The Mechanics of Soft Cohesive Sediments During Early Diagenesis

Abstract

Natural, surficial, cohesive (clay-bearing), aquatic sediments are subject to a variety of phenomena in which physics, rather than say chemistry, plays an essential role; this includes, but is not limited to, bioturbation, self-weight compaction, and phase growth. Scientific monographs (e.g., Berner, 1971, 1980; Boudreau, 1997; DiToro, 2001; Burdige, 2006; Schultz and Zabel, 2006) that focus on early diagenesis, i.e., those changes occurring in the top 1–10 meters (m) of aqueous sediments, make only passing reference to the physics of early diagenetic phenomena. In contrast, civil engineers, soil physicists and geophysicists have afforded great attention to the physics/mechanics of compaction, particularly in soils, anthropogenic sediments and basin-scale studies (e.g., Yong and Warkentin, 1966; Giles, 1997; Wang, 2000; Craig, 2004; Mitchell and Soga, 2005; Das, 2008); yet, this knowledge has not been effectively transferred to obtain a better understanding of early diagenesis.

APPENDIX 4A

If a material is mapped (each point given a coordinate), then deformed, and the same points in the medium remapped, the resulting change in the position of an arbitrary point is called its displacement vector, u. The spatial derivatives of the displacement define the strain tensor, ε. Formally,

$$ \varvec{\varepsilon} =\frac{1}{2}\left[ {\nabla \varvec{u}+{{{(\nabla \varvec{u})}}^T}} \right] $$

(4.A1)

where ∇u is the displacement gradient matrix and the superscript T indicates the transpose. Thus, the tensile/compressive strain that occurs in the x direction is given by

$$ {\varepsilon_{xx }}=\frac{{\partial {u_x}}}{{\partial x}} $$

(4.A2)

and the subscripts can be dropped for a purely one-dimensional system, e.g., steady-state sediment compaction.