Biogenic carbonate detrital

A global map of quartz abundance is given in Figure 14.12. In this case, the contribution of quartz is presented as the contribution to the bulk sediment from which biogenic carbonate and silica have been removed. This map is very similar to the global distribution of dust presented in Figure 11.4, reflecting the importance of aeolian transport for this detrital silicate. 

The sand grains that make up aeolian dunes can include detrital biogenic carbonate grains (e.g. Ward, 1973, 1975), ooids (e.g. Budd, 1988) and... 

Cementation occurred chiefly by diffusive supply of Ca " and HCOj" derived from detrital carbonate grains uniformly distributed in sandstone beds and, in formations with mudrock interbeds, from detrital and biogenic carbonate in mudrocks. Local factors, many of which remain unidentified, influenced the cementation process and resulted in substantial heterogeneity in the distribution and form of calcite cement (Fig. 2). 

Whole-rock samples of mudrock from both shallowly and deeply buried rocks have similar carbon isotopic ratios, but distinctly different oxygen isotopic ratios (Fig. 8). 5 C values for most samples are from -2 to +l%o, values typical of marine biogenic carbonate or detrital clasts of marine limestone. One anomalously light sample (-8%o) in the Antog-nola Formation, and other samples with 5 C values less than -2%o, contain some authigenic carbon derived from organic material. 

Escanaba Trough has a range from -12.2 to -3.9%o, and 5 C values increase with CO2 content, presumably due to increased magmatic contributions (Taylor 1992). The vent fluids at Middle Valley show a range from -38.9 to -10.6%o, indicating substantial contributions from pyrolysis of organic carbon in the sediments and dissolution of detrital biogenic carbonates (Taylor 1992). 

Carbonate minerals contained in lake sediments consist of inorganic and biogenic components. One or both components may include detrital (formed outside the catchment) and/or terrestrial (formed in catchment) fractions. Whether these non-lacustrine fractions must be removed depends on the amount and the delta values of these foreign fractions compared to lacustrine fractions. Inorganic and biogenic carbonates may also need to be separated from each other for the very same reasons. 

The two prime mechanisms of carbon transport within the ocean are downward biogenic detrital rain from the photic zone to the deeper oceans and advection by ocean currents of dissolved carbon species. The detrital rain creates inhomogeneities of nutrients illustrated by the characteristic alkalinity profiles (Fig. 11-9). The amount of carbon leaving the photic zone as sinking particles should not be interpreted as the net primary production of the surface oceans since most of the organic carbon is recycled... 

Sayles FL, Martin WR, Chase Z, Anderson RF (2001) Benthic remineralization and burial of biogenic Si02, CaCOs, organic carbon and detrital material in the Southern Ocean along a transect at 170° west. Deep-Sea Research II 48 4323-4383... 

In terms of organic carbon generation, the coccolithophorids are a minor player, representing only 6 to 8% of global marine primary production. But their detrital remains contribute disproportionately to the burial of carbon in marine sediments. This is due to near complete loss of POC via remineralization as the detrital hard and soft parts settle to the seafloor. As estimated from Broecker s Box model in Chapter 9, only about 1% of the POM that sinks out of the surfece water is buried in marine sediments. In comparison, about 20% of the biogenic PIC survives to become buried in the sediments. 

This reaction is similar to Eq. 21.8. Wollastonite is an example of a calcium silicate mineral produced by the metamorphosis of detrital biogenic calcium carbonate and BSi. 

The oceanic carbon inventory was presented in Table 15.3. Most of the carbon is inorganic (98%), predominantly in the form of bicarbonate (87%), and is located in the intermediate and deep waters. Of the 2% that is organic, the majority is DOC (see Table 23.2). At present, the ocean is acting as a net sink for atmospheric CO2. In the modern-day carbon cycle, the sole oceanic sink fitr carbon is burial in the sediments in the form of detrital biogenic PIC and POC. 

The delivery of PIC and POC to the sediments depends on biological production in the surface waters. The input of terrestrial carbon is relatively minor. The relative proportions of PIC and POC generated in the surfece waters reflect the species composition of the plankton, i.e., calcifiers versus noncalcifiers. The success of detrital PIC and POC in surviving the trip to the seafloor is also dependent on the species composition of the plankton. As discussed in Chapter 23.5.4, the presence of biogenic hard parts confers protection on POC, inhibiting its remineralization. 

Figure 1 Conceptual model for the origin of mixed detrital-biogenic facies relating the three major inputs to the processes that control them. The major inputs are shown in boxes with bold-type labels. ControlUng factors are shown in italics. Large and medium scale arrows represent fluxes of key components involved in sedimentation and the biogeochemical cycles of carbon, sulfur, and oxygen. Thin arrows illustrate relationships between major controlling factors and depositional processes and/or feedback. Dashed thin arrows apply to major nutrient fluxes only. Dotted thin arrows apply to major authigenic fluxes only. See text for further explanation.

Carbonate and opaline-silica-rich sediments are exceptions to these generalizations. They are very low in detrital iron, because calcareous and siliceous skeletal debris is much lower in iron than terrigenous material. In these dominantly biogenic sediments, iron may become limiting the degree of pyritization is very high (>80%) and... 

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