Sedimentary rock cycle

Mackenzie F.T. and Pigott J.P. (1981) Tectonic controls of Phanerozoic sedimentary rock cycling. J. Geol. Soc. London 138, 183-196. 

Here, 3.75 mol of organic matter are consumed for each mole of pyrite deposited, and an equivalent quantity of 02 is left behind in the atmosphere-ocean system. The excess 02 is used up again in the oxidation of pyrite when it is brought to Earth s surface by the sedimentary rock cycle. With regard to the oxygen budget, it is important to note that disulfide represents... 

Garrels, R. M., and F. T. MacKenzie (1972). A quantitative model for the sedimentary rock cycle. Marine Chem. 1, 27-61. 

The sedimentary rock cycle a simple model for rock formation... 

The most stable minerals are often physically eroded before they have a chance to chemically decompose. Minerals that decompose contribute to the dissolved load in rivers, and their solid chemical-weathering products contribute to the secondary minerals in the solid load. The secondary minerals and the more stable primary minerals are the most important constituents of clastic sedimentary rocks. Consequently, the secondary minerals of one cycle of erosion are... 

Ronov, A. B., Migdisov, A. A., and Barskaya, N. V. (1969). Tectonic cycles and regularities in the development of sedimentary rocks and paleogeographic... 

A clear avenue of future research is to explore the S-Fe redox couple in biologic systems. Bacterial sulfate reduction and DIR may be spatially decoupled, dependent upon the distribution of poorly crystalline ferric hydroxides and sulfate (e.g., Canfield et al. 1993 Thamdrup and Canfield 1996), or may be closely associated in low-suUate environments. Production of FIjS from bacterial sulfate reduction may quickly react with Fefll) to form iron sulfides (e.g., Sorensen and Jeorgensen 1987 Thamdrup et al. 1994). In addition to these reactions, Fe(III) reduchon may be coupled to oxidation of reduced S (e.g., Thamdrup and Canfield 1996), where the net result is that S and Fe may be cycled extensively before they find themselves in the inventory of sedimentary rocks (e.g., Canfield et al. 1993). Investigation of both S and Fe isotope fractionations produced during biochemical cycling of these elements will be an important future avenue of research that will bear on our understanding of the isotopic variations of these elements in both modem and ancient environments. 

Using the rock cycle as an example, we can compute the turnover time of marine sediments with respect to river input of solid particles from (1) the mass of solids in the marine sediment reservoir (1.0 x 10 g) and (2) the annual rate of river input of particles (1.4 X lO g/y). This yields a turnover time of (1.0 x 10 " g)/(14 x lO g/y) = 71 X lo y. On a global basis, riverine input is the major source of solids buried in marine sediments lesser inputs are contributed by atmospheric feUout, glacial ice debris, hydrothermal processes, and in situ production, primarily by marine plankton. As shown in Figure 1.2, sediments are removed from the ocean by deep burial into the seafloor. The resulting sedimentary rock is either uplifted onto land or subducted into the mantle so the ocean basins never fill up with sediment. As discussed in Chapter 21, if all of the fractional residence times of a substance are known, the sum of their reciprocals provides an estimate of the residence time (Equation 21.17). 

What has happened to the bicarbonate and calcium delivered to the ocean by river runoff As described later, these two ions are removed from seawater by calcareous plankton because a significant fraction of their hard parts are buried in the sediment. In contrast, the only sedimentary way out of the ocean for chloride is as burial in pore waters or precipitation of evaporites. The story with sodium is more complicated— removal also occurs via hydrothermal uptake and cation exchange. Because the major ions are removed from seawater by different pathways, they experience different degrees of retention in seawater and uptake into the sediments. Another level of fractionation occurs when the oceanic crust and its overlying sediments move through the rock cycle as some of the subducted material is remelted in the mantle and some is uplifted onto the continents. 

A second mechanism by which CO2 is regenerated as part of the crustal rock cycle is thought to occur imder high pressures and temperatures such as found in subduction zones and under thick sedimentary prisms in the continental rise. This decarbonation... 

Si, Fe and Fe is variable. Illite also appears to be the early product of weathering in cycles of intense alteration or one of the stable products under intermediate conditions (Jackson, 1959). It is apparently stable, or unaffected by transport in rivers for relatively short periods of time (Hurley, et al., 1961) but does change somewhat in the laboratory when in contact with sea water (Carroll and Starkey, 1960) it has been reported to be converted to chlorite or expandable minerals upon marine sedimentation (Powers, 1959). However, Weaver (1959) claims that much sedimentary illite is "reconstituted" mica which was degraded to montmorillonite by weathering processes. It is evident that a certain and usually minor portion of illite found in sedimentary rocks is of detrital origin (Velde and Hower, 1963) whether reconstituted or not. 

Mineral hardness is also important in sedimentary rocks. Harder minerals tend to be able to travel longer distances down river systems. Quartz can often undergo several cycles of erosion, transportation and lithification (change of sediments to rock). 

To begin the discussion, we will present briefly a view of the modern carbon cycle, with emphasis on processes, fluxes, reservoirs, and the "CO2 problem". In Chapter 4 we introduced this "problem" here it is developed further. We will then investigate the rock cycle and the sedimentary cycles of those elements most intimately involved with carbon. Weathering processes and source minerals, basalt-seawater reactions, and present-day sinks and oceanic balances of Ca, Mg, and C will be emphasized. The modern cycles of organic carbon, phosphorus, nitrogen, sulfur, and strontium are presented, and in Chapter 10 linked to those of Ca, Mg, and inorganic C. In conclusion in Chapter 10, aspects of the historical geochemistry of the carbon cycle are discussed, and tied to the evolution of Earth s surface environment. 

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