Deccan Volcanism Linked to the Cretaceous-Tertiary Boundary ...

JOURNAL GEOLOGICAL SOCIETY OF INDIA 

Vol.78, November 2011, pp.399-428 

Deccan Volcanism Linked to the Cretaceous-Tertiary Boundary 

Mass Extinction: New Evidence from ONGC Wells in 

the Krishna-Godavari Basin 

G. KELLER 1 , P.K. BHOWMICK 2 , H. UPADHYAY 2 , A. DAVE 2 , A.N. REDDY 3 , 

B.C. JAIPRAKASH 3 and T. ADATTE 4 

1 Geosciences Department, Princeton University, Princeton, NJ 08544, USA, 

2 KDMIPE, ONGC, Dehradun, India 

3 ONGC, Regional Geoscience Laboratory, Chennai, India 

4 Geological and Paleontological Institute, Anthropole, CH-1015 Lausanne, Switzerland 

Email: gkeller@princeton.edu 

Abstract: A scientific challenge is to assess the role of Deccan volcanism in the Cretaceous-Tertiary boundary (KTB) 

mass extinction. Here we report on the stratigraphy and biologic effects of Deccan volcanism in eleven deep wells from 

the Krishna-Godavari (K-G) Basin, Andhra Pradesh, India. In these wells, two phases of Deccan volcanism record the 

world’s largest and longest lava mega-flows interbedded in marine sediments in the K-G Basin about 1500 km from the 

main Deccan volcanic province. The main phase-2 eruptions (~80% of total Deccan Traps) began in C29r and ended at 

or near the KTB, an interval that spans planktic foraminiferal zones CF1-CF2 and most of the nannofossil Micula prinsii 

zone, and is correlative with the rapid global warming and subsequent cooling near the end of the Maastrichtian. The 

mass extinction began in phase-2 preceding the first of four mega-flows. Planktic foraminifera suffered a 50% drop in 

species richness. Survivors suffered another 50% drop after the first mega-flow, leaving just 7 to 8 survivor species. No 

recovery occurred between the next three mega-flows and the mass extinction was complete with the last phase-2 megaflow 

at the KTB. The mass extinction was likely the consequence of rapid and massive volcanic CO 2 

and SO 2 

gas 

emissions, leading to high continental weathering rates, global warming, cooling, acid rains, ocean acidification and a 

carbon crisis in the marine environment. 

Deccan volcanism phase-3 began in the early Danian near the C29R/C29n boundary correlative with the planktic 

foraminiferal zone P1a/P1b boundary and accounts for ~14% of the total volume of Deccan eruptions, including four of 

Earth’s longest and largest mega-flows. No major faunal changes are observed in the intertrappeans of zone P1b, which 

suggests that environmental conditions remained tolerable, volcanic eruptions were less intense and/or separated by 

longer time intervals thus preventing runaway effects. Alternatively, early Danian assemblages evolved in adaptation to 

high-stress conditions in the aftermath of the mass extinction and therefore survived phase-3 volcanism. Full marine 

biotic recovery did not occur until after Deccan phase-3. These data suggest that the catastrophic effects of phase-2 

Deccan volcanism upon the Cretaceous planktic foraminifera were a function of both the rapid and massive volcanic 

eruptions and the highly specialized faunal assemblages prone to extinction in a changing environment. Data from the 

K-G Basin indicates that Deccan phase-2 alone could have caused the KTB mass extinction and that impacts may have 

had secondary effects. 

Keywords: Cretaceous-Tertiary, Mass extinction, Deccan volcanism, Longest lava flows, Krishna-Godavari Basin. 

INTRODUCTION 

The biologic and environmental effects of Deccan 

volcanism and its potential cause-and-effect relationship with 

the demise of the dinosaurs and the Cretaceous-Tertiary 

boundary (KTB) mass extinction are the major unsolved 

problems in KTB studies today. The Deccan volcanic 

province is one of the largest volcanic eruptions in Earth’s 

history and today covers an area of 512,000 km 2 (Fig. 1A), 

or about the size of France or Texas. The original size prior 

to erosion is estimated to have been 1.5 million km 2 and the 

volume of lava extruded about 1.2 million km 3 , which today 

can be seen as layers of lava flows with a total thickness of 

3500 m (Fig. 1B; Chenet et al. 2007). 

Deccan volcanism has been advocated as the potential 

0016-7622/2011-78-5-399/$ 1.00 © GEOL. SOC. INDIA

400 G. KELLER AND OTHERS 

Fig.1. (A) Map of India with current distribution of Deccan traps, including the Earth’s longest lava flows to the Krishna-Godavari 

Basin and out into the Bay of Bengal; black dots mark KTB locations studied. (B) Layered Deccan lava flows (traps) form 

Mahalabeshwar. (C) Map of the K-G Basin with locations of Rajahmundry quarries and ONGC wells studied for this report. 

(D) Lower and upper basalt flows exposed in the Gauripatnam quarry of Rajahmundry separated by intertrappean sediments of 

earliest Danian (zone P1a) age. 

cause for the KTB catastrophe for over thirty years (e.g., 

McLean, 1978, 1985; Courtillot et al. 1986, 1988; Duncan 

and Pyle, 1988; Venkatesan et al. 1993; Raju et al. 1995; 

Sheth et al. 2001; Pande et al. 2004). But this hypothesis 

was considered unlikely because a direct link to the mass 

extinction remained elusive in the absence of Deccan lava 

flows interbedded with marine sediments rich in microfossils 

to assess the nature of the mass extinction, and also because 

volcanism was generally believed to have occurred over at 

least one million years, leaving sufficient time for recovery 

between eruptions. 

Over the past several years a number of multidisciplinary 

studies have changed this perception and 

directly linked Deccan volcanism to the KTB mass 

extinction: (1) Improved dating of the 3500 m thick Deccan 

lava pile revealed that the major eruptions occurred in three 

phases with the initial eruption, phase-1, in the late 

Maastrichtian base of C30n (67.4 Ma), the main phase-2 in 

C29r below the KTB, and the last phase-3 in the early Danian 

base C29n (Fig. 2; Chenet et al. 2007, 2008, 2009; Jay and 

Widdowson, 2008). (2) Massive eruptions created the 

longest and largest lava flows on Earth (Self et al. 2008a, 

b). And (3) a direct link between the main phase of Deccan 

eruptions and the KTB mass extinction was documented in 

Rajahmundry quarries (Andhra Pradesh) and Jhilmili 

(Madhya Pradesh) based on planktic foraminifera, which 

suffered the most devastating mass extinction globally 

(Keller et al. 2008, 2009a, b, c). At these two localities, no 

Maastrichtian marine sediments are exposed but the earliest 

Danian species are present in the intertrappean sediments 

between phase-2 and phase-3 mega-flows. 

Still missing from these early results is critical 

JOUR.GEOL.SOC.INDIA, VOL.78, NOV. 2011

DECCAN VOLCANISM LINKED TO THE CRETACEOUS-TERTIARY BOUNDARY MASS EXTINCTION 401 

Fig.2. Relative thickness of Deccan lava flows in each of the three 

phases of volcanic eruptions calculated as percent of total 

Deccan trap thickness. Ages based on paleomagnetic time 

scale (modified from Chenet et al. 2007, 2008). 

information concerning the onset and age of the main Deccan 

phase, the nature and tempo of the mass extinction relative 

to eruption pulses, and the number of the longest lava flows, 

here termed ‘mega-flows’. No outcrops exist that can yield 

this information because deposition in India occurred mainly 

in terrestrial and some shallow inner neritic environments 

(e.g., Rajahmundry, Jhilmili), which lack diverse fossil 

assemblages, and the lava mega-flows are fused, preventing 

environmental studies (Fig. 1D). 

The only area that can yield the missing information is 

in the Krishna-Godavari Basin, which spans about 75 km 

from Rajahmundry towards the Bay of Bengal (Fig. 1C). 

During KTB time, there was progressive deepening seaward 

from the inner neritic environment of Rajahmundry to outer 

neritic depths (100-150 m) accompanied by increasingly 

diverse planktic foraminiferal assemblages (Jaiprakash et 

al. 1993; Raju et al. 1994). During the Cenozoic, the high 

sediment input by the Krishna and Godavari drainage 

systems and a complex system of horst and graben structures 

resulted in rapid subsidence and today the KTB sequences 

dip between 2500 m to 3500 m below the surface towards 

the Bay of Bengal. The only access to these critical KTB 

records are deep wells drilled by India’s Oil and Natural 

Gas Corporation Ltd. (ONGC) in the K-G Basin. The nature 

of information that can be gained from these ONGC wells 

is evident from various publications by ONGC scientists 

that show a series of lava flows and intertrappean sediments 

spanning from the upper Maastrichtian to the lower 

Paleocene (e.g., Govindan, 1981; Mehrotra and Sargeant, 

1987; Raju et al. 1994, 1995, 1996; Jaiprakash et al. 1993; 

Prasad and Pundeer, 2002; Misra, 2005; Raju, 2008). 

Despite this effort, locating the precise position of the KTB 

in these wells relative to the Deccan mega-flows remained 

elusive. 

With new insights gained from recent studies, reinvestigation 

of ONGC deep wells yielded critical 

information on the relative timing of the largest and longest 

lava mega-flows and the environmental conditions as 

inferred from planktic foraminiferal assemblages. Here we 

report the results from ten wells from the onshore K-G Basin 

and one offshore well (Fig. 1C). The results demonstrate: 

(a) up to four of Earth’s longest and largest lava mega-flows 

(traps) separated by intertrappean sediments in each phase- 

2 and phase-3; (b) the nature and tempo of the mass 

extinction, as indicated by sediments below the mega-flows 

(infratrappean), and between mega-flows (intertrappean); 

and c) the close link between Deccan volcanism and the 

KTB mass extinction. 

BACKGROUND 

Deccan Eruption Phases 

Detailed paleomagnetic and radiometric dating ( 40 K/ 40 Ar 

and 40 Ar/ 39 Ar) of the 3500 m thick Deccan lava pile in the 

western Ghats revealed that volcanic eruptions occurred in 

a series of rapid pulses grouped in three main phases (Chenet 

et al. 2007, 2008, 2009). A rough estimate of the relative 

volume can be estimated by the thickness of the major lava 

flows in each of the three eruption phases across the Deccan 

volcanic province (Fig. 2). Syed F.R. Khadri estimated the 

cumulative maximum total thickness as possibly reaching 

5000 m (personal communication, 2011). Based on the more 

conservative estimate of 3500 m, about 6% of this lava pile 

is attributed to the initial and smallest phase-1 (Latifwadi 

Formation), which is dated at ~67.4 Ma near the base of 

C30n. Less intense volcanic eruptions likely continued 

during the late Maastrichtian. 

The main phase-2 (Jawhar and Ambenali Formations) 

occurred in C29r below the KTB and accounts for about 

~80% of the total Deccan thickness. The shear volume of 

phase-2 suggests that this eruption phase could have been 

detrimental to life. Chenet et al. (2007, 2008) estimated that 

each of 30 to 100 major eruptive pulses in phase-2 emitted 

volumes ranging from 20,000 km 3 to 120,000 km 3 , attained 

a thicknesses up to 200 m, and was emplaced over hundreds 

of kilometers in a relatively short time interval in C29r below 



the KTB. The last phase-3 (Mahalabeshwar Formation) is 

estimated at about 14% of the total lava pile and began in 

the early Danian at or near the base of C29n about 270 ky 

after the KTB mass extinction (Fig. 2; time scale of Cande 

and Kent, 1995). 

The Longest Lava Flows 

Paleomagnetic and geochemical studies have correlated 

the lower and upper basalt flows of the Rajahmundry quarries 

(Andhra Pradesh, Figs. 1D) to the Ambenali and 

Mahalabeshwar Formations, or phase-2 and phase-3 of the 

Deccan lava pile, respectively (e.g., Knight et al. 2003, 2005; 

Baksi et al. 1994; Baksi, 2005; Jay and Widdowson, 2008; 

Jay et al. 2009). Age determinations based on 40 K/ 40 Ar and 

40 Ar/ 39 Ar place these lava mega-flows in C29r and near the 

base of C29n, respectively, although error margins are 1% 

or 0.6 Ma (e.g., Knight et al. 2003, 2005; Baksi, 2005). 

This marks the phase-2 and phase-3 eruptions as the largest 

and longest lava flows on Earth, spanning over 1500 km 

from the main Deccan province across India to the Krishna- 

Godavari Basin and out into the Bay of Bengal (Figs. 1A, 

C). Self et al. (2008a) interpreted these mega-flows as very 

large volume pahoehoe flow fields that for the last 400 km 

of their journey were confined to the pre-existing Godavari 

valley drainage system that channeled their flow to the 

eastern estuaries near Rajahmundry and into the Bay of 

Bengal. They estimated these mega-flows as the world’s 

largest at 5000 km 3 of eruptive volume. 

Deccan and the KTB Mass Extinction 

The above studies demonstrate that Deccan volcanic 

phase-2 and phase-3 bracket the KTB mass extinction, but 

cannot establish a direct link. Paleontological investigations 

first discovered this link in 4 to 9 m thick intertrappeans 

between phase-2 and phase-3 mega-flows in six 

Rajahmundry basalt quarries (Figs.1D; Keller et al. 2008; 

Malarkodi et al. 2010). In this estuarine environment early 

Danian (zone P1a) planktic foraminiferal assemblages 

directly overlie the top of phase-2 eruptions and indicate 

that the mass extinction occurred at or near the end of this 

volcanic phase (Keller et al. 2008). These results were 

confirmed in intertrappean sediments in central India 

(Jhilmili, Madhya Pradesh, Keller et al. 2009a, b, c). 

MATERIAL AND METHODS 

ONGC wells from the Krishna-Godavari Basin were 

chosen for their apparent continuity across the KTB 

transition, the number of basalt flows and intertrappean 

sediments, and the availability of recovered cores in addition 

to well cuttings. A total of eleven wells have been analyzed 

for this study, including one offshore well (G-4-6; Fig. 1C). 

Sample material from each well was collected in the ONGC 

core library in Rajahmundry and supplemented by samples 

from the core libraries at Dehradun and Chennai. Well 

samples were taken at 5 m or 1 m intervals from cuttings, 

and at 20 cm intervals in recovered core sections. About 

200 gr sediments were collected per sample for analysis 

and a total of 665 samples were analyzed. Samples were 

processed by standard micropaleontological techniques 

(Keller et al. 1995). 

For biostratigraphic analysis the washed residues of each 

sample was searched for foraminifera in several size 

fractions, including 38-63 µm, 63-105 µm, 105-150 µm, 

150-250 µm and >250 µm in order to analyze all species 

from the very small to the very large. Foraminifera were 

picked from each size fraction, identified at the species level 

and recorded. The species census data was filtered to exclude 

down-core contamination that is common in well cuttings. 

Theoretically, this means that any species first appearances 

may be the result of down-core contamination. To avoid 

such artificial range extension, we attributed any isolated 

species occurrences at the base of the range to down-core 

contamination. Last appearances of species were relied 

upon for stratigraphic age control, except for isolated 

species that could be the result of reworking. Based on this 

filtered dataset, combined with the stratigraphic control 

from core intervals, and the resistivity and gamma ray well 

log data, good age control was achieved for all wells 

analyzed. 

Preservation of foraminiferal tests in upper Maastrichtian 

sediments ranges from good to poor, with predominantly 

poor preservation in very deep wells (> 3000 m) and poor 

preservation due to dissolution effects in intertrappean 

sediments. In contrast, Danian assemblages are relatively 

well preserved. SEM’s of late Maastrichtian and early 

Danian planktic foraminifera illustrate faunal assemblages 

of the KTB transition in the Krishna-Godavari Basin. 

STRATIGRAPHY OF DECCAN BASALT 

MEGA-FLOWS 

The lithostratigraphy of the Krishna-Godavari Basin as 

determined from outcrops (Rajahmundry area) and 

subsurface wells is shown in Fig.3. In surface outcrops, the 

Rajahmundry sandstone overlies the upper Deccan megaflows, 

or phase-3, and the Tirupati sandstone underlies the 

lower Deccan mega-flows, or phase-2. We observed in both 

outcrops and recent drilling that the Tirupati sandstone ends 

with a marine bed consisting of abundant Turritella, few 



Fig.3. Generalized lithostratigraphy of the Krishna-Godavari Basin (modified after 

Venkatarengan et al. 1993). Note the outcrop lithostratigraphy is representative of 

Rajahmundry quarries. Well locations studied for this report are located in both sand 

(landward) and shale lithologies (basinward). 

other macrofossils and rare benthic foraminifera. Below the 

Turritella bed sediments consist of clay and silt, representing 

flood plain and paleosoils, which alternate with sandstones 

indicative of fluvial and channel environments. At the top 

of phase-3 mega-flows, an erosion surface marks a major 

hiatus, which is overlain by sandstone of middle Oligocene 

age and corresponding to the Nimmakuru sandstone (Fig.3). 

Phase-2 and phase-3 mega-flows are separated by 

intertrappean sediments consisting of dolomitic mudstone 

at the base followed by estuarine to shallow marine limestone 

and paleosoil in the upper part (Keller et al. 2008). 

Basinwards from Rajahmundry, the sandstones, shales 

and limestones thin out and are replaced by marly and clayey 

shales (Fig. 3). Wells for this study were taken from 

middle/outer neritic environments that cut through the distal 

end-members of the Tirupati sandstone, Razole Formation 

and Palakollu shale, as well as from deeper neritic 

environments dominated by shales (Fig. 3). In most of the 

wells, the Razole Formation consists of up to eight and 

occasionally nine Deccan mega-flows separated by 

intertrappeans. Three to four and occasionally five megaflows 

are located below the KTB and mark Deccan phase- 

2 and three to four mega-flows mark Deccan phase-3 in the 

lower Danian (Jaiprakash et al. 1993; Raju et al. 1994, 1995, 

1996; Misra, 2005; Raju, 2008; Jay and Widdowson, 2008; 

this study). 

In the Rajahmundry quarries, the pulsed volcanic 

eruptions that created the mega-flows of phase-2 in the 

Krishna-Godavari Basin can be differentiated (Keller et al. 

2008), but are not separated by intertrappeans as they are in 

the Krishna-Godavari Basin wells and logs (Fig. 4). 

JOUR.GEOL.SOC.INDIA, VOL.78, NOV. 2011 

Resistivity values for normal 

sandstones, siltstones and shales vary 

between 1-6 qm, unless they are 

hydrocarbon bearing. In contrast, 

resistivity values for the basalts vary 

anywhere from 50 qm to > 200 qm 

depending on the degree of sediments 

incorporated as a result of erosion at 

the base and top. In all wells, e – logs 

show high to very high resistivity 

peaks against the basalt flows. Most 

basalts are seen as a distinct resistivity 

peak on the logs, whereas some 

basalts are less distinct due to mixed 

basalt and sediments. Gamma logs 

show significantly lower values in 

basalt flows relative to the intertrappean 

clastic sediments (Fig. 4). 

The cores and drill cuttings from 

these mega-flows are dark grey to greenish grey in colour, 

very hard and compact. 

Deccan mega-flows in the Krishna-Godavari Basin are 

generally 5 m to 15 m thick, except for two wells where the 

lava flows in phase-3 are 60 m thick (Fig. 5, CTP-A and 

RZL-A). The variation in the number of basalt flows and 

variable thicknesses can be explained by topography and 

erosion. The variable thickness of intertrappeans is a function 

of topography, subsidence and influx of sediments eroded 

from shallower areas, as indicated by an abundance of sand 

in some wells (Figs. 3, 4, e.g., MTP-A, CTP-A, RZL-1, 

PNM-A). The overall pattern of the mega-flows in each 

volcanic phase is consistent with sheet flows of very large 

volume pahoehoe flow fields, as suggested by Self et al. 

(2008a). 

BIOSTRATIGRAPHY 

Identifying the KT Boundary 

The high-resolution biostratigraphic zonal scheme 

developed by Keller et al. (1995, 2002) for the Danian and 

by Li and Keller (1998a, b) for the Maastrichtian (Fig. 5) is 

applied in the K-G Basin wells. Ages for biozones are 

calculated for the time scales of Cande and Kent (1995; 

KTB at 65 Ma) and Gradstein et al. (2004; KTB at 65.5 

Ma, Fig. 6). The KTB can be globally identified based on a 

number of criteria: the mass extinction of planktic 

foraminifera, the evolution of the first Danian species within 

a few centimeters above the extinction horizon, a clay layer 

with a millimeter thin oxidized red layer at the base, an 

iridium anomaly in the red layer, and a 2 to 3 permil δ 13 C


Fig.4. Correlation of Krishna-Godavari Basin wells based on biostratigraphy, Deccan mega-flows and well log data (gamma and resistivity). Note that Deccan phase-2 and phase-3 

each contain three to four lava flows that represent Earth’s largest longest mega-flows separated by intertrappean sediments. These phase-2 and phase-3 mega-flows correlate 

with the “fused” lower and upper traps in Rajahmundry quarries. 



Fig.5. Biostratigraphy and planktic foraminiferal zonal scheme by Keller et al. (1995, 2002) and Li and Keller (1998a,b) for the late 

Maastrichtian and early Danian in the El Kef stratotype section and point (GSSP) with illustrations of index species, the Ir 

anomaly (Rocchia et al. 1996) and δ 13 C shift (Keller and Lindinger, l989) are correlated with the paleomagnetic time scale and 

Deccan volcanic events. The nannofossil zonal scheme (*) by Tantawy (2003), and the planktic foraminiferal zonation (**) by 

Bergren et al. (1995) are shown for comparison. 

shift across the clay layer (Fig. 5; Keller et al. l995; Cowie 

et al. 1989; Remane et al. 1999). Among these, only 

extinction and evolution events are unique KTB-defining 

criteria. All others (Ir anomaly, clay and red layers, δ 13 C 

shift) are KTB-supporting criteria that cannot stand alone 

as KTB markers because they are not unique events. In India, 

all of these KTB markers are present in the Meghalaya 

section (Gertsch et al. 2011), but to date the Ir anomaly and 

δ 13 C shift have not been documented in the Krishna- 

Godavari Basin due to lack of suitable marine sequences 

with high-resolution sample spacing. 

Rajahmundry Quarries 

A close link between Deccan volcanism and the KTB 

mass extinction was first established in Rajahmundry 

quarries based on zone P1a planktic foraminiferal 

assemblages in intertrappean sediments between phase-2 

and phase-3 lava mega-flows (Fig. 1D; Keller et al. 2008). 

These intertrappeans contain the first Danian species, which 

evolved in the aftermath of the mass extinction (e.g., 

Parvularugoglobigerina extensa, P. eugubina, Globoconusa 

daubjergensis, Woodringina hornerstownensis; Fig. 5). The 

index species P. eugubina marks this assemblage as zone 

P1a, which together with zone P0 (boundary clay) spans 

C29r above the KTB. The boundary clay was not observed. 

Based on this information, the KTB was placed at the base 

of the intertrappean above phase-2 (Figs. 1D). No sediments 

are present above the phase-3 mega-flows and sediments 

below phase-2 consist of beach sand with rare benthic 

foraminifera. 

Krishna-Godavari Basin 

Maastrichtian below phase-2 mega-flows: Zones CF2-CF3 

In the Krishna-Godavari Basin, about 75 km seaward 

from Rajahmundry, sediment deposition occurred in a 

shallow middle neritic environment (


Fig.6. Late Maastrichtian and early Danian planktic foraminiferal zonal schemes and ages of biozones based on two time scales with the 

KT boundary at 65.0 and 65.5 Ma. Also shown for comparison are the zonal schemes of Caron (1985), Berggren et al. (1995) and 

the nannofossil zonation of Tantawy (2003). CF=Cretaceous Foraminifera. 

environments (Keller and Abramovich, 2009). In general, 

the most diverse assemblages were observed in the 

cored intervals, such as shown for PLK-A and NSP-A wells 

(Figs. 7 and 8). Since the cored intervals contain the most 

reliable data, the lower diversity in core cuttings is likely an 

artifact of preservation and culling of species suspected to 

be down-core contaminants. In wells with predominantly 

sand and silt deposition, such as MTP-A and PNM-A, 

(Figs. 12-13), foraminifera are rare due to increased 

dissolution and dilution by high sediment influx. 

Biostratigraphic control in these wells is more difficult to 

establish. 

In ten out of eleven wells analyzed for this study, late 

Maastrichtian faunal assemblages below phase-2 megaflows 

are typical of zones CF2-CF3. In the absence of 

Gansserina gansseri these two zones cannot be 

differentiated. Zone CF2 spans 120 ky (65.66-65.78 Ma) 

and zone CF3 spans 1.21 Ma (65.78 to 66.99 Ma, time scale 

of Gradstein et al. 2004; Fig. 6). Zone CF3 is nearly 

equivalent to the Micula murus nannofossil zone. Saxena 

and Misra (1994, 1995) and von Salis and Saxena (1998) 

identified the M. murus zone assemblage below phase-2 

mega-flows in the RZL-A, NSP-B and PLK-A wells (Figs. 

7, 9, 12). Only in the offshore well G-4-F to the northeast of 

the K-G Basin (Fig. 1B) is the upper Maastrichtian missing 

(zones CF1-CF5, Fig. 14). In this well, a diverse assemblage 

of 43 species identifies zone CF6 (69.08-69.61 Ma) 

including the index species (first appearance of 

Contusotruncna contusa and last appearance of 

Globotruncana linneiana) underlying one mega-flow and 

the KTB. Zone CF6 precedes Deccan phase-1 dated about 

67.4 Ma. Late Maastrichtian planktic foraminiferal 

assemblages from the K-G Basin are illustrated in Plates 

1-3. 

Volcanic phase-2 intertrappeans: Zone CF1 

In the K-G wells, phase-2 intertrappeans are generally 

between 5 m and 15 m thick. But in two wells they reach a 

maximum of 60 m (CTP-A and RZL-A; Figs. 1C, 11), 

probably due to topographic lows and high sedimentary 

influx. Alternatively, this area may be cut by faults and 

thrusts. Paleomagnetic and radiometric analyses placed the 

Rajahmundry lower traps (equivalent to phase-2 megaflows) 

in C29r below the KTB (e.g., Knight et al. 2003, 

2005; Baksi, 2005; Chenet et al. 2007, 2008, 2009), which 

is equivalent to zones CF2 (65.66-65.78 Ma) and CF1 



Fig.7. ONGC well PLK-A with biostratigraphy, species occurrences, phase-2 and phase-3 mega-flows plotted against lithostratigraphy 

and e-logs (gamma and resistivity). Core segment shown is from the base of the section, and another core segment from the last 

mega-flow in phase-3. 

Fig.8. ONGC well NSP-A with biostratigraphy, species occurrences, and phase-2 mega-flows plotted against lithostratigraphy and e- 

logs (gamma and resistivity). A 4 m cored interval below the first mega-flow of phase-2 records a 50% diversity crash, which 

appears to be related to the onset of Deccan phase-2 volcanism. No samples are available from the intertrappean of this well, but 

in other wells there is another 50% crash after the first mega-flow (see Fig. 7). Phase-3 mega-flows are not present in NSP-A. A 

cosmic spherule was found at 3365 m. 



Fig.9. ONGC well NSP-B with biostratigraphy, species occurrences, phase-2 and phase-3 lava flows plotted against lithostratigraphy 

and e-logs (gamma and resistivity). Note the low species diversity in infra- and intertrappeans of phase-2 volcanism is partly due 

to poor preservation and dissolution effects. 

(65.50-65.66 Ma) and most of the nannofossil Micula prinsii 

zone (Figs. 5 and 6). Based on this correlation the phase-2 

mega-flows and intertrappeans of the Krishna-Godavari 

Basin were most likely deposited in zone CF1 with the onset 

of phase-2 volcanism in zone CF2 (Fig. 6). In the K-G Basin 

the fragile zone CF1 index species, Plummerita 

hantkeninoides, was not observed, either because of poorly 

preserved assemblages, or because of exclusion due to stress 

conditions. Very few species are present in intertrappean 

sediments due to extinctions, dissolution and poor 

preservation due to acid rains associated with Deccan 

volcanism. The stress conditions during deposition of these 

intertrappeans are discussed below. 

KT boundary and early Danian: Zone P1a 

In Krishna-Godavari Basin wells, the KT boundary is 

identified in the intertrappean sediments between phase-2 

and phase-3 mega-flows by the lower Danian zone P1a 

planktic foraminiferal assemblages. Most wells contain 

species that evolved in the lower part of zone P1a (subzone 

P1a(1), including Parvularugogloigerina extensa, 

P. eugubina, Eoglobigerina edita, Globoconusa 

daubjergensis, G. taurica, and Woodringina hornerstownensis 

(Figs. 7, 11 and 12). However, most wells also 

contain species that evolved in the upper part of zone P1a 

(subzone P1a(2), such as Subbotina triloculinoides, 

Parasubbotina pseudobulloides, Globigerina pentagona, 

Chiloguembelina midwayensis, and Globanomalina 

archeocompressa (Plates 4, 5). Because of poor sample 

control, these subzones cannot be identified at this time and 

must await high resolution sampling in future drilling. 

Nevertheless, the current data show that zone P1a is 

preserved throughout the Krishna-Godavari Basin during a 

period of local volcanic inactivity prior to eruptions of the 



Fig.10. ONGC well ELM-A with biostratigraphy, species occurrences, phase-2 and phase-3 mega-flows plotted against lithostratigraphy 

and e-logs (gamma and resistivity). Note there are five thin phase-3 mega-flows, but only one in phase-2 below the KTB, which 

is likely due to erosion. 

last Deccan phase-3, as also observed in Rajahmundry 

quarries and Jhilmili, Madhya Pradesh (Keller et al. 2008, 

2009a, b). 

Volcanic phase-3 intertrappeans: Zone P1b 

Volcanic phase-3 began near the C29r/C29N boundary 

(Knight et al. 2003, 2005, Baksi, 2005; Chenet et al. 2007, 

2008), correlative with the zone P1a/P1b boundary. In the 

Krishna-Godavari Basin, the three to four intertrappeans of 

phase-3 all contain planktic foraminiferal assemblages 

typical of zone P1b, which marks the interval between the 

extinction of P. eugubina and P. longiapertura and the first 

appearance of Subbotina varianta (Figs. 7-13, Plates 4, 5). 

Faunal assemblages show increased abundances of G. 

daubjergensis, Guembelitria and biserial species and better 

preservation than Maastrichtian assemblages from 

intertrappeans of phase-2. However, there are variations 

depending on the local depositional environment, such as 

in well MTP-A where few species are present due to poor 

preservation in sandy shale (Fig. 12). 

Danian above Phase-3 intertrappeans: Zone P1c or P2 

Sediments above volcanic phase-3 contain the first 

significantly more diverse Danian assemblages with the first 

larger (> 150 mm) morphotypes after the KTB mass 

extinction. In most K-G Basin wells, the assemblage is 

indicative of zone P1c with common subbotinids and the 

first appearances of Praemurica inconstans and Subbotina 



Fig.11. ONGC well RZL-A with biostratigraphy, species occurrences, phase-2 and phase-3 mega-flows plotted against lithostratigraphy 

and e-logs (gamma and resistivity). Note the relatively thin mega-flows in phase-2, but absence of foraminifera in the intertrappean 

due to dissolution. Note also the unusually thick (55 m) mega-flow in phase-3, which likely is due to topographic variation. 

varianta (Figs. 7, 9, 12). But in some wells there is a 

significant hiatus with zone P2 overlying P1b, as indicated 

by the presence of assemblages with P. uncinata, M. 

angulata, M. praeangulata, A. strabocella, and S. 

triangularis (e.g., CTP-A, ELM-A, RZL-A, PNM-A, G-4- 

F (Figs. 1C, 10, 11, 13, 14). This hiatus may be related to 

local topographic variations, as suggested by the locations 

of the wells in shallower water (PNM-A), other hiatuses 

(G-4-F), and anomalously thick basalt mega-flows (RZL-A 

and CTP-A). 

BIOTIC EFFECTS OF DECCAN VOLCANISM 

Biotic effects of the world’s largest and longest lava flows 

Planktic foraminifera in intertrappeans record the 

environmental conditions after the eruption of each megaflow. 

In the K-G Basin, this documentation is hampered by 

the limitation of samples and poor preservation. The former 

is largely a function of the difficulties to recover 

intertrappean sediments sandwiched between basalt flows 

in deep wells, and the latter is mainly a function of ocean 

acidification (acid rain) due to the volcanic eruptions. 

Because of the sporadic faunal records in individual wells, 

and because nine wells analyzed are within close proximity 

to each other in the Krishna-Godavari Basin (Fig. 1C), a 

composite was assembled based on nine wells with all data 

integrated into the litholog of PLK-A (Fig. 15). All wells 

can be easily correlated based on biostratigraphy, gamma 

and resistivity logs, and the mega-flows below and above 

the KTB (Fig. 4). This dataset offers a glimpse into the 

environmental conditions and stresses associated with the 

world’s largest and longest lava flows. 



Fig.12. ONGC well MTP-A with biostratigraphy, species occurrences, phase-2 and phase-3 mega-flows plotted against lithostratigraphy 

and e-logs (gamma and resistivity). Core segment shown is from the intertrappean just below the mega-lava flow in phase-3. In 

this relatively shallow sandy environment, dissolution reduced overall species diversity and no species were recovered from 

phase-2 intertrappeans where dissolution is strongest. 

Onset of high-stress below phase-2 mega-flows 

During the late Maastrichtian, the Krishna-Godavari 

Basin wells show normal middle neritic diversity (28 

species) during zone CF2-CF3, except for a decrease in the 

middle of this zone. Whether or not this diversity low is due 

to Deccan volcanism or poor preservation is uncertain, 

although it is likely due to culling of suspected down-core 

contaminants and poor preservation. Near the end of this 

interval, which is likely zone CF2, a 4 m long core in well 

NSP-A details the stress conditions immediately preceding 

phase-2 mega-flows (Fig.8). At the base of this core, diversity 

is normal at 28 species (typical for middle neritic depths, 

Keller and Abramovich, 2009), rapidly decreases to 18 

species by the middle of the core and drops to a low of 14 

species in the uppermost 2 m below the first mega-flow. 

This 50% faunal crash is likely due to environmental stresses 

attributable to increasing volcanism leading to the acme that 

corresponds to the mega-flows of phase-2 in the Krishna- 

Godavari Basin. A cosmic spherule was detected at 3365 m 

(Fig. 8). Such millimeter-sized metallic spherules are not 

uncommon in sediments of any age (Keller et al. 1983). They 

originate from extraterrestrial materials that melted during 

high-velocity entry into the atmosphere. In contrast, glassy 

impact spherules (e.g., Chicxulub impact) result from hypervelocity 

impacts of large meteorites with earth’s surface. 

Maximum high-stress in intertrappeans of phase-2 

Intertrappean sediments of phase-2 (C29r, zones CF1) 

in the Krishna-Godavari Basin wells record severe 

environmental stresses in the aftermath of each of the four 

mega-flows, as earlier observed by Jaiprakash et al. (1993). 

Just 8 species were found after the first mega-flow, 13 and 



Fig.13. ONGC well PNM-A with biostratigraphy, species occurrences, and phase-3 mega-flows plotted against lithostratigraphy and e- 

logs (gamma and resistivity). Note that in this relatively shallow, sandy locality, the lower lava flows could not be identified 

because they are very small and weathered, or absent. Foraminifera are generally absent in the sandy layers. 



Fig.14. ONGC offshore well G-4-F with biostratigraphy, species occurrences and phase 2 and phase-3 mega-flows plotted against 

lithostratigraphy and e-logs (gamma and resistivity). Note there is a single phase-2 megaflow overlying lower Maastrichtian zone 

CF6 (69.08-69.61 Ma) faunal assemblages indicating that the upper Maastrichtian below the mega-flow is missing. Poor preservation 

and low diversity zone P1a-P1b assemblages are identified between phase-2 and phase-3. Another major hiatus is above the 

single phase-3 mega-flow. 

12 species after the second and third mega-flows (Fig. 15). 

However, these data are not culled for down-core 

contamination and reworking. A culled record, eliminating 

all isolated single occurrences (open circles; Fig. 15) leaves 

just 7 to 8 species (black circles) in the first and second 

intertrappeans, and six species in the third intertrappean. 

This indicates a 50% reduction from the assemblages in the 

infratrappean below, which already suffered a 50% faunal 

crash just prior to the onset of mega-flows in Deccan 

phase-2 (Figs. 8, 15). 

We may argue that this is a crude estimate and that the 

actual number of survivors may be higher or lower. However, 

since most of the species in this survivor group are among 

the environmentally most adaptable (Guembelitria cretacea, 

Heterohelix globulosa, Rugoglobigerina rugosa, Trinitella 

scotti, Globotruncana arca, G. aegyptiaca, G. dupeublei, 

G. conica), and two are KTB survivors (G. cretacea and H. 

globulosa), this estimate is probably not far off the mark. A 

more accurate assessment must await new coring of the 

intertrappeans. 

Evidence of the detrimental effects of phase-2 volcanism 

has also been observed in the middle to inner neritic marine 

environment of the Um Sohryngkew River in Meghalaya, 

NE India (Gertsch et al. 2011). At this locality, about 

800 km from the main Deccan volcanic province, the last 4 

m of sediments below the KT boundary were deposited in 

nannofossil Micula prinsii zone (Garg et al. 2006), which is 

equivalent to C29R and zones CF1-CF2 below the KTB 

(Fig. 6). In this interval, the disaster opportunist 

Guembelitria cretacea dominates (~95%), with only rare 

and sporadic occurrences of 24 other Cretaceous species. 

But in the last meter below the KTB, all but seven species 



disappeared. This pattern is very similar to that observed in 

the Krishna-Godavari Basin and suggests the same 

detrimental environmental effects of phase-2 volcanism at 

a large distance from the volcanic province. 

Based on the current Krishna-Godavari Basin dataset 

and the similar record observed in the Meghalaya section, 

we conclude that in India and its surrounding area, the 

Cretaceous planktic foraminifera were already near 

extinction before the KT boundary as a result of the pulsed 

volcanic eruptions of phase-2 that created the world’s largest 

and longest lava flows (Fig. 15). This data also indicates 

that high-stress environmental conditions continued 

unabated between the pulsed mega-eruptions and prevented 

marine recovery. Such prolonged high-stress conditions 

likely resulted from the rapid succession of Deccan eruptions 

in phase-2 and the corollary effects of gas emissions, climate 

change and increased weathering rates (Gertsch et al. 2011). 

KT boundary Event 

In all eleven Krishna-Godavari Basin wells analyzed the 

intertrappean above the phase-2 mega-flows contain the 

earliest Danian zone P1a assemblage and occasionally rare 

reworked Cretaceous species (Figs. 7-15) consistent with 

previous observations in Rajahmundry quarries (Keller et 

al. 2008; Malarkodi et al. 2010). This demonstrates that the 

mass extinction of Cretaceous species occurred prior to 

deposition of the intertrappean and was coeval with Deccan 

volcanic phase-2, suggesting a cause-and-effect relationship. 

High-resolution core sampling will be necessary to evaluate 

the presence of the boundary clay (zone P0) and lower part 

of zone P1a, measure d 13 C values and evaluate the presence 

of Ir and other PGEs. 

Continued high-stress in early Danian zone P1a intertrappean 

fauna 

Intertrappeans between Deccan phase-2 and phase-3 

mega-flows were deposited in C29R above the KTB, which 

is equivalent to planktic foraminiferal zone P1a, or about 

380 ky of the basal Danian (Fig. 6), as also indicated by 

40 Ar/ 39 Ar dating of phase-3 mega-flows (Knight et al. 2003, 

2005; Baksi, 2005). Evolution of Danian species in this 

intertrappean follows the same pattern as observed globally, 

Fig.15. Composite species ranges of nine wells in the Krishna-Godavari Basin plotted against biostratigraphy and phase-2 and phase-3 

lava flows of the PLK-A well. Cored intervals at the base of the section, below the first phase-2 mega-flow and below the last 

mega-flow of phase-3 record the most reliable species richness data. A maximum of 28 species in the upper Maastrichtian is 

typical for middle neritic environments (~100 m depth). Note the mass extinction began with the onset of phase-2 volcanism 

(50% drop in species richness), with another 50% drop after the first lava flow, and was complete by the last mega-flow at or near 

the KTB. Phase-2 intertrappeans: open circles = contamination and reworking, black circles = in situ species. 



Fig.16. Depth ranking of species in high diversity optimum planktic foraminiferal assemblages from outer neritic to open oceanic 

environments of the late Maastrichtian. Most large specialized (k-strategy) species evolved and thrived in thermocline and 

subthermocline deep depths. Smaller (r-strategy) species, tolerant of fluctuations in oxygen, salinity and temperature, thrived in 

surface, and thermocline depths. (modified from Keller and Abramovich, 2009). 1. Pseudoguembelina palpebra, 2. Heterohelix 

planta, 3. Pseudoguembelina hariaensis, 4. Heterohelix navarroensis, 5. Pseudoguembelina costulata, 6. Pseudoguembelina 

kempensis, 7. Pseudoguembelina excolata, 8. Rugoglobigerina rotundata, 9. Rugoglobigerina rugosa, 10. Pseudotextularia 

elegans, 11. Racemiguembelina fructicosa, 12. Pseudotextularia deformis, 13. Heterohelix globulosa, 14. Plummertita 

hantkeninoides 15. Globotruncana aegyptiaca, 16. Rugoglobigerina scotti, 17. Planoglobulina acervulinoides, 18. Hedbergella 

monmouthensis, 19. Globigerinelloides aspera, 20. Heterohelix labellosa, 21. Globotruncana arca, 22. Contusotruncana 

contusa, 23. Globotruncanita stuarti, 24. Globotruncanita stuartiformis, 25. Heterohelix rajagopalani*, 26. Gublerina acuta, 

27. Globotruncanella citae, 28. Laeviheterohelix glabrans, 29. Abathomphalus mayaroensis, 30. Gublerina cuvillieri, 

31. Planoglobulina multicamerata.* rare or not present in neritic environments. 

although first appearances of some species may differ due 

to poor preservation or large sample spacing (Figs. 7-14). 

All evolving early Danian species are very small (< 100 

mm and frequently < 63 mm), with simple chamber 

arrangements and unornamented morphologies that reflect 

adaption for survival in highly stressed environments (e.g., 

Keller and Pardo, 2004; Pardo and Keller, 2008). The fact 

that these assemblages mirror the global evolutionary pattern 

demonstrates that environmental conditions after the main 

phase-2 of Deccan volcanism remained stressed in India 

and globally. 

Continued high-stress in early Danian (zone P1b) Deccan 

Phase-3 

Faunal assemblages in phase-3 intertrappeans are similar 

to zone P1a, except for the disappearance of P. eugubina, 

the decreased abundance of early zone P1a species (e.g., 

Parvularugoglobigerina extensa, Eoglobigerina edita, 

Woodringina claytonensis, W. hornerstownensis, E. 

eobulloides), and increased abundance of other species 

(Figs. 8-14). Species sizes remained small, with 

morphologies generally < 150 mm, as also observed globally 

(Keller, 1988; 1989; Luciani, 2002; Coccioni and Luciani, 



Fig.17. Depth ranking of species in high-stress, low diversity planktic foraminiferal assemblages from middle to inner neritic environments 

of the late Maastrichtian. High biotic stress selectively eliminates large specialized (k-strategy) species from subsurface and 

thermocline depths, leaving impoverished assemblages. Smaller (r-strategy) species thrive, particularly the low oxygen tolerant 

heterohelicids. These biotic effects are also observed in high-stress conditions related to major volcanism. (Modified from 

Keller and Abramovich, 2009). 1. Heterohelix planta, 2. Pseudoguembelina hariaensis, 3. Guembelitria cretacea, 4. Heterohelix 

navarroensis, 5. Pseudoguembelina costulata, 6. Pseudotextularia elegans, 7. Rugoglobigerina rugosa, 8. Heterohelix globulosa, 

9. Globigerinelloides aspera, 10. Hedbergella monmouthensis, 11. Contusotruncana contusa, 12. Globotruncana arca, 

13. Globotruncana aegyptiaca, 14. Abathomphalus mayaroensis. 

2006; Keller et al. 2007a, b, 2009e). No major differences 

are observed between faunal assemblages of the three 

intertrappeans, which suggests that environmental conditions 

remained tolerable during volcanic phase-3. Alternatively, 

since these early Danian species evolved during high-stress 

conditions, they were primed for survival, unlike most 

species in the late Maastrichtian, which were highly 

specialized and adapted for narrow ecological niches 

(Abramovich et al. 2003; Keller and Abramovich, 2009). 

Recovery after phase-3 Deccan volcanism 

Planktic foraminiferal assemblages from sediments 

above the last phase-3 mega-flows reveal generally larger 

species sizes and increased diversity. On a global basis, the 

first Danian species with morphology sizes > 150 mm are 

generally observed near the end of zone P1b and full marine 

recovery did not occur until zone P1c (Keller, 1988, 1989; 

Keller et al. 2009e). It is tempting to speculate that the long 

delay in the global ecosystem recovery was due to Deccan 

volcanism. Studies are now underway to investigate this 

possibility. 

DISCUSSION 

Planktic Foraminifera – Proxies for Environmental Change 

We can assess the biologic effects of Deccan volcanism 

based on planktic foraminiferal assemblages, which are 

highly sensitive to environmental changes. At the KTB 

planktic foraminifera suffered the most devastating mass 

extinction with just a few environmentally more tolerant 



species surviving for a short time into the early Danian and 

the disaster opportunist Guembelitria cretacea the sole longterm 

survivor. Consequently, this microfossil group has 

become the strongest paleontological proxy for evaluating 

the biological effects of catastrophes, whether meteorite 

impacts, volcanism or climate change (e.g., Pardo and Keller, 

2008; Coccioni and Luciani, 2006; Keller and Abramovich, 

2009; Abramovich et al. 2003, 2010). 

Planktic foraminifera can be grouped into surface, 

intermediate (subsurface) and deep dwellers based on stable 

isotopic ranking (Keller, 2001; Abramovich et al. 2003; 

Keller and Abramovich, 2009). Optimum assemblages are 

characterized by low diversity surface dwellers, high 

diversity intermediate dwellers and very low diversity deep 

dwellers (below thermocline) (Fig. 16). The intermediate 

assemblages consist of many large, ornamented and 

highly specialized taxa (K-strategists), adapted to specific 

ecological niches and are therefore most strongly 

affected by environmental changes, such as variations in 

temperature, salinity, oxygen, nutrients and acidity of 

the water column. Any variations in these factors can 

result in high-stress conditions whether in open oceans, 

restricted basins, marginal marine settings or volcanic 

activity (Keller and Abramovich, 2009; Kidder and Worsley, 

2010). 

During high-stress conditions diversity drops most 

strongly among intermediate dwellers (K-strategists) leaving 

a survivor assemblage of dwarfed species (Lilliput effect) 

and less specialized (r-strategist) taxa (e.g., heterohelicids, 

guembelitrids, globigerinellids, and few rugoglobigerinids, 

pseudoguembelinids, globotruncanids, such as R. rugosa, 

P. costulata, G. arca, Fig. 17; Keller and Abramovich, 2009). 

Increasing biotic stress results in the complete disappearance 

K-strategists, the dwarfing of species more tolerant of 

environmental changes (r-strategists) and dominance by low 

oxygen tolerant small heterohelicids. At the extreme end of 

the biotic response are volcanically influenced environments 

which cause the same detrimental biotic effects as observed 

in the aftermath of the KTB mass extinction, including the 

disappearance of most species and blooms of the disaster 

opportunist Guembelitria (Fig. 18, Abramovich and Keller, 

2002; Abramovich et al. 2002; Keller, 2003; Keller et al. 

2007a). Volcanically induced high-stress conditions have 

been documented from Ninetyeast Ridge, Andean volcanism 

and the Deccan volcanic province (Keller, 2003; Keller et 

al. 2007a; Gertsch et al. 2011; this study). 

We can interpret the biologic response of planktic 

foraminifera to Deccan volcanism based on global 

observations of depth-ranked species and stress conditions 

in various habitats (Figs. 16-18). In the K-G Basin the change 

from optimum to high-stress assemblage occurred in the 4 

m below the Deccan phase-2 mega-flows (Fig. 8). The 50% 

gradual decrease in species richness indicates increasing 

stress, probably related to increasing volcanic activity 

leading up to Earth’s largest and longest mega-flows. 

During phase-2 mega-flows super-stress conditions 

approached the catastrophic with another 50% drop in 

species richness leaving just a few generally dwarfed 

survivors in intertrappeans and the mass extinction was 

complete at the last mega-flow of phase-2 (Fig. 15). In 

general, Guembelitria and Heterohelix species dominate 

super-stress to catastrophic conditions (Fig. 18). Their rarity 

and absence in the Krishna-Godavari Basin wells is an 

artifact of preservation. Above the KTB the low diversity 

early Danian assemblages of small, unornamented species 

with simple chamber arrangements persisted until after 

Deccan volcanism ended with phase-3. This long-delayed 

recovery in the marine ecosystem has long been an 

enigma. The current K-G Basin data suggest that the 

delayed recovery may have been due to continued Deccan 

volcanism. 

Climate Change and Deccan Volcanism 

Major global climate changes occurred during the late 

Maastrichtian C29R (zones CF1-CF2), including maximum 

Cretaceous cooling at the end of zone CF3, rapid global 

warming beginning in zone CF2 reaching a maximum in 

zone CF1, followed by rapid cooling in the upper part of 

CF1 and across the KTB (e.g., Li and Keller, 1998c; Kucera 

and Malmgren, 1998; Olsson et al. 2001; Abramovich and 

Keller, 2003; Wilf et al. 2003; Nordt et al. 2003; Keller and 

Abramovich, 2009; Kidder and Worsley, 2010). This global 

climate change documented in South Atlantic DSDP Site 

525 is representative for India, which was at the equivalent 

southern latitude (Fig. 19). During the global warming in 

CF2 to CF1, deeper water temperatures recorded in benthic 

foraminifera increased by about 4°C, whereas surface water 

temperatures fluctuated between 15 and 17°C. At the same 

time planktic foraminifera suffered under high-stress 

conditions leading to species dwarfing (60% of fauna), 

decreased diversity and abundance of specialized large 

species (e.g., intermediate dwellers). Global temperatures 

rapidly cooled about 50 ky or 100 ky prior to the KTB (time 

scale of Gradstein et al. 2004). Cooling was accompanied 

by a rapid decline in surface, intermediate and deep dwellers 

and ended in the KTB mass extinction (Keller and 

Abramovich, 2009; Keller et al. 2009e). This end- 

Maastrichtian global cooling and mass extinction appears 

coeval and likely related to the main Deccan phase-2 in the 

Krishna-Godavari Basin. 



Fig.18. The effects of increasing environmental stress upon planktic foraminiferal assemblages from optimum to catastrophe conditions 

shows the successive elimination of large, specialized k-strategy species, the survival of small r-strategy species, the overall 

dwarfing of these species and their great abundance. All of these factors characterize the Lilliput effect and are characteristic also 

of high-stress conditions associated with major volcanism (modified from Keller and Abramovich, 2009). 

Environmental Effects of Deccan Volcanism 

Environmental consequences of Deccan phase-2 

eruptions were likely devastating. Based on rare gas bubbles 

preserved in Deccan volcanic rocks, Self et al. (2008b) 

estimate annual gas rates released at many times the rate of 

anthropogenic emissions of SO 2 

and more than an order of 

magnitude greater than the current global background 

volcanic emission rate. Chenet et al. (2007, 2008) estimated 

gas emissions based on the volume of the largest 30 Deccan 

eruption pulses, with each pulse injecting 30-150 GT of SO 2 

gas over a very short time (decades). Thus each of the 30 

Deccan eruption pulses could have injected quantities of 

SO 2 

equivalent to that of the Chicxulub impact (e.g. 50-500 

GT). Indeed, the main phase-2 Deccan eruptions are 

estimated to have released 30 to 100 times the amount of 

SO 2 

released by the Chicxulub impact. Given these 

estimates, the environmental effects of Deccan volcanism 

were likely orders of magnitude worse than those of the 

Chicxulub impact. 

CO 2 

and SO 2 

gas emissions 

The global greenhouse warming of about 3-4°C 

beginning in zone CF2 and ending in zone CF1 resulted in 

major biologic stress for the Maastrichtian fauna leading 

to decreased species population abundances, decreased 

diversity, and species dwarfing (Fig. 19). Researchers 

have attributed this warm event to Deccan volcanism. 

However, climate models predict at most a 2°C warming, 

suggesting that the CO 2 

emissions from Deccan volcanism 

alone would have been insufficient to cause this warming 

(DeConto et al. 2000; Donnadieu et al. 2006). In the absence 

of any other likely CO 2 

source for the rapid greenhouse 

warming Deccan volcanism remains the only realistic 

event. 

Global cooling followed the warm event during the last 

~50-100 ky of the Maastrichtian and may be correlative with 

the mega-flows of phase-2 Deccan volcanism (Fig. 19). This 

cooling could have been the result of SO 2 

gas released by 

Deccan volcanism. SO 2 

injected into the stratosphere forms 

sulfate aerosol particulates, which act to reflect incoming 

solar radiation and cause global cooling. Because sulfate 

aerosol has a short lifespan in the atmosphere, the cooling 

would be short-term (years to decades), unless repeated 

injections from volcanic eruptions replenished atmospheric 



Fig.19. Biotic response to greenhouse warming at South Atlantic DSDP Site 525 (data from Li and Keller, 1998c; Abramovich and 

Keller, 2003). During the greenhouse warming, diversity (H’) dropped, large specialized (k-strategy) species reached adulthood 

at less than 50% of their former adult size with up to 60% of the specimens dwarfed, and low oxygen tolerant Heterohelix species 

temporarily decreased in abundance. Dwarfed species decreased at the end of the Maastrichtian although no recovery occurred 

and k-strategy species remained rare (


of Deccan volcanism: the main phase-2 at the end of the 

Maastrichtian accounts for about 80% and phase-3 in the 

early Danian for about 14% of the total Deccan volume. 

Deccan main phase-2 volcanism and its corollary effects 

(warming, cooling, acid rain, ocean acidification, carbon 

crisis) are viable and the likely main cause of the KTB mass 

extinction. The shear volume and rapid rate of volcanic 

eruptions and the number of mega-flows make phase-2 

volcanism far more destructive than a single large impact. 

Instead of a single instantaneous catastrophe, the KTB 

killer was likely a cascade of rapid and massive volcanic 

eruptions that formed the largest and longest (1500 km) lava 

flows known on Earth, with SO 2 

and CO 2 

gas emissions 

estimated to have exceeded those of the Chicxulub impact 

by at least 30 times (Chenet et al. 2007, 2008). The last 

phase-3 of Deccan eruptions in the early Danian was much 

smaller (14% of total Deccan Traps) and caused no 

significant species extinctions, but resulted in high-stress 

conditions that may be the cause for the long delayed full 

marine recovery after the mass extinction. Major findings 

from the Krishna-Godavari Basin study support this 

scenario. 

Deccan phase-2 volcanism (~80% of total Deccan Traps) 

began in C29R and ended at the KTB. This interval of 

C29R is equivalent to zones CF1-CF2, which span the 

last 280 ky of the Maastrichtian and is equivalent to most 

of Micula prinsii zone (Fig. 6). However, phase-2 

eruptions may have occurred over a much shorter time 

interval and mainly concentrated in zone CF1. Deccan 

phase-2 ended with massive eruptions that formed 

four of Earth’s largest and longest lava mega-flows 

(~1500 km) across India and out into the Bay of Bengal. 

· The KTB mass extinction began in Deccan phase-2 with 

a 50% faunal crash prior to the first of four mega-flows, 

followed by another 50% crash after the first mega-flow, 

leaving just 6 to 8 survivors. No recovery occurred 

between mega-flows and the mass extinction was 

complete with the last mega-flows that marks the end of 

phase-2 and the KTB. 

The kill effect was likely due to the rapid, pulsed 

eruptions of massive CO 2 

and SO 2 

gas emissions, leading 

to high continental weathering rates, global warming, 

cooling, acid rains, ocean acidification and a carbon 

crisis that prevented recovery. 

After the KTB mass extinction, early Danian (zone P1a) 

assemblages in India mirror the global evolutionary 

pattern and global high-stress conditions. 

Deccan phase-3 volcanism (~14% of total Deccan 

Traps) began in the early Danian near the C29R/C29N 

boundary, which is equivalent to the P1a/P1b boundary 

and also formed three to four of Earth’s largest and 

longest lava flows. The onset of phase-3 coincided with 

the extinctions of P. eugubina and P. longiapertura. 

Deccan phase-3 (zone P1b) reveals no major differences 

between faunal assemblages in the three intertrappeans 

or the global record. This suggests that environmental 

conditions remained tolerable, possibly because volcanic 

eruptions were less intense or separated by longer time 

intervals, and/or that early Danian species were well 

adapted to the environmental stresses. 

Recovery of the marine ecosystem occurred after the 

last Deccan phase-3, as indicated by larger species 

morphotypes and evolution of more diverse assemblages. 

The long delayed post-KTB recovery in the marine 

environment has long been an enigma. Data from the 

Krishna-Godavari Basin wells suggest that continued 

high-stress conditions caused by Deccan volcanism and 

its corollary effects may have prevented full recovery 

for over 0.5 Ma. 

Acknowledgments: This project would not have been 

possible without the support of former Director 

(Exploration) Dr. D.K. Pande and the current Director Dr. 

S.V. Rao of the Oil and Natural Gas Corporation Ltd., India. 

The senior author is deeply grateful for the permission to 

study the Krishna-Godavari Basin wells that made this study 

possible. A special thanks to Dr. D.S.N. Raju for sharing his 

extensive knowledge of the Krishna-Godavari Basin wells, 

and to Dr. Sunil Bajpai who facilitated this study in many 

ways. We are also very grateful to Mr. D.K. Bharktya, DGM 

(Geology) RGl, Chennai, for taking SEMs of the foraminifera. 

This study is based upon work supported by the US National 

Science Foundation through the Continental Dynamics 

Program, Sedimentary Geology and Paleobiology Program 

and Office of International Science & Engineering’s India 

Program under NSF Grants EAR-0207407, EAR-0447171, 

and EAR-1026271. 



Plate 1. SEM illustrations of late Maastrichtian, scale bar = 100 µm. 1. Globotruncanita stuarti (de Lapparent, 1918), Well RZL-A, 

3650 m. 2-4. Globotruncanita stuartiformis (Dalbiez, 1955), Wells ELM-A, 3590 m, NSP-A, 3363 m. 5-8. Globotruncana arca (Cushman, 

1926), Wells PNM-A, 2555 m, CTP-A, 3980 m, RZL-A, 3650 m. 9-12. GLobotruncana insignis Gandolfi, 1955, Wells PNM-A, 

2545 m, RZL-A, 3650 m. 13-16. Globotruncana rosetta (Carsey, 1926), Wells PNM-A, 2565 m, CTP-A, 4010 m, RZL-A, 3650 m. 



Plate 2. SEM illustrations of late Maastrichtian, scale bar = 100 µm. 1-2. Abathomphalus mayaroensis (Bolli, 1951)Well CTP-A, 

4010 m. 3-4. Rosita patelliformis (Gandolfi, 1955), Well CTP-A, 3960 m. 5-6. Globotruncanita conica (White, 1928), Wells NSP-A, 

3363 m, RZL-A, 3650 m. 7-8. Rosita walfishensis (Todd, 1970), Well CTP-A, 4010 m. 9-10. Globotruncan dupeublei (Caron et 

al.1984), Well RZL-A, 3650 m. 11-12. Glotobruncanita pettersi (Gandolfi, 1955), Well PNM-A, 2565 m. 13-15. Rosita contusa (Cushman, 

1926), Well PNM-A, 2565 m. 



Plate 3. SEM illustrations of late Maastrichtian, scale bar = 100 µm. 1. Racemiguembelina fructicosa (Egger, 1899), Well RZL-A, 3650 

m. 2. Racemiguembelina powelli Smith and Pessagno, 1973, Well MTP-A, 3160 m. 3-4. Planoglobulina brazoensis (Plummer, 1931), 

Well ELM-A, 3590 m. 5-6. Heterohelix labellosa, Nederbragt, 1990, Well NSP-A, 3339.2 m. 7. Pseudoguembelina palpebra Brönnimann 

and Brown, 1953, Well NSP-A, 3339.5 m. 8. Planoglobulina carseyae (Plummer, 1931), Well NSP-A, 3339.5 m. 9-10. Heterohelix 

globulosa (Ehrenberg), Well NSP-A, 3339.5 m, 3339.2 m. 11-12. Pseudoguembelina hariaensis Nederbragt, 1990, Well NSP-A, 

3339.5 m. 13. Heterohelix planata (Cushman, 1936), Well RZL-A, 3650 m. 14-15. Pseudoguembelina costulata (Cushman, 1938), 

Well NSP-A, 3339.5 m. 16. Pseudotextularia nuttalli (Rzehak, 1886), Well PNM-A, 2545 m. 17. Pseudotextularia elegans (Rzehak, 

1886), Well PNM-A, 2535 m. 



Plate 4. SEM illustrations of early Danian, scale bar = 100 µm. 1-7. Parasubbotina pseudobulloides (Plummer, 1926), Wells PNM-A, 

2345 m, Razole-1, 3385 m. 8-11. Subbotina triloculinoides (Plummer, 1926), Wells PNM-A, 2345 m, 2350 m, Razole-1, 3330 m. 

12-15. Subbotina varianta (Subbotina, 1953), Well PNM-A, 2250 m. 16. Globigerina (Eoglobigerina) tetragona (Morozova, 1961), 

Well PNM-A, 2295 m. 



Plate 5. SEM illustrations of early Danian, scale bar = 100 µm. 1-2. Subbotina trivialis (Subbotina, 1953), Wells PNM-A, 2295 m, 

RZL-A, 3365 m. 3. Globoconusa daugjergensis (Brönnimann, 1953), Well PNM-A, 2295 m. 4-6. Eoglobigerina edita (Subbotina, 

1953), Well RZL-A, 3370 m. 7-9. Globigerina (Eoglobigerina) pentagona (Morozova, 1961), Well RZL-A, 3370 m. 10-11. Praemurica 

taurica (Morozova, 1961), Well PNM-A, 2345 m. 12, 16. Praemurica inconstans (Subbotina, 1953), Well PNM-A, 2350 m. 

13-15. Praemurica uncinata (Bolli, 1957), Wells PLK-A, 2565 m, PNM-A, 2190 m. 



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(Received: 20 May 2011;Revised form accepted: 9 June 2011)

Deccan Volcanism Linked to the Cretaceous-Tertiary Boundary ...

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