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EPSS Colloquium - winter-2017

On the Dynamics of Planets (and also Stars and Black Holes) - New Insights from Triples

Jan. 20, 2017
4 p.m. - 5 p.m.
Geology 3656

Presented By:

  • Smadar Naoz - UCLA
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On the Dynamics of Planets (and also Stars and Black Holes) - New Insights from Triples

Many observed triple systems in our Universe are in a hierarchical configuration: two objects orbit each other in a relatively tight inner binary while the third object is on a much wider orbit. Furthermore, the secular approximation for the evolution of hierarchical triple body systems has been proven to be very useful in many astrophysical contexts, from planetary to triple-star systems and even black holes. In this approximation the orbits may change shape and orientation, on timescales longer than the orbital periods, but the semi-major axes are constant. In early studies of hierarchical secular three-body systems (Kozai 1962; Lidov 1962), the wider orbit was set to be circular and one of the tight binary members was assumed to be a test (massless) particle. In this situation, the component of the tight orbit’s angular momentum along the total angular momentum is conserved, and the lowest order of the approximation (i.e., the quadrupole approximation) is valid. I will discussed recent developments that showed that considering systems beyond the test particle approximation, or circular orbits, requires the next level of approximation for a correct representation of the physics, called the octupole-level. This leads to qualitative different behavior of the system. In this case, the angular momenta component of the tight and wide orbits along the total angular momentum is not conserved. Most interestingly, at this level of approximation, for an eccentric wide orbit, the tight orbit can reach extremely high eccentricities and undergo chaotic flips of its orientation. This behavior has important implications to the evolution of many systems, and I will present some nominal examples, such as retrograde hot Jupiters, blue stragglers and low-mass X-ray binaries.

Earth’s Magnetic Field: Reversals, Stochastic Models and Physical Interpretations

Feb. 2, 2017
4 p.m. - 5 p.m.
Geology 3656

Presented By:

  • Cathy Constable - UCSD
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Earth’s Magnetic Field: Reversals, Stochastic Models and Physical Interpretations

Direct observations of the modern geomagnetic field enable us to understand its role in protecting us from the depredations of the solar wind and associated space weather, while paleomagnetic studies provide geological evidence that the field is intimately linked with the history and thermal evolution of our planet. In the past the magnetic field has reversed polarity many times: such reversals occur when its overall strength decays, and there are departures from the usual spatial structure which at Earth’s surface predominantly resembles that of an axially aligned dipole. Reversals are one element of a continuum of geomagnetic field behavior which also includes geomagnetic excursions (often viewed as unsuccessful reversals), and paleosecular variation. The fragmentary and noisy nature of the geological record combined with distance from the field’s source in Earth’s liquid outer core provide a limited view, but one that has been partially characterized by time series analysis, and development of stochastic models describing the variability. Analyses of changes in the dipole moment have revealed distinct statistical characteristics associated with growth and decay of field strength in some frequency ranges. Paleomagnetic studies are complemented by computationally challenging numerical simulations of geomagnetic field variations. Access to details within the numerical model allow the evolution of large scale physical processes to be studied directly, and it is of great interest to determine whether these computational results have Earth-like properties. The parameter regime accessible to these simulations is far from ideal, but their adequacy can be assessed and future development guided by comparisons of their statistical properties with robust results from paleomagnetic observations. Progress in geomagnetic studies has been greatly facilitated by the application of statistical methods related to stochastic processes and time series analysis, and there remains significant scope for continued improvement in our understanding. This is likely to prove particularly important for understanding the scenarios that can lead to geomagnetic reversals.

Reconstructing Southern California: New Developments

Feb. 9, 2017
4 p.m. - 5 p.m.
Geology 3656

Presented By:

  • Raymond Ingersoll - UCLA EPSS
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Reconstructing Southern California: New Developments

Southern California is a critical component in paleotectonic models for: (1) the evolution of the USA-Mexico Cordillera; (2) the interaction of continental and oceanic plates; and (3) relations between subduction and transform processes during the Mesozoic and Cenozoic. Detailed palinspastic reconstruction of both offshore and onshore components of the diverse and complex settings of southern California is essential in order to test paleotectonic models for the evolution of the broader region. The unique geologic history of southern California can be described in terms of distinct phases of tectonic development, which resulted in corresponding distinct tectonostratigraphic sequences. Steep-slab subduction of the Farallon plate characterized most of the Cretaceous history of the southwestern USA, whereas flat-slab subduction characterized the Laramide orogenic event (80-40 Ma). As the subducting Farallon plate rolled back following the Laramide orogeny, the Pacific plate first came into contact with the North American plate in southern California soon after 30 Ma. Two triple junctions then traveled in opposite directions along the continental margin. The southern triple junction had a complex history, including three distinct stages of capture of Farallon microplates and contiguous parts of the North American margin by the Pacific plate. These three microplate-capture events resulted in transrotation (18-12 Ma), transtension (12-6) and transpression (6-0 Ma) in the Los Angeles region. As the rigid Sierra Nevada and Peninsular Ranges batholiths have converged along opposite sides of the San Andreas fault (6-0 Ma), the intervening San Andreas fault has rotated counterclockwise, thus tightening restraining double bends and resulting in clockwise rotation of crustal blocks moving through these bends. Reversal of 240 km of dextral slip on the San Andreas fault, 70 km of dextral slip on the San Gabriel/Canton fault and varied clockwise rotations results in a coherent set of SW-NE-trending normal faults, basins and antiformal structures. Reconstructing this complex history is an extraordinarily challenging and rewarding endeavor.

Problematical Fossils

Feb. 16, 2017
4 p.m. - 5 p.m.
Geology 3656

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Problematical fossils are those that are fascinating, well preserved and abundant, but are difficult to classify and understand. They range in age from Archean to almost Modern, but are most commonly found in the early part of the Phanerozoic when the animal phyla were diverging. I’ll review examples encountered during my career and discuss current approaches to solving the mysteries of the Problematica.

Biogeographic evolution of tropical Americas: Reconciling old fossils with new interpretations.

Feb. 23, 2017
4 p.m. - 5 p.m.
Geology 3656

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Seminar Description coming soon.

Sedimentary archives: The good, the bad and the ugly

March 2, 2017
3:30 p.m. - 5 p.m.
Geology 3656

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Sedimentary archives: The good, the bad and the ugly

The oxygenation of the Earth’s ocean-atmosphere system from the late Precambrian to the early Phanerozoic is thought to play a major role in shaping the biosphere of our modern world. However, the timing of the oxygenation of Earth’s surface environments and its link to biological evolution remains contentious. The use of non-traditional stable isotope geochemistry on marine sedimentary archives has recently emerged as a powerful tool in transforming our understanding of the rise of oxygen. Recently, a trend towards the analysis of large data sets has provided exciting new insights, however studies often lack careful consideration of the samples’ sedimentary and diagenetic history. This can have major implications for how results are interpreted. For example, component-specific analyses of carbonates suggest large variability in metal isotope and trace metal signatures between depositional and burial diagenetic phases. Within a single hand sample, uranium isotope composition can span nearly the entire range of measured ?238U in modern systems. These findings necessitate a return to petrographic and sedimentological analysis prior to geochemical studies in order to make robust interpretations about environments in deep time.

As an example of this more holistic approach, well preserved marine carbonates have revealed exciting new details about oxygenation of the Earth’s oceans in the Neoproterozoic and Paleozoic that challenge the traditional view of a unidirectional rise of oxygen through Earth’s history. Investigation of rare earth elements (REEs), specifically Ce anomalies, in petrographically screened carbonate marine cements suggest only transient marine oxic conditions in the Ediacaran, during the rise of animals, followed by a return to large-scale anoxia through much of the Paleozoic. It is not until the late Devonian, co-incident with the rise of large, vascular land plants, that modern-like REE profiles and true negative Ce anomalies develop in shallow marine seawater. This implicates a protracted oxygenation of the Earth, with the establishment of forest ecosystems in the Paleozoic driving the final oxygenation of the ocean-atmosphere system.

Sediment Transport in Carbonate Environments: A Case Study in the Role of Abrasion in Ooid Growth

March 9, 2017
4 p.m. - 5 p.m.
Geology 3656

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Sediment Transport in Carbonate Environments: A Case Study in the Role of Abrasion in Ooid Growth

I will present experimental, modeling, and field data sets demonstrating the utility and value of applying a quantitative, process-based approach to sediment transport to a long-standing puzzle in carbonate sedimentology: how ooids form. Ooids are common and enigmatic concentrically coated carbonate sand grains that provide a deep-time archive of changes in climate and seawater chemistry and are arguably the world’s most economically significant petroleum reservoirs. Substantial debate persists concerning the roles of physical, chemical, and microbial processes in their growth, including whether carbonate precipitation on ooid surfaces is driven by seawater chemistry or microbial activity, and what role—if any—sediment transport and abrasion play. To test these ideas, I developed an approach to study ooids in the laboratory—these experiments produced ooid abrasion and precipitation rates four orders of magnitude faster than radiocarbon net growth rates for natural ooids, with the corollary expectation that ooids approach a stable size representing a dynamic equilibrium between precipitation and abrasion. These results also demonstrate that the physical environment is as important as seawater chemistry in controlling ooid growth. The expansive ooid shoals surrounding Little Ambergris Cay in the Turks and Caicos Islands, provide a natural laboratory to further test the dynamic equilibrium hypothesis. Grain size and shape, surface and internal textures, and radiocarbon age data all indicate active ooid growth and abrasion occur during transport in the high energy shoal, but not in lower energy environments that might otherwise be identified as likely “ooid factories” under the assumptions of prevailing ooid formation theories. The upshot of this finding that ooid growth is likely governed by the balance of chemical and physical processes is significant for interpreting ooids in the rock record, suggesting that variations in properties like grain size, shape, and texture can be connected to and predicted by paleoenvironmental conditions including current energy and seawater carbonate chemistry.

A New View of Mid-Ocean Ridge Eruptions

March 16, 2017
4 p.m. - 5 p.m.
Geology 3656

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A New View of Mid-Ocean Ridge Eruptions

Seafloor spreading is generally viewed as a relatively steady state process, with near-continuous production of fresh seafloor through mid-ocean eruptions. However, recent evidence from present day eruptions, as well as seafloor bathymetric and hydrothermal output, suggest that seafloor eruptions might in fact wax and wane, exhibiting sensitivity to orbital and sea-level forcings over a wide range of time scales. Technological revolutions in our ability to monitor seafloor earthquakes have helped fuel a new understanding of this fundamental planetary process and illuminated some important differences between seafloor spreading and caldera-centered eruptions. Furthermore, a long-term pulsing of mid-ocean ridge eruptions has implications for global geochemical and physical cycles, with volcanism responding to sea level changes while also acting as a possible climatic feedback. These findings highlight that the solid earth system should not be viewed in isolation from the ocean and atmospheric systems, and that they most likely operate in a delicate balance.

Dynamics of geyser systems, El Tatio, Atacama

March 24, 2017
4 p.m. - 5 p.m.
Geology 3656

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Dynamics of geyser systems, El Tatio, Atacama

Geysers are hot springs that periodically or episodically erupt liquid water and vapor. Eruptions of geysers resemble volcanic eruptions, but on a different scale. Geysers are uncommon compared to other non-eruptive hot springs. Fewer than 1000 geysers have been reported on Earth, most concentrated in three geyser fields: Yellowstone National Park (Wyoming, United States), Geyser Valley (Kamchatka, Russia), and El Tatio (Atacama, Chile). Despite more than 200 years of scientific study, the internal dynamics of geyser systems remain poorly characterized. As a consequence, there remain fundamental questions about the thermodynamics of eruptions, the geometry of subsurface pathways, and the factors modulating eruption cycles. To provide answers to these questions, Dr. Munoz-Saez will present unique data collected from El Tatio geyser field, including thermodynamic measurements from inside of geysers conduits and at the surface, and laboratory scale models.