کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4742817 1641584 2008 14 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Correcting distorted paleosecular variation in late glacial lacustrine clay
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات فیزیک زمین (ژئو فیزیک)
پیش نمایش صفحه اول مقاله
Correcting distorted paleosecular variation in late glacial lacustrine clay
چکیده انگلیسی
An undisturbed, horizontal chronostratigraphic marker horizon of laminated red glacio-lacustrine clay crops out over ∼25,000 km2 in northern Ontario, Canada. The primary, clastic hematite laminae possess two stable vector components of magnetization. We sampled a 1.6 m vertical section at overlapping 2 cm intervals in cubic specimens (8 cm3, n = 106), precisely oriented in geographic coordinates which permitted measurement of inclination and declination. Alternating field demagnetization (12-17 steps per specimen) isolated a characteristic (ChRM), primary component (coercivity ≥40 mT) approximately 30° shallower than the mean geomagnetic field inclination at this latitude, with distorted paleosecular secular variation (PSV). A lower coercivity overprint (20-40 mT) is 6° shallower than the present geomagnetic field and similarly inclined to the depositional-remanence deflection when the clay was re-sedimented in the laboratory. We believe this angle to be representative of the inclination of the deflected primary remanence inclination during deposition, caused by the magnetic anisotropy of the clay. Using this as a proxy for the initial inclination, the ChRM (hard-component) inclinations were restored to their original values assuming vertical compaction, which averages to 51%. The restored inclinations are compatible with site-latitude and the restored secular-variation loops centre reasonably on the geographic North Pole. The structural correction based on homogeneous vertical shortening over-simplifies the reality of heterogeneous particulate flow in which grain rotations depend on shape, size and packing and effectively combines influences of compaction and depositional settlement. Nevertheless, this correction makes the PSV data more useful and interpretable in terms of paleopole migration. The more logical correction technique using anisotropy of anhysteretic remanence (AARM; Jackson, M.J., Banerjee, S.K., Marvin, J.A., Lu, R., Gruber, W., 1991. Detrital remanence, inclination errors, and anhysteretic remanence anisotropy: quantitative model and experimental results. Geophys. J. Int. 104: 95-103) is foiled here due to the high-coercivity of the remanence-bearing grains and their unknown orientation-distribution and shape-distribution.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Physics of the Earth and Planetary Interiors - Volume 166, Issues 1–2, January 2008, Pages 30-43
نویسندگان
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