Department of Earth and Planetary Sciences

... Karlstrom KE,; Crow R.,; McIntosh W.,; Peters L.,; Pederson J.,; Raucci J.,; Crossey LJ,; Umhoefer P.,; Dunbar N.,. 0016-7606(2007)119[1283:AAFSOQ]2.0.CO;2 Karlstrom KE, Crow R., McIntosh W., Peters L., Pederson J., Raucci J., Crossey LJ, Umhoefer P., Dunbar N., 2007, 40 Ar ...

... mantle and groundwater systems of the western United States: Evidence from travertine springs and regional He isotope data Dennis L. Newell, Laura J. Crossey, Karl E. Karlstrom, Tobias P.Fischer, and David ... Short Courses and K-16 Workshops: Call for Proposals, 41. ...

40 Ar/ 39 Ar dates on basalts of Grand Canyon provide one of the best records in the world of the interplay among volcanism, differential canyon incision, and neotectonic faulting. Earlier 40 K/ 40 Ar dates indicated that Grand Canyon had been carved to essentially its present ...

... 850–750 Ma) strata records equally large δ 13 C excursions that are not associated with direct sedimentologic evidence of glaciation (eg, Kaufman and Knoll, 1995; Kaufman et al., 1997; Karlstrom et al., 2000; Hill and Walter, 2000; Halverson et al., 2002; Corsetti and Kaufman ...

The Unkar Group of the Grand Canyon Supergroup is one of the best-preserved remnants of Mesoproterozoic sedimentary rocks in the southwestern United States. It provides an exceptional record of intracratonic basin formation and associated tectonics kinematically compatible ...

... to estimate the flux of deeply derived (endogenic) CO 2 through springs and ground-waters into ... The dissolution process is best illustrated by the chemical equation: 1 In a simple geochemical model, the ... The result from this analysis is that a significant flux of CO 2 is carried to the ...

The Unkar Group of the Grand Canyon Supergroup is one of the best-preserved remnants of Mesoproterozoic sedimentary rocks in the southwestern United States. It provides an exceptional record of intracratonic basin formation and associated tectonics kinematically compatible ...

We report new mapping, soils, survey, and geochronologic (luminescence, U-series, and cosmogenic-nuclide) data from Pleistocene deposits in the arid setting of eastern Grand Canyon. The result is a stratigraphic framework of inset fill gravels and associated terraces that provide a record of the responses of hillslopes, tributary streams, and the Colorado River to the last ˜400 kyr of glacial-interglacial climate change. The best-preserved last 80 kyr of this record indicates a stratigraphic-chronologic disconnect between both deposition and incision along the Colorado River versus along the trunks of local tributaries. For example, the Colorado River finished aggrading and had already begun incising before the main pulse of aggradation in the trunks of local catchments during Marine Isotope Stage 3, and then tributary incision followed during the millennial-scale fluctuations of the last glacial epoch, potentially concurrent with mainstem aggradation. The mainstem record appears to broadly correlate with regional paleoclimate and upstream geomorphic records and thus may be responding to climatic-hydrologic changes in its mountain headwaters, with aggradation beginning during full-glacial times and continuing into subsequent interglacials. The contrasting lag time in responses of the dryland catchments within Grand Canyon may be largely a function of the weathering-limited nature of hillslope sediment supply.

The Colorado River system (CRS), the single river system that drains the western slope of the Colorado Rocky Mountains, is a sensitive gauge of the uplift history and landscape evolution of the western U.S. It has a double concave-up longitudinal profile with a transient knickzone at Lees Ferry, Arizona. This knickzone separates the Lower and Upper CR basins, each with different and interacting uplift histories. The Lower CRS profile has evolved, and Grand Canyon has been incised, since 6 Ma due to drainage integration in response to base level fall associated with opening of the Gulf of California and dynamic uplift of the SW Colorado Plateau. Evidence for ongoing uplift comes from geodynamic models that find that mantle flow induces dynamic topography in the Colorado Plateau region. Mantle-driven tectonism is also recorded by the eastwards sweep of basaltic magmatism and a Neogene change from lithospheric- to asthenospheric-sourced basalts in the W Grand Canyon region. The Upper CR basin profile has been shaped by epeirogenic uplift of the Colorado Rockies.Geomorphic analysis of river profiles along the Green and Colorado rivers reveals steeper (normalized) channel gradients along the upper Colorado, despite greater discharge, and 40% greater topographic roughness of the upper CR relative to the Green River. Both are interpreted to reflect differential rock uplift across the W slope of the Colorado Rockies. Tomographic images show a N-trending low velocity anomaly (Aspen Anomaly) that extends to 200-250 km depth beneath the headwaters of the CRS, whereas the Green River basin in underlain by high velocity mantle. Apatite fission track analyses show rapid exhumation above the Aspen Anomaly beginning 10-5 Ma, preserved at modern elevations ranging from 1.5 to 4 km. This indicates substantial pre-10 Ma relief on a broad epeirogenic uplift. 10-5 Ma upper CRS denudation is not explained by climate change at ~3.5 Ma, nor by upstream propagation of incision driven by lower CRS integration at 6 Ma. Geodynamic models suggest that rock uplift may be driven by a combination of upper mantle buoyancy variations and mantle flow pressures. Analysis of the geoid (for sources shallower than 500 km) is consistent with 400/800 m of dynamic topography in the CP/RM respectively. Presence of mantle 3He in Colorado hot springs is interpreted as the youngest tectonic signal of ongoing mantle-driven uplift. The isostatic response to denudation accounts for several hundred meters of rock uplift, but is insufficient to account for the total magnitude of modeled and inferred uplift. Throughout the CRS, climatic influences on the profile and incision history are 100 ka time scale oscillations superimposed on Ma-scale persistent tectonic uplift forcings.

Rivers in the Rio Grande drainage of southern Colorado and northern New Mexico drain the southern Rockies southwards through the Rio Grande rift and across the NE trending Jemez lineament. We test the hypothesis that Quaternary tectonism (both faulting and broad doming due to magmatism and mantle driven dynamic uplift) may be recorded by drainage patterns and river profiles. These effects are not easy to distinguish from those of base level fall, drainage reorganization, and climate changes, but a regional look at New Mexico's rivers through time may help distinguish tectonic from climatic and geomorphic forcings. Longitudinal profiles of major drainages in northern New Mexico were constructed from 7.5 minute topographic maps, and DEM analysis. Bedrock lithologies, geometry of elevated terrace, and positions of basalt flows were compiled for each river. There are a striking number of reaches that exhibit sharp knickpoints and/or convexities in the profile. Some of these convexities and knickpoints seem to be bedrock-controlled; that is, they exist at hard rock-soft rock contacts. However, some convexities are not controlled by bedrock (e.g. entirely in shale); and similarly, some hard rock areas show no convexity, suggesting that bedrock control cannot always be used to explain convexities. The Rio Grande exhibits a double concave profile suggesting ongoing adjustments to neotectonic and geomorphic forcings. In map pattern, DEM analysis suggests a regional spatial correlation between the appearance of multiple convexities in numerous drainages and the Jemez lineament, a northeast trending zone of Quaternary magmatism and tectonism. Slope-area analysis, combined with Hack index analysis and topographic roughness analysis show good correlations of topographic parameters: 1) high gradient reaches (normalized for discharge), 2) regions of highest topographic roughness, and 3) zones of lowest mantle velocity. Thus, we support and expand the hypothesis that convexities in drainages crossing the Jemez lineament are the result of the drainages" response to Neogene (last 6 Ma) epeirogenic warping. These further tests of the interactions of tectonics and river incision can lead to fundamental insights about neotectonics in the Rocky Mountains and Rio Grand rift as well as processes of river incision.

Thematic field-lab-classroom workshops can be successful in training secondary teachers in planetary geology and astrobiology, from the LPI's 4 years experience. A typical workshop includes ˜4 days of field study and ˜3 days of related classroom/lab lectures and exercises. Up to 30 teachers have participated at once, and the staff averages 5 researchers and educators. The 2003 workshop, The Great Desert, focused on geology and life in the Colorado Plateau as analogs for Mars. Specific emphases were on geologic processes exemplified in the Grand Canyon, Sunset Crater and Meteor Crater, and on biotic communities in desert soils and hot springs. The classroom portion, hosted by UNM, included lectures, lab work, and teaching exercises keyed to the field experience and its extensions to Mars. Formal followups: non-directive exit questionnaires; email list-serves for participants; websites with images, presentations, and exercises from the workshop, and links to related materials (e.g., http://www.lpi.usra.edu/education/EPO/yellowstone2002/index.html); and interviews for six-month retrospective. Graduate and continuing education credit are available. Past workshops, all relevant to Mars, have targeted: geology and extremophiles of Yellowstone NP, geology of the Cascade volcanos; and giant floods and lava flows of central Washington. The greatest benefit of this workshop format is the teachers' intense, deep experience, emphasizing scientific content. They learn from field, classroom, and laboratory perspectives, and work with PhD level researchers who contribute their excitement, demonstrate and teach critical thought processes, and provide authoritative background and answers. The small group size permits personal interactions (among teachers and presenters) that complement each other's understanding and appreciation of the subject. They log ˜65 contact hours with the staff, in small groups or one-on-one. Teachers return to the classroom with personal experiences, with heightened appreciation, excited, and energetic. The teachers are asked to share their knowledge in their districts (in one case, saving the district thousands of dollars). For the presenters, the workshop format allows personal interactions with the teachers, leading to enhanced appreciation of their perspectives and needs. This year, teacher input assisted with an NSF-sponsored National Park education initiative. And in one case, a meaningful research collaboration has come from these workshops. Logistics is the greatest challenge of this workshop format. Hosts and teaching/lab venues need to be arranged early in sites dictated by science content, not convenience. Travel and lodging must be arranged for teachers and presenters at several sites, usually all distant from the organizing institution. Logistics also dictates that each workshop cannot serve more than about 30 teachers. The depth of knowledge imparted and its long-term effects on the teachers and their districts offsets the small number of teachers reached per year. Authors here are the 2003 organizers and presenters. Many others have organized and presented at past workshops - especially Dr. A.J. Irving of U. Wash. We are grateful for past support from NASA Broker/Facilitator, and now from Sandia National Laboratory and NASA OSS/EPO.

... The Ochoa Point Member of the Dox Formation has numerous surfaces with exquisitely preserved salt casts (Fig. 4B) and mudcracks. ... A) Wave ripples, Hakatai Formation; clinometer staff is 50 cm. B) Salt casts, Ochoa Point Member; chapstick bar code is 3 cm. ...

Travertine deposits of the western Great Artesian Basin (GAB) are associated with mound springs (many still active) and form calcium carbonate precipitates due to CO2 degassing as the highly carbonated groundwaters emerge along faults. They collectively, provide a record that can be used to link the present hydrogeological system to the paleohydrogeology of the GAB. The GAB is a very large artesian sedimentary basin which contains groundwater that has evolved over hundreds of thousands to millions of years. Although the equipotential surface has declined since development of the aquifer, anthropogenic draw down is superimposed on less well understood transient effects due to paleoclimate cycles which requires better understanding of the flow paths and paleohydrologic fluctuations in the GAB. Travertines can provide proxy data to understand the relative magnitude and chronology of spring discharge through time, which will aid in the development of a transient conceptual groundwater model of the system. The travertine deposits also provide underutilized and sensitive gauges of neotectonics in Australia, generally thought of as one of the oldest, flattest, and least tectonically active of the continents, but one that is neotectonically active in the western GAB area. U-Series dates provide age constraints on travertine deposition. Travertines at Dalhousie Springs range from 687 ± 228 ka to 163 ± 7 ka. Travertines along the mound springs line range from 372 ± 14 ka (Beresford extinct mound) to 0.12 ± 0.001 ka (Sulfur spring). The dates indicate persistent deposition at discrete spring vents over at least 700 thousand years. Our hypothesis is that times of largest travertine accumulations (10 - 20 ka, 120 ka, 250 ka, and 350 - 400 ka) may have corresponded to wetter times. Stable isotope analyses of the dated travertines reveals that spring groups have different carbon isotope values that vary by 4 - 6 per mil in O, reflecting local spring chemistry and/or paleoclimate variations. These results demonstrate that the extensive travertine deposits can be used to develop a paleohydrogeology record at both 100 ka and 10 - 1 ka time scales for comparison with other paleoclimate proxies. Mound spring discharge is aligned along faults that parallel lithosopheric zones of weakness along the Tasman line and Torrens hinge zone, these separate the actively uplifting Flinders and Dennison Ranges from subsiding Lake Eyre region. An age of 372 ± 14 ka from the elevated extinct Beresford mound indicates bedrock denudation rates of the Bulldog shale surface of 67 m/Ma that are likely driven by neotectonics. More comprehensive dating may show differential uplift depending on position relative to uplifting versus subsiding domains on either side of the mound springs line. Collectively, the lowest elevations in the Australian continent, the mound springs lineaments, and the resulting locations of the main discharge areas of the GAB are seen as a product of different interacting scales of active tectonism in central Australia.

The dominant paradigm for the Great Artesian Basin over the last several decades has documented recharge in the eastern Australian Great Dividing Ranges, relatively simple regional SW flow paths in a confined aquifer system (J-K aquifer), and discharge in springs and bores in the western GAB. New geochemical and hydrologic data suggest this model needs modifications in several fundamental ways. 1) 3He/4He synthesis of springs and bores from the GAB show persistent but variable inputs of deeply derived fluid that contain mantle 3He. 3He/4He values up to 3.4 RA are present in the eastern GAB , comparable to RA of 3-4 in the southeastern GAB, and RA of 3 from volcanic regions outside the GAB, e.g. Caroline Well of Mt Gambier volcanic district. These high values (relative to MORB RA= 8) suggest that up to 40% of the He in some GAB groundwaters is from the mantle and that fluid/gas composition is influenced by basalt transfer in the lower lithosphere, microseismicity in the upper crust, and ascent of fluids up faults into the aquifer. 3He/4He data from mound springs in the western GAB have RA up to 0.09 and CO2/3He= 4x109 (Bubble Mound Springs). Given the high 4He contributions from radiogenic crust in the region and the old age of these waters, these values also suggest input of mantle fluids that have traveled up deep-seated faults into the J-K aquifer. 2) Water chemistry and C-isotope values also suggest mixing of endogenic (deeply derived) fluids with aquifer waters such that water quality in the J-K aquifer is a product of water evolution along far-traveled flow paths from the Great Dividing ranges plus local inputs of fluids from below into the aquifer. C-isotope data show that a significant percentage of the CO2 is also likely from mantle sources. 3) Hydrochemical data indicate that spring groups in the western GAB that were considered the dominant discharge springs (Dalhousie and South Australian mound springs) are hydrochemically distinct from each other and from evolved recharge waters, requiring multiple scales of hydrologic flow systems and vertical cross-stratal fluid movement facilitated by faults. Hence, new models for GAB flowpaths need to consider faults as high permeability pathways that disrupt and modify westerly (and radial) flowpaths in the J-K aquifer, and local topographically driven flow systems that give rise to separate hydrologic sub-basins. 4) 87Sr/86Sr of 0.718 (Dalhousie) to 0.76 (Paralana Hot Springs) indicate significant, but variable, fluid-rock interaction with granitic crust below the J-K aquifer and also indicate the importance of vertical fluid transport along faults. Taken together, these data suggest that new understandings of the Great Artesian Basin sub-basins will require holistic models that merge these hydrologic, geochemical, and tectonic perspectives.