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Abstract

Most mass extinctions coincide in time with outpourings of continental flood basalts (CFB). Some 20 years ago, it was shown [Courtillot, V., Besse, J., Vandamme, D., Montigny, R., Jaeger, J.-J., Cappetta, H., 1986. Deccan flood basalts at the Cretaceous/Tertiary boundary? Earth Planet. Sci. Lett. 80, 361–374; Courtillot, V., Feraud, G., Maluski, H., Vandamme, D., Moreau, M.G., Besse, J., 1988. Deccan flood basalts and the Cretaceous/Tertiary boundary. Nature 333, 843–846; Duncan, R.A., Pyle, D.G., 1988. Rapid eruption of the Deccan flood basalts at the Cretaceous/Tertiary boundary. Nature 333 841–843] that the age of the Deccan traps was close to the Cretaceous–Tertiary (KT) boundary and its duration under 1 Myr. We have undertaken a new geochronological study, using the (unconventional) 40K–40Ar Cassignol–Gillot technique which is particularly well suited to the potassium-poor Deccan lavas. The mean of 4 determinations from the topmost (Ambenali and Mahabaleshwar) Formations is 64.5±0.6 Ma. They straddle the C29r/C29n reversal boundary for which they provide a new constraint. The mean age of 3 determinations from the oldest (Jawhar) Formation is 64.8±0.6 Ma. The difference in age between top and bottom of a 3500 m composite section, probably comprising 80% of the total Deccan volume, is statistically insignificant, with the overall mean age being 64.7±0.6 Ma (N=7). Our results are consistent with the most recent 40Ar/39Ar determinations [Knight, K.B., Renne, P.R., Halkett, A., White, N., 2003. 40Ar/ 39Ar dating of the Rajahmundry Traps, eastern India and their relationship to the Deccan traps. Earth Planet. Sci. Lett. 208, 85–99; Knight, K.B., Renne, P.R., Baker, J., Waight, T., White, N., 2005. Reply to ‘40Ar/39Ar dating of the Rajahmundry Traps, Eastern India and their relationship to the Deccan Traps: Discussion’ by A.K. Baksi. Earth Planet. Sci. Lett. 239, 374–382], confirming that there should be no systematic difference between the two methods when they are used in an optimal way. An earlier, smaller but significant, pulse of volcanism between 68 and 67 Ma, extending over at least 500 km in latitude in the northern part of the Deccan CFB has also been identified. After 2 to 3 Ma of quiescence, the second, major phase of volcanism occurred near 65 Ma, expanding over most of the area covered by the first pulse and another 500 km to the South, consistent with drift of India by 300 to 450 km at ∼150 mm/yr during the quiescence period. New paleontological data from the remote Rajahmundry section [Keller, G., Adatte, T., Gardin, S., Bartolini, A., Bajpai, S., Humler, E., in prep. The Cretaceous–Tertiary boundary in Deccan Traps of the Krishna–Godavari Basin of southeastern India. EPSL to be submitted] suggest that this second pulse can itself be divided into two major pulses, one starting in C29r and ending at the KT boundary, the second starting in the upper part of C29r and ending within C29n.

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... They crop out over large areas of western and central peninsular India including Gujarat, Madhya Pradesh, Maharashtra, Karnataka, and Andhra Pradesh, with outliers to the southeast in Rajahmundry in the Krishna-Godavari basin (K-G basin) (Fig. 1). The oldest flows commenced in the northwestern part in Gujarat, with successively younger flows overlapping these and extending more to the south (Chenet et al., 2007). ...
... Current understanding of the geology is mostly based on the study of lava sequences from the Western Deccan Volcanic Province (WDVP, including Western Ghats), which are generally barren of any associated sedimentary beds except the Paleocene intertrappean beds of the Mumbai region. It has been proposed that the Deccan basalts were produced during three main phases (Chenet et al., 2007(Chenet et al., , 2008(Chenet et al., , 2009, each comprising multiple eruptions. The first phase, about 2 million years before the KPB (C30n/ C30r), was estimated to account for ~6% of Deccan basalt volume. ...
... The last phase, in the early Paleocene (onset at C29r/C29n boundary), was considered to have been less extensive, accounting for ~14% of the basalt volume, extending to ca. 300 Kyr after the boundary (Keller et al., 2012). However, new high-precision dating of the Deccan traps (Schoene et al., 2015;Renne et al., in press) does not corroborate the three-pulse model as presented in Chenet et al. (2007Chenet et al. ( , 2008Chenet et al. ( , 2009, and suggests instead that the DVP eruption was continuous over ~750 ky. ...
Article
During the Cretaceous and Paleogene, the Indian subcontinent was isolated as it migrated north from the east coast of Africa to collide with Asia. As it passed over the Reunion hotspot in the late Maastrichtian–early Danian, a series of lava flows extruded, known as the Deccan Traps. Also during this interval, there was a major mass-extinction event at the Cretaceous–Paleogene boundary, punctuated by a meteorite impact at Chicxulub, Mexico. What were the biological implications of these changes in paleogeography and the extensive volcanism in terms of biodiversity, evolution, and biogeography? By combining chronostratigraphic, paleosol, and paleobotanical data, an understanding of how the ecosystems and climates changed and the relative contributions of the Chicxulub impact, Deccan Traps volcanism, and paleogeographic isolation can be gained. Understanding relative ages of paleobotanical localities is crucial to determining floristic changes, and is challenging because different methods (e.g., magnetostratigraphy, radiometric dating, vertebrate and microfossil biostratigraphy) sometimes give conflicting answers, or have not been done for paleobotanical localities. Climatic data can be obtained quantitatively by studying paleosol geochemistry, as well as qualitatively by examining functional traits and nearest living relatives of fossil plants. An additional challenge is revising macrofossil data, which includes some confidently identified taxa and others with uncertain affinities. This is important for understanding ecosystem composition both spatially and temporally, as well as the biogeographic implications of an isolated India.
... Previous studies considered that Deccan Trap erupted over ca. 1.6 × 10 6 km 3 (Jay and Widdowson 2008) of magma volume that presently covers an area of over 500,000 km 2 mainly in central and western India (Peng et al. 1998;Chenet et al. 2007Chenet et al. , 2008. ...
... However, it is challenging to extend or correlate the chemostratigraphy of WG to other geographically separated Deccan provinces where the lava flows are classified mainly based on the litho-stratigraphy. The volcanic piles of WG have also been chronologically well dated (Duncan and Pyle 1988;Widdowson et al. 2000;Knight et al. 2003;Chenet et al. 2007;Hooper et al. 2010;Renne et al. 2015;Schoene et al. 2015;Sheth et al. 2018;Sprain et al. 2019). In the provinces away from the WG where the intertrappean beds occur at different levels in the DVS (Hansen et al. 2005;Mohabey 2009, 2014;Mohabey and Samant 2013) such chronological dating is either lacking completely or limited making it difficult to have chrostratigraphic constraint on the exposed sequences. ...
... The precisely coeval nature of the K-Pg event and Chicxulub impact strongly supports the latter as the primary trigger of the mass extinction (Schulte et al., 2010;Hull et al., 2020). However, the impact and mass extinction also occurred during the time of volcanic emplacement of the Deccan Traps large igneous province (Courtillot et al., 1986;Duncan and Pyle, 1988;Chenet et al., 2007;Schoene et al., 2019;Sprain et al., 2019;Schoene et al., 2021;Mittal et al., 2022). The temporal overlap of these three phenomena has been interpreted as suggesting a causal relationship between the large igneous province and the extinction (Courtillot et al., 1988;Keller et al., 2004), and even between the impact and the Deccan eruption rate (Richards et al., 2015). ...
... In this context, a shift in 187 Os/ 188 Os (i) ratios from ∼0.6 to ∼0.4 around the C30n-C29r magnetochron boundary in uppermost Maastrichtian strata is generally interpreted to reflect the emplacement of juvenile, easily weathered Deccan Trap basalts, which increased the runoff of less radiogenic, mantle-like Os to the global ocean relative to older and more radiogenic crustal material (Ravizza and Peucker-Ehrenbrink, 2003;Robinson et al., 2009). This interpretation is consistent with the documentation of the C30n-C29r boundary near the base of the "main" phase of Deccan lavas (Chenet et al., 2007;Schoene et al., 2019;Sprain et al., 2019). Because those basalts have a very low Os concentration Wimpenny et al., 2007;Schulz et al., 2016), it has been proposed that their erosion alone could not have caused this shift in oceanic 187 Os/ 188 Os (i) (Ravizza and Peucker-Ehrenbrink, 2003). ...
Article
The Cretaceous−Paleogene boundary is marked by a large impact and coeval mass extinction event that occurred 66 m.y. ago. Contemporaneous emplacement of the volcanic Deccan Traps also affected global climate before, during, and after the mass extinction. Many questions remain about the timing and eruption rates of Deccan volcanism, its precise forcing of climatic changes, and its signature in the marine geochemical sedimentary proxy record. Here, we compile new and existing mercury (Hg) concentration and osmium isotope (187Os/188Os) records for various stratigraphic sections worldwide. Both geochemical proxies have been suggested to reflect past variations in Deccan volcanic activity. New data from deep marine pelagic carbonate records are compared to contemporaneous records from shallower marine sites correlated through high-resolution cyclostratigraphic age models. The robustness of the proxy records is evaluated on a common timeline and compared to two different Deccan eruption history scenarios. Results show that the global 187Os/188Os signal is clearly reproducible, while the global Hg record does not form a consistent pattern. Moreover, the deep marine sections investigated do not record clear variations in the Hg cycle, particularly in the latest Cretaceous, prior to the extinction event. A detailed reevaluation of the precise depth of the redistribution of impactor-sourced platinum group elements does not exclude the possibility of a minor drop in 187Os/188Os corresponding with a pulse of Deccan volcanism ∼50,000 years before the Cretaceous−Paleogene boundary. Simple Os isotope mass balance modeling indicates that the latest Cretaceous was marked by significant levels of basalt weathering. CO2 sequestration during this weathering likely overwhelmed the emission of Deccan volatiles, thereby contributing to the end of the late Maastrichtian warming.
... So, palaeomagnetic studies can play a crucial role in constraining the timing of Deccan volcanic events (e.g. Chenet et al., 2007Chenet et al., , 2009. A combined palaeomagnetic and radioactive datings have suggested that the Deccan lavas erupted in three short, yet discrete megapulses (Chenet et al., 2007). ...
... Chenet et al., 2007Chenet et al., , 2009. A combined palaeomagnetic and radioactive datings have suggested that the Deccan lavas erupted in three short, yet discrete megapulses (Chenet et al., 2007). The earliest pulse occurred at ~67.5 ± 1 Ma ( 40 K-40 Ar plagioclase/microlite ages) near the C30r/C30n transition and the following two at ~65 ± 1 Ma; one entirely within C29r just before the K-Pg boundary (KPB) and the other shortly afterward spanning the C29r/C29n reversal (Chenet et al., 2009). ...
Article
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The study of Deccan volcano-sedimentary successions is significant for understanding the palaeomagnetic correlation, eruption history and palaeoenvironmental conditions of the Central India during the Cretaceous-Paleogene (K-Pg) transition. In this study, we applied an integrated magnetostratigraphic and sedimentological approach to the Deccan Intertrappean Succession exposed at the Mothi Hill (Malwa Subprovince), Sagar, to provide palaeomagnetic age constraints for the lava flows, depositional environment and end-Cretaceous palaeogeography. Palaeo-magnetic data suggest that the lower and upper Trap lava flows associated with the Mothi Intertrappean deposits are not coeval, and they correspond to C29r and C29n magnetochrons, respectively, which points to the age duration of 66.3–65.1 Ma (late Maastrichtian-early Danian). The palaeomagnetic data also marks the presence of upper magnetic polarity transition (C29r/C29n) in the eastern part of the Malwa Subprovince, which indicates the occurrence of C30n-C29r-C29n magnetostratigraphic sequence for the Subprovince. The Malwa, eastern Mandla and Western Ghats Subprovinces can be palaeomagnetically correlated and are partly synchronous with each other. The Mothi Intertrappean deposition occurred in a low energy shallow water lacustrine setup with swampy to brackish depositional condition similar to shallow coastal lake type environment. The occurrence of such coastal type depositional environment at Sagar in the central part of India, points to the influence of temporary marine incursion and existence of marine pathway up to Central India, possibly through the western corridor of Narmada-Tapti rift zone during the late Maastrichtian-early Danian period. Moderate to intense chertification within the argillaceous limestone suggests post-depositional diagenetic modification and secondary silica generation due to interaction with silica enriched meteoric water diagenesis.
... Voluminous (>10 6 km 3 ) basaltic eruptions are a plausible explanation for globally recognized Late Maastrichtian changes through the injection of climate altering gases (Self et al., 2006) Resolution of the issues outlined here is dependent to a variable extent on precise and accurate geochronology. Attempts at dating the duration of Deccan volcanism have been presented over several decades utilizing 40 K/ 40 Ar (Alexander, 1981;Chenet et al., 2007;Kaneoka & Haramura, 1973;Wellman & McElhinny, 1970), 40 Ar/ 39 Ar (Chenet et al., 2007;Courtillot et al., 1988;Duncan & Pyle, 1988;Hofmann et al., 2000;Hooper et al., 2010;Pande et al., 2004;Renne et al., 2015;Schöbel et al., 2014), magnetostratigraphic (Schöbel et al., 2014;Vandamme et al., 1991), and U-Pb (Eddy et al., 2020;Schoene et al., 2019) data sets. More recent constraints on the timing of Deccan main phase volcanism as well as the likely location of the KPB within the stratigraphy (Schoene et al., 2019;Sprain et al., 2019) have vastly improved the time frame that is relevant to the relationship between the Deccan Traps and the KPB. ...
... Voluminous (>10 6 km 3 ) basaltic eruptions are a plausible explanation for globally recognized Late Maastrichtian changes through the injection of climate altering gases (Self et al., 2006) Resolution of the issues outlined here is dependent to a variable extent on precise and accurate geochronology. Attempts at dating the duration of Deccan volcanism have been presented over several decades utilizing 40 K/ 40 Ar (Alexander, 1981;Chenet et al., 2007;Kaneoka & Haramura, 1973;Wellman & McElhinny, 1970), 40 Ar/ 39 Ar (Chenet et al., 2007;Courtillot et al., 1988;Duncan & Pyle, 1988;Hofmann et al., 2000;Hooper et al., 2010;Pande et al., 2004;Renne et al., 2015;Schöbel et al., 2014), magnetostratigraphic (Schöbel et al., 2014;Vandamme et al., 1991), and U-Pb (Eddy et al., 2020;Schoene et al., 2019) data sets. More recent constraints on the timing of Deccan main phase volcanism as well as the likely location of the KPB within the stratigraphy (Schoene et al., 2019;Sprain et al., 2019) have vastly improved the time frame that is relevant to the relationship between the Deccan Traps and the KPB. ...
Article
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The eruptive history of the Malwa Plateau Subprovince of the Deccan Traps is addressed by dating 21 lavas spanning the exposed stratigraphic extent, using the ⁴⁰Ar/³⁹Ar method applied to plagioclase separates. Major, minor, and trace element geochemistry was determined for each of the dated lavas and four additional ones. Dating results indicate that the eruptions began prior to 66.8 Ma, at least 400 ka before the oldest known lava in the more extensively studied Western Ghats, representative of the main Deccan province, to the south. Eruption rates peaked from 66.4 to 66.3 Ma and then diminished until 65.6 Ma. The peak in eruption rates coincides with the well‐documented Late Maastrichtian Warming event. Malwa lavas show some major and trace element affinities with geochemically defined lava flow formations of the Western Ghats, but are generally out of the stratigraphic sequence manifest in the Western Ghats. The distinct geochemical evolution of Malwa Plateau lavas compared with those of the Western Ghats is at least in part a consequence of differences in crustal composition between the two subprovinces. Modeling of REE concentration patterns of Malwa lavas suggests that they were derived by slightly lower degrees of partial melting, at lower mantle temperatures and depths, than those in the Western Ghats. The Malwa Plateau thus appears to record an earlier, cooler stage of the Deccan plume's evolution and continued to erupt through a large part of the lifetime of the main Deccan province.
... The high-frequency, precessional pacing of the carbon export in the tropical Pacific persisted throughout the Maastrichtian. This suggests it was a consistent, intrinsic feature of the end-Cretaceous cool greenhouse, despite longer (and larger) scale changes, e.g., early Maastrichtian cooling pulse (EMCP; Haynes et al., 2020), warm mid-Maastrichtian event (MME; MacLeod and Huber, 1996), the early phase of Deccan Traps volcanism (67.5 to 67.1 Ma;Chenet et al., 2007;Keller et al., 2016), or the Latest Maastrichtian Warming Event (LMWE; Li and Keller, 1998;Gilabert et al., 2021). ...
... Organic carbon export appears largely decoupled from the abundance and eventual extinction of inoceramid bivalves related to the MME, suggesting that additional drivers (e.g., emplacement of large igneous provinces) played an important role in biotic change during this time. An increase in amplitude of the variations in carbon export recorded towards the end of the Cretaceous suggests an amplified sensitivity to orbital forcing when CO 2 was higher during Deccan volcanism, beginning around 67.5 Ma (Chenet et al., 2007). As anthropogenic CO 2 emissions increase today, we need to consider whether or not sensitivity to seasonal insolation in the tropics might increase and dominate changes in the oceancarbon-climate system in this key region. ...
Article
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The marine biological carbon pump, which exports organic carbon out of the surface ocean, plays an essential role in sequestering carbon from the atmosphere, thus impacting climate and affecting marine ecosystems. Orbital variations in solar insolation modulate these processes, but their influence on the tropical Pacific during the Late Cretaceous is unknown. Here we present a high-resolution composite record of elemental barium from deep-sea sediments as a proxy for organic carbon export out of the surface oceans (i.e., export production) from Shatsky Rise in the tropical Pacific. Variations in export production in the Pacific during the Maastrichtian, from 71.5 to 66 million years ago, were dominated by precession and less so by eccentricity modulation or obliquity, confirming that tropical surface-ocean carbon dynamics were influenced by seasonal insolation in the tropics during this greenhouse period. We suggest that precession paced primary production in the tropical Pacific and recycling in the euphotic zone by changing water column stratification, upwelling intensity, and continental nutrient fluxes. Benthic foraminiferal accumulation rates covaried with export production, providing evidence for bentho-pelagic coupling of the marine biological carbon pump across these high-frequency changes in a cool greenhouse planet.
... Most later workers followed this classification of the Bagh Beds (= Bagh Group, Jaitly and Ajane 2013). Among numerous previous contributions on lithostratigraphy, fossils and age of the Bagh Beds, mention may be made of Bose (1884), Rode and Chiplonkar (1935), Roy Chowdhury and Sastri (1962), Dassarma and Sinha (1975), Chiplonkar and Ghare (1976), Guha (1976), Tripathi (2006), Jaitly and Ajane (2013) and Ruidas et al. (2018). The Bagh Beds are overlain by the latest Cretaceous Lameta Group, which, in turn, is succeeded by the Deccan Traps volcanic flows, interbedded with intertrappean beds. ...
... The age of the Deccan basaltic flows was considered to be early Eocene by earlier workers (e.g., Hislop 1860;Sahni 1934;Hora 1938;Bhalla 1974). During the past four decades or so, based mainly on radiometric and magnetostratigraphic data, the age of the Deccan lavas was re-assessed as latest Cretaceous-early Palaeocene between 67 and 63 Ma, with bulk of the Deccan eruptions occurring in a short period of less than one million years (e.g., Courtillot et al. 1986;Vandamme et al. 1991;Chenet et al. 2007). Palaeontological data from the Deccan intertrappeans currently favour either a Late Cretaceous (Maastrichtian) or an early Palaeocene age, broadly in agreement with the geochronological and magnetostratigraphic constraints (Sahni and Bajpai 1988;Bajpai and Prasad 2000;Keller et al. 2009;Wilson Mantilla et al. 2022). ...
Article
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We here report on the first lizard fossils from the Deccan intertrappean strata (latest Cretaceous/Palaeocene) exposed at Kesavi, District Dhar in the Malwa Plateau of lower Narmada Valley, central India. The material is only fragmentary, but tentatively three tooth morphotypes of non-acrodontan lizards can be identified. Besides these, two oblong osteoderms, resembling paramacellodid osteoderms, are described as Squamata indet. The 4th isolated tooth is questionably referred to Squamata. Although the intertrappean deposits of the Deccan volcanic province have been explored for over three decades, lizards are scarce and many aspects remain unclear. However, the tentative absence of agamids in Kesavi and other localities yielding pre-Eocene deposits (e.g., Naskal and Kisalpuri) appears to be interesting, because a high diversity of agamids has been reported from early Eocene localities of India. There is, in contrast, a total absence of non-acrodontan lizards. The contrast between pre-Eocene and Eocene localities seems to be puzzling in the context of India’s supposed physical isolation from Asia during this time. Only future researches can shed light on that. Although the material described here brings only limited new insight, it supports that non-acrodontan lizards were present in India during the latest Cretaceous/earliest Palaeocene.
... Thus, this succession contains PGE anomaly at the two stratigraphic levels which corresponds to biozones CF4 and CF2. The first phase of late Maastrichtian Deccan volcanic eruptions occurred during the biozone CF3 [ages ∼67.5 ± 1 Ma (Chenet et al. 2007(Chenet et al. , 2009 6.3-66.15 Ma (Schoene et al., 2019). ...
... Ma (Schoene et al., 2019). The most vigorous second phase of the eruption occurred at the biozone CF2 during 65 ± 1 (Chenet et al. 2007(Chenet et al. , 2009, 66.225±0.077Ma (Schoene et al., 2015(Schoene et al., , 2019. ...
Article
Earlier studies on the Mahadeo-Cherrapunji road (MCR) section have documented the Cretaceous-Palaeogene Boundary (KPB ca. ~ 66 Ma), but rare data exist on the Deccan volcanism induced KPB transition and related faunal crises. The environmental stress on biota has been postulated as the main cause of mass extinction. Thus, the study of organic matter (OM) entrapped in the Maastrichtian-Danian shelf sediments has attained importance, although the existing data is inadequate. In this situation, layer-wise n-alkanes and n -fatty acids analyses were carried out using GC-MS. Obtained data show sudden increase in the short chain n -alkane (SCA ~ 6-fold), n-fatty acid (FA) and hopane (> sterane) concentrations. This suggests enhanced continental runoff and soil bacteria biomass passage into the marine realm. Comparing the MCR to the published KPB bearing shallow-marine facies of the Um-Sohryngkew River (USR) section data, we document high SCA and FA contents together with the abundance of the even carbon numbered SCA (n-C16 and n-C18). This suggests thermal degradation and partial combustion of non-woody biomass. The presence of C17n-alkane and hopane is indicative of their derivation from the algae, fungi and bacteria. A sudden SCA concentration increase coincides with the reported major foraminifers’ extinction between the CF1 and P0 biozones of the MCR section. Further, a similar anomaly exists in the lower part of the CF3 biozone of the USR section and precedes extinction of the main foraminifers’ assemblages. The excursions in SCA content along with hopane and FA are matching well with the major incidences of the Deccan volcanic episodes and convergence of the Indian-plate with the Eurasian plate occurred at 66 Ma (Beck et al. 1995) and with the Burmese-plate during Maastrichtian (Wakita and Metcalfe 2005). These events were responsible for the sea-water disturbances, eustatic and depositional changes, including the retreat of the Tethys. Thus, a combination of extra-basinal and tectono-thermal events together with the greenhouse effects led to unexpected temperature rise and recurrent local sea-level changes that may have resulted in stress and faunal crisis.
... Pune region. In the second phase, this position shifted to a new location beneath the west coast 253 (Chenet et al., 2007;Ju et al., 2013). Additionally, Deccan Trap (DT) rocks have been reported 254 from the Rajahmundry region, south of the Godavari Rift, suggesting that the plume activity 255 reactivated the rift and facilitated magma eruptions through faults in the reactivated zone 256 (Singh et al., 2012). ...
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Indian craton comprises a number of old rifts, e.g., the Narmada, the Mahanadi and the Godavari rifts, which reactivated in multiple stages during the supercontinent breakup events. The latest reactivation of the Indian rift system occurred at the Cretaceous-Tertiary boundary when the Réunion plume interacted with the Indian plate, leading to the massive Deccan volcanism at 66 Ma. Although the plume-driven rift tectonics has been a subject of lively research over past decades, how a pre-existing rift system can modulate the plume dynamics, particularly in continental settings, remains inadequately explored. This study addresses this problem in the context of the Réunion plume encountering the Indian lithosphere. We develop 2D thermomechanical models to simulate plume-rift interactions, systematically investigating the modes of interactions as a function of plate velocity (Vp) and plume–rift (δ) distance. Our numerical experiments reveal that small δ (< 250 km) or high Vp (> 1cm/year) conditions redirect a large portion of the plume material towards the pre-existing rift, resulting in significant underplating and subsequent melting beneath the rift undergoing reactivation. Increasing δ or lowering of Vp weakens the plume-rift interaction, leaving the pre-existing rift zone almost passive, where the underplated plume materials stagnate beneath the lithosphere with little melting. The model results suggest that the Narmada rift, which was closer to the Réunion plume, caused significant deflection of the plume and its melting with Moho upwraping. In contrast, the Godavari rift, located at a larger distance from the plume, behaved passively, allowing underplating of the plume at the lithospheric base with no significant melting and Moho downwraping, as supported by geophysical observations. Finally, this study provides a new insight into the differential responses of the Indian rift system during the Reunion plume event.
... Various other researchers documented the magnetostratigraphy of the DVIP (Deutsch et al., 1958;Sahsrabudhe, 1963;Wensink and Klootwijk, 1971) . Absolute ages or chronostratigraphy/ geochronology has been done in detail (Courtillot et al., 1986;Vandamme et al., 1991;Chenet et al., 2007;Schoene et al., 2015 and others). Beane et al. (1986) divided the DVIP of the Western Ghats (India) into three subgroups and 10 formations. ...
Article
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Palaeoweathering unearths hidden mysteries of the previously weathered (paleo) surfaces. Researchers have shown that each mineral weathers/alters in a particular manner and is process-specific. Micromorphology is the most reliable and well-established technique to identify process-specific features imparted in an alterite under a given set of conditions. The Indian Deccan traps form one of the world's largest flood basalt volcanic provinces and has numerous exposures. Notwithstanding, systematic micromorphological studies of Deccan flood basalts are lacking compared to such flood basalts of global occurrences. The episodic nature of Deccan volcanism provided subsequent phases of interaction with the Earth's surface processes, thereby making the basalt alterites an ideal repository of surficial conditions and subsequent duration. Deccan basalt alterite exposed in the Kharghar hill of Mumbai (Maharashtra) has been selected for detailed micromorphology. Micromorphological results from the top to bottom of >70 cm thick, buried basalt alterite show changes in specific pattern of primary mineral alteration, formation of secondary minerals, development and patterns of secondary porosity. For example, the top of studied alterite (i.e. top 30 cm) has irregular, speckled and patchy patterns of mineral alteration, intramineral secondary pores, dominance of secondary products and only isolated alteromorphs that too with large elongate patches. Whereas towards the bottom (i.e. below 30 cm), the alterite shows planar patterns of mineral alteration, which is preceded at places by a linear/speckled pattern and most distinct is the dominance of intermineral pore system connected with transmineral fractures. Therefore, the basalt alterite can be subdivided from top to bottom into two distinct layers namely, alloterite and isalterite. This distinction significantly indicates a change in process with time as well as duration of basalt interaction with then prevailing surficial conditions. Thus, it can be concluded that alteroplasmation was progressively and gradually replaced with pedoplasmation resulting in dominance of supergene processes over hypogene processes.
... These differing bottom water and trophic conditions between sites (mentioned above) during the Dan-C2 event suggest (a) that local conditions and bathymetry played a much bigger role in species distribution, and/or (b) that there is an inherent heterogeneity in the characteristics of the Dan-C2 event (see also Arreguín-Rodríguez et al., 2021). Interestingly, this short-lived hypothermal Dan-C2 event has also been linked to the last and third phase of the Deccan volcanism (Chenet et al., 2007(Chenet et al., , 2009). However, our low-resolution data does not allow any further inferences based on the benthic foraminiferal response to this magmatic event. ...
... The age of Deccan Intertrappean sediments in Madhya Pradesh is considered to be the latest Maastrichtianeearliest Danian (close to the base of Chron 29R) based on radiometric 40 Ar/ 39 Ar dating, planktonic foraminifera, and magnetostratigraphy (Venkatesan et al., 1997;Khosla, 1999;Hofmann et al., 2000;Sheth et al., 2001;Chenet et al., 2007;Keller et al., 2009;Shrivastava et al., 2015;Renne et al., 2015;Schoene et al., 2015;Smith et al., 2015). ...
... The age of Deccan Intertrappean sediments is considered to be the latest Maastrichtian (late Cretaceous)earliest Danian (early Paleocene) (c. 66-65 Ma) based on the study of radiometric dating ( 40 Ar/ 39 Ar dating), planktonic foraminifera and magnetostratigraphy (Venkatesan et al. 1997;Hofmann et al. 2000, Sheth et al. 2001Chenet et al. 2007Chenet et al. , 2009Schoene et al. 2015;Srivastava et al. 2015;Smith et al. 2015;Sprain et al. 2019). The present fossil described here is from the intertrappean beds of the Mandla Lobe (c. ...
... Later, the Kerguelen (~120 Ma) and Reunion (~67 Ma) hotspots induced epeirogenic uplift of the eastern and western margins of the Indian landmass, respectively (Raval, 1999;O'Neill et al., 2003). Thus, the Indian Peninsular Shield has undergone several episodes of crustal and lithospheric development (Chenet et al., 2007). The opening of the Kaladgi rift basin is inferred to be associated with the Columbia supercontinent break-up (Mukherjee et al., 2016), and the carbonate-rich sediments of the basin indicate Paleoproterozoic rift setting (Saha et al., 2016;Roy et al., 2023). ...
Article
Peninsular India is traversed by several major Paleoproterozoic rift basins, among which the Kaladgi rift basin is a prominent one. Here, we present results from Magnetotelluric (MT) studies in the eastern section of this rift basin. The data were acquired along a ∼120 km long profile passing through Belavanik-Bagalkot-Ukkali regions covering the basin, Deccan basalts and gneisses/granites of the Dharwar craton. The lithospheric electrical structure was obtained from joint inversion of TE- and TM-modes data using a 2-D nonlinear conjugate gradient algorithm. The results reveal that the Kaladgi sediments are ∼500-1000 m in thickness overlying a fractured crystalline basement. Proterozoic sediments are exposed beneath the Deccan basalt cover and in the shallow fractured zones. The conductive-resistive transitions in the model at the crustal depths correspond to major tectonic faults and deformed crustal rocks. The transition boundary at ∼50 km depth defines the electrical Moho. At the same time, a ∼25 km wide, steep conductive feature from ∼75 km to upper mantle lithosphere depths (∼180-200 km) is interpreted as the trace of the Chitradurga Suture Zone (CSZ). The observed crustal heterogeneity, conductivity variations, and resistive lithosphere are attributed to the geological history of the region, including Archean collisional events and subsequent reactivation associated with the Reunion hotspot. The crustal conductors are associated with mafic intrusions from the underplated basalts, and also the high conductivity may be due to the sulfide mineralization in the fault zones. The MT study provides valuable insights into the deep tectonic framework of the region.
... The Deccan flood basalt province is one of the world's largest continental flood basalt provinces, presently covering ~500,000 km 2 that erupted across the K-T boundary (~68 to ~63 My; Pande, 2002;Chenet et al., 2007;Renne et al., 2015;Schoene et al., 2015;Sprain et al., 2019). Hitherto, the geochemistry of the basalts published in the Main Deccan Plateau (Fig. 1) has provided important insights into the nature and evolution of the Deccan Traps and the associated mantle plume, continental crust and lithospheric components involved therein (e.g. ...
... Initially, the age of the Deccan volcano was considered early Tertiary (Hislop, 1860;Hora, 1938). Subsequent studies, based on radiometric dating, magnetostratigraphy and macroand micropaleontology, suggested that most of the eruption (>80%) occurred in less than one million years around the Cretaceous-Paleogene boundary at 65 Ma (Bajpai & Prasad 2000;Bajpai et al., 2013;Chenet et al., 2007;Courtillot et al., 1986;Duncan & Pyle, 1988;Kania et al., 2022;Keller et al., 2009aKeller et al., , 2009bKhosla & Lucas, 2020a, 2020b, 2020c, 2020dKhosla et al., 2022;Mantilla et al., 2022;Schoene et al., 2019;Self et al., 2022;Vandamme et al., 1991;Verma & Khosla, 2019;Verma et al., 2016;and references therein). ...
Article
We here report a new freshwater ostracod assemblage comprising 11 species ( Frambocythere tumiensis anjarensis, Gomphocythere paucisulcatus, G. strangulata, Limnocythere deccanensis, Zonocypris spirula, Eucypris intervolcanus, Cypria cyrtonidion, Stenocypris cylindrical, Cypridopsis hyperectyphos, Candona amosi, Eucypris sp.) from a newly discovered intertrappean locality at Kesavi, Dhar District, Madhya Pradesh. This locality lies in the lower Narmada Valley of Malwa sub-province, a poorly studied region of the Deccan Traps volcanic province of peninsular India compared to the other volcanic sub-provinces. The ostracod assemblage from Kesavi is similar to those known from different parts of the Deccan volcanic province and lacks any brackish or marine elements. The endobenthic crawler Frambocythere tumiensis dominates the assemblage, indicating a lacustrine freshwater depositional environment.
... At the end of the Maastrichtian, isotopic foraminiferal records indicate that ocean temperatures rose about 3e4 C (Li and Keller, 1998b; Barrera and Savin, 1999). This warming event roughly coincided with the volcanic activity in the Deccan Province in India, which would have been accompanied by a substantial increase in the emissions of greenhouse gas, causing environmental stress in the oceans (Courtillot et al., 1986;Chenet et al., 2007). ...
... An transient episode of oceanic acidification should thus be expected during each Deccan volcanic eruption, as CO 2 is actively emitted into the atmosphere. However, as trap emplacement likely occurred as discrete rapid pulses (Chenet et al., 2007;Keller et al., 2020), the acidification itself would likely be short-lived, lasting only about 10 ky. We argue that such short-term acidification events, if they occurred, cannot be resolved in our record. ...
... In addition to Precambrian LIPs ranging back to 3.35 Ga (cf. Samal et al., 2021;Srivastava et al., 2022), major Cretaceous mafic-ultramafic magmatic events are also documented in the Indian shield; including both the Greater Kerguelen LIP connected to the Kerguelen plume Kent et al., 1996Kent et al., , 1997Kent et al., ,2002Coffin et al., 2002;Srivastava et al., 2020aSrivastava et al., , 2020bSingh et al., 2020Singh et al., , 2021Srivastava, 2022) and the Deccan LIP connected to the Réunion plume (Courtillot et al., 1988;Chenet et al., 2007;Hooper et al., 2010). Kerguelen plume related mafic magmatism was previously recognized in the Chhota Nagpur Gneissic Terrane (CNGT) of north-eastern Indian Shield (e.g., Storey et al., 1992;Kent et al., 1997Kent et al., , 2002Coffin et al., 2002;Ghatak and Basu, 2013;Srivastava et al., 2014Srivastava et al., , 2020aSrivastava, 2020Srivastava, , 2022 and Shillong Plateau (e.g., Ray and Pande, 2001;Ray et al., 2005;Ghatak and Basu, 2011;Srivastava et al., 2005Srivastava et al., , 2019b) (see Fig. 1). ...
Article
Early Cretaceous NNW- to WNW-trending dolerite dykes of the eastern Indian Shield, collectively termed the Raniganj-Koderma swarm, are studied for their emplacement ages and petrogenetic history, and assessed for a possible linkage with the Greater Kerguelen plume. ⁴⁰Ar/³⁹Ar dates of four dolerite dykes from different locations in the Chhota Nagpur Gneissic Terrane, indicate three pulses of emplacement ca. 118-116 Ma, ca. 112-111 Ma, and ca. 109 Ma. Geochemistry of 19 samples analysed herein (and an additional 12 samples from literature) shows sub-alkaline high-Mg tholeiitic basaltic andesite compositions. All the dyke sets belonging to the Raniganj-Koderma swarm with sub-sets WNW-trending ca. 118 Ma, NNW-trending ca. 116 Ma Salma, and a N-S trending ca. 109 Ma dyke show similar chemistry. However, NW-trending dykes emplaced ca. 112-111 Ma have slightly different geochemical characteristics. Key trace element geochemistry data, particularly Nb/Y, Zr/Y, Nb/Yb, Ti/Yb, Th/Nb and Th/Yb ratios, indicates derivation from mantle melts generated from interaction of a plume with a spreading ridge (producing OIB – E-MORB melts) with a minor role for interaction with an enriched lithospheric mantle metasomatized during an earlier (pre-Mesozoic time) subduction event. Spatiotemporal distribution of the studied dolerite dykes connects them with the second plume head phase of the Greater Kerguelen mantle plume.
... Finally, the Cretaceous-Paleogene (K-Pg) extinction was the last of the Big Five, it is a popular event because was responsible for the extinction of non-avian dinosaurs (Chiarenza et al. 2020, but see Sakamoto et al. 2016, Condamine et al. 2021 for alternative hypothesis), and because of the extinction of several species of well-known taxa like plants, birds, fish, and insects (e.g., Longrich et al. 2011). There are two main plausible causes for the K-Pg, one is the trivial biogeochemical (warming-anoxia-acidification) process triggered by volcanism of the Deccan Traps, in north India (Wignall 2001, Chenet et al. 2007); and the second was an extra-terrestrial cause, a collision of a meteor that occurred in the Chicxulub peninsula of Mexico (Alvarez et al. 1980, Schulte et al. 2010. In this last scenario, the impact was enough to shut down photosynthesis at the global level, causing a mass extinction of herbivores (Alvarez et al. 1980). ...
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The Earth has undergone numerous geological and biological changes over billions of years. The evolution of plants and animals had a direct relationship with the elements’ changes in the atmosphere and the development of the biogeochemical cycles on Earth. The Anthropocene is the age of the Homo sapiens leaves its geological signature on the planet. Human domination and/or interference in the biogeochemical cycles results in an environmental change that affects not only ecosystems, in general, but also the biota and global biodiversity. In this way, we are creating another mass extinction event, the “sixth extinction wave” as well as transforming the ecosystems’ functions and services.
... Notwithstanding the conclusions of Venkatesan & Pande (1996), the recent high-precision geochronology of the WGs showed that the basal part of the WGs is consistent in age with the ~C30N/C29R transition, ~400 ka before the K-Pg boundary (Renne et al. 2015;Schoene et al. 2015). Based on geochronological and paleontological results (Chenet et al. 2007;Keller et al. 2008) combined with paleomagnetic studies of the lavas, Chenet et al. (2009) have proposed that Deccan volcanism occurred in three short, discrete phasesan early one at ~67.5±1 Ma near the C30R-C30N reversal, which might have lasted only a few thousand years and after ca. 2.5 Ma of quiescence, the two larger occurred at ~65±1 Ma (one within C29R and the other at the boundary of C29R-C29N reversal). ...
Thesis
The first and foremost information generated during this study was about the nature of magnetic mineralogy. The routine rock magnetic method applied here clearly indicate the overall ferrimagnetic mineralogy to add to the previously known work inferring magnetite (M) of different magnetic domain size (SP- SD, MD-PSD) and that too within a single sample facilitating multiple analyses like AMS and Paleomagnetism. The petrographic analyses reveal a fairly high concentration of magnetite(s) within the studied slides. hereby revealing the carrier mineral responsible for the ChRM. Also, olivine megacrysts are abundant among the finer grained plagioclase crystals which form the groundmass along with Opaques. There are a few clinopyroxenes macrocrysts present with the Olivine. Within the Lamproites the major mica is biotite, which is observed as yellowish flakes and dispersed within the groundmass. Altogether the samples show a fairly high concentration of ferrimagnetic minerals facilitating paleomagnetic and rock magnetic studies. The presence of plagioclase as small crystals probably microlites implies rapid rate of cooling or high number of nucleation sites thereby enriching the groundmass in plagioclase nuclei rather than well developed crystals. A variety of directions and magnitudes are observed in the AMS results of the studied dykes. The distinct fabric observed is prolate with K1 parallel to the dyke wall. However, many other varieties including the oblate fabrics with K1 near horizontal is observed. Apart from this the well clustered K1 and K2-K3 girdle can also be observed. This indicates that each dyke has different style of fabric formation and indicated the instantaneous stress regime recorded by the AMS. The well clustered K1 parallel to the dyke walls and shallow but well clustered K3 and K2 suggest higher stress regime vis-a-vis rapid cooling experienced by the dyke. The shallow K1, high angle K3 and mixed K2 with oblate fabrics suggest slow cooling and relatively low stresses from the walls. Similarly, the random fabrics too indicate slow cooling and low stresses. The high angle K1 shows directions in different quadrants indicating the intrusive directions. It is proposed that the dykes from Deccan traps can be classified based on their AMS characters that are influenced by the intensity and directions of intrusion and the stress regime penultimate to cooling. From the Paleomagnetic results it is observed that the samples obtained from the margins of the dike show stable directions while those obtained from the core (central portions) show scattered results. This could be in fact due to higher rate of cooling along the dike walls, on account of contact with the country rocks leading to chilling and recording of a point event. While, the central portions require time to cool thereby forming multidomain grains of varying grain sizes these could lead to the scatter observed in the data. The results from the Declination show a large scatter while inclinations show fairly good consistency. The ‘α95’ and ‘k’ are fairly good to produce a broad idea of the paleomagnetic distribution. The VGP pole lat/long are distributed in both hemispheres due to normal and reversals, whereas the paleolatitudes are normalised to indicate the true geographic positions of the dykes. The mean paleolatitude is 16° South with a standard deviation of 7.79 varying between 37° and 9.38°. The median value is 16.64°. When these values are compared with the published data on Deccan Trap lava flows and dykes, the above paleolatitude fall in some of the youngest regimes of Deccan volcanism or even later to it. However, considering the large statistical variation accounted to mineralogical reasons (domain size), more detailed sampling and analysis is required. From the present paleomagnetic attempt following two alternative hypotheses can be derived: a) The studied dykes represent one of the youngest event in the Deccan volcanic episodes OR b) There is a significant Southward dipping tectonic tilt related to the West Coast tectonics. These two hypotheses need to be tested with more detailed studies in line with the present thesis.
Chapter
Microbiotic assemblages from the Deccan Trap intercalated intertrappean sediments of the east-west, central and southern parts of peninsular India are less known. This work was undertaken to bring detailed information for the first detailed descriptions of microbiota including charophytes, ostracods, planktic foraminiferans and fishes from the Cretaceous-Palaeogene transition of the Eastern Deccan Volcanic Province, Chhindwara District, Madhya Pradesh, with the following objectives: (i) documenting the diversity of the Upper Cretaceous-Lower Palaeocene biota of the Chhindwara area, (ii) reconstructing the palaeoecology and palaeoenvironments and (iii) inferring the palaeobiogeographical implications of biota in the context of the drifting Indian plate. This chapter documents field and laboratory investigations of microbiota preserved in intertrappean beds. The microbiota-bearing localities have been divided into four localities (Jhilmili, Ghat Parasia and Shriwas (=Shiraj) and Government wells in Chhindwara District, Madhya Pradesh). The microbiota-rich intertrappean beds are variable and show its thickest development (14 m) at Jhilmili, 170 cm thick in the Ghat Parasia, 1 m thick in the Government well and 1 m thick at Shriwas (=Shiraj) well. From 2017 to 2020, fossil collections were made during three field trips, and a total of four stratigraphic successions containing microbiota were chosen for the current study. Extensive research was conducted to determine the taxonomic, palaeoenvironmental, palaeoecological, biostratigraphic and palaeobiogeographical inferences of microbiota-bearing intertrappean beds.KeywordsIndian DeccanMicrobiota intertrappean bedsLate Cretaceous-Early Palaeocene
Article
The magma source for mafic dykes from South Rewa Basin (SRB) in central India is invariably linked to Rajmahal volcanism (117 Ma) for Damodar, Raniganj-Jharia, and Bengal basin (Permian - Quaternary) to the east, and Deccan volcanism (66 Ma) for Satpura Basin to the west of SRB. However, the magmatic events linked to the SRB are not explicit. To ascertain the dyke association with these volcanic events, we performed a comprehensive paleomagnetic study on the exposed dykes and basalts from Shahdol region in SRB. Rock magnetism indicate that magnetite or titano-magnetite is the main remanence carrier mineral in these dykes. The measured directions produce a mean declination (Dm) of 338° and mean inclination (Im) of - 35° (α95= 8.4°, k = 25.3, N = 13), is close to Deccan normal directions. The calculated Pole position (λp) is at 42.02°N, and (Lp) is at 289.33°E, suggesting that the studied dykes are emplaced simultaneously along with Deccan Traps (36.96°N/78.70°W) and not of Rajmahal Traps (11.37°N/297.58°E). These dykes can be the result of multiple Deccan magma intrusions along the Narmada-Tapti lineament and intra-basinal faults in the SRB of central India.
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Plain Language Summary Mantle plumes, originated in deep Earth’s interior are thought to be a major source of enormous magma supply required for the formation of large igneous provinces (LIPs). This article focuses on the pulsating nature of Deccan volcanism in peninsular India, which is a remarkable LIP event at the end of the Cretaceous Period in the geological history. From thermo‐chemical model simulations, the present study establishes a link of this volcanic event with the Reunion hotspot, which originated from the African large low shear wave velocity province (LLSVP) at the core‐mantle boundary. The ascending Reunion plume eventually encountered the mid‐mantle transition zone and produced periodically a sequence of plume pulses. Each plume pulse then ascended to shallower depths and started to produce partial melts in developing secondary pulses. The model analysis suggests that the time‐periodicity of primary pulses depends mainly on the following physical factors: pile‐ambient mantle viscosity ratio, buoyancy number, and heat‐producing element concentration. Finally, the entire Deccan volcanic event is explained in terms of plume pulses with two distinct time periodicities: primary pulses with a periodicity of 5–8 Ma and secondary melt pulses with a periodicity of 0.15–0.4 Ma.
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Magnetic Polarity and Stratigraphic studies of the Gulerghat section from Akot and Amravati districts area(Lat. 21 0 00'-21 0 15'N; Long. 77 0-77 0 15'E) are carried out. Total thousands of oriented samples from fresh basalts were collected at close intervals. Detailed palaeomagnetic investigation where carried on 250 samples collected from 20 lava flows belonging to 17 selected traverses were subjected to progressive thermal demagnetizer at 15 different steps of temperatures from 50˚C to 600˚C. Traverse attaining a total thickness of 800m in the study area. Some rocks may fail to retain the magnetic record due to the modification subsequence to their formations by a number of natural phenomena like geotectonic disturbance, metamorphism and alteration, which can produce various degrees of secondary magnetisation in the rock. The secondary magnetisation acquired by the rock is unstable as compared to naturally remain magnetism which can be removed by cleaning techniques like stepwise Alternating field demagnetisation (AFD) and Thermal demagnetisation (TD). The palaeomagnetic results indicate that the most of the flows showed irregular natural remnant directions while a few specimen even from other flows for which a meaningful NRM could be deciphered also showed inconsistent directions. Only 35% of the samples showing irregular directions initially improved on alternating field and stepwise thermal demagnetization. High degree of alteration of the flows appears to have affected the stability of the palaeomagnetic directions. The mean palaeomagnetic directions indicate the presence of lower transitional directions at the bottom part of the sequence and upper reversed polarity in remaining part of the sequence with a few samples showing scattered behavior. The polarity transition has take place in the study area. Ancient latitude calculated for the study area is 30 o S and that of Nagpur is 31 o S indicating that India has drifted by 51 o due N which is more than 5000 Kms. since the formation of this lavas.
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This contribution presents chemical data on clays (SEM–EDS and trace elements) along with bulk organic carbon (δ¹³Corg) isotopes from the Mahadeo–Cherrapunji (MCR) section sediments to evaluate Deccan volcanism-induced paleoenvironmental perturbations across Cretaceous/Paleogene boundary (K/PgB). The assemblages of clay minerals (illite, chlorite, kaolinite, and smectite) in this section under study demonstrated that the climate during the late Maastrichtian–early Danian period was humid to arid/semi-arid. The rare earth element (REE) patterns normalized to chondrite reveal flat, heavy REE (HREE) patterns with negative europium (Eu) anomalies and enriched light REE (LREE) patterns. The MCR section suggests that the basin experienced intermittent oxic to anoxic depositional conditions, as indicated by the low to moderate values of Total Organic Carbon (TOC), V, and U, along with low Ni/Co and U/Th ratio values. The average δ¹³Corg value of MCR section clays is − 24.85‰. However, the pre-K/PgB gray calcareous shale layer (MC-12A) in biozone CF1 shows a δ¹³Corg value of − 28.91‰, which is significantly (~ 4‰) lower than the immediately lying below and above layers. The meager δ¹³Corg value (~ 4‰) during the K/PgB transition is attributed to the highly anoxic oceanic environment. Elevated levels of CO2 were attained through the release of warm greenhouse gasses resulting from Deccan volcanic activity. The findings of this investigation are supported by the shallow marine Therriaghat (Um-Sohryngkew River) section in Meghalaya, as well as other recognized K/PgB successions worldwide.
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The Cretaceous Period was marked by the formation of numerous Large Igneous Provinces (LIPs), several of which were associated with geologically rapid climate, environmental, and biosphere perturbations, including the early Aptian and latest Cenomanian Oceanic Anoxic Events (OAEs 1a and 2, respectively). In most cases, magmatic CO 2 emissions are thought to have been the major driver of climate and biosphere degradation. This work summarises the relationships between Cretaceous LIPs and environmental perturbations, focussing on how volcanism caused climate warming during OAE 1a using osmium-isotope and mercury concentration data. The new results support magmatic CO 2 output from submarine LIP activity as the primary trigger of climate warming and biosphere stress before/during OAE 1a. This submarine volcanic trigger of OAE 1a (and OAE 2), two of the most climatically/biotically severe Cretaceous events, highlights the capacity of oceanic LIPs to impact Earth's environment as profoundly as many continental provinces. Cretaceous magmatism (and likely output of CO 2 and trace-metal micronutrients) was apparently most intense during those OAEs; further studies are needed to better constrain eruption histories of those oceanic plateaus. Another open question is why the Cretaceous Period overall featured a higher rate of magmatic activity and LIP formation compared to before and afterwards. Supplementary material at https://doi.org/10.6084/m9.figshare.c.7026011
Article
The modern agricultural work mainly involves the use of synthetic fertilizers and large scale deforestation. The numerous agricultural activities around the Darna and the Gangapur Reservoirs of the Nashik Distirct, India have started the environmental issues such as an early or rapid eutrophication and heavy metal accumulations. Agricultural runoff and industrial wastes are proved to be the potential sources of heavy metals. The heavy metals may accelerate the effect of pollution on the environment with the decline in the biodegradability of the organic pollutants. The impacts of the anthropogenic activities with the passing time have been recorded in the form of geochemical elements accumulated as the part of bottom sediments of the reservoirs. The present study has revealed that the heavy metal concentration from the core sediments of the reservoirs displays the moderately high to highly positive inter-correlation. The historical profiles of both the reservoirs show the highest enrichments for Cr, Ni, Cu, Co, V, Sc and Eu. The impact of metal pollutants on both the reservoirs is explored with regard to the ages derived from the 210Pb geochronology and the constant rate of supply (CRS) model.
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Four stratigraphic sections (Jhilmili, Ghat Parasia, Shriwas (= Shiraj) well and, Government well) in the Chhindwara area, Madhya Pradesh, were chosen as part of the field investigations for this study. The basement rocks in the Chhindwara region are Archaean and Gondwana, which are unconformably overlain by the 1–14-m-thick, microbiota-rich intertrappean beds. The sections surrounding Chhindwara are made up of shale, clays, claystones, clayey limestones, cherts, marl, mudstones and siltstones. In terms of taxonomic diversity, intertrappean beds of Jhilmili and Ghat Parasia have yielded 10 taxa of charophytes, 3 of which are new; 34 taxa of ostracods, 3 of which are new (recovered from all of the four above-mentioned localities); and 10 taxa of planktic foraminiferans, from the sole locality of Jhilmili. In all of the four investigated stratigraphic sections, the intertrappean beds are overlain by the Deccan Traps.KeywordsGeologyChhindwara areaIntertrappeansGhat ParasiaGovernment wellJhilmiliShriwas (=Shiraj) wellMicrobiotaNarmada River region
Article
Paleontological investigations in the Late Cretaceous sedimentary units associated with Deccan traps of the lower Narmada valley, western Central India were carried out in order to ascertain ostracod diversity and its biostratigraphic and paleoecological implications. Eighteen species of twelve genera of Cytheroidea, Darwinuloidea and Cypridoidea ostracods recovered from four sections of the Deccan intertrappean beds are described. The species include the specimens from two new intertrappean sections, Kakarda and Bara Bheralya and additional ostracod taxa recorded from two previously studied sections, Gujri and Uthawali. The biostratigraphic, taphonomic and paleoecological analysis of the newely recovered ostracod assemblage in conjunction with the recent published data from the study area depict Maastrichtian age and freshwater fluvio-lacustrine environment for the studied sections.
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The Raageshwari Volcanic Formation (RVF) is a volcanic complex in the southern part of the Barmer Basin, NW India, localized around a large rift centre horst block, the Central Basin High. The RVF comprises an initial sequence of acid igneous rocks, which are of ignimbritic origin, termed the Agni Member, overlain by a stacked sequence of basaltic lava flows interbedded with subordinate pyroclastic deposits, the Prithvi Member. Seismic data confirms that the volcanic complex has a conical overall geometry and a layered internal structure produced by successive and extensive flows of basalt and ignimbrite, very similar to that observed in the main Deccan lava outcrops along the western margin of India. U–Pb zircon ages near the top of the Agni Member in the Raageshwari‐26 well give an age of 68+/−2 Ma for a tephrite pyroclastic unit, whilst Ar–Ar analysis of a distal basalt containing phenocrysts of biotite from the Saraswati‐4 well gave an older robust Ar–Ar plateau age of 73.7 ± 1.4 Ma. A typical Deccan age of 67.9 ± 1.7 Ma was obtained from the isolated unaltered basaltic andesite in well NE‐South‐1. Due to depositional on‐lap onto the Central Basin High, the overlying alluvial Dandlawas and Fatehgarh formations are absent on the crest of the Central Basin High and Barmer Hill Formation lake sediments rest directly on the basalts. This relationship indicates that the volcanic cone was a structural or topographic high during deposition onto which the Fatehgarh and Barmer Hill formations lake sediments eventually on‐lapped. The RVF of the Barmer Basin along with the Deccan volcanics in the Cambay Basin, Narmada Rift and in Saurasthra are all developed within fault‐bounded rift basins, in which deep seated faults extend beneath the Deccan volcanic sequence. They are associated with thermal anomalies and thinned continental crust and the presence of a linear low velocity zone at ~100 km depth in the upper mantle region beneath the Barmer and Cambay basins. This is interpreted to be the position of the “conduit” through which plume head material passed through the upper mantle before arriving at the base of the Indian lithosphere. The RVF therefore appears to be an early eruption of differentiated ultrabasic magma from a shallow, secondary magma chamber produced by partial crustal melting. The Raageshwari Volcanic Formation (RVF) is a volcanic complex in the Barmer Basin, localized around a rift centre block, comprising a sequence of basaltic flows interbedded with pyroclastic deposits. It is associated with thinned continental crust, interpreted to be the position of the “conduit” through which plume head material passed.
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Covering a key connection between geological processes and life on Earth, this multidisciplinary volume describes the effects of volcanism on the environment by combining present-day observations of volcanism and environmental changes with information from past eruptions preserved in the geologic record. The book discusses the origins, features and timing of volumetrically large volcanic eruptions; methods for assessing gas and tephra release in the modern day and the palaeo-record; and the impacts of volcanic gases and aerosols on the environment, from ozone depletion to mass extinctions. The significant advances that have been made in recent years in quantifying and understanding the impacts of present and past volcanic eruptions are presented and review chapters are included, making this a valuable book for academic researchers and graduate students in volcanology, climate science, palaeontology, atmospheric chemistry, and igneous petrology.
Chapter
Covering a key connection between geological processes and life on Earth, this multidisciplinary volume describes the effects of volcanism on the environment by combining present-day observations of volcanism and environmental changes with information from past eruptions preserved in the geologic record. The book discusses the origins, features and timing of volumetrically large volcanic eruptions; methods for assessing gas and tephra release in the modern day and the palaeo-record; and the impacts of volcanic gases and aerosols on the environment, from ozone depletion to mass extinctions. The significant advances that have been made in recent years in quantifying and understanding the impacts of present and past volcanic eruptions are presented and review chapters are included, making this a valuable book for academic researchers and graduate students in volcanology, climate science, palaeontology, atmospheric chemistry, and igneous petrology.
Chapter
Covering a key connection between geological processes and life on Earth, this multidisciplinary volume describes the effects of volcanism on the environment by combining present-day observations of volcanism and environmental changes with information from past eruptions preserved in the geologic record. The book discusses the origins, features and timing of volumetrically large volcanic eruptions; methods for assessing gas and tephra release in the modern day and the palaeo-record; and the impacts of volcanic gases and aerosols on the environment, from ozone depletion to mass extinctions. The significant advances that have been made in recent years in quantifying and understanding the impacts of present and past volcanic eruptions are presented and review chapters are included, making this a valuable book for academic researchers and graduate students in volcanology, climate science, palaeontology, atmospheric chemistry, and igneous petrology.
Chapter
Covering a key connection between geological processes and life on Earth, this multidisciplinary volume describes the effects of volcanism on the environment by combining present-day observations of volcanism and environmental changes with information from past eruptions preserved in the geologic record. The book discusses the origins, features and timing of volumetrically large volcanic eruptions; methods for assessing gas and tephra release in the modern day and the palaeo-record; and the impacts of volcanic gases and aerosols on the environment, from ozone depletion to mass extinctions. The significant advances that have been made in recent years in quantifying and understanding the impacts of present and past volcanic eruptions are presented and review chapters are included, making this a valuable book for academic researchers and graduate students in volcanology, climate science, palaeontology, atmospheric chemistry, and igneous petrology.
Chapter
Covering a key connection between geological processes and life on Earth, this multidisciplinary volume describes the effects of volcanism on the environment by combining present-day observations of volcanism and environmental changes with information from past eruptions preserved in the geologic record. The book discusses the origins, features and timing of volumetrically large volcanic eruptions; methods for assessing gas and tephra release in the modern day and the palaeo-record; and the impacts of volcanic gases and aerosols on the environment, from ozone depletion to mass extinctions. The significant advances that have been made in recent years in quantifying and understanding the impacts of present and past volcanic eruptions are presented and review chapters are included, making this a valuable book for academic researchers and graduate students in volcanology, climate science, palaeontology, atmospheric chemistry, and igneous petrology.
Chapter
Covering a key connection between geological processes and life on Earth, this multidisciplinary volume describes the effects of volcanism on the environment by combining present-day observations of volcanism and environmental changes with information from past eruptions preserved in the geologic record. The book discusses the origins, features and timing of volumetrically large volcanic eruptions; methods for assessing gas and tephra release in the modern day and the palaeo-record; and the impacts of volcanic gases and aerosols on the environment, from ozone depletion to mass extinctions. The significant advances that have been made in recent years in quantifying and understanding the impacts of present and past volcanic eruptions are presented and review chapters are included, making this a valuable book for academic researchers and graduate students in volcanology, climate science, palaeontology, atmospheric chemistry, and igneous petrology.
Chapter
Covering a key connection between geological processes and life on Earth, this multidisciplinary volume describes the effects of volcanism on the environment by combining present-day observations of volcanism and environmental changes with information from past eruptions preserved in the geologic record. The book discusses the origins, features and timing of volumetrically large volcanic eruptions; methods for assessing gas and tephra release in the modern day and the palaeo-record; and the impacts of volcanic gases and aerosols on the environment, from ozone depletion to mass extinctions. The significant advances that have been made in recent years in quantifying and understanding the impacts of present and past volcanic eruptions are presented and review chapters are included, making this a valuable book for academic researchers and graduate students in volcanology, climate science, palaeontology, atmospheric chemistry, and igneous petrology.
Chapter
Covering a key connection between geological processes and life on Earth, this multidisciplinary volume describes the effects of volcanism on the environment by combining present-day observations of volcanism and environmental changes with information from past eruptions preserved in the geologic record. The book discusses the origins, features and timing of volumetrically large volcanic eruptions; methods for assessing gas and tephra release in the modern day and the palaeo-record; and the impacts of volcanic gases and aerosols on the environment, from ozone depletion to mass extinctions. The significant advances that have been made in recent years in quantifying and understanding the impacts of present and past volcanic eruptions are presented and review chapters are included, making this a valuable book for academic researchers and graduate students in volcanology, climate science, palaeontology, atmospheric chemistry, and igneous petrology.
Experiment Findings
The work was initiated by the preparation of database with complete documentation of the palaeomagnetic data published since 1955. Over 76 publications, including thesis presenting the palaeomagnetic studies from Deccan traps (and dykes) till date, were reviewed and the database was presented in an excel Ble format for the processing. Vast majority of these publications unambiguously reported the palaeomagnetic directions (declinations and inclinations or D/I) in agreement with the N–R–N sequence of the C30n–29r–29n geomagnetic polarity time scale. The data was independently produced by various teams during last 65 years, and majority of the analysis performed in reputed national/international laboratories with standard instrumental setups (information given in SDF).
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The Cretaceous-Paleogene (K/Pg) mass extinction is the only major mass extinction event that is known to be related to a major meteorite impact (Chicxulub, Mexico) and also occurred during major flood basalt eruptions (Deccan Traps, India). Here, we present geochemical proxies for impact and volcanism analysed in the same sediment samples from the deep-marine sedimentary record of the Gosau Group spanning the K/Pg boundary at Wasserfallgraben, Germany. We measured major and trace elements, including iridium (Ir), tellurium (Te), mercury (Hg), total organic carbon (TOC), and organic carbon isotopes (δ¹³Corg) on 33 samples from 2 m below to 1.36 m above the K/Pg boundary, a timespan of ∼260 ka. Results show an undisturbed profile, confirmed by changes in calcareous nannofossils assemblages, with a sharp positive Ir peak (2.3 ppb) at the K/Pg boundary (0–10 cm, 25 cm). Volcanic proxies (Hg/TOC, Te/Th) show three distinct peaks not corresponding to the Ir peak, suggesting a volcanic origin, and higher values in the earliest Danian. Compared to the profile in Bidart the proxies of volcanism are less intense in our profile, indicating that the “Deccan Signal” is either diluted or not present in some locations worldwide. The time recorded in the sampled sediments is short (∼0.26 Ma) compared to Deccan flood basalt eruptions (∼1Ma), but elevated Hg/TOC and Te/Th ratios in the Danian sediments suggests the impact happened prior to the main volcanic outgassing of the Deccan Traps. Our results support the hypothesis that the impact might have triggered the largest, rapidly-erupted Deccan lava formations.
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Geomorphologic studies can set important constraints on the petroleum geosciences of sedimentary basins. In the western Rajasthan area of Indian shield, constituting Barmer and other basins, rift-related sedimentation took place during Late Neoproterozoic to Cambrian Periods and during Mesozoic to Tertiary time. We analyze the Quaternary geomorphology of the Barmer basin mainly in terms of its watersheds by applying Digital Elevation Model aided by field verifications. In detail, we study aeolian landforms, drainage orientation, pattern, rejuvenation, terraces and abandoned gullies. Small streams display cross-valley anomalies. Gorge-like morphology in the eastern part of the basin near Sarnoo and knick-points in gullies near Lini/Sukri characterize the eastern boundary of the Barmer rift basin and parallel NE–SW river characterizes offset lineaments. Amongst the five delineated watersheds, watersheds-1 and 2 are recognised as the most tectonically active having lower index of active tectonics (IAT). This is also supported by the linear-scale parameters stream length gradient index (SL), sinuosity index (SI) and the long-profiles. Sub-watershed analysis using SL and SI of the watershed-1 disclose the tectonically active region within the basin. Micro-scale basin analysis has also been made applying several quantitative indicators. Watersheds-1 and 2 were found to be tectonically active. Using the normalized difference vegetation index (NDVI), the NW–SE line of vegetation across the Giral coal mine in the northern part of the basin indicates a shallow groundwater level (~7 mbgl), and can indicate presence of blind fractures. Geomorphologic analysis of the Barmer basin.Watersheds 1 and 2 are tectonically active.Sub-surface brittle planes ascertained from watershed-1. Geomorphologic analysis of the Barmer basin. Watersheds 1 and 2 are tectonically active. Sub-surface brittle planes ascertained from watershed-1.
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Temporal distribution of planktonic and benthonic foraminifera across the K/T boundary in the Palakollu deep well section of Krishna-Godavari (KG) Basin, India, suggests that the lower Deccan trap flows have erupted during Zone M-18 of the latest Maastrichtian (66.5-65.5 m.y.) to Danian and the upper flows in lower Zone P 2 of the Early Paleocene (61.2-60.7 m.y.). The span of volcanism will be approximately 6 m.y. -Authors
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Large spheroid deposits at Albion Island and Armenia in northern and central Belize and the spherule deposits of southern Belize and eastern Guatemala have the same glass origin based on the presence of almost pure Cheto smectite derived from alteration of impact glass from the Chicxulub impact on Yucatan, Mexico. The same origin has also been determined for altered glass spherules in Mexico, Haiti and the Caribbean. However, the spherule layers have variable ages as a result of erosion and redeposition, with an early Danian (Parvularugoglobigerina eugubina) zone pla(1) age in southern Belize, Guatemala, Haiti, southern Mexico and the Caribbean, and a pre-K-T (Plummerita hantkeninoides) zone CF1 age of 65.27 +/- 0.03 Ma in NE Mexico. A pre-K-T age for the Chicxulub impact has now also been determined from the new Yaxcopoil 1 core drilled in the impact crater. These data show that Chicxulub was not the K-T impact that caused the end-Cretaceous mass extinction, but an earlier impact event. A multiple impact hypothesis, volcanism and climate change appears the likely scenario for the end-Cretaceous mass extinction.
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The Deccan Trap geology of Bombay (Mumbai) differs from the main Deccan flood basalt province in several ways. Very few geological, geochemical and geochronological studies exist on the Deccan geology of Bombay. The basalt of Gilbert Hill, Andheri occupies a special place in Bombay geology on account of its spectacular columnar jointing, more than 50 m high, and for this has been designated a National Geological Monument by the Geological Survey of India. We have obtained an 40Ar-39 Ar plateau age of 60.5 ± 1.2 Ma (2σ) for the Gilbert Hill basalt, and this basalt can be argued to have erupted considerably later (∼ 6 m.y.) than the lower part of the Western Ghats lava pile, and the total duration of Deccan volcanism as a whole appears to have been at least ∼ 8 m.y.
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Based on the Ar-40-Ar-39 results for Deccan Traps samples, we have investigated the relationships between the Ar-40-Ar-39 age release pattern and conditions of basaltic samples. Ar-40-Ar-39 age release patterns are divided into five types, which might be related to the conditions of samples such as their petrological textures and alteration state. A peak of non-radiogenic component of Ar is observed at the temperature around 800 degrees C in the Ar release patterns of Deccan Traps samples. Based on the above observations, criteria for sample selection and data treatment for the Ar-40-Ar-39 dating are summarized as follows. (1) It is recommended to use fresh samples as much as possible and minimize the use of samples which contain mesostasis. (2) Fine-grained holocrystalline rocks are preferable to get reasonable Ar-40-Ar-39 ages. (3) If a sample is affected by secondary alteration and shows a high Ar-36 release in the intermediate temperature fractions, in age calculation it is better to exclude the isotopic data for the temperature fractions lower than about 800 degrees C where the high Ar-36 release is observed.
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The 40Ar/39Ar radioisotopic dating technique is one of the most precise and versatile methods available for dating events in Earth's history, but the accuracy of this method is limited by the accuracy with which the ages of neutron-fluence monitors (dating standards) are known. Calibrating the ages of standards by conventional means has proved difficult and contentious. The emerging astronomically calibrated geomagnetic polarity time scale (APTS) offers a means to calibrate the ages of 40Ar/39Ar dating standards that is independent of absolute isotopic abundance measurements. Seven published 40Ar/39Ar dates for polarity transitions, nominally ranging from 0.78 to 3.40 Ma, are based on the Fish Canyon sanidine standard and can be compared with APTS predictions. Solving the 40Ar/39Ar age equation for the age of the Fish Canyon sanidine that produces coincidence with the APTS age for each of these seven reversals yields mutually indistinguishable estimates ranging from 27.78 to 28.09 Ma, with an inverse variance-weighted mean of 27.95 ± 0.18 Ma. Normalized residuals are minimized at an age of 27.92 Ma, indicating the robustness of the solution.
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Knight et al. presented age and chemical data on two (sets of) lava flows from the Rajahmundry area, on either bank of the Godavari River. The age and petrogenesis of these flows and their possible link to sections of the main Deccan Province are of importance to the understanding of many aspects of flood basalt volcanism. I comment on (a) the use of geochemical fingerprints for lava identification/correlation at Rajahmundry, superceding (apparent) field relations, (b) their 40Ar / 39Ar data and its refinement based on statistical tests and the alteration state of the samples (c) correlation of age data and the magnetic polarity of the lavas to the geomagnetic polarity time scale and (d) the possibility that both lavas at Rajahmundry were formed by intracanyon flows derived from ∼1000 km away.
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Large igneous provinces (LIPs) are a continuum of voluminous iron and magnesium rich rock emplacements which include continental flood basalts and associated intrusive rocks, volcanic passive margins, oceanic plateaus, submarine ridges, seamount groups, and ocean basin flood basalts. Such provinces do not originate at “normal” seafloor spreading centers. We compile all known in situ LIPs younger than 250 Ma and analyze dimensions, crustal structures, ages, and emplacement rates of representatives of the three major LIP categories: Ontong Java and Kerguelen-Broken Ridge oceanic plateaus, North Atlantic volcanic passive margins, and Deccan and Columbia River continental flood basalts. Crustal thicknesses range from 20 to 40 km, and the lower crust is characterized by high (7.0–7.6 km s−1) compressional wave velocities. Volumes and emplacement rates derived for the two giant oceanic plateaus, Ontong Java and Kerguelen, reveal short-lived pulses of increased global production; Ontong Java's rate of emplacement may have exceeded the contemporaneous global production rate of the entire mid-ocean ridge system. The major part of the North Atlantic volcanic province lies offshore and demonstrates that volcanic passive margins belong in the global LIP inventory. Deep crustal intrusive companions to continental flood volcanism represent volumetrically significant contributions to the crust. We envision a complex mantle circulation which must account for a variety of LIP sizes, the largest originating in the lower mantle and smaller ones developing in the upper mantle. This circulation coexists with convection associated with plate tectonics, a complicated thermal structure, and at least four distinct geochemical/isotopic reservoirs. LIPs episodically alter ocean basin, continental margin, and continental geometries and affect the chemistry and physics of the oceans and atmosphere with enormous potential environmental impact. Despite the importance of LIPs in studies of mantle dynamics and global environment, scarce age and deep crustal data necessitate intensified efforts in seismic imaging and scientific drilling in a range of such features.
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The present paper completes a restudy of the main lava pile in the Deccan flood basalt province (trap) of India. Chenet et al. (2008) reported results from the upper third, and this paper reports the lower two thirds of the 3500-m-thick composite section. The methods employed are the same, i.e., combined use of petrology, volcanology, chemostratigraphy, morphology, K-Ar absolute dating, study of sedimentary alteration horizons, and as the main correlation tool, analysis of detailed paleomagnetic remanence directions. The thickness and volume of the flood basalt province studied in this way are therefore tripled. A total of 169 sites from eight new sections are reported in this paper. Together with the results of Chenet et al. (2008), these data represent in total 70% of the 3500-m combined section of the main Deccan traps province. This lava pile was erupted in some 30 major eruptive periods or single eruptive events (SEE), each with volumes ranging from 1000 to 20,000 km3 and 41 individual lava units with a typical volume of 1300 km3. Paleomagnetic analysis shows that some SEEs with thicknesses attaining 200 m were emplaced over distances in excess of 100 km (both likely underestimates, due to outcrop conditions) and up to 800 km. The total time of emission of all combined SEEs could have been (much) less than 10 ka, with most of the time recorded in a very small number of intervening alteration levels marking periods of volcanic quiescence (so-called ``big red boles''). The number of boles, thickness of the pulses, and morphology of the traps suggest that eruptive fluxes and volumes were larger in the older formations and slowed down with more and longer quiescence periods in the end. On the basis of geochronologic results published by Chenet et al. (2007) and paleontological results from Keller et al. (2008), we propose that volcanism occurred in three rather short, discrete phases or megapulses, an early one at ˜67.5 ± 1 Ma near the C30r/C30n transition and the two largest around 65 ± 1 Ma, one entirely within C29r just before the K-T boundary, the other shortly afterward spanning the C29r/C29n reversal. We next estimate sulfur dioxide (likely a major agent of environmental stress) amounts and fluxes released by SEEs: they would have ranged from 5 to 100 Gt and 0.1 to 1 Gt/a, respectively, over durations possibly as short as 100 years for each SEE. The chemical input of the Chicxulub impact would have been on the same order as that of a very large single pulse. The impact, therefore, appears as important but incremental, neither the sole nor main cause of the Cretaceous-Tertiary mass extinctions.
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We present an integrated geomagnetic polarity and stratigraphic time scale for the Triassic, Jurassic, and Cretaceous periods of the Mesozoic Era, with age estimates and uncertainty limits for stage boundaries. The time scale uses a suite of 324 radiometric dates, including high-resolution Ar-40/Ar-39 age estimates. This framework involves the observed ties between (1) radiometric dates, biozones, and stage boundaries, and (2) between biozones and magnetic reversals on the seafloor and in sediments. Interpolation techniques include maximum likelihood estimation, smoothing cubic spline fitting, and magnetochronology. The age estimates for the 31 stage boundaries (in mega-annum) with uncertainty (millions of years) to 2 standard deviations, and the duration of the preceding stages (in parentheses) are Maastrichtian/Danian (Cretaceous/-Cenozoic) is 65.0 +/- 0.1 Ma (6.3 m.y.), Campanian/Maastrichtian is 71.3 +/- 0.5 Ma (12.2 m.y.), Santonian/Campanian is 83.5 +/- 0.5 Ma (2.3 m.y.), Coniacian/Santonian is 85.8 +/- 0.5 Ma (3.2 m.y.), Turonian/Coniacian is 89.0 +/- 0.5 Ma (4.5 m.y.), Cenomanina/Turonian is 93.5 +/- 0.2 Ma (5.4 m.y.), Albian/Cenomanian is 98.9 +/- 0.6 Ma (13.3 m.y.), Aptian/Albian is 112.2 +/- 1.1 Ma (8.8 m.y.), Barremian/Aptian is 121.0 +/- 1.4 Ma (6.0 m.y.), Hauterivian/Barremian is 127.0 +/- 1.6 Ma (5.0 m.y.), Valanginian/Hauterivian is 132.0 +/- 1.9 Ma (5.0 m.y., Berriasian/Valanginian is 137.0 +/- 2.2 Ma (7.2 m.y.), Tithonian/Berriasian (Jurassic/Cretaceous) is 144.2 +/- 2.6 Ma (6.5 m.y.), Kimmeridgian/Tithonian is 150.7 +/- 3.0 Ma (3.4 m.y.), Oxfordian/Kimmeridgian is 154.1 +/- 3.2 Ma (5.3 m.y.), Callovian/Oxfordian is 159.4 +/- 3.6 Ma (5.0 m.y.), Bathonian/Callovian is 164.4 +/- 3.8 Ma (4.8 m.y.), Bajocian/Bathonian is 169.2 +/- 4.0 Ma (7.3 m.y.), Aalenian/Bajocian is 176.5 +/- 4.0 Ma (3.6 m.y.), Toarcian/Aalenian is 180.1 +/- 4.0 Ma (9.5 m.y.), Sinemurian/Pliensbachian is 195.3 +/- 3.9 Ma (6.6 m.y.), Hettangian/Sinemurian is 201.9 +/- 3.9 Ma (3.8 m.y.), Rhaetian/Hettangian (Triassic/Jurassic) is 205.7 +/- 4.0 Ma (3.9 m.y.), Norian/Rhaetian is 209.6 +/- 4.1 Ma (11.1 m.y.), Carnian/Norian is 220.7 +/- 4.4 Ma (6.7 m.y.), Ladinian/Carnian is 227.4 +/- 4.5 Ma (6.9 m.y.), Anisian/Ladinian is 234.3 +/- 4.6 Ma (7.4 m.y.), Olenekian/Anisian is 241.7 +/- 4.7 Ma (3.1 m.y.), Induan/Olenekian is 244.8 +/- 4.8 Ma (3.4 m.y.), Tatarian/Induan (Permian/Triassic) is 248.2 +/- 4.8 Ma. The uncertainty in the relative duration of each individual stage is much less than the uncertainties on the ages of the stage boundaries.
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40Ar/39Ar dating results on seven volcanic rocks from four areas of the Deccan Traps, India, suggest that volcanic activity more than 70 Ma ago might have occurred at least in limited areas. In the Igat Puri area, the uppermost flow shows an 40Ar/39Ar age of 63 Ma, whereas a lower flow has an age of around 82-84 Ma. 40Ar/39Ar ages of samples from the Bombay area also seem to favor the occurrence of volcanic activity more than 70 Ma ago. One rhyolite dyke from the Osam Hill in the Girnar Hill area shows a well-defined plateau age of 68 Ma, whereas two tholeiitic basalts from the Mahabaleshwar area indicate a total 40Ar/39Ar age of around 63-64 Ma, though they show the effect of secondary disturbance in the age spectra. The volcanic activity(ies) more than 70 Ma ago may correspond to precursory one(s) for the main volcanic activity around 65 Ma ago in the Deccan Traps.
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K/Ar ages on rocks from the Deccan Traps include results on exposed lava flow sequences at Mahabaleshwar and Amboli. Several criteria were used to assess their reliability. The calculated ages range from 40 my to 66 my and are not concordant with the stratigraphy. This can be explained by the altered state of most samples, which is visible in hand specimen and in thin section. This conclusion is further supported by the measured H2O(+) contents, almost all of which exceed one percent. Consideration of these factors, in addition to the possible error magnification of a large air correction in some samples, leads to the conclusion that the age of these flows is at least 60–65 my.
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A review of the available radiometric and paleomagnetic data from the Deccan Flood Basalt Province (DFBP) suggests that the volcanism was episodic in nature and probably continued over an extended duration from 69 Ma to 63 Ma between 31R and 28N. It is likely that the most intense pulse of volcanism at 66.9 ± 0.2 Ma preceded the Cretaceous Tertiary Boundary (KTB, 65.2 ± 0.2Ma) events by R∼1.7Ma. The magnetostratigraphic record in the Deccan lava pile is incomplete and it is therefore possible that the lava flows constituting the reverse polarity sequence were erupted in more than one reversed magnetic chron.
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Recently reported radioisotopic dates and magnetic anomaly spacings have made it evident that modification is required for the age calibrations for the geomagnetic polarity timescale of Cande and Kent (1992) at the Cretaceous/Paleogene boundary and in the Pliocene. An adjusted geo-qtagnetic reversal chronology for the Late Cretaceous and Cenozoic is presented that is consistent with astrochronology in the Pleistocene anq Pliocene and with a new timescale for the Mesozoic.
Article
Tke K/T boundary of Beloc (Haiti) contains an abundant population of remarkably preserved glass particles, probable relics of impact-derived tektites. These glass particles have been dated with the K-Ar method. The average of two measurements indicates a K/T boundary age of 64.0±0.7 (2 σ) Ma. This value strongly supports the 64-65 Ma age derived from the study of basal tertiary (Danian) bentonite levels of North-American continental sections. There is an abridged English version. -English summary
Article
40Ar-39Ar ages of whole rock basalt samples from the lava flows swiching the Ir-rich intertrappean at Anjar are indistinguishable from the Cretaceous/Tertiary Boundary (KTB) age. These results imply that the Ir-rich layer represents the KTB boundary layer. The presence of several flows below the lower dated flow supports our earlier observation1, based on the geochronological studies of Western Ghat lava flow sequence, that the initiation of the Deccan volcanism predated KTB.
Article
The detailed stratigraphy of 650 m thick Thakurvadi Formation of the Western Deccan Volcanic Province has been developed on the basis of extensive field, petrographic and geochemical data supported by discriminant analysis. This paper describes the revised flow stratigraphy of the Thakurvadi Formation originally proposed by Beane et al. (1986). Chemically, the flows of the Thakurvadi Formation are largely composed of nine chemical types with an overall compositional range MgO 3.5-17%, TiO2 1.3-3.3%, P2O5 0.12-0.30% and CaO 7.47-12.5%; The repeated occurrence of each of these CTs at various stratigraphic levels highlights the cyclic nature of these eruptions. The results of various statistical techniques confirm the field stratigraphy. Fractional crystallization appears to be the dominant process in the evolution of Thakurvadi Formation. -from Authors
Article
Detailed stratigraphy based on whole-rock geochemistry is presented for a 1200 m sequence of basaltic lava flows in the Western Ghats escarpment near Mahabaleshwar. Five separate sections are used to define a regional dip of approximately 0-5° to the SW. From the base upwards the following formations are described: Bushe, Lower Poladpur, Upper Poladpur, Ambenali, and Mahabaleshwar. Inter-formation boundaries, with the exception of the Upper Poladpur-Ambenali, are sharp, and are particularly well defined by breaks in Sr-isotopic composition. Two of the formation bases are marked by abnormally mafic flows- the Kamshedi picrite horizon at the base of the Upper Poladpur, and the Kelghar mafic unit at the base of the Mahabaleshwar. Major element compositions are controlled throughout largely by the degree of gabbro fractionation. Intense crustal contamination further modifies compositions in the lower part of the sequence (Bushe-Upper Poladpur) and has strong effects on trace elements and Sr-isotopes. Contamination decreases up-sequence leading to the comparatively uniform Ambenali rocks. The Mahabaleshwar Formation represents a change towards magmatism generated in an enriched mantle with many characteristics similar to those of oceanic island basalts. The geochemical discussion deals mainly with two well-developed mixing lines, one between Ambenali magmas and granitic crust, the other between ambenali magmas and the products of the postulated enriched mantle source. The detailed stratigraphic sequences strongly support the RTF (replenished, tapped, fractionated) magma chamber model of O'Hara &Mathews (1981) and the idea of periodical replenishment by picritic magmas (e. g. Huppert & Sparks, 1980b). This is believed to be the first demonstration of such processes operating on a large scale in a continental basalt province.
Article
Bhandari et al. [Bhandari et al., Geophys. Res. Lett. 22 (1995) 433–436; Bhandari et al., Geol. Soc. Am. Spec. Paper 307 (1996) 417–424] reported the discovery of iridium-bearing sediments sandwiched between basalt flows in the Anjar area (Kutch province, India). They concluded that the signature of the K/T impact had been recorded and that onset of volcanism in the Deccan traps preceded the K/T boundary, excluding the possibility of a causal connection. This paper reports complementary analyses of Anjar outcrops by a joint Indo–French team, where we focused on cosmic markers (iridium and spinels) in the intertrappean sediments and 40Ar/39Ar dating and paleomagnetism of the lava flows. Anomalous Ir concentrations (up to 0.4 ng/g) are confirmed, with up to three thin and patchy enriched layers which cannot be traced throughout the exposed sections. Despite careful search, no Ni-rich spinels were found. Eight basalt samples provided 40Ar/39Ar results, four on plagioclase bulk samples, four on whole rocks. Spectra for whole rocks all indicate some amount of disturbance, and ages based on plagioclase bulk samples seem to be consistently more reliable [Hofmann et al., Earth Planet. Sci. Lett. 180 (2000) 13–28]. The three flows underlying the Ir-bearing sediments are dated at ∼66.5 Ma, and two overlying flows at ∼65 Ma. Magnetic analyses (both thermal and by alternating fields) uncovered clear reversed primary components in the upper flows, and more disturbed normal components in the lower flows, with evidence for an additional reversed component. There are reports [Bajpai, Geol. Soc. India Mem. 37 (1996) 313–319; Bajpai, J. Geol. Soc. London 157 (2000) 257–260] that the intertrappean sediments contain uppermost Maastrichtian dinosaur and ostracod remains above the uppermost Ir-bearing level, and may not be mechanically disturbed. We propose the following scenario to interpret these multiple field and analytical observations. Deccan trap volcanism started within uppermost Maastrichtian normal chron C30N at ∼66.5–67 Ma in the Anjar area. Volcanism then stopped at least locally, and lacustrine sediments were deposited over a period that could be in the order of 1–2 Ma. The K/T bolide impact was recorded as a deposit of Ir, and possibly (though not necessarily) spinels. Volcanism resumed shortly after the K/T boundary, within reversed chron C29R, as witnessed by the three reversely magnetised overlying basalt flows dated ∼65 Ma. This was responsible for erosion and destruction of part of the uppermost sediments (including spinels if there were any) and heterogeneous and non-uniform redeposition of Ir at a number of underlying sedimentary levels. This was also responsible for the partial remagnetisation of the underlying flows. These findings generally confirm and complement those of Bhandari et al. [Bhandari et al., Geophys. Res. Lett. 22 (1995) 433–436; Bhandari et al., Geol. Soc. Am. Spec. Paper 307 (1996) 417–424], and are compatible with the occurrence of the K/T impact at the paleontological K/T boundary, and of Deccan trap volcanism straddling the boundary and starting before the impact. Anjar provides evidence for minor volcanism somewhat earlier than suggested by some authors, though still within normal chron C30N. There is no indication contradicting the view that the bulk of Deccan trap volcanism occurred over only three chrons (C30N, C29R, C29N) [Courtillot, Evolutionary Catastrophes: the Science of Mass Extinctions, Cambridge University Press, 1999; Courtillot et al., Earth Planet. Sci. Lett. 80 (1986) 361–374; Vandamme et al., Rev. Geophys. 29 (1991) 159–190].
Article
Less than one thousand years dating of the youngest volcanic episode of the Teide volcano (Canary Islands, Spain) has been performed using the K/Ar Cassignol technique. Analyses of about 20 g of pure alkali-feldspar yielded a weighted mean age of 800+/-300 years. Stratigraphic, historic and archeomagnetic dating validate this age and rule out the hypothesis of the presence of significant excess argon contamination for this flow. Our result shows that the last effusive activity of the Teide volcano took place shortly before European settlement in Tenerife Island. This study confirms that the Cassignol technique can be applied with success for historic dating and demonstrates that it can now even be extended to the last millennium.
Article
We propose that continental flood basalt (CFB) lavas were predominantly emplaced as inflated compound pahoehoe flow fields via prolonged, episodic eruptions. Our most detailed observations come from the ˜14.7 Ma Roza flow field of the Columbia River Basalt (CRB) Group. The Roza flow field seems to be typical of many flood basalt lavas. Individual flows show a wide range of pahoehoe surface features and a three-part internal structure in vesicularity and other textural parameters. This three-fold division into an upper crust, core, and basal crust appears to be diagnostic of the inflation process and is ubiquitous in basaltic lava flows over a remarkable range of sizes. The pahoehoe surface features and indications of inflation are inconsistent with rapid emplacement of these lava flows. Instead, we interpret the observations to imply that the Roza, and other CFB flows, were emplaced over an extended period of time. From the thickness of the upper crust, which we suggest formed while the flow was actively inflating, and an empirical expression for the rate of crust growth of Hawaiian inflated sheet flows, we estimate that individual Roza flows were emplaced over 5 to 50 months and that the Roza flow field was constructed over a period of 6 to 14 years. However, even with this longer eruption duration, the average lava effusion rate of ˜4000 m3/s is similar to that of the highest-effusion-rate eruption in recorded history (the 1783-4 Laki eruption in Iceland). Our observations of lava characteristics in other CRB flows and in the Deccan Traps suggest that this emplacement style is typical of many, if not most, CFB flows. Initial estimates of the volatile release from the Roza eruption indicate that prodigious amounts of S, Cl, and F were injected into the upper troposphere and lowermost stratosphere; thus this single flood basalt eruption could have had a significant effect on the global atmosphere If other flood basalt eruptions produced similar amounts of volatiles, volatile release might provide a link between flood basalt eruptions and mass extinctions.
Article
Review of available radiometric age determinations of the Deccan traps (India) shows a spectrum of K-Ar ages that is highly polluted by argon loss. Stepwise 40Ar-39Ar age determinations include estimates of data quality and thus avoid contaminated results. The absolute age of the Deccan traps determined using 22 40Ar-39Ar plateau age spectra is 65.5 ± 2.5 Ma. Paleontological data on infratrappean and intertrappean sediments constrain Deccan age to between the A. mayaroensis zone, in the Upper Maestrichtian (about 67 Ma), and the P2 foraminifer zone, in the Lower Paleocene (about 60.5 Ma). Paleomagnetic study of a Nagpur-Bombay traverse (preliminary results of which were used by Courtillot et al. (1986a, b) for a general discussion about Deccan volcanism and the Cretaceous-Tertiary boundary) is presented in detail. All available paleomagnetic results from the Deccan traps (563 flows) are then compiled. Results considered to be transitional or to come from suspicious sites are removed leaving 485 flow results. This extensive data set from a single geological unit allowed us to look in some detail at its statistical distribution. The virtual geomagnetic poles (VGP) are approximately Fisher distributed but present a complex asymmetry. No regional variation can be seen (to within paleomagnetic uncertainties). Although the 3.5° angular difference between the separate normal (pole) and reversed (antipole) data is not statistically significant, it can be explained by either a 2.1 m.y. drift along the apparent polar wander path (APWP) of the Indian plate assuming a normal-reverse-normal (N-R-N) magnetostratigraphy, or a 3.5% contamination by a present field overprint, or a slight nondipole field component. A quality coefficient has been assigned to each result on the basis of existence and value of published 95% confidence angle. Because the normal and reversed mean poles become more precisely antipodal with higher-quality data and with more recent publication date (as a consequence of the evolution of paleomagnetic techniques), we favor the overprint hypothesis. The angular standard deviation of our VGP set is 20% larger than the value predicted by the paleosecular variation model of McFadden and McElhinny (1984). Finally, our best estimate of the overall mean pole is located at 281.3°E, 36.9°N, A95 = 2.4° (calculated from the 163 highest-quality flow VGPs). It is in remarkable agreement with the reference APWP of Besse and Courtillot (1991), leading to an independent estimate of the age of Deccan volcanism at 67.2 ± 6.6 Ma. The same comparison following Acton and Gordon (1989) provides an estimated age at 67 ± 5 Ma. These estimates which are based on paleomagnetic data only are in perfect agreement with both radiometric and paleontological ages.
Article
Flow-by-flow reanalysis of paleomagnetic directions in two sections of the Mahabaleshwar escarpment, coupled with analysis of intertrappean alteration levels shows that volcanism spanned a much shorter time than previously realized. The sections comprise the upper part of magnetic chron C29r, transitional directions and the lowermost part of C29n. Lack of paleosecular variation allows identification of four directional groups, implying very large (40 to 180 m thick) single eruptive events (SEEs) having occurred in a few decades. Paleomagnetism allows temporal constraints upon the formation of 9 out of 23 thin red bole levels found in the sections to no more than a few decades; the two thickest altered layers could have formed in 1 to 50 ka. The typical volumes of SEEs (corresponding to magnetic directional groups) are estimated at 3000 to 20,000 km3, with flux rates ∼100 km3 a−1, having lasted for decades. Flood basalt emission can be translated into SO2 injection rates of several Gt a−1, which could have been the main agent of environmental change. The total volume of SO2 emitted by the larger SEEs could be on the order of that released by the Chicxulub impact. Moreover, each SEE may have injected 10 to 100 times more SO2 in the atmosphere than the deleterious 1783 Laki eruption. The detailed time sequence of SEEs appears to be the key feature having controlled the extent of climate change. If several SEEs erupted in a short sequence (compared to the equilibration time of the ocean), they could have generated a runaway effect leading to mass extinction.
Article
Many hypotheses including asteroidal and cometary impacts, Deccan volcanism, impact induced volcanism and coincidental impact and volcanism have been put forth to explain the observed enhancement of iridium and mass extinction at the K/T boundary (KTB). The identification of KTB layer within the Deccan intertrappean sediments at Anjar, about half way between Flow III and Flow IV provides new constraints on some of these hypotheses. The chemical characteristics of this layer show high concentrations of Ir, Os and other siderophiles accompanied by enrichment of chalcophiles and depletion of lithophiles. The Os/Ir ˜1.1, close to the meteoritic value and other chemical and stratigraphic criteria indicate that it may be the ejecta fallout layer, resulting from a bolide impact at the KTB. Presence of three basalt flows below this layer implies that the volcanism was already active when this layer was deposited and impact of the K/T bolide did not trigger Deccan volcanism.
Article
We propose an alternative calibration of Lower Cretaceous stage durations constrained by direct absolute dating of each stage combined with orbital chronology. Ten glauconitic horizons sampled in the Vocontian basin (SE, France) from the base of the Lower Hauterivian to Upper Albian, yielded K–Ar ages from 123.3 ± 1.7 Ma to 96.9 ± 1.4 Ma, respectively. The relative duration of each stage has been derived by cyclostratigraphy previously obtained in the south-east France and central and south Italy basins. Using the GL-O standard from the Albian–Cenomanian boundary at 95.3 Ma as the anchor point, a cyclostratigraphic age for each stage boundaries has been extrapolated and thus compared with the K–Ar ages. This shows a very well-defined linear correlation which demonstrates the robustness of the proposed durations of the Lower Cretaceous stages. The estimated durations are 5.3 ± 0.4 my, 5.1 ± 0.3 my, 6.8 ± 0.4 my and 11.6 ± 0.2 my for the Hauterivian, Barremian, Aptian and Albian stages, respectively. It also shows that glauconite minerals are powerful radiochronometric tools, when precisely stratigraphically defined and carefully selected. Moreover, the large discrepancy of the estimated Aptian duration of more than 6 my between the most recent published time scale and this study highlights the problem of the radiometric calibration of the M-0 magnetic chron. Finally, the stage durations and boundary ages proposed here bring strong constraints towards the calibration of the Lower Cretaceous time scale. Such accurate temporal calibration is required before any relationship between major biological crises and magmatic emplacement, for instance, could be further investigated.
Article
A suite of basaltic rocks sampled over a vast exposure and stratigraphic thickness in the Deccan traps has been investigated for Os isotopic systematics. The results plot on a very well defined Re–Os isochron corresponding to an age of 65.6±0.3 Ma (2σ uncertainty). This age is in excellent agreement with previous K–Ar and Ar–Ar data. Os data also imply a short duration of volcanism, which should have important implications on mantle geodynamics. The 187Os/188Os initial ratio is typically chondritic: 0.12843±0.00047 (2σ) and indicates that metasomatism and crustal contamination played only a very minor role in the Re–Os budget during formation of the Deccan traps.
Article
Nine basalt samples collected from the bottom to the top of a > 2.5 km thick composite section in the western margin of the Deccan Flood basalt province, India, yield 40Ar-39Ar plateau ages between 67 and 62.5 Ma relative to an age of 520.4 Ma for the monitor standard MMhb-1. These ages are consistent with the stratigraphy and comparable to earlier results [1]. They indicate that the lower ~ 2 km thick reversely magnetised lava sequence erupted within ~ Ma close to 67 Ma ago and the eruption interval even for the exposed and surviving units of the Deccan was not less than 3 Ma. With the Cretaceous/Tertiary boundary as demarcated by Haiti tektites (65.2 +/- 0.1 Ma) [2] and melt rock glasses from Chicxulub crater dated precisely at 64.98 +/- 0.10 Ma [3] relative to MMhb-1 (age 520.4 Ma), our results on the thick reversely magnetised lava units imply their eruption before the Cretaceous/Tertiary boundary events by more than the 1.0 Ma.
Article
New paleomagnetic results from two widely separated areas of the Deccan traps allow one to test the simple normal-reversed-normal (NRN) magnetostratigraphic model previously proposed. The new data from the Mandla region (to the northeast of the main outcrop of the Deccan traps), together with earlier apparently conflicting results, are all compatible with the NRN stratigraphy, provided the flows are not strictly horizontal but have a synform-antiform structure with 500 m amplitude and 150 km wavelength. The structure parallels the Paleozoic Narmada-Son rift system, with slopes never exceeding 0.5°. Sampling in Rajahmundry, a remote southeastern outlier of the Deccan with well-constrained age, allowed identification of the RN boundary in an area where only normal polarities had been reported. It has also been possible to correlate the detailed geochemical stratigraphy in the Western Ghats with the NRN magnetic stratigraphy. A compilation of 35 magnetic studies, together with the above findings, confirms the general applicability of the NRN model and reveals the large-scale topography of the RN boundary, which is an isochron, over most of the Deccan. The RN isochron surface displays a boomerang shape, with topography ranging from sea-level to above 1600 m. This observed topography is consistent with a simple model in which doming and renewed rifting and dyke intrusion resulted from impingement, 70-65 Ma ago, of the Reunion plume under the Indian lithosphere. The Narmada-Son rift was rejuvenated, and a continental rift system with minor extension with a triple junction in the Cambay Graben resulted and was subsequently covered by the Deccan flows, although in places tectonic faulting and volcanism continued to interfere. The Rajahmundry outcrops constrain the original extent and southeastward dip away from the triple junction of much of the traps, a significant part of which has now been removed by erosion and rifting away of the Seychelles.
Article
We have identified the iridium-rich Cretaceous-Tertiary boundary (KTB) layer within the third intertrappean sediment bed at Anjar, located in Kutch near the western periphery of the Deccan volcanic province. This chocolate-colored limonitic layer (<1 cm thick) is characterized by high concentration of Ir (1,271 pg/g) and Os (1,414 pg/g), about 15 times higher than in the adjacent sediments and more than 2 orders of magnitude higher compared to the underlying basalt. High concentration of Ir and Os and other siderophiles is accompanied by enrichment of such chal-cophiles as Se, Sb, Ag, As, and Zn and depletion of such lithophiles as Sc, Hf, and Al compared to the underlying basalt. Some of these characteristics are similar to those found in other continental and marine KTB sections. The Os/Ir ratio of ∼1.1, close to the meteoritic value and other chemical and stratigraphic criteria, indicates that the limonite layer is the fallout ejecta layer, resulting from the bolide impact at the KTB. Absence of enrichment of Ir and other platinum group elements in many other inter-trappean sediments indicates that the volcanic contribution of iridium, during Dec-can eruption, was small and cannot account for the Ir enhancement at the KTB.