Nicholas L. Swanson-Hysell

Cryogenian Glaciation and the Onset of Carbon-Isotope Decoupling

A Dip in the Carbon Pool Before the diversity of animal life exploded in the Cambrian, Earths carbon cycle was apparently strongly altered by multiple glaciation events across the globe. Carbon isotope signatures from rocks in Australia measured by Swanson-Hysell et al. (p. 608) suggest that an organic carbon reservoir formed between two global glaciations, or “snowball Earth,” several hundred million years earlier than expected. Anoxic sulfate-limited waters, caused by increased river outputs from melting glaciers, may have prohibited bacterial respiration, allowing for the accumulation of organic carbon. As organic carbon levels dropped, CO2 was released, allowing the atmosphere to warm, preventing further glaciations, and permitting the eventual accumulation of oxygen in the oceans that led to the Cambrian explosion. A large oceanic organic carbon reservoir developed in the period between two global glaciations. Global carbon cycle perturbations throughout Earth history are frequently linked to changing paleogeography, glaciation, ocean oxygenation, and biological innovation. A pronounced carbonate carbon-isotope excursion during the Ediacaran Period (635 to 542 million years ago), accompanied by invariant or decoupled organic carbon-isotope values, has been explained with a model that relies on a large oceanic reservoir of organic carbon. We present carbonate and organic matter carbon-isotope data that demonstrate no decoupling from approximately 820 to 760 million years ago and complete decoupling between the Sturtian and Marinoan glacial events of the Cryogenian Period (approximately 720 to 635 million years ago). Growth of the organic carbon pool may be related to iron-rich and sulfate-poor deep-ocean conditions facilitated by an increase in the Fe:S ratio of the riverine flux after Sturtian glacial removal of a long-lived continental regolith.

An Appalachian Amazon? Magnetofossil evidence for the development of a tropical river‐like system in the mid‐Atlantic United States during the Paleocene‐Eocene thermal maximum

On the mid-Atlantic Coastal Plain of the United States, Paleocene sands and silts are replaced during the Paleocene-Eocene Thermal Maximum (PETM) by the kaolinite-rich Marlboro Clay. The clay preserves abundant magnetite produced by magnetotactic bacteria and novel, presumptively eukaryotic, iron-biomineralizing microorganisms. Using ferromagnetic resonance spectroscopy and electron microscopy, we map the magnetofossil distribution in the context of stratigraphy and carbon isotope data and identify three magnetic facies in the clay: one characterized by a mix of detrital particles and magnetofossils, a second with a higher magnetofossil-to-detrital ratio, and a third with only transient magnetofossils. The distribution of these facies suggests that suboxic conditions promoting magnetofossil production and preservation occurred throughout inner middle neritic sediments of the Salisbury Embayment but extended only transiently to outer neritic sediments and the flanks of the embayment. Such a distribution is consistent with the development of a system resembling a modern tropical river-dominated shelf.

Geology of Lonar Crater, India

Lonar Crater, India, is one of the youngest and best preserved impact structures on Earth. The 1.88-km-diameter simple crater formed entirely within the Deccan traps, making it a useful analogue for small craters on the basaltic surfaces of the other terrestrial planets and the Moon. In this study, we present a meter-scale–resolution digital elevation model, geological map of Lonar Crater and the surrounding area, and radiocarbon ages for histosols beneath the distal ejecta. Impact-related deformation of the target rock consists of upturned basalt fl ows in the upper crater walls and recumbent folding around rim concentric, subhorizontal, noncylindrical fold axes at the crater rim. The rim-fold hinge is preserved around 10%– 15% of the crater. Although tearing in the rim-fold is inferred from fi eld and paleomagnetic observations, no tear faults are identifi ed, indicating that large displacements in the crater walls are not characteristic of small craters in basalt. One signifi cant normal fault structure is observed in the crater wall that offsets slightly older layer-parallel slip faults. There is little fl uvial erosion of the continuous ejecta blanket. Portions of the ejecta blanket are overlain by aerodynamically and rotationally sculpted glassy impact spherules, in particular in the eastern and western rim, as well as in the depression north of the crater known as Little Lonar. The emplacement of the continuous ejecta blanket can be likened to a radial groundhugging debris fl ow, based on the preserved thickness distribution of the ejecta, the effi cient exchange of clasts between the ejecta fl ow and the underlying histosol, and the lack of sorting and stratifi cation in the bulk of the ejecta. The ejecta profi le is thickened at the distal edge and similar to fl ejecta structures observed on Mars.

PmagPy: Software package for paleomagnetic data analysis and a bridge to the Magnetics Information Consortium (MagIC) Database

Author(s): Tauxe, L; Shaar, R; Jonestrask, L; Swanson-Hysell, NL; Minnett, R; Koppers, AAP; Constable, CG; Jarboe, N; Gaastra, K; Fairchild, L | Abstract:

Constraints on Neoproterozoic paleogeography and Paleozoic orogenesis from paleomagnetic records of the Bitter Springs Formation, Amadeus Basin, central Australia

The supercontinent Rodinia is hypothesized to have been assembled and positioned in tropical latitudes by the early Neoproterozoic Era. Paleomagnetic data from limestones of Svalbard and basaltic dikes of South China have been interpreted to record rapid changes in paleogeography driven by true polar wander that may have rotated the supercontinent in association with the ∼800 Ma Bitter Springs carbon isotope event. To further constrain early Neoproterozoic paleogeography and to test proposed rapid rotations, we have developed sequence- and chemo-stratigraphically constrained paleomagnetic data from the Bitter Springs Formation of the Amadeus Basin of central Australia. A new paleomagnetic pole for the post–Bitter Springs stage ∼770 Ma Johnnys Creek Member (Bitter Springs Formation) provides a positive test for a long-lived history of Australia and Laurentia in a single supercontinent as its similar position to late Mesoproterozoic north Australia poles reproduces the closure of the Laurentian “Grenville Loop.” This new pole also provides support for the hypothesis that there was significant rotation between north and south+west Australia at the end of the Neoproterozoic as this rotation brings the south+west Australia ∼755 Ma Mundine Well pole into much closer proximity to the north Australia Johnnys Creek pole. Syn–Bitter Springs stage carbonates of the Loves Creek Member of the formation contain a well-behaved remanence held by magnetite. The direction of this remanent magnetization falls on the Cambrian portion of Australias apparent polar wander path suggesting that the magnetite may have formed authigenically at that time. If primary, the Loves Creek direction is consistent with the true polar wander hypothesis for the Bitter Springs stage, is internally consistent with the relative sea level changes inferred from the formation, and can constrain Australia to a SouthWest North America East AnTarctica (SWEAT) fit. A remanence held by pyrrhotite in carbonates of the Bitter Springs Formation corresponds to the apparent polar wander path of Australia at ∼350 Ma. This component can be used to constrain the history of the Devonian-Carboniferous Alice Springs Orogeny as it demonstrates that regional folding of basinal sediments occurred prior to ∼350 Ma, but that the latest stages of tectonism in the hinterland drove fluids through the sediments that altered redox conditions to favor pyrrhotite precipitation.

Stratigraphy and geochronology of the Tambien Group, Ethiopia: Evidence for globally synchronous carbon isotope change in the Neoproterozoic

The Neoproterozoic Era was an interval characterized by profound environmental and biological transitions. Existing age models for Neoproterozoic nonglacial intervals largely have been based on correlation of carbonate carbon isotope values, but there are few tests of the assumed synchroneity of these records between basins. In contrast to the ash-poor successions typically targeted for Neoproterozoic chemostratigraphy, the Tonian to Cryogenian Tambien Group (Tigray region, Ethiopia) was deposited in an arc-proximal basin where volcanic tuffs suitable for U-Pb geochronology are preserved within the mixed carbonate-siliciclastic sedimentary succession. The Tambien Group culminates in a diamictite interpreted to correlate to the ca. 717–662 Ma Sturtian snowball Earth glaciation. New physical stratigraphic data and high-precision U-Pb dates from intercalated tuffs lead to a new stratigraphic framework for the Tambien Group that confirms identification of negative δ13C values from Assem Formation limestones with the ca. 800 Ma Bitter Springs carbon isotope stage. Integration with data from the Fifteenmile Group of northwestern Canada constitutes a positive test for the global synchroneity of the Bitter Spring Stage and constrains the stage to have started after 811.51 ± 0.25 Ma and to have ended before 788.72 ± 0.24 Ma. These new temporal constraints strengthen the case for interpreting Neoproterozoic carbon isotope variation as a record of large-scale changes to the carbon cycle and provide a framework for age models of paleogeographic change, geochemical cycling, and environmental evolution during the radiation of early eukaryotes.

U‐Pb zircon constraints on the age and provenance of the Rocas Verdes basin fill, Tierra del Fuego, Argentina

The Late Jurassic to Early Cretaceous Rocas Verdes basin constitutes one of the most poorly understood components of the southernmost Andes. As a result, accurate reconstructions and interpretations of deformation associated with the Andean orogeny and the kinematics of Scotia arc development also remain poorly constrained. In this data brief, we report U-Pb zircon ages from sandstones of the Rocas Verdes basin fill and from a crosscutting pluton in the southernmost Andes of Argentine Tierra del Fuego. Detrital samples contain predominant Early to early Middle Cretaceous (circa 130–105 Ma) U-Pb zircon age populations, with very small or single-grain middle Mesozoic and Proterozoic subpopulations. A very small subpopulation of Late Cretaceous ages in one sample raises the unlikely possibility that parts of the Rocas Verdes basin are younger than perceived. A sample from a crosscutting syenitic pegmatite yields a crystallization age of 74.7 +2.2/−2.0 Ma. The data presented herein encourage further geochronologic evaluation of the Rocas Verdes basin in order to better constrain the depositional ages and provenance of its contents.

Confirmation of progressive plate motion during the Midcontinent Rift's early magmatic stage from the Osler Volcanic Group, Ontario, Canada

PUBLICATIONS Geochemistry, Geophysics, Geosystems RESEARCH ARTICLE 10.1002/2013GC005180 Special Section: Magnetism From Atomic to Planetary Scales: Physical Principles and Interdisciplinary Applications in Geo- and Planetary Sciences Key Points: Paleomagnetic data reveal progressive directional change through the Osler Group Rapid plate motion was ongoing during the early magmatic stage of rifting Plume activity was ongoing in Laurentia and elsewhere Supporting Information: Readme IPython notebook with data and analysis Correspondence to: N. L. Swanson-Hysell, swanson-hysell@berkeley.edu Citation: Swanson-Hysell, N. L., A. A. Vaughan, M. R. Mustain, and K. E. Asp (2014), Confirmation of progressive plate motion during the Midcontinent Rift’s early magmatic stage from the Osler Volcanic Group, Ontario, Canada, Geochem. Geophys. Geosyst., 15, 2039– 2047, doi:10.1002/2013GC005180. Received 3 DEC 2013 Accepted 23 APR 2014 Accepted article online 27 APR 2014 Published online 30 MAY 2014 Confirmation of progressive plate motion during the Midconti- nent Rift’s early magmatic stage from the Osler Volcanic Group, Ontario, Canada Nicholas L. Swanson-Hysell 1,2 , Angus A. Vaughan 1,3 , Monica R. Mustain 1,4 , and Kristofer E. Asp 1,5 Institute for Rock Magnetism, Department of Earth Sciences, University of Minnesota, Minneapolis, Minnesota, USA, Department of Earth and Planetary Science, University of California, Berkeley, California, USA, 3 Department of Geology, Carleton College, Northfield, Minnesota, USA, 4 Department of Geology and Geography, Illinois State University, Normal, Illinois, USA, 5 Department of Geological Sciences, University of Minnesota, Duluth, Minnesota, USA Abstract As the supercontinent Rodinia was assembling ca. 1.1 billion years ago, there was extensive magmatism on at least five Proterozoic continents including the development of the North American Mid- continent Rift. New paleomagnetic data from 84 lava flows of the Osler Volcanic Group of the Midcontinent Rift reveal that there was a significant and progressive decrease in inclination between the initiation of extrusive volcanism in the region (ca. 1110 Ma) and ca. 1105 6 2 Ma (during the ‘‘early stage’’ of rift develop- ment). Paleomagnetic poles can be calculated for the lower portion of the reversed Osler Volcanic Group (40.9 N, 218.6 E, A 95 5 4.8 , N 5 30) and the upper portion of the reversed Osler Volcanic Group (42.5 N, 201.6 E, A 95 5 3.7 , N 5 59; this pole can be assigned the age of ca. 1105 6 2 Ma). This result is a positive test of the hypothesis that there was significant plate motion during the early stage of rift development. In addition to being a time of widespread volcanism on Laurentia and other continents, this interval of the late Mesoproterozoic was characterized by rapid paleogeographic change. 1. Introduction Despite being active for more than 20 million years [Davis and Green, 1997] and resulting in the thinning of prerift crust to less than 10 km [Cannon, 1992], the 1.1 Ga Midcontinent Rift failed to dismember Laurentia (cratonic North America). This failure resulted in the preservation of a thick record of rift-related volcanic and sedimentary rocks that gives geoscientists insight into the development of this ancient rift. Most mod- els for the development of the Midcontinent Rift attribute its origin to the upwelling and decompression melting of a mantle plume [Shirey, 1997]. On the basis of the great volume of generated magma and inter- pretation of geochemical data, it is argued that the early stage plateau flood basalts of the rift (ca. 1110– 1105 Ma) and the main stage volcanics that erupted into the central basin (ca. 1100–1095 Ma) were both dominated by plume-sourced melts. This deep-plume origin for the rift needs to be considered in conjunc- tion with paleogeographic change that has been inferred to have been ongoing throughout rift develop- ment. Fully constraining this paleogeographic change is essential for understanding rift development and for constraining late Mesoproterozoic paleogeographic reconstructions given the centrality of Laurentia’s apparent polar wander path to such efforts. It has long been noted that there is a significant difference in paleomagnetic inclination between the steep (dominantly reversed polarity) magnetizations of the oldest volcanics and intrusives of the Midcontinent Rift and the shallower (dominantly normal polarity) magnetizations from the younger main stage volcanics and intrusives [Halls and Pesonen, 1982]. This inclination change has been interpreted either as resulting from rapid plate motion [Robertson and Fahrig, 1971; Davis and Green, 1997] or as being the result of large nondipolar contributions to the late Mesoproterozoic geomagnetic field that led to asymmetry across rever- sals [Pesonen and Nevanlinna, 1981]. The interpretation of the record as recording stepwise inclination change across reversals associated with a significant sustained departure from a geocentric axial dipole (GAD) dominated field was challenged by the observation of a progressive decrease in paleomagnetic incli- nation across multiple geomagnetic reversals up through the succession of Midcontinent Rift lavas at Mamainse Point, Ontario [Swanson-Hysell et al., 2009, 2014]. This progressive decrease in inclination leads to the interpretation of multiple symmetric reversals when the data are considered in stratigraphic context SWANSON-HYSELL ET AL. C 2014. American Geophysical Union. All Rights Reserved. V

Preservation and detectability of shock-induced magnetization

Author(s): Tikoo, Sonia M; Gattacceca, Jerome; Swanson-Hysell, Nicholas L; Weiss, Benjamin P; Suavet, Clement; CournA¨de, Cecile

Full vector low-temperature magnetic measurements of geologic materials

GEOCHEMISTRY, GEOPHYSICS, GEOSYSTEMS, VOL. ???, XXXX, DOI:10.1029/, Full vector low-temperature magnetic measurements of geologic materials Joshua M. Feinberg 1 , Peter A. Solheid 1 , Nicholas L. Swanson-Hysell 1,2 , Mike J. Jackson 1 , and Julie A. Bowles 1,3 The magnetic properties of geologic materials offer insights into an enormous range of important geophysical phenomena ranging from inner core dynamics to pale- oclimate. Often it is the low-temperature behavior (<300 K) of magnetic minerals that provides the most useful and highest sensitivity information for a given problem. Con- ventional measurements of low-temperature remanence are typically conducted on instru- ments that are limited to measuring one single axis component of the magnetization vec- tor and are optimized for measurements in strong fields. These instrumental limitations have prevented fully optimized applications and have motivated the development of a low-temperature probe that can be used for low-temperature remanence measurements between 17 and 300K along three orthogonal axes using a standard 2G Enterprises SQuID rock magnetometer. In this contribution, we describe the design and implementation of this instrument and present data from five case studies that demonstrate the probe’s con- siderable potential for future research: a polycrystalline hematite sample, a polycrystalline hematite and magnetite mixture, a single crystal of magnetite, a single crystal of pyrrhotite and samples of Umkondo Large Igneous Province diabase sills. Abstract. Measurement System (MPMS), most often with the inten- tion of revealing information about the dominant magnetic mineral phases and grain size distribution. While these in- struments are adept at a range of low-temperature exper- iments, understanding the full behavior of a rock’s natu- ral remanence at low-temperature is hampered by the mea- surement capabilities being limited to a single axis and the instrument not providing an ultra-low field environment. If low-temperature measurements of a natural remanence (NRM) are desired using such instrumentation, great care must be taken to align the NRM with the measurement axis, and any directional change during thermal cycling will not be captured. In such an instrument, deviation from the single-axis will result in a measured magnetization that is less than the specimen’s actual total magnetization. In this contribution, we describe a low-temperature probe developed for use with superconducting rock magnetometers (SRM) at the Institute for Rock Magnetism (IRM ), Uni- versity of Minnesota. This instrument allows for three-axis full-vector measurements of magnetic remanence at temper- atures between 300 and 17 K in low-field environments (<10 nT). It was developed with different engineering, but the same intent, as a low-temperature insert that has previously been implemented at the University of Rochester Paleomag- netic Laboratory [Smirnov and Tarduno, 2011]. 1. Introduction Magnetic behavior at low temperatures (<300 K) is one of the most sensitive indicators of the iron mineral phases and their concentrations and grain size distributions in nat- ural samples. Changes in magnetocrystalline anisotropy and crystallographic structure give rise to low-temperature tran- sitions that are diagnostic of specific mineral phases. The Morin transition of hematite (at ∼262 K; Morin [1950]), the Verwey transition of magnetite (at ∼122 K; Verwey [1939]) and the Besnus transition of pyrrhotite (at ∼32 K, Besnus and Meyer [1964]) are all diagnostic of common magnetic minerals that carry remanence at Earth surface tempera- tures. Other phases that acquire remanence at low tem- perature, such as siderite (with a Ne´el temperature of 38 K; Frederichs et al. [2003]) and superparamagnetic grains [Worm and Jackson, 1999], can also be readily identified through their low-temperature behavior. In addition to the utility of low-temperature data as a diagnostic tool for mag- netic mineral identification and characterization, irreversible changes in remanence that are associated with cycling to low temperatures are often used as a tool in paleomagnetic stud- ies. Low-temperature steps in paleodirectional and paleoin- tensity study are applied in some protocols with the goal of preferentially removing magnetic remanence held by mul- tidomain grains and thereby isolating magnetizations held by single-domain grains [e.g., Schmidt [1993]; Dunlop [2003]; Yamamoto et al. [2003]]. Low-temperature remanence experiments are routinely conducted on the Quantum Designs Magnetic Properties 2. Instrument design In order to develop the capacity to make three-axis mea- surements of remanence in an ultra-low-field environment, a cryostat insert was developed at the IRM in coopera- tion with ColdEdge Technologies (Allentown, PA) (Figure 1). This low-temperature instrument (IRM-LTI) allows for three-axis measurements to be made between room temper- ature and ∼17 K using horizontal-loading SRMs. There are many advantages to outfitting a superconducting rock mag- netometer for measurements at low-temperatures. First, these instruments are specifically designed for three-axis re- manence measurements, and ambient fields are minimized using a superconducting lead shield. Nulling fields are ap- plied by external coils while the shield cools to superconduct- ing temperatures, ultimately trapping a ∼2-3 nT field along 1 Institute for Rock Magnetism, Department of Earth Sciences, University of Minnesota, Minneapolis, Minnesota, USA 2 Department of Earth and Planetary Science, University of California, Berkeley, California, USA 3 Department of Geosciences, University of Wisconsin, Milwaukee, WI, USA Copyright 2015 by the authors.