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 (6,562 ft) thick and cover an area of 500,000 km2 (193,051 sq mi). 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.
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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 non-avian dinosaurs.
Before the Deccan Traps region was reduced to its current size by erosion and plate tectonics, 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 area of directly observable lava flows is estimated to be around 512,000 km2 (197,684 sq mi).
The release of volcanic gases, particularly sulfur dioxide, during the formation of the traps contributed to contemporary climate change. Data point to an average fall in temperature of 2 °C in this period."[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 large impact crater has been claimed to exist 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 and subsequent temperature drop, the formation of the traps is seen as a major stressor on biodiversity at the time. This is confirmed by a mass extinction topping 17 families per million years (about 15 families per million years above the average)”[8] Sudden cooling due to sulfurous volcanic gases released by the formation of the traps and localised gas concentrations may have been enough to drive a less significant mass extinction, but the impact of the meteoroid that formed the Chicxulub Crater (which made a sunlight blocking dust cloud that killed much of the plants) made this one of the most pronounced mass extinctions in the Phanerozoic.[9]
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.
- ^ Royer, D. L., Berner, R. A., Montañez, I. P., Tabor, N. J., Beerling, D. J., 2004, "CO2 as a primary driver of Phanerozoic climate", GSA Today, v. 14, pp.4-10, ISSN: 1052-5173
- ^ 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.
- ^ Futuyma, D. J., 1998, Evolutionary Biology, Sinauer Ass.
- ^ Choi, Charles Q. ""Double Trouble: What Really Killed the Dinosaurs." LiveScience.com, 12 November 2007.
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