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:

Increased Volcanism:
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 volcanism, however:
Deccan Traps

• 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 too early.

So, Deccan Traps themsevles were a MAJOR event, and might have contributed greatly to the extinction event.

Even earlier geological change:
Maastrichtian Regression

• 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, colder winters)
• 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).

Predictions:

• 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