Deccan Traps
The Deccan Traps are a large igneous province located on the Deccan Plateau of west-central India (between 17–24N, 73–74E) and one of the largest volcanic features on Earth. They consist of multiple layers of solidified flood basalt that together are more than 2,000 m thick and cover an area of 500,000 km². The term 'trap', used in geology for such rock formations, is derived from the Swedish word for stairs (trappa, or sometimes trapp)[1], referring to the step-like hills forming the landscape of the region.
History
The Deccan Traps formed between 60 and 68 million years ago,[2] at the end of the Cretaceous period. The bulk of the volcanic eruption occurred at the Western Ghats (near Mumbai) some 66 million years ago. This series of eruptions may have lasted fewer than 30,000 years in total.[3] The gases released in the process may have played a role in the Cretaceous–Tertiary extinction event, which included the extinction of the dinosaurs.
Before the Deccan Traps region was reduced to its current size by erosion and continental drift, it is estimated that the original area covered by the lava flows was as large as 1.5 million km², approximately half the size of modern India. The present volume of directly observable lava flows is estimated to be around 512,000 km².
The release of volcanic gases during the formation of the traps "contributed to an apparently massive global warming. Some data point to an average rise in temperature of 8 °C (14 °F) in the last half million years before the impact at Chicxulub."[4]
Chemical Composition
Within the Deccan Traps at least 95% of the lavas are tholeiitic basalts, however other rock types occur:
Mantle xenoliths have been described from Kachchh (northwestern India) and elsewhere in the western Deccan.
Fossils
The Deccan Traps are famous for the fossils that have been collected from the intertrappean beds. Particularly well known species include the frog Oxyglossus pusillus (Owen) of the Eocene of India and the toothed bufonid Indobatrachus allied to Australian forms.[5]
Theories of Formation
It is postulated that the Deccan Traps eruption was associated with a deep mantle plume. The area of long-term eruption (the hotspot), known as the Réunion hotspot, is suspected of both causing the Deccan Traps eruption and opening the rift that once separated the Seychelles plateau from India. Seafloor spreading at the boundary between the Indian and African Plates subsequently pushed India north over the plume, which now lies under Réunion island in the Indian Ocean, southwest of India. The mantle plume model has, however, been challenged.[2]
Link to Shiva Crater
A suspected large impact crater has been recently reported in the sea floor off the west coast of India. Called the Shiva crater, it has also been dated at sixty-five million years, right at the K–T boundary. The researchers suggest that the impact may have been the triggering event for the Deccan Traps as well as contributing to the acceleration of the Indian plate in the early Tertiary.[6] However, opinion in the geologic community is not unanimous that this feature is actually an impact crater.[7] Also, the reported age is in the middle of the ages given for the Deccan rocks.
Formation's Effects on Life
Due to the volcanic gases causing a drastic climate change, the formation of the traps is seen as a major stressor on all life at the time. Dr. Norman Macleod, of the Natural History Museum in London, points out “We're talking about catastrophic effects in terms of changes in habitat, changes in rain fall patterns, changes in climate, all of these you can think of all of the things that are going on in the modern world magnified many many times, many many orders of magnitude indeed.”[4] While the fossil record of dinosaurs at this time is hard to interpret, those of other types of life are more conclusive, as Macleod states “Six million years prior to the K–T boundary there were about twenty species of ammonites in the world's oceans. Three million years before the K–T boundary there were only fifteen or so and one million years prior to the K–T boundary we have less than half of what we started out with, we have less than ten species so the extinction event has already been going on for millions of years. The amazing thing is that we see the same pattern in the fish record, we see the same pattern in the terrestrial reptile record, we even see the same pattern in the mammal record. All of these groups were undergoing an extinction event for millions of years and it would be absolutely amazing to me if dinosaurs weren't undergoing the same sort of extinction and indeed I think they were undergoing the same sort of long term extinction.”[4] Many scientists[who?] theorize that due to the climate change caused by the volcanic formation of the traps the dinosaurs were already doomed, but the impact of the meteoroid that formed the Chicxulub Crater (which made a sunlight blocking dust cloud that killed much of the plants) pushed them over the edge into extinction.[4][8]
See also
References
- ^ "Dictionary Definition of trap." Encyclopedia.com Free Online Dictionary. Accessed on 1 January 2009.
- ^ a b Sheth, Hetu C. "The Deccan Beyond the Plume Hypothesis." MantlePlumes.org, 2006.
- ^ "India's Smoking Gun: Dino-killing Eruptions." ScienceDaily, 10 August 2005.
- ^ a b c d Ayres, Yolanda (Production Manager). "What Really Killed the Dinosaurs." BBC Horizon.
- ^ Noble, Gladwyn Kingsley, "The Fossil Frogs of the Intertrappean Beds of Bombay, India." American Museum of Natural History, Volume 401, 1930.
- ^ Chatterjee, Sankar. "The Shiva Crater: Implications for Deccan Volcanism, India-Seychelles Rifting, Dinosaur Extinction, and Petroleum Entrapment at the KT Boundary." Paper No. 60-8, Seattle Annual Meeting, November 2003.
- ^ Mullen, Leslie. "Shiva: Another K-T Impact?" Astrobiology Magazine, 4 November 2004.
- ^ Choi, Charles Q. ""Double Trouble: What Really Killed the Dinosaurs." LiveScience.com, 12 November 2007.