by A key problem has been finding sedimentary rocks that were formed at exactly the right time to capture all of the events that might have contributed to the extinction. The rocks need to contain plenty of fossils too, to reveal exactly when the various species disappeared.
Thomas Tobin at the University of Washington in Seattle has just found rocks that fit the bill on Seymour Island, just off the Antarctic Peninsula. "It is really far south, so any climate changes are likely to be strongest there and have more biological effects," he says.
He found evidence of two extinctions, one at the time of the Chicxulub impact, and one about 40 m below in the rocks, about 150,000 years earlier, when the Deccan Traps eruptions were occurring in the Indian subcontinent. These were flood basalt eruptions, where lava would pour over large areas, making a large igneous province.
Each disaster produced characteristic mass extinctions. The eruptions produced global warming going up to 7 C, heating the oceans and making their lower waters anoxic, causing a mass extinction there. Then the Chicxulub meteorite struck, causing a mass extinction of near-surface forms.
ScienceDirect.com - Palaeogeography, Palaeoclimatology, Palaeoecology - Extinction patterns, δ18 O trends, and magnetostratigraphy from a southern high-latitude Cretaceous–Paleogene section: Links with Deccan volcanism
Although abundant evidence now exists for a massive bolide impact coincident with the Cretaceous–Paleogene (K–Pg) mass extinction event (~ 65.5 Ma), the relative importance of this impact as an extinction mechanism is still the subject of debate. On Seymour Island, Antarctic Peninsula, the López de Bertodano Formation yields one of the most expanded K–Pg boundary sections known. Using a new chronology from magnetostratigraphy, and isotopic data from carbonate-secreting macrofauna, we present a high-resolution, high-latitude paleotemperature record spanning this time interval. We find two prominent warming events synchronous with the three main phases of Deccan Traps flood volcanism, and the onset of the second is contemporaneous with a local extinction that pre-dates the bolide impact. What has been termed the K–Pg extinction is potentially the sum of multiple, independent events, at least at high latitudes.
ScienceDirect.com - Earth and Planetary Science Letters - Nature and timing of extinctions in Cretaceous-Tertiary planktic foraminifera preserved in Deccan intertrappean sediments of the Krishna–Godavari Basin, India
In C29r below the Cretaceous-Tertiary boundary (KTB) massive Deccan Trap eruptions in India covered an area the size of France or Texas and produced the world’s largest and longest lava megaflows 1500 km across India through the Krishna–Godavari (K–G) Basin into the Bay of Bengal. Investigation of ten deep wells from the K–G Basin revealed four lava megaflows separated by sand, silt and shale with the last megaflow ending at or near the KTB. The biologic response in India was swift and devastating. During Deccan eruptions prior to the first megaflow, planktic foraminifera suffered 50% species extinctions. Survivors suffered another 50% extinctions after the first megaflow leaving just 7–8 species. No recovery occurred between the next three megaflows and the mass extinction was complete with the last mega-flow at or near the KTB. The last phase of Deccan volcanism occurred in the early Danian C29n with deposition of another four megaflows accompanied by delayed biotic recovery of marine plankton. Correlative with these intense volcanic phases, climate changed from humid/tropical to arid conditions and returned to normal tropical humidity after the last phase of volcanism. The global climatic and biotic effects attributable to Deccan volcanism have yet to be fully investigated. However, preliminary studies from India to Texas reveal extreme climate changes associated with high-stress environmental conditions among planktic foraminifera leading to blooms of the disaster opportunist Guembelitria cretacea during the late Maastrichtian.
So the volcano-induced global warming turned some tropical jungles into deserts.
That's consistent with predictions of increased aridity as a result of present-day global warming.The Earth has several other flood-basalt plains, including the Columbia River basin in the northwest US and the Siberian Traps whose eruptions may have caused the Permo-Triassic mass extinction. That was even bigger than the K-T one, though it did not involve organisms as spectacular as dinosaurs. It also involved global warming, but by as much as 8 C, and the Siberian Traps flood-basalt eruptions were likely involved in that also.
These eruptions may have been caused by meteorite impacts, but it's not something I'd consider well-established. Shiva crater, off the west coast of India, was likely produced by an impact that may also have caused the Deccan Traps eruptions.
For the Siberian Traps, some impacts have also been proposed, like Wilkes Land crater in Antarctica and Bedout, northwest of Australia. They would have been antipodal or close to antipodal to the Siberian Traps at the P-Tr time; that location would have focused the impact shock on the other side of the Earth: Princeton University - Impact study: Princeton model shows fallout of a giant meteorite strike
There are likely additional connections between mass extinctions, big impacts, and massive eruptions:
Asteroid/comet impact clusters, flood basalts, and mass extinctions: Significance of isotopic age overlaps, by Andrew Glikson (PDF)
The lunar maria ("seas") are also flood-basalt plains, though they formed about 3.5 - 3 billion years ago (Lunar mare).
