JOURNEY THROUGH TIME WITHOUT OXYGEN or HOW FAR IT CAN BE TO GET DEEP KNOWLEDGE

             

As everybody knows, oxygen is an essential gas both for plants and human or animals to live. “Is it so important to know?” – maybe someone asks. Really, YES, because if without food human can live about 1 month, without water up to 1 week but without oxygen just 5 minutes. So, our dependence on oxygen makes to think about its distribution in air and causes of its appearance in an atmosphere. “Is it important to know why oxygen appears?” – maybe asks other body. Apparently, yes, because knowing reasons of oxygen inception we can predict its future and naturally fortune of mankind. 

As history of Earth numbers 4,6 billions years scientists need to travel through time using records (sedimentary and volcanic rocks) remained from deep time to understand processes occurred on the Earth’s surface. For this purpose in summertime 2007 a group of people set off for a time travel called FAR-DEEP (The Fennoscandia Arctic Russia - Drilling Early Earth Project) in Arctic Russia as place where records are well-preserved. This journey was conceived by Professor Victor A. Melezhik from Geological Survey of Norway, Trondheim and University of Bergen. The main idea was to understand processes and events which occurred during the Archean- Palaeoproterozoic (AR-PR) transition period (2,500-2,000 million years ago (Ma)) when as believed the oxygen level was dramatically increased. On the Figure 1 you can see places of drilling where volcanic-sedimentary consequences are presented. This is Murmansk region and Karelia located on the Fennoscandian shield where summer is mostly like winter in Washington, DC. Latitudes of these regions equal to latitudes of Alaska in the USA and geologists needed to not only survive but work very hard to get core material (Figure 2).

Well, FAR-DEEP fieldwork started and finished in 2007, where I also took part for 2.5 months to carry out the documentation of the core. There was a great experience of fieldwork and a collective collaboration. During the fieldwork stage our group faced many difficulties needed to be overcome. We worked 7/24 in our field camp (Figure 3) to receive the core material and if your turn was to work at night be prepared to fight with unsparing wind and perishing cold.

  Even change the place was a big trouble because of absent of a road and slash. Eventually 15 holes were drilled to get 3650 meters core what sounds like a distance between the Lincoln Memorial and the US Capitol in DC but reflects 500 million years as 1/9 part of the all Earth’s history. After summer 2007 the core was brought to Trondheim for further sampling among collaborators and multidisciplinary studying.

During those 500 millions years many events and changes occurred in and on the Earth. Among them are:

1.           Global rifting (simply said huge cracks in the ground with the size of more then New York state) with the worldwide spread LIP (Large Igneous provinces) related with the richest deposits of copper, nickel, chromium, platinum etc.

2.       The GOE (Great Oxidation Event) when oxygen changed from almost 0% to 1% of present atmospheric level (now the oxygen concentration is 21%) that means that oxygen is presented in the atmosphere just for half of its history. And question is: “What trigger was to make oxygen to appear?”

3.             Signatures of the first petroleum generation (so-called Shunga Event). Petroleum which we use for human needs (e.g. plastic, gasoline, clothes and even cosmetics) and which price is a crucial factor in current economy as large deposits appeared about 600 million years ago but scientists found its trace 2,000 million years ago.

            Picture 4 represents other global events which like a mystery occurred at the same time near AR-PR boundary. Scientists want to understand which one was a cause and which one was a consequence.   

Figure 4. δ¹³C - time plot with main events happened at Palaeproterozoic time

          The collaborators involved in the project are from many countries (Russia, the USA, Norway, Germany, Scotland etc.) and they are doing research ranging from palaebiology to geochronology. Currently, the core samples are analyzing and comparing with similar succession from Gabon.

           Here are some links and references about this challenging Project:
Official page of the FAR-DEEP

One of the recent posts with nice pictures

Melezhik, V.A., Fallick, A.E., Hanski, E.J., Kump, L.R., Lepland, A., Prave, A.R., and Strauss, H., 2005. Emergence of the aerobic biosphere during the Archean-Proterozoic transition: Challenges of future research. Geol. Soc. Am. Today, 15:4–11. full text of the paper

Reconstructing the sedimentary diagenetic paleogeofluids!

As the petroleum exploration continues in Tarim basin, recently it has been found that the Cambrian and Ordovician petroliferous carbonate reservoir rocks develop abundant vugs and veins (Fig 1), resulting in good porosity for the hydrocarbon storage. Where do the fluids come from? What’s the source and geochemical composition of the diagenetic fluids? In which kind of mechanism did they alter the carbonate rocks? Can this kind of diagenesis result in considerable petroliferous carbonate reservoir rocks? These questions are still up in the air. “This is our focus right now. To figure out the cause of this kind of carbonate diagenesis and reconstruct the properties of the according diagenetic fluid is very important for our ongoing petroleum exploration!”, Wenqing Pan, the executive of  the petroleum exploration department of Tarim PetroChina Corporation, says in the departmental routine meeting.

Fig. 1 Various phenomena found in the outcrops. A, diagenetic altered dolostone; B, hand specimen of saddle dolomite, which is normally regarded as a typical product of hydrothermal dolomitization; C, silicified dolostone with quartz vugs in the hole; D, calcite vugs with clay inside; E, calcite and dedolostone; F, vugs and according thin section view under polarized light microscope.

The Peking University sedimentary geochemistry research group(PKU-SGRG) led by Professor Ping Guan, the chief scientist in Institute of oil and gas-PKU , decided to meet this challenge. Huan Cui, his graduate student, conducted most of this research project as part of his master degree thesis. In the field, they chose several outcrops (Fig. 2) and collected many samples for further indoor geochemistry analysis.

Fig. 2 The locations of studied outcrops in Tarim basin, NW China.

Through the petrographic studies with microscopes in the lab, it is found that the carbonate rocks in northern Tarim basin have developed a diagenetic paragenetic sequence of silicification, hydrothermal dolomitization and calcitization (Fig. 3). These three major types of diagenesis greatly altered the studied carbonate rocks.

Fig. 3 Thin sections of major diagenesis that caused the alternation of the studied carbonate rocks in Tarim basin. A-B are typical thin sections showing silicification diagenesis, C-D are thin sections showing hydrothermal dolomitization diagenesis and E-F are thin sections showing calcitization diagenesis, stained by Alizarin Red S. Dol-dolomite, SD- saddle dolomite, MD-matrix dolomite, Cal-calcite, Qz-quartz, DeDol-dedolomite.

To reconstruct the temperature and salinity of the paleofluids is important for our understanding of the diagenetic alternation. Using heating and freezing stage, Cui measured the melting and homogenization temperatures of fluid inclusions in the calcite, quartz and fluorite crystals and reconstructed the salinity and temperature of the diagenetic fluids that caused the alternation of the carbonate rocks (Fig. 4). Most of the silicification fluids show high salinity and high temperature (120-140℃), indicating a hydrothermal feature compared with the normal geothermal temperature. The calcitization fluids show high temperature but a little bit low salinity, indicating a mixture of high-salinity fluid and low-salinity meteoric water or formation water.

Fig.4 The measuring process of melting and homogenization temperatures of fluid inclusions. The measured homogenization temperature represents the simultaneous temperature of the fluids at that time. With the measured melting temperatures we can calculate the salinity of the fluids.

Many lines of evidences, such as the quartz fluid inclusion with a high salinity and homogenization temperature, the positive Eu anomaly in REE pattern of the saddle dolomite, and the calculated δ18OSMOW (+5.5‰–+12‰) (Fig. 5) of the fluid which precipitated the calcite crystals, all indicate that there exist magmatic hydrothermal fluids. 

Fig. 5 Using the fluid temperature got from the thermometric analysis of fulid inclusions in the calcite crystals and the oxygen isotopic values of the precipitated calcite crystals, we can calculate that the oxygen isotope of the fluids that precipitate the calcite crystals. The calculated value indicates that the equilibrium fluid is magmatic hydrothermal fluids.

Things revealed are far more complicated than our initial expectations. With carbon, oxygen and strontium isotopic analysis, it is also found that the hydrothermal diagenetic fluids have been mixed with organic carbon, meteoric water or the 87Sr rich formation water(Fig. 6) in different degree. 

Fig. 6 Altered carbonate rocks and calcite veins in different sections all show 87Sr/86Sr increase compared with the unaltered carbonate counterpart, indicating the diagenetic fulids are 87Sr rich, which may be an imprint of formation water source. LST-limestone, MD-matrix dolomite, SD-saddle dolomite, Cal-calcite veins, Dol-dolostone.

Based on the geochemical results, it is proposed that the carbonate rocks in the research area have an according diagenetic response to the “magmatic hydrothermal fluids-formation water compound fluid system”. The magmatic hydrothermal fluid is an important Si and REE source of the diagenetic fluid flow and is also a heat engine that drives the magmatic hydrothermal fluids and formation water cycle underground, consequently result in large scale of diagenetic alternations in the carbonate strata. The hydrothermal fluid dissolution indicates that the open fault area is a promising target for the petroleum reservoir exploration in the future. “The fault area in the seismic profiles is now our future target to find more oils!” Wenqing Pan says.

However, this is not an end, but a second new start! How to use the 3-D seismic data to predict this kind of reservoir rocks in a larger scale? Is there any appreciable difference in geophysical properties between the altered reservoir rocks and the surrounding unaltered rocks? Can we use seismic data to detect them deep underground? Is there any 3-D distribution pattern of different kinds of diagenetic alternations? These still need to be further studied. Together with the colleagues in the Institute of Geology and Geophysics, Chinese Academy of Science, funded as part of the National Key Research Project, the members in Professor Guan’s PKU-SGRG group are still on the exploring way!

Bad-Ash Rocks: Forensic Geology Unearthed and Explained

"Every contact leaves a trace." This is the mantra repeated by forensic geologists around the globe and was first postulated by 20th century scientist Edmond Locard, director of the first crime laboratory in Lyon, France. Trace evidence is any type of material left at or taken from a crime scene, or the result of contact between two objects, such as shoes and the floor or soil.

Forensic geology applies geological principles and analytical techniques to aid in solving criminal and legal investigations. Common examples include soil evidence in provenance studies or to locate a body, determining gem or painting fraud, tracking oil spills, and much more. Although seemingly unfamiliar to most people, forensic geology is largely prevalent in the news. Recent examples include Forensic Geologist Maureen Bottrell testifying at the Casey Anthony trial. Bottrell analyzed soil material found in the trunk of Anthony's car as well as several pairs of Anthony's shoes to determine whether a link could be made between the collected sediment and possible burial site of the deceased toddler, Caylee. Other local examples include a recent string of robberies and murders over expensive shoes in the D.C. metro area.

My research follows the recent crime in our area. I will be taking several pairs of shoes, of varying tread size, and walk around selected areas; I am interested in observing the characteristics of the material that is transferred from the scene of interest to the shoe. These transferred sediments will then be compared with bulk soil samples from the area to determine if and how material is preferentially transferred based on shoe tread size. The aim of my research is to increase the efficiency and accuracy of trace evidence analysis with respect to geological materials. I am focusing on using cost-effective, practical analyses that may readily be used in laboratories across the world.

Image Source

Squeezin' A Rock Around d' Clock

Changes in temperature, pressure, and stress affect fluid transport properties such as porosity and permeability. The response to this applied stress or change in pore pressure is seen as either a compaction or dilation of pore space. It is important to understand rock deformation processes because of the extremely relevant geological applications, which include the oil/gas exploration and groundwater industries. Many experiments have been conducted on sandstones and granites, however, there is a greater need for the understanding of calcite deformation. I am observing the way in which Indiana Limestone responds to various pressure and temperature conditions. Indiana Limestone is an excellent specimen in which to observe calcite deformation because it is relatively homogeneous, comprising more than 97% calcite.

Deformation can either be elastic, where the material returns to its original shape after the applied load has been removed, or inelastic, where deformation is non-recoverable. Inelastic deformation is further divided into brittle and plastic deformation. Brittle deformation is seen as fractures and plastic deformation is seen via crystal plasticity, in which one sees either dislocation slip or twinning. Previous deformation experiments have been conducted on Indiana Limestone at room temperature. Stress-strain curves (Vajdova et al., 2004) show the transition from brittle to ductile deformation; because crystal plasticity, part of the plastic deformation mechanism, is temperature dependent, I am interested in observing the effect of temperature. Additionally, the Vajdova experiments were conducted in unsaturated cores. My experiments include cores that are saturated with distilled water, so there will be an added comparison of the effect that water has on deformation.

I hypothesize that crystal plasticity behavior in calcite will affect the bulk deformation behavior as well as transport properties. The effect of dislocation slip and twinning on transport properties can be seen in appreciable amounts. I additionally hypothesize that as temperature increases, the effects of crystal plasticity will be more pronounced. This is because as rocks increase in temperature, they increasingly behave as a plastic. Current experiments follow the Vajdova data accordingly.

Further reading: Vajdova et al., 2004

Fig. 1: Prepared sample, pre-deformation. The core is jacketed with copper and has strain gages attached.

Fig. 2: Post-deformation twinning comparison between a sample that has experienced an effective pressure of 10 MPa and one that has undergone 50 MPa. The twinning is much more intense in the 50 MPa sample, leading me to believe that this twinning is most definitely deformation-induced (not natural).

Leaf vein density: The angiosperm advantage

Angiosperms are flowering plants that bear fruits and reproduce with seeds. Although angiosperms are the most diverse group of land plants today, they appear in the fossil record only 140 million years ago, during the Cretaceous Period. Since then, flowering plants have become more diverse and widely spread, transforming global ecology.

Scientists attribute the global spread of angiosperms to their increased ability to photosynthesize, or create sugars within the leaf. This unrivalled photosynthetic capacity is facilitated in flowering plants by an increased density of veins, which provide the plumbing within a leaf. Leaf vein density is projected to have increased along with angiosperm diversity throughout the fossil record. I am studying the increase in leaf vein density of the sycamore family since the Cretaceous, comparing the carbon isotope ratios of fossil and modern sycamores. Through this comparison, I will determine whether the difference in carbon isotope ratios is related to a difference in leaf vein density, and correspondingly water use within the leaf.

Leaf veins, as seen in this image of Platanus occidentalis, have evolved since the Cretaceous. The increase in leaf vein density is suggested to have enabled a major increase in the photosynthetic capacity of flowering plants. [Image source: OnlinePlantGuide]

Photosynthesis is the process by which plants use energy from sunlight to convert carbon dioxide and water into sugar and oxygen. This process occurs within the leaf, which can control how widely the stomata are open. Stomata, pore-like structures in a leaf, allow for gases to be exchanged with the atmosphere. When these pores are open, carbon dioxide can enter the leaf to facilitate photosynthesis, and oxygen is able to leave. As a downside, the leaf loses

water vapor when these pores are open. Leaf veins, which are essentially the plumbing of the leaf, provide water from the stem of the plant. The angiosperm advantage lies in the evolution of a greater density of leaf veins, allowing for more water to get to the leaf, the stomata to be open longer, and for there to be more photosynthetic activity.

The anatomy of a leaf, showing the stoma on the bottom of the diagram, which the plant can open or close to let carbon dioxide in or let oxygen out. [Image source: H. McKenna]

With more widely-opened stomata, we will expect to find a lighter isotopic composition within a leaf. For my senior thesis, I am comparing carbon isotope ratios determined from fossil and modern specimens of angiosperms to the ratios found from fossil and modern ferns. Through this comparison, we will determine if the increased leaf vein density in flowering plants correlates to differences in isotopic composition.

Further reading:

Brodribb, T.J., T.S. Feild, and G.J. Jordan, 2007, Leaf Maximum Photosynthetic Rate and Venation Are Linked by Hydraulics. Plant Physiology, 144(4): 1890-1898.

Boyce, C.K., T.J. Brodribb, T.S. Feild, and M.A. Zwieniecki, 2009, Angiosperm leaf vein evolution was physiologically and environmentally transformative. Proceedings of the Royal Society B, 276: 1771-1776.

Ice, Ice, Baby! Rifting on the Icy Satellites of the Outer Solar System

The Jovian moons of Europa and Ganymede, and the Saturnian moon Enceladus have all been shown to have prominent extensional features analogous to rifts on Earth.  For my senior thesis, I am developing numerical models in order to better understand the geodynamics of how these rifts form, and in particular, how the emplacement of magmatic dikes can affect their evolution.

“Icy satellites” is the term we use to describe most of the collected moons of the large, gaseous Jovian planets of the outer solar system (Jupiter, Saturn, Uranus and Neptune).  As the name suggests, these moons are composed primarily of ices (water ice, as well as hydrocarbon ices like ethane or methane), but are cold enough that these ices behave more like rocks here on Earth.  The mean surface temperature on Enceladus is only about 75 Kelvin, or -325 degrees Fahrenheit.  These moons range in size from bigger than planets (Ganymede is larger than Mercury) to smaller than countries (Enceladus is a mere 500 km across - smaller than Colorado).  It has also been hypothesized that many of these moons have subsurface oceans beneath their icy crusts, which could potentially be refuges for extra-terrestrial life.

Three icy satellites, along with the Earth and Moon, to scale.

Despite these geologic differences, a number of features on these worlds are identified as similar to terrestrial rifts (such as the East African Rift, or the Basin and Range in Western North America).  These rifts have been categorized based upon observed morphology as either narrow rifts with localized extension or wide rifts with extension over a larger region.  Although past geodynamic models have been able describe the formation of these rifts, they require the use of unusual initial conditions (surface temperature, ice crust thickness, etc.) that conflict with satellite observations and other geodynamic models.  Our hypothesis is that by including previously ignored effects of magmatic dikes into these geodynamic models, we will be able to rectify this conflict between model predictions and observable parameters.

Examples of the different types of rifts on the different icy satellites, along with hypothetical geologic cross sections across the rifts, displaying the different observed morphology, and hypothesized structure.

Dikes are vertical, sheet-like magmatic intrusions.  Dikes and other volcanic processes on these moons are driven by cold liquid water and hydrocarbons (as opposed to molten rock, here on Earth), in a process called “cryovolcanism.”  Dikes have been inferred to exist at least on Enceladus due to the observation of large water-ice plumes originating from rifts on the moon’s southern pole.

Cassini-Huygens image of water geysers erupting from the rifts on Enceladus.

This research can potentially provide further insight into the general processes of extension and rifting, in addition to further understanding of these strange alien worlds.

For more information about the geodynamics involved in my model, and general information on rifting on both Earth and these icy satellites, see the following two papers:

• Buck, W.R. (1991), Modes of continental lithospheric extension, J. Geophys. Res., 96 (B12), 20, 161-20, 178. (direct link)
• Nimmo, F. (2004), Dynamics of rifting and modes of extension on icy satellites, J. Geophys. Res., 109, E01003, doi: 10.1029/2003JE002168. (direct link)

-James T. Keane, 3/14/2011

Model Paints Picture of Deep Earth's Mineral Grains

Earthquakes create seismic waves of two main types: P-waves and S-waves.

P-wave and S-wave diagrams

image credit: http://www.physics.uiowa.edu/adventure/spr_2006/feb_18-06.html

P-waves are faster in solids than in liquids. S-waves cannot travel through liquids at all. When a body of rock is partially molten, S-waves can travel through but are slowed drastically. Based on how much the types of waves are slowed, we can determine the elastic moduli of the rock. Elastic moduli are measures of how much a wave is slowed that are changed by density and phase of the rock through which the waves travel. Using elastic moduli, geophysicists can infer the melt volume fraction, which measures how much of a rock is liquid versus solid.

At a fixed melt volume fraction, grain shape can change the elastic moduli. The shape of an area of melt between grains can be described by its dihedral angle.

Dihedral angle of a grain junction

image credit: http://www.springerimages.com/Images/Chemistry/1-10.1007_s10853-008-3008-0-7

(German, Suri, and Pavan 2008)

A new computational model that I helped Dr. Saswata Hier-Majumder develop at the University of Maryland creates idealized cross-sections of a single channel of melt, starting with the physics of the area. The paper describing the results was published in Earth and Planetary Sciences Letters in 2010 (Hier-Majumder and Abbott, 2010). The full text may be found at http://www.geol.umd.edu/~saswata/pubs.shtml for UMD students and faculty. To sum it up succinctly, the dihedral angle can be predicted by the physical model, and the dihedral angle can be used to predict how the arrangement and shape of grains affects the elastic moduli. There are a wide range of melt volume fractions possible for one set of elastic moduli, but knowing the shape allows us to eliminate much of the uncertainty.

Image of partially molten rock produced by the Laboratory for Rock Physics by Dr. Zhu

image credit: http://www.geol.umd.edu/~wzhu/

My current research is changing the code to represent a realistic body of rock instead of an idealized unit cell. This lets us take the relationship between shape, melt volume fraction, and elastic moduli out of the world of theoretical physics and into real-world scenarios. Recent advances in imaging by the University of Maryland's own Dr. Wen-lu Zhu provide an experimental result. Comparing the model to the experiments and to data from seismic studies will allow us to know if the model is doing a good job of predicting shape.

When we have the model matching experimental and real-world data, we can provide very good predictive information about melt volume, melt fraction, and microstructure shape in any area of the earth that has partially molten rock. The shape of the melt channels can also be used to determine melt focusing, which is to say the path along which melt travels most easily. In short, if the model meets our expectations we can take seismogram readings and say how much melt is in a rock and where it will go.

For a more in-depth look into the microstructure of partially molten materials, please peruse the references below:

German, RM, P Suri, and SJ Park (2008) Review: Liquid Phase Sintering. Journal of Materials Science 44:1, doi: 10.1007/s10853-008-3008-0.

Hier-Majumder, S and M Abbott (2010) The Influence of Dihedral Angle on Seismic Velocities of Partially Molten Rocks. Earth and Planetary Sciences Letters 299, doi: 10.1016/j.epsl.2010.08.007.

Yoshino, T, Y Takei, DA Wark, and B Watson (2005) Grain Boundary Wetness of Texturally Equilibriated Rocks, With Implications for Seismic Properties of the Upper Mantle. Journal of Geophysical Research 110, doi: 10.1029/2004JB003544.