Title: 23. JURASSIC TO PALEOCENE PALEOLATITUDES OF THE PACIFIC PLATE DERIVED FROM THE PALEOMAGNETISM OF THE SEDIMENTARY SEQUENCES AT SITES 800, 801, AND 8021
Abstract: The remanent magnetizations contained in the three sedimentary sections recovered by Leg 129 are of relatively strong intensities and have notably minor amounts of secondary magnetization. Both alternating field and thermal demagnetization techniques readily separate magnetization components, resulting in remanent directions that are exceptionally single component at the higher stages of demagnetizati on. In all types of lithology, the magnetization is carried by a mineral with blocking temperatures below 570°C, presumably a member of the titanomagnetite series. The resulting inclinations are generally very consistent among samples from the same time periods. Substantially incomplete recovery at each site, a result of the disruptive effect on coring and recovery in mixed sediments of chert interspersed with calcareous and clayey sediments, prevented reconstruction of complete magnetostratigraphic records from these sedimentary sequences. The inclination records from the three holes provide a relatively continuous history of the paleolatitudinal motion of the oldest portion of the Pacific plate from the Campanian stage of the Late Cretaceous to the Callovian/Bathonian boundary of the Middle Jurassic; data of somewhat lessor quality were also obtained for the early Miocene through Paleocene. All data indicate that this embryonic portion of the Pacific plate was in southern paleolatitudes from the Middle Jurassic to the Late Cretaceous and probably crossed the equator between the Turonian and the late Paleocene. These data suggest that during the Late Jurassic and Cretaceous, the plate was never too far from the equator, varying between about 20°S and equatorial latitudes. If the phenomenon of inclination error is operative in these sediments, as has been claimed for many oceanic sediments, then obviously the plate was at higher southern latitudes than indicated by these data. However, qualitative estimates of paleolatitudes from nannofossil abundances (Erba, this volume) indicate paleolatitudes quite similar to those calculated from the remanent inclinations. Moreover, calculations of expected inclination error from published analyses result in paleolatitudes much farther south than predicted by Seamount paleopoles or magnetic anomaly skewness. Therefore, the paleolatitudes determined from the inclinations recorded in the sediments of this study may represent approximately the true paleopositions of the Pacific plate.
Publication Year: 1992
Publication Date: 1992-01-01
Language: en
Type: article
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Cited By Count: 11
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