Sedimentation and Burial

After initial sedimentation, the burial of sediments is usually accomplished rapidly in nearshore or lacustrine basin environments. 

Hamilton (1959) has shown that a 150-700 meter-thick layer of unconsolidated sediments exists even on most deep sea floors. Let us consider a little more closely then the difference between the open sea situation, where sedimentary clays are in contact with sea water of roughly constant composition and an unconsolidated sediment which contains a pore fluid. 

Meade (1966) shows that claystones have a porosity decreasing to 0% at 1 Km depths and sandstones, 20% porosity at the same depth. Manheim (1970) shows that ionic diffusion rates in sediments are 1/2 to 1/20 that of free solutions when the sediments have porosities between 100 - 20%. It is evident that the burial of sediments creates a very different physical environment than that of sedimentation. As a result of reduced ionic mobility in the solutions, a different set of silicate-solution equilibria will most certainly come into effect with the onset of burial. The activity of ions in solution will become more dependent upon the chemistry of the silicates as porosity decreases and the system will change from one of perfectly mobile components in the open sea to one approaching a closed type where ionic activity in solution is entirely dictated by the mass of the material present in the sediment-fluid system. Although this description is probably not entirely valid even in rocks with measured zero porosity, for practical purposes, the pelitic or clayey sediments must certainly rapidly approach the situation of a closed system upon burial. 

The abrupt change in the composition of pore fluids in deep sea cores found to occur at depths of several tens of centimeters (Bischoff and Ku, 1970, 1971 Bischoff, et al., 1970 Mangelsdorf, et al., 1969) tends to corroborate this deduction. 

The porosity of sedimentary rocks and the migration of water between pore spaces (permeability) influence in another way silicate mineral equilibria. Fluid mobility in a rock leads to the realization of a mechanical equilibrium where fluid pressure (hydrostatic pressure) is 

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These grains have an exterior of mica (illite) which is "invaded" by a new material at the ends and in the center due to the response of mica to the new chemical and physical conditions of sedimentation and burial. 

Compositional Transformations Associated with Sedimentation and Burial of Organic Matter... 

The main removal process for oceanic components is via sedimentation and burial thus, the interaction of dissolved metals with particles in sea water is a major indication of their concentration and distribution in the world s oceans. In open ocean areas the particle cycle is driven by the biological production of particles in the surface layers, which after processes of mineralization and packaging reach the necessary size and density to fall to the ocean bottom. On the basis of this consideration, one can say that in the open ocean area the biogeochem-ical cycle of trace metals determining their distribution and speciation is frequently dominated by biological processes. In eoastal areas or particular geographical zones, other phenomena, e.g., inorganic precipitation, can take place. 

CoccoUthophores produce long-chain alkenones that have proved particularly useful for palaeo-temperature reconstruction they can be found in almost all marine sediments from the present day back to at least 140 million years, and are remarkably unaffected during sedimentation and burial. It turns out that in order to maintain the flexibility of their cell membranes, coccolithophores alter the number of double bonds in the alkenone chain in response to temperature. Laboratory experiments using cultures of Emiliani huxleyi have shown that the relative abundance of alkenones containing 37 carbon atoms and two double bonds (C37 2) is higher in cooler waters, while the relative abundance of alkenones containing 37 carbon atoms and three double bonds (C37-3) is higher in warmer waters (Prahl Wakeham 1987). The alkenone unsaturation index, Ul, is thus defined as ... 

Values of forg reflect biological productivity, organic decomposition, and also those processes that control sedimentation and burial of C. Given the requirement that isotopic mass balance be preserved, variations in forg can be linked to variations in values of Sea and 5org, as illustrated in Figure 3. 

Note that this estimate of the annual O2 loss to weathering processes is approximately equal to the estimated annual production of oxygen estimated above. Hence, the weathering of rocks and burial of organic carbon in sediments during their formation are important processes for the oxygen content of the atmosphere. 

Stallard, R. F. (1998). Terrestrial sedimentation and the carbon cycle Coupling weathering and erosion to carbon burial. Glob. Biogeochem. Cycles 12, 231-252. 

Ruttenberg, K. C. and Berner, R. A. (1993). Authigenic apatite formation and burial in sediments from non-upwelling, continental margin environments. Geochim. Cosmochim. Acta 57,991-1007. 

The predictable flux of °Thxs to the seafloor means that the flux of other components into marine sediments can be assessed by simply measuring their concentration relative to that of °Th (Fig. 5). This approach, termed °Thxs profiling, has seen widespread use in the last decade and has become a standard technique for measuring accumulation rates of many chemical species and sedimentary components. °Thxs provides possibly the best constraint on such accumulation rates for late Pleistocene sediments and is therefore an important tool. It is the best constrained of the constant flux proxies which include ofher chemical species such as Ti (Murray et al. 2000) and He (Marcantonio ef al. 1995). As wifh these other proxies, °Thxs is not mobilized during sediment dissolution because of its extreme insolubility so that °Thxs profiling assesses the final sedimentary burial flux, rather than the flux that initially arrives at the seafloor. 

In the Broecker Box model, the total amount of water in the ocean is assumed to remain constant over time. In other words, the evaporation rate and burial of water in the sediments is equal to the rate of water input from river runoff and precipitation. The sizes of the surface- and deep-water reservoirs are also assumed to remain constant over time. This requires the global rate of upwelling to equal the global rate of downwelling. 

The geographic distribution of opal in the surfece sediments is controlled by (1) the local rain rate of biogenic silica, (2) the degree of its preservation in the sediments, and (3) the relative rate of accumulation of other types of particles. Preservation is promoted by rapid burial as this isolates BSi from seawater. But if the BSi is buried by other particle types, the relative contribution of BSi to the sediment is diluted. This dilution effect causes the BSi content of most continental margin sediments to be low despite high rain rates. Preservation efficiency is also dependent on (1) the intensity of bioturbation and suspension feeding and (2) the various factors that control... 

Some particles, particularly the biogenous ones, are prone to alteration as they settle onto the sediments and then imdergo burial. The likelihood of particle preservation is generally enhanced in settings where the trip to the seafloor is short and burial rates are fast. The time a particle takes to settle onto the seafloor is determined by water depth and particle sinking rates. The latter is a function of particle shape and density. Seawater... 

Following burial, marine sediments are recycled via two pathways a crustal route or a mantle route. In the crustal route, burial followed by diagenesis, catagenesis, and metagenesis transfers sediments into either sedimentary or metamorphic rocks. These rocks are eventually uplifted onto land by crustal motions associated with plate tectonics. In the mantle recycling route, sediments and sedimentary rocks are subducted at... 

Some component of the terrestrial POM must be extremely nonreactive to enable a higher burial efficiency as compared to autochthonous POM. A possible candidate for this nonreactive terrestrial POM is black carbon. This material is a carbon-rich residue produced by biomass burning and fossil fuel combustion. Some black carbon also appears to be derived from graphite weathered from rocks. It is widely distributed in marine sediments and possibly carried to the open ocean via aeolian transport. 

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