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Wednesday, October 4, 2017

Geologic Mélange: A Mixed Bag of Lithologies

      A geologic mélange consists of a jumble of large blocks of varied types of rocks.  A mélange is a large-scale breccia (rock consisting of angular fragments cemented together).  It is a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all different sizes, contained in a fine-grained deformed matrix.

       Large-scale mélanges formed in active continental margins generally consist of altered oceanic crustal material and blocks of continental slope sediments in a sheared mudstone matrix.

       The mixing mechanisms in such settings may include tectonic shearing forces, ductile flow of a water-charged or deformable matrix (such as serpentinite), 

and sedimentary action (such as slumping or gravity-flow). 

     Some larger blocks of rock may be as much as 1 kilometer (0.62 mi) across. Smaller-scale localized mélanges may also occur in shear or fault zones, where coherent rock has been disrupted and mixed by shearing forces.

      For my money, mélange is an beautiful-sounding word for a jumbled mess of lithologies. Sorting out environmental conditions in a mélange is a geological puzzle with well over 1,000 pieces.

Happy sorting and solving all those puzzle pieces!

Deer and Dear Maizie---Fall in the Rockies:

Thursday, September 14, 2017

Two Hundredth Post: More Continental Crust on South America's Andean Plateau

       This is our 200th blog post and our 48th month of publishing Partial Ellipsis of the Sun! Thanks for your support over the past four years!

      "Seismologists investigating how earth forms new continental crust have compiled more than 20 years of seismic data from a wide swath of South America's Andean Plateau and determined that processes there have produced far more continental rock than previously believed.

     "When crust from an oceanic tectonic plate plunges beneath a continental tectonic plate, as it does beneath the Andean Plateau, it brings water with it and partially melts the mantle, the layer below earth's crust," said Rice University's Dr. Jonathan Delph, co-author of the new study published this week. "The less dense melt rises, and one of two things happens: It either stalls in the crust to crystallize in formations called plutons or reaches the surface through volcanic eruptions."

     Dr. Delph said the findings suggest that mountain-forming regions like the Andean Plateau, which geologists refer to as "orogenic plateaus," could produce much larger volumes of continental rock in less time than previously believed.

     Co-author Dr. Kevin Ward, a researcher at the University of Utah, said, "When we compared the amount of trapped plutonic rock beneath the plateau with the amount of erupted volcanic rock at the surface, we found the ratio was almost 30:1. That means 30 times more melt gets stuck in the crust than is erupted, which is about six times higher than what's generally believed to be the average. That's a tremendous amount of new material that has been added to the crust over a relatively short time period."

     The Andean Plateau covers much of Bolivia and parts of Peru, Chile, and Argentina. Its average height is more than 12,000 feet, and though it is smaller than Asia's Tibetan Plateau, different geologic processes created the Andean Plateau. The mountain-building forces at work in the Andean plateau are believed to be similar to those that worked along the western coast of the U.S. some 50 million years ago. Dr. Delph said it's possible that similar forces were at work along the coastlines of continents throughout Earth's history.

     Most of the rocks that form Earth's crust initially came from partial melts of the mantle. If the melt erupts quickly, it forms basalt, which makes up the crust beneath the oceans on Earth; but there are still questions about how continental crust, which is more buoyant than oceanic crust, is formed. Drs. Delph and Ward spent several months combining public datasets from seismic experiments. Seismic energy travels through different types of rock at different speeds, and by combining datasets that covered a 500-mile-wide swath of the Andean Plateau, Ward and Delph were able to resolve large plutonic volumes that had previously been seen only in pieces.

     Over the past 11 million years, volcanoes have erupted thousands of cubic miles' worth of material over much of the Andean Plateau. Ward and Delph calculated their plutonic-to-volcanic ratio by comparing the volume of regions where seismic waves travel extremely slowly beneath volcanically active regions, indicating some melt is present, with the volume of rock deposited on the surface by volcanoes.

     "Orogenic oceanic-continental subduction zones have been common as long as modern plate tectonics have been active," Dr. Delph said. "Our findings suggest that processes similar to those we observe in the Andes, along with the formation of supercontinents, could have been a significant contributor to the episodic formation of buoyant continental crust."

Happy 200th!

Monday, August 28, 2017

Trig Warning: 3700-Year-Old Babylonian Tablet

     A Babylonian clay tablet known as Plimpton 322 was discovered early in the 20th century in present-day Iraq. An Australian mathematician, Dr. David Mansfield, who has been analyzing its meaning, announced his conclusions in late August, 2017, saying that "cracking the meaning of the tablet, as big as the palm of a human hand, could simplify our study of triangles."

      Up to now, trigonometry has been based on study of angles and irrational numbers. The analysis of Plimpton 322 reveals that the Babylonians used ratios during 2800 to 1700 BC.  “This gives us a different way of looking at trigonometry,” Dr. Mansfield said. “The beautiful thing about it is that it’s much simpler.” 

      "Trigonometry is not a fusty, {I find the use of the word"fusty" is awesome here!} esoteric branch of mathematics. It is essential to architecture, engineering, astronomy, surveying, and even oceanography. Up to now, it’s been taught using Greek principles. But this tablet proves that the Babylonians beat the Greeks in the discovery of trigonometry by about 1,000 years."

       The tablet was unearthed in southern Iraq, believed to be near the onetime Sumerian city of Larsa, by Edgar Banks, a collector of antiquities in the 1890s. Banks was not collecting cuneiform tablets as an archaeologist, but while using his position as the American consul to Baghdad. He sold the tablets to universities, libraries, and museums.

      "The Greek astronomer Hipparchus has been considered the father of trigonometry. But this tablet was created long before Hipparchus lived."

      Dr. Mansfield said, “Babylonian mathematics may have been out of fashion for more than 3,000 years but it has possible practical applications in surveying, computer graphics and education.”

      "The tablet got its name because an American publisher and collector named George Arthur Plimpton bought it. (He is the grandfather of writer and editor George Plimpton, founder of the Paris Review and author of Paper Lion.) In 1936, not long before he died, Plimpton donated the Babylonian tablet along with many other manuscripts to Columbia University."

     "In the 1940s, researchers who were studying the tablet concluded that the cuneiform numbers on it corresponded to the Pythagorean Theorem. But that was far as they got until Dr. Mansfield and his team took up the challenge.

      The tablet “is a fascinating mathematical work that demonstrates undoubted genius,” says Dr. Mansfield. “The tablet not only contains the world’s oldest trigonometric table; it is also the only completely accurate trigonometric table, because of the very different Babylonian approach to arithmetic and geometry.”

Not at all a fusty fuss, eh?

Elk in downtown Evergreen, CO >>>

Sunday, August 20, 2017

LIDAR, Connecticut Forests, and Iowa Marching Bear Effigy Mounds

       Dr. Katharine Johnson from the University of Connecticut (UConn) focuses on uncovering  
hidden remnants of the past using LIDAR imaging. The name LIDAR, sometimes considered an acronym of Light Detection And Ranging (sometimes Light Imaging, Detection, And Ranging), was originally a portmanteau of light and radar. Johnson and her colleagues have been piercing dense forest cover to uncover historic sites in New England (as seen here in Plainfield, Connecticut).


     Many of the tree-covered landscapes of modern New England were not always so green. In the 17th century, the region was the site of widespread deforestation, as European colonists built farms and homesteads. Between 60 to 80 percent of the land was cleared for fields, pastures, and orchards; these were surrounded with stone walls, houses, outbuildings, and roads.

      The natural-color photograph above was shot during an aerial survey in 2012. The monochromatic light detection and ranging (LIDAR) image, captured in 2010, shows the same area with greater contrast and reveals features on the ground. 

      LIDAR instruments send out rapid pulses of laser light that reflect off of solid surfaces (such as tree limbs or the ground). A receiver detects the photons that bounce back to the instrument, parsing out subtle variations in land elevation and allowing researchers to distinguish bumps and surfaces on the terrain.

      LIDAR has been used by archaeologists in other landscapes, perhaps most famously in Belize, where researchers have used it to uncover ancient Maya sites. The startling Marching Bear Effigy Mounds in northeastern Iowa were highlighted with LIDAR as well.


     “You can see patterns people made as they were dividing the landscape and farming,” said Johnson. LIDAR imaging helped them uncover traces of stone walls, dams, abandoned roads, building foundations, farm structures, and relict charcoal hearths—all of which have been slowly hidden over the past two centuries as the forest reclaimed the land.

 “The biggest surprise was being able to see the extent to which historic land use had impacted the landscape, which is not something that is readily visible in high-resolution aerial photos.”

Happy 24th birthday to Zoë today! Here she is celebrating with fellow Peace Corps volunteers in Ethiopia.

Have you used LIDAR?

Eclipse photos. Moonshadow. Moonshadow. . .How was your solar eclipse experience?

Eclipse at the Great Sand Dunes, Colorado--whoa!

Tuesday, August 8, 2017

Crinoids for Cri-nerds

     We discussed crinoids,
also known as sea "lilies," here at Partial Ellipsis of the Sun in April. This extraordinarily well-preserved Paleozoic crinoid fossil sample (below) inspired another look at this animal that looks like a plant.

      Compare the sample above to the "Smarties" stem pieces we found in northern Arkansas in April. The disarticulated crinoid stems or stalks are relatively common, but the delicate, lacy crown pieces are much rarer.

      Modern day crinoids and the fossil animals are quite similar, hence they are often referred to by the non-scientific term "living fossils."

       The parts of crinoid animals are labelled below, though the terms are quite plant-based:

I guess you could say I'm a bit of a cri-nerd ;-).

     How about you?

Monday, July 31, 2017

DNA of Ancient Canaanites: Levant, Lebanon, and Lines

      Researchers have deciphered the complete DNA of five Canaanite skeletons. By comparing these five Canaanite genomes with those of other ancient and modern populations, the scientists identified the Canaanites’ ancestors and discovered their descendants were modern Lebanese people.

     The results, reported July 27 in the American Journal of Human Genetics, give new insight into the origins and fate of a people whose story has largely been told through the secondhand accounts of its contemporaries.

     "The Canaanites emerged in the Levant, a region east of the Mediterranean Sea, 3,000 to 4,000 years ago. This cultural group, which established extensive trade networks and colonies across the Mediterranean region, left behind few written records, perhaps because they wrote on papyrus rather than clay. So most knowledge of the Canaanites comes from ancient Egyptian, Hebrew and Greek documents."

     "But, doubt surrounds some of those accounts. For one thing, Greek historians thought the Canaanites originated near the Persian Gulf, whereas archaeological records suggest they arose from farming communities that settled the Levant up to 10,000 years ago. For another, the Old Testament makes reference to the destruction of Canaanite communities, but some of their cities, such as Sidon in Lebanon, appear to have been continually inhabited through the present day."

     "Researchers reconstructed the genomes of the 3,700-year-old remains of five Canaanites unearthed in Sidon. Comparisons of these genomes with those of other ancient Eurasian peoples indicate that Canaanite ancestry was split roughly 50-50 between the early farmers who settled the Levant and immigrants of Iranian descent who arrived later, between 6,600 and 3,550 years ago."

     “You’d need a lot of migration for roughly half of the population to be replaced by the incoming Iranian-related populations,” says Iosif Lazaridis, a geneticist at Harvard Medical School who was not involved in the study. “This must have been some important event in the history of the Near East.” One possibility is the spread of the Akkadian Empire, which controlled a region spanning from the Levant to Iran between 4,400 and 4,200 years ago. That connection may have presented the opportunity for interbreeding between these far-flung populations."

     "The researchers also determined that modern Lebanese people can attribute about 93 percent of their ancestry to the Canaanites. The other 7 percent comes from Eurasians who probably arrived in the Levant 3,700 to 2,200 years ago. Study coauthor Chris Tyler-Smith, was surprised by how much Canaanite heritage dominated modern Lebanese DNA. He says he expected to see a more mixed gene pool because so many populations have crossed through the Levant in the last few thousand years."

     "This study alone may not paint the complete picture of the Canaanite lineage, says Aaron Burke, an archaeologist at UCLA, because the researchers examined the genomes of only five Canaanites."

      "However, the study’s Canaanite genetic data do provide “a snapshot of history in the area,” Lazaridis said. Identifying which populations crop up in the Canaanite lineage — and when — can help trace the historical movements of people throughout the Near East. With DNA analyses of enough ancient people, Lazaridis says, “I think it will be possible to reconstruct the whole timeline of what happened in Lebanon and other parts of the world.” 

No lamentations; looking forward to more data!