Burial Consolidation Processes of Deep-Sea Sediments: An Example of Core Sediments Collected from the Labrador Sea in the Northwest Atlantic

Abstract

Progressive change of microfabrics of deep-sea sediments during early diagenesis was analyzed using two drill cores collected from the Sites U1305 and U1306 of the Integrated Ocean Drilling Program Expedition 303 in the Labrador Sea in the northwest Atlantic Ocean. Microfabrics were analyzed by scanning electron microscope and deduced from anisotropy of magnetic susceptibility. DiŠerent microfabrics in three layers were distinguished in both cores: Surface layer with general void ratio À2.5, subjacent layer with void ratio 2.5-1.5, and deep layer with void ratio º1.5. Microfabrics of the sediments change downward (toward deeper part), as well as magnetic susceptibility anisotropy. Microfabrics in the surface layer are non-directional and characterized by the presence of many macropores larger than 10 mm in diameter. Clay platelets in this layer are linked to each other with edge-to-edge or high-angle edge-toface (EF) contact. In the underlying layer, contact relations of clay platelets change to low angle EF type. Coarse siliciclastic fractions of this layer show horizontal preferred orientation, most probably due to overloading of the surface layer. Sizes of macropores decrease to several mm in diameter. In the lowest layer, clay platelets take horizontal preferred orientation according to further burial consolidation. Thus, the microfabrics of the sediments are developed from non-directional to preferred horizontal orientation with burial consolidation by following processes; 1) rotation of coarse grains in the layer with the void ratio À2.5 and 2) change of clay microfabrics in the layer with the void ratio º2.5.

An improved sample preparation method for imaging microstructures of fine‐grained marine sediment using microfocus X‐ray computed tomography and scanning electron microscopy

“…5). Previous studies have reported clay microaggregates in soils and continental margin sediments (e.g., Edwards and Bremner 1967;Ransom et al 1997Ransom et al , 1998Kawamura 2010;Nishida et al 2013). The present observation of clay microaggregates in pelagic sediments indicates that such microstructure is a common characteristic of clay in various environmental sediments.…”

“…Sample prep for microstructure observation 472 t-Butyl alcohol freeze-drying method t-Butyl alcohol freeze-drying was performed according to previously reported procedures (Takizawa et al 1995;Kawamura and Ogawa 2004;Kawamura 2010;Nishida et al 2013). The tiny agarose-embedded sample plugs allow rapid sample processing for subsequent fluid displacement.…”

“…However, during the current sediment t-butyl alcohol freeze-drying method (Kawamura 2010;Nishida et al 2013), samples are dehydrated directly and then freeze-dried without pretreatment. These processes lead to substantial changes in sample microstructures, making them unsuitable for sediment microstructure observations.…”

“…An approach using t-butyl alcohol freeze-drying was reported by Takizawa et al (1995), Kawamura and Ogawa (2004), Kawamura (2010), and Nishida et al (2013). This method displaces sediment interstitial water using t-butyl alcohol and is followed by freeze-drying, after which microstructures are observed on the fractured sample surfaces.…”

Texture Development of Clay‐Rich Sediments Across the Costa Rica Subduction Zone

“…The microfabric anisotropy of phyllosilicate-rich sediments generally increases during burial and progressive compaction in marine environments (e.g., Bennett & Hulbert, 1986;Day-Stirrat et al, 2012;Ho et al, 1999), of course, also depending on mineral composition and distribution (e.g., Sintubin, 1994). This can be determined indirectly by, for example, AMS (anisotropy of the magnetic susceptibility) measurements, void ratios, or preferred alignment of larger grains, for example, illite flakes (e.g., Agar et al, 1989;Bowles et al, 1969;Kawamura & Ogawa, 2004;Kawamura, 2010;Maffione & Morris, 2017;Schumann, Stipp, Leiss, et al, 2014) or by analyzing crystallographic preferred orientations using diffraction techniques (e.g., Aplin et al, 2006;Day-Stirrat et al, 2012;Kopf & Behrmann, 1997;Schumann, Stipp, Leiss, et al, 2014).…”