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 Cretaceous-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 foraminifera from 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 Lameta Formation 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/year (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 be addressed. 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 Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/152/2/289/4890368/gsjgs.152.2.0289.pdf by guest on 02 October 2021 290 G. V. R. PRASAD & C. K. KHAJURIA 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 Maastrichtian 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 in sea-level from a bathymetry 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 dinosaur 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 dinosaurs(Lydekker 1890). But recent investigations Europe, Buffetaut (1987) favoured a Maastrichtian age. In brought to light the presence of dinosaurremains in the recent years,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 been reported 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 Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/152/2/289/4890368/gsjgs.152.2.0289.pdf by guest on 02 October 2021 DECCAN BIOTA AND THE K-T BOUNDARY 291 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 Coelurosauria J Phareodus sp. J J Megalosauridae l J Apateodus cf. A. striatus J J Indosaurus J Enchodus sp. J J matleyi Arius sp. J Indosuchus J Eoserranus