Physical, chemical and biological changes at geological boundaries: causes, consequences and clues based on the study of Indian sections
DOI:
https://doi.org/10.54991/jop.1997.1316Keywords:
Mass extinction, Iridium anomaly, Deccan Volcanism, Siberian Volcanism, Asteroidal impact, Cometary impacts, Cretaceous-Tertiary Boundary, Permian-Triassic BoundaryAbstract
Significant and abrupt biological changes are known to occur at the geologic boundaries and are invariably accompanied by some specific physical and chemical changes in the sedimentary deposits. At the Cretaceous-Tertiary Boundary (KTB), for example, shocked minerals, nickel-rich spinels, anomalously high iridium concentration and a variety of other physical and chemical markers have been found. It is generally believed that the biological changes are a consequence of physico-chemical processes which are triggered by some high energy, physical events such as a bolide impact, supernova explosion in the vicinity of the Earth or volcanic episodes. To understand the cause and nature of these physico-chemical processes, a high resolution stratigraphic analysis of physical, chemical, geological, environmental and biological markers of stratigraphic boundaries has been made over the past few decades.
In this article, we summarise the main features of some important bioevent horizons based on typical stratigraphic sequences and then dwell upon various processes which could possibly be responsible for them. The Cretaceous-Tertiary and Permian-Triassic boundaries are discussed in some detail. The clues obtained from the study of stratigraphic sections from India are used to build possible scenarios prevailing at these bioevents.
Downloads
Metrics
References
Abbas S & Abbas A 1996. Comments on biological effects of stellar collapse neutrinos. astro-ph 9612003 preprint, University of Bhuvaneshwar, India.
Alekseev AS, Barsukova LD, Kolesov GM, Nazarov MA & Grigoyan AG 1983. Permian-Triassic boundary event: geochemical investigation of the Trans Caucasia (abstract). Lunar Planet. Sci. 14: 7-8.
Alt D, Sears JM & Hyndmann DW 1988. Terrestrial Maria: the origins of large basalt plateaus, hot spot tracks and spreading ridges. J. Geol. 96: 647-662.
Alvarez LW, Alvarez W, Asaro F & Michel HV 1980. Extraterrestrial cause of the Cretaceous/Tertiary extinction. Science 208: 1095-1108.
Alvarez W 1996. Trajectories of ballistic ejecta from the Chicxulub Crater. Geol. Soc. Am. Spec. Pap. 307: 141-150.
Basu AR, Poreda RJ, Renne PR, Teichmann F, Vasiliev YR, Sobolev NV & Turrin BD 1995. High He plume origin and temporal spatial evolution of the Siberian flood basalts. Science 269: 822-825.
Berner AR 1992. Palaeo-CO, and climate. Nature 358: 114.
Bhandari N 1991. Collisions with Earth over geologic times and their consequences to the terrestrial environment. Curr. Sci. 61: 97-104.
Bhandari N, Gupta M, Pandey J & Shukla PN 1994. Chemical profiles in K/T boundary section of Meghalaya, India: Cometary, asteroidal or volcanic. Chem. Geol. 113: 45-60.
Bhandari N, Gupta M & Shukla PN 1993a. Deccan volcanic contribution of Ir and other trace elements near the K/T boundary. Chem. Geol. 103: 129-139.
Bhandari N, Shukla PN & Azmi RJ 1992. Positive europlum anomaly at the Permo-Triassic boundary, Spiti, India. Geopbys. Res. Letts 19: 1531-1534.
Bhandari N, Shukla PN & Castagnoli GC 1993. Geochemistry of some K/T sections in India. Palaeogeogr. Palaeoclimatol. Palaeoecol. 104: 199-211.
Bhandari N, Shukla PN, Ghevariya ZG & Sundaram SM 1995. Impact did not trigger Deccan volcanism: evidence from Anjar K/T boundary intertrappean sediments. Geophys. Res. Letts. 22: 433-436.
Bhandari N, Shukla PN, Ghevariya ZG & Sundaram SM 1996. K/T boundary layer. in Deccan intertrappeans at Anjar, Kutch. Geol. Soc. Am. Spec. Pap. 307: 417-424.
Bhandari N, Shukla PN & Pandey J 1987. Iridium enrichment at Cretaceous-Tertiary boundary in Meghalaya. Curr. Sci. 56: 1003-1005.
Bohor BF 1990., Shocked quartz and more: Impact signatures in Cretaceous/Tertiary boundary clays. Geol. Soc. Am. Spec. Pap. 247: 335-342.
Bohor BF, Betterton WJ & Krogh TE 1993. Impact-shocked zircons : discovery of shock induced textures reflecting increasing degrees of shock metamorphism. Earth Planet. Sci. Letts 119: 419-424.
Bohor BF, Foord EE, Modreski PJ & Triplehorn DM 1984. Mineralogic evidence for an impact event at the Cretaceous-Tertiary boundary. Science 224: 867-869.
Bostwick JA & Kyte FT 1996. Size and abundance of shocked quartz in Cretaceous-Tertiary boundary sediments from the Pacific basin. Geol. Soc. Am. Spec. Pap. 307: 403-415.
Brooks RR, Hock PL, Reeves RD, Wallace RC, Johnston JH, Ryan DE, Holzbechee J & Collen JD 1985. Weathered spheroids in a Cretaceous/Tertiary boundary shale at Woodside Greek, New Zealand. Geology 13: 738-740.
Caldeira KG & Rampino MR 1990. Deccan volcanism, green house warming and the Cretaceous/Tertiary boundary. Geol. Soc. Am. Spec. Pap. 247: 117-123.
Campbell IH, Czamanske K, Fedorenko VA, Hill RI & Stepanov V 1992. Synchronism of the Siberian traps and the Permian-Triassic boundary. Science 258: 1760-1763.
Carlise DB 1992. Diamonds at the K/T boundary. Nature 357: 119-120.
Carlise DB 1995. Dinosaurs, diamonds and things from outer space: the great extinctions. Stanford University Press.
Chatterjee S 1990. A possible K-T impact site at the India-Seychelles boundary. (abstract). Lunar Planet. Sci. XXF 182-183.
Chatterjee S 1992. A kinematic model for the evolution of the Indian Plate since the Late Jurassic. In: Chatterjee S & Hotton N III (Editors) - New concepts in global tectonics: 33-62. Texas Univ. Press, Lubbock.
Cloue-Long JC, Zichao Z, Guogan M & Shaohua D 1991. The age of the Permian-Triassic boundary. Earth Planet. Sci. Letts 105: 182-186.
Clark DL, Wang CY, Orth CJ & Gilmore JS 1986. Conodont survival and low iridium abundance across the Permian-Triassic boundary in South China. Science 233: 984-986.
Clube SVM & Napier WM 1986. Giant comets and the galaxy: Implications of the terrestrial record. In: Smoluchowski R, Bahcall JN & Matthews MS (Editors) - The galaxy and the solar system.: 260-285. The University of Arizona Press, Tucson, Arizona,
Colodner DC, Boyle EA, Edmond JM & Thompson J 1992. Post-depositional mobility of platinum, iridium and rhenium in marine sediments. Nature 358: 402-404.
Courtillot V 1995. La Vie en Catastrophes, Feyard (Editor).
Courtillot V, Besse J, Vandamme D, Montigny R, Jaeger JJ & Cappetta H 1986. Deccan flood basalts at the Cretaceous-Tertiary boundary. Earth Planet. Sci. Letts 80: 361-374.
Courtillot V, Jaeger JJ, Yang Z, Feraud G & Hofmann C 1996. The influence of continental flood basalts on mass extinctions: where do we stand? Geol. Soc. Am. Spec. Рар. 307: 513-525.
Davis M, Hut P & Muller RA 1984. Extinction of species by periodic comet showers. Nature 308: 715-717.
Ellis J & Schramm D 1995. Could a supernova explosion have caused a mass extinction. Proc. natn. Acad. Sci. Washington 92: 235-238.
Erwin DH 1994a. The Permo-Triassic extinction. Nature 367: 231-236.
Erwin DH 1994b. The end-Permian mass extinction a complex multicaused extinction: In new developments regarding the KT event and other catastrophes in Earth history. LPI Contribution No. 825, Houston, p.33 (abstract).
Erwin DH 1996. The mother of mass extinctions. Scient. Am. 275: 56-62.
Felitzyn SB & Vaganov PA 1988. Iridium in the ash of Kamchatkan volcanoes. Int. Geol. Rev. 30: 1288-1291.
Garg R & Jain KP 1995. Significance of terminal Cretaceous calcareous nanoplankton marker Micula prinsii at the K/T boundary in Um Sohryngkew section, Meghalaya, India. Curr. Sci. 60: 1012-1017.
Gardener A, Hildebrand A & Gilmour I 1992. Isotopic composition and organic geochemistry of nitrogen at the Cretaceous-Tertiary boundary. Meteoritics 27: 221-223.
Ghosh P, Bhattacharya SK & Jani RA 1995. Palaeoclimate and palaeovegetation in central India during the Upper Cretaceous based on stable isotope composition of the palaeosol carbonates. Palaeogeogr. Palaeoclimatol. Palaeoecol. 114: 285-296.
Gilmour I, Russell SS, Arden JW, Lee MR, Franchi IA & Pillinger C 1992. Terrestrial carbon and nitrogen isotopic ratios from Cretaceous-Tertiary boundary nanodiamonds. Science 258: 1624-1626.
Graup G & Spettel B 1989. Mineralogy and phase chemistry of an Irenriched pre-K/T layer from the Lattengebirge, Bavarian Alps, and significance for the KTB problem. Earth Planet. Sci. Letts 95: 271- 290.
Grieve RAF 1991. Terrestrial impact: the record in the rocks. Meteoritics 26: 175-194.
Hallam A 1992. Phanerozoic sea-level changes. Columbia University Press, New York.
Haq BU, Hardenbol J & Vail PR 1987. Chronology of fluctuating sea levels since the Triassic. Science 235: 1156-1167.
Heymann D, Chibante LPF, Brooks RR, Wolbach WS, Smit J, Korochantsev A, Nazarov MA & Smalley RE 1996. Fullerenes of possible wildfire origin in Cretaceous-Tertiary boundary sediments., Geol. Soc. Am. Spec. Pap. 307: 453-464.
Hildebrand AR, Penfield GT, Kring DA, Pilkington M, Camargo A, Jacobsen SB & Boynton WV 1991. Chicxulub Crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico. Geology 19: 867-871.
Hills J 1981. Comet showers and the steady state infall of comets from the Oorts' cloud. Astron. J. 86: 1730-1740.
Hills J 1986. Deflection of comets and other long-period solar companions into the planetary system by passing stars. In: Smołuchowski R, Bahcall JN & Matthews MS (Editors) - The galaxy and the solar system: 397-408. The University of Arizona Press, Tucson, Arizona.
Hofmann C, Courtillot V, Bhandari N, Shukla PN, Kusumgar S, Ghevariya ZG, Gallet V, Fraud G & Rocchia R 1997. Timing of bolide impact and flood basalt volcanism at the K/T boundary based on the study of Kutch sections. Abstract, 21/3 A06, E.G.S. Meeting, Strasbourgh.
Hollander DJ, McKenzie JA & Hsu KJ 1993. Carbon isotope evidence for unusual plankton blooms and fluctuations of surface water CO, "Strangelove Ocean" after terminal Cretaceous event. Palaeogeogr. Palaeoclimatol. Palaeoecol. 104: 229-237.
Hoiser WT & Magaritz M 1992. Cretaceous/Tertiary and Permian/Triassic boundary events compared. Geochim. Cosmochim. Acta 56: 3297-3309.
Holser WT, Schonlaub HP, Attrep M, Boeckelmann K, Klein P, Magaritz M, Orth CJ, Feninger A, Jenny C, Kralik M, Mauritsch H, Pak E, Schramm JM, Stattegger K & Schmoller R 1989. A unique geochemical record at the Permian-Triassic boundary. Nature 337: 39-44.
Hoyt WG 1980. Planet X and Pluto. The University of Arizona Press, Tucson, Arizona.
Hsu KJ & Mckenzie JA 1990. Carbon isotope anomalies at era boundaries :global catastrophes and their ultimate cause. Geol. Soc. Am Spec. Pap. 247: 61-70.
Hut P, Alvarez W, Elder WP, Hansen T, Kauffman EG, Keller G, Shoemaker EM & Weissman PR 1987. Comet showers as a cause of mass extinctions. Nature 329: 118-126.
Isozaki Y 1997. Permo-Triassic boundary superanoxia and stratified Superocean: records from lost deep sea. Science 276: 235-238.
Ivany LC & Salawitch RJ 1993. Carbon isotope evidence for biomass burning at the K-T boundary. Geology 21: 487-490.
Izett GA, Dalrymple GB & Snee LW 1991. 40 Ar-39 Ar age of Cretaceous- Tertiary boundary tektites from Haiti. Science 252: 1539-1542.
Jafar SA & Singh OP 1992. K/T boundary species with Early Eocene nanofossils discovered from Subathu Formation, Shimla Himalaya, India. Curr. Sci. 62: 409-413.
Javoy M & Courtillot V 1989. Intense acidic volcanism and the Cretaceous- Tertiary boundary. Earth Planet. Sci. Letts 94: 409-416.
Kaiho K 1994. Planktonic and benthic foraminiferal extinction events during the last hundred m.y. Palaeogeogr. Palaeoclimatol. Palaeoecol. 111: 45-71.
Kajiwara Y & Kaiho K 1992. Oceanic anoxia at the Cretaceous/Tertiary boundary supported by the sulfur isotope record. Palaeogeogr. Palaeoclimatol, Palaeoecol. 99: 159-162.
Kamo SL & Krogh TE 1995. Chicxulub crater source for shocked zircon crystals from the Cretaceous-Tertiary boundary layer, Saskatchewan: evidence from new U-Pb data. Geology 23: 281-284.
Kapoor HM 1992. Permo-Triassic boundary of the Indian subcontinent and its intercontinental correlation. In: Sweet, WC, Zunyi Y & Dickins Yin H (Editors) - Permo-Triassic events in the eastern Tethys: 21-36. Cambridge University Press.
Keller G 1994. Global biotic effects of the K/T boundary event: Mass extinction restricted to low latitudes. Lunar Planet. Inst. Contrib. 825: 57-58.
Keller G, Li L & Mac Leod 1995. The Cretaceous/Tertiary boundary stratotype section of El Kef, Tunisia: how catastrophic was mass extinction. Palaeogeogr. Palaeoclimatol. Palaeoecol. 119: 221-254.
Kring DA & Boynton WV 1991. Altered spherules of impact melt and associated relic glass from K/T boundary sediments in Haiti. Geochim. Cosmochim. Acta 55: 1737-1742.
Kring DA & Boynton WV 1993. K/T melt glasses. Nature 363: 503-504.
Kring DA, Melosh HJ & Hunten DM. 1996. Impact-induced perturbations of atmospheric sulfur. Earth Planet. Sci. Letts 140: 201-212.
Krogh TE, Kamo SL, Sharpton VL, Marin LE & Hildebrand AR 1993. U- Pb ages of single shocked zircons linking distal K/T ejecta to the Chicxulub crater. Nature 366: 731-734.
Kuiper GP 1951. On the origin of the solar system. In: Hynek A (Editors) "Astrophysics a topical symposium": 357-424. McGraw Hill, New York.
Kyte FT 1988. The extra terrestrial component in marine sediments: description and interpretation. Palaeoceanography 3: 235-247.
Kyte FT 1996. A piece of the K/T bolide? (abstract). Lunar Planet. Sci. XXVII: 717-718.
Kyte FT, Bostwick JA & Zhou L 1996. The Cretaceous-Tertiary boundary on the Pacific plate: composition and distribution of impact debris. Geol. Soc. Am. Spec. Pap. 307: 389-401.
Kyte FT & Wasson JT 1986. Accretion rate of extraterrestrial matter: Iridium deposited 33 to 67 million years ago. Science 232: 1225-1229.
Lahiri TC, Sen MK, Raychaudhuri AK & Acharyya SK 1988. Observations on Cretaceous/Tertiary boundary and reported iridium enrichment, Khasi Hills, Meghalaya. Curr. Sci. 20: 1335-1336.
Luck JM & Turekian KK 1983. Osmium-187/Osmium-186 in manganese nodules and the Cretaceous-Tertiary boundary. Science 222: 613- 615.
Martin EE & McDougall JD 1991. Sea water Sr isotopes at the Cretaceous/ Tertiary boundary. Earth Planet. Sci. Letts 104: 166-180.
Matese JJ & Whitmire DP 1986. Planet X as the source of the periodic and steady-state flux of short period comets. In: Smoluchowski, Bahcall JN & Matthews MS (Editors) - The galaxy and the solar system: 297-312. The University of Arizona Press, Tucson, Arizona.
McLaren DJ & Goodfellow WD 1990. Geological and biological consequences of giant impacts. Annl. Rev. Earth Planet. Sci. 18:123-171.
McLean DM 1985. Deccan traps mantle degassing in the terminal Cretaceous marine extinction. Cretaceous Res. 6: 235-259.
Montanari A, Hay RI., Alvarez W, Asaro F, Michel HV, Alvarez LW & Smit J 1983. Spheroids at the Cretaceous-Tertiary are altered droplets of basaltic composition. Geology 11:668-671.
Morgan JW 1978. Lonar crater glasses and high-magnesium australites: trace element volatilisation and meteoritic contamination. Proc. Lunar Sci. Conf. IX: 2713-2730.
Nakazawa K, Okimura Y & Tokuoka T 1992. Permian and Triassic problems in the Tethys. Abst. Symp. Himalayan Geology, Shimane 32.
Napier WM 1985. Dynamical interactions of the solar system with massive nebula. In: Carusi A & Valsecchi GB (Editors) - Dynamics of comets: their origin and evolution: 41-31 D.Reidel.
Negi JG, Agrawal PK, Pandey OP & Singh AP 1993. A possible K-T boundary bolide impact site offshore near Bombay and triggering of rapid Deccan volcanism. Phys. Earth Planet. Inter. 76: 189-197.
Nelson BK, Macleod GK & Ward PD 1991. Rapid change in strontium isotopic composition of sea water before the Cretaceous-Tertiary boundary. Nature 351: 644-647.
O'Keefe JD & Ahrens TJ 1989. Impact production of CO, by the Cretaceous-Tertiary extinction bolide and the resultant heating of the earth. Nature 338: 247-249.
Olmez 1, Finnegan DL & Zoller WH 1986. Iridium emissions from Kilauea volcanoes. J. geophys. Res. 91: 653-662.
Pandey J 1978. Palaeocene smaller foraminifera of Um Sohryngkew River section, Meghalaya. In: Rasheed RDA (Editor) - Proc. 7th Indian Colloq. Micropaleont. Stratgr., Madras Univ., Madras: 70- 152.
Pandey J 1980. Cretaceous foraminifera of Um Sohryngkew River section, Meghalaya. J. palaeont. Soc. India 25: 53-75.
Pandey J 1990. Cretaceous/Tertiary boundary, iridium anomaly and foraminifer breaks in the Um Sohryngkew River section, Meghalaya. Curr. Sci. 59: 570-575.
Pospichal JJ 1996. Calcareous nannoplankton mass extinction at the Cretaceous/Tertiary boundary: An update. Geol. Soc. Am. Spec. Pap. 307: 335-360.
Prinn RG & Fegley B 1987. Bolide impacts, acid rain, and biospheric traumas at the Cretaceous-Tertiary boundary. Earth Planet. Sci. Letts 83: 1-15.
Rampino MR & Caldeira KG 1993. Major episodes of geological change: correlations, time structure and possible causes. Earth Planet. Sci. Letts 114: 215-227.
Rampino MR & Haggerty BM 1996. Impact crises and mass extinctions: a working hypothesis Geol. Soc. Am. Spec. Pap. 307: 11-30.
Rampino MR & Volk T 1996. Multiple impact event in Paleozoic: collision with a string of comets or asteroids? Geophys. Res. Letts 23: 49-52.
Raup DM 1972. Taxonomic diversity during the Phanerozoic. Science 177: 1065-1071.
Raup DM & Sepkoski JJ 1986. Periodic extinction of families and genera. Science 231: 833-836.
Renne PR & Basu AR 1991. Rapid eruption of the Siberian trap flood basalts at the Permo-Triassic boundary. Science 253: 176-179.
Renne PR, Zichao Z, Richards MA, Black MT & Basu AR 1995. Synchroneity and causal relations between Permian-Triassic boundary crises and Siberian flood volcanism. Science 269: 141- 1416.
Retallack GJ 1995. Permian-Triassic crisis on land. Science 267: 77-80.
Retallack GJ 1996. Paper presented at the Geological Society of America Meeting.
Robin E, Bonte P, Forget L, Jehanno C & Rocchia R 1992. Formation of spinels in cosmic objects during atmospheric entry: a clue to the Cretaceous-Tertiary boundary event. Earth Planet. Sci. Letts 108: 181-190.
Robin E, Rocchia R, Bhandari N & Shukla PN 1997. Imprints of cosmic bolide in the Meghalaya K/T section (in preparation).
Rocchia R, Robin E, Froget 1. & Gayraud J 1996. Stratigraphic distribution of extraterrestrial markers at the Cretaceous-Tertiary boundary in the Gulf of Mexico area: implications for the temporal complexity of the event. Geol. Soc. Am. Spec. Рар. 307: 279-286.
Sarkar A, Bhattacharya SK, Shukla PN, Bhandari N & Naidin DP 1992. High-resolution profile of stable isotopes and iridium across a K/ T boundary section from Koshak Hill, Mangyshlak, Kazakhstan. Terra Nova 4: 485-590.
Schmitz B, Keller G & Stenvall O 1992. Stable isotope and foraminiferal changes across the Cretaceous-Tertiary boundary at Stevns Klint, Denmark: arguments for long-term oceanic instability before and after bolide impact event. Palaeogeogr. Palaeoclimatol. Palaeoecol. 96: 233-260.
Schuraytz BC, Lindstrom DJ, Marin LE, Martinez RR, Mittlefehldt DW, Sharpton VL & Wentworth SJ 1996. Iridium metal in Chicxulub impact melt: forensic chemistry on the K-T smoking gun. Science 271: 1573-1576.
Sepkoski JJ 1982. A compendium of marine fossil families. Milwaukee Public Mus: Contrib. Biol. Geol. 51: 1-125.
Sepkoski JJ 1992. Ten years in the library: new data confirm paleontological patterns. Paleobiology 19: 43-51.
Sharpton VL, Marin LE, Carney JL, Lee S, Ryder G, Schuraytz BC, Sikora P & Spudis PD 1996. A model of the Chicxulub impact basin based on evaluation of geophysical data, Well logs, and drill core samples. Geol. Soc. Am. Spec Pap. 307: 55-74.
Signor PW & Lipps JH 1982, Sampling bias, gradual extinction patterns and catastrophes in the fossil record. Geol. Soc. Am. Spec. Pap. 190: 291-296.
Sigurdsson H, D'Hondt 5 & Carey 5 1992. The impact of Cretaceous/Tertiary bolide on evaporite terrain and generation of major sulphuric acid aerosol. Earth Planet. Sci. Letts 109: 543-559.
Smit J & Klaver G 1981. Sanidine spherules at the Cretaceous-Tertiary boundary indicate a large impact event. Nature 292: 47-49.
Smit J & Kyte FT 1984. Siderophile-rich magnetic spheroids from the Cretaceous-Tertiary boundary in Umbria, Italy. Nature 310: 403. 405.
Stanley SM 1987. Extinction. Scientific American Books, San Francisco.
Sweet WC, Zunyi Y, Dickins JM & Yin H (Editors) 1992. Permo-Triassic events in the eastern Tethys: 1-8. Cambridge University Press.
Swisher CC, Nishimura JMG, Montanari A, Margolis SV, Claeys P, Alvarez W. Renne P, Pardo EC, Maurrasse FGMR, Curtis GH, Smit J& Williams MO 1992. Coeval Ar/Ar ages of 65 million years ago from Chicxulub crater melt rock and Cretaceous-Tertiary boundary tektites. Science 257: 954-958.
Sutherland FL 1994. Volcanism around K/T boundary time its role in an impact scenario from the K/T extinction events. Earth Sci. Rev. 36: 1-26.
Teichert C 1990. The Permian-Triassic boundary revisited. In: Kauffman E & Walliser G (Editors) - Extinction events in Earth history, Lecture Notes in Earth Sciences 30:199-237.
Valentine JW & Moores EM 1970. Plate-tectonic regulation of faunal diversity and sea level a model. Nature 228: 657-659.
Vandamme D, Courtillot V, Besse J & Montigny R 1991. Palaeomagnetism and age determinations of Deccan traps results of a Nagpur-Bombay traverse and review of earlier work. Rev. Geophys. 29: 159-190.
Van Den Bergh S 1994. Astronomical catastrophes in Earth history. Astronom. Soc. Pacific. 106: 689-695.
Van Valen LM 1984. A resetting of Phanerozoic community evolution. Nature 307: 50-52.
Venkatesan TR, Kumar A, Gopalan K, Al'Mukharnedov AI 1997. Of Siberian volcanism and Permo-Triassic boundary changes. Chemical Geology (in press).
Venkatesan TR, Pande K & Ghevariya ZG 1996. 40Ar/39 Ar ages of Anjar Traps, Western Deccan Province (India) and its relation to Cretaceous-Tertiary boundary events. Curr. Sci. 70: 990-996.
Venkatesan TR, Pande K & Gopalan K 1993. Did Deccan volcanism predate the K/T transition? Earth Planet. Sci. Letts 119: 181-189.
Weissman PR 1982. Terrestrial impact rates for long and short period comets. Geol. Soc. Am. Spec. Pap. 190: 15-24.
Wetherill GW & Shoemaker E 1982. Collision of astronomically observable bodies with the Earth. Geol. Soc. Am. Spec. Pap. 190: 1-13.
Wignall PB & Twitchett RJ 1996. Oceanic anoxia and the end Permian mass extinction. Science 272: 1155-1158.
Wolbach WS, Gilmour 1 & Anders E 1990. Major wild fires at the Cretaceous-Tertiary boundary. Geol. Soc. Am. Spec. Pap. 247: 391-399.
Wolbach WS, Lewis RS & Anders E 1985. Cretaceous extinctions: evidence for wildfires and search for meteoric material. Science 230: 167-170.
Yayanos AA 1983. Thermal neutrons could be a cause of biological extinctions 65 Myr ago. Nature 303: 797-800.
Zahnle K & Grinspoon D 1990. Comet dust as a source of amino acids at the Cretaceous/Tertiary boundary. Nature 348: 157-160.
Zhao M & Bada JL 1989. Extraterrestrial amino acids in Cretaceous/Tertiary boundary sediments at Stevns Klint, Denmark. Nature 339: 463-465.
Zhou L & Kyte FT 1988. The Permian-Triassic boundary event: a geochemical study of three Chinese sections. Earth Planet. Sci. Letts 90: 411-421.
Downloads
Published
How to Cite
Issue
Section
License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
