Great Research Advances: Past and Present

Geoscience faculty and researchers at The University of Texas at Austin have a rich tradition. Some of their signal accomplishments are described below.

Historic Milestones in the Department of Geological Sciences

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In 1967, W. L. Fisher published with J. H. McGowen a paper entitled "Depositional Systems of the Wilcox Group of Texas and their relationship to the occurrence of oil and gas." In this paper they introduced the concept of depositional systems which was later to become a household term in the geological literature. Depositional systems were defined as three-dimensional assemblages of lithofacies, genetically linked by active (modern) process or inferred (ancient) processes in environments. A rational and systematic way of integrating process sedimentology and lithofacies stratigraphy was established. The notion of depositional systems was enlarged at a 1969 Department Colloquium on "Delta Depositional Systems in the Exploration for Oil and Gas" organized by Fisher, L. F. Brown, A. J. Scott, and J. H. McGowen. More than 400 geologists from throughout the U.S attended and the colloquium was repeated by invitation to most of the major geological societies in North America, to several universities and to a dozen companies. The proceedings volume for the colloquium sold nearly 45,000 copies. Fisher and Scott initiated a graduate course in depositional systems at UT in 1968 which has been taught every year since, recently becoming split into two courses: terrigenous depositional systems taught by William Galloway and carbonate depositional systems taught by Brenda Kirkland George. Depositional systems has been the subject and title of numerous books, including an especially noteworthy one by William Galloway and Dave Hobday, and hundreds of technical articles. The concept helped secure the Department's position in the forefront of soft rock geology, a position it enjoys to this day.

For more information, contact Dr. William L. Fisher at (512) 471-5600.

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Dr. Philip Bennett in the Department of Geological Sciences has discovered that the mineralogy of an aquifer is a fundamental control of the biology, which is itself a fundamental control of water chemistry and mineral weathering. Subsurface microorganisms aggressively destroy otherwise resistant minerals in search of trace nutrients, weathering some minerals hundreds of times faster than expected. This finding raises the possibility that mineral weathering in the geologic past was not always a "random event" with two related minerals dissolving at the same rate. Rather, it is possible that minerals that contain trace phosphorus, for example, were rapidly destroyed by bacteria, while similar minerals without nutrient value are left untouched, and remain in the geologic rock record.

For more information, contact Dr. Philip Bennett at (512) 471-3587.

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In 1997, the University became the host, in its Department of Geological Sciences, of a one-of-a-kind instrument for X-ray computed tomography (CT) that allows geologists to visualize internal features of rocks and fossils non-destructively, just as medical CAT-scanners are used to look inside the human body. Previously, imaging systems capable of the high spatial resolution and great penetrating power of the UT machine were not routinely available to scientific researchers, but were restricted to a small handful of government, military, and industrial laboratories. Now, in a facility open to researchers both at UT and elsewhere, the academic community has easy access to this state-of-the-art technology for the first time. In the first months of operation, the facility performed research on the planet's oldest dinosaur fossils, a fragment of the Mars meteorite that may hold evidence of ancient life, seafloor-vent deposits from the depths of the ocean, diamond-rich rocks from more than a hundred miles beneath the earth's surface, soils that trap or transport environmental contaminants, limestones that harbor reservoirs of oil in west Texas, and more. The laboratory has drawn to the Austin campus scientists and students from six continents, and specimens from all seven! The UT scanner was purchased with a combination of funding from the W. M. Keck Foundation, the National Science Foundation, and the University.

For more information, contact Dr. William Carlson at (512) 471-4770, or Dr. Timothy Rowe at (512) 471-1725, or Dr. Richard Ketcham at (512) 471-0260.

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In the summer of 1971 a then graduate student in Geological Sciences, Douglas A. Lawson, made a discovery in Big Bend National Park that electrified scientists and non-scientists alike. What Lawson found were the fragmentary fossilized remains of a wing belonging to the largest of all flying creatures. After removing the broken and fragile pieces from the sandstone that surrounded them, about 200 fragments of petrified bone, ranging in size from that of a fist to that of a postage stamp were tediously fitted back together by the staff at the Texas Memorial Museum's Vertebrate Paleontology Laboratory. By 1975, studies of the specimen by Lawson and his supervisor, Wann Langston, Jr. Had determined that the animal, a 65 million year old pterodactyl from the Age of Dinosaurs, had a wing spread of about 40 feet, greater than a 4-place Cessna airplane or an F-18 fighter. It was about twice as large as the biggest pterodactyl known up to that time. With the discovery of additional, though smaller, fossilized skeletal remains in the Big Bend in 1973, it was possible to reconstruct the entire skeleton of the pterodactyl which Lawson named Quetzalcoatlus northopi. Based upon what had been learned from these discoveries, the world-renowned aeronautical engineer, Paul MacCready, with the assistance of Professor Langston created a large flying replica of Quetzalcoatlus which performed over the California desert for the Smithsonian Museum's IMAX film "on the Wing" in 1985. Lawson's discovery attracted world-wide attention, being reported in newspapers and magazines and on TV from New York to Tokyo and Canada to Argentina. "On the Wing" was shown around the world. ABC 20-20, the news program, produced a 20 minute segment on MacCready's work, and Sir David Attenborough traveled to Texas to film segments for his BBC series "Lost Worlds - Vanished Lives." Quetzalcoatlus continues to attract attention within scientific circles and the press because of the exciting questions it raises about how the long extinct pterodactyls flew, how big a flying creature can be, and why such successful animals went extinct along with the dinosaurs sixty-five million years ago.

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In the 1980’s, a new approach to subdividing the stratigraphic record of sedimentary basins into genetic units was presented and popularized. The primary stratigraphic unit, a depositional sequence, was defined by bounding surfaces--discontinuities within the depositional record. This approach, which had its roots in the petroleum industry and its reliance on seismic data analysis, increasingly became wedded in its terminology and interpretive application to a conception of sea level as the ubiquitous and dominating control on all aspects of the stratigraphic and depositional record. Sequence-bounding unconformities were related exclusively to sea-level falls, and interpretation of the depositional record increasingly was built around sequence description and concomitant creation of a site-specific relative sea level curve. In the face of this band wagon, W. E. Galloway, in 1989, published a paper in the Bulletin of the American Association of Petroleum Geologists outlining an alternative approach for sequence recognition and interpretation based on the conceptual paradigm of the depositional episode. The genetic sequence was defined as a primary stratigraphic unit bounded by surfaces that reflected sediment starvation and associated transgressive flooding of basin margins. Use of this alternative model greatly reduced operator variability, considered a full range of variables, including tectonism and sediment supply, as well as sea level, as potential controls on sequence development. Further, the model emphasized three-dimensional interpretation of sedimentary deposits within the sequence context based on their observed rather than model-predicted features. A companion paper illustrated application of the paradigm to Cenozoic deposits of Gulf of Mexico basin and demonstrated the important role of sediment supply in sequence development.

Although presented and defended only in the 1989 duet of papers, genetic sequence stratigraphy has proved a durable and robust alternative to the popular and much-published depositional sequence model. It is reviewed as a viable and often useful approach in the two current textbooks on sequence stratigraphy. For the past seven years, the American Association of Petroleum Geologists has sponsored an annual short course by Galloway. Application of the model has been tested and expanded by research projects in the Gulf of Mexico, North Sea and Australian sedimentary basins.

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Carbonatites (igneous rocks made mostly of carbonate minerals) come from the Earth's mantle, but the carbon that they contain had been on the Earth's surface before being recycled deep into the mantle and dispersed. Rock fragments from the upper mantle, brought up by volcanoes, commonly show the effects of reaction, over long time spans, with carbonate-rich fluids. Carbonate-rich liquid can only survive its upward passage if the mantle through which it flows has already lost its capacity to react further. The rarity of carbonatite magma in the crust is probably caused by physical and chemical barriers to its ascent, rather than by a shortage of raw materials.

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The idea of nannobacteria is either a career-busting fiasco, or a revelation having great impact on geology, pedology, biology, medicine and astronomy. First, the negative: biologists are almost all adamant that the lower limit of life is around 0.2 microns. Of course viruses, which are about 0.01-0.02 microns, are not independent life, but they are some type of crypto-biologic thing. Mineralized nannobacteria (typically .05-.2 microns) were first discovered in 1990 in the hot spring deposits of Viterbo, near Rome, Italy. Since then they have been discovered in a great many earthly rocks and minerals, soils, and ore deposits, and it appears that they are accomplishing a great deal of earth's surface chemistry; most important, perhaps, is their role in changing resistant minerals into clay minerals and fertile soils. Nannobacteria are also believed to be responsible for corrosion of copper, aluminum, and lead as well as rusting of iron. They help plug up plumbing in Austin. Nannobacteria appearing exactly like those on earth were found in the Martian meteorite by NASA and are also abundant in some carbon-bearing meteorites. A Finnish group has found nannobacteria in mammal blood (including humans), so one concludes that they are some sort of life form intermediate between normal bacteria and viruses and are widespread in our own bodies as well as on earth and in space.

For more information, contact Dr. Robert L. Folk at (512) 471-4885.

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Some minerals, like garnet, grow deep in the Earth's crust, where the process of crystal formation can't be seen or studied. And they form very slowly, so the process can't be reproduced in a laboratory — it may take millions of years to grow a garnet the size of a matchhead. But scientists in the Department of Geological Sciences at the University of Texas at Austin have found a way to figure out what happens at the atomic scale as these crystals grow. The results have a lot to say about what's going on tens of miles beneath the Earth's surface, and the extent to which garnet crystals store a chemical record of their history. The UT scientists' theories predict that rocks forming by various processes will look different — because of the size, number and location of crystals — depending on how fast mineralogical reactions take place at depth, and how fast different chemical elements can move through fluids in the tiny spaces between mineral crystals. To test these theories, measurements of crystal size and spacing were needed for thousands of crystals in a 3-D volume of rock. And that could be done only at UT, where an instrument for high-resolution X-ray CT — essentially, a CAT-scanner for rocks — was recently installed. With this new technology, it was learned that transport rates for some of the chemical elements in the garnet crystals control their formation, which means that the chemical composition of the crystals is at best an imperfect record of their geologic history.

For more information, contact Dr. William D. Carlson at (512) 471-4770.

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Researchers in the Department of Geological Sciences have documented how various kinds of sediment (sand and mud) are converted to rocks in the 12 km-thick accumulation of hydrocarbon rich sediments beneath the Coastal Plain of Texas. Increased temperatures with increased depth cause numerous chemical reactions which lead to the destruction of some minerals and the formation of new minerals. Except for the common mineral quartz, the sediments are completely reconstituted as they are converted to rocks. Some reactions lead to loss of porosity, whereas other reactions create porosity. One of the most important is the conversion of detrital plagioclase to the stable mineral albite. Written simply:

CaAl2Si2O8 + 2 Na+ + 4SiO2 ---> 2NaAlSi3O8 + Ca++

This reaction is also responsible for the chemical composition of many water samples which are co-produced along with oil and gas. The composition of the water reflects the mineral reactions which have taken place, in cases far removed laterally and/or vertically from the location where the water is eventually sampled.

For more information, Dr. John (Jack) Sharp, Jr. at (512) 471-3317.

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Most of the earth is as inaccessible to direct study as the far reaches of space. The deepest drill holes penetrate only 12 km, an insignificant fraction of the 6400 km radius of the earth. Fortunately fragments of the earth are erupted from great depths, and like meteorites, they provide precious samples of regions we cannot visit. Doug Smith in the Department of Geological Sciences studies these rocks from diamond deposits in Africa and from volcanic deposits in Texas and elsewhere in the southwest. He has found ways to track where water has been in the deep earth and what elements have been transported by it. Such water influences how rocks flow and melt. The research helps in understanding earthquakes, mountains, and volcanoes, and it will lead to a better knowledge of how plate tectonics operates.

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The first tectonic map of North America in plate tectonic terminology has been compiled by Dr. William Muehlberger in the Department of Geological Sciences. This map was published in two sections by the American Association of Petroleum Geologists in 1992 and 1997. The map extends north from the northern edge of South America (from 4°N) to the North Pole. Six feet on a side, at a scale of 1:5,000,000, it shows the major units that built North America through geological time. The mapped elements are the major building blocks of continents as recognized in plate tectonics: volcanic island arcs, fold/thrust belts that develop during plate collisions, rift basins, continental shelves, etc.

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Most people are aware that North America was part of a supercontinent called "Pangea" 200 million years ago when dinosaurs roamed the earth. Less well known, is the fact that our continent has existed as a discrete geographic entity for at least 500 million years. It broke away from an earlier supercontinent at the end of Precambrian times when the multi-celled life forms suddenly developed from the single-celled forms that had existed for billion of years before that - almost since the planet was formed 4, 500 million years ago. Dr. Ian W. D. Dalziel, Senior Research Scientist and Associate Director at the Institute for Geophysics and Professor in the Department of Geological Sciences believes that the geology of Texas holds critical clues to the earlier wanderings of North America. He and his colleagues in the Department of Geological Sciences, Drs. James Connelly, Wulf Gose and Mark Helper have been investigating the possibility that the rocks that form the Llano uplift of Central Texas, and exposed in Enchanted Rock State Park, can be traced into Antarctica. Another fragment of the southern edge of North America, perhaps once an eastern peninsula of present-day Texas, has been found in northwestern Argentina.

For more information, contact Dr. Ian W. D. Dalziel at (512) 47- 0431.

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Jay Banner and his research team in the Department of Geological Sciences have shown that spleothems (cave deposits) record history of climate-groundwater interactions in aquifers. These mineral deposits of calcite that form from groundwater infiltrating caves preserve a record of how the chemical composition of groundwater varies over time. They use advanced mass spectrometry methods to detect variations in 238U-series isotopes that enable precisely dating of individual calcite growth layers. Sr and O isotope measurements are used to trace the influence of changes atmospheric temperature, rainfall, soil and host limestone compositions on groundwater chemical compositions. These variations over centuries to millennia provide a history of how flow pathways and amount of recharge to an aquifer have varied over time.

For more information, contact Dr. Jay Banner at (512) 471-5016.

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Sharon Mosher and her graduate students in the Department of Geological Sciences have shown that the collision of Africa with North America helped form the New England Appalachians about 275 million years ago. Previously this part of the Appalachians was thought to have formed much earlier and to have been unaffected by the African collision that formed the Southern Appalachians. Investigation of the ~290 million year old Narragansett Basin sedimentary rocks and surrounding older rocks proved that southeastern New England was deformed as Africa slid past it along a transform margin. These rocks provide a complete record of complex plate interactions during an oblique collision from deposition of sediments in tectonic basins to deformation during deep burial and during subsequent uplift. Study of these rocks gives us a better understanding of deformation along active, modern transform plate boundaries.

For more information, contact Dr. Sharon Mosher at (512)-471-4135.

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The decline of U.S. natural gas production in the 1970s appeared to confirm the symmetrical life cycle model of resource depletion which held that discovery and subsequent production of a nonrenewable resource would increase exponentially, peak, and then decline exponentially. Based on the model, the common expectation of the remaining natural gas resource in the U.S. during the 1970s was on the order of 250 trillion cubic feet (TCF), barely more than 10 years supply at then levels of consumption. Thus natural gas, constituting nearly 40% of U.S. energy production was judged to be a rapidly depleting resource. Congressional action sought to limit use and to prioritize remaining supplies.

W. L. Fisher proposed in the 1980s that the natural gas resource base was subject to "technological stretch." In a national panel Fisher convened for the U.S. Department of Energy in 1987-88 our concept of oil and gas immobility in geologically complex reservoirs was tested against the application of emerging technologies, especially seismic imaging. As a result, we tripled the amount of gas remaining and recoverable in existing fields and added an entirely new class of resource, the so-called nonconventional gas resources. Our estimate of remaining gas resources was about 1100 TCF, a four-fold increase. The Fisher panel report focused much attention to the role of technology in offsetting depletion to the extent that subsequent estimates of remaining resources of natural gas by government and industry have risen to the current volume of 2300 TCF, nearly an order of magnitude greater than the estimates of the 1970s.

For more information, contact Dr. William L. Fisher at (512) 471-5600.

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Literally, billions of dollars have been spent trying to assess how contaminants move in the Earth and in trying to clean up polluted groundwaters. We now recognize that almost all Earth materials (rocks and soils) are fractured and that the fractures control the spread of contaminants. Research in the Department of Geological Sciences is among the very first to describe the effects of fracture skins on these processes. Fracture skins are observed on all fractures through which fluids flow. They are zones of alteration and coatings on the fracture surfaces. We have demonstrated through mathematical analyses, field observations, and laboratory tests that the skins are extremely significant in either retarding or accelerating the rate of spread of contaminants. These processes are also of importance in petroleum and water production as well as processes of mineralization. Laboratory studies have characterized skin properties and suggest that two flow regimes may exist in some fractures - a "core" of fast moving fluids which are little affected by the fracture surfaces and a boundary layer zone which is affected by a variety of processes, including adsorption. These results cast doubt on the validity of even the most sophisticated numerical models to predict either contaminant transport or the effects of remediation efforts. More field and laboratory analyses are presently underway to document skin evolution and its effects.

For more information, contact: Dr. John (Jack) Sharp, Jr. at (512) 471-3317 or Dr. Philip Bennett at (512) 471-3587.

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Research in the Department of Geological Sciences indicates that the crust of the earth may have far more radioactivity than previously thought, a development that has large implications for current ideas concerning temperatures at great depths. Dr. Richard Ketcham used a gamma ray spectrometer to measure concentrations of the radioactive elements U, Th, and K -- the elements that generate the interior heat of the Earth. A field study of the recently exposed mountain ranges in Arizona was done to reconstruct the amount and distribution of these elements with depth. This direct-measurement approach demonstrated that previous indirect theoretical approaches underestimated the amount of heat production in this region by 50-100%. Calculations and geological inference suggest that this is probably the case in most other regions as well. These results directly and substantially impact current theory concerning a wide range of geological processes in which heat is a controlling factor, from the mechanical behavior of the crust at depth to basin subsidence modeling to the development of petroleum and mineral deposits.

For more information, contact Dr. Richard Ketcham at (512) 471-0260.

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Studies in the Department of Geological Sciences have defined genetic relationships among petroleum destruction, metal supply by "oil field brines", sulfate reduction, and mineral precipitation in environments ranging from the ocean floor to deep reservoirs in the Gulf of Mexico sedimentary basin. Metal sulfide, sulfate, and elemental sulfur concentrations have been identified in salt dome cap rocks and in shelf carbonates in the Gulf Coast. Salt dome mineralization is the result of the episodic injection of deep-sourced, relatively hot, metal-bearing brines into the shallow cap rock environment where it mixed with cool, dilute ground waters rich in hydrogen sulfide produced by sulfate-reducing bacteria. The Gulf Coast mineral concentrations share many features with ore deposits that provide much of the world's supply of zinc, lead, silver, barite, and elemental sulfur, and comparative studies provide insight into the localization and formation of mineral resources in older sedimentary basins.

For more information, contact Dr. Richard Kyle at (512) 471-4351.

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While global climatic change has international attention, few realize the extent of natural climatic change on Earth and the effects on its environments. For example, 10,000 years ago, the Sahara Desert was a grassland with scattered trees and relatively abundant rivers and lakes. Neolithic peoples were widespread. This change from a Green Sahara to the desert of today is the result of global climatic change brought on by periodic changes in the Earth's orbital parameters around the Sun. Gary Kocurek in the Department of Geological Sciences, working along with his French colleagues in several areas of the Sahara, have helped document, however, that what had been considered to be gradual climatic change on the scale of tens of thousands of years rather occurs as environmental change on a much smaller time scale. For example, in southern Tunisia, during the past 10,000 years there have been five cycles of arid-humid times, as indicated by the stratigraphy of aeolian, river and lake deposits. These cycles occur superimposed upon the larger cycle resulting from Earth orbital change. The causes of the short cycles remain an issue of considerable debate, but the timing of these environmental changes largely coincide with abrupt climatic changes recorded elsewhere, such as in ice cores from Greenland. This suggests a global-scale cause and interaction of Earth systems, as opposed to local change.

For more information, contact Dr. Gary Kocurek at (512) 471-5855.

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The amount of pore space in sandstones decreases during burial by overlying rocks as grains are squeezed closer together (compacted) and pores are filled in by minerals precipitated from groundwater (cemented). Sand initially has 45% porosity, but after burial to 2 or 3 km the porosity may range from 0 to 25%. However, the thermal breakdown of organic matter in associated shales plus other chemical reactions commonly generate acids that attack and dissolve various minerals to generate "secondary pores". The main minerals that dissolve to various degrees are feldspar sand grains, calcareous fossils, and calcite cement. Secondary pores may be sufficiently abundant to generate hydrocarbon reservoir sandstones from sandstones that once were non-reservoir rocks. Work is continuing to generate models that can predict the amount of secondary porosity one can expect to find at a particular depth of burial.

For more information, contact Dr. Earle F. McBride at (512) 471-1905.

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Much of the prehistoric archeological record in Texas is characterized by the presence of accumulations of burned rocks. These features vary widely in size and structure and have been referred to as hearths, dumps, and middens. A cultural interpretation of these features is often ambiguous or impossible due to the lack of data which can establish the functional use of these rocks. The application of paleomagnetic techniques to burned rocks is a novel approach and has yielded information previously unattainable. The results demonstrate whether a feature has remained undisturbed since its last use and allow an estimate of the temperature of the fire place. In combination with archeological analyses, the magnetic data also shed light on the usage of burned rock features.

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Clark Wilson and his graduate student Roberto Gutierrez demonstrated in 1987 that the slight variations in the orbit of the geodetic satellite LAGEOS were due to the changing gravity field of the Earth arising from the redistribution of the atmosphere, and to a lesser extent, water. This was the first demonstration that measured changes in the gravity field could be used to monitor global properties of the Earth's atmosphere and climate. This field of study has led, eventually, to the Gravity Recovery And Climate Experiment (GRACE) mission selection by NASA in 1997, led by the University of Texas, which will be dedicated to this application.

For more information, contact Dr. Clark Wilson at (512) 471-5008.

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Understanding the nature of convective flow in the mantle of the Earth is important for deciphering the Earth's thermal history, its internal composition, the differentiation processes that produce magma, and the tectonic forces that make mountains and earthquakes. From the careful analysis of the travel times of earthquake waves through the Earth interior, Stephen Grand has become the first to trace the subducted part of the Pacific Plate from western North America to a depth of nearly 2700 km and a position beneath the Atlantic ocean. This deep end of the plate is approximately 100 million years old and is now located near the core of the Earth. Before this work, many geophysicists believed that subducted plates only reach depths near 700 km and that this depth was somehow a barrier to the further sinking. The ultimate fate of sunken plates that pile up near the core is now the subject of much interest for their melting would generate new magma and the presence of cold material may affect the pattern of convection in the overlying mantle and in the iron core, the source of the Earth's magnetic field.

For more information, contact Dr. Stephen Grand at (512) 471-3005.

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Sharon Mosher and her graduate students in the Department of Geological Sciences have shown that prior to thrust faulting, fluids can be channelized into thin zones parallel to bedding in sedimentary rocks. The influx of fluids causes these zones to deform plastically without loss of cohesion at shallow crustal levels and changes the chemistry of the affected rock. Rocks on either side of these thin zones are undeformed and unaffected by the fluid chemistry. Where fluids are not present, brittle thrust faults, more typical of shallow crustal levels, form. Detailed studies of limestones in the northern Apennine thrust belt of Italy and sandstones and limestones in the Maria Tectonic Belt of west central Arizona show that this process is important in a variety of tectonic environments. Movement of these fluids in front of advancing thrust faults can cause mineralization and migration of hydrocarbons.

For more information, contact Dr. Sharon Mosher at (512)-471-4135.

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The second and fully revised edition of the International Stratigraphic Guide prepared by the International Subcommission on Stratigraphic Classification (ISSC) was jointly published in 1994 by the International Union of Geological Sciences and the Geological Society of America. The purpose of this second edition of the Guide, as had been that of the first edition published in 1976, was to promote international agreement on principles of stratigraphic classification, and to develop an internationally acceptable stratigraphic terminology and rules of stratigraphic procedure that would make possible international communication, coordination, and understanding and thus effectiveness in stratigraphic work throughout the world. This the second edition of the Guide seems to be accomplishing as more stratigraphers in more countries have recognized and accepted its recommendations since its publication. The second edition of the Guide was edited by Amos Salvador from the Department of Geological Sciences who was Chairman of the ISSC from 1976 to 1992.

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UT scientists, in collaboration with colleagues from the UK, Mexico, Canada, and the USA, are currently studying the structure of the Chicxulub impact crater. This crater, which lies partially offshore the Yucatan Peninsula, is believed to mark the site of the impact which is linked to the mass extinction at the Cretaceous/Tertiary boundary, including the demise of the dinosaurs. In the fall of 1996, BIRPS (British Reflection Profiling Syndicate) collected three seismic lines across the offshore portion of the impact crater; UT scientists used the R/V Longhorn to place 34 ocean bottom seismograph receivers along two of these three lines. These instruments were built and are maintained by the University of Texas Institute for Geophysics, and were used together with the BIRPS seismic lines to constrain the structure of the impact crater. Results indicate that the crater is at least 180-210 km in diameter. Deformation associated with the impact extends into the lower crust and perhaps into the mantle. These results confirm that Chicxulub is one of the largest impact craters on Earth, and appears to be of multi-ring morphology. Other well-preserved craters of this type are only located on other planets or moons.

For more information, contact Dr. Richard Buffler at (512) 471-0448 or Dr. Yosio Nakamura at (512) 471-0428.

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A beautifully preserved skull of a small primate was found in far west Texas by John A. Wilson on July 1, 1964. It was named after the S. P. Rooney family who provided support for faculty and students doing field work in the area west of Marfa Texas. The specimen is unusual because it is a late survivor of the early primates that had been plentiful in North America and also for its unusual preservation. All the teeth except for the incisors are present. The basicranium with both ear regions are preserved. The top of the skull was eroded away, but the surface of the brain cast is so detailed that the casts of small blood vessels are visible. The specimen is currently being studied by Dr. John Kappelmann of the UT Department of Anthropology and Dr. Timothy Rowe with the new X-ray computer tomography facility housed in the Department of Geological Sciences.

For more information, please contact Dr. Timothy Rowe at (512) 471-1725.

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To celebrate its centennial decade, the Geological Society of America published in the late 1980s and early 1990s 38 volumes and numerous maps and continent-ocean transects, in an attempt to bring together current knowledge about all aspects of the geology of North America and its surrounding oceanic regions - from the Caribbean to the Arctic, and from Mid-Atlantic Ridge to Hawaii. This massive project represents the cooperative efforts of more than 1,000 individuals from academia, industry, and state and federal agencies of many countries, and will remain for many years the most authoritative source of geologic information on North America. Amos Salvador, in the Department of Geological Sciences, edited the entire volume on the Gulf of Mexico Region and wrote the major chapters synthesizing a wide variety of geological data for the Gulf of Mexico Basin of southern U.S. and Mexico. This work will be the standard reference on the Gulf of Mexico for decades to come.

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Porphyry copper ore deposits are rare bodies that are now the source of most of the world's copper and molybdenum and significant gold and silver. Their origin has been debated and most research has focused on chemical factors. Students, research scientists and faculty in the Department of Geological Sciences have discovered important relationships between faulting and mineral veining in the Grasberg Cu-Au orebody in western New Guinea -- an extraordinary porphyry copper-type system (~109 tons of ore grading at 1.4 wt. % Cu and 1.8 g/t Au). The UT team discovered that the Grasberg igneous complex was emplaced into a 1 km wide pull-apart zone connecting two major strike-slip faults. Veining by the copper mineral chalcopyrite is concentrated in the center of this zone. The UT team proposes that Grasberg-style orebodies form during the early stages of rapid, deep-seated (>5 km) cooling of granitic magma. This forms bubbles of metal-rich brine that rise along the margins of the chamber and accumulate in a cupola at the top of the crystallizing magma chamber. Strike-slip fault movement during earthquakes causes extension fracturing in the pull-apart zone that ruptures the top of a cupola and drains the metal-rich fluids. These fluids rapidly rise, cool and precipitate metal sulfides. Enormous ore deposits, like the Grasberg, form where the rate of cupola tapping by episodes of strike-slip faulting and fluid generation by pluton cooling are sufficiently balanced to prevent explosive detonation of the magma chamber and dispersal of the ore metals into the stratosphere as occurred in 1982 at El Chichon in Mexico and 1991 at Mt. Pinatubo in the Philippines.

For more information, contact Dr. Mark Cloos at (512) 471-4170.

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Learning to recognize, identify and document geological features (by voice and/or photographs) is a necessary skill for astronauts. Whether they land on the Moon (or just study it from orbit) or circle the Earth, astronauts have made significant contributions to our understanding of these planets. Because most astronauts have never taken geology courses, Dr. William Muehlberger has taken the Shuttle astronauts on a geological field trip to northern New Mexico to observe and study the wide variety of geology that is well exposed in that region: active faults, sand dunes (ancient and modern), volcanoes of all shapes, sizes, and chemistry, valleys cut by rivers and glaciers, continental to marine transitions, and intrusive equivalents of the volcano types. After studying the details of each type, then photographs taken from orbit are used to place the astronauts back to their broader perspective. Their airplane flights across the United States (Houston to West Coast; Houston to Florida) are discussed so that they are aware of similar scenes that they will fly over before being assigned to a space mission.

Lunar geological training was much more intensive since the astronauts were landing and doing geological studies. Their training consisted of lecture courses, study of lunar samples already returned from the Moon, and numerous 2-day geological field trips that were operated as if they were on the Moon and their observers were all in Mission Control. The latter moon missions (Apollo's 15, 16, 17), which had vehicles to drive and enhanced space suits, had as much geology as a typical Master's degree in geology - but of a very specialized kind!

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The geology of the North Atlantic region (northeastern Canada, Greenland, Scotland and Scandinavia) is unique in that it contains some of the oldest rocks on earth and has been reworked multiple times throughout the Precambrian during events that are recognized worldwide. This region thus holds clues to the formation and progressive stabilization of the outer earth and mechanisms that modified it during this early period. Field work integrated with precise state-of-the-art U-Pb geochronology has shown that rocks only previously known as "circa 2.8 billion year old gneisses" can reveal complex but tangible tectonic histories including: the development of subduction-related magmatic arcs between 2870-2840 million years followed by immediate reworking between 2790-2730 million years with attendant syn- and late-tectonic granitoid magmatism. This research thus greatly clarifies existing models that have implied the earth had sufficiently cooled by 2.8 billion years to allow formation of coherent continental and oceanic lithosphere that interacted along margins in a manner similar to that in the Phanerozoic.

For more information, contact Dr. James Connelly at (512) 471-6166.

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Big faults, and the earthquakes they generate, are among the most conspicuous manifestations of plate tectonics. The theory of plate tectonics is based on the idea that the Earth's lithosphere consists of a relatively small number of rigid plates. The plates move about the Earth and deform near the faults that bound them, but negligible deformation is supposed to occur within the plates. Research by Randy Marrett has challenged this latter contention. Within basins such as the North Sea and the Gulf of Mexico, few faults have offsets greater than a kilometer but vast numbers (quadrillions!) of faults have offsets of at least a millimeter. In spite of their size, little faults produce an important cumulative effect due to how many of them there are. The deformation resulting from all the little faults might even be as large as the deformation from the biggest faults.

For more information, contact Dr. Randall Marrett at (512) 471-2133.

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Crinoids (also known as "sea lilies") were the dominant class of echinoderms (spiny-skinned invertebrates) in the shallow marine shelves of the Paleozoic Era (from 530-245 million years ago). They have survived on to the present day along with groups such as starfish and sea urchins. In 1973, Dr. James Sprinkle in the Department of Geological Sciences described a possible ancestral crinoid named Echmatocrinus from the famous Middle Cambrian Burgess Shale (about 510 million years old). Although many other paleontologists have agreed with this proposal, a few others have recently argued that Echmatocrinus with its primitive morphology is not related to later crinoids and instead have proposed a different ancestor for crinoids. Since 1989, Jim Sprinkle and his colleague Thomas Guensburg of Rock Valley College have been searching for additional rare fossil echinoderms from Early Ordovician sections (about 490 million years ago) in southern Oklahoma, west Texas, northern and western Utah, and central and southern Nevada. They recently discovered a striking new, but very primitive, Early Ordovician crinoid based on four specimens that is intermediate in many features between Echmatocrinus and more advanced crinoids.

For more information, contact Dr. James Sprinkle at (512) 471-4264.

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Research on the world's oldest rocks has provided new insights into the early development of the earth. Discoveries made by a team of scientists, including Todd Housh in the Department of Geological Sciences indicate that the widespread formation of continental crust on the earth is significantly older than has commonly been believed. Standard models of earth development display a gradual increase through time of the amount of continental crust present on the earth since it was formed approximately 4.55 billion years ago. U/Pb geochronology, radiogenic isotope and trace element studies of the recently discovered 3.6 to 4.05 billion year old Acasta gneisses in Canada's Northwest Territories, however, indicate that by 4.1 billion years ago the earth had already formed a significant portion of its continental crust and that since that time the formation of new continental crust has been roughly balanced by the recycling of older continental crust back into the mantle. These discoveries not only provide us with insights into the earliest history of the earth, but they also help us to understand the development of mantle reservoirs sampled by magmas today.

For more information, contact Dr. Todd Housh at (512) 471-5750.

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In 1965, Keith Young began teaching the first formal University course offered in the United States with the title of "Environmental Geology." This course focussed on the role of man as a geologic agent, water and air pollution, soil formation and erosion, trace nutrients and health, landslides, earthquakes, volcanic hazards, Earth's climate, population and land use. In 1970, Young presided over a session at the national Geological Society of America meeting on the teaching of environmental geology. Also in 1970, Peter T. Flawn, Professor in the Department of Geological Sciences and Director of the Bureau of Economic Geology published an advanced text titled "Environmental Geology." In 1975, Keith Young published the text for his course titled "Geology: The Paradox of Earth and Man." Today, there are many dozens of environmental geology textbooks, but these two were the forerunners, and Keith Young's class was the first of its kind in the nation.

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Faculty and students from the University of Texas at Austin have done field studies in the remote Central Range of New Guinea that place important timing and process constraints on the plate tectonics of the most recent, large (1400 km long) arc-continent collision on Earth. They have discovered that in New Guinea, the northwards dipping subduction of the oceanic end of the Australian Plate began more than 20 million years ago. Approximately 16 million years ago, the continental margin of Australia began to be subducted and a thick pile of bulldozed sediment became highly deformed and metamorphosed in the subduction zone. However, the actual jamming of the subduction zone by the partial underthrusting of Australian continental crust only began 6 million years ago. At that time, an enormous block of continental basement was decapitated from the downgoing plate and pushed southwards 10 to 20 km forming a gigantic fold. The subducted oceanic end of the Australian Plate did not stop and dangle, but rather broke off. The tectonic aftermath of subterranean plate rifting between 6 and 3 million years ago included widespread magmatism from the melting of the lower continental lithosphere and a rapid vertical uplift of 1-2 km of the collision-generated fold belt. The UT team terms this fundamental tectonic process "collisional delamination." This process probably occurred during the final stages of continent-continent or arc-continent collision at many places and times on Earth, but only in New Guinea is the timing and geometric relations readily deduced because the event is so recent that erosion and post-collision deformation has not obscured critical field relationships.

For more information, contact Dr. Mark Cloos at (512) 471-4170.

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Ever since Darwin proposed his revolutionary theory of Evolution, one of the biggest challenges he and his supporters have faced is the problem of the origin of living birds. If all living species are connected through lines of descent, then who are the ancestors of birds? What did proto-birds look like, how did the intermediates between terrestrial vertebrates and flying birds function? For a century and a half, this has been an area of controversy. Work carried on here in the Department of Geological Sciences is providing important new evidence that birds are the living descendants of Mesozoic dinosaurs. The evidence comes both from the fossil record and from the embryology of living birds, using imagery generated by our high-resolution X-ray CT scanner. By scanning a number of Mesozoic dinosaurs, we have uncovered new evidence in the pneumatic system of the skull and skeleton linking birds to dinosaurs. We have recently traced some of this evidence to the oldest known dinosaurs, which were brought to UT from Argentina, where they were discovered, to be scanned. Additional evidence has come from scanning embryonic birds, to learn how their skeletons develop while still inside the egg. We are now documenting a series of transformations of the skeleton leading from egg to adult that closely resembles the series of evolutionary changes occurring over the history of extinct Mesozoic dinosaurs. Taken together, the information from embryology and the fossil record presents a compelling case that birds are the living descendants of extinct Mesozoic dinosaurs, specifically the descendants of the carnivorous theropod dinosaurs. With a detailed map of bird relationships, we can now begin to study the problem of how flight originated.

For more information, contact Dr. Timothy Rowe at (512) 471-1725.

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Research by Ernie Lundelius, Director of the Vertebrate Paleontology Laboratory and Professor in the Department of Geological Sciences concerns the response of mammalian communities to environmental change. He has developed a detailed picture of changes in the Pleistocene and Holocene faunas of Texas and Australia. This interval of time, the last 40,000 years, covers the last interstadial, the last glacial maximum and the Holocene. This is the period of time that saw many major environmental changes and the rise of humans as a significant environmental factor. It is also an interval that can be dated by C-14 which makes it possible to obtain a detailed chronology of the faunal changes. Ernie Lundelius, his former graduate student Russ Graham, and a number of other collaborators, have compiled a massive data base of North American mammals for the last 40,000 years -- a computer data set they have named FAUNMAP. This data set makes it now possible to rapidly compare how the faunal changes correspond to other records of climate change such as those recorded in deep sea cores, polar ice cores, and pollen stratigraphies from lakes.

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During the middle portion of the Tertiary period, between about 45 and 30 million years ago, much of western Mexico and the adjacent Trans-Pecos region of Texas was blanketed by explosive volcanic activity. The vast (250 x 1200 km) Sierra Madre Occidental of Mexico is the largest contiguous remnant of this activity. A long-term investigation in the Sierra by students, research scientists and faculty in the Department of Geological Sciences represents the only systematic geologic study of this important volcanic field. The project is built upon a foundation of geologic mapping and includes geochronology, geochemistry, and isotopic studies. The understanding gained of this intense volcanic event has been important for two reasons. First, a major portion of Mexico's mineral wealth was created during this process. Second, the appearance at the surface of a large volume of evolved magma over a short period of time requires transfer of a much larger quantity of more primitive magma and/or a major influx of heat from the earth's mantle into the continental lithosphere. Thus, the process is a fundamental way in which the earth's heat engine operates to modify and transform the continental infrastructure upon which we depend for resources.

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Faculty, graduate students, and a postdoctoral scientist at the University of Texas at Austin Department of Geological Sciences have shown that the southern margin of North America was involved in a plate tectonic collision at about 1.1 billion years ago during assembly of the Grenville supercontinent, Rodinia. Rocks in central Texas represent the core of an ancient mountain chain similar to the Alps or Himalayas and record collision of both a volcanic island arc and a continent with North America. By studying these ancient rocks, we can look at the processes that took place, and are presumably taking place today deep in the crust.

For more information, contact Dr. Sharon Mosher at (512)-471-4135.

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Normally we do not give any thought to the ground we are standing on—we just take it for granted as "dirt underfoot." In reality, this dirt is a complex mixture of minerals, prominently of a family called clay minerals. Leon Long and his students have been investigating the ages and origins of clay minerals using the very long-lived radioactive decay of an isotope of rubidium, an element that occurs in these minerals in trace quantities. The decay product is an isotope of another trace element, strontium, and together these isotopes comprise a geologic "clock." Each time there is a process of recycling of the earth, the clock is re-set. For example, when the minerals in an igneous or metamorphic rock are weathered to make soil, the clock begins again in these newly-formed clay minerals. Since weathering goes on all the time, most soil is of fairly recent origin, but some soil zones have been preserved as much as millions of years. The radioactivity clock is used to date these ancient soils, hence "dating dirt." Soil is part of the landscape, hence dating dirt may be important to interpretations of how landscapes change through geologic time.

For more information, contact Dr. Leon E. Long at (512) 471-7562.

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How do terrestrial vertebrate species respond to climatic change? Much of our understanding of North American vertebrate faunal dynamics in the Pleistocene comes from excavation and analysis of late Pleistocene localities. Climatic perturbations and the arrival of humans on the North American continent at the end of the Pleistocene resulted in dramatic changes in the overall appearance of vertebrate communities. For mammals, these changes resulted in extinction of many large-bodied species, and major geographic range changes for smaller species. During this same time, however, reptile and amphibian communities appear to have been little affected, suffering few extinctions and maintaining relatively stable geographic distributions. Identification, excavation and analysis of several early and middle Pleistocene fossil localities in the western United States provides a new data set against which the late Pleistocene record may be evaluated. Are herpetofaunal stability, mammalian extinction and community reorganization characteristic responses to climate change? Recent findings suggest that with respect to vertebrate faunal dynamics, the late Pleistocene record is unique and cannot be viewed as a paradigm for species response to climate change.

For more information, contact Dr. Chris Bell at (512) 471-7301.

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