• 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

    R. E. Kopp; D. Schumann; T. D. Raub; D. S. Powars; L. V. Godfrey; N. L. Swanson-Hysell; A. C. Maloof; H. Vali
    Journal Article

    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...

  • Apparatuses and methods for serial sectioning and imaging

    B. Samuels; K. W. Kellerson; B. Girit; A. Lukyanov; A. C. Maloof; W. Rozen
    Patent

    In some embodiments, an apparatus comprises: a stage moveable on first and second axes; a material removal tool moveable on a third axis; a linear slide and a guide parallel to the third axis; a mount for an imaging device coupled to the linear slide using carriages; an armature coupled to the material removal tool and the guide that moves the...

  • The arc of the Snowball: U-Pb dates constrain the Islay anomaly and the initiation of the Sturtian glaciation

    S. MacLennan; Y. Park; N. Swanson-Hysell; A. C. Maloof; B. Schoene; M. Gebreslassie; E. Antilla; T. Tesema; M. Alene; B. Haileab
    Journal Article

    In order to understand the onset of Snowball Earth events, precise geochronology and chemostratigraphy are needed on complete sections leading into the glaciations. While deposits associated with the Neoproterozoic Sturtian glaciation have been found on nearly every continent, time-calibrated stratigraphic sections that record...

  • Astronomically forced hydrology of the Late Cretaceous sub-tropical Potosí Basin, Bolivia

    Adrian Tasistro-Hart; Adam Maloof; Blair Schoene; Michael P. Eddy
    Journal Article

    Periodic variations in Earth’s orbital parameters force climate on local and global scales, with global responses particularly sensitive to the presence of ice sheets and their associated feedbacks. Therefore, determining whether orbital forcings influenced sedimentary records of the past, and if so, which had such an effect, can shed light on...

  • Atmosphere–ocean oxygen and productivity dynamics during early animal radiations

    Tais W. Dahl; James N. Connelly; Da Li; Artem Kouchinsky; Benjamin C. Gill; Susannah Porter; Adam C. Maloof; Martin Bizzarro
    Journal Article

    We have discovered 2 major oceanic anoxic events (OAEs) in the early Cambrian at the time when animals markedly diversified. We present a multiproxy constraint on the global biogeochemical cycles to show that these events, in contrast to most younger OAEs, could have been driven by declining atmospheric O2 levels, plausibly set off by the...

  • Ca and Mg isotope constraints on the origin of Earth’s deepest δ13C excursion

    J. M. Husson; J. A. Higgins; A. C. Maloof; B. Schoene
    Journal Article

    Understanding the extreme carbon isotope excursions found in carbonate rocks of the Ediacaran Period (635–541Ma), where δ13C of marine carbonates (δ13Ccarb) reach their minimum (-12‰) for Earth history, is one of the most vexing problems in Precambrian geology. Known colloquially as the ‘Shuram’ excursion, the event has been interpreted by many...

  • The Ca and Mg isotope record of the Cryogenian Trezona carbon isotope excursion

    Anne-Sofie C. Ahm; Christian J. Bjerrum; Paul F. Hoffman; Francis A. Macdonald; Adam C. Maloof; Catherine V. Rose; Justin V. Strauss; John A. Higgins
    Journal Article

    The Trezona carbon isotope excursion is recorded on five different continents in platform carbonates deposited prior to the end-Cryogenian Marinoan glaciation (>635 Ma) and represents a change in carbon isotope values of 16–18‰. Based on the spatial and temporal reproducibility, the excursion previously has been interpreted as tracking the...

  • Calibrating the Cryogenian

    F. A. Macdonald; M. D. Schmitz; J. L. Crowley; C. F. Roots; D. S. Jones; A. C. Maloof; J. V. Strauss; P. A. Cohen; D. T. Johnston; D. P. Schrag
    Journal Article

    The Neoproterozoic was an era of great environmental and biological change, but a paucity of direct and precise age constraints on strata from this time has prevented the complete integration of these records. We present four high-precision U-Pb ages for Neoproterozoic rocks in northwestern Canada that constrain large perturbations in the...

  • Chains, clumps, and strings: Magnetofossil taphonomy with ferromagnetic resonance spectroscopy

    R. E. Kopp; B. P. Weiss; A. C. Maloof; H. Vali; C. Z. Nash; J. L. Kirschvink
    Journal Article

    Magnetotactic bacteria produce intracellular crystals of magnetite or greigite, the properties of which have been shaped by evolution to maximize the magnetic moment per atom of iron. Intracellular bacterial magnetite therefore possesses traits amenable to detection by physical techniques: typically, narrow size and shape distributions, single-...

  • Chancelloriid sclerites from the Dyeran–Delamaran (‘Lower–Middle’ Cambrian) boundary interval of the Pioche–Caliente region, Nevada, USA

    J. L. Moore; S. M. Porter; M. Webster; A. C. Maloof
    Journal Article

    Chancelloriids are a poorly understood group of phylogenetically problematic Cambrian metazoans; complete specimens show they were sessile, radially symmetrical, club‐shaped organisms covered with sclerites in the form of rosettes of spines. While isolated sclerites are common components of Cambrian shelly assemblages, they have been relatively...

  • Chemostratigraphic and U–Pb geochronologic constraints on carbon cycling across the Silurian–Devonian boundary

    J. M. Husson; B. Schoene; S. Bluher; A. C. Maloof
    Journal Article

    The Devonian Period hosts extraordinary changes to Earth's biosphere. Land plants began their rise to prominence, with early vascular vegetation beginning its colonization of near-shore environments in the latest Silurian. Across the Silurian–Devonian (Pridoli–Lochkovian) transition, carbon isotope analyses of bulk marine carbonates (δ13Ccarb)...

  • Climate-Driven Variability in Runoff Erosion Encoded in Stream Network Geometry

    Alexander Getraer; Adam C. Maloof
    Journal Article

    Abstract Climate signatures recorded in the geometry of branching streams provide insight into climate and landscape histories on Earth and other planetary bodies. Recent findings establish that branching angles are narrower and stream profiles are straighter in more arid climates. However, these two observations have been attributed to...

  • Combined paleomagnetic, isotopic, and stratigraphic evidence for true polar wander from the Neoproterozoic Akademikerbreen Group, Svalbard, Norway

    A. C. Maloof; G. P. Halverson; J. L. Kirschvink; D. P. Schrag; B. P. Weiss; P. F. Hoffman
    Journal Article

    We present new paleomagnetic data from three Middle Neoproterozoic carbonate units of East Svalbard, Norway. The paleomagnetic record is gleaned from 50 to 650 m of continuous, platformal carbonate sediment, is reproduced at three locations distributed over >100 km on a single craton, and scores a 5–6 (out of 7) on the Van der Voo (1990)...

  • Comment on: A complex microbiota from snowball Earth times: Microfossils from the Neoproterozoic Kingston Peak Formation, Death Valley, USA

    F. A. Corsetti; S. M. Awramik; D. Pierce
    Journal Article

    A thin carbonate unit associated with a Sturtian-age (750–700 million years ago) glaciogenic diamictite of the Neoproterozoic Kingston Peak Formation, eastern California, contains microfossil evidence of a once-thriving prokaryotic and eukaryotic microbial community (preserved in chert and carbonate). Stratiform stromatolites, oncoids, and rare...

  • Constraining the Timing and Amplitude of Early Serpukhovian Glacioeustasy With a Continuous Carbonate Record in Northern Spain

    A. Campion; A. C. Maloof; B. Schoene; S. Oleynik; J. Sanz-López; S. Blanco-Ferrera; O. Merino-Tomé; J-R. Bahamonde; L. P. Fernández
    Journal Article

    Abstract During the Late Paleozoic Ice Age (LPIA, 345?260 Ma), an expansion of ice house conditions at ?330 Ma caused a nearly synchronous, global unconformity. Subaerially exposed paleotropical carbonates were dissolved by meteoric waters, mixed with the light terrestrial carbon, and recrystallized with overprinted, diagenetic C values. In...

  • Constraints on early Cambrian carbon cycling from the duration of the Nemakit-Daldynian–Tommotian boundary δ13C shift, Morocco

    A. C. Maloof; J. Ramezani; S. A. Bowring; D. A. Fike; S. M. Porter; M. Mazouad
    Journal Article

    The Nemakit-Daldynian–Tommotian (ND-T) boundary marks the first appearance of metazoan reefs and calcite biomineralizers and is associated with the largest δ13C shift during the Phanerozoic Eon. Biological transitions in Earth history are often accompanied by excursions in the carbon isotopic composition (δ13C) of the ocean, where δ13C...

  • Constraints on mantle viscosity and Laurentide ice sheet evolution from pluvial paleolake shorelines in the western United States

    J. Austermann; C.Y. Chen; H.C.P. Lau; A.C. Maloof; K. Latychev
    Journal Article

    The deformation pattern of the paleoshorelines of extinct Lake Bonneville were among the first features to indicate that Earth's interior responds viscoelastically to changes in surface loads (Gilbert, 1885). Here we revisit and extend this classic study of isostatic rebound with updated lake chronologies for Lake Bonneville and Lake Lahontan...

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

    N. L. Swanson-Hysell; A. C. Maloof; J. L. Kirschvink; D. A.D. Evans; G. P. Halverson; M. T. Hurtgen
    Journal Article

    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...

  • Constraints on the origin and relative timing of the Trezona δ13C anomaly below the end-Cryogenian glaciation

    Catherine V. Rose; Nicholas L. Swanson-Hysell; Jon M. Husson; Laura N. Poppick; John M. Cottle; Blair Schoene; Adam C. Maloof
    Journal Article

    The Neoproterozoic Era was punctuated by the ‘Sturtian’ (~710million years ago) and ‘Marinoan’ (~635million years ago) low-latitude glaciations. Carbonates preceding the younger Marinoan glacial succession record an ~18‰ negative shift in the δ13C of carbonate around the world. This ‘Trezona’ isotopic anomaly is the largest δ13C shift in Earth...

  • Cover Photograph

    A. C. Maloof
    Artwork
  • Cryogenian Glaciation and the Onset of Carbon-Isotope Decoupling

    N. L. Swanson-Hysell; C. V. Rose; C. C. Calmet; G. P. Halverson; M. T. Hurtgen; A. C. Maloof
    Journal Article

    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,...

  • Cryogenian glaciations on the southern tropical paleomargin of Laurentia (NE Svalbard and East Greenland), and a primary origin for the upper Russøya (Islay) carbon isotope excursion

    P. F. Hoffman; G. Halverson; E. Domack; A. C. Maloof; N. L. Swanson-Hysell; G. M. Cox
    Journal Article

    Neoproterozoic successions in NE Svalbard and East Greenland host a pair of glacigenic formations, the younger of which are correlated with the terminal Cryogenian (Marinoan) glaciation based on their lithologically and isotopically diagnostic cap dolostones. A deep negative carbon isotope excursion (CIE) occurs stratigraphically beneath the...

  • Deriving tidal structure from satellite image time series

    Emily C. Geyman; Adam C. Maloof
    Journal Article

    Abstract In shallow coastal regions, tides often control the water flux, which in turn directs sediment transport, nutrient delivery, and geochemical gradients. However, tides in shallow areas are spatially heterogeneous, making it challenging to constrain the geographic structure of tidal phase and amplitude without extensive networks of tide...

  • A diurnal carbon engine explains 13C-enriched carbonates without increasing the global production of oxygen

    Emily C. Geyman; Adam C. Maloof
    Journal Article

    We present stable carbon isotope (δ13C) data from modern carbonate sediment that require a decoupling of the carbon cycles in the global ocean versus shallow carbonate shelves. This realization is important because, for the first 97% of Earth history, many inferences about global paleoclimate and seawater chemistry rely on interpretations of...

  • The earliest Cambrian record of animals and ocean geochemical change

    A. C. Maloof; S. M. Porter; J. L. Moore; F. Ö. Dudás; S. A. Bowring; J. A. Higgins; D. A. Fike; M. P. Eddy
    Journal Article

    The Cambrian diversification of animals was long thought to have begun with an explosive phase at the start of the Tommotian Age. Recent stratigraphic discoveries, however, suggest that many taxa appeared in the older Nemakit-Daldynian Age, and that the diversification was more gradual. We map lowest Cambrian (Nemakit-Daldynian through...

  • An early diagenetic deglacial origin for basal Ediacaran “cap dolostones”

    A-S. C. Ahm; A. C. Maloof; F. A. Macdonald; P. F. Hoffman; C. J. Bjerrum; U. Bold; C. V. Rose; J. V. Strauss; J. A. Higgins
    Journal Article

    The beginning of the Ediacaran Period (∼635 Ma) is marked by conspicuous dolostone units that cap Marinoan glacial deposits worldwide. The extent and sedimentary characteristics of the cap dolostones indicate that anomalous carbonate over-saturation coincided with deglacial sea-level rise and ocean warming. However, the geochemical variability...

  • The End-Cryogenian Glaciation of South Australia

    C. V. Rose; A. C. Maloof; B. Schoene; R. C. Ewing; U. Linnemann; M. Hofmann; J. M. Cottle
    Journal Article

    The Elatina Fm. records the younger Cryogenian ice age in the Adelaide Rift Complex (ARC) of South Australia, which has long-held the position as the type region for this low-latitude glaciation. Building upon a legacy of work, we document the pre- and syn-glacial sedimentary rocks to characterize the dynamics of the glaciation across the ARC....

  • Evolution of the 87Sr/86Sr composition of Neoproterozoic seawater

    G. P. Halverson; F. Ö. Dudás; A. C. Maloof; S. A. Bowring
    Journal Article

    The limited availability and low resolution of biostratigraphic and radiometric data in the Precambrian necessitate using marine chemostratigraphy to correlate and integrate the fragmentary stratigraphic record. We present a new composite record of the strontium isotope composition of seawater during the Neoproterozoic (1000–542 Ma) Era that is...

  • An expanded record of Early Cambrian carbon cycling from the Anti-Atlas Margin, Morocco

    A. C. Maloof; D. P. Schrag; J. L. Crowley; S. A. Bowring
    Journal Article

    We present a δ13C record from the Anti-Atlas mountains of Morocco and place it in the context of a detailed regional tectonostratigraphy. We place the litho- and chemostratigraphic record in a temporal framework using precision U–Pb zircon geochronology of ashes interbedded with the same carbonate units that provide δ13C data. The variations in...

  • Facies control on carbonate δ13C on the Great Bahama Bank

    Emily C. Geyman; Adam C. Maloof
    Journal Article

    The carbon isotopic (δ13C) composition of shallow-water carbonates often is interpreted to reflect the δ13C of the global ocean and is used as a proxy for changes in the global carbon cycle. However, local platform processes, in addition to meteoric and marine diagenesis, may decouple carbonate δ13C from that of the global ocean. We present new...

  • Geologic evidence for an icehouse Earth before the Sturtian global glaciation

    Scott A. MacLennan; Michael P. Eddy; Arthur J. Merschat; Akshay K. Mehra; Peter W. Crockford; Adam C. Maloof; Scott Southworth; Blair Schoene
    Journal Article

    Snowball Earth episodes, times when the planet was covered in ice, represent the most extreme climate events in Earth’s history. Yet, the mechanisms that drive their initiation remain poorly constrained. Current climate models require a cool Earth to enter a Snowball state. However, existing geologic evidence suggests that Earth had a stable,...

  • Geology of Lonar Crater, India

    A. C. Maloof; S. T. Stewart; B. P. Weiss; S. A. Soule; N. L. Swanson-Hysell; K. L. Louzada; I. Garrick-Bethell; P. M. Poussart
    Journal Article

    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...

  • Glacioeustasy, meteoric diagenesis, and the carbon cycle during the Middle Carboniferous

    B. Dyer; A. C. Maloof; J. A. Higgins
    Journal Article

    Abstract Middle Carboniferous carbonates in the western U.S. have undergone Pleistocene Bahamas-style meteoric diagenesis that may be associated with expanding late Paleozoic ice sheets. Fourteen stratigraphic sections from carbonate platforms illustrate the regional distribution and variable intensity of physical and chemical diagenesis just...

  • Helium and thorium isotope constraints on African dust transport to the Bahamas over recent millennia

    C. T. Hayes; D. McGee; S. Mukhopadhyay; E. A. Boyle; A. C. Maloof
    Journal Article

    Despite its potential linkages with North Atlantic climate, the variability in Saharan dust transport to the western North Atlantic over the past two millennia has not been well-characterized. A factor of 4 increase in dust production in sub-Saharan Africa has been attributed to the onset of Sahelian agriculture 200 yr ago. The regional extent...

  • The Holocene shallowing-upward parasequence of north-west Andros Island, Bahamas

    A. C. Maloof; J. P. Grotzinger
    Journal Article

    Abstract Many pre-Mesozoic records of Earth history are derived from shallow water carbonates deposited on continental shelves. While these carbonates contain geochemical proxy records of climate change, it is the stratal architecture of layered carbonate units that often is used to build age models based on the idea that periodic astronomical...

  • How is sea level change encoded in carbonate stratigraphy?

    Emily C. Geyman; Adam C. Maloof; Blake Dyer
    Journal Article

    The history of organismal evolution, seawater chemistry, and paleoclimate is recorded in layers of carbonate sedimentary rock. Meter-scale cyclic stacking patterns in these carbonates often are interpreted as representing sea level change. A reliable sedimentary proxy for eustasy would be profoundly useful for reconstructing paleoclimate, since...

  • The lead-up to the Sturtian Snowball Earth: Neoproterozoic chemostratigraphy time-calibrated by the Tambien Group of Ethiopia

    Yuem Park; Nicholas L. Swanson-Hysell; Scott MacLennan; Adam C. Maloof; Mulubrhan Gebreslassie; Marissa M. Tremblay; Blair Schoene; Mulugeta Alene; Eliel Antilla; Tadele Tesema; Bereket Haileab
    Journal Article

    The Tonian-Cryogenian Tambien Group of northern Ethiopia is a mixed carbonate-siliciclastic sequence that culminates in glacial deposits associated with the first of the Cryogenian glaciations—the Sturtian “Snowball Earth.” Tambien Group deposition occurred atop arc volcanics and volcaniclastics of the Tsaliet Group. New U-Pb isotope dilution−...

  • A library of early Cambrian chemostratigraphic correlations from a reproducible algorithm

    C. C. Hay; J. R. Creveling; C. J. Hagen; A. C. Maloof; P. Huybers
    Journal Article

    The visual alignment of chemostratigraphic excursions enables correlation of sedimentary successions within the bounds of geochronology or biostratigraphy. This correlation facilitates the extrapolation of ages from radiometrically calibrated stratigraphic sections to others lacking temporal constraints. For Ediacaran and Cambrian applications...

  • Long-term Earth-Moon evolution with high-level orbit and ocean tide models

    Houraa Daher; Brian K. Arbic; James G. Williams; Joseph K. Ansong; Dale H. Boggs; Malte Müller; Michael Schindelegger; Jacqueline Austermann; Bruce D. Cornuelle; Eliana B. Crawford; Oliver B. Fringer; Harriet C.P. Lau; Simon J. Lock; Adam C. Maloof; Dimitris Menemenlis; Jerry X. Mitrovica; J.A. Mattias Green; Matthew Huber
    Journal Article

    Abstract Tides and Earth-Moon system evolution are coupled over geological time. Tidal energy dissipation on Earth slows Earth's rotation rate, increases obliquity, lunar orbit semi-major axis and eccentricity, and decreases lunar inclination. Tidal and core-mantle boundary dissipation within the Moon decrease inclination, eccentricity and semi...

  • Magmatic activity and plate motion during the latent stage of Midcontinent Rift development

    N. L. Swanson-Hysell; S. D. Burgess; A. C. Maloof; S. A. Bowring
    Journal Article

    The Keweenawan Midcontinent Rift of North America records significant continental rifting between ca. 1110 and 1085 Ma, and preserves the most detailed paleomagnetic record of plate motion of any continent in Precambrian time. U/Pb dates from extrusive and intrusive rocks of the western Lake Superior Basin suggest a latent stage of reduced...

  • The Marinoan glaciation (Neoproterozoic) in northeast Svalbard

    G. P. Halverson; A. C. Maloof; P. F. Hoffman
    Journal Article

    Two separate and distinct diamictite-rich units occur in the mixed carbonate-siliciclastic Polarisbreen Group, which comprises the top kilometer of >7?km of Neoproterozoic strata in the northeast of the Svalbard archipelago. The platformal succession accumulated on the windward, tropical to subtropical margin of Laurentia. The older...

  • A multiscale approach reveals that Cloudina aggregates are detritus and not in situ reef constructions

    A. Mehra; A. C. Maloof
    Journal Article

    Little is known about how the Ediacaran index fossil Cloudina lived and what impact it had on its surroundings. This uncertainty is due to the fact that Cloudina often is preserved with the same mineralogy as the rocks in which it is found; the lack of density contrast means that traditional imaging techniques cannot be used to reconstruct and...

  • Neoproterozoic sand wedges: crack formation in frozen soils under diurnal forcing during a snowball Earth

    A. C. Maloof; J. B. Kellogg; A. M. Anders
    Journal Article

    Thermal contraction cracking of permafrost produced sand-wedge polygons at sea level on the paleo-equator during late Neoproterozoic glacial episodes. These sand wedges have been used as evidence for high (≥54°) paleo-obliquity of the Earth’s ecliptic, because cracks that form wedges are hypothesized to require deep seasonal cooling so the...

  • New constraints on equatorial temperatures during a Late Neoproterozoic snowball Earth glaciation

    R. C. Ewing; I. Eisenman; M. P. Lamb; L. Poppick; A. C. Maloof; W. W. Fischer
    Journal Article

    Intense glaciation during the end of Cryogenian time (∼635 million years ago) marks the coldest climate state in Earth history – a time when glacial deposits accumulated at low, tropical paleolatitudes. The leading idea to explain these deposits, the snowball Earth hypothesis, predicts globally frozen surface conditions and subfreezing...

  • New Software for Plotting and Analyzing Stratigraphic Data

    K. W. Lewis; T. L. Keeler; A. C. Maloof
    Journal Article

    Stratigraphy, the study of layering in rock, ice, and sediment records, lies at the heart of the geological sciences. The lithology, grain size, and texture of layered successions, along with a host of measurable geochemical and geophysical parameters, record information about past environmental and geographic conditions. Despite the importance...

  • No asymmetry in geomagnetic reversals recorded by 1.1-billion-year-old Keweenawan basalts

    N. L. Swanson-Hysell; A. C. Maloof; B. P. Weiss; D. A.D. Evans
    Journal Article

    Interpreting the past latitude and geography of the continents from palaeomagnetic data relies on the key assumption that Earth’s geomagnetic field behaves as a geocentric axial dipole. The axial dipolar field model implies that all geomagnetic reversals should be symmetric. However, palaeomagnetic data from volcanic rocks produced by the 1.1-...

  • Paleomagnetism of impact spherules from Lonar crater, India and a test for impact-generated fields

    B. P. Weiss; S. Pedersen; I. Garrick-Bethell; S. T. Stewart; K. L. Louzada; A. C. Maloof; N. L. Swanson-Hysell
    Journal Article

    Planetary surfaces have been ubiquitously melted by meteoroid impacts throughout solar system history. The resulting impact melts form some of the youngest igneous samples from rocky bodies like the Moon, Mars, and asteroids. Upon cooling, these melts may record any ambient planetary magnetic fields as well as postulated transient fields...

  • Paleomagnetism of Lonar impact crater, India

    K. L. Louzada; B. P. Weiss; A. C. Maloof; S. T. Stewart; N. L. Swanson-Hysell; S. A. Soule
    Journal Article

    Lonar crater, India, is the best preserved terrestrial impact crater formed in basalt and is a unique terrestrial analogue for small, simple craters on terrestrial planets and the Moon. We investigated the paleomagnetic and rock-magnetic properties of the 1.88 km diameter crater in order to understand the effect of impacts on magnetization in...

  • Pervasive remagnetization of detrital zircon host rocks in the Jack Hills, Western Australia and implications for records of the early geodynamo

    B. P. Weiss; A. C. Maloof; N. Tailby; J. Ramezani; R. R. Fu; V. Hanus; D. Trail; Bruce Watson; T. M. Harrison; S. A. Bowring; J. L. Kirschvink; N. L. Swanson-Hysell; R. S. Coe
    Journal Article

    It currently is unknown when Earth's dynamo magnetic field originated. Paleomagnetic studies indicate that a field with an intensity similar to that of the present day existed 3.5 billion years ago (Ga). Detrital zircon crystals found in the Jack Hills of Western Australia are some of the very few samples known to substantially predate this...

  • Physical and chemical stratigraphy suggest small or absent glacioeustatic variation during formation of the Paradox Basin cyclothems

    B. Dyer; A. C. Maloof
    Journal Article

    The Paradox Basin cyclothems previously have been interpreted as Milankovitch style glacial–interglacial cycles from the Late Paleozoic Ice Age, but an unambiguous test for a glacioeustatic origin has not been conducted. A high resolution coupled chemical and physical stratigraphic analysis of two outcrop sections and three core segments...

  • Possible animal-body fossils in pre-Marinoan limestones from South Australia

    Adam C. Maloof; Catherine V. Rose; Robert Beach; Bradley M. Samuels; Claire C. Calmet; Douglas H. Erwin; Gerald R. Poirier; Nan Yao; Frederik J. Simons
    Journal Article

    The Neoproterozoic era was punctuated by the Sturtian (about 710 million years ago) and Marinoan (about 635 million years ago) intervals of glaciation. In South Australia, the rocks left behind by the glaciations are separated by a succession of limestones and shales, which were deposited at tropical latitudes. Here we describe millimetre- to...

  • A probabilistic analysis of meteorically altered δ13C chemostratigraphy from late Paleozoic ice age carbonate platforms

    B. Dyer; J. A. Higgins; A. C. Maloof
    Journal Article

    The stratigraphic expression of meteoric diagenesis in carbonates is a glimpse into the weathering, fluid transport, and biological productivity of the ancient near-surface terrestrial environment. To infer this environmental information, we use a probabilistic approach to merge an isotope-based reactive transport model with chemostratigraphic...

  • Probabilistic assessment of sea level during the last interglacial stage

    Robert E. Kopp; Frederik J. Simons; Jerry X. Mitrovica; Adam C. Maloof; Michael Oppenheimer
    Journal Article

    With polar temperatures ∼3–5 °C warmer than today, the last interglacial stage (∼125 kyr ago) serves as a partial analogue for 1–2 °C global warming scenarios. Geological records from several sites indicate that local sea levels during the last interglacial were higher than today, but because local sea levels differ from global sea level,...

  • A probabilistic assessment of sea level variations within the last interglacial stage

    Robert E. Kopp; Frederik J. Simons; Jerry X. Mitrovica; Adam C. Maloof; Michael Oppenheimer
    Journal Article

    The last interglacial stage (LIG; ca. 130–115 ka) provides a relatively recent example of a world with both poles characterized by greater-than-Holocene temperatures similar to those expected later in this century under a range of greenhouse gas emission scenarios. Previous analyses inferred that LIG mean global sea level (GSL) peaked 6–9 m...

  • Quantifying the relationship between water depth and carbonate facies

    B. Dyer; A. C. Maloof; S. J. Purkis; P. M. Harris
    Journal Article

    Carbonate facies often are used to define meter-scale parasequence (or cyclic) structure in ancient sedimentary basins. These parasequences constitute the fundamental stratigraphic unit in many studies of ancient climate and life on Earth. Of interest is the uncertainty associated with the assumptions that underpin the parasequence definition...

  • Reevaluating the evidence for a Hadean-Eoarchean dynamo

    CS Borlina; BP Weiss; EA Lima; F Tang; RJM Taylor; JF Einsle; RJ Harrison; RR Fu; EA Bell; EW Alexander; HM Kirkpatrick; MM Wielicki; TM Harrison; J Ramezani; AC Maloof
    Journal Article

    The time of origin of the geodynamo has important implications for the thermal evolution of the planetary interior and the habitability of early Earth. It has been proposed that detrital zircon grains from Jack Hills, Western Australia, provide evidence for an active geodynamo as early as 4.2 billion years (Ga) ago. However, our combined...

  • Regional and global chemostratigraphic correlation of the early Neoproterozoic Shaler Supergroup, Victoria Island, Northwestern Canada

    D.S. Jones; A.C. Maloof; M.T. Hurtgen; R.H. Rainbird; D.P. Schrag
    Journal Article

    High resolution inorganic carbon isotope stratigraphy provides a new tool for correlating the Neoproterozoic Shaler Supergroup with the Mackenzie Mountains Supergroup. Previous stratigraphic studies established a widely accepted basis for correlation between the two supergroups. This contribution introduces a revised, testable hypothesis for...

  • Revisiting the deformed high shoreline of Lake Bonneville

    C. Y. Chen; A. C. Maloof
    Journal Article

    Since G. K. Gilbert's foundational work in the eastern Great Basin during the late 1800s, the late Pleistocene Lake Bonneville (30–10 ka) has been recognized as a natural laboratory for various Quaternary studies, including lithospheric deformation due to surface loading and climate-forced water balance changes. Such studies rely on knowledge...

  • Sedimentary iron cycling and the origin and preservation of magnetization in platform carbonate muds, Andros Island, Bahamas

    A. C. Maloof; R. E. Kopp; J. P. Grotzinger; D. A. Fike; T. Bosak; H. Vali; P. M. Poussart; B. P. Weiss; J. L. Kirschvink
    Journal Article

    Carbonate muds deposited on continental shelves are abundant and well-preserved throughout the geologic record because shelf strata are difficult to subduct and peritidal carbonate units often form thick, rheologically strong units that resist penetrative deformation. Much of what we know about pre-Mesozoic ocean chemistry, carbon cycling, and...

  • Self-reversed magnetization held by martite in basalt flows from the 1.1-billion-year-old Keweenawan rift, Canada

    N. L. Swanson-Hysell; Joshua M. Feinberg; Thelma S. Berquó; A. C. Maloof
    Journal Article

    In some basalt flows of the 1.1-billion-year-old Keweenawan Rift exposed at Mamainse Point, Ontario, there is a magnetic phase that holds a remanence antiparallel to the populations of magnetite and hematite that are typical of flows in the succession. The paleomagnetic and geological context of this component demonstrates that it is not a...

  • A Simple Method for Extracting Water Depth From Multispectral Satellite Imagery in Regions of Variable Bottom Type

    E. C. Geyman; A. C. Maloof
    Journal Article

    Satellite imagery offers an efficient and cost-effective means of estimating water depth in shallow environments. However, traditional empirical algorithms for calculating water depth often are unable to account for varying bottom reflectance, and therefore yield biased estimates for certain benthic environments. We present a simple method that...

  • Snowball Earth climate dynamics and Cryogenian geology-geobiology

    P. F. Hoffman; D. S. Abbot; Y. Ashkenazy; D. I. Benn; J. J. Brocks; P. A. Cohen; G. M. Cox; J. R. Creveling; Y. Donnadieu; D. H. Erwin; I. J. Fairchild; D. Ferreira; J. C. Goodman; G. P. Halverson; M. F. Jansen; G. Le Hir; G. D. Love; F. A. Macdonald; A. C. Maloof; C A. Partin; G. Ramstein; B. E.J. Rose; C. V. Rose; P. M. Sadler; E. Tziperman; A. Voigt; S. G. Warren
    Journal Article

    Geological evidence indicates that grounded ice sheets reached sea level at all latitudes during two long-lived Cryogenian (58 and ≥5 My) glaciations. Combined uranium-lead and rhenium-osmium dating suggests that the older (Sturtian) glacial onset and both terminations were globally synchronous. Geochemical data imply that CO2 was 102 PAL (...

  • The snowball theory still holds water

    P. F. Hoffman; A. C. Maloof
    Journal Article

    Sir — D. M. Williams et al. propose a mechanism whereby an initial high obliquity for the Earth could have rapidly changed to its present low value of ~23.5º near the end of the Proterozoic eon.

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  • Stratigraphic expression of Earth's deepest δ13C excursion in the Wonoka Formation of South Australia

    J. M. Husson; Maloof A. C.; B. Schoene; C. Y. Chen; J. A. Higgins
    Journal Article

    The most negative carbon isotope excursion in Earth history is found in carbonate rocks of the Ediacaran Period (635-541 Ma). Known colloquially as the “Shuram” excursion, workers have long noted its broad concordance with the rise of abundant macro-scale fossils in the rock record, collectively known as the “Ediacaran Biota.” Thus, the Shuram...

  • Stratigraphy and geochemistry of a ca 800 Ma negative carbon isotope interval in northeastern Svalbard

    G. P. Halverson; A. C. Maloof; D. P. Schrag; F. Ö. Dudás; M. Hurtgen
    Journal Article

    The Neoproterozoic Akademikerbreen Group in northeastern Svalbard comprises 2 km of nearly pure carbonate section. The carbonates are generally highly 13C-enriched (δ13C>5‰), but this trend is interrupted by an ∼325 m interval of low δ13C values (−4 to 0‰) in the upper Grusdievbreen and lower Svanbergfjellet formations. An abrupt negative...

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

    N. L. Swanson-Hysell; A. C. Maloof; D. J. Condon; G. R.T. Jenkin; M. Alene; M. M. Tremblay; T. Tesema; A. D. Rooney; B. Haileab
    Journal Article

    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...

  • Superposed folding at the junction of the inland and coastal belts, Damara Orogen, NW Namibia

    A. C. Maloof
    Journal Article

    Two adjoining dome structures in Neoproterozoic Otavi Group sediments are located at the intersection of the Outjo (inland branch) and Kaoko (coastal branch) fold and thrust belts of the Damara Orogen on the farm Vrede. northwestern Namibia. Systematic mapping of outcrop-scale cleavage and folding relationships has unraveled three temporally...

  • Sutton hotspot: Resolving Ediacaran-Cambrian Tectonics and true polar wander for Laurentia

    R. N. Mitchell; T. M. Killian; T. D. Raub; D. A.D. Evans; B. Wouter; A. C. Maloof
    Journal Article

    Hotspot tracks represent plate motions relative to mantle sources, and paleomagnetic data from magmatic units along those tracks can quantify motions of those mantle anomalies relative to the Earth's magnetic field and rotational axis. The Ediacaran Period is notable for rapid and large paleomagnetic apparent polar wander (APW) for many...

  • A syn-depositional age for Earth’s deepest δ13C excursion required by isotope conglomerate tests

    J. M. Husson; A. C. Maloof; B. Schoene
    Journal Article

    The most negative carbon isotope excursion in Earth history is found in carbonate rocks of the Ediacaran Period (635–542 Ma). Workers have interpreted the event as the oxidation of the Ediacaran oceans [Rothman et al., Proc. Natl. Acad. Sci. USA100 (2003) 8124; Fike et al., Nature444 (2006) 744; McFadden et al., Proc. Natl. Acad. Sci. USA105 (...

  • Testing models for post-glacial ‘cap dolostone’ deposition: Nuccaleena Formation, South Australia

    C. V. Rose; A. C. Maloof
    Journal Article

    Sedimentologically and geochemically distinctive carbonate sequences consistently drape the glacial deposits associated with the younger Cryogenian ice age. The presence of ice-rafted debris in the basal dolostone implies that at least the lower portion of the cap sequence records deglaciation. An isochronous model proposes that cap dolostones...

  • Three-Dimensional Morphometry of Ooids in Oolites: a new tool for more accurate and precise paleoenvironmental interpretation

    Bolton Howes; Akshay Mehra; Adam Maloof
    Journal Article

    Abstract The prevalence of ooids in the stratigraphic record, and their association with shallow-water carbonate environments, make ooids an important paleoenvironmental indicator. Recent advances in the theoretical understanding of ooid morphology, along with empirical studies from Turks and Caicos, Great Salt Lake, and The Bahamas, have...

  • Three-dimensional reconstructions of the putative metazoan Namapoikia show that it was a microbial construction

    A Mehra; WA Watters; JP Grotzinger; AC Maloof
    Journal Article

    Strata from the Ediacaran Period (635 million to 538 million years ago [Ma]) contain several examples of enigmatic, putative shell-building metazoan fossils. These fossils may provide insight into the evolution and environmental impact of biomineralization on Earth, especially if their biological affinities and modern analogs can be identified...

  • Tilting At Snowballs, A comment on Proterozoic equatorial glaciation: Has 'snowball Earth' a snowball's chance?

    P. Hoffman; A. C. Maloof
    Journal Article

    Ten arguments were recently presented in The Australian Geologist [1] against the ‘snowball Earth’ scenario for equatorial glaciation, a scenario that explains many previously enigmatic features of Neoproterozoic Earth history such as post-glacial cap carbonates, large shifts in stable isotope ratios of seawater proxies, and extensive oxide-...

  • To tune or not to tune: Detecting orbital variability in Oligo-Miocene climate records

    C. Proistosescu; P. Huybers; A. C. Maloof
    Journal Article

    We address the problem of detecting quasi-periodic variability at orbital frequencies within pre-Pleistocene climate records using depth-derived and orbitally tuned chronologies. Many studies describing orbital variability in pre-Pleistocene sediment hosted isotope records employ climatic records that are set on orbitally tuned chronologies,...

  • The Tonian-Cryogenian transition in Northeastern Svalbard

    G. P. Halverson; M. Kunzmann; J. V. Strauss; A. C. Maloof
    Journal Article

    The Neoproterozoic stratigraphic succession in northeastern Svalbard is uniquely important in documenting the evolution of Neoproterozoic life, seawater chemistry, and paleoenvironments. This contribution focuses on the stratigraphic and geochemical records spanning from the late Tonian to the onset of Cryogenian glaciation in the Hecla Hoek...

  • Toward a Neoproterozoic composite carbon-isotope record

    Galen P. Halverson; Paul F. Hoffman; Daniel P. Schrag; Adam C. Maloof; Hugh N. Rice
    Journal Article

    Glacial deposits of Sturtian and Marinoan age occur in the well-studied Neoproterozoic successions of northern Namibia, South Australia, and northwestern Canada. In all three regions, the Marinoan glaciation is presaged by a large negative δ13C anomaly, and the cap carbonates to both glacial units share a suite of unique sedimentological,...

  • Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer

    H. B. Dang; A. C. Maloof; M. V. Romalis
    Journal Article

    We describe an ultrasensitive atomic magnetometer based on optically pumped potassium atoms operating in a spin-exchange relaxation free regime. We demonstrate magnetic field sensitivity of 160 aT/Hz1/2 in a gradiometer arrangement with a measurement volume of 0.45 cm3 and energy resolution per unit bandwidth of 44. As an example of an...