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.

Abstract-A stony meteorite fell at Itawa Bhopji, Rajasthan, India on 2000 May 30. This is the fifth recorded fall in a small area of Rajasthan during the past decade. The meteorite is an ordinary chondrite with light clasts in a dark matrix, consisting of a mixture of equilibrated (mainly type 5) and unequilibrated components. Olivine is Fa24-26 and pyroxene FS 20-22 but, within the unequilibrated components, olivine (Fa5-29) and low calcium pyroxene (FS 5-37) are highly variable. Based on petrographic studies and chemical analyses, it is classified as L(3-5) regolith breccia. Studies of various cosmogenic records, including several gamma-emitting radionuclides varying in half-life from 5.6 day 52Mn to 0.73 Ma 26AI, tracks and rare gases have been carried out. The exposure age of the meteorite is estimated from cosmogenic components ofrare gases to be 19.6 Ma. The track density varies by a factor of -3 (from 4 to 12 x 10 6/cm2) within the meteorite, indicating a preatmospheric body of -9 ern radius (corresponding to a meteoroid mass of -11 kg) and small ablation (1.5 to 3.6 ern). Trapped components in various rare gases are high and the solar component is present in the dark portion of the meteorite. Large excess of neutron-produced 82Kr and 128Xe in both the light and the dark lithology but very low 60Co, indicating low neutron fluxes received by the meteoroid in the interplanetary space, are clear signatures of an additional irradiation on the parent body.

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. Several fragments weighing <2 kg and a single large fragment weighing ∼10 kg were recovered from the strewn field, which extended over several tens of square kilometers. Chemical, petrographic, and oxygen isotopic studies indicate it to be, in most aspects, a typical H5 chondrite, except the unusually low K content of ∼340 ppm. A cosmic ray exposure of 9.7 Ma is inferred from the cosmogenic noble gas records. Activities of eleven cosmogenic radionuclides were measured. 26 Al and 22 Na activities as well as the 22 Na/ 26 Al activity ratio are close to the values expected on the basis of solar modulation of galactic cosmic rays. The low 60 Co activity (<1 dpm/kg) is indicative of a small preatmospheric size of the meteorite. Cosmic ray heavy nuclei track densities in olivine grains range from ∼10 6 cm −2 in samples from the largest fragment to approximately (4-9) × 10 5 cm −2 in one of the smaller fragments. The combined track, radionuclide, and noble gas data suggest a preatmospheric radius of ∼20 cm for the Dergaon meteorite.

Chemical analysis of nine Deccan flow basalts at Anjar, Kutch, western India, indicates that all, except the uppermost flow F-9, are alkaline. In their major and trace element composition, the alkali basalts resemble Ocean island basalts (OIB). Similarities of many diagnostic trace element ratios (e.g. Sm/Nd, Ba/Nb,Y/Nb and Zr/Nb) are similar to those found in the Réunion Island basalts. The uppermost basalt is tholeiitic and chemically resembles the least contaminated Deccan basalt (Ambenali type). The Anjar basalts have iridium concentration ranging between 2 and 178 pg/g. Some of these values are higher by about an order of magnitude compared to the Ir concentration in other basalts of the Deccan. A synthesis of chemical, palaeomagnetic and geochronologic data enables us to construct a chemical and magnetic stratigraphy for these flows. The three flows below the iridium enriched intertrappean bed (IT III) show normal magnetic polarity whereas all except one of the upper basalts show reversed magnetic polarity. The sequence seems to have started in polarity zones 31N and probably continued up to 28R or 27R. The results presented here support the view that Deccan volcanism in Kutch occurred on a time span of a few million years.

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 chalcophiles 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 intertrappean sediments indicates that the volcanic contribution of iridium, during Deccan eruption, was small and cannot account for the Ir enhancement at the KTB.

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Abstract-We demonstrate the presence of solar flare as well as neutron capture effects in the isotopic composition of rare gases in the Fermo regolith breccia acquired on its parent body based on the measurements of tracks, rare gases and radionuclides. The track density along a 3.2 cm long core decreases by a factor of about 6 and by more than a factor of 13 within the meteorite, indicating small (2-9 cm) and asymmetrical ablation. Rare gases show a large trapped component; the isotopic ratios, particularly 20NePNe = 11 and 20Ne/36Ar = 10 are indicative of a solar component. The galactic cosmic-ray exposure age is determined to be 8.8 Ma. Activities of a dozen radionuclides ranging in half-life from 16 day 48V to 0.73 Ma 26A1 are consistent with their expected production rates. Track, rare gas and radionuclide data show that the meteoroid was a small body (5 120 kg) and had a simple, one-stage exposure history to cosmic rays in the interplanetary space. However, 82Kr and 128Xe show an excess due to neutron irradiation on the parent body of the meteorite. The presence of solar gases and the neutron capture effects indicate several stages of irradiation on the parent asteroid. The chemical composition of Fermo confirms that it belongs to the H group of ordinary chondntes with lithic clasts having varying compositions. d15N is found to be 8.3 ? 1.2%0, close to the typical values observed in H chondrites. INTRODUCTION AND SAMPLE DETAILS