“HAUNTED BY A CRYPTIC OROGEN: THE SIERRA NEVADA AND ITS IMPACT ON THE EVOLUTION OF CALIFORNIA”
Craig H. Jones
University of Colorado, Boulder, CO
The presence of the Sierra Nevada became much more puzzling when seismic studies in the southern Sierra revealed that the crust was only about 35 km thick. Petrologic studies of xenoliths and their host basalts led to to suggestion that dense lithosphere was removed from beneath the range about 3.5 to 5 Ma. Such removal of dense material has long been proposed both for developing a silica-rich continental crust and for driving so-called post-orogenic collapse of orogens, but observations of the process have been lacking. The most direct consequence of the removal of dense material is uplift, which now (once again) seems to have occurred between about 8 and 3 Ma. Such uplift should produce extensional stresses and potentially normal faulting; basin and range topography in the 50-100 km just east of the Sierra developed since 5 Ma. As Pacific-North America motion has been unchanged since about 10 Ma, increased extension in the westernmost Great Basin should cause contraction elsewhere or a decrease in extension elsewhere. The California Coast Ranges developed starting about 3-5 Ma, possibly in response to the extension. Finally, narrowing the rigid Sierra-Great Valley block should permit an increase in the strike-slip motion on its east side; available evidence in compatible with a decrease in San Andreas slip and an increase in the slip rate of the Eastern California Shear Zone about 4-5 Ma.
Although an appealling integration, the scenario above predicts that material was removed along the length of the Sierra, a prediction in need of testing. If this did occur, it appears that the downwelling material got focused into “drains” at either end of the Sierra. This geometry has not been anticipated by numerical models of lithospheric removal and so suggests that our understanding of the dynamics of lithospheric foundering is incomplete. These issues are hopefully to be tested as part of EarthScope in the coming years.
“DAMAGE EVALUATIONS OF THE RECENT MW 6.6 NIIGATA KEN CHUETSU EARTHQUAKE IN JAPAN”
Colorado School of Mines, Golden, CO
The 23 October 2004 Niigata Ken Chuetsu, Japan, Mw 6.6 Earthquake was the most significant earthquake to affect Japan since the 1995 Kobe earthquake. Forty people were killed and almost 3,000 injured and numerous landslides destroyed entire upland villages. Landslides were of all types, and dammed streams, creating new lakes likely to overtop their new embankments at any moment and cause flash floods and mudslides. Landslides and permanent ground deformations caused extensive damage to roads, rail lines and other lifelines, resulting in major economic disruption. A major factor contributing to the large number of landslides that occurred during the earthquake was heavy rain due to Typhoon Tokage – precipitation measured in the epicentral region was 100 mm (4 inches) on Oct. 20 and 13 mm (0.5 inches) on Oct. 21. In excess of 100,000 persons sought temporary shelter, and as many as ten thousand will be displaced from their upland homes for several years, if not permanently. Total costs of damage are estimated at USD 40 billion, making this the second most costly Japanese natural disaster in history, after the 1995 Kobe earthquake.
Dr. Scott Kieffer from the Colorado School of Mines was a member of the scientific team mobilized by the U.S. Earthquake Engineering Research Institute to study geotechnical aspects of the Ken Chuetsu Earthquake. Dr. Kieffer will discuss some of the novel aspects of this earthquake, and their relation to extensive geotechnical failures.
February 2005 – Emmons Lecture
“THE LAST FRONTIER OF SILICIC PYROCLASTIC VOLCANISM”
Richard S. Fiske
National Museum of Natural History, Smithsonian Institution, Washington, D.C.
The last frontier of silicic pyroclastic volcanism is located along submarine convergent margins in present-day oceans, where many volcanologists least expected to find it. One of the best places to explore this frontier is along the front of the Izu Bonin arc, south of Japan, where nine submarine rhyolitic calderas are lined up like proverbial beads on a string. Study of these structures is just beginning, but we already know that one of them hosts a large and actively growing polymetallic sulfide deposit rich in gold and silver. All of them produced huge volumes of rhyolite pumice during their caldera-forming eruptions and, surprising to some, much of this familiar low-density material immediately sank, forming extensive sea-floor tephra deposits. These and other seeming improbabilities will be of little surprise to geologists who have studied greenstone belts and other ancient convergent-margin terrains, where evidence for submarine silicic volcanism has long been known to abound.
“PRINCETON SCIENTIFIC EXPEDITION OF 1877: THE FLORISSANT, COLORADO SEGMENT”
Steven W. Veatch
Department of Earth Science, Emporia State University, Emporia, Kansas
Early scientific information and fossil specimens from what is now the Florissant Fossil Beds National Monument came from a group of college students who, in 1877, traveled to the Florissant area from Princeton (then the College of New Jersey). Original expedition documents and photographs from Princeton’s Mudd Manuscript Library and other sources provide a clear and complete chronology of the Princeton Scientific Expedition and reveal new details of this early phase in the history of paleontology at Florissant.
While in their junior year (1876), three of Arnold Guyot’s students, Henry F. Osborn, William B. Scott, and Francis Speir Jr., envisioned a scientific expedition to the West. They sought advice from the paleontological profession, but because of the feud between E.D. Cope and O.C. Marsh, such information was classified. Undaunted, they organized the expedition throughout their senior year. On June 21, 1877, the Princeton Scientific Expedition left New Jersey for the West. After arriving in Denver four days later, the students spent time buying equipment, wagons, mule teams, and recently captured Indian ponies. The students first explored the Garden of the Gods in Colorado Springs. Upon arriving in Florissant in mid-July, they camped near what is now the park’s visitor center and began their search for fossils.
The insects the students collected filled five trays. The collection of plants comprised 25 trays containing more than 900 specimens. At least 180 of the plant and insect specimens became type specimens. Samuel Scudder and Leo Lesquereux described many of these type specimens. Osborn, Scott, and Speir described a number of fish specimens collected at Florissant, including the new species Trichophanes copei.
The expedition diaries, journals, and photographs document a remarkable expedition and contribute to the history of paleontology in America. The fossils of the Princeton expedition have allowed researchers in the past, and will allow those in the future, to better understand the paleontology and paleoecology of the Florissant fossil beds.
Steven Veatch is the author of a number of articles on earth science topics. He is an adjunct professor at Emporia State University and lectures extensively on Colorado’s geology and paleontology. He lives next to the Florissant Fossil Beds National Monument where he is a volunteer.
“COMPILING THE NEW GEOLOGIC MAP OF NORTH AMERICA—SOME THOUGHTS AND REMINISCENCES “
U. S. Geological Survey
The new Geologic Map of North America, the final product of the DNAG project, portrays the grand architecture of the continent as we understood it in the closing years of the 20th century. It was compiled by Jack Reed (USGS), John Wheeler (GSC), and Brian Tucholke (Woods Hole Oceanographic Institution). The map is at a scale of 1:5M and covers about 15 % of the earth’s surface.
The previous geologic map of North America was published in 1965, before general acceptance of plate tectonic, before radiometric dates were widely available, and when the geology of the sea floors was largely unknown. The old map distinguished about 100 rock units, all of them onshore. The new map distinguishes 939 units, of which 142 are offshore. It also depicts many geologic features not shown on the previous map, including volcanoes, calderas, impact structures, axes of submarine canyons, spreading centers, transform faults, magnetic isochrons, and subduction zones. For the first time it portrays the relationships between the geology of the continent and the geology of the ocean basins that flank it. The map was compiled over an interval of almost 25 years and its assembly spanned the technological change from tradition cartography to digital cartography. Although the map is not yet available in digital form, plans are underway for construction of a digital database and ultimately for the release of GIS compatible files.
No map of this kind is ever really “finished”; the best the compilers can hope for is to produce a map raises new questions and encourages new work in critical areas. We hope that this new map will help promote new ideas and fresh discussions, and play a role in the training of a new generation of earth scientists. Perhaps it may even help guide prudent political decisions about management of the lands, waters, and resources of our continent and the seas that surround it.
April 2005 – Annual Family Night
“BACK TO THE JURASSIC: SHEDDING NEW LIGHT ON LOCAL DINOSAUR HERITAGE”
Bob Bakker, author of The Dinosaur Heresies and
Matt Mossbrucker, Director of the Morrison Natural History Museum
Colorado’s first giant Jurassic dinosaurs were discovered in the foothills of Jefferson County. What was the world of the dinosaur like in the Front Range? The Morrison Natural History Museum’s Ajax Discovery Project* takes paleontologists and geologists back to historic quarry sites, including Quarry 10 where Apatosaurus ajax was first discovered in 1877, to uncover clues that add to our understanding of ancient environments. Join Jurassic “crime scene investigators” Dr. Robert Bakker and Matthew Mossbrucker as they shed new light on the life and times of Jurassic giants and announce an important new dinosaur first for Colorado.
* The Ajax Discovery Project is funded by grants from Aggregate Industries and the Jefferson Co. Cultural Council (SCFD).
“Monkey puzzles and parking lots: Why every Mesozoic landscape you have ever seen is wrong”
Chief Curator of the Denver Museum of Nature and Science
Many paintings of dinosaurs look the same. Three elements that reoccur are the central spectacular dinosaur(s), a distant stand of conifers, and a foreground of pounded brown dirt. Did the Mesozoic really look like this? Probably not. Are we the collective victims of an artistic/scientific conspiracy? Certainly not, but several repeated biases have resulted in an iconography of dinosaur landscapes that loves the animal but hates the place.
How do you reconstruct an extinct landscape? What covers the ground in a world before grass? Kirk Johnson has worked with painters and sculptors to reconstruct many prehistoric landscapes for the Denver Museum of Natural History’s award-winning Prehistoric Journey exhibit, the Ancient Denvers Project, and a new project to place ten large paintings of Ancient Colorado in the Colorado Convention Center later this year. In this talk he will explore the techniques of combining science and art to create credible and beautiful ancient landscapes.
“What is the origin of the Anton Scarp?”
Manager Special Ops, Colorado Geological Survey
Colorado’s High Plains consist of a broad expanse of Miocene and younger sediments that dip gently eastward into Kansas and Nebraska. This young surface is not completely flat, however. East of Fort Morgan and Limon, the surface appears to be offset into many topographic horsts and grabens. The area is crossed by numerous lineations and scarps between high and low areas, many of which have a NW-SE orientation. The largest of these scarps, informally named the Anton scarp, is at least 95 miles long and up to 65-80 ft high. During 2004, the Colorado Geological Survey (CGS) and its research partners conducted different types of field investigations in order to assess the origin, age, and evolution of this feature, including the possibility that it was formed, at least in part, by faulting.
At the main study site, 7 miles northeast of Anton, the scarp is 80 ft high, about 1,350 ft wide, and has a maximum slope angle of seven degrees. Fieldwork included scarp profile measurement, GPR and refraction seismic surveys, trenching and trench wall logging, sampling for C14 and optically stimulated luminescence (OSL) dating, and borehole drilling and core logging. A 600 ft long, 15-20 ft deep trench was dug down the scarp. This trench exposed 72 ft of stratigraphic section, almost all of which dips gently to the west and thus is truncated by the scarp. No direct evidence of faulting was found in the trench. Continuous cores of up to 12 m deep were drilled along the trench and to the east, within a closed depression, to extend the depth and lateral extent of lithofacies correlations.
Another site that was investigated was a trench for a 36-inch, natural gas pipeline, located 11 miles southwest of Akron. Where the pipeline trench crossed the Anton scarp, a steeply dipping, organic-rich, extremely heavily burrowed zone that may represent a biologically modified fault zone underlies the base of the scarp.
The two trench investigations allowed CGS an unprecedented opportunity to observe and describe near-surface lithofacies relationships beneath the High Plains. Of particular interest is the “algal limestone” in the Ogallala Formation, which may prove to be an important mapping unit because of its limited vertical and lateral extent.
“Re-Os SYSTEMATICS IN BLACK SHALES: MARKING TIME AND THE RISE OF ATMOSPHERIC OXYGEN”
Judith L. Hannah
AIRIE Program, Department of Geosciences, Colorado State University
How do we mark absolute time in sedimentary sections? How do we determine the age of sedimentary rocks when fossils are lacking? How can we use the chemistry of sedimentary rocks to understand earth surface processes in the past? All of these are long-standing questions and current hot topics, and the rhenium- osmium (Re-Os) isotopic system offers some answers.
Like more familiar isotopic systems (e.g., U-Pb, Rb-Sr, Sm-Nd) the decay of 187Re to 187Os can be used to determine the age of geologic materials, and the 187Os/188Os ratio can be used to fingerprint source materials. Re and Os are chalcophile/siderophile elements concentrated in metals, sulfides, and organic material. Both elements are soluble in oxidizing environments but fixed by reduction. Consequently, they are enriched in organic material in shales deposited under suboxic conditions, and concentrated in diagenetic pyrite.
We have successfully dated diagenetic pyrite in 2.32 Ga shale from the Transvaal Group in South Africa. This system also yielded a surprisingly low 187Os/188Os ratio, suggesting that oxidative weathering was still minimal at the earth’s surface at this time, even though sulfur isotope data show that oxygen had already begun to accumulate in the earth’s atmosphere. We are exploring additional shale sequences near the Archean- Proterozoic boundary (~2.5 Ga) to track the rise of atmospheric oxygen through its reflection in Os cycling in surface materials. Preliminary work on other systems shows that some similar shales are disturbed, perhaps by exchange of Re and/or Os between coexisting organic material and sulfides during low-grade metamorphism. Research is underway on direct analysis of chemically extracted organic material to refine methods of dating shales and tracking Os sources through time.
This work was done in collaboration with my colleagues at AIRIE, Holly Stein and Richard Markey, and supported by the National Science Foundation.
NecroSearch International is a non-profit organization that assists law enforcement agencies with locating clandestine gravesites. The 30+ NecroSearch volunteer members include a wide variety of scientists and crime scene investigators who specialize in animal scavenging, anthropology, archeology, botany, cadaver dogs, criminalistics, data processing, entomology, geography (GIS), geology, geophysics, meteorology, psychology, remote sensing, serology, underground and underwater exploration. The three primary goals are:
Research: For the past 15 years, NecroSearch has buried pigs at the Highlands Ranch Law Enforcement Training Facility in order to study the processes associated with burials.
Training: NecroSearch conducts annual one-week hands-on classes for law enforcement investigators from all over the world.
Assistance: NecroSearch members assist law enforcement investigators at crime scenes in the search and/or recovery of human remains and other evidence.
Bio: Jim Reed studied geology at the University of Wyoming and Washington University in St. Louis. He has worked for NASA, Freeport Exploration, AMAX Exploration, and Wold Minerals. In 1983, Jim founded RockWare, a geological software company that services the mining, petroleum, civil engineering. and environmental industries. Jim’s role in NecroSearch typically involves the integration and synthesis of disparate date sets into exploration targets.
“FLOOD REGULATIONS AND FLOOD INSURANCE IN DEBRIS FLOWS AND ALLUVIAL FANS”
Colorado Water Conservation Board
Many Colorado municipalities and counties are affected by flood hazards associated with alluvial fans (including debris flows). The counties affected include Clear Creek, Boulder, El Paso, Eagle, Garfield, Pitkin, Gunnison, Hinsdale, Ouray, San Miguel, and Montezuma. At least two other counties, Rio Grande and La Plata, have had such problems greatly exacerbated by recent wildfires. All of the above counties (and many municipalities within them) participate in the National Flood Insurance Program (NFIP).
Alluvial fans are acknowledged by the NFIP, but mapping or regulating these hazards is not explicitly mandated. Flood insurance is available, but it does not fully recognize the unique character of alluvial fans. Alluvial fans have been mapped in detail by FEMA in three Colorado communities (Glenwood Springs, Ouray, and Telluride). No model regulations have been developed by the State of Colorado or FEMA to provide local governments or property owners with specific guidance for managing these hazard areas. There is a significant void in technical and administrative direction for mapping of hazards, design or review of proposed mitigation measures, or determination of appropriate insurance rates.
Mapping must include a combination of geologic and engineering methodologies. Both disciplines must join with planners and building officials to develop standards for the design and review of mitigation measures. Technical criteria for approving or disapproving mitigation measures for conventional riverine flooding have existed in Colorado for many years, but they do not exist for debris flows and alluvial fans. Probabilistic analysis guides flood insurance rates. A “100-year” flood has a 1% chance of occurring in any year, and a “10-year” flood has a 10% chance. Alluvial fans involve a complication. Within the 100-year fan a single 100-year flood event may go to the left, to the right, or down the center. The center is typically higher in elevation because historic events have deposited more debris there. However, gravity may make the lower flow paths to the sides preferable for future floods. Quantifying risk in alluvial fans is not for the faint-hearted.
Brian Hyde is a Senior Water Resource Specialist in the Flood Protection Section of the Colorado Water Conservation Board, where he has worked for 25 years. He is currently managing river watershed restoration projects for the Alamosa River and Fountain Creek
“CHINA’S AND INDIA’S RAVENOUS APPETITE FOR NATURAL RESOURCES–THE IMPACT ON COLORADO”
Colorado Geological Survey
Colorado’s history is steeped in its rich horde of natural resources. Today the state is still a major provider of mineral and mineral fuels. However, worldwide shortages of many resources caused by the explosive and unprecedented economic growth of the two most populous nations on earth, China and India, will put increasing strains and pressures on Colorado’s rapidly expanding and rapidly urbanizing population. An already strong demand for Colorado’s rich reserves of oil, natural gas, coal, uranium and metals will only increase as unparalleled competition for Earth’s limited resources grows.
Vince Matthews is our Colorado State Geologist, Director of the Colorado Geological Survey, and president of the Colorado Scientific Society. Before joining the CGS in 2000, Vince spent over 20 years in the petroleum industry, working for a number of companies. He was on the faculty at the University of California, University of Northern Colorado, Arizona State University, the Frank Lloyd Wright School of Architecture, and the University of Texas of the Permian Basin. Vince Matthews has conducted research and published on the San Andreas fault, global tectonics, subduction zone tectonics, igneous and metamorphic petrology, and Laramide deformation.
STUDENT PAPERS FOR 2005
“Submarine mass transport complex evolution and control on overlying siliciclastic deposition, Permian Cutoff Formation, west Texas”
Robert Amerman1 (speaker), Eric P. Nelson1, Michael H. Gardner2,and Bruce Trudgill1
1Colorado School of Mines, Department of Geology and Geological Engineering, 2Montana State University, Department of Earth Sciences
The Williams Ranch Member of the Cutoff Formation consists of six offlapping, basinward-stepping lithologic units of highstand carbonate turbidites deposited across a drowned Early Permian carbonate platform, then partially redistributed in slumps on the slope and basin floor. Slumps are intercalated with undeformed carbonate turbidites; the ratio of slumps to undeformed sediment increases basinward. Upslope evacuation scars correlate to downslope slump bodies. Gravity flow deposition and subsequent mass movement caused basinward thickening of the Williams Ranch Member and caused the toe of slope to shift 2 km basinward relative to the underlying Bone Spring Limestone. This shift controlled landward pinchouts of the overlying Permian Bushy Canyon Formation channel and sheet sandstone bodies.
Williams Ranch Member deposition both responded to and modified inherited bathymetric relief. Williams Ranch isopach thicks correspond to larger underlying lows and smaller overlying highs and exhibit a higher ratio of undeformed to slumped sediment and a higher percentage of soft-sediment folds relative to soft-sediment truncation surfaces. These slump “pile-ups” appear to be concentrated in inherited lows. Slump bodies show a general southward transport vector, with significant local variation possibly reflecting underlying bathymetric influence. With repeated slump events, “pile-up” zones resulted in local positive bathymetry. Brushy Canyon sand fairways and ponded sheets are focused in bathymetric lows, and sands are sidelapped against highs atop the Williams Ranch Member. Increased understanding of mass transport complex evolution may lead to better prediction of overlying reservoir geometry, both within the Brushy Canyon FOrmation and in analogous reservoirs in other deepwater settings.
“Effects of Growing Structures and Physiography on Deepwater Depositional Elements of a Niger Delta Intra-slope Basin – Implications on Reservoir Distribution and Architecture”
Colorado School of Mines, CoRE
Hydrocarbon exploration and exploitation in deep water environments is financially intensive, hence to achieve success, adequate and relevant knowledge of reservoirs is paramount. Reservoirs in deep water Niger delta occur in elusive forms as lobe or channel deposits, this is different from those on the shelf where they are mostly sheet-like.
This study is aimed at determining the influence of growing structures on depositional elements, reservoir distribution and architectural characterization in the Niger delta slope, by interpreting deep water channels and fan systems, determining reservoir geometry, internal architecture and facies distribution and relating these to depositional processes.
In the translational zone between the extensional growth faults dominated region and the deepwater compressional thrust fault domain, growing structures such as mobile shale, mud diapir and growth faults have tremendous influence on depositional processes and sedimentation, and ultimately determine the development, distribution and architecture of reservoir facies.
Isochron maps and proportional slices of interpreted horizons on EDGE (enhanced detection of geologic events) as well as 3D seismic amplitude were used to study channel pattern evolution and structural geometry. Extracted root mean square (RMS) seismic amplitude provided insight on spatial and temporal distribution of reseroir facies. We rely on seismic amplitude and analogs from other basins where there are well data for general lithofacies differentiation. Timing of structural movement would be evaluated using growth strata.
This study interval mostly between 1350 and 2500 ms is being used as analogs to study the relationship between shale diapirs and depositional sequences and their variations in thickness, internal architecture, facies distribution and geometry, this could be applied to deeper prospective level.
“Hydrothermal alteration and its effects on slope stability in Alum Creek, Eastern San Juan Mountains, South-central, Colorado”
Douglas C. Kreiner
Warner College of Natural Resources, Department of Geosciences, Colorado State University
Hydrothermal alteration results in a change in mineralogy, which may structurally weaken or strengthen a rock as well as influence the evolution of a slope. Alum Creek is a highly altered natural drainage, unaffected by anthropogenic activities, and will be used to evaluate the effects of hydrothermal alteration on slope stability.
Alum Creek is part of a high-sulfidation, sub-economic deposit associated with the Alamosa River stock. Andesitic lava flows were subsequently intruded by an equigraular and porphyritic monzonite. The latter brought a mineralizing fluid responsible for hydrothermal alteration with zones of quartz-sericite-pyrite (QSP), quartz-kaolinite (QK), argillic, quartz-alunite (QA) and propylitic.
Alum Creek began downcutting dominantly in the argillic, QK and QSP facies. The slopes resulting from this downcutting are oversteepened and show evidence of several mass movement events. The slopes are composed of massive amounts of fine-grained unconsolidated clay in the argillic zone. The QK and QSP facies are more coherent with large areas of outcrop persisting on the slopes, however acid production during weathering has attacked outcrops and resulted in minor supergene alteration on these slopes.
The stability of the slopes is dominated by two main factors: talus armoring and/or the angle of repose of the physically weakest mineralogic assemblage; which govern the angle at which the slopes are stable. Mapping the mineralogy of slopes, slope cover and slope gradient aids in understanding the degree to which each factor influences the slopes. The results have global implications to the construction of mine waste facilities.
“Fault Related Bleaching and Sediment-Hosted Copper Mineralization at the Cashin Mine, Montrose County, Colorado”
Timothy J. MacIntyre
Colorado School of Mines
The Cashin Mine in western Montrose County, Colorado is a sandstone-hosted copper deposit located in Jurassic Wingate Sandstone on the southwest side of the Paradox Valley salt anticline. The Wingate is typically a red/orange fine-grained eolian sandstone, but in the study area it has been bleached to a white/tan color. Reduced fluids, likely associated with hydrocarbons, appear to have traveled up along steeply dipping, northeast-trending normal faults before traveling laterally into gently dipping high permeability sandstones. These reduced fluids mobilized and reduced iron from red bed sandstones, depositing pyrite and making otherwise unfavorable strata into potentially reactive hosts for copper mineralization. Bleaching in the Wingate sandsone is assymmetrically distributed around the Cashin fault forming a reduced zone approximately 10 km by 5 km with preferred flow direction to the northwest. Within this reduced zone and centered on the Cashin fault lies the Casin copper deposit. The Cashin deposit consists predominately of chalcocite, bornite, and chalcopyrite in veins along the fault and disseminated within adjacent Wingate Sandstone for up to 600 m from the fault.
Thin section petrography reveals that bleaching alteration in the Cashin area occurred early, prior to significant quartz overgrowth formation or carbonate cementation. Bleaching removed iron oxide coatings from detrital grains, preferentially dissolved iron from ilmenite grains, and significantly corroded sodium-plagioclase grains while also precipitating cubic pyrite. Later introduction of oxidized copper-bearing brines into the bleached sandstone resulted in precipitation of copper sulfides that replace pyrite, dolomite cement, and quartz.
“3D Strain at Transitions in Foreland Arch Geometry: Structural Modeling of The Beartooth Arch – Rattlesnake Mountain Transition, NW Wyoming”
Colorado State University
How is 3D strain accommodated at transitions in foreland arch geometry? End-member hypotheses to explain 3D strain at foreland arch transitions include 1) uniformly directed slip on pre-existing basement structures, and 2) anomalously directed slip necessary for 3D strain accommodation. The Beartooth arch, SW Montana and NW Wyoming, transitions to the SE into a structurally complex zone characterized by a blind master thrust with anomalously oriented and backthrust hanging wall structures. The Rattlesnake Mountain anticline is a SW-vergent backthrust within this hanging wall and is linked to the NE-vergent Beartooth arch by the S- vergent Pat O’Hara Mountain anticline. Inferred ideal sigma-1 orientations from over 1,200 slickensided minor faults and shear bands at the southern Beartooth arch transition show a uniformly oriented 065o stress field at sites located away from anticlinal axes. Inferred sigma-1 orientations at sites located within anticlinal axes are inconsistent with the regional 065o orientation, and show more northerly orientations (~030o to 045o). If the geometry of the structues is dictated by 3D strain accommodation, slip perpendicular to anticlinal axes would be predicted. Instead, slip is oblique to structural trends and also oblique to the inferred regional stress direction. These observations can be explained by uniformly directed slip on oblique pre- existing structures reulting in material rotation within zones of oblique-slip. The consistency of regional sigma-1 orientations, abrupt along-strike structural terminations, and documented local extension at structural terminations further support this hypothesis, which is a first-order constraint for current modeling using 3Dmove software.
“Hydrologic Margins of the Dry Valleys of Antarctica”
Colorado School of Mines
In the Dry Valleys of Antarctica lies a controlled laboratory in which hydrology of hyporheic zones in dry environments can be studied without interfering factors. It is proposed that the characteristics of soil change across wetted margins of streams and lakes as soils progress from wet to dry. These changes include gradients in soil moisture, electrical conductivity, and soil chemistry, all of which may affect the microbiology of the transition zone.
Variations in soil properties along hydrologic margins have been examined at eleven plots along lakes and streams in the Dry Valleys. At stream locations, values of electrical conductivity are very low and show no marked pattern, reflecting the ability of streams to flush away salts. Conversely, data from lake locations show a peak in electrical conductivity near the dry edge of the wetted margin, demonstrating the tendency of lake shores to concentrate salts. Work-in- progress includes evaporation-pan experiments, and collection of stream, lake, and soil water for isotopic analysis. Thermocouple devices also have been installed to monitor temperature patterns at depth in the hyporheic zone. The isotopic signature of soil waters will help determine an evaporation rate. Evaporation rates will be used, along with temperature data, to model flow paths and capillary action in the active zone, using the program Hydrus 2d. Variations in soil properties along hyporheic zones will be associated with flow paths and evaporation, with an ultimate goal of determining how these factors affect microbiology in the hyporheic zone.
“Geology of the Epithermal Explorador vein within the Selene Mining district, Apurimac, Peru”
Colorado School of Mines
The Miocene magmatic arc of the southern Peruvian Andes hosts many mineral occurrences of the three well-known epithermal deposit types: low-, intermediate- and high-sulfidation deposits. The Selene Mining district is an important mining district which hosts many epithermal systems, including the Explorador vein.
The host rock to the deposit is part of a complex stratovolcano displaying caldera-like circular features. Extrusive and hypabisal rocks range in composition and textures from intermediate andesitic flows to felsic domes and pyroclastics. The volcano litho-stratigraphy, structural, mineral paragenesis, host rock alteration, geochemical zonation, and age of mineralization are poorly known. The purpose of this research is to study these aspects of the geology to develop an ore control model for directing future exploration.
Mapping at scale of 1/10,000 were conducted during the summers of 2004 and 2005. Rock samples were collected and are being studied petrographically and by Pima infrared spectrometric mineralogical analysis. Geological cross sections are being constructed to better understand the volcano litho-stratigraphic setting. Structural analysis on the Explorador dome and vein, the main mineralization-host rock, will be undertaken.
Results of these studies will be synthesized to undertand controls on the mineralization of the Explorador vein and to guide future exploration of satellite mineralizaed structures. Preliminary observations have indicated both a strongly structural control and a stong association of mineralization to lately emplaced domes.
December 2005 – Presidental Address
“WAS EMMONS WRONG?”
University of Colorado, Boulder
In his inaugural address to the Colorado Scientific Society in January of 1883, the Society’s first president, Samuel F. Emmons, made some rather strong assertions about the geology and mineral resources of Colorado, to wit:
“In Colorado ….we have coal fields whose extent is probably greater than those of Pennsylvania.”
“In silver, Colorado stands pre-eminent.”
“From a mineralogical point of view, the wealth of Colorado exceeds that of the other states.”
In comparing gold to California: “the field for investigation and for the application of scientific methods is all the larger.”
“For the study of the Archaean … it is safe to say we have nowhere else in the world such opportunities.”
“On all the broad extent of these United States certainly no region can be found which presents more facts of interest, more opportunities for investigation, and greater possibilities of new discoveries than the State of Colorado.”
Given that he had served admirably on the King Survey of the 40th parallel examining the geology in California, Nevada, Idaho, Utah, Wyoming, and Colorado; he appears to have had a good comparative basis upon which to make some of these assertions. But was he right, particularly on the last assertion? Or was he simply engaging in boosterism? This address will attempt to show that his statement is as true today, as it was then.