GEOL 104 Dinosaurs: A Natural History
Fall Semester 2006
The Cretaceous-Tertiary Extinction III: Not With a Bang, But a Whimper
Media (and some professional scientists) act as if K-T impact was only global change
occurring at K-T boundary.
However, equally good geological evidence for some other big changes:
Long known that a period of intense volcanism begins in later part of Cretaceous. In
North America, associated with change in mountain building in Rockies. Biggest aspect of
- GIGANTIC series of lava flows in western India
- A major flood basalt event, like the Siberan Traps at the Permo-Triassic boundary
or those formed by the break up of Pangaea at the Triassic-Jurassic boundary
- Some places the Deccan Traps are 2.4 km (1.44 MILES) thick
- Second largest volcanic event in last half-billion years: only Siberian Traps are bigger
- Was not a single continuous event: erupts, cools, life returned, reerupted, etc.
- If single eruptions like Tambora can effect global climate for a few weeks, what of
this much larger, longer scale event?
- Once thought to have begun millions of years prior to impact (67 Ma) and continued
through boundary into early part of Tertiary, but now known to have all formed in 1
million years or less, centered on K-T boundary
- Begins during a magnetic normal time (C30N), so can be no closer than 400 kyr from the impact
- Would have similar climatic effects to impact (lots of ash and dust, blotting out
skies and reducing incoming sunlight)
- Only larger volcanic event, the Siberian Traps, coincides directly with Permo-Triassic
extinction!! (and the Triassic-Jurassic extinction also coincides with a flood basalt!)
Some try to dismiss Deccan Traps as a side effect of Chicxulub crater, but begins a little
So, Deccan Traps themsevles were a MAJOR event, and might have contributed greatly to the
Even earlier geological change:
- Maastrichtian: last Age of Late Cretaceous Epoch; Regression: any period
of sea-level drop
- Change in mid-ocean ridge activity meant ocean levels drop
- Shallow seaways typical of Late Cretaceous drain, exposing lots of land
- Climates worldwide becomes more continental (more extreme: hotter summers,
- Change in climate produces change in ocean circulation (and amount of nutrients)
- Change in climate produces changes in growing seasons of plants
Maastrichtian Regression clearly happens (latest Maastrichtian terrestrial rocks on top of
earlier Maastrichtian shoreline rocks on top of earlier marine rocks).
- Gradual change over period of millions of years
All three events (Chicxulub impact, Deccan Traps volcanism, Maastrichtian Regression) are
known to occur. Can we separate their effects in the geological record?
And which, if any, seems to have an effect on dinosaur diversity?
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Last modified: 14 July 2006