Sediments fluid muds

Due to rapid and high sedimentation rates in the ETM, the accumulation of particles in the BBL can result in the formation of mobile and fluid muds. Fluid muds are defined as sediments suspended in concentrations of greater than 10 g L-1. 

The high vertical flux of particulates in river/estuarine plume regions commonly results in the accumulation of particles in the formation of a benthic boundary layer (BBL) and/or mobile and fluid muds (see chapter 6 for more details). The BBL is defined by Boudreau and Iprgensen (2001, p. 1) as those portions of sediment and water columns that are affected directly in the distribution of their properties and processes by the presence of... 

Fluid mud high concentration of sediment suspended in mass concentrations of greater than 10 g L-1. 

Figure 17. 2 Schematic representation of the seasonal variations in physical forces, discharges, and suspended sediment inventory on the Amazon shelf (from Nittrouer and DeMaster 1996, and Kineke et. al. 1996). The suspended sediment inventories include the fluid mud layers, which can comprise more the 90% of the suspended material on the shelf. The timing of the 4 AmasSeds cruises are shown at the bottom of the figure. In the upper figure NBC refers to the North Brazilian Coastal Current,...

Amazon deltaic deposits are reworked extensively by tides and waves (Geyer et al. 1996, Kineke et al. 1996, Sternberg et al. 1996). Over 10% of the Amazon subaqueous delta is covered by fluid muds (suspended solid concentration > 10 g L O, which can be several meters thick in some places. These sediments and the water contained therein can be mobilized by changes in frontal dynamics or by fortnightly tidal cycles (Kineke et al. 1996, Geyer et al. 1996). Even in nonfluid mud areas, the sediment can be... 

A more serious consideration for shelf and coastal dynamics would be the creation of significant dams along the mainstem of the Amazon River. Such structures certainly would reduce the delivery of sediment to the continental shelf. Benthic processes such as fluid mud formation and suboxic diagenetic reaction balances could be altered by these activities. Downdrift coastal mud banks and coastal mangrove environments also could be affected. 

Resuspension may be conveniently defined as the net transfer of sediment from bottom sediment into the water column. Since the gross transfer of sediment is called erosion, resuspension is the net result of bottom erosion and deposition of suspended sediment. Transfer of sediment changes the wave-mean-suspended sediment concentration with elevation 2 (= z + h, conveniently chosen as the coordinate with respect to the rigid bed as datum) and time t. This choice of datum means that, referring to Fig. 27.3 the rigid-bed level, the static-bed level and the mean position of the fluid mud-water interface are one and same. Fluid mud, if it occurs above this level is taken to be within the water layer (above z = 0). The concentration C z, t) is obtained from the simple sediment mass balance equation in the vertical direction ... 

The functional form of Fef depends on whether the bottom is a bed or fluid mud. The density prnf at the boimdary between these two states varies with inorganic sediment composition and is further influenced by the amount of organic matter. A density range as wide as 1,002 to 1,300 kg m has been reported.The lower limit arose from sediment rich (40% by weight) in organic matter.However, as a rule of thumb, the range for fluid mud may be taken as 1,050 to 1,200 kg m . Expressions for Fef are as follows. For a bed pm > Pmf kgm ) ... 

Modes of resuspension interactively depend on the concentration profile. The vertical structure of concentration is conveniently subdivided into four zones (Fig. 27.11). In the upper zone the suspension layer (DSL) is dilute, and is characterized by Newtonian flow behavior. The lower zone is occupied by the benthic nepheloid layer (BNL), which contains fluid mud. In the benthic suspension layer (BSL), the concentration is intermediate between DSL and BNL. The suspension in BSL is non-Newtonian but the concentration is not high enough for setthng to be hindered. Finally, at the bottom a consolidating bed (CB) occurs. It possesses an effective stress but is soft enough (i.e., not fully consolidated) for the sediment to be susceptible to resuspension when wave forcing is sufficiently strong. 

The typical viscous behavior for many non-Newtonian fluids (e.g., polymeric fluids, flocculated suspensions, colloids, foams, gels) is illustrated by the curves labeled structural in Figs. 3-5 and 3-6. These fluids exhibit Newtonian behavior at very low and very high shear rates, with shear thinning or pseudoplastic behavior at intermediate shear rates. In some materials this can be attributed to a reversible structure or network that forms in the rest or equilibrium state. When the material is sheared, the structure breaks down, resulting in a shear-dependent (shear thinning) behavior. Some real examples of this type of behavior are shown in Fig. 3-7. These show that structural viscosity behavior is exhibited by fluids as diverse as polymer solutions, blood, latex emulsions, and mud (sediment). Equations (i.e., models) that represent this type of behavior are described below. 

Roberts, D.J., Rabke, S. and Bernier, R. (2005) Evaluation of marine sediment qualities and their effect on the marine closed bottle test for testing biodegradability of synthetic drilling mud base fluids. SPE 94430 SPE/EPA//DOE Exploration and Production Environmental Conference 7-9 March 2005, Galveston, TX. Society of Petroleum Engineers, Richardson, TX, pp. 7. 

Chemical and isotopic evidence for the nature of the fluid in CH -containing sediments of the Hakon Mosby Mud Volcano. Geo-Marine Letters, 19 76-83. 

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