568 resultados para 1259


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Ash layers from Deep Sea Drilling Project site 178 in the northeast Pacific Ocean have been dated by the 40Ar-39Ar stepwise heating technique to resolve published discrepancies concerning the length of time explosive volcanism has affected the eastern Aleutian arc and Alaskan Peninsula. The results of the investigation indicate that the record of ash-fall deposition at site 178 extends back at least 6.5 m.y. Assuming that 6.5 m.y. ago marks the onset of renewed calc-alkalic volcanism of the volcanic arc, proposed models of continuous and discontinuous motion between the Pacific and North American lithospheric plates can be evaluated. If appreciable time elapsed between the onset of subduction and the onset of arc volcanism, the 6.5-m.y. record of ash-fall deposition in the north-east Pacific is most compatible with models of continuous plate motion throughout late Cenozoic time.

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Secondary carbonate minerals were recovered within the basalts at both ODP Sites 768 and 770 in the Sulu and Celebes seas. Petrographic and X-ray diffraction analyses indicate that the carbonates are calcites. Other alteration products recognized in the thin sections are smectites, iron oxides, and gypsum. The 13C values of carbonates from both sites range from 1.6 per mil to 2.3 per mil, which are indicative of inorganic carbonate formation with no contributions from 13C-depleted sources such as oxidized organic carbon or methane. The oxygen isotopes at Site 770 range from 30.8 per mil to 31.6 per mil, which indicates a pervasive circulation of cold seawater (9° to 12°C) during alteration of the Celebes Sea basalts. In contrast, carbonates associated with Site 768 basalts have less positive d18O values (21.0 per mil to 27.3 per mil). A lighter 18O isotopic signature indicates the formation of secondary calcite at either higher temperatures or in a system closed to seawater. The rapidly deposited pyroclastic flows at Site 768 would have limited water access to the crust very soon after its formation, which leads us to speculate that the carbonates in the Sulu Sea basalts were formed by isotopically modified fluids resulting from basalt alteration in a closed system.

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Bibliographical foot-notes.

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Commentary on Vehbi's rhymed Arabic to Turkish vocabulary.

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Snorra-eddasvo-kl̈lud: Formáli. Gylfa-ginning. Bragarædur Epitirmáli.--Skádda: Kenningar. Okend helti. Fornöfn. Bragarhættir.--Málslistarrit: Latinu stafroñð. Málslistarrinnar grundvölir. Figúrur i ræunni. Viðrauki útgefarans.--Registur.

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"Abbreviatio chronicorum Angliae," v. 3, p. 151-348, erroneously attributed to Paris by the editor. cf. Dict. nat. biog.

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v.1. 1227-1231. -- v.2. 1231-1234. -- v.3. 1234-1237. -- v.4. 1237-1242. -- v.5. 1242-1247. -- v.6. 1247-1251. -- v.7. 1251-1253. -- v.8. 1253-1254. -- v.9. 1254-1256. -- v.10. 1256-1259. -- v.11. 1259-1261. -- v.12. 1261-1264. -- v.13. 1264-1268. -- v.14. 1268-1272.

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In 3 sections; the first, originally "to a great extent, from the pen of Matthew Paris"; the second, "a compilation by an anonymous hand"; the third, beginning with 1308, "undoubtedly the compilation of Thomas Walsingham". cf. v. 1, p. x.

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"A composite chronicle, containing the St. Albans compilation to the end of 1188, Roger de Wendover's chronicle, 1189-1235, both revised by Paris, and his own work from 1235 to 1259." -Dict. nat. biog.