The Komplex KP
Non-trivial paleontology
- A complex record preserved in
vast ocean sediments, usually not-yet-lithified
- Diversity decreased several million years before and after the boundary event!
- Yet abundance certainly plummetted because of a catastrophic event!
Iridium anomoly (Alvarez, 1980)
- Finding Ir anomalies in
deep-sea limestones and KP boundary
layer clays of Italy, Denmark, and New Zealand, Alvarez et al
hypothesize an extraterrestrial cause for the "Cretaceous-Tertiary)
extinction. (too simple)
Deccan traps controversy(Officer and Drake)
- Anomalous Ir is found in air-borne particles from Kilauea
- Some Ir anoms are spread thru 30-40 cm ==>~100-200ky in deep sea seds...
- Alvarez et al counter that volcanism can't provide degree and
global extent of platinum group anomaly.
Chicxulub
- Microtektites in Haiti, New Mexico, Texas, the Dakotas, and
the Caribbean lead to
proposition that a Manson, Iowa crater which penetrated cretaceous
strata may have been related to the extinctions.
- Tsunami deposits are conjectured in Haiti, and much discourse over
tektite diagenesis, etc. ensues...
- PEMEX engineers point out Chicxulub cenotes and unusual
drill samples.
- With gravity and magnetic data in hand, and geophysical work in
the making, the impact hypothesis becomes predominantly accepted.
"Geochemical measurements (40 trace, Ir, Os-Pt-Au) performed on
bio-event horizons from Pre/Cambrian to late Eocene support KT boundary
Ir anomaly, but find no evidence
for impact-generation of Ir in the few horizons in
which it was detected..." (Orth et al, 1990).
Thus, sometimes there are no direct products of
an impact at a mass kill horizon. Why? What other catastrophic
mechanisms are involved in extinctions evidenced by the fossil
record?
Or does the paleontological signal reflect actual extinction events?!
How much of the signal results from stratigraphic overprint: hiatus, incomplete
sampling (cm scale is uncommon), or diagenetic effects??
(Ward, 1990).
Finally, how can we explain the (periodic?!?!) pattern of extinctions?
