Saturday, January 26, 2019

Geology of the National Parks Through Pictures - Hot Springs

My next post about the Geology of the National Parks Through Pictures is an old park visit, but one I never actually published as part of this series. I visited this park back in 2003, before I was focused on the geology of the parks. 


You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

This post relates to the Arkansas Geological State Symbols post that came out earlier this week.

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Hot Springs National Park


The water within Hot Springs National Park is unique in that it has traveled a very long way down into the ground surface. These waters have been heated up by geothermal activity (the heat inside the Earth) as opposed to the volcanic activity that you would see at springs in areas like Yellowstone. Here is Bathhouse Row, where the bathhouses are lined up along the areas where the natural springs come to the surface.

Friday, January 25, 2019

Geological State Symbols Across America - Arkansas

The next state up for the Geological State Symbols Across America is:

Arkansas


You can find any of the other states geological symbols on my website here: Dinojim.com (being updated as I go along this year).

                                                                                        Year Established
State Rock: Bauxite                                                                  1967
State Mineral: Quartz Crystal                                                  1967
State Gemstone: Diamond                                                       1967
State Dinosaur: Arkansaurus fridayi                                       2017

State Rock: Bauxite
ACT 128

AN ACT to Designate the Diamond the State Gem, Quartz Crystal the State Mineral, and Bauxite as the State Rock.

Be It Enacted by the General Assembly of the State of Arkansas:

SECTION 3. Bauxite is hereby adopted and designated the official State Rock of the State of Arkansas.

SECTION 4. It is hereby found and determined by the General Assembly that there is presently no officially designated State Gem, State Mineral or State Rock, for the State of Arkansas; that there are many clubs and individuals throughout the United States that collect, trade, and sell official State Gems, Minerals and Rocks, and that it is essential that the General Assembly immediately designate a State Gem, Mineral and Rock, in order that the various interested clubs and individuals in Arkansas can trade official State Gems, Minerals and Rocks, with like clubs and individuals in other States. Therefore, an emergency is hereby declared to exist and this Act being necessary for the preservation of the public peace, health and safety, shall be in effect from the date of its passage and approval.
An example of bauxite from Little Rock, Arkansas. Photo courtesy of geology.com.

Bauxite is a sedimentary rock, which is usually produced when most of the minerals are leached from the soil leaving high levels of alumina behind in wet tropical or subtropical environments. Bauxite is often thought of as an aluminum mineral (that is even how it was present in several intro geology labs I was in charge of) however it isn't just one mineral; bauxite is primarily composed of gibbsite (Al(OH)3), boehmite (AlO(OH)), and diaspore (AlO(OH)). All of these minerals are extremely soft, occurring between 1 and 3 on Moh's Hardness Scale, meaning bauxite itself is a soft rock. The formation of bauxite produces a pissolitic texture, which resembles little balls glued together (as seen in the picture to the left). The majority of the aluminum in the world comes from bauxite ores. To extract the aluminum from the bauxite, the bauxite is crushed into a powder and the aluminum is leached out via several chemical procedures. The obvious use of aluminum is as a metal, but it can also be used for abrasives (one of the by-products of the leaching process has a hardness on Moh's scale of 9), in cements, and as proppants (high density spherical grains used by the oil and gas industry in fracking). Currently, the United States is not even in the top ten for bauxite producers and it is only found in a handful of localities in the United States (Arkansas, Georgia, and Alabama).

Mineral resources of Arkansas, highlighting the Bauxite deposits, which are the light pink areas. Map courtesy of the Arkansas Geological Survey.

Arkansas bauxite was formed from richly alkaline igneous intrusive rocks that intruded into the Paleozoic age sedimentary rocks of the central region of Arkansas. The weathering of these igneous intrusive rocks during the Eocene provided the material to form the bauxite deposits. The igneous rock intrusion is a complex series that includes bodies of nepheline syenite and porphyritic alkalic syenite, as well as dikes and border phases of related rocks. These rock strike towards the northeast of Arkansas and dip gently towards the southeast. The bauxite is found within two regions of Arkansas, covering 275 square miles, located within Pulaski and Saline Counties. These are mapped on Mineral Resources map (to the right). Bauxite deposits are highlighted by the pink areas covering the two counties. In Arkansas, bauxite production started in 1899, and increased until 1923 when Arkansas produced half of the world's supply at 500,000 tons that year. The peak of production was in 1943 when 6,000,000 long tons were produced, but it has had a steady decline ever since. In 1982, mining of bauxite was ceased for aluminum metal with the current bauxite mining being used primarily for the production of proppants.


State Mineral: Quartz Crystal 
ACT 128

AN ACT to Designate the Diamond the State Gem, Quartz Crystal the State Mineral, and Bauxite as the State Rock.

Be It Enacted by the General Assembly of the State of Arkansas:

SECTION 2. Quartz crystal is hereby adopted and designated the official State Mineral of the State of Arkansas.

SECTION 4. It is hereby found and determined by the General Assembly that there is presently no officially designated State Gem, State Mineral or State Rock, for the State of Arkansas; that there are many clubs and individuals throughout the United States that collect, trade, and sell official State Gems, Minerals and Rocks, and that it is essential that the General Assembly immediately designate a State Gem, Mineral and Rock, in order that the various interested clubs and individuals in Arkansas can trade official State Gems, Minerals and Rocks, with like clubs and individuals in other States. Therefore, an emergency is hereby declared to exist and this Act being necessary for the preservation of the public peace, health and safety, shall be in effect from the date of its passage and approval.
Quartz crystal from Hot Springs, Arkansas located at the Chicago Field Museum. Image by myself.

Quartz is one of the most common minerals on Earth, primarily due to its simple structure and chemical formula, SiO2. Quartz also has an extremely high hardness, 7 on Mohs hardness scale, meaning that it doesn't scratch very easily and therefore does not break down easily. As the rocks on Earth are slowly eroded over time, most of the other minerals will break down into clay while quartz grains will generally just gets smaller and smaller. The result is that most beach sand is composed of quartz that has a slight hematite (rust) stain to it to give the sand grains their slight yellowish color. Although quartz is a simple mineral, it can come in a variety of colors depending on what type of impurities are present in the crystal structure; pure quartz crystal is clear, milky quartz is white, smoky quartz is grey, amethyst is purple quartz, citrine is yellow quartz, rose quartz is pink, as well as some other colors and varieties. Quartz does not have any cleavage, meaning that when it breaks it doesn't form along perfect surfaces. Instead as the quartz crystals grow, individual mineral molecules of quartz are added to the outside of the crystal from water rich in dissolved SiO2 or mineral melt (liquid rock like lava or magma).

Worlds largest quartz crystal, mined at Old Coleman Mine in Jessieville, Arkansas. Image courtesy of allthingsarkansas.com.

Although the mineral quartz is the most common mineral on the surface of the Earth, quartz crystals are a little rarer. The deep running hydrothermal waters in Arkansas, which had made the town of Hot Springs famous, have produced some of the finest varieties of quartz crystals on the planet. The Ouachita Mountains, home to the hot springs, has been known for centuries by Native Americans for their beautiful quartz crystals that were considered to have spiritual and sacred significance. The Ouachita Mountains began to be formed 600 million years ago, when a local rift basin started to open up. This rift basin accumulated sediment that eventually formed into sandstone and shale. These deposits were subsequently uplifted producing the mountain complex. Hydrothermal fluids started circulating through these rocks approximately 245 million years ago producing silica rich fluids that precipitated the quartz veins within cracks in these rocks. Native American artifacts from these rock crystals date back to 9,000 BC., with many of the early Native American arrow tips being fashioned from the quartz crystals themselves. In the modern days, these quartz crystals are considered to be some of the most beautiful quartz crystals in the world. People travel from all over to go to Mount Ida and Hot Springs to the many "dig your own quartz crystal" mines. The town Mount Ida even proclaims itself the "Quartz Crystal Capitol of the World". Currently, there has been an estimated 1,200 tons of quartz crystal ever mined from this region, totalling approximated 5% of the estimated total quartz crystal reserves. There is still plenty of quartz crystals left to be mined, perhaps finding one larger than the current world's largest quartz crystal, which was mined from the Old Coleman Mine in Jessieville, Arkansas (pictured left).

State Gemstone: Diamond
ACT 128

AN ACT to Designate the Diamond the State Gem, Quartz Crystal the State Mineral, and Bauxite as the State Rock.

Be It Enacted by the General Assembly of the State of Arkansas:

SECTION 1. The Diamond is hereby adopted and designated the official State Gem of the State of Arkansas.

SECTION 4. It is hereby found and determined by the General Assembly that there is presently no officially designated State Gem, State Mineral or State Rock, for the State of Arkansas; that there are many clubs and individuals throughout the United States that collect, trade, and sell official State Gems, Minerals and Rocks, and that it is essential that the General Assembly immediately designate a State Gem, Mineral and Rock, in order that the various interested clubs and individuals in Arkansas can trade official State Gems, Minerals and Rocks, with like clubs and individuals in other States. Therefore, an emergency is hereby declared to exist and this Act being necessary for the preservation of the public peace, health and safety, shall be in effect from the date of its passage and approval.

The Cullinan Diamond, which was polished into nine large diamonds and many more smaller diamonds. Image courtesy of The Cape Town Diamond Museum.

One of the most famous gemstones, the diamond, is also one of the hardest minerals on earth (it is actually the third hardest after two extremely rare minerals called Wurtzite Boron Nitride and Lonsdaleite (Newscientist.com)). A diamond is made up entirely of carbon (like its mineral cousin graphite), where the arrangement of the carbon atoms and the strength of the bonds are what give the two minerals completely different properties. Diamonds are measured in carats, where a carat is equal to 200 milligrams. Diamonds range in size from the microscopic diamond dust to the largest diamond ever discovered, the Cullinan Diamond, weighing in at 3106 carats, or ~1.4 pounds. The Cullinan Diamond (pictured right) was eventually cut into over 100 separate stones, with two of the largest stones forming part of the Crown Jewels. Diamonds are most often found in structures called kimberlites or lamproites. Kimberlites are magmatic rocks that are formed deep within the Earth. The high pressure converts the carbon into diamonds and the structures make their way to the surface as buoyant globs of rock. Due to being formed at such high pressure, diamonds are inherently unstable on the Earth's surface, however they degrade at such a slow rate that it isn't much of an issue in jewelry. Many diamonds today are found in these isolated structures, however not many kimberlites or lamproites are known to exist within the United States, with only two knowingly existing.

Some of the diamonds found at Crater of Diamonds State Park in Arkansas. Image courtesy of Arkansas State Parks.

The main locality for finding diamonds in the US is a lamproite located in Crater of Diamonds State Park, Arkansas. Here visitors are allowed to mine for diamonds and keep what they find (as pictured to the left); the only such diamond mine on Earth. It was originally assumed that the diamonds in Arkansas were formed from a kimberlite, however recent research has shown that lamproites, which differ from kimberlites in how they are formed and in their chemistry, more closely align with the deposits in Arkansas. Generally, the diamonds found within Arkansas have a tendency to be smaller in size than their counterparts in Africa. However, there have been some significant finds including the the largest diamond ever found in North America, called "The Uncle Sam". The Uncle Same was discovered in 1924 and weighed 40.42 carats before it was cut (pictured below).

The Uncle Sam Diamond, which was the largest diamond every found in the United States. It was found in the location which eventually became Crater of Diamonds State Park, Arkansas. Image courtesy of diamondshop09.blogspot.com.

State Dinosaur: Arkansaurus fridayi
 
HCR 1003
HOUSE CONCURRENT RESOLUTION
TO DESIGNATE THE ARKANSAURUS FRIDAYI AS THE OFFICIAL STATE DINOSAUR.

WHEREAS, for public and educational benefits, the Ninety-First General Assembly of the State of Arkansas will select an official state dinosaur from the known population of dinosaurs represented in Arkansas's fossil record: Arkansaurus, sauropod dinosaur, and theropod dinosaur tracks of currently uncertain taxonomic affiliation; and

WHEREAS, from these species, the Arkansaurus fridayi shall be selected, since it is unique to the State of Arkansas, brings recognition to the State of Arkansas, and promotes an interest paleontology in Arkansas; and

WHEREAS, by designating an official state dinosaur, Arkansas would join nine (9) other states in the country with a unique designation of an official state dinosaur; and

WHEREAS, the Arkansaurus fridayi was discovered in a gravel pit near the community of Lockesburg, Arkansas, in August 1972 by Joe B. Friday and studied by Professor James Harrison Quinn of the University of Arkansas in 1973 and by paleontologist ReBecca Hunt since 2003, and the official recognition of this dinosaur would provide valuable research and educational opportunities in our state; and

WHEREAS, the State of Arkansas shall declare an official state dinosaur for the first time in its history and for the tenth time in the history of the United States of America; and 

WHEREAS, the State of Arkansas recognizes that "Arkansaurus fridayi" remains, for now, the unofficial name of the dinosaur; and

WHEREAS, Arkansaurus fridayi shall be selected to represent the State of Arkansas in the small community of State Dinosaurs in the United States,

NOW THEREFORE,
BE IT RESOLVED BY THE HOUSE OF REPRESENTATIVES OF THE NINETY-FIRST GENERAL ASSEMBLY OF THE STATE OF ARKANSAS, THE SENATE CONCURRING THEREIN: 

THAT the House of Representatives recognizes and designates the Arkansaurus fridayi as the official dinosaur of Arkansas.

BE IT FURTHER RESOLVED that upon adoption of this resolution, an appropriate copy shall be provided to the Arkansas Geological Survey, the University of Arkansas Department of Geosciences, and the mayor of Lockesburg, Arkansas, by the Chief Clerk of the House of Representatives.
Arkansaurus fridayi reconstructed illustration by Brian Engh

Besides fragmentary bits of bones and some dinosaur tracks, Arkansaurus fridayi is the only known dinosaur fossil recovered from the state of Arkansas to date. The fossil was initially discovered by Joe B. Friday on his land in 1972 during an earthmoving project. The fossil comprised of bones from the right foot of the animal. They were discovered within the Early Cretaceous Trinity Group (Albian-Aptian, ~113 million years ago) near Locksburg, Arkansas. 

Cast of the reconstructed Arkansaurus fridayi material. Photo courtesy of ReBecca Hunt-Foster.

These bones were initially described back in 1973, however not much else was done with the fossil material until 2018 when they were redescribed by Hunt and Quinn as a new species of ornithomimosaur (the kind of dinosaurs you saw running around in flocks on Jurassic Park). The remains of Arkansaurus were compared to other known dinosaurs and determined to be an early relative of the Late Cretaceous ornithomimids Ornithomimus and Struthiomimus. Ornithomimids are usually identified by their resemblance to modern day ostriches (hence the name "ornithomimid" means "ostrich mimic"), and the bones of Arkansaurus were similar enough to the known ornithomimids to declare it as an early ancestor of those species. The genus name Arkansaurus means "Arkansas' reptile" and the species name fridayi was in honor of Joe B. Friday, who initially discovered the remains. 

References:
https://statesymbolsusa.org/states/united-states/arkansas
http://www.soskids.ar.gov/pdfs-09/Arkansas_State_Symbols.pdf
https://thebauxiteindex.com/en/cbix/industry-101/bauxite-101/bauxite-formation
https://www.geology.arkansas.gov/minerals/industrial/bauxite.html
http://geology.com/minerals/bauxite.shtml
http://www.geology.arkansas.gov/pdf/pamphlets/Bauxite.pdf 
https://www.geology.arkansas.gov/docs/pdf/education/mineral-resources-poster.pdf 
https://www.arkansas.com/articles/quartz-crystals
https://www.arkansas.com/mount-ida
http://www.arkansas.com/things-to-do/crystal-hunting/ 
http://www.rockngem.com/arkansas-quartz-origin-and-history/
https://pubs.usgs.gov/pp/0299/report.pdf
http://www.bluemooncrystals.com/Crystal_Mining.html
http://rockhoundingar.com/feepay.php
http://www.soskids.ar.gov/5-8-history-state-symbols.html
https://www.allthingsarkansas.com/weekly-blog-about-all-things-arkansas/quartz-crystal-in-arkansas
https://4cs.gia.edu/en-us/diamond-carat-weight/
http://www.newscientist.com/article/dn16610-diamond-no-longer-natures-hardest-material.html
http://www.sciencedaily.com/releases/2012/01/120123094523.htm 
http://www.geology.ar.gov/pdf/pamphlets/AGES%20BROCHURE-DIAMONDS%2011-13-07.pdf
http://m.encyclopediaofarkansas.net/media/detail/?mediaID=6544
http://www.capetowndiamondmuseum.org/blog/2017/04/top-8-largest-diamonds-in-the-world/
https://link.springer.com/article/10.1134/S0869591111010024
https://www.arkansasstateparks.com/parks/crater-diamonds-state-park/history/why-can-diamonds-be-found
https://geology.com/articles/crater-of-diamonds/
http://diamondshop09.blogspot.com/2009/06/uncle-sam-diamond.html
http://dontmesswithdinosaurs.com/
ReBecca K. Hunt & James H. Quinn (2018): A new ornithomimosaur from the Lower Cretaceous Trinity Group of Arkansas, Journal of Vertebrate Paleontology

Friday, January 18, 2019

Geological State Symbols Across America - Arizona

The next state up for the Geological State Symbols Across America is:

Arizona


You can find any of the other states geological symbols on my website here: Dinojim.com (being updated as I go along this year).


                                                                                        Year Established
State Gemstone: Turquoise                                                        1974
State Fossil: Petrified Wood (Araucarioxylon arizonicum)        1988
State Metal: Copper                                                                    2015

I also have several Geology of the National Parks Through Pictures that I have done for Arizona previously. These include:
Canyon de Chelly National Monument
Casa Grande Ruins National Monument
Glen Canyon National Recreation Area
Grand Canyon National Park
Hohokam Pima National Monument
Petrified Forest National Park
Saguaro National Park
Sunset Crater Volcano National Monument
Tonto National Monument
Tumacácori National Historical Park
Walnut Canyon National Monument
Wupatki National Monument

State Gemstone: Turquoise
CHAPTER 55
House Bill 2109
AN ACT
RELATING TO STATE GOVERNMENT; PROVIDING THAT TURQUOISE BE THE STATE GEMSTONE, AND AMENDING TITLE 41, CHAPTER 4.1, ARTICLE 5, ARIZONA REVISED STATUTES, BY ADDING A NEW SECTION 41-858.
Be it enacted by the Legislature of the State of Arizona:
Section 1. Title 41, chapter 4.1, article 5, Arizona Revised Statutes, is amended by adding a new section 41-858, to read:
41-858. State gemstone·
TURQUOISE IS THE OFFICIAL STATE GEMSTONE.
A piece of turquoise from Madagascar.
Image courtesy of carionmineraux.com.

Turquoise is a blue-green mineral made up of copper, aluminum, and hydrous phosphate (CuAl6(PO4)4(OH)). The name turquoise comes from the French expression for "Turkish Stone", illustrating that the early sources for European turquoise were from the Middle East. Turquoise has long been considered valuable and is one of the oldest known gemstones. It has been found in ancient Egyptian and Chinese archeological expeditions, showing that those people used turquoise as far back as 3,000 years ago. It is formed by the flowing of groundwater through copper deposits that eventually react with phosphate and aluminum minerals. Turquoise is also only found in arid (desert) environments because that is one of the few places that allows the groundwater to maintain a high enough copper concentration for long enough to interact with the other minerals. The result is a gemstone unlike traditional, gemstones like ruby or emerald, which is most commonly opaque. The opaqueness is due to the structure of turquoise, which is made up of many microcrystalline structures instead of one large mineral crystal. These microcrystals give the turquoise its appearance, either a mottled look or a smooth finish, which is due to the size of these microcrystals. It is also extremely soft and easy to carve. All of these attributes make it useful for many different purposes from jewelry to architectural adornments.

Spiderweb turqouise jewlery.
Image courtesy of Durango Silver.

Turquoise mines can be found all across the southwestern United States, with the largest concentration found in Arizona. As mentioned above, turquoise mines in Arizona are often associated with copper mines (many of them open-pit mines in AZ). The largest and most well known of the turquoise mines is the Bisbee Mine, near Bisbee, AZ, located adjacent to the Copper Queen copper mine. In 1880, the mine was founded as a gold, silver, and copper mine, which are often found together due to the formation of these minerals from the waters associated with subduction zone magmatism. The hydrothermal waters associated with the former subduction zone in the region circulated throughout the rocks depositing the heavy metal deposits within the bedrock. These heavy metal deposits eventually interacted with the local groundwater producing these turquoise deposits. The Bisbee Mine turquoise was discovered in the 1950's and quickly became prized for it's spider-webbing patterns throughout the turquoise stones (pictured left). Although most of the turquoise has been mined out, this has resulted in these variety of the gem to become prized collectors items. Native Americans (primarily the Anasazi and the Hohokam) mined the turquoise in Arizona for use in jewelry and for trade. Arizona is also home to one of the largest domestic turquoise mines, located in Kingman.

State Fossil: Petrified Wood (Araucarioxylon arizonicum)
CHAPTER 88
SENATE BILL 1455
AN ACT
RELATING TO STATE GOVERNMENT; PROVIDING FOR ADOPTION OF PETRIFIED WOOD AS THE
OFFICIAL STATE FOSSIL, AND AMENDING TITLE 41, CHAPTER 4.1, ARTICLE 5, ARIZONA REVISED STATUTES, BY ADDING SECTION 41-853.

Be it enacted by the Legislature of the State of Arizona:
Section 1. Title 41, chapter 4.1, article 5, Arizona Revised Statutes, is amended by adding section 41-853, to read:
41-853. State fossil
PETRIFIED WOOD, OR ARAUCARIOXYLON ARIZONICUM, IS THE OFFICIAL STATE FOSSIL.
Petrified wood from Petrified Forest National Park.
Image taken by me.

Petrified wood is not actual wood, however it was wood at one point. Petrified wood is a fossil that formed from pieces of wood that have been mineralized. Mineralization is a process where groundwater moves through the wood and replaces all of the wood molecules with molecules of other substances, most often silica (i.e. quartz). This means that petrified wood actually isn't wood anymore, but a fossil of the former wood.

The specific species of petrified wood (Araucarioxylon arizonicum) that is the Arizona state fossil is an extinct conifer (like an evergreen) that can been found throughout Arizona and New Mexico. There is a problem with the state fossil though; the original name of the species was based on three different species. This means that although one of the three was correct, two had to be renamed, resulting in several of the trees identified since the initial 1889 description were likely named incorrectly. The problem is that proper identification can only be made with thin sections and close analysis, which is not likely going to happen for a majority of the samples previously identified, at least not any time soon. Arizona is host to one of the largest assemblages of petrified wood logs, with ~20% of all the petrified wood in northeastern Arizona found in Petrified Forest National Park. The concentrations of logs in Petrified Forest was a result of a log jam that flowed down a prehistoric river. The logs where then quickly buried, which allowed the mineralization process to proceed on the logs, converting them into fossils.

State Metal: Copper
CHAPTER 77
S. B. 1441
AN ACT AMENDING TITLE 41, CHAPTER 4.1, ARTICLE 5, ARIZONA REVISED STATUTES, BY ADDING SECTION 41-860.03; RELATING TO STATE EMBLEMS.
Be it enacted by the Legislature of the State of Arizona:
Section 1. Title 41, chapter 4.1, article 5, Arizona Revised Statutes, is amended by adding section 41-860.03, to read:
41-860.03. State metal
COPPER IS THE OFFICIAL STATE METAL.
An example of native copper.
Photo courtesy of the Flandrau Science 
Center at the University of Arizona

Copper is an elemental metal mineral, meaning that it is entirely composed of one element; copper (Cu) in this instance. It is also the only elemental metal, besides gold, which is not naturally silver or grey. Copper is the oldest known metal to have been manipulated by humanity. The Copper Age took place after the Neolithic (Stone) Age, and lasted from ~4500 BC to ~3500 BC, overlapping with the early Bronze Age. The earliest known Middle Eastern artifact is also made of copper, a pendant dating back to 8700 BC. In the modern day, copper is the third most consumed industrial metal in the world. Mining of copper in the US began with high grade ore deposits found in Arizona and Michigan in the late 1800's, however newer processes that were able to filter the copper out of low-grade deposits made excavating low-grade ores more economical, leading to more abundant uses of strip and open-pit mining for the recovery of copper. These processes enabled the US to become one of the leading producers of copper in the world. 

Arizona's metallic mining map from the
Arizona Geological Survey

In the late 1600's, Spanish explorers traveled the west looking for metallic deposits, specifically gold and silver. The association of these metals with copper enabled them to discover numerous copper deposits as well, even though it was not their primary focus. Eventually, the modern age of mining in Arizona was born in 1854 with the creation of the Arizona Mining and Trading Company in Ajo, AZ. Mining for copper was initially restricted to deep mine tunnels of fairly high quality ore. However, the success of the open-pit Bingham Mine in Utah illustrated that open-pit mining and new processing methods for low-grade copper ore worked well and Arizona began using similar processes, increasing their copper yield significantly. Currently, copper is the most valuable metallic commodity in Arizona, followed by gold, silver, molybdenum, and lead. In 2017, the US produced 1.27 million tons of copper with 68% of that coming from Arizona. There are currently over 3,000 Arizona locations that have copper listed as a commodity. These metallic deposits form a northwest to southeast band across the state (as seen on the map to the left). Along this band, most of the copper deposits are found within southeastern portion of the state (red on the map). These deposits are found mostly in granitic rocks that intruded within the region 70 to 55 millions years ago.

References
https://statesymbolsusa.org/states/united-states/arizona
https://www.gia.edu/turquoise
http://www.azsos.gov/public_services/kids/kids_state_symbols.htm
http://en.wikipedia.org/wiki/Turquoise
http://www.turquoise-museum.com/arizonaturquoisemines.htm
http://www.turquoisemines.com/bisbee-turquoise-mine/
https://www.durangosilver.com/spiderweb-turquoise-cabochons.html
http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/turquoise.html
http://indianvillage.com/arizonaturquoisemines.htm
http://www.traderoots.com/Turquoise_About.html#Introduction
http://www.carionmineraux.com/mineraux_avril_09.htm 
https://www.usatoday.com/story/travel/experience/america/national-parks/2018/03/28/petrified-forest-national-park-10-tips-your-visit/463822002/
http://en.wikipedia.org/wiki/Araucarioxylon_arizonicum 
http://waynesword.palomar.edu/pfnp.htm 
http://www.nps.gov/pefo/index.htm
http://factsanddetails.com/world/cat56/sub362/item1495.html
https://www.livescience.com/29377-copper.html
https://minerals.usgs.gov/minerals/pubs/commodity/copper/mcs-2018-coppe.pdf
http://repository.azgs.az.gov/sites/default/files/dlio/files/nid1609/ofr92-10copperoxideresources.pdf

Thursday, January 10, 2019

Geological State Symbols Across America - Alaska

The next state up for the Geological State Symbols Across America is:

Alaska


You can find any of the other states geological symbols on my website here: Dinojim.com (being updated as I go along this year).

                                                        Year Established
State Mineral: Gold                                 1968
State Gem: Jade                                        1968
State Fossil: Woolly Mammoth                1986

State Mineral: Gold
SB 223 Chapter 50
AN ACT
Providing for a state mineral.

BE IT ENACTED BY THE LEGISLATURE OF THE STATE OF ALASKA:

* Section 1. AS 44.09 is amended by adding a new section to read:
Sec. 44.09.110. STATE MINERAL. Gold is the official state mineral.
Panning for gold in Alaska.
Photo from GoldDaughters.com.

The chemical symbol for gold is Au, and gold is one of the unique minerals that, in its pure form, is composed entirely of one element. It has a hardness of 2.5 to 3 on the Mohs hardness scale meaning that it actually is very soft (your fingernail is 2.5). For this reason most gold jewelry is mixed with another metal to prevent scratching and bending easily. The karat rating of the gold represents it's purity, where 24 karat is 99.9% pure, 22 karat 91.7%, 18 karat 75%, and so on. Gold naturally does not corrode or tarnish, so even when it is mixed with other metals it usually has a resistance to tarnishing, enhancing its value for jewelry. When gold is found in place, the highest grade of gold is often found in association with quartz veins. Currently gold is considered one of the most valuable metals on Earth, being used as the standard for most money (gold standard). Gold is often formed initially in relation to volcanic regions, where fluids associated with volcanoes carry the heavy metals up towards the surface and deposit them in rocks. These are found in areas of current or former subduction zones, places where two plates came together forcing one place down and melting it, while the other plate is forced upwards into mountains. Afterwards, erosion will take the gold out of the mountains and carry them down stream. However, since gold is so dense it does not travel easily down rivers and will often settle to the bottom of the river within the rocks and mud within the river sediment. These gold deposits are known as placer deposits and are the primary place where gold panners find gold. They can then use the locations of these placer deposits to backtrack to the original sources of the gold within the streams.

Map of the Alaskan Gold Fields from 1897.
Map courtesy of the World Digital Library.

 Gold has an important history in Alaska. Originally when the territory was purchased it was referred to as Steward's Folly because this big hunk of land couldn't be worth anything. That was before gold was discovered. It began in the 1870's and continued through most of the 1900's. The beginnings of many communities in Alaska got their start as gold mining towns. Today Alaska is more known for its oil exploration but gold still holds a prominent place in its heart with Fairbanks remaining as a major gold exploration area. From the 1880's to 2005, Alaska has produced ~1250 metric tons of gold. Even though gold is going by the wayside in Alaska, it is still one of the major producers of gold in the United States, producing the second most gold after Nevada for the last decade. To the left is the major gold mines up to 1897, which follows a similar pattern of known gold deposits today, with a large swath of gold mines spread across the central portion of the country. One of the locations that gold was originally discovered was a placer deposit within the Yukon River and several mines of gold have been discovered from there, expanding ever outwards from the central strip.

State Gemstone: Jade
SB 222 Chapter 51

AN ACT
Providing for a state gem.

BE IT ENACTED BY THE LEGISLATURE OF THE STATE OF ALASKA:
* Section 1. AS 44.09 is amended by adding a new section to read:
Sec. 44.09.100. STATE GEM. Jade is the official state gem.

An example of the jade variety of "Nephrite".
Photo courtesy of the International Gem Society

Jade is a green gemstone that has a bit of an ambiguous mineralogy. It turns out that samples of gemstones that have been called jade actually fall into three different mineral categories. Typically what happens with gemstones, is that they are a name of a specific colored mineral; i.e. purple quartz is known as amethyst. Well in this instance the green gemstone jade can be one of three minerals: jadeite, actinolite, or tremolite. And even the combination of actinolite and tremolite goes by a different name: nephrite. There is a strong physical similarity between all these minerals, hence the confusion of which mineral jade could belong to and so all of these, as long as they are green, can be considered jade.
An example of a carved piece of Jade.
Photo by John Hill through Wiki Commons

All of these minerals have a hardness of 6 to 7 on Mohs Hardness Scale and all are silicates, although with significantly different chemical formulas. Jadeite is a aluminum-rich pyroxene (NaAlSi2O6) and actinolite and tremolite are magnesium-rich amphiboles (Ca2(Mg,Fe)5Si8O22(OH)2). All three of these minerals are formed through the process of metamorphism. Jadeite is a metamorphosed variety of albite, a plagioclase mineral and actinolite/tremolite are commonly formed from the metamorphism of ultramafic and mafic igneous rocks, such as those formed in oceanic crust. Due to the durability of the jade minerals, they can be formed into tools, however the green color has caused many artisans to use them more for jewelry and sculptures (such as the Mayan jade sculpture to the right).

The Jade plaque located within the Washington Monument in Washington D.C.
 Photo courtesy of Sit News

Alaska has large deposits of jade throughout the state but its principle claim to fame is an entire mountain made out of jade, aptly named Jade Mountain. The mountain is located far from any road, north of the Arctic Circle, near Kobuk. Very large blocks have been taken out of the mountain and used to create statues including a 3,600 lb block for a police memorial statue in Fairbanks. Currently, jade statues and jewelry produced from Alaska's famed Jade Mountain can be found all over the world, including a plaque embedded in the Washington Monument (pictured left). The mineral tremolite, which is one of the mineral varieties of jade, also can form another similar mineral, asbestos. It is the asbestos from Jade Mountain that received much of the commercial interest in the early days, of the modern "discovery" of the mountain (despite it being known about for thousands of years by the local Eskimos). The jade from Jade Mountain is the nephrite variety, however the amount of jade is dwarfed by the amount of tremolite asbestos in the region, and the quality is often not good enough to be considered gem grade. However, enough of the jade has been mined and used as jewelry and sculptures to warrant recognition. The age of the original, premetamorphosed ultramafic and mafic rocks, are Early to Middle Jurassic. These rocks were likely metamorphosed from contact with hydrothermal fluids associated with plate tectonics along the ocean floors and serpentinized. Eventually, plate tectonics along the convergent plate boundaries caused these deep ocean deposits to be uplifted into the Brooks Range (the mountain range where Jade Mountain is located).

State Fossil: Woolly Mammoth (Mammuthus primigenius)
SB 475
4/10/86
Resources
BY THE RESOURCES COMMITTEE
IN THE SENATE
SENATE BILL NO. 475
IN THE LEGISLATURE OF THE STATE OF ALASKA
FOURTEENTH LEGISLATURE - SECOND SESSION
A BILL

For an Act entitled: 
"An Act designating the woolly mammoth as the state fossil." 

BE IT ENACTED BY THE LEGISLATURE OF THE STATE OF ALASKA: 
* Section 1. LEGISLATIVE INTENT. By designating the woolly mammoth as the state fossil, the legislature intends to give recognition to this animal that was the largest and one of the most prevalent animals in the state but whose remains are now found only as fossils. * 

Sec. 2. AS 44.09 is amended by adding a new section to read: 

Sec. 44.09.120. STATE FOSSIL. The woolly mammoth is the official state fossil.

Wooly Mammoth (Mammuthus primigenius) from WikiCommons by Lou Gruber.

The preserved remains of Lubya, a baby mammoth
from Siberia. Image from Britannica.com.

The Woolly Mammoth, also known as Mammuthus primigenius, is a species closely related to modern day elephants. One notable difference between the extinct species and the modern day elephant is that the mammoth notably was covered with hair, allowing it to thrive in the arctic environments of modern day Alaska, Siberia, and Canada. Unlike most of the other state fossils, mammoths are frequently found as complete specimens, such as the complete baby mammoth found from Siberia (image on the left). They are usually frozen in the snow or buried in an Arctic swamp. Most of the ~100 remains of fully preserved mammoths have been found in Russia and Alaska. Mammoth remains are found throughout the northern reaches of the state as well as scattered throughout other regions. The local prehistoric people were known to have had interactions with the mammoths. Evidence includes tools that were created from their tusks. It is believed that these interactions with prehistoric humans are what drove the mammoths into extinction. A small island off the coast of Alaska is also one of the last remaining locations where woolly mammoths lived (until ~3,750 BC). Since the island was small the mammoths that have been found here evolved into dwarf varieties of the typical continental mammoths (pictured right).

Size comparison of an island dwarf mammoth compared 
to a "normal" sized mammoth. Photo from the Daily Curiosity

One of the common questions that comes up when discussing mammoths, is "What is the difference between a mammoth and a mastodon?". Although they are fairly closely related, and all related to modern day elephants, there are a few significant differences between the two species. The easiest feature to identify in a fossil specimen is the huge difference in their teeth (pictured below). These differences were due to the way that they ate their food. The cone-shaped molars of the mastodon were used to crush leaves, twigs, and branches, while the flatter ridged molars of the mammoth were used to cut through vegetation and graze similar to modern day elephants.

Comparison of the teeth of a mammoth versus a mastodon. Image from the FossilGuy.com.

References
https://statesymbolsusa.org/states/united-states/alaska
http://www.commerce.state.ak.us/ded/dev/student_info/student.htm
http://www.eed.state.ak.us/temp_lam_pages/library/goldrush/index.htm
http://alaska.gov/kids/student_printer.htm 
http://www.alaskascenes.com/alaskagold.html 
https://www.wdl.org/en/item/13496/
https://www.nr.gov.nl.ca/nr/mines/outreach/education/gold.html
https://www.goldmapsonline.com/alaska-gold-mines-yesterday-today.html
http://www.sitnews.us/JuneAllen/AlaskaJade/100504_jade_mountain.html 
https://geology.com/gemstones/jade/
https://en.wikipedia.org/wiki/File:Mayan_Jade.jpg
http://dggs.alaska.gov/webpubs/dggs/pn/text/pn003r.pdf
http://www.nature.com/nature/journal/v429/n6993/full/nature02612.html
http://www.shgresources.com/ak/symbols/fossil/ 
http://thedailycuriosity.tumblr.com/post/9277019095/a-dwarfed-form-of-the-woolly-mammoth-lived-on 
https://www.britannica.com/animal/woolly-mammoth
https://www.fossilguy.com/sites/peace-river/peace-river-fossils.htm
https://www.livescience.com/34446-mammoth-or-mastodon.html
https://en.wikipedia.org/wiki/Woolly_mammoth

Saturday, January 05, 2019

Geology of the National Parks Through Pictures - Russell Cave



You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

This post relates to the geological state symbols post that came out earlier this week. 

Unfortunately this is the only National Park I have visited in Alabama but eventually there will be more.
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During a trip to Chattanooga for my wife's Ironman race, we took a tour of some of the nearby National Parks. This included a brief foray into Alabama to see the small, but cool Russell Cave.

Entrance Sign

Wednesday, January 02, 2019

Geological State Symbols Across America - Alabama

The first state up for the Geological State Symbols Across America is:

Alabama



You can find any of the other states geological symbols on my website here: Dinojim.com (being updated as I go along this year).

                                                                    Year Established
State Rock: Marble                                         1969
State Mineral: Hematite                                 1967
State Gemstone: Star Blue Quartz                  1990
State Fossil: Basilosaurus cetoides                 1984


State Rock: Marble

Act No. 755 H.562 - Smith
An Act
To designate marble as the official rock of the State of Alabama.

Whereas marble, a rock composed primarily of calcium carbonate, is most plentiful in Alabama, being found in the counties of Talladega, Bibb, Calhoun, Clay, Coosa, Etowah, Lee, Macon, St. Clair, and Shelby, and having been quarried in the State since 1840; and,

Whereas one of the most remarkable beds of marble in the world, at least 200 feet thick, occurs near Sylacauga, in Talladega County, being fine-grained and mostly white, of exceptional purity and hardness, taking a beautiful polish, and havig high resistance to abrasion; and,

Whereas buildings throughout this State and the United States have been constructed and ornamented with Alabama marble and this rock has been made a part of some of the nation's most beautiful buildings; and,

Whereas, in addition to its decorative uses, crushes and ground marble is growing in importance as industrial raw material, having application in textiles, paints, electrical insulation, plastics and foods, among others; now, therefore, 
Be It Enacted by the Legislature of Alabama:
Section 1. Marble is hereby designated and names the official rock of Alabama.
Section 2. This Act shall become effective immediately upon its passage and approval by Governor, or upon its otherwise becoming a law.
Approved September 12, 1969.

Book covering the history of
the Sylacauga marble. (sylacauga.net)

Marble is a metamorphosed variety of the sedimentary rock limestone. This means that the original sedimentary rock underwent periods of increased temperatures and pressures to change the rock itself. The primary minerals in marble are calcite (CaCO3) or dolomite ((Ca,Mg)CO3) but it will usually have other mineral contaminates mixed in as well (i.e., clay, mica, quartz, pyrite, and iron oxide, etc.). Since, the primary mineral in marble is calcite, most marbles will have a white color with swirls of darker colors (the contaminates) but marbles can be found in many different colors depending on what impurities were present in the initial limestone. During metamorphism of the original limestone, the calcite is recrystallized to form interlocking crystals, which will usually destroy any remnants of the original rock, including any fossils present.


Sculpting the Sylacauga Marble during
 the Magic of Marble Festival in 2010. (sylacauga.net

The primary source of marble in Alabama is the Sylacauga marble found in Talladega County. The Sylacauga, or Alabama, Marble has been quarried and used in art and building stones throughout Alabama and the US. The marble is named for the town Sylacauga and has been called the "whitest marble in the world" for its purity. The Sylacauga Marble has been used in several famous landmarks including the Washington Monument, the Lincoln Memorial, and the U.S. Supreme Court. The marble formed during metamorphism associated with the Appalachian orogen (mountain building) and is approximately Cambrian to Ordovician in age. Besides the pure white sections of the marble, there are also sections that have green, pink, gray, black, and gold veins in the ~5.5 cubic mile deposit. Official descriptions of the marble state it as "white and pale-blue to light-gray calcite marble, locally containing interlayered dolomite marble and thin phyllite layers" (mrdata.usgs.gov).

State Mineral: Hematite
Act No. 503 S. 81 - Vacca, Hawkins, Bailes
An Act
To designate Hematite as the official mineral of the State of Alabama

Whereas, Red Iron Ore, with the scientific name of Hematite, and the chemical formula of Fe2O3, is one of the most valuable and important minerals found in the State of Alabama, and

Whereas, Hematite is used for iron and steel and many industries in this State got their initial start with this important, Alabama-produced mineral, and

Whereas this valuable natural resource has aided the economy of Alabama by contributing to it, since, 1863, 316 million long tons at a value of 850 million dollars.

Be It Enacted by the Legislature of Alabama:
Section 1. Hematite is hereby designated and named the official mineral of the State of Alabama.
Section 2. This Act shall become effective immediately upon its passage and approval by the Governor, or upon its otherwise becoming a law.
Approved September 7, 1967.
Images of red and silver hematite
(geology.com).

Hematite is a mineral that is produced from the oxidation of iron, and forms iron oxide in the form of Fe2O3. In everyday language, this means that hematite is more commonly known as rust. Hematite is primarily composed of iron and is abundant on the Earth's surface,resulting in hematite becoming one of our most common sources of iron ore. Although typically found as a red "earthy" deposit, there is also a variety of hematite that has a silver/steel-grey metallic appearance to it (pictured left). Both varieties of hematite can be easily identified by the characteristic bright red streak of the mineral. Hematite has a hardness of 5 to 6, meaning that it is approximately as hard as a plane of glass (5.5). The mineral hematite was originally named "aematitis lithos" in ~300 BCE by the Greek Theophrastus and its name means "blood stone". The name was translated by Pliny the Elder to haematites, meaning "bloodlike", and that name eventually evolved to the modern spelling of "hematite".


Cast iron statue of Vulcan from
Birmingham, AL (wikipedia.com).

The hematite in Alabama was primarily mined from the Red Mountain Formation until 1975, where it became cheaper to import it. At one time it was Alabama's most developed, non-fuel, mineral industry, helping to build up Birmingham as an industrial center. In the 135 years hematite was mined, ~375 million tons of ore was excavated. The Red Mountain Formation is primarily a Silurian interbedded shale-sandstone with some siltstone and limestone deposits intermixed. The hematite is largely from cross-bedded sandstone members of the Red Mountain Formation, which were deposited as shoreface (essentially beach) deposits. The production of hematite within the sandstone was precipitated during periods of sediment starvation and reworking during a regression (sea-level drop). Birmingham is also known for the largest cast-iron structure ever made, the statue of Vulcan (picture right), produced entirely with the Birmingham iron ore.


State Gemstone: Star Blue Quartz
Act No. 90-203 S.J.R. 7 - Senator Hale
Senate Joint Resolution

Designating the Star Blue Quartz as the official gemstone for the State of Alabama.

Be it resolved by the Legislature of Alabama, both houses thereof concurring, that the Star Blue Quartz be designated as the official gemstone for the State of Alabama.
Approved March 29, 1990
star blue quartz
Star blue quartz (Alabama.gov).

Quartz is one of the most common minerals on Earth, primarily due to its simple structure and chemical formula, SiO2. Quartz also has an extremely high hardness, 7 on Mohs hardness scale, meaning that it doesn't scratch very easily and therefore does not break down easily. As the rocks on Earth are slowly eroded over time, most of the other minerals will break down into clay while quartz grains will generally just gets smaller and smaller. The result is that most beach sand is composed of quartz that has a slight hematite (rust) stain to it to give the sand grains their slight yellowish color. Although quartz is a simple mineral, it can come in a variety of colors depending on what type of impurities are present in the crystal structure; pure quartz crystal is clear, milky quartz is white, smoky quartz is grey, amethyst is purple quartz, citrine is yellow quartz, rose quartz is pink, as well as some other colors and varieties. Quartz does not have any cleavage, meaning that when it breaks it doesn't form along perfect surfaces. Instead as the quartz crystals grow, individual mineral molecules of quartz are added to the outside of the crystal from water rich in dissolved SiO2 or mineral melt (liquid rock like lava or magma).

Unlike the other varieties of quartz (such as citrine or amethyst), pure blue quartz has not yet been found in nature. Instead, the quartz crystals appear blue because of the inclusions of other minerals or properties of the mineral itself that make the light reflect through the mineral and makes it appear blue. The reason that Star Blue Quartz is blue is that it contains little bits of amphibole (another type of mineral) and displays asterism (a star pattern in the light) when polished. The problem with this variety of quartz though is that there is little to no information on where to find it or why it was even listed as the state gemstone. The best that I can find is the constantly rehashed phrase from when it was promoted to the state: "(star blue quartz) is one of the most beautiful gemstones on earth, and the cheapest because there are so many." It appears that this very common mineral is rare to non-existent in Alabama. There have been reports of it along the Flint River, but most of those occurrences are generally in neighboring Georgia.


State Fossil: Basilosaurus cetoides
Act No. 84-66 H.J.R. 78 - Rep. Onderdonk
House Joint Resolution
Designating "Species Basilosaurus cetoides," the ancient whale fossil as the official Alabama fossil.

Whereas, the Alabama Legislature notes that the ancient whale "Species Basilosaurus Cetoides," (sic) named after the forty million year old whale fossil was discovered in Washington County, Alabama; and

Whereas, this ancient whale fossil is most abundant in the State of Alabama, and two of the most comprehensive skeletons of the "Species Basilosaurus Cetoides" (sic) were discovered in Alabama, on discovered by Mr. Ronald "Bones" Rhoads and now located in the Red Mountain Museum, Birmingham, Alabama, and the second, a fifty-five foot skeletal exhibit is on display in the Smithsonian Institute, Washington, D.C.; and

Whereas, the Alabama Legislature feels it is most appropriate that the interest in and the study of this ancient aquatic mammal predator, with serrated posterior molars, be encouraged and perpetuated for scientific and historical reasons; now therefore,

Be it resolved by the Alabama Legislature, both houses thereof concurring, That the Alabama Legislature does hereby designate as the official State of Alabama Fossil the "Species Basilosaurus Cetoides." (sic)

Resolved further, That no fossil "Species Basilosaurus Cetoides" (sic) shall be removed from the State of Alabama, in whole or in part, except by prior written approval of the Governor.

Be it further resolved, That copies of this resolution shall be sent to the Washington County governing body, the Director of the Department of Archives and History, the governor and to the red Mountain Museum, Birmingham, Alabama, for appropriate display.

Approved March 13, 1084

Basilosaurus skeleton from the National Museum of Natural History (Wikimedia.org).

Basilosaurus is a member of the whale family (Cetacea) first discovered in Alabama in 1834. It was originally thought to be a swimming reptile but was later discovered that it was indeed a whale from the Eocene period (40-35 million years ago). Unlike modern day whales, Basilosaurus still retained its hind limbs. These were thought to be mostly nonfunctional, however there is a theory that they could have been used during sex. Basilosaurus is one of the closest related animals to modern day cetaceans (dolphins, whales, etc.) that still retains their hind-limbs, although the pelvis is not connected to the vertebrae, limiting any function that it could provide.

Phylogenetic relationships of early cetaceans (from Houssaye et al., 2015)

The group Basilosauridae contained a few other species that had body proportions similar to modern day dolphins but Basilosaurus had an "exceptionally long body and tail" resulting in the animal having a more snake-like appearance. The body length ranged from 49 to 59 ft and is one of the largest known animals during the Paleocene-Eocene time period. Basilosaurus is most abundant in Alabama and has been found in Clarke, Choctaw, and Washington counties.

References
https://statesymbolsusa.org/states/united-states/alabama
http://www.sylacauga.net/library/sections/Sylacauga%20Marble%20Fiestival/Marble%20Fiestival%202010.htm
http://en.wikipedia.org/wiki/Vulcan_statue
http://geology.about.com/od/regional_geology/ig/stategems/stateblueqtz.htm
http://www.encyclopediaofalabama.org/face/Multimedia.jsp?id=m-3931
http://legacy.decaturdaily.com/decaturdaily/news/050206/marble.shtml
https://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=ALsgq%3B7
http://geology.com/rocks/marble.shtml
https://www.mindat.org/min-1856.html
https://geology.com/minerals/hematite.shtml
https://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=ALSrm%3B3
https://en.wikipedia.org/wiki/Basilosaurus
Chowns, Tim & Rindsberg, Andrew. (2015). Stratigraphy and depositional environments in the Silurian Red Mountain Formation of the southern Appalachian basin. 10.1130/2015.0039(04). 
Houssaye A, Tafforeau P, de Muizon C, Gingerich PD. Transition of Eocene whales from land to sea: evidence from bone microstructure. PLoS One. 2015;10(2):e0118409. Published 2015 Feb 25. doi:10.1371/journal.pone.0118409