flood had died in 1889 and his daughter sold the gutted building to the Pacific Union Club.  They hired the architectural firm run by Daniel Burnham to redesign the mansion.  Ironically, Burnham was the architect of the World’s Columbian Exposition and its White City, which contributed to white stone replacing brownstone as a favored building material.  The Flood residence is listed on the National Register of Historic Places.  Only members and their guests are allowed in the building now.

 

Sunday, December 14, 2008

A Streetcar to Subduction

I wish I could lay claim to coming up with the title for this post, but I cannot. The title, officially Streetcar to Subduction and Other Plate Tectonic Trips by Public Transport in San Francisco, is from a wonderful paper by the late Clyde Wahrhaftig. Originally written for the AGU in 1979, the paper was updated in 1984. Wahrhaftig described six trips that one could take by public transport around San Francisco to see the area's geology. The rare and expensive booklet (six copies were available on amazon.com from between $60 to $130) is a pleasure to read, not only for the geology but also for Wahrhaftig's insights on history and architecture.

The J Church line is the so designated Streetcar to Subduction. With a little effort you can see pillow basalt, sandy turbidites, and radiolarian chert, basically a microcosm of typical oceanic crust. You can learn about how two high school student broke into the supposedly impregnable New Mint Building, just weeks after it opened, and you can learn to identify and avoid poison oak. On another route Wahrhaftig gives an introduction to San Francisco architecture and on one more he reveals how residents saved their houses during the post-1906 earthquake fire by soaking cloth in wine and spreading the material on their roofs. He also shows where to see serpentine throughout the city.

Born in Fresno, California in 1919, Wahrhaftig was an avid outdoor explorer and field geologist. He died in 1994; a thoughtful obituary is available on the UC Berkeley web site. He didn't drive and often eschewed conventional means of travel. As someone devoted to making geology accessible to everyone, he put together his now legendary guides to San Francisco rocks. In addition to Streetcar, he also wrote A Walker's Guide to the Geology of San Francisco, which does contain one walk that focuses specifically on the building stone of the city.

Tuesday, December 9, 2008

Gary Cooper and the Stones of San Francisco

With the upcoming AGU annual fall meeting, I want to look at some of the building stone used in San Francisco.  Despite the area's abundant stone, the earliest fireproof granite building used stone quarried, cut, and fitted together in China.  Known as the Parrott Block, it was built in 1852.  The blocks had been labeled with Chinese characters and shipped to San Francisco, to be assembled by Chinese workers.  The three-story building survived the 1906 earthquake and fire but was razed in 1926 for the Financial Center Building, now remodeled as the Omni Hotel. 

Various rock trickled into San Francisco in the following decades. By the end of the century two of the most prominent were a sandstone quarried near Sites and a granite from Raymond.  Sites is about 100 miles north of the bay area, in the Sacramento Valley, whereas Raymond is 150 southeast in the foothills of the Sierras.  Both rocks reached the city by train. 

Colusa sandstone quarry - From: http://quarriesandbeyond.org/states/ca/quarry_photo/ca-colusa_photos.html

Two quarries in Sites provided stone.  A. D. Knowles opened his quarry in 1886, followed in 1890 by the John McGilvray Stone Company.  Known in the trade as Colusa Sandstone (the town of Colusa is about 25 miles away), the rock comes from the Upper Cretaceous Venado Formation, a several-hundred meter thick layer of submarine fan deposits.  They are part of the Great Valley Group, tens of thousands of feet of muds, silts, and sands that accumulated in a forearc basin found between the Sierra Nevada magmatic arc and the Franciscan subduction complex. 

The Ferry Building was the first great structure made of Colusa rock.  Other well-known buildings are the St. Francis Hotel, Music Temple in Golden Gate, and the Flood Building.  The stone was also shipped to Hawaii.  It is generally bluish gray or buff, though a recently opened quarry about one mile north of the original quarries markets the sandstone as a brownstone.  Like other sandstones during fires, the Sites rock spalled heavily during the post-1906 earthquake infernos. 

Raymond Granite Quarry - 1905 -- From: http://www.sjvls.org/photoheritage

The Raymond granite quarry opened in 1888 on property locally known at the time as Dusy’s Rock Pile.  Light gray in color, the Raymond rock is classic, Sierra Nevada subduction zone granite, and is now sold as Sierra White by the quarry’s present owner Cold Spring Granite.  Raymond granite was used in the San Francisco Civic Center, City Hall, Palace Hotel, and numerous buildings on the UC Berkeley campus.  The new main San Francisco library, built in 1996, also has a granite fa├žade from the Raymond quarry. 

The stone, or at least the quarries, achieved a bit of notoreity in 1949 in the movie adaptation of Ayn Rand’s The Fountainhead.  At a low point in his career, architect Howard Roark, played by Gary Cooper, retreats to a job in a quarry.  The quarry in the book is in Connecticut, but since the film was shot in California the Raymond quarries had to stand in for Connecticut.  Although limited, the scenes in the quarry with Cooper and Patricia Neal are some of the movie’s most famous and controversial because of their sexual imagery.  And for those inclined to stone, the shots do a fine job of depicting quarry technology.

Sunday, December 7, 2008

The HMS Challenger Sets Sail

As Michael Ryan notes on his Paleoblog, today is the anniversary of the day the HMS Challenger set sail in 1872. The expedition spent four years sailing over 69,000 nautical miles charting the depths of the seas.  The crew's discoveries, including the deepest spot on the planet, an immense chain of subaqueous volcanoes, and unexpected diversity, added more evidence to the validity of the theory of evolution and laid the groundwork for one of the other great theories of science, plate tectonics. If you want to know more about the HMS Challenger, I recommend geologist and science writer Richard Corfield's first rate book, The Silent Landscape.  

Corfield mixes journal information from expedition members with details from the scientist’s 20-volume report to tell the tale of the HMS Challenger, what Corfield calls the world’s first sea voyage devoted exclusively to science. As he notes, the journey of the HMS Challenger marked several turning points.  It was the last great voyage of the Victorian era.  It helped lay to rest “the belief that secular questions can be answered by religion.”  It showed that science and the search for knowledge were worthy of government funding and it opened up nearly two-thirds of the planet to exploration that continues to this day.  The expedition deserves to be included on the short list of great British voyages, and Corfield does a fine job of showing why. 

Wednesday, December 3, 2008

The Stones of Florence

I thought I would follow up my previous post on Brunelleschi’s Il Badalone by looking at the stone used in the Duomo, or Santa Maria del Fiore, as it is officially known.  According to Ross King in his highly readible Brunelleschi’s Dome, the planners ordered three colors: verdi di Prato, marmum rubeum, and bianchi marmi—green, red, and white, respectively.  Like many writers, King refers to the stone as marble.  Only the white stone, however, is a true marble.  

As the name implies, the first stone is green.  It is a serpentine, quarried for centuries near the town of Figline, a few miles from Prato, northwest of Florence. The name comes from the stone’s resemblance to a serpent’s skin, or so say some, from the stone’s use as a medicinal remedy against snake poison.  In the building trade, serpentine is commonly called Verde Antique, or Verde Antico if the seller is feeling fancy.  Serpentine forms from the metamorphism of magnesium-rich rock such as peridotite. 

The red stone of the Duomo is a very fine grained limestone quarried in several locales near Florence.  It was deposited in an open, marine environment around 190 million years ago.  Geologists refer to this layer as the Rosso Ammonitico, due to the abundant ammonite fossils.

Bianchi marmi is better known as Carrara marble, the material that Brunelleschi’s Il Badalone was supposed to carry up the Arno River.  The Carrara began life as a fine-grained, calcite mud deposited in the same sea as Rosso Ammonitico but 10 million years later.   It became marble around 27 million years ago when the Corsica-Sardinian microplate rammed into the Italian peninsula.  As the plate’s basalt, gabbro, and sediments piled on the limestone, it metamorphosed it into a marble that is almost 100 percent calcite. 

(View up toward Mount Maggiore, Carrara, Italy)

King is not alone in using the term marble to describe non-marble stone.  To the Romans, who called marble marmor, from the Greek adjective marmareos, meaning shining or shimmering, marble referred to any hard rock suitable for sculpture or architecture.  Such “marbles” might include granite, breccia, porphyry, or serpentine.  Go to any store selling architectural stone and you will find that the Roman tradition continues with a plethora of non-metamorphosed limestone labeled as “marble.”  I have no idea if any are good for snake bites.