Reunion on Old Orchard Beach

I hadn't taken into account that water has a way of exploiting a weak point.  On geologic maps, a black line with arrows on one side suggests one slab of rock has slid underneath another.  I convinced my wife to drive out to the site of the fault, with the added enticement that it intersected the coast.  A trip to the beach, on a day above 40 in the winter was not to be passed up.  We pulled into Ocean Park, and while my wife fed my son, I scouted the site.  

What I hoped to see was a reunion.  Five hundred million years ago the rock to the south of Ocean Park and the rock to the north found their home on the fringe of a continent called Gondwana. The goliath Gondwana covered an area of Earth a tad bigger than modern Asia centered around the South Pole.  If Gondwana was Asia, then Biddeford and the rock to the south of Ocean Park were part of Japan; Old Orchard, and the rock to the north,the coast of China.  Four hundred ninety million years ago, plate tectonics ripped Gondwana apart.  These hunks of land set sail across the proto-Atlantic, their near hundred million year journey landing them on Maine's coast 400 million years ago.  Unfortunately, tectonics did not set them gently on the coast.  The force of the plates shoved the edge of the Biddeford land mass underneath the one that underlies Old Orchard.  In a moment I could see Gondwana reunited on Maine's shores.

As I climbed the dune to get a view of this collision, I'd already began to lose hope.  The wind blown sand pointed to the fact that no natural bedrock hindered the movement of sediment. Cresting the dune, I saw beautiful beach for miles in either direction, but no fault.  My wife enjoyed the beach, my son gleefully played in the sand and I pursued the only rock bigger than a pebble, only to be chased away by cold waves.  I looked up the beach at Prout's Neck, and down at Biddeford Pool, wistfully considering my chances of convincing my wife to add some miles to our trip.  If I could just see the rocks on either end, I might find evidence of the Gondwanan meeting point.  Why were they so far away?

A wave hit the shore and my mind traveled back that 400 million years.  That wave would have hit the junction of those collided islands.  It would have found the minute space in between that ancient Japan and that forgotten China.  As it rushed in it would have torn away the smallest piece of sediment.  As it poured out, it would have stolen another.  The space in between would have grown larger and larger. Grain by grain it would be filled in with the small fragments that were broken away.  For 400 million years, the trend would continue.  The end point of this scenario had become clear.  

As we walked back down the beach, on the way to our car, I looked at Biddeford Pool and Prout's Neck as stalwart survivors of an intense collision, then a slow bleed.  Each a reminder of a reunion too long ago to have withstood the relentless abrasion of water.

"Avalon Terrane Field Trip." MIT Geology Field Camp. MIT, n.d. Web. 16 Mar. 2014. <http://web.mit.edu/12.114/05_fall/www/nonGIS_data/worlds_end_bos_basin_field_guide_sm.pdf>.

Dorais, Michael J., Robert P. Wintsch, Wendy R. Nelson, and Michael Tubrett. "Insights Into The Acadian Orogeny, New England Appalachians: A Provenance Study Of The Carrabassett And Kittery Formations, Maine." Atlantic Geology 45.0 (2009): 50-71. Print.

"Geology of Massachusetts." Wikipedia. Wikimedia Foundation, 22 Feb. 2014. Web. 16 Mar. 2014. <http://en.wikipedia.org/wiki/Geology_of_Massachusetts>.

Nance, R. Damien. "Late Precambrian–early Paleozoic arc-platform transitions in the Avalon terrane of the Northern Appalachians; Review and implications."Geological Society of America Special Papers 245 (1990): 1-12. Print.

Osberg, Philip H., Hussey, Arthur M., II, and Boone, Gary M. (editors), 1985, Bedrock geologic map of Maine; Maine Geological Survey (Department of Conservation), scale 1:500,000  

Maine Geology Timeline

I tend to write blog posts in the order I become interested in them.  I may include how long ago events occurred, but when you're dealing with hundreds of millions of years, things get a little abstract. Today I decided to present the information of my blog in timeline form.  Using a web tool at knightlab.com, I created this.  There are some limitations in the software - primarily, the timeline tool does not go back in time to millions of years ago, so I did some messing around with dates to make it work.  Try clicking the arrows on the slides or clicking around the timeline itself to navigate Maine geologic history.  Also, click the links on the slides to find more about each event and how it shows up in the Maine landscape.  Enjoy.

How to Make Bricks in Three Easy Steps

Last weekend my son and I foresook our weekly grocery shopping trip at the West Falmouth Hannaford.  Instead we crossed the bridge on the south end of the parking lot and ended up taking a walk on an ancient sea floor.  Don't get me wrong, this is not a magical bridge that can transport one to a fantasyland.  The bridge was built in 1859 by the railroad company to connect the Hobbs farm to the rest of society.  John Hobbs homesteaded the land in 1775, and before 1859 when the railroad isolated it and the Hobbs sold it, put it to a variety of industrious uses.  Like people of earlier times are fabled to have done, the Hobbs put every part of the land to use.  The trees became oak shingles, the soil was farmed and the clayey sediment was extracted to make bricks.  The story of these bricks extends far beyond the Hobbs enterprising spirit and thousands of years before the clay was first dug.

The story of our bricks began about 22,000 years ago when glaciers covering much of the globe decided to call it a day and begin the slow commute home from Long Island, New York (Long Island formed as the flowing ice of the glacier delivered gigantic piles of rock to its melting endpoint).  At this point, Maine and the rest of northern North America were buried in ice. Heavy, heavy ice.  The normally firm raft of rock, on which our continent sits, sank like a rowboat upon boarding.  As melting glaciers contributed to a growing ocean, this depressed plate would make way for the intrusion of a sea much larger than today's Atlantic.

The land above the sea couldn't wait to cast off its icy water.  Massive streams poured tons of melted ice into the growing sea, but the water didn't come alone. As the rivers raced to the sea their fast current picked up every stone, pebble, sand grain or mote of clay they could carry.  Massive material, like stones and pebbles may have been dropped long before reaching the sea.  When the stream met the water, it rapidly decelerated. Upon slow down, enough sand was dropped to create a river delta as deep with sand as a football field is long.  The sand from this river's mouth can still be spied along I95 between Gray and Lewiston and is currently being quarried in Gray.  But what about the bricks?

The slow moving water, at this point, would have dropped nearly everything.  Robbed of most of its energy by the trudge into the ocean, the sluggish water couldn't carry much.  Luckily, clay is small and light.  The water transported these small grains the farthest, finally dropping them at the sight of the future Hobbs' farm.  About 13,000 years ago, with the weight of ice removed, the plate rebounded, and the sea level dropped.  The acreage of the Hobbs' farm was revealed.  Soil developed.  Oaks grew.  Eventually, the Hobbs would dig up their bricks and my son's and my weight would leave footprints in the ancient seabed.  

McCully, Betsy. "Ice Age." New York Nature. N.p., n.d. Web. 11 Feb. 2014. <http://www.newyorknature.net/IceAge.html>.

Robinson, Michael A., Stewart K Sandberg, and Kirkpatrick Melissa D.,. "Using transient electromagnetic soundings to map the thickness of the Gray Delta, Maine, and correction of data using coil calibration to improve resolution. ." Geological Society of America Abstracts with Programs 33.1 (2000): 1. Print.

Weddle, Thomas K., Gray Quadrangle, Maine, 1:24,000, Augusta, ME: Natural Resources Information and Mapping, Maine Geological Survey, 1997.

"Surficial Geologic History of Maine." Maine Geological Survey. N.p., 6 Oct. 2005. Web. 11 Feb. 2014. <http://www.maine.gov/dacf/mgs/explore/surficial/facts/surficial.htm>.

"River Point Conservation Area." The Town of Falmouth . The Town of Falmouth , n.d. Web. 11 Feb. 2014. <http://www.town.falmouth.me.us/pages/falmouthme_parks/trailmaps/RiverPoint>.

Maine's Pinatubo: Unearthing a Natural Disaster

Soon J.D. Irving Limited may be freed to start thinking about how to take 22 million tons of copper ore out of the ground in northern Maine. The Maine legislature may relax laws regulating the mining of metals in Aroostook County. While Irving consider strategies for extracting copper and zinc, as well as relatively small amounts of gold and silver, I have been thinking about how the metal rich rock, called sulfide ore, got there in the first place. It all occurred about 500 million years ago when a series of islands, not too unlike the Philippine islands, were forming off the coast of North America.

The best lens from which to consider what went into creating the ancient ore might be to consider a more recent event. Twenty-one years previous to the bill being passed, Mount Pinatubo was cooling off after a long summer of letting off steam. In the summer of 1991, the Philippine Sea Plate subducted beneath the Eurasian plate, releasing 10 billion tons of magma in a volcanic eruption. As the magma neared the surface, it released chemicals that refused to join with others to form minerals. Valuable metals, like zinc and copper and dangerous ones like cadmium and lead, were distributed as ash across the Philippine region. Far from a rain of wealth, the ashfall is thought to have significantly shortened human lifespan on nearby islands. Sulfur combined with oxygen in the atmosphere to form sulfur dioxide gas, which in turn joined with moisture in the atmosphere to form sulfuric acid. Aircraft throughout the Northern Hemisphere experienced corrosion damage from the acid for years afterward. It is with good reason that the eruption of Mount Pinatubo was regarded as a natural disaster.

Five hundred million years ago no one was around to experience the ash or acidity of eruptions that formed the islands that would become the metal-rich rock in northern Maine. The islands and the ore formed as two oceanic plates in a proto-Atlantic ocean collided. One plunged beneath, bringing loads of ocean water with it. As the water and the rock descended, both heated. The water would have rushed through subterranean rock, dissolving unmatched elements along the way. The scalding liquid would have picked up sulfur, then metals. It would wend its way upward, cooling as it went. As its temperature dropped the dissolved sulfur, submerged and lacking its partner oxygen, would seek out other mates, finding them in the unmatched metals that flowed alongside. The sulfur/ metal pairs, sulfides, solidified and were stored underground preventing life's exposure to corrosive acids or dangerous metals.

In the next decade J.D. Irving may decide it is worth unearthing the metal-bearing sulfides of Aroostook County. But the price of digging up a natural disaster must be paid. Payment can be rendered in advance if the mining company works to prevent the spread of sulfur and metals into the environment. It can be paid after the fact by the citizens of Maine, in the form of clean up costs. Or, it can be paid by sacrificing the beauty and balance of northern Maine's natural ecosystem. Regardless, the cost must be rendered, and it's best to consider this before the bill comes due.

Beck, Fredrick. "A History of Non-Ferrous Metal Mining and Exploration in Maine." Geological Society of Maine. N.p., n.d. Web. 1 Jan. 2014. <http://www.gsmmaine.org/wp-content/uploads/2010/02/Beck-A-History-of-non-ferrous-metal-mining-and-exploration-in-Maine.pdf>.

Casadevall, Thomas J. , Perla J. Delos Reyes, and David J. Schneider. "The 1991 Pinatubo Eruptions and Their Effects on Aircraft Operations." Fire and Mud: Eruptions and Lahars of Mount Pinatubo. U.S. Geological Society, 10 June 1999. Web. 1 Jan. 2014. <http://pubs.usgs.gov/pinatubo/casa/>.

"Environmental Health and Safety Guidelines Base Metal Smelting and Refining." International Finance Corporation. International Finance Corporation, 30 Apr. 2007. Web. 1 Jan. 2014. <http://www.ifc.org/wps/wcm/connect/4365de0048855b9e8984db6a6515bb18/Final%2B-%2BSmelting%2Band%2BRefining.pdf?MOD=AJPERES&id=1323152449229>.

"Open-pit Metal Mining in Maine." Natural Resource Council of Maine. Natural Resource Council of Maine, n.d. Web. 1 Jan. 2014. <http://www.nrcm.org/issue_mining.asp>. 

"Volcanic Gases and Their Effects." Volcano Hazards Program. U.S. Geological Survey, n.d. Web. 1 Jan. 2014. <http://volcanoes.usgs.gov/hazards/gas>. 

"Volcano or Environmental Disaster?." VolcanoCafe. N.p., 18 Nov. 2013. Web. 1 Jan. 2014. <http://volcanocafe.wordpress.com/2013/11/18/volcano-or-environmental-disaster/>.

The Outcrop in the Crystal

It's my 20th post!  This blog post is the first of several that will highlight an outcrop that drove my interest in Maine geology.  If you're looking for the outcrop it's on Rte. 115 on the Gray/ Windham border.  Or check it out on the Sphere app.  

The outcrop told the story of Maine.  The white rock, a granite, bubbled up when Africa's coast collided with our own 450 million years ago, sealing Maine into the Pangeaic interior.  The black basalt resulted from one of the volcanoes that once again cleaved the supercontinent in two when Pangea split.  The glittery schist told the tale of a muddy ocean bottom that predated both two igneous rocks.  But how did the green rock get there?

There were obvious clues.  The parallel stripes of white, green, and sometimes even gray told tales of piling layers.  The fact that these layers took turns with schist, a mudstone altered by heat and pressure, as one scanned the outcrop from left to right suggested that it, too, formed in that muddy sea.  Other facts didn't add up.  The tough rock scored glass.  Most of the usual sedimentary suspects wouldn't do that; unmetamorphosed mudstone and limestone were just too soft.  Their metamorphic progeny, schist and marble would have crumbled as well.  Sandstone, and its postbear quartzite, would do the job, but the look wasn't right.  The rock lacked the granularity of sandstone, and the sugariness of quartzite.

The truth became clearer as I began to research Silurian time, a period between 416 and 444 million years ago, in which the green rock formed.  The ocean bottom that it gathered in was flanked on three sides.  To the north lie North America, to the south, a hunk of land that would become Maine's coast. To the east, Western Europe plugged another opening preventing the flow of currents.  The phlegmatic basin, just south of the equator, became poor in oxygen, but rich in life.  Lacking our usual breath of life, the creatures of the sea resorted to extreme measures - consuming sulfur.  

The chemistry of this bounded sea played an important role in the green rock's formation.  As a coral reef, in an aerated ocean, degrades, it forms limestone, which is composed of the elements calcium, carbon and oxygen.  Our sluggish sea would have produced a similar product, with one small difference: the sulfur consumption exchanges some of the sediment's calcium for a new element - magnesium.  The rock it forms goes by a different name: dolomite.

Even dolomite doesn't have the strength to scratch glass.  The rock would require one final transformation.  As plates moved, the basin grew smaller, and then disappeared.  The formation of Pangea spurred an influx of fluids: some large, like the bulb of magma that formed the white granite, some less immense, like the infusion of quartz and water that flowed through the ancient ocean bottom.  This liquid sought out any channel it could access, including spaces in the schist, and the dolomite.  The schist proved passable, but inert.  The dolomite was reactive.  The heat and chemicals in the flowing fluid released carbon and oxygen from the dolomite (as carbon dioxide).  Some of the quartz stuck around, providing the white layers of the rock.  The green crystals, a mineral called diopside, kept the calcium and magnesium of the dolomite and replaced the CO2 with silicon and oxygen from the quartz.  

The outcrop is a testament of Maine's geological history.  It documented the marine roots and the accordion push-pull of continents.  The green diopside crystal, a fractal of that outcrop, records the deoxygenated ocean bottom in its calcium and magnesium.  It further tells the tale of the pushing and pulling continents in its silicon and oxygen.  The green crystal, a mere fragment of the outcrop, tells the outcrop's entire story.

Bickle, M. J. , H. J. Chapman, J. M. Ferry, D. Rumble, and A. E. Fallick. "Fluid Flow and Diffusion in the Waterville Limestone, South—Central Maine: Constraints from Strontium, Oxygen and Carbon Isotope Profiles." Journal of Petrology 38.11 (1997): 1489-1512. Print.

Ferry, J. M.. "A Comparative Geochemical Study Of Pelitic Schists And Metamorphosed Carbonate Rocks From South-central Maine, USA." Contributions to Mineralogy and Petrology 80.1 (1982): 59-72. Print.

Fischer, Dan , Tammy (Yue) Liu, Emily Yip, and Korsen Yu. "The Silurian Period."The Silurian Period. University of California Museum of Paleontology, 5 July 2011. Web. 6 Dec. 2013. <http://www.ucmp.berkeley.edu/silurian/silurian.php>.

Hussey, Arthur M., II, 1996, Bedrock geology of the North Windham 7.5' quadrangle, Maine; Maine Geological Survey (Department of Conservation), Open-File Report 96-16, 6 p.

Helmholtz Centre for Ocean Research Kiel (GEOMAR) (2012, June 7). How does dolomite form?. ScienceDaily. Retrieved December 8, 2013, from http://www.sciencedaily.com/releases/2012/06/120607105815.htm

Wilde, Pat , William Berry, and Mary Quinby-Hunt. "Silurian Oceanography."Marine Sciences Group. University of California, Berkeley, n.d. Web. 8 Dec. 2013. <http://www.marscigrp.org/sil91.html>.

Beyond Pangea: The Chain Lakes' Long History

Every middle schooler hears about Pangea.  You look at the world map and envision the ocean closing and that land before time re-forming.  And that's the end.  You don't think about what happened before because no one ever told you that there was a before.  Well, I am here to set you straight.

Don't get me wrong.  Pangea is old.  When Pangea was THE place to be, dinosaurs had not yet set foot on this Earth.  In fact, the dry center of the giant continent set the stage for water loving amphibians to evolve into drought tolerant reptiles.  Later, these reptiles gave birth to the generations that would become the feared lizards we call dinosaurs.  Here in Maine, however, you will find no trace of dinosaurs, because nearly every rock was formed before the oceans that collapsed to make way for Pangea produced their parting waves.

What's important to realize is that the formation of whole Earth continents, like Pangea, is a cycle.  These so-called supercontinents occur occasionally throughout Earth history.    Six hundred million years ago, the supercontinent of the day, one that we call Pannotia, would have filled much of the space taken up by the modern day western Pacific Ocean, and a large hunk of Antarctica, too.  About 1.3 billion years ago, Rodinia was gathering all the Earth's land masses at the equator.  This is the point at which we will begin our journey back to the future.

The Chain Lakes Massif, an elevated hunk of land just north of Sugarloaf, may be the best perch from which to watch the story unfold.  A supercontinent is formed when an ocean closes.  The weighty seafloor rock descends into the Earth beneath the lighter continental shoreline. The diving rock melts, and then reascends, forming a chain of volcanoes, not unlike the modern Andes.  The larger the colliding continents, the larger the mountain chain - and Rodinia was big!  The billion year old mountain chain is now the core of North America, running the 3000 miles from Newfoundland, Canada to Veracruz, Mexico.  Big mountains fall fast, and as rain and ice dragged sediment from the peaks it dropped it into the closing ocean.  Some scientists think it was this sediment that would become the Massif.  As the ocean closed, the sediment may have changed from mud to stone.

A billion years ago Rodinia was formed, but this, too, must pass.  The mega-continent shattered.  While the 3000 mile backbone, called the Grenville Province, stayed intact, the sedimentary shorelines drifted away.  While the cycle continued, the sedimentary island moved along the Earth's surface, but 400 million years after it started its journey, the Massif came home.  As its ocean closed, and Pannotia gathered, the piece of land that would become the Chain Lakes became nestled in the heart of the new supercontinent.  Nestled may be an understatement, because the crushing force of the continent forming squeezed, buried, and roasted the rock, altering it from a simple sedimentary rock to a banded metamorphic one called gneiss.

Pannotia didn't last long, and when the proto-Pangea split, the Massif hung on to what would become North America.  In fact at that time it would have been coastal property, but that would change as oceans closed one more time.  The Iapetus Ocean (Iapetus was the father of Atlas, and the Iapetus was the predecessor of the Atlantic) closed in stages.  The first impact was a set of Carribean-like islands, the next a small continent called Avalon.  Each collision provided more heat and more pressure, driving the gneissic metamorphism of the once sedimentary rock even further; and making the geologic puzzle harder to solve.

The final crunch came as Africa found its place in the Pangeaic landscape.  The world, different than the one in which we now reside, would at least be familiar to our geographic sensibilities.  South America cuddled up with western Africa, and northern Africa spooned by New England.  Pangea may be the first chapter in our middle school geology texts, but it was one of the last in this corner of Maine.

DiPietro, Joseph A. Landscape Evolution in the United States: An Introduction to the Geography, Geology, and Natural History. Burlington, MA: Elsevier, 2013. Print.

Landing, Ed. "Vestiges of Rodinia: Adirondack and Hudson Highlands." New York State Geological Survey. New York State Museum, n.d. Web. 11 Nov. 2013. <http://www.nysm.nysed.gov/nysgs/nygeology/tectonic/02.html>.

Meert, Joseph . "A History and Preview of Supercontinents through Time." Gondwana Research. N.p., n.d. Web. 11 Nov. 2013. <http://gondwanaresearch.com/hp/supercon.pdf>.

A Piece of Deer Isle: Rapakivi Fingerprints

When I first started learning about rocks I remember being impressed that each rock formation was unique.  The reddish color of a brownstone cobble in Finlayson, Minnesota informed me that the rock had made the 50 mile trip from the iron rich shores of Lake Superior.  I've started to look for fingerprints in rocks, and there is none more common in Maine than the rapakivi crystals of Deer Isle granite.

Deer Isle Stonework in Falmouth, Maine

While the formation has its home on its namesake island downeast, Deer Isle granite is everywhere.  You can hardly take a step in the L.L. Bean flagship store without resting your sole on a slab. I've noted its presence in kitchen counters, cutting boards, and outdoor stonework.  It even secreted itself into the foundation of Yankee Stadium, a long trip for a stone from Red Sox territory.  In any of these locations the rock would be instantly recognizable by its round pink crystals wrapped in a ring of white.

Close up of Deer Isle granite.  Notice the rounded pink crystal
in the center, and the white rim surrounding it.

The ring not only gives up the source location, it tells a story.  The pink mineral, microcline feldspar, is not normally round. When it developed deep under the surface it would have taken the form of a prismatic rod with regular angles. But this was under pressure.  Where the microcline first solidified may have been 10 miles under the surface. That means 10 miles of rock weight are pressing down on our magma stream like the grasp of Superman.  Just like the hero's clutch could turn coal into diamond, the added pressure that comes with this weight turned liquid rock into solid.  But the crystal had formed before its time.

As this slurry of magma and loose crystals rose up toward the surface, the weight pressing on it subsided.  Without the added pressure, the geometric crystals began to melt, leaving only their rounded centers behind. As the ooze ascended, crystal formation conditions changed.  The microcline, more stable in the deeper conditions, would now be replaced by a different mineral, white plagioclase feldspar.  Because the two minerals are very similar, the plagioclase quickly continues the pattern disrupted by the pressure drop.

Conditions must be just so to create this pattern. A cooler magma channel, the white mineral never forms.  The pressure drops too quickly and the pink feldspar melts altogether. Deer Isle granite's unmistakeable fingerprint is a result of its unique story of formation, dissolution, and restoration. This distinctness may be one trait that makes the stone desirable, but it is certainly one that makes it recognizable.

Eklund, O., and A.D. Shebanov. "The origin of rapakivi texture by sub-isothermal decompression." Precambrian Research 95.1-2 (1999): 129-146. Print.

Hooke, Roger Leb.. "A Geologic History of Deer Isle, Maine." College of the Atlantic, Serpentine Ecology Conference. July 2007. Web. 14 Oct. 2013. <www.coacommunity.net/downloads/serpentine08

Nekvasil, Hanna. "Ascent of Felsic Minerals and Formation of Rapakivi." American Mineralogist 76 (1991): 1279-1290. Print.

Prinz, Martin. Rocks and Minerals Simon & Schuster's Guide to Rocks and Minerals.. New York, NY: Simon and Schuster, 1978. Print.