An active area of research in the earth sciences concerns oscillating trends in the composition and mineralogy of Phanerozoic carbonates and halites – trends that have been correlated with changes in seawater chemistry and rates of sea floor spreading. A paper about to be published in Science (Coggon et al. 2010) reports efforts to reconstruct past seawater Mg/Ca and Sr/Ca ratios from calcium carbonate veins formed when seawater interacts with basalts on the flanks of mid-ocean ridges. The abstract says:
Proxies for past seawater chemistry such as Mg/Ca and Sr/Ca ratios provide a record of the dynamic exchanges of elements between the solid Earth, atmosphere and hydrosphere, and the evolving influence of life. Here, we estimate past oceanic Mg/Ca and Sr/Ca ratios from suites of 1.6 to 170-million-year-old calcium carbonate veins precipitated from seawater-derived fluids in ocean ridge flank basalts. Our data indicate that prior to the Neogene, oceanic Mg/Ca and Sr/Ca were lower than in the modern ocean. Decreased ocean spreading since the Cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early Tertiary may explain the recent rise in these ratios.
Data like these provide important clues into what was happening to ocean water chemistry both during and after the flood, and have significant implications for our understanding of how carbonates and precipitites formed. Note also the implied slowing of sea floor spreading since the Cretaceous – evidenced by the apparent reduction in chemical exchange between crust and seawater – another interesting trend from a creationist perspective.
Coggon, R. M., Teagle, D. A. H., Smith-Duque, C. E., Alt, J. C., Cooper, M. J. 2010. Reconstructing past seawater Mg/Ca and Sr/Ca from mid-ocean ridge flank calcium carbonate veins. Science, DOI: 10.1126/science.1182252