Paleomagnetism is the study of ancient pole positions and also makes use of remanent magnetization to rebuild the direction and strength the the geomagnetic ar in the past.
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From: planet as an Evolving Planetary device (Second Edition), 2011
T.H. Torsvik, in Encyclopedia the Geology, 2005
Palaeomagnetism and Palaeogeography: the large Picture
Quantitative reconstructions space most commonly derived indigenous hotspot traces (Cretaceous–Tertiary times) and ocean-floor magnetic anomalies, but prior come the more quickly in situ ocean floor preserved today (approximately 175 Ma), the placing of continents have the right to only it is in quantitatively well-known by palaeomagnetism. Together longitude is unknown indigenous palaeomagnetic data, the identification and also discrimination of faunas and also floras deserve to indicate that continents with similar faunas were in proximity to one another; conversely, different faunas that the same period can suggest the separation the the continents.
In order to construct a an international palaeogeographical map, palaeomagnetic data native individual continent or terranes must be compiled and evaluated in terms of reliability. At any kind of given time, palaeomagnetic data may not exist for all continents and added criteria, such together fauna, flora, facies, and also tectonic and magmatic history, should be included in stimulate to build rational maps. Number 10 illustrates an early Ordovician (490–470 Ma) reconstruction; that does not show all the continent or terranes that existed at this time, yet some major players, such together Gondwana, Baltica, Laurentia, and some selected peri-Gondwanan terranes v palaeomagnetic and/or faunal data (Avalonia, Armorica, Perunica, and Taurides). No all the Gondwanan continents have actually reliable palaeomagnetic data because that this time. However, Gondwana to be amalgamated at around 550 Ma and continental elements, such as southern America and India (no palaeomagnetic data), remained attached to Africa until the breakup the the Pangea supercontinent throughout the Mesozoic.
Figure 10. Reconstruction for early Ordovician time (490–470 Ma) through the major terranes and also some crucial Arenig–Llanvirn trilobite faunas. Laurentia (located at the equator) has North America, Greenland, and also the brother Isles north of the Iapetus Suture. Baltica (intermediate southerly latitudes) contains most the Scandinavia and also Russia eastwards to the Urals. The core of Gondwana consists of Africa, Arabia, Madagascar, greater India, most of Antarctica, most of Australia, Florida, and also most of south America. Gondwana developed at about 550 Ma and also covered more than 90° that latitude in the early Ordovician. Gondwanan dispersal history commenced with the rifting turn off of Avalonia in ~ ca. 465 Ma. Avalonia contains the brothers Isles and north-west Europe south of the Iapetus Suture, eastern Newfoundland, most of the maritime Provinces the Canada, and also parts of the eastern USA. Armorica contains the Armorican Massif the Normandy and also Brittany, the Massif Central, and the Montagne Noire areas of France, in addition to parts that the Iberian Peninsula. Perunica comprises the area north of the Barrandian container of Bohemia. The Taurides comprises most of main and southerly Turkey.
An integrated approach of palaeomagnetic and also faunal analysis is applicable because that the whole Phanerozoic, however works ideal for the early on Palaeozoic and, notably, the early Ordovician (Figure 10). In ~ this time, Gondwana extended from the southern pole (Africa) to the equator (Australia and also East Antarctica), Baltica occupied intermediate southerly latitudes, be separate by the Tornquist Sea, whereas Laurentia straddled the equator. Laurentia to be separated indigenous both Baltica and Gondwana by the Iapetus ocean that had opened in the late Precambrian. The Iapetus s (approximately 5000 km across the british sector) and the Tornquist Sea (approximately 1100 km in between southern Baltica and also Armorica–Perunica) to be at their widest. This is probably why benthic trilobites indigenous Laurentia (bathyurid) and also north-west Gondwana (calymenacean–dalmanitacean) are so markedly various from those the Baltica (megalaspid).
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In summary, palaeomagnetism can be seen to be the best and only quantitative an approach to create the location of old terranes and also continents together they drifted throughout the globe over geology time.