946 resultados para Extreme west of Paraná


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Diatom assemblages from the middle part of the Pliocene (3.2-2.5 Ma) were investigated from Ocean Drilling Program Sites 1016, 1021, and 1022 in an effort to infer paleotemperature fluctuations off California. Diatoms are very sparse in virtually all of the samples that were examined from Sites 1016 and 1021. This is presumably because these sites were seaward (west) of the coastal zone of diatom productivity during the middle part of the Pliocene. Diatoms are relatively common in the vast majority of samples that were examined from Hole 1022A. Diatom assemblages are dominated by Chaetoceros spores (a coastal upwelling component), the cold-water (subarctic) taxa Neodenticula kamtschatica and its descendant Neodenticula koizumii, and Thalassionema nitzschioides, a temperate taxon that is typically found at the seaward edge of coastal upwelling zones. Paleotemperature interpretations, however, are not possible at this time because of the scarcity of comparative modern core-top data.

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Magnetic field strength and magnetic susceptibility were logged with the geological high-resolution magnetic tool (GHMT) at three of the holes drilled during Ocean Drilling Program Leg 178 to the west of the Antarctic Peninsula. Polarity stratigraphies derived from the GHMT logs bear close resemblance to the polarities determined from core paleomagnetism at two of the holes and were used for magnetostratigraphic dating, especially in intervals where no core was recovered. Polarity is determined in the following way. First, the susceptibility log is used to determine the induced magnetization of the sediment. Then the background field, the field of the metal drill pipe, and the field anomaly of the sediment's induced magnetization are removed from the measured total field to leave the downhole anomaly of the sediment's remanent magnetization. The sign (positive or negative) of this anomaly gave a good polarity stratigraphy for Holes 1095B and 1096C, which are located in sediment drifts. A further step, correlation analysis, is based on the fact that in an interval of normal polarity sediment the remanent anomaly will correlate with the induced anomaly, whereas in reversed polarity sediment they will anticorrelate. The magnetite-rich, fine-grained sediments found in the two holes drilled into the sediment drift have a ratio of remanent to induced magnetization (the Koenigsberger ratio) of ~1. In contrast, the coarser-grained diamict sediments on the shelf have a Koenigsberger ratio of ~0.2, and extracting the remanent part of the downhole anomaly is much more difficult. By the comparison of core and log results, we can assess the viability of the GHMT polarities in detail, what proportion of the overprint in the cores is imparted by the coring process, and whether any paleointensity information is extractable from the GHMT logs.

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Petrographical and mineral chemistry data are described for the mist representative basement lithologies occurring as clasts (pebble grain-size class) from the CRP-1 drillhole. Most pebbles consits of either undeformed or foliated biotite with or without hornblende monzogranites. Other rock types include biotite with or without garnet syenogranitr, biotite-hornblende granodiorite, tonalite, monzogranitic porphyries, haplogranite, quartz-monzonite (restricted to the Quaternary section), Ca-silicate rocks and biotite amphibolite (restricted to the Miocene strata). The common and ubiquitous occurence of biotite with or without hornblende monzogranite pebbles, in both the Quaternary and Miocene sections, apparently mirrors the dominance of these rock types in the granitoid assemblages which are presently exposed in the upper Precambrian-lower Paleozoic basement of the south Victoria Land. The other CRP-1 pebble lithologies show petrographical features which consitently support a dominant supply from areas of the Transantarctic Mountains located to the west and south-west of the CRP-1 site, and they thus furthercorroborate a model of local provenance for the supply of basement clasts to the CRP-1 sedimentary strata.

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During cruises in the Norwegian Sea in 1969 and 1972 seven heat flow values were measured between Iceland and the Voring Plateau. The six eastern values of this profile show a positive trend east-southeastwards which coincides with a possible transition from oceanic to continental crust suggested by seismic results. One heat flow value taken near Iceland and 250 miles west of the others reflects the influence of the Mid-Atlantic Ridge. An estimation of the heat flow at a depth of 15 km below the measuring localities yields values with a small, possibly insignificant negative trend towards the east-southeast. The temperatures at 15 km depth are estimated to be 190 °C beneath the zone of seamounts and 280 °C beneath the Voring Plateau.

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Geophysical data acquired using R/V Polarstern constrain the structure and age of the rifted oceanic margin of West Antarctica. West of the Antipodes Fracture Zone, the 145 km wide continent-ocean transition zone (COTZ) of the Marie Byrd Land sector resembles a typical magma-poor margin. New gravity and seismic reflection data indicates initial continental crust of thickness 24 km, that was stretched 90 km. Farther east, the Bellingshausen sector is broad and complex with abundant evidence for volcanism, the COTZ is ~670 km wide, and the nature of crust within the COTZ is uncertain. Margin extension is estimated to be 106-304 km in this sector. Seafloor magnetic anomalies adjacent to Marie Byrd Land near the Pahemo Fracture Zone indicate full-spreading rate during c33-c31 (80-68 Myr) of 60 mm/yr, increasing to 74 mm/yr at c27 (62 Myr), and then dropping to 22 mm/yr by c22 (50 Myr). Spreading rates were lower to the west. Extrapolation towards the continental margin indicates initial oceanic crust formation at around c34y (84 Myr). Subsequent motion of the Bellingshausen plate relative to Antarctica (84-62 Myr) took place east of the Antipodes Fracture Zone at rates <40 mm/yr, typically 5-20 mm/yr. The high extension rate of 30-60 mm/yr during initial margin formation is consistent with steep and symmetrical margin morphology, but subsequent motion of the Bellingshausen plate was slow and complex, and modified rift morphology through migrating deformation and volcanic centers to create a broad and complex COTZ.

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Hydrogenetic ferromanganese crusts were dredged from four seamounts in the western Pacific, OSM7, OSM2, Lomilik, and Lemkein, aligned in a NW-SE direction parallel to Pacific Plate movement. The crusts consist of four well-defined layers with distinct textural and geochemical properties. The topmost layer 1 is relatively enriched in Mn, Co, Ni, and Mo compared to the underlying layer 2, which is relatively enriched in Al, Ti, K, and Rb and Cu, Zn, and excess Ba. Textural and geochemical properties of layer 2 suggest growth conditions under high biogenic and detrital flux. Such conditions are met in the equatorial Pacific (i.e., between the Intertropical Convergence Zone (ITCZ) and equatorial high-productivity zone). Layer 2 likely formed when each seamount was beneath the equatorial Pacific along its back track path. On the other hand, layer 1 probably started to grow after seamounts moved northwest from the ITCZ. This interpretation is consistent with the thickness of layer 1 across the four crusts, which increases to the northwest. Ages of the layer 1-layer 2 boundary in each crust, a potential proxy for northern margin of the ITCZ, also increase to the northwest at 17, 11, 8, and 5 Ma for OSM7, OSM2, Lomilik, and Lemkein, respectively. Assuming Pacific Plate motion of 0.3°/Myr, the seamounts were located at 12°N, 11°N, 9°N, and 8°N at the time of boundary formation. This result suggests that the north edge of the ITCZ has shifted south since the middle Miocene in the western Pacific, which agrees with information from the eastern Pacific.

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Five sites were drilled on the Iberia Abyssal Plain, west of the Iberian Peninsula. Four holes (897C, 897D, 899B, and 900A) yielded Eocene sediments that consist of turbidites and contourites. The Eocene section above the continental crust at Site 900 is continuous (from nannofossil Zones NP10 to NP20) and considerably expanded because of the site's relatively shallow depth, which remained consistently above the carbonate compensation depth (CCD). Sites 897 and 898, situated in deeper water above the ocean/continent transition, on the other hand, have noncontinuous, relatively short Eocene sections (from Zones NP14 to NP20 at Site 897 and from Zones NP19 to NP20 at Site 899). Nannofossils are abundant, diverse, and moderately to poorly preserved; they provide the primary means of dating the Eocene sediments recovered during Leg 149.

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Built 1884. Used as boilerhouse until 1914 or 1994. Was south of original medical building, just west of present day West Engineering (West Hall)

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v.1. Lines east of the Mississippi River.--v.2. Lines in Iowa and Missouri.--v.3. Lines west of the Missouri River.

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Vol. 3 subtitled: Articles of incorporation, leases, mortgages, decrees, consolidations, deeds, trackage and depot contracts, and history of affiliated companies.

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No. 17 forms pt.2 (app.71) of the Annual report of the chief signal officer for the year 1885 (Annual report of the secretary of war ... 1885, vol. IV, pt. 2) It is issued also in the Congressional series, no. 2375 (49th Cong., 1st sess. House. Ex. doc.1, pt.2).

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A later edition, New York, 1849, published under title: The border warfare of New York, during the revolution; or, The annals of Tryon county.

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Taken two blocks west of central campus looking east

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Taken west of Division and Packard, looking east. On verso: University of Michigan News Service, 3528 Administration Bldg., Ann Arbor, Michigan 48104