Sediment supply

Delta retreat and coastal erosion (reduced sediment supply)... 

The rates of accumulation in coastal deposits are commonly greater than deep-sea deposits. This disparity is not true everywhere since coastal areas can be dehcient in sediment supply or may be subject to efficient erosive processes. Accumulations can occur in estuaries, coastal depressions, and salt marshes. Attempts at geochronometry with a number of nuclides have been made in all of these areas. Confounding the record for both coastal and deep-sea sediments is the effect of bioturbation. Sediments deposited under anoxic conditions are free of this effect but all other sediments are subject to a variety of scales of bioturbation. 

Condensed sections occur within a TST and the lowermost section of a HST if the sediment supply is low (Curiale et al., 1992 Wignall and Maynard, 1993). The deposits of a condensed section are generally fine-grained rocks that usually have a high concentration of organic matter and are formed in sediment starved, deep-water conditions (Wignall and Maynard, 1993). 

What can late Archaean sedimentary basins tell us about the early Earth system1 Sedimentary basins develop as a response to the interaction between sediment supply and crustal subsidence. In detail this reflects the complex interplay of tectonism, magmatism, eustasy and weathering rates, which are themselves a function of paleoclimate (Eriksson et al., 2001). In the late Archaean probably a number of these factors were different from the modern. For example there is evidence that climatic regimes were different and so it is likely that weathering rates and sediment supply were also different (Chapter 5, Section 5.3.2.1). In addition, many believe that the mantle was hotter at this time. If this is the case then tectonic processes and subsidence rates would also be different from those of modern sedimentary basins. 

There are many equations which allow calculation of sediment transport rate within a water body, or sediment flux (see for example Task Committee of Computational Modeling of Sediment Transport Processes, 2004 for a review). However, these equations tend to be for a uniform sediment distribution, which is far from the variable source supply of material seen in events when the majority of sediment is moving. It is also generally considered that a particular flow has a maximum capacity to transport sediment, although the concentration this relates to depends again on sediment characteristics. Hence tliere are examples in China where sediment concentrations can reach several tens of thousands of parts per million for very fine particles, whereas a flow may become saturated with sand-sized particles at far lower concentrations. Rivers are often considered to be either capacity- or supply-limited in terms of their sediment transporting dynamics. However, in practice for most rivers, most of the time, sediment transport is limited by a complex and dynamic pattern of sediment supply. 

The concepts of limited sediment supply to rivers and an upper limit to the capacity of a particular flow rate to transport sediment of a particular particle size distribution and density explain the phenomenon of hysteresis, where sediment concentration for a given flow rate differs on the rising and falling limbs of a flow event. There is thus no simple relationship between flow and concentration, and a sediment rating curve will inherently have wide error bars. 

Fraction of Sound bottom covered by mud Sediment supply rate from rivers 56%... 

The physical properties at any depth are a function of the effective stress, temperature and of the primary sediment composition which is very difficult to predict. This is because the sediment supply and deposition is difficult to model. 

Fig 8 Simplified outline of geological processes controlling sediment supply, deposition, early diagenesis and late diagenesis. 

One of the most important factors affecting nodule abundance on the seafloor is the rate of accumulation of their associated sediments, low sedimentation rates favoring high nodule abundances. Areas of the seafloor where sedimentation is rapid are generally only sparsely covered with nodules. For example, most continental margin areas have sedimentation rates that are too rapid for appreciable nodule development, as do turbidite-floored deep-sea abyssal plains. Low rates of sedimentation can result either from a minimal sediment supply to the seafloor or currents inhibiting its deposition. Large areas in the centers of ocean basins receive minimal sediment input. Under these... 

In wetlands, N2O production via denitrification and subsequent emission is governed by the oxygen status of the sediment, supply of nitrifiable nitrogen, moisture content, and temperature. Since the denitrification pathway requires anaerobic conditions, a low partial oxygen pressure during the denitrification process enhances the formation of NjO. 

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