Reviewers list 2007

Abstract

Continental Triassic sediments with good fossil control have been sampled in two thick sections (Hancheng, 35.5°N, 110.2°E and Tongchuan, 35.2°N, 109.1°E) from the southern margin of the Ordos basin, Shaanxi Province, China. Detailed analysis of 633 samples coming from 69 sites has been carried out with progressive alternating field and/or thermal demagnetization. Most sites display a low unblocking temperature component up to 200–400°C, which is undistinguishable from the Present Earth Field (PEF) direction, and a characteristic component with higher unblocking temperature with both normal and reversed polarity, which differs from the PEF and later Mesozoic paleomagnetic directions. The pole position from the lower Triassic part of the Hancheng section is at 61.9°N, 348.3°E (A95 = 3.8°, N = 16 sites). The directions of the characteristic magnetization of the middle Triassic sites from the Tongchuan section pass the fold test and are consistent with those from middle Triassic sites of the Hancheng section, giving a mean paleopole at 59.8°N, 359.9°E (A95 = 4.0°, N = 17 sites). The late Triassic sites from the Tongchuan section yield a pole at 62.3°N, 7.7°E (A95 = 3.8°, N = 11 sites). The early Triassic pole from the Ordos basin is consistent with poles obtained from Shanxi province. A late Permian to late Triassic apparent polar wander path of the North China block (NCB) is proposed. It is found that poles from the NCB and from the two adjacent blocks (South China block and Siberia) were widely separated until at least the end of the Triassic, pointing to major motion between the blocks probably during the Jurassic. At the end of the Triassic, the two Chinese blocks were already at similar latitudes but still were to undergo a 78 ± 28° relative rotation. Both were some 38 ± 4° to the south of Siberia (calculated for a reference point at 45°N, 115°E on the NCB/Siberia boundary).