Volcanic Stratigraphy and Age Model of the Kimama Deep Borehole (Project Hotspot): Evidence for 5.8 Million Years of Continuous Basalt Volcanism, Central Snake River Plain, Idaho

The Snake River Plain of central Idaho represents the world’s best example of a mantle hotspot track impinging upon continental crust and provides a record of bimodal volcanism extending over 12 Ma to the present. Project Hotspot recovered almost 2 km of continuous drill core from the Kimama borehole, located in central Idaho on the axial volcanic zone. The Kimama drill core represents the most complete record of mafic volcanism along the Yellowstone–Snake River Plain hotspot track. A total of 432 basalt flow units, representing 183 basalt flows, 78 basalt flow groups, and 34 super groups, along with 42 sediment interbeds are recognized using volcanic facies observations, stratigraphic relationships, borehole geophysical logs, and paleosecular variation in magnetostratigraphy. Rhyolite and other non-basaltic volcanic materials were not encountered in the drill core. Ages for six basalt lava flows were determined by 40Ar/39Ar using incremental heating experiments. Paleomagnetic inclination was measured on over 1200 samples collected at roughly 2-m-depth intervals, yielding mean values of paleosecular variation between ±50° to ±70° in Kimama flow groups, close to the expected 61° axial dipole average for the Kimama borehole location. Twenty-three magnetic reversals were identified and correlated to dated geomagnetic chrons and subchrons and compared with the 40Ar/39Ar radiometric ages. A linear fit to 40Ar/39Ar dates, geomagnetic chron and subchron boundaries, and volcanogenic zircon U-Pb ages defines a mean accumulation rate of ∼320 m/m.y. and extrapolates to a bottom hole age of 6.3 Ma. Average thicknesses of lithologic units increase from 2.7 m (sediment), 4 m (flow units), 10 m (flows), 23 m (flow groups), to 53 m (super groups). On average, one lava flow inundated the Kimama borehole location every 33 k.y. Intercalated sediments, ranging from 0.06 to 24.5 m thick, make up roughly 6% of the drill core and indicate lulls in local volcanic activity that may have lasted up to 77 k.y. Neutron and gamma-ray logs supplement observations from the drill cores: neutron logs document individual flow units through the contrast between massive flow interiors and more porous flow surfaces, and gamma-ray logs document the depth and thickness of sedimentary interbeds and high–K-Fe basalts. The 5.8 m.y. duration of basaltic volcanism in the Kimama drill core implies a steady rate of volcanism, indicating a relatively stable rate of mantle upflow along the lithosphere-mantle boundary in the wake of Yellowstone–Snake River Plain plume volcanism

Climate Science Special Report: Fourth National Climate Assessment (NCA4), Volume I

New observations and new research have increased our understanding of past, current, and future climate change since the Third U.S. National Climate Assessment (NCA3) was published in May 2014. This Climate Science Special Report (CSSR) is designed to capture that new information and build on the existing body of science in order to summarize the current state of knowledge and provide the scientific foundation for the Fourth National Climate Assessment (NCA4)

Holocene geomagnetic secular variation in the western United States : implications for the global geomagnetic field

A record of Holocene geomagnetic secular variation in the western United States has been measured from volcanic rocks dated by ^(14)C. Analysis of errors associated with the paleomagnetic techniques used suggests that all laboratory measurement errors are smaller than those introduced by deformation of the volcanic units and the errors of orientation of cores in the field. The dispersion in the calculated virtual geomagnetic poles introduced by the geographic spread of sample localities around the western United States is less than the average uncertainty from an individual locality, about 2 deg. The history of secular variation of field direction in the western United States has been reconstructed where sufficient time control exists. This history can be approximately reconstructed for the past 3000 years; in this time period, inclination varied from 44 to 72 deg and declination varied from 344 to 22 deg. These variations of the local field direction have periods between 500 and 1500 years. Prior to 3000 years B.P., the available observations allow reconstruction of the secular variation history only for short time intervals. The mean VGP obtained from paleofield directions measured from 77 volcanic units of Holocene and late Pleistocene age in the western United States does not coincide with the geographic pole of the Earth, but is displaced 2.5 deg from the geographic pole in a direction away from the sampled region. This displacement is just at the limit of significance at 95 percent confidence. Using a 10^(-5) torr vacuum furnace, paleointensities have been obtained by the Thelliers' method from both high-temperature oxidized and unoxidized basic volcanic rocks. Specimens which have undergone incomplete high-temperature oxidation in nature commonly fail the Thellier experiment; the relationship between NRM lost and TRM gained in a known magnetic field is not linear. Despite the vacuum, oxidation can still occur above 300°C in the furnace ovens. The best determinations of paleointensity come from specimens in which the remanence resides primarily in single phase titanomagnetite or in intergrowths of Ti-poor magnetite in ilmenite which have been formed by natural high-temperature oxidation. Paleointensity determined from these specimens varies from 0.364 x 10^(-4) to 0.865 x 10^(-4) T (1.0 x 19^(-4) T = 1 Oe); the period of oscillation of paleointensity is about 500 to 1000 years. Close agreement has been found between the paleointensity measurements from this study and those from archeomagnetic studies in the southwestern United States. The similarity of the periods of intensity variation to those of field direction changes may indicate that variations of the nondipole components of the geomagnetic field dominate both. By combining paleomagnetic and archeomagnetic data from globally distributed localities, the magnetic dipole can be shown to have wobbled with a period as short as 2000 years. Local variation of the field can be described as the consequence of fluctuation of the dipole moment, wobble of the dipole, and longitudinal drift of a nondipole field similar to that of the present. During the Holocene, the dipole moment of the Earth has fluctuated with a period of approximately 8000 years, though when viewed from a single region, the fluctuation of the dipole moment is obscured by variation of nondipole components of the field

Palaeomagnetic intensity from 14C-dated flows on the Big Island, Hawaii: 0-21kyr

Thellier–Thellier experiments were carried out on 216 lava samples collected by the USGS on the Big Island. 35 individual flows from the Kilauea, Mauna Loa and Hualalai volcanoes are represented and independent radiocarbon dating of the flows yields absolute ages ranging from 290 to 20,240 yrs old. The palaeomagnetic analysis was carried out at the Laboratoire des Sciences du Climat et de l'Environnement in Gif-sur-Yvette, France, in two custom built, large capacity furnaces that have been specifically designed to minimise oxidation. The temperature steps were adapted to accommodate the characteristic loss of magnetisation at low temperatures seen in the Curie balance results and the use of half-size samples allowed secondary experiments to be carried out where necessary. The strict PICRIT-03 selection criteria were rigorously applied to the data and a high success rate of 53% has been achieved on a sample level. The flow averaged results almost double the existing 14C-dated palaeointensity dataset for this time window and confirm a period of high intensity over the past 4 kyr preceded by a period in which the dipole moment was weaker. However, the values attained in this study are on average higher than previously published data; reliability of these values is discussed.<br/

How Old is "Cinder Cone" - Solving a Mystery in Lassen Volcanic Park, California

This United States Geological Survey (USGS) on-line publication highlights the controversy surrounding the age of Cinder Cone volcano in Lassen Volcanic National Park. This report follows the beginning of the controversy in the 1870s through recent discoveries about when the volcano was formed. Early geologic studies are covered, as well as the recent findings through paleomagnetism, field and laboratory work and by reinterpreting data from previous studies. Educational levels: High school, Undergraduate lower division, Undergraduate upper division

Comparison and Renormalization of Holocene Paleointensity Records From Central North America (17°N–51°N, 205°E–295°E)

This paper develops a composite absolute paleointensity record for Holocene paleomagnetic secular variation (PSV) from central North America. Twelve full-vector (inclination, declination, paleointensity) PSV records were assessed in order to build the composite record. Nine of the paleointensity records come from sediment paleomagnetic studies and are considered relative in intensity. Three of the paleointensity records come from absolute paleointensity measurements of archeological materials and lava flows. This paper develops a new method to normalize the sediment relative paleointensity records to the absolute intensity records. The final composite paleointensity record describes intensity variability over a region of Central North America delineated by 35°–48.6°N and 240.4–291.4°E (∼14° × 50°). This composite record shows a distinctive long-duration (∼104 year) oscillation and a series of millennial-scale intensity oscillations that are consistent over our study region

Embedded Fragments from U.S. Military Personnel—Chemical Analysis and Potential Health Implications

Background: The majority of modern war wounds are characterized by high-energy blast injuries containing a wide range of retained foreign materials of a metallic or composite nature. Health effects of retained fragments range from local or systemic toxicities to foreign body reactions or malignancies, and dependent on the chemical composition and corrosiveness of the fragments in vivo. Information obtained by chemical analysis of excised fragments can be used to guide clinical decisions regarding the need for fragment removal, to develop therapeutic interventions, and to better anticipate future medical problems from retained fragment related injuries. In response to this need, a new U.S Department of Defense (DoD) directive has been issued requiring characterization of all removed fragments to provide a database of fragment types occurring in combat injuries. Objectives: The objective of this study is to determine the chemical composition of retained embedded fragments removed from injured military personnel, and to relate results to histological findings in tissue adjacent to fragment material. Methods: We describe an approach for the chemical analysis and characterization of retained fragments and adjacent tissues, and include case examples describing fragments containing depleted uranium (DU), tungsten (W), lead (Pb), and non-metal foreign bodies composed of natural and composite materials. Fragments obtained from four patients with penetrating blast wounds to the limbs were studied employing a wide range of chemical and microscopy techniques. Available adjacent tissues from three of the cases were histologically, microscopically, and chemically examined. The physical and compositional properties of the removed foreign material surfaces were examined with energy dispersive x-ray fluorescence spectrometry (EDXRF), scanning electron microscopy (SEM), laser ablation inductively-coupled plasma mass-spectrometry (LA-ICP-MS), and confocal laser Raman microspectroscopy (CLRM). Quantitative chemical analysis of both fragments and available tissues was conducted employing ICP-MS. Results: Over 800 fragments have been characterized and included as part of the Joint Pathology Center Embedded Fragment Registry. Most fragments were obtained from penetrating wounds sustained to the extremities, particularly soft tissue injuries. The majority of the fragments were primarily composed of a single metal such as iron, copper, or aluminum with traces of antimony, titanium, uranium, and lead. One case demonstrated tungsten in both the fragment and the connected tissue, together with lead. Capsular tissue and fragments from a case from the 1991 Kuwait conflict showed evidence of uranium that was further characterized by uranium isotopic ratios analysis to contain depleted uranium. Conclusions: The present study provides a systematic approach for obtaining a full chemical characterization of retained embedded fragments. Given the vast number of combat casualties with retained fragments, it is expected that fragment analysis will have significant implications for the optimal short and long-term care of wounded service members