| mhorn | Дата: Saturday, 28.07.2012, 11:12 | Сообщение # 1 |
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| Iglesia Llanos M.P. (2012) Palaeomagnetic study of the Jurassic from Argentina: magnetostratigraphy and palaeogeography of South America // Revue de Paléobiologie, Vol. spéc. 11: 151-168
Pdf http://www.ville-ge.ch/mhng/paleo/paleo-pdf/spec-11/pal-spec-11-12.pdf
A palaeomagnetic study has been carried out in five Lower Jurassic sections from the Neuquén basin, made up mainly of ammonitebearing sedimentary and, subordinately, volcanic rocks. Sampled sections are located to the north of the basin, along the Atuel river (Hettangian to Toarcian) and to the centre (Pliensbachian to Toarcian) of the basin. The palaeomagnetic study shows two magnetic components carried by titanomagnetites, one soft with a direction in coincidence with the local dipolar field, and another harder that is interpreted as the original Jurassic based on the field tests for palaeomagnetic stability. From the polarity successions obtained in each locality, a composite magnetostratigraphic scale for the Southern Hemisphere has been constructed. The resultant scale bears 11 zones of dominant reverse polarity (JR1 to JR 11), and 12 zones of dominant normal polarity (JN1 to JN12), which have been tied to 19 ammonite zones of the Andean Region. The regional scale has, in turn, been correlated to the international geomagnetic time scale. A good fit between the two scales is observed, allowing to date intervals with no diagnostic fossils. On the other hand, two palaeomagnetic poles have been calculated, one for the Hettangian-Sinemurian interval (223°E, 51°S, A95= 6°, N = 25) and the other for the Pliensbachian-Toarcian (67°E, 74°S, A95= 5°, N = 52). Such poles were combined with others from the literature to obtain the apparent polar wander (APW) path for South America, which turns out to be remarkably dissimilar from the classical ones that show the continent in a stationary position throughout the Mesozoic. From the new APW path, it has been interpreted that South America may have rotated clockwise while it moved to the north. Eurasia’s path is also presented in this study, revealing the same shape and chronology of tracks. These latitudinal changes that we observed from the palaeomagnetic data are supported by palaeoecological data.
Middle Jurassic - Lower Cretaceous ammonites & aptychi
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