|mhorn||Дата: Wednesday, 15.09.2010, 14:49 | Сообщение # 1|
|Meijers M.J.M., Langereis C.G., van Hinsbergen D.J.J., Kaymakcı N., Stephenson R.A., Demir A. (2010) Jurassic–Cretaceous low paleolatitudes from the circum-Black Sea region (Crimea and Pontides) due to True Polar Wander // Earth and Planetary Science Letters. Vol.296. P.210-226. |
In a recent study, paleomagnetic and paleoenvironmental data from Adria (as part of the African plate) suggest a trend toward much lower (15°) latitudes from Early Jurassic to Earliest Cretaceous at the position of Adria than suggested by the apparent polar wander (APW) paths. The smoothing of existing (APW) paths has most likely caused this low-latitude episode to be overlooked. In this study, we test if the low paleolatitudes in the Jurassic to Early Cretaceous can also be found in Eurasia, i.e. Crimea (Ukraine) and the Pontides (Turkey) that are situated in the present-day Black Sea region. Our Eurasian data suggest the same low Late Jurassic to Early Cretaceous paleolatitudes as shown for Africa. The Jurassic to Lower Cretaceous time span is characterized by Tethys subduction between the African and Eurasian continents and these subduction zones likely functioned as an anchor in the mantle. Therefore, we regard it unlikely that both the African and Eurasian plates moved by N1500 km south and subsequently north with respect to the mantle, as suggested by the paleomagnetic results. True polar wander (TPW) provides a mechanism that rotates the Earth's crust and mantle with respect to its core, and it was recently quantified. The period from 195–135 Ma (Early Jurassic to Earliest Cretaceous) is subject to clockwise TPW, which could well explain our results. We conclude that TPW rather than plate tectonics is the cause of low Late Jurassic to Early Cretaceous African and Eurasian paleolatitudes in the eastern Mediterranean area.
Middle Jurassic - Lower Cretaceous ammonites & aptychi