paleozoic geography

موضوع: paleozoic geography 2007-11-08, 9:11 pm

Paleozoic Geography

Since the continental cratons all move with respect to each other, we need to pick an East-West point of reference to keep things straight. Paleozoic paleocartographers have somehow fallen into the habit of placing this reference longitude slightly east of Greenland. For most of the Paleozoic, Greenland remained close to the equator and, after Baltica sutured to Laurentia (North America plus Greenland) during the Silurian, this longitude came to correspond quite closely to the longitude of the future Greenwich, England, which defines the present conventional 0° longitude line. We will adopt this convention, although it is important to understand that it's just a convention. We have no absolute measures of East-West continental drift, and must be content with noting movements relative to some arbitrary geographical point.

The early Paleozoic saw many of the continents clustered around the equator, with Gondwana (representing the bulk of old Rodinia) slowly drifting south across the South poles, and Siberia, Laurentia (North America plus Greenland) and Baltica converging in the tropics. There was a large ocean between Laurentia and Eastern Gondwanaland.

It seems that Gondwanaland underwent a large clockwise rotation around an axis close to Australia during the Early Paleozoic. Laurentia underwent a large eastward movement, as well as a northward drift.

Baltica joined with Laurentia during the Silurian, drifting from a moderate southern hemisphere position in Cambro-Ordovician time to an equatorial position in Silurian-Devonian time. The combined continent is sometimes referred to as Euramerica, Laurasia, or Laurussia. Siberia, and possibly the Kazakhstan terranes, drifted across the equator to the northeast. All the East and Southeast Asian terranes, as well as the microcontinents which later formed Mexico, the east coast of North America, and southern Europe, were still part of the north coast (India-Australia margin) of Gondwana during the Early Palaeozoic.

During the middle and late Paleozoic (Devonian to Permian), about a third of the Gondwanan mass was torn into small pieces and moved rapidly to equatorial regions. Most of these blocks were assembled by a series of plate collisions into the supercontinent of Euramerica by the Devonian, which by addition of further landmasses became Laurasia by the late Carboniferous. Most of western Gondwana (South America and Africa), then rotated clockwise and moved northward to collide with Laurasia. By Permian time, Siberia and the Kazakhstan terranes were sutured to Euramerica (Laurussia) and the Chinese blocks started accreting to them. The result was the supercontinent Pangaea.

موضوع: رد: paleozoic geography 2007-11-10, 11:07 am

thanks so much

good topic

موضوع: رد: paleozoic geography 2007-12-09, 5:56 pm

تعرف هي حلوة قوي بس الدكترة بيجيبوا حجات مختلفة عن دي

موضوع: شكرا 2007-12-17, 9:09 pm

شكرا يا جماعة على الردود الجميلة ديه وعلى فكرة الدكاترة بيجيبوا نفس الكلام دهبس بطريقة تانية............. afro