A Cretaceous pole from south China, and the Mesozoic hairpin turn of the Eurasian apparent polar wander path

Abstract

To contribute to the apparent polar wander path (APWP) of the South China Block and Eurasia in general, we collected paleomagnetic samples from Mesozoic red beds around the city of Ya' an (30°N, 103°E) in the western tip of the Sichuan Basin. In this paper we present the results from 373 oriented cores taken from one section representing 3 km of sedimentary rocks. The section is dated with continental ostracods and with a magnetostratigraphic correlation between a densely sampled 272‐m sequence and the polarity time scale, giving an upper Jurassic to Upper Cretaceous or Lower Tertiary age. The remanent direction is remarkably stable throughout the section (D=2.0°, I=34.2°, k=63.1,α95=3.6°, N=26/28 sites). While this fact might suggest that the section has been remagnetized, paleomagnetic and rock magnetic tests indicate that the remanence is primary. The pole position (78.6°N, 273.4°E, dp=2.4°, dm=4.1°) corresponds to a rather low paleolatitude (λ=18.8°±2.4°) but is consistent with other Cretaceous poles from China. If one accepts the Eurasian APWP of Irving and Irving (1982), this result would imply that more than 1000 km of shortening took place between South China and Eurasia, following the acquisition of the remanence. However, there is no geological evidence for this large shortening. We propose that the remanence was acquired within the time corresponding to the tip of the hairpin turn (∼150–50 Ma) in the revised APWP of Besse and Courtillot (this issue). The local geology suggests that the syncline from which the samples were taken has been rotated by 15°±5° counterclockwise, which is reflected in a similar discrepancy between the measured paleodeclination and that predicted by the Besse and Courtillot (this issue) Eurasian APWP. After correcting for this rotation, the pole position is 70.9°N, 225.2°E (dp=2.4°, dm=6.5°). We conclude that Eurasia was fully assembled by the end of the Jurassic and that the Mesozoic Eurasian hairpin turn is a real feature.

Longmen Shan fold-thrust belt and its relation to the western Sichuan Basin in central China: New insights from hydrocarbon exploration

“…Location is shown on Figures 1 and 11. strata is well known with magnetic-polarity stratigraphy (Zhuang et al, 1988;Enkin et al, 1991) and biostratigraphic data (BGMRSP, 1991;Gu and Liu, 1997), we interpret the main growth interval to lie between the near-top Cretaceous and the Oligocene. Eastward, only poorly developed growth strata are observed in seismic profiles, including some unclear reflectors that onlap the forelimbs of the anticlines.…”

Anomalously shallow inclination in middle-northern part of the South China block: palaeomagnetic study of Late Cretaceous red beds from Yichang area

“…Good correlation among the amount of inclination flattening, the degree of anisotropy and sedimentary facies indicates that the depositional processes produced the observed shallow inclination in the Yichang area. Because the far‐sided pole position (78.6°N, 273.4°E, dp / dm = 2.4°/4.1°) is reported from Cretaceous red beds in the Sichuan basin in the SCB (Otofuji et al 1990; Enkin et al 1991a,b), further palaeomagnetic and rock magnetic studies are required to study the shallowing effect in this basin.…”

Inclination variation in the Late Jurassic to Eocene red beds from southeast Asia: lithological to locality scale approach

“…1, locality-based variation in inclination shallowing has been observed in the Cretaceous red beds of the South China Block (SCB). Although, inclination shallowing has not been detected in the coastal area of the SCB (Morinaga & Liu 2004;Zhu et al 2006), anomalously large shallowing has been reported from the Sichuan Basin of the same block (Otofuji et al 1990;Enkin et al 1991a). Following these observations, demand for further investigations became high to trace local origin of the inclination shallowing.…”

“…2006), anomalously large shallowing has been reported from the Sichuan Basin of the same block (Otofuji et al . 1990; Enkin et al . 1991a).…”