Calling: Earth #036 - Joseph Panzik, Paleomagnetist

In this episode of Calling: Earth, we talk with Joseph Joe Panzik, Research Assistant Professor in the USF School of Geosciences, about his work in paleomagnetism (ancient Earth magnetism) and scientific literacy, as well as the importance of learning transferable skills. More about Joe can be found here: https://josephepanzik.wordpress.com/ Joe\u27s Science Fact Friday Blog: https://josephepanzik.wordpress.com/blog/ Joe\u27s Twitter: https://twitter.com/jepanzi

Polyampholytes via cyclopolymerization

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Proterozoic GAD Hypothesis: Reliability Test Using Dyke Swarms

Pre-Mesozoic continental reconstructions and paleoclimatic inferences from paleomagnetism rely critically upon the assumption of a time-averaged geocentric axial dipole (GAD) magnetic field. A shallow inclination bias has been discovered in the paleomagnetic database for the Paleozoic and Precambrian [Kent and Smethurst 1998]. Possible explanations include sampling bias of low latitude continents, lumped results from far-traveled terranes, quadrupole or octupole field components (at surprisingly high values of 10% and 25%, respectively, of the dipole at the Earth\u27s surface), or some other unrecognized bias. A 25% octupole is found to be inconsistent with evaporite paleolatitudes for most of the last two billion years [Evans 2006]. This result suggests that continents have preferentially sampled the equator or there might be some other issue with the database-wide inclination test. We have been testing the GAD assumption and localized non-dipole components in a different manner, by observing directional variations within the Matachewan and Mackenzie dyke swarms. Large dyke swarms, commonly emplaced within a few million years, provide the necessary broad areal coverage for testing time-averaged geomagnetic field topology. We vary the quadrupole and octupole values of the generalized paleolatitude equation to determine a minimal angular dispersion and maximum precision of paleopoles. Current results of the Matachewan and Mackenzie swarms have best fits that are non-dipolar but with less than a 25% octupole contribution. Further analysis will include the Franklin dyke swarm, and Central Atlantic Magmatic Province (CAMP) volcanics as a test case for the method

Ice Layers Origins in Icy Satellites and Icy Giants

Icy giant planets such as Uranus and Neptune are believed to have differentiated into three primary sections: an atmosphere of helium, methane gas, and molecular hydrogen; an ``icy\u27\u27 mantle of water, ammonia, and methane; and a core of rock and iron. Icy satellites of the gas giant planets Jupiter and Saturn are also thought to have layers of ices that include carbon monoxide and carbon dioxide, although at reduced pressures and temperatures. Here we investigate ammonium bicarbonate (NH4)HCO3, which degenerates to water, carbon dioxide and ammonia between 36 and 60 °C at room pressure. We performed quasi-hydrostatic high-pressure diamond-anvil cell (DAC) experiments up to 30 GPa over a range of temperatures (22 to 150 °C). Preliminary analysis shows that ammonium bicarbonate not only breaks down to its icy components with increased temperature, but also at increased pressures of ~2 GPa. The individual reaction components reformed into ammonium bicarbonate upon pressure quenching for unheated samples

Seismic Refraction Surveys of a Portion of Naval Station Newport, Rhode Island

A surface geophysical survey was performed in a portion of Naval Station Newport that was impacted by historical releases of chlorinated solvents. The purpose of the survey was to investigate the depth to water table, depth to bedrock, and especially to characterize variations in bedrock seismic velocity along profile lines that might provide insight into more permeable zones that were anticipated at shallow depths and which could exhibit enhanced groundwater flow. Seismic refraction tomography (SRT) was selected as the most appropriate method for the site, based on the desired depth of penetration and numerous site constraints, including infrastructure, deep well casings, and surface modifications (parking lots, roads, riprap, and vegetated areas), especially those in areas of particular interest. Data were acquired along ten profile lines, ranging from 115-470 feet in length. Seismic data were acquired with a 48-channel Geometrics Geode system using a sledge hammer as the seismic energy source and 4.5 Hz geophones as receivers. The receivers were placed at 5 feet spacing on seven of the ten lines. The remainder of the lines had geophone spacing at 10-foot intervals. Data were processed using the Rayfract software package, from Intelligent Resources, Inc. This software allows analysis of seismic refraction data using conventional wavefront and plus-minus methods as well as tomographic inversion based on the Waveform Eikonal Tomography (WET) method. Prior to the geophysical investigation, and based on results of the previous investigations, the threshold for a well installation to be considered a success was a sustained flow rate of 0.75 gpm. Subsequent well locations, based on the seismic work showed substantial improvement, with flow rates over six gpm in one of the wells. Our conclusion, therefore, is that the seismic tomography was a valuable tool for enhancing the remediation at this site, and could be beneficial for other sites

Assessing the GAD Hypothesis with Paleomagnetic Data from Large Proterozoic Dike Swarms

Previous compilations of paleomagnetic studies have suggested that the Proterozoic geomagnetic field may have had as large as 12% quadrupole and 29% octupole components, relative to the dipole intensity. These values would have significant implications for geodynamo secular cooling and outer core dynamics, and for paleogeographic reconstructions. Herein we test the validity of one method, using paleomagnetic remanence of three Proterozoic large igneous provinces (LIPs), as well as younger paleomagnetic datasets, to determine zonal geomagnetic field models. Our results show that individual LIPs are not laterally widespread enough to support claims of significant global non-dipole field components in Proterozoic time. The geocentric axial dipole hypothesis remains viable for Proterozoic paleogeographic and geodynamic models

Proterozoic Geomagnetic Field Geometry

Pre-Mesozoic continental reconstructions and paleoclimatic inferences from paleomagnetism rely critically upon the assumption of a time-averaged geocentric axial dipole (GAD) magnetic field. We have been testing the GAD assumption and localized non-dipole components in a different manner, by observing directional variations within the Matachewan, Mackenzie and Franklin dyke swarms. Large dyke swarms, commonly emplaced within a few million years, provide the necessary broad areal coverage to perform a test of global geomagnetic field geometry. Our analysis varies the quadrupole and octupole values of the generalized paleolatitude equation to determine a minimal angular dispersion and maximum precision of paleopoles from each dyke swarm. As a control, paleomagnetic data from the central Atlantic magmatic province (CAMP) show the sensitivities of our method to non-GAD contributions to the ancient geomagnetic field. Within the uncertainties, CAMP data are consistent with independent estimates of non-GAD contributions derived from global tectonic reconstructions (Torsvik & Van der Voo, 2002). Current results from the three Proterozoic dyke swarms all have best fits that are non-dipolar, but they differ in their optimal quadrupole/ octupole components. Treated together under the hypothesis of a static Proterozoic field geometry, the data allow a pure GAD geodynamo within the uncertainty of the method. Current results were performed using Fisherian statistics, but Bingham statistics will be included to account for the ellipticity of data

A Paleomagnetic Reanalysis of the Auborus Formation, Namibia

Along the western margin of the Kalahari craton in southern Namibia, late Mesoproterozoic volcanic and sedimentary rocks of the Sinclair region are locally preserved at subgreenschist metamorphic grade [Hoal, 1993, Precambr. Res. 63, 143-162], thus amenable to paleomagnetic study. The youngest unit in the Sinclair succession is the Auborus Formation. comprising redbeds deposited after the cessation of Sinclair magmatism and during the waning stages of regional folding. A previous study of the Auborus Formation, utilizing data only from the natural remanent magnetization (NRM), found a well clustered, single-polarity direction differing from the present field at the sampling sites [Piper, 1975, Geophys. J. R. astr. Soc. 40, 313-344], suggesting that the Auborus Formation is likely to produce a high-quality paleomagnetic pole with proper demagnetization and field tests. We collected oriented samples through most of the Auborus stratigraphy in 2011 and 2012. Preliminary results from detailed thermal demagnetization exhibit broad agreement with Piper’s [1975] NRM data, and show a two-polarity hematite-borne characteristic remanence directed shallowly N-S. Directions are better grouped after correction for tectonic tilt, indicating a Proterozoic age of remanence because the Ediacaran-Cambrian Nama Group is flat-lying throughout the region. Present results are limited to the lower part of the Auborus Formation, in which a single reversal of the magnetic field has been documented. Analysis of the upper part of the formation is in progress, but we have already added three quality criteria (vector analysis, positive fold test, and reversals) to the Auborus pole of Piper [1975]. Along with a companion study of older units in the Sinclair terrane [Panzik et al., this meeting], our results will provide important constraints on regional tectonics of the western Kalahari craton, its role in Rodinia reconstructions, and late Mesoproterozoic geomagnetic reversal frequency

Applicability of Combined GPR and Gradiometer to Detect Buried Shallow Targets for Near-Surface Investigations

Applications of geophysical tools have always been an integral practice in near-surface characterization. We present an effective combination of ground penetrating radar (GPR) and magnetic gradiometry to detect buried objects within ~1 m of the surface. These objects are comprised of both metallic and non-metallic materials, representing a range of different sizes and shapes. To detect these features, we conducted 3D GPR and gradiometer surveys over an area of 40 m-by-50 m with 2m and 1 m grid spacing respectively. Overall, the datasets represent high signal-to-noise (S/N) ratio, although the gradiometer data were relatively noisier than the GPR at the southwestern part of the survey around the fence. Results show that the models derived from GPR and gradiometer were able to detect most of the features independently. However, when both methods are combined, we were able to identify all the targets, especially the coil of copper wire (target no. 14), which showed no indication in the GPR survey but was readily detectable with the gradiometer. With GPR, all the detectable objects represent an increase in dielectric constant with respect to the background. On the other hand, magnetic field gradient measured by the gradiometer represents both positive and negative magnetic field strengths. This is probably due to the metallic vs non-metallic nature of the objects with respect to the host material in the area. The metal well caps located at the surface were detected in both the surveys, which essentially were used as means to validate the models

Analysis of Geomagnetic Field Geometry Technique Consistency Using Geodynamo Simulations

Most applications of geomagnetism operate under the assumption that the time-averaged geomagnetic field behaves closely to a geocentric axial dipole (GAD; Hospers, 1955). While there have been numerous investigations over the validity of this assumption using both numerical simulations and paleomagnetic data, the results have yielded varying, and sometimes conflicting, interpretations about the dipolarity of a time-averaged geomagnetic field (e.g. Evans, 1976; Kent & Smethurst, 1998; Evans 2006; Panzik & Evans 2014). We address the reliability of methods used to determine geomagnetic field behavior used to interpret paleomagnetic data using a time-averaged geodynamo simulation. The produced field model from the simulations is analyzed for field morphology with two methods used to approach paleomagnetic field geometries: 1) a percent-based histogram using the final time-averaged model inclination data at all grid points along the surface, and 2) a percent-based inclination histogram determined by the best-fit Gaussian coefficients based on the dipole, quadrupole, and octupole field strength. These two methods describe the same geomagnetic field model, but may yield different morphologies which would force a change in the way paleomagnetic data is interpreted