Lecture 30 – End of Permian and Triassic Climate Variations

Q: What is the End Permian mass extinction also known as, and how severe was it?

“The Great Dying” — the worst known extinction in the Phanerozoic. It wiped out 95% of oceanic species and 70% of vertebrate animals on land.

Q: What key groups were lost in the End Permian extinction?

Trilobites, sea scorpions (eurypterids), and tabulate/rugose corals, among many others.

Q: What were the climate and environmental conditions at the time of the End Permian extinction?

It occurred at the end of a long icehouse period, accompanied by a massive (10×) increase in atmospheric CO₂.

Q: What volcanic event is linked to the End Permian extinction?

The Siberian Traps volcanism, which occurred over 1–2 million years (252–250 Ma) at the end of the Permian.

Q: How did the Siberian Traps form?

Liquid magma was released from numerous extended fissures due to a large mantle plume of upwelling magma below Earth’s crust in Siberia, creating a large igneous province (LIP).

Q: How large were the Siberian Traps?

They covered an area of 7 million km² (larger than the EU, 60–70% the size of the USA) and deposited over 4 million km³ of basaltic lava in stacked flows.

Q: Why is the Siberian Traps event considered a likely cause of the End Permian extinction?

It is the largest volcanic event in the last 500 million years, its timing is consistent with the extinction, and many other mass extinctions are also associated with massive continental flood basalts or oceanic plateaus.

Q: What was the first environmental consequence of Siberian Traps volcanism?

Massive release of CO₂ into the atmosphere, causing global warming via the greenhouse effect — global average temperatures increased by about 10°C within a million years.

Q: What does the carbon isotope excursion (CIE) at the End Permian tell us?

δ¹³C of organic carbon shifted from about −24 to −32‰, indicating an additional CO₂ source with very negative δ¹³C values beyond volcanic emissions alone.

Q: What was the additional CO₂ source that explains the carbon isotope excursion?

Magma intruded into coal-bearing sedimentary basins and set coals on fire, releasing additional CO₂, CH₄, and SO₂/H₂S into the atmosphere.

Q: Why is CH₄ release from coal fires significant?

CH₄ has a much higher greenhouse warming potential than CO₂ alone, amplifying the warming effect.

Q: How much carbon was needed to explain the CIE if coal fires are included?

Less than 20,000 Gt of carbon (less than 6,000 ppm of atmospheric CO₂), compared to about 600 Gt of carbon in the atmosphere today.

Q: How did ocean acidification occur during the End Permian?

CO₂ + H₂O → carbonic acid, and SO₂/H₂S + H₂O → sulfuric acid, which compromised carbonate shell formation in marine organisms.

Q: How did ocean anoxia develop during the End Permian?

Higher temperatures enhanced marine plankton productivity; dead organic matter sank and consumed O₂ during re-oxidation until all O₂ was gone, creating anoxic dead zones in the lower ocean and collapsing food webs.

Q: What processes contributed to ocean anoxia beyond enhanced plankton productivity?

Warmer oceans led to more stratified water (less circulation and mixing), more algal blooms, and reducing conditions where no O₂ remained — killing any organism requiring oxygen.

Q: Why is the asteroid impact hypothesis not viable for the End Permian extinction?

No suitable impact crater of the appropriate age has been identified, no elevated iridium contents have been found, and no shocked quartz pieces have been discovered.

Q: What were sea floor spreading rates like during the Triassic (252–201 Ma)?

They reached their lowest levels during the Triassic.

Q: Despite low sea floor spreading, why was the Triassic climate hot?

Atmospheric CO₂ concentrations remained elevated (approximately 6× pre-industrial, ~1,680 ppm), and the unique paleogeographic constellation of the supercontinent Pangea contributed to warming.

Q: What was Pangea, and what was its scale?

A supercontinent containing over 75% of all land, up to 12,000 km wide and long.

Q: What did GCMs predict for Pangea’s interior at low latitudes?

Very dry conditions — precipitation less than 500 mm/yr with vast areas of semi-arid to arid climate.

Q: What geological evidence supports arid conditions in the Triassic?

Abundant evaporite and calcrete formation (both require warm, arid conditions). The highest evaporite formation rates in the Phanerozoic occurred around 220 Ma.

Q: What extreme seasonal temperature differences did GCMs predict for Pangea?

Summers above 30°C and winters below −15°C due to extreme continentality.

Q: Why couldn’t ice sheets form during the Triassic despite cold winters?

Summer temperatures above 3°C melted any winter snow/ice deposits, preventing ice sheet growth.

Q: What monsoon circulation pattern did GCMs predict for Pangea?

Strong seasonal reversal — in winter, cold dry air sinks and flows toward oceans; in summer, hot air rises, drawing moist air inward from the oceans.

Q: What are red beds, and what do they indicate about Triassic climate?

Red-colored sedimentary deposits formed by wet-season moisture followed by dry-season oxidation of iron to red Fe-oxides (hematite). They indicate strong seasonal contrasts in precipitation.

Q: Were Triassic climate models and geological evidence in agreement?

Yes — both show that on continents, climate was hot and dry (despite slow sea floor spreading) due to elevated atmospheric CO₂ and the unique paleogeography of Pangea.