Journal of the Geological Society, London, Vol. 152, 1995, pp. 289-296, 1 fig. 1 table. Printed in Northern Ireland

Implications of the infra- and inter-trappean biota from the Deccan, India, for the role of volcanism in -Tertiary boundary extinctions

G. V. R.PRASAD & C. K. KHAJURIA P. G. Department of Geology, University of Jammu, Jammu-180004, India

Abstrad The fossil record shows a remarkable similarity between the biota that existed before and after the initiation of Deccan volcanic activity. Virtually all the available palaeontological evidence, such as thefauna and flora of thefreshwater infra- and inter-trappean beds and the planktonic foraminiferafrom the subsurface infra- and inter-trappean beds of the southeastern coast, do not favour the initiation of Deccan volcanism as the cause of mass extinctions at the Cretaceous-Tertiary (K-T) boundary. Instead, a combination of events, such as an extended period of volcanism, changes in sea-level and related climatic changes, and certain local factors, may have played a significant role in selectively eliminating various groups of organisms. This view is further reinforced by the biotic changes across the K-T iridium layer in the UmSohryngkew River section of Meghalaya, north- eastern India.

Keywords: Deccan Traps, Inter-trappean beds, K-T boundary, mass extinctions.

The terminal Cretaceous mass extinctionshave been between the flows, and overlying theupper flows are explained in terms of environmental crises caused either by informally known asinfra-trappean ( = Lameta),inter- the impact of a bolide (Alvarez et al. 1980; Hsii 1980) or by trappean, and supra-trappean beds, respectively (Table 1). extensive volcanism (McLean 1985; Officer et al. 1987; The infra-trappean orLameta beds have been formally Courtillot et al. 1990). Supporters of the volcanic hypothesis designatedas afterthe Lameta Ghat considered eruption of the Deccan Traps of peninsular India typesection nearJabalpur. The infra-and inter-trappean tobe a possible cause of extinctionsat the Cretaceous- beds are prominentlydistributed along thesouthern, Tertiary (K-T) boundary.It has been suggested thatthe southeastern,eastern, northeastern, and northwestern Deccan basalts erupted episodically, at an average rate of margins of the main mass of Deccan Traps (Fig. 1). All the 3 km3/ (Courtillot et al. 1986), adding several thousand infra- and inter-trappean beds investigated so far, with the tons of gases to the atmosphere which would have returned exception of the Kutch inter-trappean beds, fall onthe to the Earth’s surface in the form of acid rain (Officer et al. eastern andsoutheastern margins of the Deccan Trap 1987). The acid rain and volcanogenic aerosols that produce province and in the Krishna-Godavari basin. changes in the pH values of surface ocean waters and global The infra-trappean outcrops at Marepalli, Dongargaon, temperature, and cause a depletion of the ozone layer, were Pisdura, Jabalpur and Rahioli are, in general, composed of supposed to have affected the biosphere severely (McLean sandstones, limestones and marls, and are supposed to have 1985; Officer et al. 1987). been deposited in fluvio-lacustrine basins of a coastal-plain The main purpose of this paper is to test the volcanic environment (Sahni 1983; Jain & Sahni 1983; Brookfield & hypothesis by examining the fossil record from sedimentary Sahni 1987). The lithology of the inter-trappeanoutcrops strata below and intercalated with Deccan volcanic flows. In varies from locality to locality, but primarily consists of this regard, an important question needs to beaddressed. sandstones,carbonaceous shales, limestones, mudstones, What were the effects of volcanism atthe actualsite of marls and chert.Based on sedimentological and palaeon- eruption inpeninsular India, if Deccan volcanism was a tological data,an environment similar tothat of the cause of K-T boundary extinctions? infra-trappeanbeds has been suggested forthe inter- trappean surface sections (Sahni 1983; Prasad & Sahni 1987; Khajuria & Singh 1992). The marineinfra- and inter- Stratigraphy and age of the Deccan Traps trappean successions have been identified in the Oiland The Deccan Traps,one of the largest continental basalt Natural Gas Commission (ONGC) wells atNarsapur accumulations in the world, originally covered anarea (Narsapur-l), Palakollu(Palakollu-A), Elamanchili between 1.5 million km2 (Krishnan 1982) and 2.6 million (Elamanchili-A) and Modi (Modi-A). These subsurface km2 (Pascoe 1964) with an estimatedvolume of 2 million sections are located in the Krishna-Godavari basin, km3, if onetakes into consideration the basaltic flows 10-15 km inland from the coast of the Bay of Bengal (Fig. encountered as farnorth as Sind (Pakistan) and Lalitpur 1).The infra- andinter-trappean beds of Narsapur-lare (UttarPradesh), and those lying off the western coast composed of clays and claystones. The fauna1 evidence (Cocliin, Ratnagiri, Bombay) and on the southeastern coast indicates thatthe infra-trappean beds of this well were (Krishna-Godavaribasin; Fig. 1) of India. After con- deposited in middle toouter shelf depths,whereas the siderable erosion, the Deccan Traps now occupy an area of inter-trappean beds were deposited in inner to middle shelf about 500 000 km2 in peninsular India (Fig. 1) and have a depths (Govindan 1981). The Palakollu-A is the thickest of thickness of more than 2500 m in the Western Ghat section. all the subsurface sections and is the best studied from the The sedimentary beds underlying the basal flows, enclosed point of view of foraminiferal biostratigraphy. In this well, 289

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Bar,-. Hill.. wno~ 7 o > Mamoni Lalitpur

. . ~ vv vv Pisduro vvv Bombay .. .. . >AAsifobad So0 km O- O- Rotnogiri

INDEX

MADRAS v v v Deccan Traps k. lyyl 3 - and inter trappean lit ies

Fig. 1. Map showing the distribution of infra- and inter-trappean beds in peninsular India.

the infra-trappean beds are predominantly claystones with 1990; Prasad & Cappetta 1993). The recent report of a thin sandstone partings, andtheinter-trappean and palynological assemblage represented by Ariadnaesporites, supra-trappeanbeds consist mainly of shales. The Leptolepidites, PFoxapertites, Palmidites, Liliacidites, depositional environment changed from outer shelf to upper Aquilapollenites, Scollardia and Dinogymnium from slope conditions at the base, through the deeper part of the Jabalpur (Dogra et al. 1988) furnishes the strongest evidence inner shelf, to very shallow marine conditions at the top of in favour of a late age for the infra-trappean the infra-trappean succession (Raju et al. 1991; Jaiprakash et beds. Inthe Narsapur-l well, the basal flows overlie al. 1993). According tothese authors, open marine infra-trappeanbeds bearing the planktonicforaminifera conditions with a bathymetry of 50m were present during Abathomphalus mayaroensis, which indicates that the basal deposition of theinter-trappean beds,whereas a gradual flows are no older than late Maastrichtian here (Govindan drop insea-level from abathymetry greater than 50m to 1981). This is also true for the infra-trappean beds of the very shallow marine conditions occurred during deposition Palakollu-A, Elamanchili-A and Modi-A wells, which have of the supra-trappean beds. yielded planktonic foraminiferal assemblages corresponding A revision of theinfra-trappean fauna led to the late Maastrichtian Abathomphalus mayaroensis Zone Buffetaut (1987) to discard the long held Turonian age for (Raju et al. 1991). the infra-trappean beds (Huene & Matley 1933). Based on The Deccaninter-trappean beds were previously the similarities of theinfra-trappean titanosaurids to regarded as early Tertiary in age because of the absence of Titanosaurus fromthe Maastrichtian of Madagascar and (Lydekker 1890). But recent investigations Europe, Buffetaut (1987) favoured a Maastrichtian age. In brought to light the presence of dinosaurremains in the recent ,biostratigraphically significant fish taxa of inter-trappean beds of Asifabad, Nagpur, Ranipurand Maastrichtianage, such as Zgdabatis, Rhombodus,Apate- Kutch (Rao & Yadagiri 1981; Prasad & Sahni 1987; odus and Stephanodus, have also beenreported from the Vianey-Liaud et al. 1987; Sahni & Bajpai 1988; Ghevariya infra-trappean sections of Marepalli, Pisdura and Jabalpur 1988; Prakash et al. 1990). The inter-trappean beds of (Jain & Sahni 1983; Courtillot et al. 1986; Sahni & Tripathi Gurmatkal, Naskal,Asifabad, Nagpur and Kutch have

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Table 1. Fauna1 and floral list ofthe freshwater infra-and inter-trappean sequences of peninsular India Table 1. (Continued) Taxa Infra-trappean Inter-trappean Taxa Infra-trappean Inter-trappeanInfra-trappean Taxa Inter-trappean Infra-trappean Taxa L ameta) beds beds beds (= Lameta) beds beds (= Lameta)

Fish Titanosaurus J Igdabatis indicus J J cf. T. indicus Rhombodus sp. J J Laplatasaurus J Raja sudhakari J cf. L. madagas- Lepidotes sp. J J carensis Lepisosteus indicus J J Antarctosaurus J Pycnodus lametae J septentrionalis P. bicresta J J J Phareodus sp. J J l J Apateodus cf. A. striatus J J Indosaurus J Enchodus sp. J J matleyi Arius sp. J J Eoserranus hislopi J raptorius ?Sphyraena J J (abelisaurid) Ostracion sp. J J Stephanodus lybicus J indicus Eotrigonodon indicus J J (? nodosaurid) E. wardhaensis J J Omithischia J Pisdurodon spatulatus J Indotrigonodon ouatus J J Mammals Palaeolabrus cf J Deccanolestes J P. dormaalensis hislopi Fish otoliths Gastropods Lepisosteidae J Physa prinsepii J Elopidae J Paludina normalis J Clupeidae J Paludina sp. J Serranidae J Lymnaea subbulata J J Bivalves Apogonidae J Unio deccanensis J J Amphibians Ostracodes Pelobatidae ?J J Paracypretta J J Discoglossidae J jonesi ? Hylidae J Eucandona J Leptodactylidae: J Darwinula J Indobatrachus Cyprinotus J pusillus Mongolianella J khamariniensis Reptiles Cytheridella J strangulata Crocodylidae J J Candona J Dyrosauridae J altanulaensis Alligatoridae J Candoniella J Turtles altanica Pelomedusidae: J J Leiria sp. J Shweboemys Altanicypris J pisdurensis szczechurae Talicypridea J Snakes biformata Boidae J J Cypridea J Nigerophiidae: cavernosa Indophis sahnii J Lizards Charophytes Platychara J J ? Scincomorpha J Anguidae J perlata P. raoi J J Dinosaurs P. sahnii J J Titanosaurid J J Microchara J J egg shells sausari Titanosaurus J Nemegtichara J blandfordi grambasti

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Table 1. (Continued) press), and Ranipur and Padwar (Azolla, Aquilapollenites, Gabonisporites, Lycopodiumsporites, Proxapertites, Spinizo- Taxa Inter-trappeanInfra-trappean nocolpites, Cyathidites, Palmaepollenites, Podocarpidites, (= Lameta)bedsbeds Diporoconia etc.; Mathur & Sharma 1990; Prakash et al. Harrisichara J 1990), with affinities tolate Maastrichtian palynological muricata assemblages of the Cauvery basin, Narsapur-l well and Peckichara varians J J Bengal basin, indicatea similar age forthese beds. Stephanochara J However, the upper part of the Gurmatkal section yields cf. S. levis characteristic European charophyte taxa of early Palaeocene age, such as Peckichara varians, Harrisichara muricata and Pollens and spores Stephanochara cf. S. levis, indicating that the topmost strata Aquilapollenites J J F-ngalensis of this section were possibly deposited very close to the K-T boundary (Srinivasan et al. 1992). The subsurfaceinter- Azolla cretacea J Gabonisporites J trappeanbeds of Narsapur-l have been assigned a late vigourouxii Maastrichtianage based onthe Globotruncana stuarti-G. Ariadnaesporites J J gagnebini foraminiferal assemblage (Govindan 1981). In SP. contrast, the inter-trappean succession of Palakollu-A yield Triporoletes sp. J foraminifera of the Globorotalia (A.)praecursoria praecur- Lycopodiumsporites J soria Zone, corresponding tothe P,, and P, planktonic SP. foraminiferalzones of early Palaeocene age (Raju et al. Podocarpidites sp. J J 1991; Jaiprakash et al. 1993). Ephedripites sp. J With the exception of marine subsurface sections, no Tricolpites sp. J fossiliferous supra-trappean beds are known from the Proxapertites J Deccan Trap province. The presence of Morozovella crassimurus uncinata, Planorotalites compressa, Subbotina P. cursus triloculinoides, corresponding to the P, planktonic foramini- P. operculatus feral Zone, in the supra-trappeanbeds of Narsapur-l is Callialasporites J suggestive of an earlyPalaeocene age for these strata Leptolepidites J (Govindan 1981). In the Palakollu-A, the supra-trappean verrucatus beds overlying the youngest basaltic flow yielded an early Scollardia conferta Palaeoceneforaminifera of the Globorotalia (A.) Dinogymnium sp. praecursoria carinata Zone (upper P, planktonic foraminife- Cyathidites sp. J Palmidites maximus ral Zone; Raju et al. 1991; Jaiprakash et al. 1993). Diporoconia sp. J The geochronological dataonthe DeccanTraps, Liliacidites J althoughmeagre, provide valuable information onthe microreticulatus initiation andduration of Deccan volcanism. The Deccan Spinizonocolpites J basalt outcrops,at Rajahmundry, 70 km northeast of the baculatus Narsapur and Palakollu subsurface sections, have yielded a Palmaepollenites sp. J 40Ar/39Ardate of 64 f 1 Ma (Baksi & Brahman 1985). The lowermost flows atDongargaon, overlying the dinosaur- Data from Rao & Yadagiri (1981), Sahni et al. (1982), Jain & Sahni bearinginfra-trappean beds, and in the Narmada valley, (1983),Gayet et al. (1984),Sahni et al. (1984),Rana (1984, south of Indore, underlain by Upper Cretaceous Bagh beds, 1987,1988, 1990), Spinar & Hodrovi (1985),Prasad (1985, havebeen datedat 66.4 f 1.9Maand 65.1 f 0.6 to 1989),Jain (1986), Buffetaut (1987), Prasad & Sahni(1987, 67.6 f 1.8 Ma, respectively, by the 40Ar/39Ar dating tech- 1988),Vianey-Liaud et al. (1987),Sahni & Bajpai(1988), nique (Courtillot et al. 1988). An 40Ar/39Arplateau age of Ghevariya (1988), Dogra et al. (1988), Khajuria (1989), Bajpai 68.6 f 2.4 Ma was obtained for a sample near the Girnar et al. (1990),Bhatia et al. (1990 a,b), Mathur & Sharma Hill, Gujarat (Kaneoka 1980). In the Kutch region, where (1990),Mohabey (1990), Prakash et al. (1990), Prasad & Srinivasan(1990), Sahni & Tripathi(1990), Prasad & Rage the inter-trappean fauna indicates a Maastrichtian age, the (1991), Rage & Prasad(1992), Srinivasan et al. (1992) and Deccan basalts yielded an 40Ar/39Arplateau age at Prasad & Cappetta (1993). 66.8 f 0.3 Ma (Pande et al. 1988). Duncan & Pyle (1988) suggested 40Ar/39Ar whole rock isochron ages ranging between 66.7 f 1.0 Ma to 68.5 f 0.6 Ma for a 2000m thick yieldedMaastrichtian a ichthyofauna (Igdabatis, sequence of basalts in the WesternGhats. More recently, Rhombodus, Apateodus, Stephanodus etc.) similar to that of Venkatesan et al. (in press) analysed the basalts from a theinfra-trappean beds (Gayet et al. 1984; Prasad 1989; 2500 m thick sequence, which includes the study area of Bajpai et al. 1990; Prasad & Srinivasan 1990; Prasad & Duncan & Pyle (1988), by the 40Ar/39Ar dating technique Cappetta 1993). Apart from the vertebrates,a Maastrichtian and presenteda new set of dates. According to these ostracodeassemblage represented by Talicypridea, authors, the lower part of the section from 600 to 2500m Altanicypris, Cypridea, Candona and Mongolianella has also furnishes a mean age of 67.1 f 0.1 Ma, whereas the samples beendocumented from the inter-trappean beds of from intervals between 250-600 m and 0-250 m yield dates Gurmatkal, Naskal, Asifabad, Nagpur and Mamoni (Bhatia at 64.2 f 0.4 Ma and 62.3 f 0.3 Ma, respectively. Hence a et al. 1990a, b; Srinivasan et al. 1992). Above all, the duration of 4.8 f 0.3 Ma has been suggested for the Deccan palynological assemblagesfrom the inter-trappean beds of volcanism (Venkatesan et al. in press). Based onthe Naskal (Ariadnaesporites, Gabonisporites etc.; Sahni et al. in occurrence of a common mineral assemblage (montmorillo-

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nite, chlorite and illite) in the infra-trappean beds as well as by a single family, the ?Pelobatidae, which is joined by the basal volcanic flows overlying theinfra-trappean beds Discoglossidae, Leptodactylidae and?Hylidae and the inter-trappean beds of Jabalpur, the infra-trappean (Indobatrachus pusillus) in the inter-trappean fauna. beds are supposed to have been deposited either Theinfra-trappean crocodiles are represented by the synchronously with or after the initiation of volcanic activity families Crocodylidae and Dyrosauridae. In addition to the (Salil 1993). Crocodylidae, the family Alligatoridae occurs in the Inthe light of the recovery of late Maastrichtian inter-trappean biota. The pelomedusidturtles and boid foraminifera of the Abathomphalus mayaroensis Zone from snakes are known fromthe infra-trappeanas well as the marine infra-trappean beds,a late Maastrichtian inter-trappean beds. palynological assemblage from the infra-trappean outcrops, The dinosaur fauna of the infra-trappean beds is widely and the clustering of geochronological dates around 66 Ma documented(see Buffetaut 1987 fora review of previous forthe lowermost basaltic flows which weresupposed to work) and includes skulls and postcranialbones of have served as provenance for the infra-trappean beds (Salil titanosauridsauropods, coelurosaurs, abelisaurids, megalo- 1993), it is reasonable to conclude that the infra-trappean saurids and ?nodosaurids(Table 1). The titanosaurids are strata were deposited during the late Maastrichtian. Because also known by egg shells and clutches. Some unidentified of the marked similarity of the fauna and flora between the ornithischianshave also been reportedfrom the infra- infra- and inter-trappean beds and the occurrence of a late trappean beds of Rahioli, Gujarat (Mohabey 1990). At Maastrichtian palynological assemblage in theinter- present, the dinosaur fauna of the inter-trappean beds is not trappean outcrops, a similar age is also favoured for these fully known. Although the inter-trappean beds were earlier beds. The fossil data from the Gurmatkal outcrops and the supposed to lack adinosaur fauna (Lydekker 1890), the subsurface sections of the southeastern coast (Palakollu-A), work done over the pastseveral years has demonstrated on the contrary, point to a slightly younger early Palaeocene unequivocally the widespreadoccurrence of dinosaur age fortheinter-trappean beds. In conclusion, the remains in these beds (Rao & Yadagiri 1981; Vianey-Liaud palaeontological data suggest a late Maastrichtian initiation et al. 1987; Prasad & Sahni 1987; Sahni & Bajpai 1988; forDeccan volcanism atthe top of the Abathomphalus Ghevariya 1988; Prakash et al. 1990). However, the dinosaur mayaroensis planktonic foraminiferal Zone (66.5 Ma) and an fauna of the inter-trappeanbeds is not very rich, being earlyPalaeocene termination atthe base of Globorotalia represented by fragmentary limb bones, teeth and egg shells. (A.)praecursoria carinata Zone (61.2 Ma; Raju et al. 1991; The sauropods and megalosaurids survived the initial Jaiprakash et al. 1993). This is consistent with the latest volcanic activity of the Deccan Traps, and are documented geochronological dates, which indicate a duration of 4.8 Ma by thin egg shells, isolated teeth (Asifabad, Nagpur, Kutch) for the Deccan Traps (Venkatesan et al. in press). and ina few cases by fragmentary postcranial bones Iridiumconcentrations from thelate Maastrichtian (Asifabad, Ranipur, Kutch). From the abundance and type inter-trappean beds of Nagpur are negligible (50-100 pg g-'; of skeletalelements reported,the inter-trappean dinosaur Bhandari et al. 1993). So far, no anomalously high iridium fauna appears tohave been less diverse. concentration comparable with concentrations in the Dental and postcranial remains of palaeoryctid mammals Cretaceous-Tertiary boundary section on the Um Sohryn- (Deccanolestes hislopi) have been described only from the gkew River of Meghalaya, northeastern India, have been inter-trappean beds of Naskal (Prasad & Sahni 1988). The recordedfrom the Deccan Trapsand their associated absence of mammals in the infra-trappean beds and other sedimentary rocks, but data are limited. inter-trappean beds seems to be an artefact of preservational bias, because the mammals occur in association with a large component of terrestrial and freshwater taxa in pedogeni- Fossil record cally altered, flood-plain lacustrinedeposits (work in The infra- and inter-trappean beds of peninsular India have progress). In marked contrast, the infra-trappean and other been known for their rich fauna1 and floral component since inter-trappean strata yield amixture of freshwater and the second half of the nineteenth century. However, it is marine fossils. only in the last decadethat these fossiliferous bedshave Among the invertebrates,pulmonate gastropods are beenstudied in asystematic and comprehensive manner, common to both infra- and inter-trappean strata even at a resulting in largea number of studies onvertebrate, species level. Some of the infra-trappean ostracode taxa are invertebrate and plant fossils (the reader may refer to the representedin theinter-trappean fauna, but thelatter is papers cited in the data source of Table 1). These studies more diverse (Table 1). have demonstratedthat the fauna and flora of the In the subsurface section of Narsapur-l, the infra- and infra-trappean beds persisted without any major change into inter-trappean beds share many planktonicforaminifers the inter-trappean beds (Table 1). (Govindan 1981), suchas Globotruncana stuarti, G. In terms of taxonomic diversity and abundance, the fish gagnebini, Heterohelix striata, Pseudotextularia brownii, comprise the largest of all the groups.Remains of Reophax texanus, Gaudryina laevigatus, Nodellurn myliobatids, pycnodontids, osteoglossids andtetraodontids vellascoensis and Cribrostromoides cf. cretaceus. Fauna1 occur abundantly, both in the infra- and inter-trappean beds. analysis of the Palakollu-Asubsurface section presentsa Except for the appearance of certain new taxa, such as Raja, different picture from that of Narsapur-l. Hereeight basaltic Palaeolabrus, ?Sphyraena, Ostracion and otoliths represent- flows were encountered ina 400 m thick succession ing the families Lepisosteidae, Elopidae, Clupeidae, (extendingfrom a depth of 2800-2400 m). The infra- Serranidae,Notopteridae and Apogonidae in theinter- trappean beds occur in the interval of 2800-2700m and the trappean assemblage, the fauna is strikingly similar, even at eight basaltic flows and associated inter-trappeanand generic and species level. supra-trappean beds appear in the 2700-2400111 interval Amphibians of the infra-trappean beds are represented (Raju et al. 1991; Jaiprakash et al. 1993). The Cretaceous

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planktonicforaminifers, such as Globotruncana arca, G. the number of taxa preserved than that of the infra-trappean aegyptica, G. conica, Racerniguernbelina fructicosa, Globot- beds, and the few biotic changes that we see (Table 1) do runcana stuarti, Gansserina wiedenmayeri, Ventilabrella sp., not indicate any catastrophic event, but are more likely to Heterohelix sp. disappear at2770 m followed by Reophax sp. be normal ecological changes. The effect of environmental and Praebulirnina corsaye at 2735 m, Rugoglobigerina scotti stressinduced by volcanism depends onthe size of the at 2720m, and Archaeoglobigerina blowii at 2710111 within province, the rate at which eruptions were taking place, and the infra-trappean beds, well before the eruption of the first the duration of intervening quiet periods (Cox 1988). It has basaltic flow (Jaiprakash et al. 1993). In the absence of index been shown that Deccan volcanic activity consisted of many taxa, the K-T boundary is not precisely delineated in this episodes spread overseveral hundred thousandyears section. Butthe interval between2710m, where the last (Courtillot et al. 1990). The first pulse, possibly lasting for Globotruncana occurs, and 2640 m, at which Guernbelitria 104 years, corresponds to the basal flows and occurs in the cretacea disappears and typical Palaeocene forms appear for Abathornphalus rnayaroensis Zone within chron 30N. the5rst time, hasbeen designatedas a K-T transition Several minor pulses occur within the A. mayaroensis Zone, (Jaiprakash et al. 1993). Only a few benthonic forms, such as but in chron 29R, and a major pulse of 104 years duration Gaudryinabronni, Guernbelitria cretacea and was supposed to have taken place atthe K-T boundary Spiroplectamrnina jarvisi, persisted during the K-T transi- (Courtillot et al. 1990). If at all significant, it is the last pulse tion and finally becameextinct at 2640m. Typical which may have intensified the environmental crisis leading Palaeocene planktonic foraminifera (10 species) make their to K-T boundary extinctions. The rate of extrusion for the first appearance at 2640 m. These include Globorotalia (T.) final pulse of Deccan volcanism might have been far higher sabina, Eoglobigerina trivialis, E.eobulloides, Boldia sp., than minimum estimates of 3km3/year (Courtillot et al. Dorothia minutula, Globorotalia (A.) praecursoria 1990). praecursoria, G. (T.) irnitata, G. (T.) pseudobulloides, G. In contrast to the freshwaterinfra- and inter-trappean (T.) cornpressa and Anomalinoidesrubiginosa. The supra- outcrops, the thick subsurface marine section of Palakollu-A trappeansediments overlying the highest basaltic flow at provides us with a different set of data. Here, extinction of 2575 m yield eightspecies of foraminifers represented by the planktonicforaminifers took place at various levels Globorotalia (T.) inconstans, Subbotina triloculinoides, within theinfra-trappean sedimentarysequence prior to Chiloguernbelina sp., Globobulimina sp., Chilostornella sp., Deccan volcanism, and before theend of the Cretaceous Globorotalia (A.) praecursoria carinata, Eoglobigerina sp. Period. From the fossil record, it appears that there was a and Quinquiloculina sp., which show a step-wise extinction gradualdecline of foraminiferalabundance andthe pattern in the 2575-2400 m interval (Jaiprakash et al. 1993). extinctions were of step-wise nature (Jaiprakash et al. 1993). The foraminiferal datafrom the subsurfacesections of A similar kind of extinction pattern was also recorded for Elamanchili-A and Modi-A are not very different from that the supra-trappean fauna of the same section (Jaiprakash et of Palakollu-A. al. 1993). The foraminiferal extinctions atthese two levels The charophyte assemblage represented by Platychara, (infra-trappean andsupra-trappean) have beencorrelated Microchara and Peckichara is widely distributedin the with global falls of sea-level during the Maastrichtian and infra-trappean as well as the inter-trappean beds. However, Danian, respectively (Jaiprakash et al. 1993). In anearby certain new forms, such as Harrisichara, Stephanochara and subsurface section at Narsapur, the infra-trappeanfauna Nernegtichara areintroduced in theinter-trappean biota. survived the initial volcanic activity without any significant Results of the palynological studies of the infra- and change. Many taxa havebeen documented from both the inter-trappeanbeds havealso indicated the presence of infra- andinter-trappean beds(Govindan 1981). In this many common elements in both the assemblages. respect, it recalls the biotic distribution across the freshwater infra- and inter-trappean strata. It is, however, difficult to establish whether the Danian foraminifers of the Narsapur Discussion section appeared suddenlyat the K-T boundary, because The foregoingevaluation of the fauna and flora from the thesupra-trappean sediments unconformably overlie the infra- and inter-trappean beds reveal that an overwhelming youngest basaltic flow. majority of taxa, especially the freshwaterlacustrine taxa, At the other extreme, in the marine facies of the Um survived the initial effects of Deccan volcanism without Sohryngkew River section of Meghalaya, northeastern undergoing any drastic change. If Deccan volcanism was the India, where the iridium producing K-T boundary layer is cause of K-T boundary extinctions, one would expect to precisely located, planktonic foraminifers cross the bound- find some effect of the volcanic activity on the biota at the ary and persist 20 cm above the K-T iridium layer (Pandey actual site of eruption in peninsular India. Absence of any 1990). Palynological data from this section reveal that significant fauna1 and floral changesbetween the infra- Dinogymnium disappeared 50cm below the K-T iridium trappean beds,deposited prior tothe initiation of the layer, whereas the land plants persist across this layer, their volcanic activity, andthe inter-trappean beds,deposited highest occurrence being lOcm above it (Pandey 1990). It during the repose periods of the volcanic activity, needs an thus appears from thepresent set of data that the extinctions explanation. of faunaand flora in this section took place over an Episodic or subdued volcanism may not affect the biota extended period of time and do not support a catastrophic seriously in normal circumstances and the biosphere would model. Extinction of the Cretaceous planktonic foraminifers bestrong enough to recoverduring intervening quiet of the Urn Sohryngkew section has been primarily attributed periods(Cox 1988). It may befor this reason thatthe to fall in sea-level and to predation by larval gastropods on freshwater biota and dinosaurs survived the initial volcanic juvenile individuals, leading todeath beforereproduction activity without undergoing any drastic change. In fact, the (Pandey 1990). In ostracodes, it has been shown that shells inter-trappean biota, except for dinosaurs, is more diverse in with strongornamentation are less likely to bebored by

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predatory gastropods (Reyment et al. 1987). But it is not -, VANDAMME,D.,BESSE, J., JAEGER,J. J. & JAVOY,M. 1990. Deccan clear from Pandey's (1990) paper whether such a selective volcanism at the Cretaceous/Tertiary boundary; data and inferences. In: predation is evident in the planktonic foraminifers of Urn SHARPTON,V.L. & WARD,P. E. (eds) Global Catastrophes in Earth History: an Interdisciplinary Conference on Impacts, Volcanism and Mass Sohryngkewsection andto whatextent predation would Mortality. Geological Society of America, Special Papers, 247, 401-409. eliminate a large number of species. Cox, K. G. 1988. Gradual volcanic catastrophes. Nature, 333,840-841. The volcanic hypothesis, therefore,does notseem to DOGRA,N. N., SINGH,R. Y. & KULSHRESTHA,S. K. 1988. Palynological account for the extinctions at the K-T boundary, because of evidence on the age of Jabalpur and Lametaformations inthe Type Area. 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Received 2 July 1993; revised typescript accepted 5 May 1994.

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