Environmental effects of Deccan volcanism across the Cretaceous–Tertiary transition in Meghalaya,...

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Environmental effects of Deccan volcanism across the Cretaceous–Tertiary transitionin Meghalaya, India

B. Gertsch a,⁎, G. Keller b, T. Adatte c, R. Garg d, V. Prasad d, Z. Berner e, D. Fleitmann f

a Earth, Atmospheric and Planetary Science Department, Massachussetts Institute of Technology, Cambridge MA 02139, USAb Department of Geosciences, Princeton University, Princeton NJ 08544, USAc Institut de Géologie et Paléontology, Université de Lausanne, Anthropole, CH-1015 Lausanne, Switzerlandd Marine Micropalaeontology Group, Birbal Sahni Institute of Palaeobotany, Lucknow 226007, Indiae Institute for Mineralogy & Geochemistry, Karlsruhe Institute of Technology, 76128 Karlsruhe, Germanyf Institute of Geological Sciences, University of Bern, CH-3012 Bern, Switzerland

a b s t r a c ta r t i c l e i n f o

Article history:

Received 22 February 2011

Received in revised form 24 July 2011

Accepted 10 August 2011

Available online xxxx

Editor: G. Henderson

Keywords:

Deccan volcanism

Iridium

Meghalaya

KT boundary

mass extinction

The Um Sohryngkew section ofMeghalaya, NE India, located 800–1000 km from the Deccan volcanic province,

is one of the most complete Cretaceous–Tertiary boundary (KTB) transitions worldwide with all defining and

supporting criteria present: mass extinction of planktic foraminifera, first appearance of Danian species, δ13C

shift, Ir anomaly (12 ppb) and KTB red layer. The geochemical signature of the KTB layer indicates not only an

extraterrestrial signal (Ni and all Platinum Group Elements (PGEs)) of a second impact that postdates

Chicxulub, but also a significant component resulting from condensed sedimentation (P), redox fluctuations

(As, Co, Fe, Pb, Zn, and to a lesser extent Ni and Cu) and volcanism. From the late Maastrichtian C29r into the

early Danian, a humid climate prevailed (kaolinite: 40–60%, detrital minerals: 50–80%). During the latest

Maastrichtian, periodic acid rains (carbonate dissolution; CIA index: 70–80) associated with pulsed Deccan

eruptions and strong continental weathering resulted in mesotrophic waters. The resulting super-stressed

environmental conditions led to the demise of nearly all planktic foraminiferal species and blooms (N95%) of

the disaster opportunist Guembelitria cretacea. These data reveal that detrimental marine conditions prevailed

surrounding the Deccan volcanic province during the main phase of eruptions in C29r below the KTB.

Ultimately these environmental conditions led to regionally early extinctions followed by global extinctions at

the KTB.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

For the past 30 years, the Cretaceous–Tertiary boundary (KTB)

mass extinction has been attributed to an extraterrestrial impact

based mainly on the presence of a global Ir enrichment in a thin KTB

red clay layer (Alvarez et al., 1980), which was subsequently

attributed to the Chicxulub impact crater on Yucatan that distributed

impact glass spherule ejecta near the KTB in Central and North

America (e.g., Pope et al., 1991; Schulte et al., 2010; Smit et al., 1996).

This theory and its corollary interpretations have remained contro-

versial because of contradictory evidence (Keller, 2010), including the

discovery of the oldest impact spherule layer in late Maastrichtian

sediments in NE Mexico and Texas that indicates a pre-KT age for the

Chicxulub impact (e.g., Keller et al., 2003, 2007, 2009a).

Also for the past 30 years, Deccan volcanism has been advocated as

potential cause for the KTB catastrophe (e.g., Courtillot et al., 1986,

1988; Duncan and Pyle, 1988; MacLean, 1985). But this hypothesis

was considered unlikely because volcanism was generally believed to

have occurred over about one million years prior to the mass

extinction leaving sufficient time for recovery between eruptions.

More recently, major studies of the Deccan Volcanic Province (DVP)

have greatly improved understanding of the age and tempo of

eruptions, revealing three major phases: initial phase-1 in C30n at

~67.4 Ma, the main phase-2 in C29r just before the KTB, and the last

phase-3 in the early Danian (base C29n). Phase-2 is the most critical

period of Deccan volcanism as it accounts for ~80% of the entire

3500 m thick Deccan lava pile, and erupted in rapid pulses over a

short interval in C29r just prior to the KTB mass extinction (Chenet

et al., 2007, 2008, 2009; Keller et al., 2008, 2009b,c). In another

interpretation, Hooper et al. (2010) suggest that although the bulk of

the major eruptions started in C29r, it continued into C29n. New data

from ten deep wells in the Krishna-Godavari Basin support Chenet et

al.'s model of two separate volcanic phases with the major phase-2 in

C29R below the KTB and Phase-3 in C29N (Keller et al., 2011). It

cannot be ruled out that minor volcanic eruptions continued in C29R

above the KTB, although these would have been locally more

restricted. Phase-2 created the world's longest lava flows, spanning

N1500 km across India and into the Gulf of Bengal (Keller et al., 2011;

Earth and Planetary Science Letters 310 (2011) 272–285

⁎ Corresponding author.

E-mail address: [email protected] (B. Gertsch).

0012-821X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.

doi:10.1016/j.epsl.2011.08.015

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Self et al., 2008). These lava flows ended at or near the KTB mass

extinction (Keller et al., 2008), as revealed in intertrappean sediments

overlying phase-2 basalt flows in Rajahmundry quarries (Andra

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

studies strongly suggest that the biotic and environmental effects of

Deccan volcanism at KTB time may have been vastly underrated.

This report investigates the climatic and environmental conse-

quences of Deccan phase-2 volcanism in themost complete KTBmarine

sequence known from India and comparable to the most complete

sequences worldwide (e.g., Tunisia, Texas, Spain). The section is

exposed along the Um Sohryngkew River in Meghalaya, NE India, and

is about 800–1000 km from themain Deccan volcanic province (Fig. 1).

A thin red clay layer enriched in Ir and other Platinum Group Elements

(PGEs) marks the KTB (Bhandari et al., 1993, 1994; Garg et al., 2006;

Pandey, 1990). Our investigations are based on the same sequence

studied by these workers and employ a multi-proxy approach that

includes: 1) biostratigraphy to provide high-resolution age control and

evaluation of the biotic effects of Deccan volcanism; 2) carbon isotope

stratigraphy as independent marker of the KTB; 3) sedimentology,

microfacies analysis andbulk rockmineralogy to identify environmental

changes; 4) clay mineralogy to infer paleoclimatic conditions, and

comparisonwith data fromother sites in India; 5) platinumgroup, trace

andmajor elements geochemistry to evaluate evidence for an impact at

the KTB; and 6) major and trace element geochemistry to identify a

causal-relationship between Deccan volcanic activity and periods of

high-stress conditions in marine environments.

2. Methods

The Um Sohryngkew section was examined in the field for

lithological changes, burrows and shell layers, which were described,

measured and photographed (by RG and VP). A total of 143 samples

were collected at an average of 50 cm, except for the KT transition

where samples were taken at 10 cm intervals. In the laboratory,

samples were processed for foraminiferal extraction using standard

methods (Keller et al., 1995).

Carbon and oxygen isotope measurements were carried out on

powdered bulk rock samples at the stable isotope laboratories at the

University of Bern, Switzerland, using an Optima (Micromass, UK)

ratio mass spectrometer equipped with an online carbonate prepa-

ration line (Multi Carb) with separate vials for each sample and a VG

Prism II ratio mass spectrometer, respectively. The results were

calibrated to the PDB scale with standard errors of 0.05‰ for δ13C.

Major and trace elements were analyzed at the Geological Institute

of the University of Lausanne, Switzerland, by XRF spectroscopy with

a PANalytical PW2400with a RX tube (Rh anode). PGEswere analyzed

at the Institute for Mineralogy and Geochemistry, University of

Karlsruhe, by isotope dilution HR-ICP-MS (Axiom, VG Elemental) after

pre-concentration and matrix reduction by Ni-fire assay (Gertsch

et al., 2011).

Bulk rock and clay mineral assemblages were analyzed by X-ray

diffraction (Xtra ARL Diffractometer) at the Geological Institute of the

University of Lausanne, Switzerland, based on procedures described

by Adatte et al. (1996). The semi-quantification of bulk-rock

mineralogy is based on XRD patterns of random powder samples by

using external standards with an error margin between 5 and 10% for

the phyllosilicates and 5% for grain minerals. Clay mineral analysis

follows the methods described by Adatte et al. (1996). The intensities

of the identified minerals are measured for a semi-quantitative

estimate of the proportion of clayminerals, which is therefore given in

relative percent without correction factors, because of the small error

margin (b5%).

3. Geological context and lithology

The Meghalaya area is located in northeastern India, north of

Bangladesh, and characterized by the Shillong Plateau, which includes

Garo, Khasi, Jaintia and Mikir hills (Fig. 1). The Shillong Plateau is

tectonically related to the formation of Himalaya and corresponds to

an uplifted Precambrian massif of the peninsular India shield

formation with up to 6 km of Cretaceous through Miocene marine

to continental sedimentary rocks that unconformably overlie the

basement along the eastern, western and southern limbs (Alam et al.,

2003; Clark and Bilham, 2008; Das Gupta and Biswas, 2000; Ghosh

et al., 2005; Rao et al., 2008; Reimann, 1993; Rowley, 1996).

The Um Sohryngkew section lies on the southern side of the

Shillong Plateau near the village of Therria along the Um Sohryngkew

river. The sedimentary record shows uninterrupted marine shelf

sedimentation from the Campanian to the Eocene during the

formation of a gulf on the northeastern edge of greater India due to

rifting along the Indo-Burmese orogen (Acharyya and Lahiri, 1991;

Banerji, 1981; Krishnan, 1968; Nagappa, 1959; Reimann, 1993).

Sediments consist mainly of thick sandstone layers, marls, shale and

carbonates characteristic of coastal, estuarine and nearshore environ-

ments (Banerji, 1981; Krishnan, 1968; Nagappa, 1959).

For this study, investigations focused only on the Maastichtian–

Danian interval of the Um Sohryngkew section. Sediments in the lower

part of the section (0–14.26 m) consist of bioturbated clayey marls

(0–8 m), silty sandy shales (8–10 m), clayey marls (10–14.26 m), and

three 10–40 cm thick sandstone beds (2.4 m, 4.5 m, 13.3 m; Fig. 2). The

KTB (14.26–14.28 m) ismarked by a 2 cm thick rust-red-colored sandy-

silty layer with abundant subangular quartz in a red-brown matrix

enriched in Ir and other PGEs, but devoid of calcite and microfossils

(Figs. 2, 3A, B). In the lower Danian, silty, sandy shalewith a 10 cm thick

bioturbated sandstone layer (15.3–15.4 m) is followed by shales, clayey

marls, marls, and marly limestones (15.5–30 m).

Fig. 1. A) Geographic map of India with position of Meghalaya and the Deccan Volcanic

Province. B) Map of the Meghalaya area with the location of the Um Sohryngkew

section near the village of Therria.

273B. Gertsch et al. / Earth and Planetary Science Letters 310 (2011) 272–285


4. Biostratigraphy

Previous micropaleontological studies of the Maastrichtian to

Paleocene Um Sohryngkew section of Meghalaya based on planktic

foraminifera failed to identify the KTB red layer and PGE anomalies,

possibly because different intervals or sections were collected, or

sampling intervals were too large (e.g., Mukhopadhyay, 2007). In

contrast, nannofossil and dinoflagellate studies (Garg et al., 2006;

Nandi, 1990) were based on sample collections of the same intervals

where PGE anomalies were identified (Bhandari et al., 1993, 1994;

Pandey, 1990). This report is based on planktic foraminifera from the

same section and samples previously reported by Garg et al. (2006),

and represents the first documentation of the mass extinction across

the KTB transition of the Um Sohryngkew section. Age and biozones

are based on the combined planktic foraminiferal zonal scheme of

Keller et al. (1995, 2002), and Li and Keller (1998).

4.1. Late Maastrichtian

The latest Maastrichtian nannofossils zone Micula prinsii marks the

4 m below the KTB (Garg et al., 2006), which correspond to planktic

foraminiferal zones CF2 and CF1 (Keller et al., 2009d). Planktic

foraminiferal assemblages in this interval are dominated byGuembelitria

blooms (N95%) that characterize zone CF1 and CF2 in shallow-water

environments globally (see reviews in Keller and Abramovich, 2009;

Pardo and Keller, 2008). The remaining assemblage consists of rare and

sporadic occurrences of heterohelicids, planoglobulinids, pseudoguem-

belinids, racemiguembelinids, globotruncanids and rugoglobigerinids

(Fig. 3). However, in the 0.6 m below the KTB only rare, dwarfed and

stress-resistant species are present (e.g., heterohelicids and guembeli-

trids). The exclusionof all subsurfacedwellers suggests a shallower inner

neritic environment. Enhanced carbonate dissolution in this interval

may be linked to Deccan volcanism. In the Micula murus zone only rare

planktic foraminifera are preserved in the predominantly sandy-silty

shales, clayey marls and sandstones.

4.2. KT Boundary and early Danian

The Um Sohryngkew section contains the most complete KTB

transition in India, which can be correlated to the El Kef stratotype

section and point (GSSP) in Tunisia (Cowie et al., 1989; Keller et al.,

1995; Remane et al., 1999). As at El Kef, the KTB is identified by the

mass extinction of planktic foraminifera followed by the first

appearances of Danian species in zones P0 and P1a (e.g., Parvular-

ugoglobigerina extensa, P. eugubina, Woodringina hornerstownensis,

Globoconusa daubjergensis; Keller et al., 1995, 2002; Molina et al.,

2006). Also present are the same three KTB-supporting criteria, the

negative δ13C shift, the Ir anomaly and other PGEs in a thin red layer.

The δ13C excursion at the Um Sohryngkew section shows the same

trend as in the complete and expanded KTB sequences in Tunisia and

Texas (Keller et al., 2002, 2009a).

Fig. 2. Litholog of the UmSohryngkew section and illustrations: A)Outcrop of the KT transitionwithMaastrichtian graymarls topped by the KT red layer andDanian shales; B) close-up of

the KT boundary. Thin section micrographs of the KT red layer show abundant sub-angular quartz crystals (gray) in a brownmatrix. (For interpretation of the references to color in this

figure legend, the reader is referred to the web version of this article.)

274 B. Gertsch et al. / Earth and Planetary Science Letters 310 (2011) 272–285


The mass extinction pattern differs from the deep-sea record by its

lower diversity (24 species as compared with over 30 in comparable

shallow environments, Keller andAbramovich, 2009), the rare, sporadic

pre-KTB species occurrences in the 4 m below the KTB, and blooms

(N95%) of the disaster opportunist Guembelitria cretacea (Fig. 3). These

faunal assemblages reflect super-stressed environmental conditions at

the time of Deccan phase-2 eruptions in C29r below the KTB, coincident

withM.prinsii andCF1 zones (Keller et al., 2011). SuchhighGuembelitria

blooms are best known from the aftermath of themass extinction in the

earliest Danian, but they have also been observed below the KTB (zone

CF1) in sections throughout the Tethys, such as Bulgaria, Israel, Sinai,

Egypt, Texas and in the volcanically active Ninetyeast Ridge (reviews in

Keller and Abramovich, 2009; Pardo and Keller, 2008).

In the earliest Danian at Um Sohryngkew, normal low diversity

assemblages evolved with the first index species, P. extensa and

P. eugubina present at 10 cm and 20 cm, respectively, above the KTB

red layer, marking zones P0 and P1a (Fig. 3). The first appearances of

Parasubbotina pseudobulloides and Subbotina triloculinoides at 1.15 m

above the KTB red layer mark the subdivision of zone P1a into

subzones P1a(1) and P1a(2). The top of subzone P1a(2) is defined by

Fig. 3. A) Planktic foraminifera, δ13C record, platinum group elements (PGEs) ans sea-level across the KT transition. The KT boundary (red line) is defined by the disappearance of

Cretaceous species, the δ13C shift and PGE enrichments in the red layer. Note the latest Maastrichtian planktic foraminiferal assemblages are dominated (N95%) by the disaster

opportunist Guembelitria cretacea. B) Zoom on platinum-group elements at Um Sohryngkew across the KT transition, which show peak values in the KT red layer and background

contents in the late Maastrichtian and early Danian. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)



the last appearance (LA) of P. eugubina at 19.8 m (Fig. 3). The presence

of these early Danian biozones indicates a relatively continuous and

high rate of sediment accumulation.

5. Carbon isotopes

In the Um Sohryngkew section, δ13C was measured on selected

bulk-rock samples that contain N10% carbonate. The δ13C values are

generally very negative (−1 to −7.5‰) but their global trends are

comparable to former studies (Barrera and Keller, 1990; Keller and

Lindinger, 1989; Stueben et al., 2002; Zachos et al., 1989). Diagenetic

influence on the δ13C values in Um Sohryngkew is evaluated by oxygen

isotope values (−8.39 to−5.64‰) and the coefficients of correlations

between δ13C values and calcite percentages (R2=0.19), and δ13C and

δ18O (R2=0.62) respectively. Very low negative δ18O values suggest

strongdiagenesis (dissolution–precipitationprocesses), but their effects

on the δ13C trends across the KTB are limited in Um Sohryngkew as

indicated by low coefficients of correlation between δ13C values and

calcite percentages, and δ13C and δ18O respectively.

In the late Maastrichtian, negative values vary between −2 and

−3‰ (11.75–13.75 m, Fig. 3). No data is recoverable in the 50 cm

below the KTB due to strong carbonate dissolution. However, just

below the KTB red layer δ13C values show a drop to−4‰ followed by

rapid decrease to −7.25‰, forming a trough (14.35–14.70 m) in

zones P0 and P1a(1). The return to pre-KTB δ13C values of −2‰ is

observed in zone P1a(2) (16.25–19.75 m; Fig. 3). In the Um

Sohrynkew section, carbonate is very low (b20%) and the dissolution

and re-precipitation processes in tropical environments, such as

precipitation from waters enriched in dissolved inorganic carbon

(DIC) with low δ13C due to oxidation of organic matter, may explain

the very negative δ13C values (Tucker and Wright, 1990).

6. Mineralogy: results

6.1. Bulk-rock

Quartz and phyllosilicates are the dominant minerals in the Um

Sohryngkew section, whereas calcite, K-feldspars and plagioclases are

intermittently abundant (Fig. 4). Unquantified minerals record impor-

tant values in the lower part of section below the KTB and consist of

poorly crystallized phyllosilicates, organic matter, phosphate minerals

and Fe-hydroxide/-oxide minerals. In upper Maastrichtian sediments,

mineralogical assemblages are dominated by detrital minerals, such as

quartz, phyllosilicates, K-feldspars and plagioclases,whereas calcite and

ankerite are rare or absent (0–25%; Fig. 4). The silty red KTB layer

consistsmainly of detrital components, suchasquartz (21%), plagioclase

(18%), K-feldspars (8.5%) and phyllosilicates (14%), together with high

goethite (19.8%) and low calcite (10%). In lower Danian (P1a zone)

sediments, calcite rapidly increases and dominates (25–40%), whereas

phyllosilicates and unquantified minerals decrease. At the P1a/P1b

boundary, calcite content drops to 10–20% and remains low, whereas

quartz, K-feldspars, phyllosilicates, and plagioclases contents increase

slightly (Fig. 4).

6.2. Clay minerals

Clay assemblages (fraction b2 μm) in the Um Sohryngkew section

are composed of smectite, kaolinite, chlorite, illite–smectite (I–S)

mixed layer and illite (Fig. 4). The basal part (0–13.4 m) is dominated

by illite (20–60%) and kaolinite (20–45%). Smectite, chlorite and I–S

mixed layer show low values (0–20%) with scattered peaks. The KT

transition (13.4–14.4 m) is marked by a gradual increase in kaolinite

(50%) and decrease in illite (10%). Smectite gradually increases (15%),

whereas chlorite (0–10%) and I–S mixed layer (2–20%) remain low

Fig. 4. Bulk-rock and clay mineralogy data of the Um Sohryngkew section. A three-points moving average is plotted for all minerals, except goethite, ankerite, chlorite, I/S mixed

layers and kaolinite/illite ratios. Unquantified minerals refer to organic matter and poorly crystallized minerals. Bulk-rock assemblages dominated by detrital minerals (quartz,

phyllosilicates, plagioclases and K-feldspars) and clay assemblages dominated by kaolinite suggest high continental runoff caused by humid and warm climates in Meghalaya. (For

interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)



and constant. The KTB red layer (14.26–14.28 m) is composed of illite

(51%), kaolinite (40%) and chlorite (9%). In the upper part of the Um

Sohryngkew section (14.4–30 m) kaolinite (40–50%) and illite (40%)

dominate. Smectite and I–S mixed layers gradually decrease (b5%),

whereas chlorite remains low with scattered peaks and no significant

trend (0–25%). The kaolinite/illite index reflects steady values

throughout the sequence, except for a gradual increase across the

KTB followed by a maximum in the lower part of subzone P1a(1)

followed by an abrupt return to background ratios.

7. Major, trace and platinum group element geochemistry

Major elements (MEs) across the upper Maastrichtian–lower

Danian at the Um Sohryngkew section are grouped based on similar

trends (Fig. 5). The largest group includes Al, K, Mg, Na, Si and Ti,

which show relatively stable high concentrations in the lower part of

the section, followed by a gradual pre-KTB decrease (K, Mg, Ti), or

abrupt KTB drop (Al, Na, Si). All reach minimum values at the KTB and

constant low values in the lower Danian. Ca shows an inverse trend,

with low concentrations in the upper Maastrichtian M. prinsii zone, a

sharp increase just above the KTB, and constant high values in the

lower Danian. In contrast, Fe and P show stable low concentrations

throughout the section, interrupted only by peak values at the KTB

(Fe=214,782 ppm (21.5 wt.%), P=3582 ppm (0.36 wt.%); Fig. 5).

Trace elements (TEs) were normalized with Al based on Van der

Weijden (2002) for two reasons: 1) The detrital fraction composed of

quartz, phyllosilicates, Na-plagioclase and K-feldspars is dominant

(60–90%), whereas calcite content is usually low (0–40%) (Fig. 4). 2)

Al shows the second lowest coefficient of variations (Table A, see

supplementary material). Trace element trends normalized to Al

reveal important changes across the KTB (Fig. 6). Nearly constant

ratios are observed in As, Co, Cr, Ni, Pb, V and Zn during the upper

Maastrichtian and lower Danian but with major positive peaks at the

KTB. Cu ratios remain relatively high with no enrichment at the KTB.

In contrast, Mn, Sr, U, and Zr show low Al-normalized values in the

upper Maastrichtian relative to the lower Danian, but differ in their

response to the KTB event (Fig. 6, Table 1).

PGEs were analyzed across the KTB transition to quantify Ir, Pd, Pt,

Rh and Ru concentrations (Fig. 3A, B). All PGEs show similar patterns

with low concentrations in the upperMaastrichtian and lower Danian,

and peak values in the KTB red layer (Fig. 3A, B). Below the KTB red

layer, Ir, Rh and Ru concentrations are stable with 0.1, 0.15, and

b0.3 ppb, respectively; Pd concentrations are at or below the

detection limit (b0.9 ppb), and Pt values range from less than 2 ppb

to 2.84 ppb. All PGEs peak within the KTB red layer (Ir: 11.79 ppb, Pd:

73.86 ppb, Pt: 86.48 ppb, Rh: 93.44, Ru: 108.24 ppb). In the basal

Danian, all PGE concentrations return to low background values. Ir, Pt,

Rh and Ru values are gradually decreasing and Pt decreases rapidly to

form a trough (4.16 ppb) followed by a slight increase.

7.1. Element geochemistry

At the Um Sohryngkew section, the detrital fraction dominates

(60–90%) across the KTB transition and is composed of phyllosilicates,

quartz, plagioclases and K-feldspars, whereas calcite content remains

low but variable (5–40%; Fig. 4). Nevertheless, there are variations

prior to, at and after the KTB (Fig. 4). For example, very low calcite

(0–20%) and very high detritus (80–90%) below and at the KTB change

to higher calcite (20–40%) and lower detritus (60–80%) in the basal

Danian. ME trends are similar to detritus, except for Ca content, which

increases in the lower Danian. MEs show a sharp drop at the KTB

followed by constant low values in the lower Danian zone P1a(1) with

constant detrital input, including Al, K, Mg, Na, Si, and Ti (Fig. 5).

Fig. 5. Major elements across the KT transition in the Um Sohrynkew section are separated into three groups with similar trends: (A) High late Maastrichtian contents followed by

lower values in the early Danian; (B) Low late Maastrichtian contents followed by higher values in the early Danian; (C) Constant late Maastrichtian and the early Danian

concentrations, but peak values at the KT boundary.



ME and TE trends can be assessed by calculating enrichment

factors (EFME=Y/Yaverage shale, where Y is a specific major element;

EFTE=(X/Al)/(X/Al)average shale, where X is a specific trace element)

using average shale values of Wedepohl (1971). Fig. 8A and B shows

this calculation for the upper Maastrichtian (pre-KTB), lower Danian

(post-KTB), the Maastrichtian–Danian combined, and separately for

the KTB red layer. Average EFME and EFTE calculated for the entire

interval are generally close to 1, which indicates a major and trace

element composition nearly similar to average shale (Fig. 7A, B).

Exceptions are Mg, Na, Cu, and Mn, which are slightly depleted

relative to average shale, whereas Ca, U, and Zr, are enriched relative

to average shale (Fig. 7A, B). For pre-KTB and post-KTB intervals, most

average EFsME and EFsTE remain relatively close to the averages

calculated for the entire interval (Fig. 7A, B), except for small

differences in the average EFTE between pre-KTB and post-KTB

sediments (Fig. 7A, B).

The KTB red layer composition in MEs and TEs differs significantly

from upper Maastrichtian and lower Danianmarls and shales (Fig. 7A,

B). MEs record enrichments in Ca, Fe and P, whereas all other major

elements are slightly depleted (Fig. 7A). TE enrichment factors display

a distinct composition relative to average shale with important

enrichments in As, Co, Cr, Ni, Pb, and Zn, whereas all other TEs show

Fig. 6. Trace elements at Um Sohrynkew are grouped into two categories based on trends: (A) Constant late Maastrichtian and the early Danian concentrations with peak values at

the KT boundary, except for Cu; (B) Low late Maastrichtian contents followed by a gradual increase to higher values in the early Danian. Dashed line represents the Al-normalized

ratio for each element in the average shale.

Table 1

Major and trace element abundances measured in red clay (Chester, 2000), chondrite (Anders and Grevesse, 1989), crust (Wedepohl, 1995), deccan basalts (Crocket and Paul, 2004,

2008) and shale (Wedepohl, 1971).

As [ppm] Ba [ppm] Ce [ppm] Co [ppm] Cr [ppm] Cu [ppm] Ga [ppm] Hf [ppm] La [ppm] Mn [ppm] Nb [ppm] Nd [ppm]

Red clay 162 371 0 184 897 10 18 0 30 331 17 0

Chondrite 2 2 1 502 2660 126 10 0 0 1990 0 0

Crust – 584 60 24 126 25 15 5 30 774 19 –

Deccan basalts – 122 32 – 135 214 – 4 – 1549 10 –

Ni [ppm] Pb [ppm] Rb [ppm] S [ppm] Sc [ppm] Sr [ppm] Th [ppm] U [ppm] V [ppm] Y [ppm] Zn [ppm] Zr [ppm]

Red clay 2135 131 46 13,407 48 131 25 9 110 35 435 225

Chondrite 11,000 2 2 62,500 6 8 0 0 57 2 312 4

Crust 56 15 78 – 16 333 9 2 98 24 65 203

Deccan basalts 90 – 8 46 36 218 2 0 – 31 109 106

Al [ppm] Ca [ppm] Fe [ppm] K [ppm] Mg [ppm] Na [ppm] P [ppm] Si [ppm] Ti [ppm]

Red clay 53,263 39,234 214,782 15,475 4539 3108 3583 158,196 3126

Chondrite 8680 9280 190,400 558 98,900 5000 1220 106,400 436

Crust 79,913 39,308 43,923 19,924 22,319 23,739 786 287,539 4076

Deccan basalts 71,499 72,899 100,017 3902 37,581 17,508 1047 227,553 13,485

Shale 88,381 15,723 48,348 29,885 15,684 11,870 698 275,383 4675



EFsTE close to 1. These enrichments correlate with large peaks in Ir, Pd,

Pt, Rh and Rh and confirm the unique geochemical composition of the

KTB red layer (Figs. 3A, B, 7A, B).

8. Geochemical proxies

8.1. Weathering indices

Chemical weathering indices were calculated based on major

element concentrations, such as Chemical Index of Alteration (CIA),

Plagioclase Index of Alteration (PIA) and Chemical Index ofWeathering

(CIW), all of which are commonly used to characterize weathering

profiles and the extent of weathering (Price and Velbel, 2003). For

example, CIA values for fresh basalt (30–45) and granite (45–55) are

very low (Nesbitt and Young, 1982). Illite, montmorillonites and

beidellites, which are formed under contrasting dry and seasonal

climates, show CIA values of 75–85. Kaolinite, a clay mineral produced

under constant humid conditions, yields highest CIA values N90. CIA

value for average shales ranges from70 to75 (Nesbitt andYoung, 1982).

In the Um Sohryngkew section, CIA, PIA and CIW yield similar trends

with relatively constant values (60) during the upper Maastrichtian,

followed by a gradual increase (70–80) in the uppermost Maastrichtian

(13.5–14.26 m, Fig. 8). A sharp decrease in all indices marks the KTB,

followed by steady low values (30–40, Fig. 8).

8.2. Volcanism proxies

The influence of Deccan volcanism can be determined based on

several volcanism proxies, including Na/K, K/(Fe+Mg), Ca/Na and

Mg/Na ratios (Dessert et al., 2003; Sageman and Lyons, 2003). Na/K and

K/(Fe+Mg) ratios reveal the balancebetweendetrital andvolcanogenic

input and are interpreted to reflect the increase or decrease of riverine

siliciclastic flux relative to background volcanic input (Sageman and

Lyons, 2003). In Meghalaya, Na/K ratio showsmostly steady low values

in the upper Maastrichtian, a gradual increase prior to the KTB, and

constant higher values in the lower Danian, whereas K/(Fe+Mg) ratio

Fig. 7. (A) and (B) Calculated enrichment factor (EF) relative to average shale for major and trace elements measured in the Um Sohryngkew section. EF are calculated for pre-KTB

and post KTB data, separately and together, and for the KT red layer; (C) Calculated enrichment factor (EF) relative to chondrite for some major, trace and platinum group elements

measured in the KTB red layer at Um Sphryngkew compared to EFs of platinum group elements of Stevns Klint, Denmark; (D) Normalized PGEs relative to continental flood basalt for

several types of rocks (e.g. flood basalts, meteorites) and KTB layers of Um Sohryngkew, Stevns Klint and Caravaca.



shows the opposite trend (Fig. 8). Compared to Sageman and Lyons

(2003), bothproxies recordvalues indicativeof a predominantly detrital

influence across the KTB transition in the Um Sohryngkew area

(0.1bNa/Kb0.3; 0.2bK/(Fe+Mg)b0.8; Fig. 8).

Ca/Na and Mg/Na ratios recorded in basaltic river waters show

remarkably high values (Dessert et al., 2003), which may have

significantly affected the geochemical signal of near-shore environ-

ments during the erosion of Deccan basalt traps. However, in the Um

Sohryngkew section, these ratios show opposite trends that render

the use of these ratios invalid as geochemical proxies for subaerial

Deccan volcanism in marine sediments (Fig. 8). This indicates that

Meghalaya was not part of the drainage domain of the Deccan

volcanic province (Dessert et al., 2003).

8.3. Hydrothermal activity proxies

Hydrothermal proxies consist mainly of Al/(Al+Fe+Mn), to-

gether with single elements, such as Pb, Zn, Cu and Co, (Chester, 2000;

Pujol et al., 2006). In the Um Sohryngkew section, hydrothermal

proxies record steady high values (0.6–0.7) in the upper Maastrich-

tian and lower Danian marls and shale, which indicates that

hydrothermal influence was absent (Fig. 8). The Al/(Al+Fe+Mn)

ratios show a negative peak that is linked to the presence of goethite

at the KTB, and not related to a potential hydrothermal influence.

These trends are corroborated by single elements, which record

constant values in the Maastrichtian and Danian, but peak only in Pb

and Zn at the KTB (Fig. 6).

8.4. Extraterrestrial proxies

Extraterrestrial impact(s) and dust input(s) were evaluated based

on the Ni/Cu ratio and PGEs. The Ni/Cu ratio has been used as

extraterrestrial proxy due to the similar Cu contents in chondrite and

continental crust, and also because of the large concentrations of Ni

(10,624 ppm) present in C1-chondrite in comparison to continental

crust (47 ppm) (Munsel et al., 2011). In the Um Sohryngkew section,

Ni/Cu ratios peak at the KTB (213.5) and suggest an extraterrestrial

source, but are constant during the upper Maastrichtian (2) and lower

Danian (4). A slight difference between Maastrichtian and Danian

Ni/Cu ratios likely results from lower oxygen conditions in the early

Danian, rather than from increased input of extraterrestrial dust

because neither element is enriched relative to average shale (Fig. 7B).

PGEs, including Ir, Pd, Pt, Ru and Rh, are common proxies used to

detect extraterrestrial impact(s) due to their rare occurrence on Earth

(Wedepohl, 1991, 1995). In the Um Sohryngkew section, a marked

peak in all PGEs occurs at the KTB, but no significant enrichment in

PGEs is recorded during the late Maastrichtian and early Danian

(Fig. 3).

9. Discussion

9.1. Depositional environment: planktic foraminifera

In the Um Sohryngkew section, planktic foraminiferal biostratig-

raphy reveals high and relatively continuous sedimentation during

the upper Maastrichtian and lower Danian (Fig. 3). However, in the

Fig. 8. Summary of all proxies used in this study (weathering, hydrothermal activity, volcanism vs detritism, basalt weathering, cosmic input) based on major and trace element

geochemistry.



uppermost 2 m of the Maastrichtian species assemblages reflect

super-stress condition, intermittent strong carbonate dissolution

(e.g., poor preservation, broken or fragmented shells), sporadic

species occurrences, variable abundances, dwarfing of species and

Guembelitria blooms. Guembelitria blooms are best known from the

aftermath of the KTBmass extinction when they thrivedworldwide to

the exclusion of other species and are therefore known as disaster

opportunists. But similar blooms are also known from the latest

Fig. 9. A) Summary of major results in the Um Sohryngkew section. Note the paleoclimatic conditions show decreasing intensities in “mock aridity” from central to eastern India,

related to Deccan volcanism. Note also the good correlation between the main Phase-2 of Deccan volcanism, high chemical weathering indices and disaster/opportunist Guembelitria

blooms during the terminal Maastrichtian, which suggest a close link between Deccan volcanism and high-stress environmental conditions. B) Model of the possible feedbacks and

environmental consequences resulting from the Deccan main phase-2 during the terminal Maastrichtian.



Maastrichtian zone CF1, where they correlate with periods of intense

continental runoff and submarine volcanic activity (reviews in Keller

and Abramovich, 2009; Pardo and Keller, 2008).

The Guembelitria blooms in Meghalaya correlate well with low

amounts of productivity sensitive elements, such as P, Cu, and Ni, and

high weathering indices during the latest Maastrichtian when Deccan

volcanic activity reached itsmaximum in phase-2 (Figs. 5, 6, 8). Strong

weathering indices indicate intense chemical weathering in nearby

continental areas of the Um Sohryngkew section and are likely due to

acid rains resulting from SO2 emissions from Deccan volcanism (Self

et al., 2006). The acidic waters lead to super-stress conditions in the

Meghalaya area inhibiting CaCO3, production, which favored blooms

of the small thin-shelled surface dwellers Guembelitria blooms and

explains the intermittent strong dissolution of planktic foraminiferal

assemblages (Fig. 9A, B). Similar Guembelitria blooms indicating high-

stress conditions are observed in the latest Maastrichtian and early

Danian throughout the Tethys and into the South Atlantic (e.g., Egypt,

Israel, Tunisia, Bulgaria, Texas, Argentina) (Abramovich and Keller,

2002; Adatte et al., 2002; Keller, 2002; Keller et al., 2007).

9.2. Sea-level: lithology and mineralogy

Combined with lithologies and foraminiferal assemblages, bulk-

rock mineralogy is an excellent environmental proxy to infer

fluctuations in sea-level and associated erosion and continental runoff

based on the distribution of calcite and detrital minerals (quartz,

phyllosilicates, plagioclases and K-feldspars; Adatte et al., 2002). High

calcite content generally indicates deeper environments, diminished

erosion and low continental runoff, whereas high detritus input

suggests shallower environments and high continental runoff.

In Meghalaya, detrital minerals in bulk-rock assemblages are

dominant and calcite is low but fluctuating in the upper Maastrichtian

marls and shale, which suggests deposition in a shallow water

environment (b100 m depth) with high terrigenous influx. For

example, the thin sand layer at 13.3 m (0.66 m below the KT

boundary) coincides with a marked decrease in species richness of

planktic foraminifera and the absence of deeper dwelling species,

which indicates a drop in sea level to inner neritic depth (Fig. 3A).

Enhanced carbonate dissolution between this sandstone layer and the

KTB may be due to the sandy, shallow water environment and/or acid

rain linked to the main phase of Deccan volcanism in C29r (Chenet

et al., 2007). Above the sandstone layer, sea level gradually increased

and reached a maximum at the KTB clay layer. Similar sea-level

changes have been observed in KTB sections from Israel, Egypt,

Tunisia, Texas, and Mexico (Adatte et al., 2002; Keller et al., 2003,

2007).

Across the KT transition and in the lower Danian high detrital

input continues into a relatively shallow though deepening marine

environment. The sandstone layer marks a small sea level drop and

possibly short hiatus, as indicated by the abrupt increase in Danian

species coincidentwith the P1a(1)/P1a(2) subzone boundary (Fig. 3). A

hiatus at this interval has been documented from many lower Danian

sequences (Keller et al., 2003). A deepening and more open marine

environments dominated by carbonate sedimentation prevailed during

the lower Danian (Figs. 3 and 4).

9.3. Climate proxies: clay and bulk-rock mineralogy

Clayminerals are byproducts resulting from the interplay between

climate, continental morphology, tectonic activity and sea-level

variations, and therefore can be used as climatic and environmental

proxies (Chamley, 1989). In the Um Sohryngkew section, clay

assemblages are dominated by kaolinite, which is formed in tropical

soils under constant warm and humid conditions, and illite, which is a

byproduct of tectonic uplift and physical weathering (Chamley, 1989;

Robert and Chamley, 1990). Illite is poorly crystallized, which

indicates significant chemical weathering caused by hydrolysis.

Illite/Smectite (I/S) mixed layers are poorly ordered (R=0) and

contain 25–50% of expandable layers. Smectite is a “smectoid”, an I/S

mixed layers with around 80–90% of expandable layers. High I/S

mixed layers and low smectite contents suggest a diagenetic overprint

linked to high burial depths (N3 km, Reimann, 1993) that resulted in

the transformation of smectite into I/S mixed layers (Chamley, 1989).

Smectites and I/S mixed layer are therefore not reliable paleoclimatic

proxies.

The paleoclimate of Meghalaya is characterized by predominantly

humid conditions and strong chemical weathering, as indicated by high

kaolinite, poorly crystallized illite and high kaolinite/illite ratios (Fig. 4).

The dominant detrital minerals (Fig. 6), high weathering indices and

palynological data (Nandi, 1990) support this general pattern (Fig. 8).

All of these indices suggest that predominant chemical weathering in

combination with physical weathering under humid conditions

prevailed across the KTB in near-shore environments of Meghalaya.

High kaolinite and poorly crystallized illite contents linked to

increasingly humid conditions across the KTB transition are not

restricted to Meghalaya but are encountered worldwide from low to

middle latitudes, except in areas close to India (Abramovich et al.,

2002; Adatte et al., 2002, 2005; Keller et al., 1998; Madhavaraju et al.,

2002; Pardo et al., 1999; Robert and Chamley, 1990). Terrestrial and

marine sections from central and eastern India close to the DVP show

dramatically different compositions of clay mineral assemblages with

high smectite and absent kaolinite, which reveals predominantly arid

to semi-arid conditions with seasonal wet and dry cycles (Keller et al.,

2008, 2009c).

Most studies relate the global increase in kaolinite and poorly

crystallized illite input into the oceans to the short warm event of the

latest Maastrichtian (zone CF1), which generated wetter conditions,

more rainfall and intensified continental runoff probably linked to

Deccan volcanism and its gas emissions (see reference above). Local

aridity close to the DVP is interpreted as a result of “mock aridity” (e.g.

volcanically induced xeric conditions and extreme geochemical

alkalinity in the context of a regionally more humid climate) induced

by Deccan volcanism (Harris and Van Couvering, 1995; Khadkikar

et al., 1999). In this context, paleoclimatic information gathered from

the Um Sohryngkew section reveals that the “mock aridity” zone

caused by Deccan volcanism across the KTB transition is restricted to

the Deccan volcanic province with gradually decreasing intensities

from central India to the rim of the DVP (Fig. 9A, B).

9.4. KTB red layer geochemistry and potential origins

On a global basis, the KTB red clay layer shows peak concentrations

in PGEs (Ir, Rh, Ru, Pd, Pt) accompanied by enrichments in several

major (Fe, P) and trace (As, Ba, Co, Cr, Cu, Ni, Sb, Sc, Th, U, V, Zn)

elements, which are all postulated to originate from a single

extraterrestrial impact based mainly on the Ir and siderophile

elements (e.g. Co, Ni) (Alvarez et al., 1980; Bhandari et al., 1993,

1994; Joyce Evans et al., 1993; Martinez-Ruiz et al., 2006). In the Um

Sohryngkew section, the KTB red layer has high silt content (Fig. 4)

with peak concentrations in major, trace and platinum group

elements, except for Cu (Figs. 3, 5, 6). Maximum values in PGEs,

specific TEs (e.g. Cr) and the Ni/Cu ratio suggest an extraterrestrial

origin (Figs. 5, 6, 8; Table 1), as previously observed by Bhandari et al.

(1993, 1994). Normalized PGEs relative to chondrite, which are

commonly used to identify extraterrestrial signals at the KTB, show a

fairly flat line but all values fall in the “extraterrestrial origin” field

defined by Kramar et al. (2001) and are similar to values of the KTB

red clay layer at Stevns Klint, Denmark (Fig. 7C). Based on the

observations that the Chicxulub impact predates the KTB (Keller et al.,

2003, 2007, 2009a), the Ir and PGE anomalies at the KTB in Meghalaya

and worldwide is likely from another large impact for which no

impact crater is known to date.



Nevertheless, the impact hypothesis can only partly account for

the PGE and TE enrichments at the KTB. Based on major and trace

element concentrations of chondrite, an extraterrestrial impact

cannot explain the peaks in As, Pb, U, and V, or the low Mn

concentrations observed in the KTB red layer at Um Sohryngkew

(Table 1). Enrichment factors based on average chondrite composition

(EFchondrite=(X/Fe)/(X/Fe)chondrite, where X is a specific major, trace

or platinum group element), are very low for most trace elements

(Cr, Ni) and high for P (Fig. 8C), which does not support an

extraterrestrial origin. Thus, elemental enrichments in the KTB red

clay layer clearly show that an extraterrestrial impact alone cannot

be the sole source of this geochemical signature.

Several studies have proposed intense phase-2 Deccan Trap

volcanism as alternative cause for the KTB mass extinction and as

alternative source for the trace and platinum group element

enrichments in the KTB red layer (Courtillot et al., 1986; MacLean,

1985; Toutain and Meyer, 1989; Zoller et al., 1983). In Meghalaya, the

volcanic proxies used in this study to investigate the volcanic

influence in the KTB show no causal link (Fig. 8, Table 1), though

single element concentrations cannot rule out volcanism as direct

(e.g. triggered by a sudden eruption) or indirect (e.g. intense basalt

weathering) source, as hypothesized by Bhandari et al. (1993, 1994).

At Um Sohryngkew, normalized PGEs relative to continental flood

basalts show high and fluctuating values for the KTB red clay layer, but

these results do not correlate with normalized PGEs for the KTB at

Stevns Klint and Caravaca (Fig. 7D). These contrasting results suggest

that further investigations are needed to evaluate the influence of

Deccan volcanism on the KTB geochemistry.

Hydrothermal activity is a frequently overlooked or underesti-

mated factor in KTB enrichments, and its proxy (Al/[Al+Mn+Fe])

indicates a significant influence in the KTB red layer (Fig. 8). However,

several problems remain: 1) Neither hydrothermal activity nor sub-

marine volcanism is known to be prevalent at the KTB and Deccan

volcanism was predominantly continental with limited interaction

with marine environments (Keller et al., 2008; Self et al., 2008). 2)

Environmental perturbations, such as lower seawater pH and acids

rains, due to lava–seawater interaction could be locally restricted

(Edmonds and Gerlach, 2006). And 3) sediments affected by

hydrothermal activity are generally enriched in both Fe and Mn

(Chester, 2000), not only Fe as in the Um Sohryngkew section (Fig. 5).

In the Um Sohryngkew section, goethite (FeO(OH)) is the main

mineral in the KTB layer and results from late diagenetic alteration of

pyrite after deposition, as observed globally (e.g. Elles, Tunisia),

except for rare localities, where a hematite-rich layer occurs at the

KTB (Adatte et al., 2005; Pardo et al., 1999). Very high enrichments in

some TEs (As, Cr, Co, Cu, Ni), high Fe contents, and highly significant

correlation rate (R2=0.8–1) of As, Cr, Co, Cu, Ni, U, V and Zn with Fe

(Table B, see supplementary material) support the primary precipi-

tation of pyrite under sulfidic redox conditions in the KTB red layer

during deposition and compaction of sediments (Gavrilov, 2010; Pujol

et al., 2006; Schmitz, 1985, 1992). However, enrichment factors of the

redox-sensitive proxies U and V are not high enough to confirm

sulfidic conditions (Fig. 7; Algeo andMaynard, 2004; Brumsack, 2006;

Tribovillard et al., 2006). Although present-day weathering may have

partly leached redox-sensitive trace elements, environmental condi-

tions are not drastically reducing, but only dysoxic, by the time of the

deposition of the red clay layer to trap abundant Fe, S andmost pyrite-

linked TEs at or below the sediment–water interface.

Reduced sedimentation rates across the KTB, which are known to

concentrate MEs, TEs and PGEs (Bruns et al., 1997; Donovan et al.,

1988), are likely significant factors in the KTB geochemistry, as

observed by extremely large PGE and P concentrations in Meghalaya.

These results suggest a strongly condensed sedimentation in the KTB

red layer linked to a rapid sea-level rise culminating in the maximum

flooding surface globally observed at or near the KTB (Fig. 3; Adatte

et al., 2002, 2005; Donovan et al., 1988).

9.5. Depositional scenario across the KT boundary

During the late Maastichtian C29r (zone CF1) Deccan volcanism

reached its maximum (phase-2) accumulating 80% of the entire

3500 m thick Deccan lava pile with some mega-flows spanning over

1500 km across India and out into the Bay of Bengal (Chenet et al.,

2007, 2008; Keller et al., 2008; Self et al., 2008). Volcanic phase-2

ended at or near the KT mass extinction as evident from planktic

foraminifera in intertrappean sediments in deep wells of the Krishna-

Godavari Basin (Keller et al., 2011), as well as shallow sequences from

Rajahmundry, Andhra Pradesh and Central India (Jhilmili, Madhya

Pradesh, Keller et al., 2008, 2009b,c).

In Meghalaya to the northeast, the late Maastrichtian at the Um

Sohryngkew section was deposited in a shallow near-shore sea

(b100 m) about 800–1000 km from the Deccan volcanic province. In

this coastal area of India, climate change due to Deccan volcanism

resulted in humid conditions that contrasted with the semi-arid

conditions and “mock aridity” that dominated the center of the Indian

continent (Fig. 9A, B). Abundant precipitation, high continental runoff

and high weathering resulted in a major influx of detritus (quartz,

K-Feldspars, plagioclases), which led to increasingly turbid and

mesotrophic waters. These high-stress environmental conditions were

amplified by periodic acid rains associated with Deccan pulses, which

increased chemical weathering (Fig. 9A, B) and led to the exclusion of

most planktic foraminifera and blooms of the disaster opportunist

Guembelitria. Similar Guembelitria blooms correlate with the main

phase-2 of Deccan volcanism in C29r below the KTB in shallow water

sequences worldwide (Keller and Abramovich, 2009; Pardo and Keller,

2008).

Prior to the KTB mass extinction increasing volcanic intensity and

SO2 release led to acid rains that raised the pH of seawater and

inhibited or reduced carbonate precipitation and production leading

to the early disappearance of many planktic foraminiferal species.

Well prior to the KTB mass extinction these conditions favored the

survival of small species leading to dwarfism, and particularly small

thin-walled species that resulted in the observed Guembelitria blooms.

In the Um Sohryngkew section, the mass extinction coincides with a

silty red layer, a major Ir anomaly and the negative δ13C shift that

marks the productivity crash due to the mass extinction. Danian

species evolved shortly thereafter as also observed globally (Figs. 3,

9A, B).

At the KTB red layer, the origin of PGEs and trace element

enrichments (e.g., As, Co, Cr, Ni, Pb, U and Zn, Figs. 3, 5 and 6) indicate

an extraterrestrial source from a second major impact postdating

Chicxulub (Keller et al., 2003, 2007, 2009a), but not as sole origin.

Other enrichment processes, including fluctuating redox conditions

and condensed sedimentation likely contributed to the KTB geo-

chemical signature. During the early Danian marine productivity

gradually recovered (upper part of zone P1a) and diversity slightly

increased, but species remained very small, indicating continued

high-stress conditions (Fig. 3). In NE India humid conditions and

abundant precipitation lead to steady detrital input into the ocean,

whereas on the Indian continent semi-arid to arid (“mock aridity”)

conditions prevailed (Fig. 9A).

10. Conclusions

• The Um Sohryngkew section of Meghalaya, India, represents one of

the most continuous Cretaceous–Tertiary boundary (KTB) sequences

in India that correlates globallywith theGSSP section at El Kef, Tunisia,

and yields critical information related to the main phase-2 of Deccan

volcanism during the latest Maastrichtian C29r.

• Sediment deposition occurred in a shallow-water environment

(b100 m) dominated by high continental runoff due to subtropical

humid conditions with abundant precipitation, which contrasts



with the local semi-aridity induced by Deccan volcanism in central

India.

• Super-stress conditions prevailed during the latest Maastrichtian

(M. prinsii, CF1 zones) as indicated by G. cretacea blooms (N95%),

which are likely due to the combination of mesotrophic conditions

and acid rains linked to Deccan volcanism.

• The KTB silty red layer is enriched in major elements (Fe, P), trace

elements (As, Co, Cr, Ni, Pb, Zn) and platinum group elements

(Ir, Ru, Rh, Pt, Pd), which are comparable to othermajor KTB localities.

An extraterrestial origin is supported in part, but condensed

sedimentation, fluctuating redox conditions at the time of deposition,

and secondary redox fluctuations likely account for the relatively high

enrichments observed at Um Sohryngkew.

Supplementarymaterials related to this article can be found online

at doi:10.1016/j.epsl.2011.08.015.

Acknowledgements

We thank Mike Widdowson and three anonymous reviewers for

insightful comments. The material of this study is based upon work

supported by the US National Science Foundation through the

Continental Dynamics Program and Sedimentary Geology Program

under NSF Grants EAR-0207407, EAR-0447171, EAR-0750664 and

EAR 1026271 (GK). We thank Tiffany Monnier for sample preparation

for XRF analysis and Jean-Claude Lavanchy (University of Lausanne)

for XRF measurements. A special thank you to André Villard

(University of Neuchâtel) for thin section preparation.

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