Posted by: paulgarner | February 9, 2010

Seawater chemistry and sea floor spreading

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.

Reference

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

Advertisements

Responses

  1. I can’t get to the article for a year (my cheapo subscription), so maybe my question is somewhere in the article.

    Is there any sort of dramatic changes which took place around the end of the Cretaceous?

    I would think the ratio changes before the Cretaceous would be interesting too. The original single supercontinent would have been separating extremely quickly during the Flood along with massive and rapid currents. The study takes samples from the mid-Jurassic (mid-Flood?) all the way through the Cretaceous, and up through the end of the Neogene/Tertiary.

    Surely with a world-wide Flood going on for the first half of the study (Jurassic and Cretaceous), and then settling sediment and slowing currents/movement for the second half of the study (Tertiary) there would be some pretty dramatic changes and fluctuations going on.

    Actually, wouldn’t there also be extremely dramatic changes going on during the Flood too? The samples are drawn from carbonate veins in ocean ridge flank basalts. That’s hundreds of miles of ocean floor forming from magma in a couple years of turbulent Flood conditions. Are the measurements from those samples dramatically different than those from the samples taken after the Flood subsided?

    It certainly seems as if they should be.

  2. How do we know that the Flood deposited Cretaceous sediments to begin with? What criteria do Flood geologists use to distinguish Flood sediments from non-Flood sediments?

    • A good question. I think several lines of evidence suggest that the Flood/post-Flood boundary is at or near the Cretaceous/Palaeogene boundary. That’s where thick, uniform and transcontinental sedimentary packages give way to regional- to local-scale ones (Austin et al. 1994), and where palaeocurrents change from consistent continent-wide patterns to scattered basin-controlled patterns (Chadwick 1993). Throughout the Cenozoic we also find fossil evidence of climatic change from wetter to drier and from warmer to cooler conditions, consistent with an earth recovering from the global flood. The mammalian stratomorphic series of the Cenozoic (e.g. the famous horse series) appear to track these environmental changes (Wise 1994). Finally, there’s the consilience of many geological and palaeontological criteria, as explained in a paper that I co-authored with John Whitmore (2008), which, when applied to the stratigraphic section in Wyoming, also points to a Flood/post-Flood boundary at or near the top of the Mesozoic.

      References

      Austin S. A., Baumgardner J. R., Humphreys D. R., Snelling A. A., Vardiman L. and Wise K. P. 1994. Catastrophic plate tectonics: a global Flood model of earth history, in: Walsh, R. E. (editor), Proceedings of the Third International Conference on Creationism, Creation Science Fellowship, Pittsburgh, pp.609-621.

      Chadwick A. V. 1993. Megatrends in North American paleocurrents, Symposium on Paleogeography and Paleoclimatology, Society of Sedimentary Geologists, SEPM Abstracts with Program, 8:5815.

      Whitmore J. H. and Garner P. 2008. Using suites of criteria to recognize pre-Flood, Flood, and post-Flood strata in the rock record with application to Wyoming (USA), in: Snelling A. A. (editor), Proceedings of the Sixth International Conference on Creationism, Creation Science Fellowship, Pittsburgh and Institute for Creation Research, Dallas, pp.425-448.

      Wise K. P. 1995. Towards a creationist understanding of ‘transitional forms’. Creation Ex Nihilo Technical Journal, 9(2):216-222.

      • Thanks for the answer, Paul, but I don’t know that those lines of evidence are as coincident as you say. For one, cratonic sequences are known well into the Cenozoic (I’m thinking of the Tejas), long after the Cretaceous, so it isn’t true that the Cenozoic is typified by regional scale hydrodynamics. Second, there is evidence for cooling trends throughout many parts of the sedimentary record, not just during the Cenozoic. The Ordovician and Carboniferous — both units supposedly deposited during the Flood — preserve evidence of major cooling trends on a scale similar to that seen during the Cenozoic (in fact, cooling during the Ordovician was even more precipitous). Third, if we assume a YEC perspective, stratomorphic series are not indicative of evolutionary relationships through time (lest all amniotes become united within a single baramin), so the point about horse ecomorphology tracking climate in the Cenozoic is essentially rendered moot.
        I do appreciate the answer, though.

        • I think you’re underplaying the differences between the Palaeozoic-Mesozoic and Cenozoic. The Tejas really isn’t comparable to, say, the Sauk, which left a major sandstone body across much of the North American craton. There was no comparable flooding of North America during the Cenozoic. Elsewhere in the world the Tejas transgression left more of a record, but even then it peaked midway through the Cenozoic. Besides, the end of the Flood was almost certainly a more gradual affair than its beginning, and is defined biblically by Noah’s departure from the ark because the earth around the ark was dry. That makes it much harder to know where to put the golden spike in the stratigraphic record, although I think the Cretaceous-Palaeogene boundary is a good approximation. When I consider all the data – whether from oxygen isotopes in the oceanic record, palynological trends in the continental record, the parallel stratomorphic series among the mammals, the change in scale of sedimentary packages, the changing trends in palaeocurrents – I don’t think any other part of the record looks post-Flood like the Cenozoic does. One final point: at least some of the data interpreted in terms of global cooling in earlier parts of the record has other explanations in creation geology (e.g. diamictites as catastrophic underwater debris flows rather than glacial indicators).

  3. So, does the study show sudden ratio changes before and after the Cretaceous point? Are there lots of ratio changes in the Jurrasic layers which would have been laid down in the middle of the Flood?

    Are there other studies that show sudden ratio changes of any sort between the pre-Cambrian and later layers like the Ordoclavian, Silurian, etc?

    Especially if the RATE study is taken seriously with its claim of million times faster radioactive decay during the Flood, various ratios between all sorts of elements should be drastically different in the Pre-, Intra-, and Post-Flood soils.

    (I’m asking this somewhat facetiously since I already know the answer is a “No.” Mainly I’m interested in an idea for why they aren’t drastically different.)

    • This study didn’t address what the ratio changes are like in older rocks because it was based on data from calcium carbonate veins in basalts on the modern ocean floor that don’t go back much beyond ~170 Ma (conventional geological date). I don’t know whether other studies have extended the trends further back, say by looking at equivalent data from ancient MORBs or ophiolites.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Categories

%d bloggers like this: