Characterization of soft-sediment deformation: Detection of cryptoslumps using magnetic methods

Abstract

Many workers have explored anisotropy of magnetic susceptibility (AMS) of sediments as an indicator of deformation. Several studies have used deflection of the eigenvector associated with the minimum in susceptibility, V 3 , as a criterion for deformation. We examine the AMS record of a well-exposed slump and find that although demonstrable deformation can occur without deflecting the V 3 directions, an oblate AMS fabric is transformed into a triaxial fabric during initial deformation. Transformation of the fabric from oblate to triaxial appears to be highly correlated with an increase in natural remanent magnetization scatter, whereas deflection of the V 3 axes is not. We suggest that subtle soft-sediment deformation can be detected by using AMS fabric.

Magnetic fabrics indicating Late Quaternary seismicity in the Himalayan foothills

“…6). The K min axis is the most sensitive proxy for the maximum shortening direction and it is normal to the field and magnetic foliations (Housen et al 1996;Lee and Angelier 2000;Schwehr and Tauxe 2003). In phyllosilicate bearing rocks the K max is also very sensitive as it shows orientation parallel to the fold axis (Borradaile 1991;Aubourg et al 1991;Owens 1993;Borradaile and Henry 1997).…”

“…These studies demonstrate that AMS is an effective tool to distinguish components of sedimentary fabric (resulting from compaction) and earthquake-induced structures. AMS has been used to characterize soft sediment deformation (Schwehr and Tauxe 2003) as it can unravel the finite strain ellipsoid orientation in weakly deformed sediments and rocks, where tectonic fabric has not developed (Borradaile and Henry 1997;Parés 2004). Levi et al (2006) have analyzed sedimentary and seismic origin of clastic dikes in the Dead Sea basin and observed that AMS can be used as an effective tool for paleoseismic records.…”

Magnetic mineral diagenesis

“…Sedimentary magnetic fabrics, which can be detected using the anisotropy of magnetic susceptibility (AMS) or other types of magnetic anisotropy (Jackson, 1991;Rochette et al, 1992), have been widely analysed in tectonic studies (e.g., Borradaile and Tarling, 1981;Kissel et al, 1986;Tarling and Hrouda, 1993;Aubourg et al, 1995;Sagnotti et al, 1998;Kanamatsu et al, 2001;Weaver et al, 2004), in analysis of paleocurrent directions (e.g., Rees, 1961Rees, , 1965Hamilton and Rees, 1970;Ellwood and Ledbetter, 1977;Kissel et al, 1997Kissel et al, , 1998Hassold et al, 2006Hassold et al, , 2009Parés et al, 2007), and to detect sedimentary disturbances (e.g., Marino and Ellwood, 1978;Rosenbuam et al, 2000;Schwehr and Tauxe, 2003). If elongated magnetic particles are aligned by paleocurrents, the magnetic fabric of the sediment will have been preserved from the time of deposition.…”

Structural and magnetic fabric studies of recess structures in the western Himalaya: Implications for 1905 Kangra earthquake

“…The orientation of K3 axis is the most sensitive proxy for shortening direction especially when it is normal to field and magnetic foliations (Borradaile, 1991;Aubourg et al 1991;Owens 1993;Borradaile and Henry, 1997;Housen et al 1996;Lee and Angelier, 2000;Schwehr and Tauxe, 2003). Change in the orientation of K3 has been used to identify the development of cleavage fabric (Pares et al 1999;Pares, 2004).…”