New Ozarks field guide digs deep into the past

'From Precambrian Rift Volcanoes to the Mississippian Shelf Margin: Geological Field Excursions in the Ozark Mountains,' edited by Kevin Evans and James Aber, is available now.

Developed in conjunction with the 2010 GSA North-Central/South-Central Section Meeting in Branson, Missouri, USA, this new volume from The Geological Society of America includes six field trips that convey discovery and insight into the long-studied geology of the Ozark region. -  Geological Society of America
‘From Precambrian Rift Volcanoes to the Mississippian Shelf Margin: Geological Field Excursions in the Ozark Mountains,’ edited by Kevin Evans and James Aber, is available now.

Developed in conjunction with the 2010 GSA North-Central/South-Central Section Meeting in Branson, Missouri, USA, this new volume from The Geological Society of America includes six field trips that convey discovery and insight into the long-studied geology of the Ozark region. – Geological Society of America


The geologic wonders of the Ozarks are documented by a long history of exploration and analysis. But there is still much to be learned. The region continues to spark new studies elucidating the complex interconnections between basement, extensive carbonate platforms, structural overprinting, mineralization, karstification, and hydrology. This guidebook highlights many of these aspects as well as the connection to culture, history, and economic development of the Ozarks region.

Developed in conjunction with the 2010 GSA North-Central/South-Central Section Meeting in Branson, Missouri, USA, this new volume from The Geological Society of America includes six field trips that convey discovery and insight into the long-studied geology of the Ozark region. This book is a valuable tool not just for the meeting attendee, but to all students of geoscience interested in following in the footsteps of the book’s authors.

Trips will examine world-class lead and zinc mineral accumulations in the tri-state mining district of Kansas, Missouri, and Oklahoma; the Precambrian and Cambrian geology of Proffit Mountain as exposed by the catastrophic reservoir-collapse and flood scour that occurred along the East Fork of the Black River in December 2005; the geologic history of Riverbluff Cave in Springfield, Missouri; the rock resources of southwestern Missouri and the impact of geology on two Civil War battlefields there; and a comprehensive geologic mapping project centered along the Ozark Scenic National Riverways.

Geologist discovers pattern in Earth’s long-term climate record

This is Lorraine Lisiecki from University of California, Santa Barbara. -  UCSB
This is Lorraine Lisiecki from University of California, Santa Barbara. – UCSB

In an analysis of the past 1.2 million years, UC Santa Barbara geologist Lorraine Lisiecki discovered a pattern that connects the regular changes of the Earth’s orbital cycle to changes in the Earth’s climate. The finding is reported in this week’s issue of the scientific journal Nature Geoscience.

Lisiecki performed her analysis of climate by examining ocean sediment cores. These cores come from 57 locations around the world. By analyzing sediments, scientists are able to chart the Earth’s climate for millions of years in the past. Lisiecki’s contribution is the linking of the climate record to the history of the Earth’s orbit.

It is known that the Earth’s orbit around the sun changes shape every 100,000 years. The orbit becomes either more round or more elliptical at these intervals. The shape of the orbit is known as its “eccentricity.” A related aspect is the 41,000-year cycle in the tilt of the Earth’s axis.

Glaciation of the Earth also occurs every 100,000 years. Lisiecki found that the timing of changes in climate and eccentricity coincided. “The clear correlation between the timing of the change in orbit and the change in the Earth’s climate is strong evidence of a link between the two,” said Lisiecki. “It is unlikely that these events would not be related to one another.”

Besides finding a link between change in the shape of the orbit and the onset of glaciation, Lisiecki found a surprising correlation. She discovered that the largest glacial cycles occurred during the weakest changes in the eccentricity of Earth’s orbit — and vice versa. She found that the stronger changes in the Earth’s orbit correlated to weaker changes in climate. “This may mean that the Earth’s climate has internal instability in addition to sensitivity to changes in the orbit,” said Lisiecki.

She concludes that the pattern of climate change over the past million years likely involves complicated interactions between different parts of the climate system, as well as three different orbital systems. The first two orbital systems are the orbit’s eccentricity, and tilt. The third is “precession,” or a change in the orientation of the rotation axis.

Early Earth absorbed more sunlight — no extreme greenhouse needed to keep water wet

Minik Rosing, a geology professor at the Natural History Museum of Denmark, University of Copenhagen, and Dennis K. Bird, professor of geological and environmental sciences at Stanford.
Minik Rosing, a geology professor at the Natural History Museum of Denmark, University of Copenhagen, and Dennis K. Bird, professor of geological and environmental sciences at Stanford.

Four billion years ago, our then stripling sun radiated only 70 to 75 percent as much energy as it does today. Other things on Earth being equal, with so little energy reaching the planet’s surface, all water on the planet should been have frozen. But ancient rocks hold ample evidence that the early Earth was awash in liquid water – a planetary ocean of it. So something must have compensated for the reduced solar output and kept Earth’s water wet.

To explain this apparent paradox, a popular theory holds there must have been higher concentrations of greenhouse gases in the atmosphere, most likely carbon dioxide, which would have helped retain a greater proportion of the solar energy that arrived.

But a team of earth scientists including researchers from Stanford have analyzed the mineral content of 3.8-billion-year-old marine rocks from Greenland and concluded otherwise.

“There is no geologic evidence in these rocks for really high concentrations of a greenhouse gas like carbon dioxide,” said Dennis Bird, professor of geological and environmental sciences.

Instead, the team proposes that the vast global ocean of early Earth absorbed a greater percentage of the incoming solar energy than today’s oceans, enough to ward off a frozen planet. Because the first landmasses that formed on Earth were small – mere islands in the planetary sea – a far greater proportion of the surface of was covered with water than today.

The study is detailed in a paper published in the April 1 issue of Nature. Bird and Norman Sleep, a professor of geophysics, are among the four authors. The lead author is Minik Rosing, a geology professor at the Natural History Museum of Denmark, University of Copenhagen, and a former Allan Cox Visiting Professor at Stanford’s School of Earth Sciences.

The crux of the theory is that because oceans are darker than continents, particularly before plants and soils covered landmasses, seas absorb more sunlight.

“It’s the same phenomenon you will experience if you drive to Wal-Mart on a hot day and step out of your car onto the asphalt,” Bird said. “It’s really hot walking across the blacktop until you get onto the white concrete sidewalk.”

Another key component of the theory is in the clouds. “Not all clouds are the same,” Bird said.

Clouds reflect sunlight back into space to a degree, cooling Earth, but how effective they are depends on the number of tiny particles available to serve as nuclei around which the water droplets can condense. An abundance of nuclei means more droplets of a smaller size, which makes for a denser cloud and a greater reflectivity, or albedo, on the part of the cloud.

Most nuclei today are generated by plants or algae and promote the formation of numerous small droplets. But plants and algae didn’t flourish until much later in Earth’s history, so their contribution of potential nuclei to the early atmosphere circa 4 billion years ago would have been minimal. The few nuclei that might have been available would likely have come from erosion of rock on the small, rare landmasses of the day and would have caused larger droplets that were essentially transparent to the solar energy that came in to Earth, according to Bird.

“We put together some models that demonstrate, with the slow continental growth and with a limited amount of clouds, you could keep water above freezing throughout geologic history,” Bird said.

“What this shows is that there is no faint early sun paradox,” said Sleep.

The modeling work was done with climate modeler Christian Bjerrum, a professor in the Department of Geography and Geology, University of Copenhagen, also a co-author of the Nature paper.

The rocks that the team analyzed are a type of marine sedimentary rock called a banded iron formation. It is characterized by thin alternating bands of quartz, magnetite, an iron-rich mineral, and siderite, a mineral with a high carbon content, but also some iron.

“Any rock carries a memory of the environment in which it formed,” Rosing said. “These ancient rocks that are about 3.8 billion years old, they actually carry a memory of the composition of the ocean and atmosphere at the time when they were deposited.”

The critical part of the rocks’ memory was the banding and that iron was found chemically bound to oxygen rather than CO2 in the bands. The alternating bands would only have been deposited if the carbon dioxide content of the atmosphere kept shifting back and forth across a threshold that controlled which mineral was deposited. But that also meant that the amount of carbon dioxide couldn’t stray too far from that threshold. If there had been either substantially more or less carbon dioxide, only one of the minerals would have been laid down.

Another constraint on early carbon dioxide levels came from life itself.

In the days before photosynthetic organisms spread across the globe, most life forms were methanogens, single-celled organisms that consumed hydrogen and carbon dioxide and produced methane as a digestive byproduct.

But to thrive, methanogens need a balanced diet. If the concentration of either of their foodstuffs veers too far below their preferred proportions, methanogens won’t survive. Their dietary restrictions, specifically the minimum concentration of hydrogen, provided another constraint on the concentration of carbon dioxide in the atmosphere, and it falls well below the level needed for a greenhouse effect sufficient to compensate for a weak early sun.

“The conclusion from all this is that we can’t solve a faint sun paradox and also satisfy the geologic and metabolic constraints by having high carbon dioxide values,” Bird said.

But the theory of a lower Earthly albedo meets those constraints.

“The lower albedo counterbalanced the fainter sun and provided Earth with clement conditions without the need for dramatically higher concentrations of greenhouse gasses in the atmosphere,” Rosing said.


Scientists obtain unique recordings of Easter earthquake in Mexico

This is Sandra Seale, left, and Jamison Steidl of UCSB's Institute for Crustal Studies, with a map pinpointing the Baja earthquake and aftershocks. -  George Foulsham, Office of Public Affairs, UCSB
This is Sandra Seale, left, and Jamison Steidl of UCSB’s Institute for Crustal Studies, with a map pinpointing the Baja earthquake and aftershocks. – George Foulsham, Office of Public Affairs, UCSB

The major earthquake that occurred in Baja California on Easter Sunday, April 4th, at 3:40 p.m. Pacific Time, is of great interest to UC Santa Barbara seismologists, who are busy collecting information from a nearby research station. The earthquake was the largest in the Southern California region since 1992.

It is estimated that two lives were lost in the magnitude 7.2 earthquake, and an unknown number of people were injured. However, the losses are small in comparison to the recent 7.0 earthquake in Haiti, which occurred in a heavily populated area. Sunday’s earthquake was also of greater magnitude than the 6.7 Northridge quake in 1994.

Scientists at UCSB will supply the information they are gathering to engineers, for use in earthquake planning of buildings and city infrastructures.

The Easter quake occurred near one of several research stations used for gathering earthquake data. The site is called the Wildlife Liquefaction Array and is run as part of the George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES) program of the National Science Foundation, through the Institute for Crustal Studies at UCSB.

“This is a great data set that will validate all the effort that has been put into these arrays,” said Ralph Archuleta, chair of UCSB’s Earth Science Department.

The Wildlife site is in an area susceptible to liquefaction, which occurs when the saturated layer of sand below the surface “liquefies” during the strong shaking of an earthquake. In order to monitor the process of liquefaction, the Wildlife site has several instruments that record variations in the pressure of the groundwater located in these saturated layers.

Jamison Steidl, a UCSB seismologist and principal investigator, left Santa Barbara Tuesday morning to deploy more sensors at the Wildlife station just north of the Mexican border. “This is an exciting and unique data set, showing the process of excess pore pressure generation that leads to the liquefaction of soils, which can cause significant damage to the built environment,” Steidl said. “It is through this type of data that scientists will be able to better predict liquefaction during earthquakes, and engineers will be able to better mitigate the damaging effects.”

Steidl said that this quake did not reach the point of liquefaction. He also noted that, due to the aftershocks, there is a possibility of another large earthquake being generated through a variety of fault lines in the area.

According to the U.S. Geological Survey, the epicenter of Sunday’s 7.2 “Sierra El Mayor” earthquake was approximately 40 miles south of the Mexican border — at shallow depth along the principal boundary between the North American and Pacific plates. They report that this is an area with a high level of historical seismicity. This is the largest event to strike in this area since 1892. The earthquake appears to have been larger than the magnitude 6.9 earthquake in 1940, or any of the early 20th century events (in 1915 and 1934) in this region.

The nees@UCSB group will present this data at a meeting of the Seismological Society of America from April 21- 23, in Portland.

Not so fast! Andes rise was gradual, not abrupt

Trailing like a serpent’s spine along the western coast of South America, the Andes are the world’s longest continental mountain range and the highest range outside Asia, with an average elevation of 13,000 feet.

The question of how quickly the mountains attained such heights has been a contentious one in geological circles, with some researchers claiming the central Andes rose abruptly to nearly their current height and others maintaining the uplift was a more gradual process.

New research by U-M paleoclimatologist Christopher Poulsen and colleagues suggests that the quick-rise view is based on misinterpreted evidence. What some geologists interpret as signs of an abrupt rise are actually indications of ancient climate change, the researchers say. Their findings are scheduled to be published online April 1 in Science Express.

The confusion results when ratios of oxygen’s two main isotopes, oxygen-18 and oxygen-16, are used to estimate past elevation, said Poulsen, an associate professor with appointments in the departments of Geological Sciences and Atmospheric, Oceanic, and Space Sciences.

“In the modern climate, there is a well-known inverse relationship between oxygen isotopic values in rain and elevation,” Poulsen said. “As a rain cloud ascends a mountain range, it begins to precipitate. Because oxygen-18 is more massive than oxygen-16, it is preferentially rained out. Thus, as you go up the mountain, the precipitation becomes more and more depleted in oxygen-18, and the ratio of oxygen-18 to oxygen-16 decreases.”

Geologists use the ratio of these isotopes, preserved in rock, to infer past elevations.

“If the ratio decreases with time, as the samples get younger, the interpretation would typically be that there has been an increase in elevation at that location,” Poulsen said. In fact, that’s exactly the conclusion of a series of papers on the uplift history of the Andes published over the past four years. Using oxygen isotopes in carbonate rocks, the authors posited that the central Andes rose about 8,200 to 11,500 feet in three million years, rather than gaining height over tens of millions of years, as other geologists believe.

But elevation isn’t the only factor that affects oxygen isotope ratios in rain, Poulsen said. “It can also be affected by where the vapor came from and how much it rained—more intense rainfall also causes oxygen-18 to be preferentially rained out.” Skeptical of the rapid-rise scenario, he and his colleagues performed climate modeling experiments to address the issue.

“The key result in our modeling study is that we identified an elevation threshold for rainfall,” Poulsen said. “Once the Andes reached an elevation greater than 70 percent of the current elevation, the precipitation rate abruptly increased. In our model, the increased precipitation also caused the ratio of oxygen-18 to oxygen-16 to significantly decrease. Our conclusion, then, is that geologists have misinterpreted the isotopic records in the central Andes. The decrease in the ratio is not recording an abrupt increase in elevation; it is recording an abrupt increase in rainfall.”

This conclusion is backed up by geochemical and sedimentological data, Poulsen said. “There is evidence that the central Andes became less arid at the same time that the isotope records show a decrease in the ratio of oxygen-18 to oxygen-16.”

Ice sheet melt identified as trigger of Big Freeze

Mapped extent of the Cordillerian and Laurentide icesheets at around 14,750 years ago (after Dyke et al 2003)
Mapped extent of the Cordillerian and Laurentide icesheets at around 14,750 years ago (after Dyke et al 2003)

The main cause of a rapid global cooling period, known as the Big Freeze or Younger Dryas – which occurred nearly 13,000 years ago – has been identified thanks to the help of an academic at the University of Sheffield.

A new paper, which is published in Nature today (1 April 2010), has identified a mega-flood path across North America which channeled melt-water from a giant ice sheet into the oceans and triggering the Younger Dryas cold snap.

The research team, which included Dr Mark Bateman from the University of Sheffield’s Department of Geography, discovered that a mega-flood, caused by the melting of the Laurentide ice sheet, which covered much of North America, was routed up into Canada and into the Arctic Ocean.

This resulted in huge amounts of fresh water mixing with the salt water of the Arctic Ocean. As a result, more sea-ice was created which flowed into the North Atlantic, causing the northward continuation of the Gulf Stream to shut down.

Without the heat being brought across the Atlantic by the Gulf Stream, temperatures in Europe plunged from similar to what they are today, back to glacial temperatures with average winter temperatures of -25oC. This cooling event has become known as the Younger Dryas period with cold conditions lasting about 1400 years. The cold of the Younger Dryas affected many places across the continent, including Yorkshire in the Vale of York and North Lincolnshire which became arctic deserts with sand dunes and no vegetation.

Before now, scientists have speculated that the mega-flood was the main cause of the abrupt cooling period, but the path of the flood waters has long been debated and no convincing evidence had been found establishing a route from the ice-sheet to the North Atlantic.

The research team studied a large number of cliff sections along the Mackenzie Delta and examined the sediments within them. They found that many of the cliff sections showed evidence of sediment erosion. This evidence spanned over a large region at many altitudes, which could only be explained by a mega-flood from the over-spilling of Lake Agassiz, which was at times bigger than the UK, at the front of the Laurentide Ice-sheet rather than a normal flood of the river.

Dr Bateman, who has been researching past environmental changes both in the UK and elsewhere in the world for almost 20 years, runs the luminescence dating lab at Sheffield. The lab was able to take the MacKenzie Delta sediment samples from above and below the mega-flood deposits, and find out when the mega-flood occurred, enabling its occurrence to be attributed to the start of the Younger Dryas.

The study will help shed light on the implications of fresh water input into the North Atlantic today. There are current concerns that changes in the salinity of the ocean today, could cause another shut down of the Gulf Stream. Current climate changes, including global warming, may be altering the planetary system which regulates evaporation and precipitation, and moves fresh water around the globe.

The findings, which show the cause, location, timing and magnitude of the mega-flood, will enable scientists to better understand how sensitive both oceans and climates are to fresh-water inputs and the potential climate changes which may ensue if the North Atlantic continues to alter.

Dr Mark Bateman, from the University of Sheffield’s Centre for International Drylands Research at the Department of Geography, said: “The findings of this paper through the combination of luminescence dating, landscape elevation models and sedimentary evidence allows an insight into what must have been one of the most catastrophic geological events in recent earth’s history. They also show how events within the Earth-climate system in North America had huge impacts in Europe.”

Researcher unravels one of science’s great mysteries

Rosing has solved one of the great mysteries of our geological past: Why the Earth's surface was not one big lump of ice four billion years ago when sun radiation was much weaker than today. Scientists have presumed that the Earth's atmosphere back then consisted of 30 percent CO2 trapping heat like a greenhouse. However, new research shows that the reason for Earth not going into a deep freeze at the time was quite different.
Rosing has solved one of the great mysteries of our geological past: Why the Earth’s surface was not one big lump of ice four billion years ago when sun radiation was much weaker than today. Scientists have presumed that the Earth’s atmosphere back then consisted of 30 percent CO2 trapping heat like a greenhouse. However, new research shows that the reason for Earth not going into a deep freeze at the time was quite different.

In 1972, the late, world famous astronomer Carl Sagan and his colleague George Mullen formulated “The faint early sun paradox. ” The paradox consisted in that the earth’s climate has been fairly constant during almost four of the four and a half billion years that the planet has been in existence, and this despite the fact that radiation from the sun has increased by 25-30 percent.

The paradoxical question that arose for scientists in this connection was why the earth’s surface at its fragile beginning was not covered by ice, seeing that the sun’s rays were much fainter than they are today. Science found one probable answer in 1993, which was proffered by the American atmospheric scientist, Jim Kasting. He performed theoretical calculations that showed that 30% of the earth’s atmosphere four billion years ago consisted of CO2. This in turn entailed that the large amount of greenhouse gases layered themselves as a protective greenhouse around the planet, thereby preventing the oceans from freezing over.

Mystery solved

Now, however, Professor Minik Rosing, from the Natural History Museum of Denmark, and Christian Bjerrum, from the Department of Geography and Geology at University of Copenhagen, together with American colleagues from Stanford University in California have discovered the reason for “the missing ice age” back then, thereby solving the sun paradox, which has haunted scientific circles for more than forty years.

Professor Minik Rosing explains, “What prevented an ice age back then was not high CO2 concentration in the atmosphere, but the fact that the cloud layer was much thinner than it is today. In addition to this, the earth’s surface was covered by water. This meant that the sun’s rays could warm the oceans unobstructed, which in turn could layer the heat, thereby preventing the earth’s watery surface from freezing into ice. The reason for the lack of clouds back in earth’s childhood can be explained by the process by which clouds form. This process requires chemical substances that are produced by algae and plants, which did not exist at the time. These chemical processes would have been able to form a dense layer of clouds, which in turn would have reflected the sun’s rays, throwing them back into the cosmos and thereby preventing the warming of earth’s oceans. Scientists have formerly used the relationship between the radiation from the sun and earth’s surface temperature to calculate that earth ought to have been in a deep freeze during three billion of its four and a half billion years of existence. Sagan and Mullen brought attention to the paradox between these theoretical calculations and geological reality by the fact that the oceans had not frozen. This paradox of having a faint sun and ice-free oceans has now been solved.”

CO2 history illuminated

Minik Rosing and his team have by analyzing samples of 3.8-billion-year-old mountain rock from the world’s oldest bedrock, Isua, in western Greenland, solved the “paradox”.

But more importantly, the analysis also provided a finding for a highly important issue in today’s climate research – and climate debate, not least: whether the atmosphere’s CO2 concentration throughout earth’s history has fluctuated strongly or been fairly stable over the course of billions of years.

“The analysis of the CO2-content in the atmosphere, which can be deduced from the age-old Isua rock, show that the atmosphere at the time contained a maximum of one part per thousand of this greenhouse gas. This was three to four times more than the atmosphere’s CO2-content today. However, not anywhere in the range of the of the 30 percent share in early earth history, which has hitherto been the theoretical calculation. Hence we may conclude that the atmosphere’s CO2-content has not changed substantially through the billions of years of earth’s geological history. However, today the graph is turning upward. Not least due to the emissions from fossil fuels used by humans. Therefore it is vital to determine the geological and atmospheric premises for the prehistoric past in order to understand the present, not to mention the future, in what pertains to the design of climate models and calculations,” underscores Minik Rosing.

Professor Rosing’s scientific research has made its mark internationally on several earlier occasions, including research on the point in time when the first fragile life appeared and the impact of life’s presence on the formation of the earth’s landmass.