Identification of Growth Strata: New Insights From Anisotropy Corrected Paleomagnetic Data

Growth strata are important for understanding regional tectonic evolution. However, it is difficult to identify growth strata in the field, because of subsequent intensive modification and erosion. To address this problem, we studied two paleomagnetic sections at the stable deposition setting and the growth end of the Miocene growth strata of the Gengma Basin. Average inclinations of the two sections show a systematic deviation of 4.7° ± 5.2°. The anisotropy of magnetic susceptibility results for the growth end of the section A demonstrate a sedimentary fabric. However, the tilt‐corrected K3 axis deviates to the southwest from the normal direction of the bedding by 5.4° ± 3.8°, the magnetic foliation deviates to the equatorial plane by 5.3° ± 4.7°. The K3 axis is perpendicular to the bedding at the stable deposition setting. The deviation of the K3 axis from the normal direction of bedding is interpreted as the growth angle, which can be used to correct the paleomagnetic inclination data. Plain Language Summary Growth strata are linked with tectonic deformation, and so they are often used as an indicator for analyzing regional tectonics. However, it is difficult to directly identify growth strata in the field, due to typically strong structural deformation. Additionally, unidentified growth strata often lead to the inaccurate correction of the paleomagnetic data, which is a source of uncertainty in estimating for the paleolatitudes of blocks. The Gengma Basin in the north of the Shan‐Tai Block is a typical graben basin. Paleomagnetic and anisotropy of magnetic susceptibility (AMS) data of Miocene growth strata show that the paleo‐inclination of the growth end deviates from that of the stable depositional setting. Moreover, the tilt‐corrected K3 axis of the sedimentary fabric at the growth end deviates from the normal to bedding by 5.4° ± 3.8°, and the magnetic foliation deviates from the equatorial plane by 5.3° ± 4.7°. However, the tilt‐corrected K3 axis at the stable deposition setting is consistent with the normal to bedding. The differences in the paleo‐inclinations and AMS results between the growth end and the stable depositional setting can be used to identify the growth strata, and to correct the paleo‐inclination. Key Points The paleo‐inclination and anisotropy of magnetic susceptibility data at the growth end of the growth strata were over‐corrected Offset angle of the K3 axis of sedimentary fabric deviating from the normal direction of the beddi