The Silurian Period is now known to have undergone several significant positive $\delta^{13}C_{carb}$ excursions, namely the early Aeronian, Late Aeronian, Valgu, Ireviken, Mulde, Lau & Klonk events (see e. g. Cramer et al. 2011; Gradstein et al. 2012). It seems to me that those excursions where mainly studied in the context of chemostratigraphy and not paleoclimatology, though.

Is there any hypotheses on what could have triggered these excursions?
How come the short (ca. 24 Myr) Silurian be so unstable has to have so many significant excursions?

_{Sources:
Cramer, et al. 2011. Revised correlation of Silurian Provincial Series of North America with global and regional chronostratigraphic units and $\delta^{13}C_{carb}$ chemostratigraphy. Lethaia, 44: 185-202.
Gradstein, Ogg, Schmidt & Ogg (Eds). 2012. The geologic time scale. Elsevier, Amsterdam: 1144pp.}