Deccan Traps Of India Research Articles

Two timelines for extinction

Mass Extinction![Figure][1] The Deccan Traps in India were a source of large-scale volcanic activity that affected the climate 66 million years ago. IMAGE: GERTA KELLER The Cretaceous-Paleogene extinction that wiped out the nonavian dinosaurs 66 million years ago was correlated with two extreme events: The Chicxulub impact occurred at roughly the same time that massive amounts of lava were erupting from the Deccan Traps (see the Perspective by Burgess). Sprain et al. used argon-argon dating of the volcanic ash from the Deccan Traps to argue that a steady eruption of the flood basalts mostly occurred after the Chicxulub impact. Schoene et al. used uranium-lead dating of zircons from ash beds and concluded that four large magmatic pulses occurred during the flood basalt eruption, the first of which preceded the Chicxulub impact. Whatever the correct ordering of events, better constraints on the timing and rates of the eruption will help elucidate how volcanic gas influenced climate. Science , this issue p. [866][2], p. [862][3]; see also p. [815][4] [1]: pending:yes [2]: /lookup/doi/10.1126/science.aav1446 [3]: /lookup/doi/10.1126/science.aau2422 [4]: /lookup/doi/10.1126/science.aaw0473

How plume‐ridge interaction shapes the crustal thickness pattern of the Réunion hotspot track

AbstractThe Réunion mantle plume has shaped a large area of the Earth's surface over the past 65 million years: from the Deccan Traps in India along the hotspot track comprising the island chains of the Laccadives, Maldives, and Chagos Bank on the Indian plate and the Mascarene Plateau on the African plate up to the currently active volcanism at La Réunion Island. This study addresses the question how the Réunion plume, especially in interaction with the Central Indian Ridge, created the complex crustal thickness pattern of the hotspot track. For this purpose, the mantle convection code ASPECT was used to design three‐dimensional numerical models, which consider the specific location of the plume underneath moving plates and surrounded by large‐scale mantle flow. The results show the crustal thickness pattern produced by the plume, which altogether agrees well with topographic maps. Especially two features are consistently reproduced by the models: the distinctive gap in the hotspot track between the Maldives and Chagos is created by the combination of the ridge geometry and plume‐ridge interaction; and the Rodrigues Ridge, a narrow crustal structure which connects the hotspot track and the Central Indian Ridge, appears as the surface expression of a long‐distance sublithospheric flow channel. This study therefore provides further insight how small‐scale surface features are generated by the complex interplay between mantle and lithospheric processes.

Measuring and modelling water transport on Skaftafellsheiði, Iceland

Areas with thick basaltic aquifers are used for drinking water supply and irrigation purposes, such as the Columbia River Basalt group in northwest USA and the Deccan Traps in India. However, rainfall-runoff processes in these basaltic areas are poorly understood. Cooling joints can transport large amounts of water, but – due to their limited porosity – they are vulnerable for over-abstraction. On Iceland, in the small Skaftafellsheiði basaltic catchment (4 x 6 km), field data were collected in 2014 and 2015. Two small streams discharge the rain surplus. Precipitation was measured at various elevations on the ridge. Also, the discharge of the streams was measured. A groundwater flow model was constructed in order to get more insight in the physical properties of the basalt aquifer and its rainfall-runoff properties. The field experiments showed that precipitation increases linearly with surface elevation. On average, the precipitation at 800 m+msl was almost double, relative to the precipitation at 200 m+msl. Calculated ETpot was rather high, due to the 19 potential sun hours per day during the Icelandic summer. Field experiments revealed quick discharge response on rainfall events, but also rather constant base flow during dryer periods. This indicates a limited infiltration capacity, but also a considerable storage capacity in the subsequent layers. The peat layer is believed to be the dominant storage/reservoir. Peat, regolith and an organic layer formed the top layer in the GMS-Modflow groundwater model. The thick basaltic aquifer was split in a series of model layers. Best results were obtained by using a decreasing hydraulic conductivity to depth. The transient model overestimated the groundwater levels at the outlet, but managed to reproduce the wet/dry conditions in the catchment rather well. This indicates that it is possible to model complex basaltic aquifers, by taking a large Representative Elementary Volume (REV) as starting point

The Basement of the Deccan Traps and Its Madagascar Connection: Constraints from Xenoliths

Paleogeographic reconstructions of India and Madagascar before their late Cretaceous rifting juxtapose the Antongil Block of Madagascar against the Deccan Traps of India, indicating that the Western Dharwar Craton extends below the Deccan lavas. Some recent studies have suggested that the South Maharashtra Shear Zone along the northern Konkan coast of India limits the northern extent of the Western Dharwar Craton, implying that the craton does not extend below the Deccan Traps, raising a question mark on paleogeographic reconstructions of India and Madagascar. The continuity of the Western Dharwar Craton north of the South Maharashtra Shear Zone below the Deccan Traps—or its lack thereof—is critical for validating tectonic models correlating Madagascar with India. In this study, zircons in tonalitic basement xenoliths hosted in Deccan Trap dykes were dated in situ, using the U-Pb isotope system. The data furnish U-Pb ages that define three populations at 2527 ± 6, 2456 ± 6, and 2379 ± 9 Ma. The 2527 ± 6 Ma ages correspond to the igneous crystallization of the tonalites, whereas the 2456 ± 6 and 2379 ± 9 Ma ages date metamorphic overprints. The results help to establish for the first time that the basement is a part of the Neoarchean granitoid suite of the Western Dharwar Craton, which extends northward up to at least Talvade in central and Kihim beach in the western Deccan. By implication, the South Maharashtra Shear Zone cannot be the northern limit of the Western Dharwar Craton. The granitoids are correlated with the Neoarchean felsic intrusions (2.57–2.49) of the Masaola suite in the Antongil Block of Madagascar, supporting the existence of a Neoarchean Greater Dharwar Craton comprising the Western Dharwar Craton and the Antongil-Masora Block.

Molecular Characterization of Prokaryotic Communities Associated with Lonar Crater Basalts

The Lonar crater is an unusually well-preserved meteorite impact structure that is located in one of the largest volcanic provinces on Earth (i.e., the Deccan Traps in India). The diversity of endoliths in Lonar crater basalts or Deccan flood basalts is not known. Here, the phylogenetic diversity of endolithic Bacteria and Archaea inhabiting basalts retrieved from four discrete sampling sites on the Lonar crater walls and the lake-bed was assessed using culture-independent molecular methods. Taxonomic classification of 16S rRNA gene sequences from all four basalt samples revealed similarities as well as dissimilarities in the presence or absence of several prokaryotic taxa. Cluster analysis of Denaturing gradient gel electrophoresis fingerprints and UniFrac analysis of clone library sequences suggested substantial variations in bacterial and archaeal diversity between crater-wall and lake-bed sites. Although sequences affiliated to the bacterial phyla Actinobacteria, Acidobacteria and Chloroflexi were relatively more abundant in crater-wall basalts than in lake-bed basalts; the reverse was observed for sequences related to Proteobacteria, Firmicutes, Cyanobacteria and Bacteroidetes. Archaea in crater-wall and lake-bed basalt libraries were almost completely represented by Thaumarchaeota and Euryarchaeota, respectively. Diversity indices and richness estimates suggested the diversity of endolithic Bacteria to be higher than that of Archaea in the Lonar crater basalts. A substantial number of clone library sequences did not affiliate with extant Bacteria and Archaea. The detection of several putative lineages associated with C, N and S cycling suggests that the Lonar crater basalts are colonized by metabolically diverse prokaryotic communities involved in biogeochemical cycling of major elements.

The effect of intra-trappean heterogeneities on seismic data: A case study from the Deccan Traps

Hydrocarbon exploration interests have renewed the need for developing new sub basalt imaging techniques. One of the most important problems encountered today is seismic imaging below basalt. In recent years, this problem appears to have been overcome partly by using long offset seismic data. However near offset data are yet to be fully utilised due to the complex waveform caused by the surface as well as internal heterogeneity of the basalts. The near normal incidence data, which influence the sub-basalt imaging, are highly useful to understand the internal structure within a basalt layer. The use of converted waves for such targets has been proposed as an alternative in a rather homogeneous basalt layer. With a few synthetic modelling exercises here we highlight the practical difficulties in dealing with more realistic and heterogeneous basalt flow. Full waveform seismograms are computed to understand the effects of intra-trappean sediments on the seismic data. A case study from the Deccan Traps of India is presented in this paper. First, we discuss the effects of intercalated sediments on the overall seismic image. Later, the sonic log data from the field are used to compute the full wave-field response using the reflectivity method and compared with the field data. The feasibility of using mode converted waves (P to S and vice-versa at the top and bottom basalt interfaces) for sub-basalt imaging in Kutch region is discussed through a series of velocity-depth profiles. By comparing with the field data we demonstrate that the effects of multiple thin layering within the basalt can strongly deteriorate the image we seek to interpret and exploit.

Structure and emplacement of the Nandurbar–Dhule mafic dyke swarm, Deccan Traps, and the tectonomagmatic evolution of flood basalts

Flood basalts, such as the Deccan Traps of India, represent huge, typically fissure-fed volcanic provinces. We discuss the structural attributes and emplacement mechanics of a large, linear, tholeiitic dyke swarm exposed in the Nandurbar–Dhule area of the Deccan province. The swarm contains 210 dykes of dolerite and basalt >1 km in length, exposed over an area of 14,500 km2. The dykes intrude an exclusively basaltic lava pile, largely composed of highly weathered and zeolitized compound pahoehoe flows. The dykes range in length from <1 km to 79 km, and in thickness from 3 to 62 m. Almost all dykes are vertical, with the others nearly so. They show a strong preferred orientation, with a mean strike of N88°. Because they are not emplaced along faults or fractures, they indicate the regional minimum horizontal compressive stress (σ 3) to have been aligned ~N–S during swarm emplacement. The dykes have a negative power law length distribution but an irregular thickness distribution; the latter is uncommon among the other dyke swarms described worldwide. Dyke length is not correlated with dyke width. Using the aspect ratios (length/thickness) of several dykes, we calculate magmatic overpressures required for dyke emplacement, and depths to source magma chambers that are consistent with results of previous petrological and gravity modelling. The anomalously high source depths calculated for a few dykes may be an artifact of underestimated aspect ratios due to incomplete along-strike exposure. However, thermal erosion is a mechanism that can also explain this. Whereas several of the Nandurbar–Dhule dykes may be vertically injected dykes from shallow magma chambers, others, particularly the long ones, must have been formed by lateral injection from such chambers. The larger dykes could well have fed substantial (≥1,000 km3) and quickly emplaced (a few years) flood basalt lava flows. This work highlights some interesting and significant similarities, and contrasts, between the Nandurbar–Dhule dyke swarm and regional tholeiitic dyke swarms in Iceland, Sudan, and elsewhere.

A case for short duration of Deccan Trap Eruption

Earth's geologic past has been punctuated by episodes of voluminous outpouring of lava that flooded large areas of continents and oceans, giving rise to what are commonly called flood basalt provinces. These flood basalt eruptions often coincided with major stratigraphic boundaries and mass extinction events.The Deccan Traps of India are a muchstudied example of a flood basalt province that erupted at or near the Cretaceous/Tertiary (K/T) boundary 65 million years ago. These lavas reach a maximum thickness of 2.7 kilometers at the Western Ghats of India.

PALEOBIOGEOGRAPHY OF PSEUDOTEXTULARIA ELEGANS DURING THE LATEST MAASTRICHTIAN GLOBAL WARMING EVENT

A latest Maastrichtian global warming event, which began approximately 450 k.y. and ended about 22 k.y. prior to the K/T boundary, is associated with the pole-ward migration of the warm-water planktonic foraminifer Pseudotextularia elegans. The warming event was apparently inititated by greenhouse warming due to the main outpouring of the Deccan Traps in India and is now well documented in the North and South Atlantic Oceans and in North America by the poleward migration of warm-water planktonic foraminifera and subtropical vegetation. A cooling trend ca 22 kyr prior to the K/T boundary caused marine δ18O values to return to climatic conditions recorded prior to the onset of warming and thus does not represent a significant change in long-term climate. Planktonic foraminifera responded by migration to the latest Maastrichtian global warming and cooling before their mass extinction at the K/T.

The Age and Duration of Flood Basalt Magmatism: Geochemical and Palaeomagnetic Constraints from the Siberian Province

Many recent models for continental flood basalt (CFB) magmatism imply that such provinces were produced rapidly. The possibility of erupting huge volumes of magma within a million years, or less, has led to the speculation that flood basalt volcanism may provide a causal mechanism for mass extinction events. For example, the Deccan Traps of India and the Siberian Traps appear respectively to be temporally associated with the Cretaceous-Tertiary (K-T) and Permo-Triassic (PTr) extinctions.

Madagascar basalts: tracking oceanic and continental sources

Extensive Upper Cretaceous volcanism in southern Madagascar was fed in part by mantle sources resembling those expressed today in the Indian Ocean at Marion and Prince Edward islands and on the central Southwest Indian Ridge. In addition, very low ε Nd( T) (to −17.4), high( 87Sr/ 86Sr) T (to 0.72126) tholeiites in southwestern Madagascar were variably but highly contaminated by ancient continental material broadly like that affecting the Bushe and Poladpur Formations of the later Deccan Traps in India. Alkalic dikes in southwestern Madagascar have a rough analogue in the Mahabaleshwar Formation of the Deccan, in that they document the influence of a low 206Pb/ 204Pb, negative ε Nd, relatively low 87Sr/ 86Sr reservoir. A very similar reservoir is manifested at present in mid-ocean ridge basalts on the central Southwest Indian Ridge near 40°E. The original location of this end-member appears likely to have been in the Madagascan lithospheric mantle, a portion of which may have been removed in the Middle Cretaceous by the action of the Marion hotspot or the rifting of Indo-Madagascar. An origin within the hotspot itself also may be possible; however, recent products of the hotspot appear to lack completely the necessary low 206Pb/ 204Pb, low ε Nd signatures.

A Volcanic Eruption

The authors proposes that dust, carbon dioxide and other emissions from an episode of enormous volcanism that formed the basaltic Deccan Traps in India produced the climate changes that led to the mass extinction at the end of the Cretaceous period. The iridium could, he says, just as easily have risen from the earth's mantle. The sheer size of the Deccan Traps suggests that their formation must have been an important event in the earth's history. An important, unresolved question was whether the data and duration of Deccan volcanism are compatible with the age and thickness of the KT boundary. Until recently the lava samples from the Deccan Traps were thought to range in age from 80 to 30 million years (estimated by measuring the decay of the radioactive isotope potassium 40 in rocks). The author presents data suggesting volcanism could not have lasted much more than one million years and was roughly simultaneous with the extinction at the end of the Cretaceous period.

Shocked quartz found at the K/T boundary

What killed the dinosaurs? This is the most popular question of the “Cretaceous/Tertiary (K/T) controversy,” which is concerned with the extinction some 65 m.y. ago of more than 75% of the world's existing floral and faunal species [Surlyk, 1980]. A popular hypothesis of their untimely demise is the impact of a meteorite [Alvarez et al., 1980]. However, despite the claim [Alvarez, 1983] that this has been proven, some serious doubts remain [Hallam, 1987; Officer et al., 1987]. A rival claim, that the dinosaurs were done in by a catastrophic volcanic eruption, has attracted some proponents and has some evidence in its favor, but that case is far from proven. However, it does have the advantage of having a definite event to point to the Deccan Traps in India. These are the largest continental flood basalts known from the Phanerozoic. According to recent studies [Courtillot et al., 1986; Feraud et al., 1988], the Deccan Traps were emplaced close to 65 m.y. ago. Is this timing a coincidence or are the two events (the mass extinction and the Deccan volcanism) related?

Volcanoes and Extinctions: Round Two

In 1979, a group of researchers injected new life into an old study of death. Led by Alvarez at the University of California at Berkeley, they proposed that an asteroid had crashed into the earth at the end of the Cretaceous period, 65 million years ago. This impact, they suggested, threw a blanket of dust into the atmosphere, which blocked out the sunlight, causing famine and mass extinctions (SN: 6/2/79, p.356). most famous casualties were the dinosaurs. Now, after stimulating a whirlwind of research in paleontology, stratigraphy, geochemistry, astrophysics and statistics, Alvarez believes the impact theory of the Cretaceous-Tertiary (K-T) extinctions on solid enough ground for him to move on to other geologic pursuits. As he concluded last fall in Eos, the weekly newspaper of the American Geophysical Union, ... the unusual features of the K-T [stratigraphic] boundary layer are exactly compatible with a major impact. competing theory that intense volcanic eruptions caused the extinctions (SN: 3/16/85, p.172), he suggested, simply cannot account for all of the evidence. Alvarez may have hoped that his Eos article, by carefully outlining all the evidence and what he sees as the shortcomings of the volcanic hypothesis, would put the debate to rest. But for some researchers, it only sparked more arguments for the volcanic cause. At issue the resolution of one of the most intriguing puzzles in science. By understanding what killed off the dinosaurs and three-quarters of the species living on earth 65 million years ago, researchers not only would solve a longstanding mystery of the past, but might catch a glimpse of what could befall the planet in the future. Walter [Alvarez] says the volcanic road shut. I think, on the contrary, it very wide open, says Vincent E. Courtillot, who visiting the University of California at Santa Barbara (UCSB) from the Institut de Physique du Globe in Paris. In a letter in the April 7 Eos, Courtillot and Stanley Cisowski of UCSB respond to Alvarez's Eos paper. The purpose of this letter, they write, is to stress that answers have changed rapidly in recent years and may still evolve, and that the case for a volcanic cause may have been determined extinct by Alvarez somewhat prematurely Courtillot and Cisowski are not alone. Charles Officer at Dartmouth College in Hanover, N.H., and his colleagues published a paper in the March 12 NATURE that outlines the volcanic arguments and looks in detail at how a series of large volcanic eruptions could affect the environment and life. Among the recent lines of evidence and theory that have motivated Courtillot and Officer to write their papers are: *A date for the Deccan Traps. Deccan Traps in India are vast flood basalts, or lava flows, that today cover an area about the size of France and may once have contained 1 million cubic kilometers of volcanic material. Proponents of the volcanic theory have suggested that the Deccan eruptions caused the K-T extinctions by spewing out sulfur and other volcanic material that darkened the skies, cooled the planet and produced acid rain. But the correlation between the K-T extinctions and the Deccan Traps has been sketchy at best, says Courtillot, because the traps have not been very precisely dated. While the most frequently quoted age for the traps falls around 60 million to 65 million years old, he says, other estimates, determined 6 68 7 72; .--.76 80 B4 88 92 96 36! (' '. |

Problemes de la construction de barrages en terre dans les traps du deccan (Inde)

The Deccan Traps of India are formed of normal augite basalt, which on decomposition in place and a long cycle of secondary changes resulted in the formation of an expansive soil. This paper discusses the problems of earth dam construction on Deccan Traps of India, including the sophistication of the material with respect to engineering and geological aspects.

Clay mineralogy and sedimentation in the eastern Indian Ocean

The distributions of clay minerals in the surface sediments based on about 100 new samples from the eastern Indian Ocean reveal several distinctive sediment sources which differ from those reported previously by other workers. We observe the following: (1) large zones around the periphery of the study area are characterized by abundant smectite. These largely volcanogenic sediments are derived from the Indonesian Archipelago in the northeast, from submarine volcanics of the Mid-Indian Ocean Ridge and nearby areas in the southwest, and from the Deccan Traps of India along the western side of the Bay of Bengal. The effect of Indonesian volcanism is also observed in the Cocos-Roo Rise area and on the Ninety East Ridge between 05°N and 15°S. The chief agents of transport in the case of Deccan smectite are turbidity currents and counter-clockwise surface water circulation, and, in the case of Indonesian volcanics, wind. (2) The Ganges Cone and the Java Trench are characterized by relatively more abundant illite and chlorite dispersed primarily by turbidity currents from the Ganges and Brahmaputra rivers. The influence of this sediment source extends well south of the equator on both sides of the Ninety East Ridge. The southwestern part of the Ganges Cone, is, however, characterized by smectite-rich sediments derived from the Deccan Traps. (3) A zone extending west of Australia to the Ninety East Ridge, contains relatively abundant kaolinite which is probably wind-borne from that continent. Comparison of clay mineralogy in several of these regions between Quaternary and pre-Quaternary sediments indicates changes in sediment sources and/or transport mechanisms in the geological past. For example, west of Australia, abundant volcanogenic smectite was deposited during the Cretaceous-Eocene and the relatively high kaolinite characteristics of the Quaternary sediments has been supplied only since the Miocene.

IV.—Pipe-Amygdaloids

Pipe-Amygdaloids, although recorded in the Deccan Traps of India and in Tertiary Basalts from Mull, are rather uncommon, rocks except in South Africa. They were described by Professor E. Cohen, who obtained his specimens through Mr. J. Orpen from the Stormberg lavas (Lower Jurassic) of Basutoland, a formation in which they are very abundant. Since then they have been found in other volcanic formations, e.g., in the very ancient lavas of the Ventersdorp System in the Divisions of Kimberley and Barkly West, in the Bushveld Amygdaloid of the Transvaal and the Basalts of the Lebombo and Zululand (which all overlie rocks belonging to the Karroo System), and in the volcanic fissure of the Zuurberg in the Cape Colony (probably of post-Neocomian age). They have a striking resemblance to organic structures, and Cohen likens them to certain corals; in some exposures of lava the little pencils of white zeolite studding the surface remind one of the casts of worm burrows.