Use of grain size and magnetic fabric analyses to distinguish among depositional environments

Abstract

Abstract. The combined use of grain size and magnetic fabric analyses provides the ability to discriminate among depositional environments in deep-sea terrigenous sediments. We analyzed samples from three different alepositional settings: turbidites, pelagic or hemipelagic interlayers, and sediment drifts. Results indicate that sediment samples from these different environments can be distinguished from each other on the basis of their median grain size, sorting, as well as the intensity and shape of magnetic fabric as determined from an examination of the anisotropy of magnetic susceptibility. We use these discriminators to interpret downcore samples from the Bermuda Rise sediment drift. We find that the finer grains of the Bermuda Rise (relative to the Blake Outer Ridge) do not result from lower alepositional energy (current speed) and so may reflect a difference in the nature of sediment being delivered to the site (i.e., distance from source) between the two locations.

Tectono-sedimentary analysis using the anisotropy of magnetic susceptibility: a study of the terrestrial and freshwater Neogene of the Orava Basin

“…The stronger the current, the lower the anisotropy degree (Pm), probably due to the lower content of anisotropic clay minerals. This observation is contrary to deep-sea sediments affected by bottom currents where a stronger current is thought to align ferromagnetic grains more effectively (Ellwood & Ledbetter 1977;Joseph et al 1998). In contrast, inhomogeneous AMS facies <Hst>, <CLt>, and <CCL> indicate the sedimentary conditions undergoing fluctuations or being affected by special sedimentary events (e.g., floods).…”

“…The application of the AMS method in orogeny-related basins and accretionary prisms predominantly concerns a structural interpretation of strain directions (e.g., Hrouda & Potfaj 1993;Parés et al 1999;Kanamatsu & Herrero-Bervera 2006;Hrouda et al 2009;Mazzoli et al 2012) and turbidity current directions (e.g., Tamaki et al 2015), while hemipelagic and pelagic sediments are examined for the occurrence and directions of bottom currents (e.g., Ellwood & Ledbetter 1977;Shor et al 1984;Joseph et al 1998;Park et al 2000;Baas et al 2007;Parés et al 2007). The sedimentological analysis supported by AMS measurements has also been done in a variety of sedimentary settings, namely: deep sea fans and turbidity deposits (von Rad 1970), deep-sea mass transport deposits (Novak et al 2014), alluvial fine-grained sediments (Garcés et al 1996;Park et al 2013), pyroclastic density currents and lahar deposits (Biró et al 2015;Ort et al 2015), as well as glacial sediments (Eyles et al 1987;Gravenor & Wong 1987).…”

Paleocurrent directions from paleomagnetic reorientation of magnetic fabrics in deep-sea sediments at the Antarctic Peninsula Pacific margin (ODP Sites 1095, 1101)

“…When used in conjunction with grain size and fabric analyses (e.g., Joseph et al, 1998), we can determine a robust record for paleocurrents in space and time.…”

“…AMS has been used as a tool in the analysis of petrofabrics since Ising (1942) first proposed its application to geology, and it has successfully been used since then to investigate the spatial and geometrical configuration of the rock components for qualitative estimation of fabric development (reviews by (Hrouda, 1982;McDonald and Ellwood, 1987;Borradaile, 1988;Tarling and Hrouda, 1993)). Determination of preferred orientation in minerals is necessary information in a variety of studies ranging from structural geology (e.g., (Housen and van der Pluijm, 1990;Parés et al, 1999;Scott and Benn, 2001;Neves et al, 2003;Parés and van der Pluijm, 2003)) to sedimentary depositional environments (e.g., (Graham, 1954;Kent and Lowrie, 1975;Hounslow, 1985;Kodama and Sun, 1990;Joseph et al, 1998;Park et al, 2000)). …”

“…Previous workers have applied AMS to sediment samples to determine relative current strength Ledbetter, 1977, 1979;Joseph et al, 1998Joseph et al, , 2004Hassold et al, 2006), but few have applied this method to determine paleodirections of current flow in sediments (e.g., Ledbetter and Ellwood, 1980;Liu et al, 2001). The high sedimentation rates and Marine Geology 242 (2007) 261 -269 www.elsevier.com/locate/margeo high concentration of terrigenous material at the drifts along the Antarctic Peninsula (Acton et al, 2002;Hassold, 2006 Chapters 3 and 4) present an opportunity to explore this potentially powerful aspect of fabric study.…”