SDSU - Department of Geological Sciences -Seminar - Stephen Self

Quoted from http://www.geology.sdsu.edu/seminars/spring10/03_17_10.html
SDSU - Department of Geological Sciences -Seminar - Stephen Self

Super-eruptions:Volcanic Activity with a Global Impact Stephen Self Volcano Dynamics Group Department of Earth Science The Open University Senior Volcanologist, US NRC Wednesday, March 17th, 2010

Every now and again, Earth suffers from tremendous explosive volcanic eruptions, much bigger than those witnessed in modern times. Although the return period for such events is long, perhaps every 10-100,000 years depending on the size, it is statistically more likely that Earth will next experience a large super-eruption (defined here as one producing more than ~ 450 km3 of rhyolitic magma) than a large meteorite impact. Depending on where the volcano is located, the effects of such an event will be felt worldwide, or at least by a whole hemisphere, and the associated phenomena will spread quickly within a couple of weeks. These effects include temporary darkness with severe reduction in amounts of solar radiation reaching the surface, unseasonal cooling and warming coupled with strange weather patterns, and, of course, widespread ash fallout. Major disruptions of services that our society depends upon can be expected for periods of months, to even a few years. Past explosive super-eruptions, including the latest very large one, the Toba event in Sumatra 74,000 years ago, will be discussed, as well as some of the impacts of such events. Another type of super-eruption has also affected our world, but at times in the distant past. These are flood basalt events, vast lava flow-producing eruptions that have occurred in 1-2 million-year-long episodes throughout Earth history. Such events have occurred every few tens of million-years or so and seem somehow to be related to mass extinctions of life on Earth. Possible linkages between these two time-series of events will also be discussed. The environmental effects of the largest historic eruptions, such as Tambora and Laki, can be usefully used as small-scale analogs for the impact of much greater volcanic events. The Laki (Iceland) eruption, which can be viewed as a small-scale flood basalt analog, took place at a high latitude and impacted the whole northern part of the North Hemisphere for several years. We must ask: Is our global society ready for the next super-eruption? Dr. Self has studied volcanic rocks in many parts of the world, concentrating on the products of explosive eruptions, large (flood) lava effusions, and the impact of volcanism on the atmosphere. His research interests include mechanisms and deposits of super-eruptions. Dr. Self holds visiting professorships at The Open University, United Kingdom, and the University of Hawaii. He was formerly chair in volcanology at The Open University (2001-2007) and past leader of the U.K.'s Volcanic and Magmatic Studies Group. Dr. Self is a fellow of the Geological Society, London, member of the American Geophysical Union, and life member of the International Association of Volcanology and Chemistry of Earth's Interior. He is the author of numerous papers and articles in both specialty, and more general, scientific journals.

SDSU - Department of Geological Sciences -Seminar - Anthony J. Park

Quoted from http://www.geology.sdsu.edu/seminars/spring10/02_10_10.html:

SDSU - Department of Geological Sciences -Seminar - Anthony J. Park

Patterned mineral deposits on Earth and Mars Anthony J. Park Sienna Geodynamics and Consulting, Inc. Computational Science Research Center (CSRC), San Diego State University Wednesday, February 10th, 2010

Well-exposed Jurassic Navajo Sandstone iron oxide concretions preserve important diagenetic records of groundwater flow and water–rock interactions. Field relationships, precipitation patterns, and geometries of the Navajo concretions provide the basis for input parameters in numerical computer simulations and laboratory chemical bench tests. Although field geometries are very difficult to replicate, numerical simulations and laboratory experiments examine end results such as nucleation and growth of iron oxide concretions, produced from known input parameters. Three numerical simulations show the development of periodic self-organized nucleation centers through Liesegang-type double-diffusion of iron and oxygen. This numerical model simulates a scenario where oxygen is provided by shallow fresh water and iron is sourced from deeper reduced formation water. Concretions form in the region where the two waters interact with each other. Model sensitivities show that advection of water is an important mechanism for supplying the iron, and that acidic conditions in the iron-charged water can cause iron to stay in solution longer to produce nucleation centers that are farther from the input source. Laboratory bench tests with reactions of FeSO4 or Fe(NO3)3 with KOH show how the precipitation of hydrated iron sulfates or iron-hydroxides may form rinds around an initial, spherical source of iron (i.e. nucleation center). These rinds may show inward growth depending on the concentration of the iron source in relation to the surrounding fluid. A number of complex factors such as concentration and flux, time, and multiple events can create banded patterns during rind growth. Comparisons of the terrestrial examples with numerical and laboratory models have strong implications for understanding similar hematite concretions on Mars.

SEMINAR - Kenneth S. Deffeyes

PEAK OIL AND THE GREAT RECESSION

Kenneth S. Deffeyes
Emeritus Prof. of Geology
Princeton University

November 4th, 2009



In 2001, my first oil book predicted that world oil production would peak in the year 2005. The most recent data from the Energy Information Agency say that it happened! Even with the extreme spike in oil prices, the year 2008 produced less oil than 2005. Production for the first half of 2009 is even lower. The invisible hand of economics has become the invisible fist; pounding the world economy down to match the reduced oil supply.
In 1956, M. King Hubbert correctly predicted that United States oil production would peak in the year 1970, although the mathematics that he used was complicated. In my second oil book, in 2005, I developed an exactly equivalent mathematical derivation using three lines of high-school algebra. My third oil book is due out in the spring of 2010. Stay tuned.
Our existing transportation system is heavily dependent on oil and our versatile petrochemical industry turns out a huge range of useful products. Agriculture is heavily dependent on oil and natural gas. During this recession, China is shopping internationally for mineral resources, especially oil.During the last few years, mature petroleum source rocks have been developed as important new sources of natural gas, although they are called “shales.” Uranium is available in sufficient amounts to support an expanded network of nuclear reactors.
A significant shortage of petroleum geologists, geophysicists, and engineers is developing as the previous generation is retiring. A banker, Matthew Simmons, calls it “no freshman class. Redeveloping existing oilfields is a remaining opportunity for an individual to become wealthy; big Texas rich.

Webinar - John Mayhew

Goodness-of-fit Criteria for Broadband Synthetic Seismograms, With Application to the 2008 Mw5.4 Chino Hills, CA, Earthquake

John Mayhew
M.S. Candidate
Department of Geological Sciences
San Diego State University
Advisor Dr. Kim Bak Olsen




ABSTRACT
We present a goodness-of-fit measure for broadband ground motion time histories. As is the case with the goodness-of-fit measure proposed by Anderson (2004), our method includes a set of user-weighted metrics such as peak ground motions, response spectrum, the Fourier spectrum, cross correlation, and energy release measures. The scale for the goodness-of-fit ranges from near 0 to 100 (perfect fit). We apply the method to broadband (0-10Hz) synthetic seismograms for the 2008 Mw5.4 Chino Hills, CA, earthquake, generated by combining a deterministic low-frequency simulation and high-frequency scattering functions at 33 strong-motion recording sites. We find generally favorable average long-period GOF_MO values for the event, in agreement with the waveform fits. Of particular importance, relatively good fits obtained in the Chino basin provide some confidence in the strong wave-guide effects from this area obtained for scenarios of northwestward-propagating ruptures on the southern San Andreas fault (TeraShake, ShakeOut). At shorter periods, the goodness-of-fits fall above our general (ad-hoc) acceptance level at about 2/3 of the selected sites for the event. An additional metric with specific interest for structural engineers, the ratios of inelastic versus elastic displacements, is also included in our method. We find an overall goodness-of-fit level for these ratios similar to that obtained from the average set of metrics for the event. Our results suggest that the accuracy of broadband scenario simulations for greater Los Angeles is entering the range required for structural engineering applications, with some room for improvement.

WEBINAR - Shawn Wright

TIR spectroscopy of shocked Deccan basalt: Implications for Mars and Martian meteorites

Shawn Wright
Institute of Meteoritics
Department of Earth and Planetary Sciences
University of New Mexico
Hundreds of thousands of impact craters dominate the surfaces of the Moon, Mercury, and Mars. There exists much geomorphic and spectral evidence for basalt on those surfaces, so basaltic target rocks are most likely common. However, little work has been done on the thermal infrared (TIR) spectroscopy of shocked basalt metamorphosed by meteorite impact. This will have a direct application to the large amount of TIR data currently being returned from Mars orbiters and Rovers. The relationship between these TIR data collected remotely and laboratory data of samples is of much interest given that our only samples of Mars are shocked basalts. Results of research involving field work and samples from Lonar Crater, India, the only known terrestrial impact site emplaced in basalt, are described. The Deccan “Traps” flood basalts have been labeled as an excellent compositional and spectral analog for plagioclase-rich basalt on Mars identified from various orbiter and Rover instruments. Petrography provides details on the approximate range of shock pressure each class of shocked basalt has been subjected to, and field work has yielded an “ejecta stratigraphy” that displays where each class of shocked basalt is located. A comparison of the TIR spectroscopy of the unshocked Deccan basalt to its shocked equivalent aids in quantifying the changes due to shock. An application of this research has provided constraints on possible source craters/regions of certain shergottite meteorites, the shocked basalts from Mars.

SEMINAR - Shawn Wright

TIR spectroscopy of shocked Deccan basalt: Implications for Mars and Martian meteorites

Shawn Wright
Institute of Meteoritics
Department of Earth and Planetary Sciences
University of New Mexico

May 6th, 2009

Hundreds of thousands of impact craters dominate the surfaces of the Moon, Mercury, and Mars. There exists much geomorphic and spectral evidence for basalt on those surfaces, so basaltic target rocks are most likely common. However, little work has been done on the thermal infrared (TIR) spectroscopy of shocked basalt metamorphosed by meteorite impact. This will have a direct application to the large amount of TIR data currently being returned from Mars orbiters and Rovers. The relationship between these TIR data collected remotely and laboratory data of samples is of much interest given that our only samples of Mars are shocked basalts. Results of research involving field work and samples from Lonar Crater, India, the only known terrestrial impact site emplaced in basalt, are described. The Deccan “Traps” flood basalts have been labeled as an excellent compositional and spectral analog for plagioclase-rich basalt on Mars identified from various orbiter and Rover instruments. Petrography provides details on the approximate range of shock pressure each class of shocked basalt has been subjected to, and field work has yielded an “ejecta stratigraphy” that displays where each class of shocked basalt is located. A comparison of the TIR spectroscopy of the unshocked Deccan basalt to its shocked equivalent aids in quantifying the changes due to shock. An application of this research has provided constraints on possible source craters/regions of certain shergottite meteorites, the shocked basalts from Mars.

WEBINAR - Elizabeth Cochran

Imaging Fault Damage Zones with Seismic and Geodetic Data

Elizabeth Cochran
Department of Earth Sciences
University of California, Riverside





During earthquakes slip is often localized on preexisting faults, but it is not well understood how the structure of crustal faults may contribute to slip localization and energetics. Growing evidence suggests that the crust along active faults suffers anomalous strain and damage during large quakes. Data collected along several faults including the Hector Mine rupture, San Andreas Fault at Parkfield, and the Calico Fault show damage zones extending from 100 m to 1 km around the active slip plane. Recent seismic and geodetic data from the Calico fault in the eastern California shear zone reveal a wide zone of reduced seismic velocities and effective elastic moduli. Using seismic travel times, trapped waves, and interferometric Synthetic Aperture Radar observations, we document seismic velocities reduced by 40 - 50% and shear moduli reduced by 65% compared to wallrock in a 1.5-km-wide zone along the Calico fault. Observed velocity reductions likely represent the cumulative mechanical damage from past earthquake ruptures, but can sustain further damage in successive events These findings indicate that faults can affect rock properties at substantial distances from primary fault slip surfaces, and throughout much of the seismogenic zone, a result with implications for the portion of energy expended during rupture to drive cracking and yielding of rock and development of fault systems.

SEMINAR - Elizabeth Cochran

Imaging Fault Damage Zones with Seismic and Geodetic Data

Elizabeth Cochran
Department of Earth Sciences
University of California, Riverside

April 29th, 2009

During earthquakes slip is often localized on preexisting faults, but it is not well understood how the structure of crustal faults may contribute to slip localization and energetics. Growing evidence suggests that the crust along active faults suffers anomalous strain and damage during large quakes. Data collected along several faults including the Hector Mine rupture, San Andreas Fault at Parkfield, and the Calico Fault show damage zones extending from 100 m to 1 km around the active slip plane. Recent seismic and geodetic data from the Calico fault in the eastern California shear zone reveal a wide zone of reduced seismic velocities and effective elastic moduli. Using seismic travel times, trapped waves, and interferometric Synthetic Aperture Radar observations, we document seismic velocities reduced by 40 - 50% and shear moduli reduced by 65% compared to wallrock in a 1.5-km-wide zone along the Calico fault. Observed velocity reductions likely represent the cumulative mechanical damage from past earthquake ruptures, but can sustain further damage in successive events These findings indicate that faults can affect rock properties at substantial distances from primary fault slip surfaces, and throughout much of the seismogenic zone, a result with implications for the portion of energy expended during rupture to drive cracking and yielding of rock and development of fault systems.

WEBINAR - Brandon Browne

Not-So-Simple Cinder Cone Plumbing Systems: Examples From the Sierra Nevada

Brandon Browne
Department of Geological Sciences
California State University Fullerton





Cinder cones situated in continental monogenetic volcanic fields are generally thought to erupt single magma batches over short periods of time. However, field mapping efforts combined with petrologic, geochemical, and thermobarometric analysis of erupted products from two unrelated volcanic fields in California (Red Cones, 5 km SW of Mammoth Mountain; and Golden Trout, 5 km SW of Mt Whitney) indicate pronounced differences in the eruption volumes and Pressure-Temperature crystallization histories of erupted basalts despite overall similarities in magma source. These findings suggest that magma plumbing systems and the mechanisms for magma supply at cinder cones are actually quite complex, and therefore require us to modify our perspectives on how they from as well as the types of geophysical signals they potentially yield before, during, and after eruptions.

WEBINAR - David T King Jr

The Cretaceous-Paleogene ("KT") Boundary In Belize and Alabama

David T. King, Jr.
Department of Geology and Geography
Auburn University, Alabama




Belize - At Albion Island in northern Belize, Cretaceous-Paleogene (KT) boundary deposits, also known as the Albion formation, rest upon karsted and fractured Maastrichtian dolostones. These deposits consist of a basal impactoclastic clay layer (~ 1 to 2-m thick) and an upper carbonate-rich, coarse impactoclastic breccia layer (up to 15-m thick). The focus of this paper is the upper layer, the Albion impactoclastic breccia. The Albion impactoclastic breccia shows several important sedimentary structures, including development of discrete sedimentation units (2 to 7-m thick), which are strata that have been enhanced by horizontal shearing, and other sedimentary structures such as normal and reverse size grading, clast imbrication, flow lamination, and isolated and linked aggregates of clasts (i.e., clast clustering).
Most carbonate clasts within the coarse impactoclastic unit show a broad range of angularities and shapes, with the most common being subangular and compact-bladed to compact-elongated, respectively. Surface texture analysis of carbonate clasts shows several types of surface markings, which display a gross sequential order (i.e., facets, polish, striations, cryptographic markings, bruises and pits, and chips). In-situ, apparent-diameter measurements of the carbonate clasts, which ranged in size from 10 to 300 mm (or -3.3 to -8.2 Ø);, resulted in cumulative grain-size (Ø) frequency curves with similar shapes through the interval –3.3 Ø and –6.25 Ø (i.e., 10 to 76 mm). Matrix, the total area comprised of less-than-10 mm (< -3.3 Ø) particles, ranged from approximately 71 to 82 percent. Modified moment measures of these curves show these breccias are “extremely poorly sorted.” The matrix content increase upward through the entire coarse impactoclastic layer, but is slightly lower near its top. The Albion impactoclastic breccia has sedimentary structures and sedimentologic characteristics suggesting its mode of emplacement during the impact aftermath was similar to that of a very large volcanic debris avalanche. Sedimentation units show evidence of early turbulent flow and a more conspicuous later stage of laminar flow with shearing accompanying emplacement of most breccia sedimentation units. Clasts within these debris flows are not locally derived for the most part. We speculate that each sedimentation unit at Albion may represent a separate emplacement event during the process of ejecta curtain collapse, perhaps owing to variations in atmospheric interaction with the debris. Alabama - At Shell Creek stratigraphic section, Wilcox County, Alabama, a < 1 m-thick, Cretaceous-Paleogene boundary sand body crops out over an area of ~ 200 m2. This sand body consists of (1) a basal impact spherule-bearing, coarse to medium sand and (2) an overlying fine sand with hummocky-type cross-lamination. This K-T boundary sand body probably represents post-impact, shelf sedimentation events involving (1) gravity-driven resedimentation of reworked impact spherule-bearing sands and (2) energetic wave reworking of the impart spherule-bearing, gravity-driven deposits or other subsequently deposited sands. Most impact spherules from Shell Creek are spherically shaped grains (~ 1 mm in diameter) that are now hollow, or were hollow prior to secondary calcite filling. Most impact spherules from Shell Creek consist of an outer shell, which is composed of smectitic clays, and an inner region of open space or sparry calcite. Most of these impact spherules still retain features like vesicles that attest to their former molten condition. This stratigraphic section is remarkable in that it represents the most easterly U.S. Gulf Coastal Plain occurrence of abundant impact spherules in a Cretaceous-Tertiary (K-T) boundary sand body.

SEMINAR - Brandon Browne

Not-So-Simple Cinder Cone Plumbing Systems: Examples From the Sierra Nevada

Brandon Browne
Department of Geological Sciences
California State University Fullerton

April 22nd, 2009

Cinder cones situated in continental monogenetic volcanic fields are generally thought to erupt single magma batches over short periods of time. However, field mapping efforts combined with petrologic, geochemical, and thermobarometric analysis of erupted products from two unrelated volcanic fields in California (Red Cones, 5 km SW of Mammoth Mountain; and Golden Trout, 5 km SW of Mt Whitney) indicate pronounced differences in the eruption volumes and Pressure-Temperature crystallization histories of erupted basalts despite overall similarities in magma source. These findings suggest that magma plumbing systems and the mechanisms for magma supply at cinder cones are actually quite complex, and therefore require us to modify our perspectives on how they from as well as the types of geophysical signals they potentially yield before, during, and after eruptions.

SEMINAR - Jill Pearse

Post-rifting deformation in Afar, Ethiopia, following the 2005 intrusion event

Jill Pearse
Scripps Institution of Oceanography
University of California, San Diego

April 15th, 2009

The 300-km wide Afar depression is located at the junction between the Red Sea, Gulf of Aden and East African rifts. In September and October of 2005, a series of large earthquakes and a volcanic eruption signaled the intrusion of a dike along the Dabbahu magmatic segment (in the Red Sea arm) of the Afar rift. Results of elastic modeling constrained by InSAR (Wright et al 2006) data suggest that the 60-km long segment opened by up to 8 m, between depths of 2-9 km. Relaxation of stresses in the crust below the brittle-ductile transition following the intrusion event should create geodetically observable surface deformation, however this signal can be obscured by continuing active intrusions. Using 3-D finite element models, we predict the surface deformation following the 2005 Dabbahu event for a range of crustal and mantle rheologies. We compare our model results to InSAR data spanning the 3 years since the intrusion to quantify the post-rifting deformation and place constraints on the rheology below the brittle-ductile transition in Afar.

WEBINAR - Greg Hirth

Understanding earthquakes at the microscopic scale

David Bowman
Department of Geology and Geophysics
Woods Hole Oceanographic Institution

I will first review of how to relate rock strength determined from lab experiments to geological and geophysical observations - emphasizing apparent paradoxes and successes. I will then introduce why understanding earthquake mechanisms in the oceanic lithosphere can provide new insights into the rheological properties of fault zones, and present an experimental study on fault stability in which analysis of the micromechanics of friction provides justification for the extrapolation of the lab data to natural conditions. With this new insight, I will then return to the problem of relating the lab data to geophysical observations.

SEMINAR - Greg Hirth

Understanding earthquakes at the microscopic scale

David Bowman
Department of Geology and Geophysics
Woods Hole Oceanographic Institution

March 25th, 2009

I will first review of how to relate rock strength determined from lab experiments to geological and geophysical observations - emphasizing apparent paradoxes and successes. I will then introduce why understanding earthquake mechanisms in the oceanic lithosphere can provide new insights into the rheological properties of fault zones, and present an experimental study on fault stability in which analysis of the micromechanics of friction provides justification for the extrapolation of the lab data to natural conditions. With this new insight, I will then return to the problem of relating the lab data to geophysical observations.

SEMINAR - David Bowman

Accelerating Moment Release Before Large Earthquakes: Life and Death of an Earthquake Prediction Scheme

David Bowman
Department of Geological Sciences
California State University, Fullerton

Postponed

It has been suggested that large earthquakes are preceded by a systematic increase in the rate of background seismicity in a broad region around the impending event. This rate change, known as “accelerating moment release” (AMR), has been proposed as a precursory signal that could be used to forecast large earthquakes. Bowman and King [GRL, 2001] demonstrate that the pre-mainshock stress field, as indicated by a simple backslip model of the event, can be used to define the critical region that optimizes the precursory AMR signal. The observation of accelerating seismicity within this region represents a period of increased likelihood of a large earthquake. With sufficient knowledge of the regional tectonics, it should be possible to estimate the likelihood of earthquake rupture scenarios by searching for AMR related to stress accumulation on specific faults. This talk will present two algorithms that randomly search global plate boundaries for AMR signals before potential large events. Each plate boundary is searched for AMR using circular regions following the method of Bowman et al.[1998] and fault-based stress accumulation regions following the approach of Bowman and King [2001]. The fault-based algorithm uses a schematic model of the plate-boundary faults to represent potential sources; subduction zones are modeled as single mega-thrust faults, spreading centers as a normal faults, and transforms as single strike-slip faults. In each approach, the entire global plate boundary network is populated by potential sources and searched for precursory AMR. False-alarm and Failure-to-predict statistics are calculated based on historical seismicity; given the heterogeneity of modern instrumental catalogs, these statistics suggest that the current AMR algorithm does not provide significant predictive power.

SEMINAR - PetroAzteca

Technical Assessment of the Barents Sea Petroleum Potential

2009 Imperial Barrel Team
John Abeid, Lelsie Clayton,
Bryant Falk, Chris Kohel
and Peter Winther
Department of Geological Sciences
San Diego State University

Wednesday, March 11th, 2009

AAPG’s Imperial Barrel Award Program (IBA) is an annual prospect/exploration evaluation competition/presentation competition between university student teams competing to win scholarship funds dedicated to petroleum geoscience education created for geoscience graduate students. The program is rigorous and contributes to AAPG’s mission of promoting petroleum geoscience training and advancing the careers of geoscience students.

This is a global competition, where the University teams analyze a complete dataset in six to eight weeks prior to the competition and (geology, geophysics, land, economics, production infrastructure, and other relevant materials). Each team delivers their results in a 30-minute presentation to a panel of industry experts.

Students gain experience using real technology on a real dataset. Additionally, students benefit from the feedback from the industry panel, the opportunity to impress potential employers in the audience, and the chance to win cash prizes for their schools, who will select the winning team on the basis of technical quality, clarity and originality.

The IBA is a hands-on opportunity for students to experience the creative process and the high-tech science that is the foundation of the Energy Industry today.

SDSU were the 2008 AAPG Imperial Barrel Pacific Section Champions

WEBINAR - Kathleen R. Johnson

Reconstructing Asian Monsoon History from Chinese Speleothems

Kathleen R. Johnson
Department of Earth System Science
University of California, Irvine



While we know that modern anthropogenic climate change is superimposed upon significant natural climate variability, the instrumental record of climate is too short to capture the full range of this variability. In order to fully understand and predict future changes, therefore, high-resolution, welldated paleoclimate records are needed to extend the record. This paleoclimate data allows us to quantify natural variability and learn how the climate system responded to past changes in boundary conditions and forcings and provides a vital test for state-of-the-art coupled climate models. Cave calcite deposits (speleothems) are widely studied paleoclimate archives that have led to significantly improved records of past climate variability over a wide range of timescales (seasonal to glacialinterglacial), most notably in low-latitude and monsoon regions. Speleothems are well-suited for terrestrial climate reconstruction because: they tend to be very pure and well-preserved; they usually contain clear visible growth banding which, like tree rings, is often annual in nature; they can be very precisely dated using uranium-series radiometric dating methods; and they contain numerous types of physical and geochemical proxy data. In this lecture, I will present an introduction to speleothem based paleoclimate proxies and describe ongoing modern calibration studies we are conducting at Heshang Cave, China to test and develop new seasonal resolution proxies of Asian monsoon rainfall. In addition, I will present multiple records of Asian monsoon rainfall obtained from stable isotope and trace element variations in Chinese speleothems and discuss the important role of the Asian monsoon in the global climate system.

WEBINAR - Jared Kluesner

Geologic and Hydrologic Role of Sill Intrusion and Delineation of the Oceanic Crustal Boundary in the Central Gulf of California

Jared Kluesner
Marine Physical Laboratory
Scripps Institution of Oceanography




Geologic and Hydrologic Role of Sill Intrusion and Delineation of the Oceanic Crustal Boundary in the Central Gulf of California High-resolution multichannel profiles recently shot in the central Gulf of California display concordant and discordant (concave-upwards) sills intruded shallowly within (I) young sediments in the axial troughs of Guaymas, Carmen and Farallon Basins, (II) off-axis in the basin floors, and (III) within the sediment cover of subsided and extended continental crust. We interpret some imaged sills as 3D saucer-shaped intrusions based on their concave-upward profiles, the overlying circular and elliptical plans of domal uplifts of the present multibeam-mapped seafloor, and their striking resemblance to field-mapped and 3-D seismically imaged saucer-like sills. Vertical zones of high-amplitude, disturbed reflectors leading up from sills are probably "blow-out pipes" acting as conduits for hydrothermal fluids and gases migrating up and away from the heated sill-sediment contact aureole, forming pockmarks on the present seafloor. Bright spots, dim spots, phase reversals, and acoustic turbidity in the sediments above sill intrusions suggest the presence of hydrocarbons and fluid flow throughout the study area. Seismic evidence of sill intrusions into the shallow crust throughout the central gulf suggests melt is being delivered not just to spreading centers, but to a much broader area of oceanic and continental crust. We have improved the delineation of the oceanic/continental crustal boundary in the central and southern gulf by sampling igneous basement (tholeiitic basalt and gabbro = oceanic; granitic = continental), by identifying the extent of magnetic stripes diagnostic of seafloor spreading, by interpreting multichannel reflection profiles, and by geomorphology. Although the "boundary" is somewhat smeared by the intrusion of shallow sills (some known to be tholeiitic, most inferred to be) into the cover of both granitic and oceanic basement, we find no evidence of "transitional zones" of hybrid crust; at those sheared and rifted margins where basement is accessible, granite commonly abuts tholeiitic flows and sills. Seafloor spreading magnetic anomalies, with low amplitudes and broad transition widths, can be read out to C2Ar in Alarcon Basin, and C2An.1 in Guaymas Basin (but only on profiles that avoid major off-axis seamounts and intrusions); in both cases they indicate significantly slower accretion during the first 1 m.y. of spreading, presumably because of concurrent continued extension of the rifted margin. Widespread sill intrusion over continental basement does hamper identifying the ocean/continental boundary on seismic reflection profiles, and because the already thin Cordilleran crust was clearly highly extended during prolonged rifting we do not think that crustal thickness is a reliable criterion for the extent of oceanic crust.

WEBINAR - Stephen T. Hasiotis

Ichnology for the 21st Century: Understanding the differences between continental and marine trace fossils, with implications to the diversity, distribution, and evolution of soil biota

Stephen T. Hasiotis
Department of Geology
University of Kansas
Coeditor PALAIOS




The study of ichnology has come a long way since its inception and it continues to evolve. In particular, progress is being made in understanding the implications of trace fossils in the continental realm and how they can be used in conjunction with subdisciplines in geology to reconstruct the past. Organisms in all domains of life display behaviors that greatly expanded our definition of ichnology. Ichnology is the study of all organism behavior-not just animals. Accordingly, a trace fossil is the product of an organism interacting with a medium in an environment, which generates a three-dimensional physical structure-the resultant trace fossil can be micrometers to kilometers in scale. Though behaviors and resultant trace fossils may be similar morphologically in continental and marine settings, the organisms and behaviors that produced them and the physicochemical factors that controlled their distribution, depth, diversity, and abundance can be strikingly different. Ongoing research with modern terrestrial and aquatic organisms in the field and laboratory reveal the behaviors behind the production of burrow morphologies whose genesis and significance would otherwise be misinterpreted. The study of these modern traces, organisms, and their distribution allows us to recognize how their burrow morphologies and sedimentary associations record the environmental, ecologic, hydrologic, and climatic settings in which they are formed. Comparison of these modern structures and their tracemakers to trace fossils in continental deposits in the geologic record provide stronger clues about the implications of trace fossils for interpreting and reconstructing the sequence of events and conditions that produced those deposits. They also provide information on the evolution and radiation of organisms and ecosystems where the body fossil record is poor. As a result of these new research endeavors, trace fossils are being used to (1) extend the fossil record and understand the radiation of organisms, (2) interpret more accurately environments of deposition and the extent of pedogenesis that have modified those deposits, (3) contribute to understanding better the effects of climate change on biota, environments, and hydrologic systems, and (4) correlate significant surfaces in continental strata and identify subtle but significant shifts in physicochemical conditions and environments.

SEMINAR - Kathleen R. Johnson

Reconstructing Asian Monsoon History from Chinese Speleothems

Kathleen R. Johnson
Department of Earth System Science
University of California, Irvine

Wednesday, February 18th, 2009

While we know that modern anthropogenic climate change is superimposed upon significant natural climate variability, the instrumental record of climate is too short to capture the full range of this variability. In order to fully understand and predict future changes, therefore, high-resolution, welldated paleoclimate records are needed to extend the record. This paleoclimate data allows us to quantify natural variability and learn how the climate system responded to past changes in boundary conditions and forcings and provides a vital test for state-of-the-art coupled climate models. Cave calcite deposits (speleothems) are widely studied paleoclimate archives that have led to significantly improved records of past climate variability over a wide range of timescales (seasonal to glacialinterglacial), most notably in low-latitude and monsoon regions. Speleothems are well-suited for terrestrial climate reconstruction because: they tend to be very pure and well-preserved; they usually contain clear visible growth banding which, like tree rings, is often annual in nature; they can be very precisely dated using uranium-series radiometric dating methods; and they contain numerous types of physical and geochemical proxy data. In this lecture, I will present an introduction to speleothem based paleoclimate proxies and describe ongoing modern calibration studies we are conducting at Heshang Cave, China to test and develop new seasonal resolution proxies of Asian monsoon rainfall. In addition, I will present multiple records of Asian monsoon rainfall obtained from stable isotope and trace element variations in Chinese speleothems and discuss the important role of the Asian monsoon in the global climate system.