Carbonate deposition (formerly oil, etc.)

>> Technical point: If organisms take CaCO3 out of solution, then more CaCO3 will go into solution, where water contacts limestone (LS), and thereby allow additional organisms to take additional CaCO3 out of solution. This process can go on in principle until the oceans are saturated with such organisms (whatever that means). But as soon as they die, their skeletons will be available to contribute to the CaCO3 in solution.<<

It's a bit more complicated than that. Dissolved carbonate is in equilibrium with bicarbonate, carbonic acid, and dissolved carbon dioxide. Thus, pH and carbon dioxide concentrations have major impacts on the amount of carbonate available to organisms to precipitate. Temperature, pressure, and differences in amounts of dissolved stuff make the deep ocean undersaturated for carbonate, whereas surface regions are generally nearer saturation; however, it requires evaporation, biological concentration, or chamical concentration in pore waters to cause precipitation of carbonates in marine settings. The balance between supply and dissolution of carbonate produces a calcite compensation depth (and corresponding, shallower, aragonite compensation depth), the depth at which dissolution equals deposition. This CCD can be traced up and down in ancient sediments, corresponding to changes in circulation pattern and water chemistry over time.

The types of organisms contributing to the deep-sea carbonate and silica layers varies with both time and geography. For example, the upwelling along the equator produces a bloom of silica skeletoned organisms in the middle of the Pacific and a corresponding pile on the seafloor. This band can be traced northwards as one goes deeper into the sediment, corresponding to the motion of the Pacific plate.

I know of no way to fit these patterns (changes in compensation depth, microfossil faunal changes, microfossil biogeography) into a single global flood depositional model. You need time to establish conditions worldwide, with regional differentiation, and then replace them with a new set of conditions, myriad times. Current ocean circulation takes about 300 years for complete mixing. Speeding this up to happen multiple times within one year seems highly unlikely.

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL 35487-0345 USA
    bivalve@mail.davidson.alumlink.com

That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa

                 
Received on Wed Nov 26 17:57:31 2003