Phanerozoic carbonates

Figure 10.7. Histograms illustrating the differences in the Mn (A) and Fe (B) distributions in Archean and Phanerozoic carbonates. Data from several authors as presented in Veizer (1985).

In Figure 10.30 the survival rate of the total sedimentary mass for the different Phanerozoic systems is plotted and compared with survival rates for the total carbonate and dolomite mass distribution. The difference between the two latter survival rates for each system is the mass of limestone surviving per unit of time. Equation 10.1 is the log linear relationship for the total sedimentary mass, and implies a 130 million year half-life for the post-Devonian mass, and for a constant sediment mass with a constant probability of destruction, a mean sedimentation rate since post-Devonian time of about 100 x 1014 g y 1. The modem global erosional flux is 200 x 1014 g y-1, of which about 15% is particulate and dissolved carbonate. Although the data are less reliable for the survival rate of Phanerozoic carbonate sediments than for the total sedimentary mass, a best log linear fit to the post-Permian preserved mass of carbonate rocks is... 

Bischoff W.D. and Burke C.D. (1989) Phanerozoic carbonate skeletal mineralogy and atmospheric CO2. Proceed of the Chapman Confer, on the Gaia Hypothesis, Amer. Geophys. Union, Washington, D.C., (in press). 

Berner, R.A. (2004) The Phanerozoic Carbon Cycle CO2 and O2. Oxford University Press, New York. 

Horita et al. (2002), in part because of their incomplete compilation of Phanerozoic carbonate rocks (Holland and Zimmermann, 2000). 

Figure 1 Phanerozoic carbon isotope record. Mass extinction intervals are shaded in gray (widths do not correspond to durations of inserts) (a) global marine carbonate record (after Veizer et al, 1999) (b) marine carbonate record from the Late Ordovician of the Baltic States (after Brenchley et al, 1994) (c) Late Devonian marine organic carbon record from New York State (after Murphy et al, 2000) (d) Late Permian marine carbonate record from China (after Bowring etal, 1998) (e) Late Triassic marine organic carbon record from Canada (after Ward etal, 2001) (f)Late Cretaceous-early Tertiary record of the carbon isotopic difference between fine fraction and benthic carbonate (left panel), between shallow dwelling planktonic and benthic foraminifera (open symbols, right panel) and between more deeper dwelling planktonic and benthic foraminifera (filled symbols, right panel) from the south Atlantic...

Geochemical Implications of the Phanerozoic Carbonate Record ACKNOWLEDGMENTS... 

The outcrops of very old Archean rocks are few and thus may not be representative of the original sediment compositions deposited. Nevertheless, it appears that carbonate rocks are relatively rare in the Archean. Based on data from the limited outcrops, Veizer (1973) concluded that Archean carbonate rocks are predominantly limestones. During the early Proterozoic, the abundance of carbonates increases markedly, and for most of this Era the preserved carbonate rock mass is typified by the ubiquity of early diagenetic, and perhaps primary, dolostones (Veizer, 1973 Grotzinger and James, 2000). In the Phanerozoic, carbonates constitute 30% of the total sedimentary mass, with sandstones and shales accounting for the rest. The Phanerozoic record of carbonates will be elaborated upon in the subsequent text. 

As stated above, carbonate rocks comprise —30% of the mass of Phanerozoic sediments. Given and Wilkinson (1987) reevaluated aU the existing data on Phanerozoic carbonate rocks, their masses, and their relative calcite and dolomite contents (Figure 38). It can be seen that, as with the total sedimentary mass (Garrels and Mackenzie, 1971a,b), the mass of carbonate rock preserved is pushed toward the front of geologic time. The Tertiary, Carboniferous, and Cambrian periods are times of significant carbonate preservation, whereas the preservation of Silurian and Triassic carbonates is minimal. 

Thus, it appears that the apparent trends in Phanerozoic carbonate mineralogy are related to changes in atmosphere-hydrosphere conditions that are driven in part by plate tectonic mechanisms. However, we are aware that this tentative proposition requires collection of more data on the detailed chemistry and mineralogy of Phanerozoic carbonate sequences worldwide as well as resolution of the problem related to the past production rates of the oceanic lithosphere. 

Walker L. J., Wilkinson B. H., and Ivany L. C. (2002) Continental drift and Phanerozoic carbonate accumulation in shallow-shelf and deep-marine settings. J. Geol 110, 75-87. 

Francois, L. M. Walker, J. C. G. 1992. Modelling the Phanerozoic carbon cycle and climate constraints from the Sr/ Sr isotopic ratio of sea water. American Journal of Science, 292, 81-135. 

Berner RA (2004) The phanerozoic carbon cycle. Oxford University Press, New York Chameides WC, Perdue EM (1997) Biogeochemical cycles. Oxford University Press, New York Ernst WG (ed) (2000) Earth systems. Cambridge University Press, Cambridge Kump LR, Kasting JR, Crane RG (1999) The earth system. Pearson-Prentice Hall, Upper Saddle River... 

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