This paper reports new Ordovician paleomagnetic results from the Aksu-Kalpin-Bachu area of the Tarim Block. Based on the systematic study of rock magnetism and paleomagnetism with limestone, argillaceous limestone, and argillaceous sandstone specimens from 44 sampling sites, all the samples could be divided into two types: the predominant magnetic minerals of the first type are hematite and subordinate magnetite. For the specimens from this type, characteristic remanent magnetization (ChRM) could generally be isolated by demagnetization temperatures larger than 600 degrees C; we assigned this ChRM as component A; whilst magnetite is the predominant magnetic mineral of the second type; progressive demagnetization yielded another ChRM (component B) with unblocking temperatures of 550 similar to 570 degrees C. The component A obtained from the majority of Ordovician specimens has dual polarity and a negative fold test result; we interpreted it as a remagnetization component acquired during the Cenozoic period. The component B can only be isolated from some Middle-Late Ordovician specimens with unique normal polarity, and has a positive fold test result at 95% confidence. The corresponding paleomagnetic pole of this characteristic component is at 40.7 degrees S, 183.3 degrees E with dp/dm=4.8 degrees/6.9 degrees and is in great difference with the available post-Late Paleozoic paleopoles for the Tarim Block, indicating that the characteristic component B could be primary magnetization acquired in the formation of the rocks. The new Ordovician paleomagnetic result shows that the Tarim Block was located in the low- to intermediate- latitude regions of the Southern Hemisphere during the Middle-Late Ordovician period, and is very likely to situate, together with the South China Block, in the western margin of the Australian-Antarctic continents of East Gondwana. However, it may have subjected to a large northward drift and clockwise rotation after the Middle-Late Ordovician period, which resulted in the separation of Tarim from the East Gondwanaland and subsequent crossing of the paleo-equator; by the Late Carboniferous period the Tarim Block may have accreted to the southern margin of the Altaids.
