E/I-corrected inclination shallowing in Cenozoic redbeds from the northern Tarim Basin, NW China: Possible causes and paleogeographic implications

Abstract

AbstractBecause of their widespread occurrence and ability to carry stable remanence, continental redbeds in central Asia are frequently used in paleomagnetic studies. However, the paleomagnetic inclinations recorded by redbeds are much shallower than the expected values, as redbeds are usually subjected to inclination shallowing. To recognize and correct the inclinations recorded by the Cenozoic redbeds, the paleomagnetic data that were used for magnetostratigraphic studies in the Kuqa Depression, northern Tarim Basin, are reanalyzed in this study. The mean inclinations of the four groups of samples (Eocene, Oligocene, Miocene, and Pliocene) are systematically ~20° shallower than the expected values calculated from the apparent polar wander paths (APWPs) of Eurasia, indicating the presence of inclination shallowing. We apply the elongation/inclination (E/I) method to correct the inclination shallowing. The mean inclinations of the Eocene, Oligocene, Miocene, and Pliocene sediments are corrected from 40.5° to 63.1°, 41.0° to 63.8°, 42.0° to 63.8°, and 44.7° to 63.2°, within 95% confidence limits between 55.1° and 71.6°, 53.7° and 70.4°, 51.5° and 72.7°, and 52.2° and 71.3°, respectively, which are indistinguishable from the expected inclination values. Our results suggest that inclination shallowing in the redbeds of central Asia can be reasonably corrected using the E/I method, and sedimentary processes such as compaction and/or imbrication in the very early stage of burial are important causes for inclination shallowing. Paleolatitudes calculated from the E/I-corrected inclinations show that the Tarim Basin should have reached or been at least close to its current latitude since the Cretaceous. The Cenozoic crustal shortening estimate of the northern Tarim Basin is not detectible for paleomagnetic study.