Tectonics & Paleontology (II): Sclerochronology

Some five years ago I had one of my first presentation-preparing seminars and the list of available topics included 'sclerochronology', supervised by the tectonophysics prof. Searching the literature I found that the term referred to the study of the accretionary growth of mineralized organismic hard parts - a bit like the tree-ring chronology transferred to animal skeletons ('interesting', so I thought and chose 'sclerochronology' for my seminar talk).

There were many papers on mollusc life strategies and environmental change during the younger Cenozoic, mostly analyzing some long-living clams. Not many studies involved 'sclerochronology' as an actual dating method, often researchers were looking for either ontogenetic signals or climatic signals, often involving distinct taxa, localities, and stratigraphic levels for comparison.

Among the animal groups considered were brachiopods, bivalves, corals, belemnites, fish (otoliths) but also higher vertebrates: Enamel and accretionary growing bone can yield sclerochronological data - the method is also called 'skeletochronology' when applied on vertebrate hard parts.

And the link to tectonics? If you consider the cross section of a shell as representing a time series of fast and slow growth phases and phases of arrested growth, how exactly can you expect a tectonic signal to show up? I asked my tectonophysics prof what story he wanted me to tell and it was this:

A reference book on Quaternary dating methods (Lettis et al. 2000) also includes a chapter on sclerochronology in recent to subrecent corals inhabiting a shallow tropical tectonically active shelf. If the shelf area is part of a block which is elevated over another block by thrust faulting (as under compression along a convergent tectonic plate margin), this tectonic movement - which is not continuous but (mostly) discrete with larger earthquakes releasing most of the stress - can have consequences for the coral growth:

During an earthquake (along a thrust fault) the uppermost part of a colony is lifted over the water level, dies, and stops growing, while deeper-lying sections stay intact and continue their growth. If you count the annual growth bands and locate the points of growth arrestment after an earthqake you can derive the timing of earthquakes and also the amount of vertical displacement for each event. These data are sufficient for deriving the earthquake characteristic of the responsible fault - a classical aim of paleoseismology.

You could argue that all that has nothing to do with deep time processes and you are right: While the paleobiological and paleoclimatological approaches employing sclerochronology are not strictly limited in time, sclerochronological dating is restricted to the youngest few thousand years of the Holocene.

Some refs: Sclerochronology

... & Tectonics:
Buddemeier, R.W. & F.W. Taylor (2000): Sclerochronology. In: Lettis, W.R., J.S. Noller & J.M. Sowers (eds): Quarternary Geochronology: Methods and Applications. - Washington, AGU, pages 25- 40.

... in vertebrates
MacFadden, B.J. (2004)(ed): Incremental Growth in Vertebrate Skeletal Tissues: Paleobiological and Paleoenvironmental Implications. In: Palaeogeography, Palaeoclimatology, Palaeoecology 206(3-4).

... in marine animals
Schöne, B.R. & D. Surge (2005)(eds): Looking back over Skeletal Diaries - High-resolution Environmental Reconstructions from Accretionary Hardparts of Aquatic Organisms. In: Palaeogeography, Palaeoclimatology, Palaeoecology 228(1-2).