Inclination Shallowing Of The Early Cretaceous Red Beds In The Sichuan Basin

Totally eighteen orientated block samples of the Early Cretaceous red beds were collected from Bazhong and Ya'an areas, which locate in northeast and west of the Sichuan Basin, respectively. Detailed paleomagnetic studies were carried out. Stepwise thermal demagnetization was used to isolate the characteristic higher temperature component (HTC) from the Bazhong (Ds/Is=25.8/18.9°, k=24.3, ?95=7.6°) and Ya'an (Ds/Is=356.7/35.6°, k=28.5, ?95=6.6°) areas. The anisotropy of magnetic susceptibility (AMS) results of the two areas both are intermediate fabric and reveal the presence of sedimentary origin fabric. Results obtained from the anisotropy of the isothermal remanence (AIR) method indicate that distinct inclination flattening occurred in our samples. The mean values of IRMz/IRMx, which are 0.8194 and 0.8909 of samples from Bazhong and Ya'an area, suggest 18% and 11% compaction rate, respectively. The results obtained from both anisotropy of the isothermal remanence(AIR) method and corrected results of the elongation/inclination model of Tauxe and Kent indicate that the presence of obvious inclination shallowing of the Early Cretaceous red beds in Sichuan Basin, which is conducted by sedimentation and/or compaction, and compaction intension in Bazhong area (northeastern Sichuan Basin) is much higher than that of Ya'an area (western Sichuan Basin).