Historical Geology Understanding Our Planet\'s Past

events, with major phases generally lasting less than 3 million years. These large

eruptions created a series of overlapping lava flows, giving many exposures a ter-

racelike appearance known as traps, from the Dutch word for “stairs.”

In a geologically brief catastrophe at the end of the Triassic, massive

rivers of basalt lava oozed out of giant fissures and paved over a continent-

sized portion of land. The volcanic crisis occurred when all the continents

Figure 143Many
occurrences of flood basalt
volcanism are associated
with continental breakup.

Historical Geology

TABLE 9 FLOOD BASALT VOLCANISM

AND MASS EXTINCTIONS

Volcanic Episode Million Years Ago Extinction Event Million Years Ago

Columbia River, USA 17 Low-mid Miocene 14

Ethiopian 35 Upper Eocene 36

Deccan, India 65 Maastrichtian 65

Cenomanian 91

Rajmahal, India 110 Aptian 110

South-West African 135 Tithonian 137

Antarctica 170 Bajocian 173

South African 190 Pliensbachian 191

E. North American 200 Rhaectian/Norian 211

Siberian 250 Guadalupian 249