Boundary events: All mixed up...

Stratigraphy at abrupt horizons (McLaren and Goodfellow, 1990)

  • There is a sequence of marine events common to most sudden extinction horizons:
    1. mass killing
    2. extraterrestrially induced sedimentary effects
    3. depauperate Strangelove ocean
    4. biomass recovery with slow or rapid radiation of new forms
    5. return to pre-event oceanic conditions but with a largely new biota
  • The corresponding sedimentary record includes:
    1. A bedding plane surface is observed at the base in which a very large proportion (or all) of the biota disappears.
    2. This is overlain by an extraterrestrial layer containing Ir and other siderophile element anomalies, chondritic Os ratios, radiogenic Sr ratios, shocked minerals, soot and spheroids, and clastic deposits including tsuanmi and storm wave deposits.
    3. A marked facies change to a carbonate-poor, organic rich sediment follows. Overlying beds are highly depauperate.
    4. A recovery interval ensues, characterized by the introduction of some new taxa and a gradual increase in del(13C) and del(18O) values.
    5. Finally, there is a return to a normal sedimentary regime, probably different from the previous regime and displaying the radiation and development of a new biota.
  • periodicity