ANDEAN EVIDENCE FOR A LONG-TERM STATE SHIFT IN BENTHIC ECOLOGY FOLLOWING THE TRIASSIC/JURASSIC MASS EXTINCTION
The siliceous sponge-dominated cherty deposits of the Aramachay Formation are a dramatic change from the carbonate biocalcifier-dominated dolomitic wackestones of the conformably underlying Upper Triassic Chambara Formation. The Aramachay Formation represents a facies change consistent with disturbances in Triassic/Jurassic carbonate records around the world (Greene et al., 2012, Earth Science Reviews 113:72-93). More importantly, facies change in the Central Peruvian record shows complete revolution in the metazoan contribution to sediment accumulation across the shelf that persisted for approximately two million years. The sponges likely responded both to habitats vacated by extinction (which selected against carbonate biocalcifiers), and to increased concentration of siliceous acid following weathering of the Central Atlantic Magmatic Province basalts. Comparison to strikingly similar facies in Nevada (USA), to more compressed records in the Austrian Alps, and to the more diverse record in the Moroccan High Atlas show that the ecological expansion of siliceous sponges to dominate shelf systems is a globally relevant ecological phenomenon and a response to the Triassic/Jurassic transition.