High-resolution, whole-core magnetic susceptibility data from Leg 130, Ontong Java Plateau

High-resolution, whole-core magnetic susceptibility data, recorded at 3-cm intervals, were obtained for advanced hydraulic piston (APC) cores at Sites 805, 806, and 807 of Leg 130 on the Ontong Java Plateau. In this initial report, we present a preliminary evaluation of these data for their use in core correlations and paleoclimatic studies. The data allow detailed intrasite correlations between the offset APC cores and provide a means for intersite correlations of Pleistocene sediments. Variations in magnetic susceptibility values probably mirror variations in terrestrial influx and may act as proxy indicators of climate. Highly coherent cyclicity, representing Milankovitch orbital frequencies, is exhibited in some intervals and provides the potential to tune sedimentation rates. Postdepositional dissolution of magnetite by reduction diagenesis, which is also reflected in the magnetic susceptibility data, may be a limiting factor in these studies

Detecting the oldest geodynamo and attendant shielding from the solar wind: Implications for habitability

The onset and nature of the earliest geomagnetic field is important for understanding the evolution of the core, atmosphere and life on Earth. A record of the early geodynamo is preserved in ancient silicate crystals containing minute magnetic inclusions. These data indicate the presence of a geodynamo during the Paleoarchean, between 3.4 and 3.45 billion years ago. While the magnetic field sheltered Earth's atmosphere from erosion at this time, standoff of the solar wind was greatly reduced, and similar to that during modern extreme solar storms. These conditions suggest that intense radiation from the young Sun may have modified the atmosphere of the young Earth by promoting loss of volatiles, including water. Such effects would have been more pronounced if the field were absent or very weak prior to 3.45 billion years ago, as suggested by some models of lower mantle evolution. The frontier is thus trying to obtain geomagnetic field records that are >>3.45 billion-years-old, as well as constraining solar wind pressure for these times. In this review we suggest pathways for constraining these parameters and the attendant history of Earth's deep interior, hydrosphere and atmosphere. In particular, we discuss new estimates for solar wind pressure for the first 700 million years of Earth history, the competing effects of magnetic shielding versus solar ion collection, and bounds on the detection level of a geodynamo imposed by the presence of external fields. We also discuss the prospects for constraining Hadean-Paleoarchean magnetic field strength using paleointensity analyses of zircons.Comment: 78 pages, 8 figures, Supplementary Content: Reconstructing the Past Sun + table of solar parameters from ZAMS to present through geological tim

Late Cretaceous Plesiosaur Teeth from Axel Heiberg Island, Nunavut, Canada

We report the discovery of Late Cretaceous plesiosaur teeth from non-marine strata on Axel Heiberg Island in the Canadian High Arctic. In comparison to other plesiosaur teeth, these specimens are most similar to the teeth of elasmosaurs: they have a smooth outer surface and crenulated inner surface, with crenulations that extend nearly to the tip of the tooth. Comparisons with elasmosaurid fossils elsewhere indicate that the Axel Heiberg teeth are from juveniles. The presence of a plesiosaur in nonmarine strata on Axel Heiberg Island supports the suggestion that juvenile elasmosaurs frequently inhabited freshwater environments. The temporal distribution of the Axel Heiberg specimens and other occurrences from the High Arctic suggests that elasmosaurids may have expanded their range during a time of extreme climatic warmth.On signale la découverte de dents de plésiosaure du Crétacé supérieur d’une strate non marine à l’île Axel Heiberg, dans l’Extrême-Arctique canadien. Comparativement aux autres dents de plésiosaures, ces spécimens ressemblent beaucoup aux dents d’elasmosaures : leur surface extérieure est lisse et leur surface intérieure est crénelée, les crénulations s’étendant presque jusqu’à la pointe de la dent. Après avoir comparé ces spécimens aux fossiles d’elasmosaures trouvés ailleurs, on a remarqué que les dents trouvées à Axel Heiberg sont les dents de juvéniles. La présence d’un plésiosaure dans une strate non marine de l’île Axel Heiberg vient étayer la suggestion selon laquelle des elasmosaures juvéniles évoluaient souvent dans les milieux dulçaquicoles. La répartition temporelle des spécimens d’Axel Heiberg et d’autres occurrences de l’Extrême-Arctique laissent suggérer que les elasmosaures auraient pu étendre leur parcours au cours d’une période d’extrême chaleur climatique

Collecting and Analyzing Eye-Tracking Data in Outdoor Environments

Natural outdoor conditions pose unique obstacles for researchers, above and beyond those inherent to all mobile eye-tracking research. During analyses of a large set of eye-tracking data collected on geologists examining outdoor scenes, we have found that the nature of calibration, pupil identification, fixation detection, and gaze analysis all require procedures different from those typically used for indoor studies. Here, we discuss each of these challenges and present solutions, which together define a general method useful for investigations relying on outdoor eye-tracking data. We also discuss recommendations for improving the tools that are available, to further increase the accuracy and utility of outdoor eye-tracking data

Petrology of Diogenite NWA 5480, A Pristine Olivine-Rich Deformed Harzburgite

Diogenites are achondrites that are part of the HED (howardite, eucrite, diogenite) meteorite group thought to originate from asteroid Vesta. This suite of igneous rocks offers a glimpse of early planetary differentiation and subsequent igneous processes. While eucrites represent asteroidal basaltic crust and howardites the impact brecciated surface, diogenites are samples of the mantle and lower crust. Most of them are orthopyroxene (Opx) dominated cumulates, although harzburgites and rare dunites have also been found. The majority of diogenites are impact breccias. This study describes NWA 5480, a pristine, i.e. hardly altered and minimally shocked, harzburgitic diogenite

Palaeoclimate - A balmy Arctic

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62910/1/432814a.pd

Detrital magnetite and chromite in Jack Hills quartzite cobbles: Further evidence for the preservation of primary magnetizations and new insights into sediment provenance

AbstractThe magnetization of zircons from sedimentary rocks of the Jack Hills (Yilgarn Craton, Western Australia) provide evidence for a Hadean to Paleoarchean geodynamo, 4.0 to 4.2 billion years old. These magnetizations pass a microconglomerate test, attesting to the fidelity of Jack Hills zircons as recorders of these most ancient magnetic signals. The lack of pervasive remagnetization of the Jack Hills is also documented through a positive conglomerate test conducted on cobble-sized clasts. A key element of the latter test is the preservation of a high unblocking temperature magnetization that can survive peak metamorphic temperatures. Rock magnetic studies suggest the mineral carrier is magnetite. Herein, we investigate the magnetic mineral carriers in cobble samples through scanning electron microscope and microprobe analyses, conduct an inter-laboratory paleomagnetic study to evaluate sensitivities required to evaluate the weak magnetizations carried by the Jack Hills sediments, and assess provenance information constrained by the opaque minerals. These data confirm magnetite as a detrital phase and the presence of high unblocking temperature magnetizations, further supporting the posit that the Jack Hills sediments can preserve primary magnetic signatures. We note that some of these magnetizations are near the measurement resolution of standard cryogenic magnetometers and thus exacting laboratory procedures are required to uncover these signals. In addition to magnetite, the cobbles contain an assemblage of Mg poor Cr–Fe chromites, Ni-sulfides and pyrrhotite that suggest a source in a layered intrusion different from the granitoid source of the zircons. Any Hadean rock fragment in these sediments, if present, remains elusive

Hotspot motion caused the Hawaiian-Emperor Bend and LLSVPs are not fixed

Controversy surrounds the fixity of both hotspots and large low shear velocity provinces (LLSVPs). Paleomagnetism, plate-circuit analyses, sediment facies, geodynamic modeling, and geochemistry suggest motion of the Hawaiian plume in Earth's mantle during formation of the Emperor seamounts. Herein, we report new paleomagnetic data from the Hawaiian chain (Midway Atoll) that indicate the Hawaiian plume arrived at its current latitude by 28 Ma. A dramatic decrease in distance between Hawaiian-Emperor and Louisville chain seamounts between 63 and 52 Ma confirms a high rate of southward Hawaiian hotspot drift (similar to 47 mm yr(-1)), and excludes true polar wander as a relevant factor. These findings further indicate that the Hawaiian-Emperor chain bend morphology was caused by hotspot motion, not plate motion. Rapid plume motion was likely produced by ridge-plume interaction and deeper influence of the Pacific LLSVP. When compared to plate circuit predictions, the Midway data suggest similar to 13 mm yr(-1) of African LLSVP motion since the Oligocene. LLSVP upwellings are not fixed, but also wander as they attract plumes and are shaped by deep mantle convection