paleobiology, paleoclimate

Highlights of the Phanerozoic: Part 2 – Mesozoic [251 – 65 Ma]

Here’s a few highlights from the history of the Earth and life during the Mesozoic Era, the second Era of the Phanerozoic, which is the fourth Eon in Earth’s history. These events are mainly focusing on North America, and the dates for Periods and Epochs have been partially rounded.

MESOZOIC (MZ) [251 – 65 Ma]

TRIASSIC (TR) [251 – 200 Ma]

  • Interior of Pangaea hot and dry
  • Red beds (low O2) and evaporates
  • Re-radiation of crustaceans, crinoids, gastropods, bivalve  molluscs
  • Archosaurs (diapsid reptiles) dominated, more efficient lungs
  • Sonoman orogeny [240 Ma] – addition of volcanic arcs and accretionary prisms to western North America
    • Beginning of subduction, terrane accretion, and magmatism of Mesozoic
  • Breakup of Pangaea – rifting on east coast of U.S.
  • *Mass extinction #4* – Central Atlantic Flood Basalts, 65% of species extinct
    • 4th worst

JURASSIC (J) [200 – 145 Ma]

  • Great deserts in western U.S.; Navajo sandstones, cross-bedding
  • Opening of Atlantic, closure of Tethys Sea
  • Age of the Ammonites (William Smith’s original index fossil)
  • Dinosaurs – Ornithischia (bird-hipped) and Saurischia (lizard-hipped)
  • Late: last significant carbonate and evaporate deposition anywhere on craton
  • Nevadan orogeny [170-150 Ma] – Sierra Nevada continental  arc
    • Subduction of Farallon plate
  • Sevier orogey [150 Ma] – Wrangellia terrane collides
    • NW Montana and Canadian Rockies (continue into Cretaceous)

CRETACEOUS (K) [145 – 65 Ma]

  • Warm and humid climate
  • Faster than average rate of seafloor spreading [145-65 Ma]
  • [130 Ma] – beginning of major sea level rise (chalk) and continuing subduction, microtrerrane accretion, and strike-slip displacement
  • Prolonged periods with no magmatic reversals [120-80 Ma]
  • Middle: greenhouse world, volcanic activity CO2
  • Mid-Late: radiation of angiosperms (flowering plants)
  • Late: worldwide episodes of ocean anoxia
  • Beginning of Laramide orogeny [65-50 Ma]
    • Thick-skinned, shallow angle subduction; still-buoyant Farallon plate
  • Deccan Traps (India), major flood basalt events
  • *Mass extinction #5* – Chicxulub crater in Yucatan
    • 5th worst
    • Meteorite impact; target rocks are carbonates, release CO2 and SO2
    • Acid rain and cooling, then intense greenhouse warming
    • Iridium spike found in K-T boundary, Gubbio, Italy 1980
    • Hardest hit: dinosaurs (except Aves), corals ammonites, brachiopods, foraminifera
    • Fared better: mammals, turtles, lizards, snakes, birds, amphibians, fish

Make sure you check out Part 1 – Paleozoic and Part 3 – Cenozoic!

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