Paleogeography and Geology of the Cretaceous:
Continued breakup of Gondwana (which has been intact since the breakup of Pannotia!). Isolated into Africa and a South America + Indomadagascar + Antarctica/Australia unit connected by now-submerged ridges.

As South Atlantic widens, beginning of Andean Orogeny in western South America (a long ongoing mountain building process, still active today).

Equatorial current allows continued warming of tropical seas.

The mid-Cretaceous saw some major worldwide events:

• Increased rate of sea-floor spreading along mid-ocean ridges
• Decreased rate of magnetic reversals (mid-Cretaceous is marked by the Long Cretaceous Normal, 40 Myr without reversals)
• Highest transgressions of the post-Pangaean world, rivaling the highest Cambrian highstands
• Many continents divided up by epeiric seas: North America divided in three by Western Interior Seaway; European Archipelago isolated from Asian mainland; Africa is divided into three; etc.)
• Black shales and anoxic waters periodically flood continental shelves and epeiric seas: black shales may be generated in part by eutrophication from continental runoff of nutrients, and in part by sluggish oceanic circulation (and thus more anoxia)
• Globally warm and mild climates

During Late Cretaceous, beginnings of regression, but main regression event not until the Maastrichtian (last Age).

In warm Cretaceous seas, important new types of deposits:

• CHALK!!! -- coccolithophorids appear in Jurassic, but take off in producing chalk during mid-to Late Cretaceous. The Chalk of Europe, Niobrara Chalk of the Western Interior Seaway, etc..
• Diatomites: diatoms first appear and become common in Cretaceous
• Foraminiferal ooze: planktonic foraminiferans arise in Cretaceous
• Rudist reefs (particularly in Tethys and along equatorial regions): rudists are reef-forming bivalves.

In Early Cretaceous, continuation of Nevadan Orogeny.

During the mid-Cretaceous:

• Increased speed of sea-floor spreading means subduction along Pacific margin of North America at a lower angle
• Various small microplates swept up by western margin of North America
  • Subducting Farallon Plate reaches melting point are regions further eastward
  • Eastward migration of mountain range from Washington/Oregon to Idaho
  • This new style is called Sevier Orogeny: lasts until near the end of the Late Cretaceous
  • Within forearc basin, many regional transgression-regression events

During Maastrichtian:

• Slowdown of seafloor spreading rate
• Huge Maastrichtian Regression: Western Interior Seaway drains to near modern Gulf Coast
• Beginning of Laramide Orogeny in Cordilleran system: foundering Farallon Plate brings uplift of region, some volcanism as far east as Colorado, Wyoming, New Mexico: continues well into Tertiary
• Deccan Traps: massive flood basalt episode in western India, third largest in Phanerozoic (begins during last magnetic normal (C30n) interval of Cretaceous, so no closer than 350 kyr from 65.51 Ma (which is during C29r, a reversed chron)
• Cooling, more continental climates

Cretaceous-Paleogene Boundary: impact of a huge (10 km diameter) asteroid at Chicxulub in the Yucatan Peninsula of Mexico: more on this later!

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Last modified: 14 January 2011