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ISSN 00014370, Oceanology, 2011, Vol. 51, No. 4, pp. 640–651. © Pleiades Publishing, Inc., 2011. Original Russian Text © M.S. Barash, 2011, published in Okeanologiya, 2011, Vol. 51, No. 4, pp. 683–695. MARINE GEOLOGY

Factors Responsible for Catastrophic of Marine Organisms at the Mesozoic–Cenozoic boundary M. S. Barash Shirshov Institute of Oceanology, Russian Academy of Sciences, Nakhimovskii pr. 36, Moscow, 117997 Russia email: [email protected] Received November 17, 2009; in final form February 17, 2010

Abstract—The mass death of organisms at the –Tertiary boundary (KT boundary) resulted in the extinction of approximately half of marine genera. Some taxa had degraded by the end of the Cretaceous to become eventually extinct either before or precisely at the KT boundary. Most of them became extinct imme diately at this boundary. The terminal Cretaceous was marked by changes in many environmental processes, which influenced the biota. These included tectonic events, powerful basalt eruptions, falls of large (impact events), anoxia, transgressions and regressions, cooling and warming episodes, and the chemistry of the atmosphere and seawater. All these factors, except for impact events, could stimulate degradation of some groups of organisms, not their extinction. The Cretaceous–Tertiary boundary was marked by major impact events, which are reflected in the occurrence of the Chicxulub, Shiva, Boltysh, Silverpit, and, probably some other impact craters. Some known craters were left by asteroids at that time or slightly earlier. At least as many asteroids undoubtedly fell into the . The combination of many factors in the terminal Cretaceous harm ful for organisms and seemingly unrelated to each other may be likely explained only by a single supreme cause beyond the Solar System. DOI: 10.1134/S0001437011040047

At the boundary between the Mesozoic and Ceno years prior to the KT boundary and at the boundary zoic eras (Cretaceous and Tertiary periods, KT proper. Some universal with simple morphol boundary), the Earth experienced perturbations that ogy survived the and continued to exist in the ini involved all its external shells (lithosphere, hydro tial Cenozoic. The decline in the diversity of ammo sphere, atmosphere, and biosphere). In most sections, nites also commenced long before the KT boundary, the KT boundary is marked by a stratigraphic hiatus. and their last specimens are found a few centimeters In deepwater sediments, it is usually characterized by below this boundary. According to many investiga sharply reduced sedimentation rates. In outer shelf tions, the KT boundary is marked by mass cata areas and the upper part of the continental slope, strophic extinction of almost all the planktonic fora mostly carbonate sediments are replaced by black miniferal species. clays. All the sections exhibit reduction of CaCO3 con The El Kef stratotype section of the KT boundary tent at that boundary. (Tunisia) demonstrates lithological and geochemical This crisis resulted in the extinction of approxi features indicating drastic environmental changes at mately half of the thenexisting genera. During the that time: a drastic decrease of the CaCO3 contents in Cretaceous, some groups such as, for example, ichthy sediments; decline in δ13С (bioproductivity indicator); osaurs and plesiosaurs, were degrading, to the point of extreme concentration of iridium, Ni spinel, and becoming extinct by its end. Many groups widely organic carbon; and significant changes in the compo developed in the Cretaceous, such as inoceramids, sition of planktonic foraminiferal and nannofossil , ammonites, and belemnites also became assemblages [34]. extinct at that time. The extinction of inoceramids in In recent decades researchers have intensely dis the initial late is considered to be glo cussed the possible impact of the events at the KT bal, being related to the influx of oxygenrich Antarc boundary on different organisms and their gradual ver tic Bottom Water. The sections in Denmark show a sus stepwise decline (above and below the boundary) sudden disappearance of most brachiopod taxa at the or sudden extinction reflecting the catastrophic crisis. very end of the Maastrichtian simultaneously with All these models have their adherents even in situa mass extinction of plankton. tions in which the same organisms are considered in No distinct regularities in their behavior were char the same section. For example, when examining acteristic of other marine invertebrates such as, for planktonic foraminifers in the El Kef stratotype sec example, mollusks. Their diversity and abundance tion of the KT boundary (Tunisia), Smit [49] argues were decreasing for several hundreds of thousands of that almost all their Cretaceous species disappeared at

640 FACTORS RESPONSIBLE FOR CATASTROPHIC EXTINCTION OF MARINE 641

Site 527 Site 690 100 50% 0 100 50% 0 Zone Polarity Stage 276 247.08 Zone Polarity Stage m Tertiary m Tertiary NP2 29N 29N Survivors NP1 Survivors NP1 NP2 247.88

280 29R 29R Cretaceous

Cretaceous Maastrichtian P. s t o v e r i A c m e Maastrichtian Danian Micula prins. 283 248.88

Fig. 1. Reorganization of calcareous nannoplankton assemblages near the KT boundary inferred from deepsea holes drilled in the South Atlantic (DSDP Hole 527) and Weddell Sea (ODP Hole 690) (after [42], simplified). the KT boundary, except for Guembelitria cretacea, believe that mass extinction was a consequence of the while Keller [30[ arrived at the conclusion that at least combined influence of several factors: longterm envi 30% of Cretaceous species crossed the latter and con ronmental changes and strong brief impactrelated tinued to exist in the . The issue is that the ones, for example, the large impact on the basal Paleocene layer almost in all the sections with the presentday shelf of the Yucatan Peninsula (Mexico). KT boundary contains some quantity of Cretaceous The quantitative analysis of nannoplankton assem foraminiferal tests. Did these specimens survive the blages, which represent an important element of pri crisis, or are they reworked? Did decline mary production in sections enclosing the KT bound prior to the boundary? Was extinction of organisms ary, through the Tethys, Indian, and South Atlantic uniform at different latitudes? All these questions are reveals that their extinction was a sudden and given ambiguous answers. For example, based on the synchronous event in all the latitudinal zones [42] analysis of microfossil assemblages, some researchers (Fig. 1). This extinction coincides with the δ13С shift at [45] believe that the event at the KT boundary was glo this level, sharp decline of carbonate sedimentation, bal. Others argue that extinction was most notable in and anomalous iridium concentration in sediments lowlatitude areas [21, 33, and others]. (Fig. 2). No substantial changes in the nannoplankton According to G. Keller and other researchers, composition happened in the terminal Maastrichtian approximately threequarters of planktonic foramin approximately 1 million years before its end, which indi iferal species became extinct at the KT boundary or cates stable environmental conditions, although, in the near the latter—tropical and subtropical species with early and middle Maastrichtian (~70–67 Ma ago), its large morphologically complex tests, which lived in assemblages experienced notable transformations. the Maastrichtian in wellstratified waters of the open Planktonic foraminifers dwelling in the surface sea at the thermocline depth or deeper. Among the layer of the ocean to depths of a few hundred meters survivors were only representatives of genera that were experienced a strong stress at the KT boundary as well. able to resist strong variations in ecological parame Analysis of their assemblages in many sections reveals ters, such as shallowwater species of wide ecological that over 90% of species became extinct at this bound tolerance that populated the upper photic layer of the ary or immediately above the latter, which is usually open ocean or stress biotopes of the coastal zone. explained by the [20]. The latter authors These species became dominant elements of both note that mass extinction of planktonic foraminifers pelagic and coastal . began near the impact level. The drastic decrease in Such a highly selective mass extinction reflects the productivity of calcareous nannoplankton and flux considerable changes in temperature, salinity, and of organic matter from the ocean surface to its bottom concentrations of dissolved oxygen and nutrients at coincided with destruction of the faunal provincial the KT boundary in the Tethys. Some researchers [31] ism. Judging from data on deepsea holes in the South

OCEANOLOGY Vol. 51 No. 4 2011 642 BARASH

Site 527 Cretaceous δ13 δ18 nannofossils, % Iridium, ppb Carbonates, % CPDB OPDB m 50 100 1 2 3 4 20 60 100 1 2 3 4 –0.5 0 0.5 Zone Stage 276

Low producti vity Cooling 280 Maastrichtian Danian Micula prins.283 NP1 NP2

Fig. 2. Correlation between abundance of Cretaceous microfossils and iridium and CaCO3 contents and isotopic composition of carbonates in sediments reflecting relative variations in productivity and temperature (after [42], simplified).

Globigerinides сm 180 160 1 110 М 4 13C/12C 60 Ir 3 2 40 2 Т 20 1 К 0 0 3 –20 –1 –40 –2 4 –60 –3 –80 –4 0 –5 –130 –6 5 10–2 10–1 110–2 –1 0 1 2 1 m Globotruncanides ng g–1

Fig. 3. The Cretaceous (K)–Tertiary (T) boundary section outcropping near Bidart of southwestern France. Lithology: (1) white , (2) red marly limestone, (3) black clay, (4) white marly limestone, and (5) gray marl. Curves show the distribution of foraminifers, iridium, and carbon isotopes (after [12] and [38], modified).

Atlantic, the faunal turnover and reduction of nanno mately 10 cm thick. The latter is underlain by upper plankton production occurred during a very brief most Cretaceous marly and overlain by period. The subsequent recovery of planktonic fora Tertiary strata represented at the base by red marly minifers was very dynamic following immediately the limestone a several tens centimeters thick replaced impact event. Nevertheless, stabilization of their com higher by pinkish marl and white limestone beds. The munities and restoration of the former organic matter KT boundary proper is marked by high concentrations flux lasted at least several hundred years. The former nan of iridium reflecting the impact event and a sharp neg noplankton productivity level was reached only 2 Myr ative shift in carbon isotopic ratios indicating sharp after the impact event. According to these researchers, bioproductivity reduction. the succession of these processes was consistent with The transformation of foraminiferal assemblages in the model of mass extinction in response to the impact response to environmental changes at the Creta event. ceous–Paleogene boundary has been analyzed in sec The most significant turnover in the foraminiferal tions of Spain, Tunisia, and France [6]. In these sec fauna may be exemplified by the distribution of their tions the KT boundary is marked by a 2mmthick assemblages in the boundary section outcropping on layer with anomalous concentrations of iridium and the presentday North Atlantic coast near Bidart in microtectites. Over 90% of late Maastrichtian plank southwestern France (Fig. 3). In this area, the KT tonic foraminifers became extinct by the end of this boundary coincides with a dark clay layer approxi age; moreover, 70% of them disappeared immediately

OCEANOLOGY Vol. 51 No. 4 2011 FACTORS RESPONSIBLE FOR CATASTROPHIC EXTINCTION OF MARINE 643 at the boundary in question. Simultaneously, benthic volcanism, cooling, warming, regression, transgression, foraminifers experienced dramatic reorganization as anoxia, tectonic movements), each or combination of well: diverse infaunal and epifaunal communities were which could, and did, affect negatively development of replaced by taxonomically impoverished assemblages marine organisms at the end of the Cretaceous Period. with a dominant role of epifaunal taxa. These data The analysis of potential hypotheses explaining Meso imply oligotrophic bottom environments immediately zoic environmental , mass extinction included after events at the KT boundary related to the signifi [2, 3] reveals that practically none of them alone could cant decrease in primary Corg production. trigger sudden catastrophic environmental changes, Detailed analysis of echinoderm assemblages in which would result in simultaneous death of many boundary sediments revealed that the feeding mode marine and terrestrial organisms that populated differ was a major factor that determined their survival dur ent ecological niches. ing catastrophic events [29] and that the immediate Two main hypotheses are currently most popular cause responsible for the mass extinction of this group among researchers: fall (an impact event) of organisms was related to the reduced flux of nutri and volcanism. The first implies disastrous changes of ents to the oceanic bottom. many environmental parameters owing to multiple This is also confirmed by investigations of marine powerful falls of large asteroids on the Earth or colli bivalve assemblages, which were dominated by filter sion with ; the second, contamination of atmo ing and detritovore species prior to and after events at sphere and oceanic waters with harmful substances the KT boundary, respectively [27]. The reduced pri that resulted from eruptions of basalts during the for mary Corg production in surface waters and corre mation of the on the Indian Plate and, sponding decrease in feeding opportunities at higher probably, simultaneous volcanism of the Hawaiian trophic levels, which lasted several hundreds thou Emperor Seamount chain in the Pacific. sands years, were the main factors responsible for mass The iridium anomaly at the KT boundary discov extinction. ered by [9] in the Gubbio section (Italy) yielded the The disappearance of many planktonic organisms most important geochemical evidence for a large destructed the entire trophic chain, large marine car bolide fall onto the Earth (impact event). nivorous organisms such as fish and reptiles included. Subsequently, an iridium anomaly 65 Ma ago was Being deprived of food because of plankton death, fil registered in many deepsea drilling cores and in land tering organisms (bryozoans, crinoids, corals, some sections. This anomaly is usually confined to a thin brachiopods, and bivalves) also experienced mass boundary layer, which confirms the momentary depo extinction. In boundary sections of Denmark, most sition of sediment with an extremely high concentra brachiopods suddenly disappeared at the very end of tion of this element at the oceanic bottom. According the Maastrichtian Age simultaneously with plankton to the calculations of the lastmentioned authors, the extinction, although no notable reduction of their asteroid must have been as large as approximately diversity or abundance has been recorded in the 10 km in diameter and have moved with a velocity of underlying sediments [51]. Among bivalves, floating around 25 km/s. This catastrophic impact event and infaunal forms suffered a stronger stress than did should have negatively affected the biota and triggered with sessile taxa. On the other hand, mudeater and several major environmental changes. There are also carnivorous species appeared to be more resistant to other indications of impact events in boundary sedi unfavorable conditions. ments such as , glassy spherules or What is the evidence for natural events near the KT microtectites, tsunamites, and, most importantly, boundary? One such piece of evidence is the δ13С shift impact craters with the peculiar structure. The Chic determined by the reduced productivity due to mass xulub crater 180–280 km across and 65 Ma in age dis death of planktonic organisms. The δ18О measure covered on the shelf of the Yucatan Peninsula ments in planktonic foraminiferal tests from the west (Mexico) [41] was the first of such structures (Fig. 4). ern North Atlantic revealed a temperature rise by 6°С The discharge of dust into the atmosphere reduced in this region for the last 3 Myr of the Maastrichtian solar insolation and caused “cosmic winter,” which Age. Thus, in the Maastrichtian, cooling was replaced was responsible for the death of many terrestrial and by warming against a background of brief climatic marine organisms and distortion of trophic chains. oscillations. The KT boundary is marked by a peak in According to [9] the impact of a large asteroid should 87Sr/86Sr values, which is explained by enhanced negatively affect marine and terrestrial organisms weathering of land areas and influx of radiogenic owing to lowered illumination, temperature changes, strontium to the ocean by river runoff in response to acid rains, and fires. The planetary distribution of dust sealevel fall and expansion of continents. According clouds consisting of mineral particles discharged from to another hypothesis, this strontium maximum is the crater and constituting the cosmic body reduced related to the impact event and accompanying acid photosynthesis and distorted the entire trophic chain. rains that accelerated weathering [26]. This effect should have been strengthened by fires. The The crisis at the Cretaceous–Tertiary boundary is discharge of the water vapor because of the asteroid fall explained by different natural processes (impact events, into the ocean should result in the .

OCEANOLOGY Vol. 51 No. 4 2011 644 BARASH Cretaceous white limestone with large (approximately 0500 km0.6 mm across) planktonic foraminifers and overlain by Tertiary pinkish limestones (eugubina Zone) with rare small foraminifers. The boundary layer contains also magnetic iron spherules with spinel, which were presumably formed in the lower atmospheric layers under a small asteroid fall angle, and grains of shocked quartz, as well as rare fish teeth and agglutinated tests Chicxulub of benthic foraminiferal species (Textulariina spp.). Occasional calcareous Osangulariidae and Gavellinel Yucatan lidae tests show signs of dissolution. During accumu Peninsula lation of this layer in the lower bathyal zone at depths of 1500–1800 m, benthic foraminiferal communities were mostly composed of detritovore infaunal species resistant to anoxic conditions (Spiroplectammina spp.). This indicates the increased flux of organic matter to the bottom and corresponding decrease in the oxygen South Americ content. The duration of the period corresponding to accumulation of the boundary clay is estimated to be approximately 50 kyr. Nevertheless, the authors believe that the glauconite layer in the lower part of the boundary clay was deposited immediately after the mass death of marine plankton. The separated peaks of concentrations of quartz grains and iridium pro Fig. 4. Location of the in the Yucatan vided grounds for the assumption that at least two Peninsula. The arrow shows the position of the shoreline in impact events occurred at the KT boundary: one on the terminal Cretaceous. the continental crust, which is reflected in shocked quartz accumulation, and another in the ocean, The discharge of carbonate dust in the case of the resulting in deposition of iridium [40]. asteroid fall onto carbonate formations (as in the The first continuous boundary section obtained by Yucatan Peninsula) increased concentrations of car the special Chicxulub Scientific Drilling Project bon dioxide and sulfate aerosols in the atmosphere. appeared to be dissimilar to its counterparts from This should result in acid rains, a temperature rise by small craters [36]. The base of this section is repre several degrees, and destruction of the ozone layer. At sented by alternating melt and impact polymictic the same time, according to some calculations, sulfate with pyroxene, plagioclase, and alkali feld aerosols should have caused significant cooling, which spar microcrystals. The melt composition indicates then was replaced by the warming tendency. The that it originates from crystalline silicate rocks under hypothesis of the global distribution of fires at the KT lying the 3kmthick . Relict frag boundary is confirmed by the extremely high concen ments of these rocks contain impact quartz, granite– tration of soot in boundary clay sediments of Den granodiorite, metaquartzite, schists, micrite lime mark, Spain, and New Zealand. The asteroid blow stone, and mafites. They imply intense destruction of should have been accompanied by an energy release the crust. comparable with that from a 100millionmegaton Borehole Yax1 drilled 60 km away from the central explosion, which exceeds the world’s nuclear arsenal part of the Chicxulub crater up to a depth of 1511 mbsf by three orders of magnitude [8]. The impact hypoth in 2001–2002 penetrated a 100mthick impact brec esis is also confirmed by other evidence: the occur cia with fragments of crystalline rocks, glassy spher rence of shocked quartz, (silica dioxide that ules, and peculiar textural features that overlies the is formed under high pressure and relatively low tem normally occurring Cretaceous shallowwater lime perature), diamond microparticles, impact glass, Ni stone sequence 617 m thick. The age of the impact spinel, soot, tsunamites, and extraterrestrial amino event was inferred from the stratigraphic position of acids; the osmium isotope ratio; and elevated concen the layer relative to the Cretaceous–Paleogene trations of rhodium in KT boundary sediments of boundary, character of intermediate sediments, and many sections [12]. planktonic foraminiferal assemblages. In the opinion of the authors of [32], the late Maastrichtian Chicxulub The Gubbio outcrops in the Province of Perugia impact event corresponded with the eruption of Deccan (Italy) have been examined by many researchers. It traps, greenhouse warming (65.4–65.2 Ma ago), and was shown that the layer of the dark boundary layer gradual reduction of biodiversity during the last accumulated during a brief anoxic episode at the 700 kyr prior to the KT boundary and advanced by water–sediment interface. This layer is underlain by 300 kyr the mass extinction.

OCEANOLOGY Vol. 51 No. 4 2011 FACTORS RESPONSIBLE FOR CATASTROPHIC EXTINCTION OF MARINE 645

40°E50° 60° 70° 80° 90°

India 20°N

10°

Africa Carlsberg Ridge

0° Seychelles

INDIAN 10° OCEAN

20°

30°S

Fig. 5. Presentday position of the Carlsberg Ridge and segments of the Shiva crater separated by rifting (after [15], simplified).

Evidence in the form of microtectites geochemi ary. All these facts provided grounds for the conclusion cally similar to their counterparts from the Chicxulub that boundary from the Cretaceous to the Paleogene crater and close in age (within limits of 200 kyr) was was marked by several impact events: the Chicxulub also found in Haiti and in Mexico. The KT boundary asteroid fall prior to this boundary, a powerful impact sections in southern and northern Mexico 540 and event immediately at the boundary, and several slightly 600 km away from the Chicxulub crater are marked by less significant impacts in the early Danian and termi a strong magnetic anomaly, in addition to geochemical nal Maastrichtian ages (the is attributed anomalies: magnetic minerals reflect rapid cooling of to the last events). the hightemperature melt that resulted from the In six deepsea holes drilled on the Demerara Rise bolide fall [55]. In northeastern Mexico, the KT (western Equatorial Atlantic), the KT boundary is boundary section contains sediments left by powerful marked by a single thin (up to 2 cm) layer of Chicxulub tsunami (tsunamites) up to 6.1 m thick with glassy discharge products with characteristic lithological, spherules and ; deposition of these sediments is geochemical, and isotopic features [47]. The distribu related to the Chicxulub impact event [48]. tion of some components revealed its twolayer struc The complex stratigraphic and genetic study of ture. The authors believe that the latter reflects differ breccias near the KT boundary in their relations with ence between compositions of ballistic discharges the Chicxulub impact event [5] conducted in Texas in from the Chicxulub crater that produced most of the the United States, northern and southern Mexico, spherules and material of the evaporated cosmic body Guatemala, Belize, Brazil, and Haiti, as well as in drill that settled down from the atmosphere. This material cores from the Chicxulub crater, revealed that impact is concentrated in the upper part of the layer. It is also glassy spherules in all these areas are characterized by assumed that material transported from land contrib a similar geochemistry. In the opinion of the latter uted as well to accumulation of the layer under consid authors, iridium anomaly and mass extinction in all eration, in addition to Chicxulub discharges [19]. the sections are registered above the breccias horizon. The mass extinction at the KT boundary is proba In the northeastern Mexico and Texas sections, the bly related to the other catastrophic impact event, earliest discharges from the Chicxulub crater are regis which left the giant Shiva crater in the Indian Ocean tered approximately 300 kyr before the KT boundary. west of Bombay correlated with the same KT bound In some sections, the iridium anomaly is recorded in ary [15–17] (Fig. 5). The existence of the crater was Danian sediments, i.e., 100–200 kyr after the bound inferred from geophysical, structural, and drilling data

OCEANOLOGY Vol. 51 No. 4 2011 646 BARASH structures along the Panvel flexure that represents the arcuate crater segment on Deccan traps. It is marked Marine by a chain of hot springs, deep normal faults, seismic microfossils Magneto strati graphy ity, high geothermal gradients, and thinned lithos phere (31–39 km). According to seismic data, the basement topography beneath Deccan lavas west of the flexure is expressed as a cratershaped depression. The central rise is represented by the Bombay High 29N 150 km across composed of Precambrian granites and

Paleogene located between the western coast of , on the one side, and the Praslin and Mahe islands of the Sey chelles Archipelago, on the other. A trough surround ing the Bombay High is filled by Tertiary shallow water marine sediments over 5000 m thick overlying ? traps. Taking into consideration the thickness of 29R 600000 years Teeth of basalts, the integral depths of the depression should Basaltic flows and mammals exceed 10 km. Fish and amphibians When the Shoemaker–Levy 9 (S–L9) col lided with Jupiter, it disintegrated into 21 fragments, which fell onto the planet’s surface over five days. Such a situation may also have taken place during the for mation of craters at the KT boundary [15]. A giant Cretaceous 30N Dinosaurs asteroid may have disintegrated into two large frag Planktonic ments: a 40km fragment formed the Shiva crater and foraminifers its 10km counterpart the Chicxulub crater. An addi tional impact event at that time occurred, probably, on the Pacific Plate, which is evident from the finding of Fig. 6. The schematic structure of the Deccan traps and some of their stratigraphic characteristics (after [12, 39], a small fragment of a bolide, Ni spinel (87% of Ni), modified). and elevated concentrations of iridium at the KT boundary in the DSDP Hole 576 section; in five neighboring holes, the KT boundary is also marked by on the Indian–Seychelles Plate. This buried elongated elevated iridium concentrations, glassy spherules, and crater is 600 × 450 km in size and 12 km deep may be shocked quartz [37]. the largest Phanerozoic . Its age is Thus, according to these data, fragments of a large determined by correlating with the base of the Deccan disintegrated asteroid or comet, Shiva and Chicxulub lava section, overlying Paleogene sediments, isotopic included, successively hit the Earth. Some of them dating (65 Ma), and rifting event (paleomagnetic may have fallen into the ocean. These catastrophic Chron 29R) in the Carlsberg Ridge that divided the events, which happened during a brief period lasting, crater in two parts. The crater is characterized by a probably, a few days, resulted in significant environ peculiar configuration in the form of a depression with mental changes that caused mass death of the oceanic a central rise, ringshaped trough, and surrounding and terrestrial biotas. It should be noted that Chatter rim. The elongated shape of the crater and asymmet jee’s hypothesis concerning the Shiva asteroid and its rical distribution of melted discharge products indi consequences needs confirmation by factual data. cate the oblique strike of the cosmic body from the The sedimentary layers between flows of Deccan southwest toward the northeast. The lastmentioned trap lavas enclose bones and eggs of dinosaurs, author assumes that, approximately 65 Ma ago, a although no such finds are known so far above traps. meteorite 40 km in diameter hit the continental shelf This means that eruption of basalts proper had no fatal of India to form the Shiva crater, damage the lithos effect on dinosaurs. The Deccan traps began erupting phere, and provoke rifting between India and Sey prior to the Shiva impact event [11, 39] (Fig. 6). The chelles. asteroid strike may have shaken the mantle and sharply This author also mentions thick tsunamites at the accelerated eruption precisely at the KT boundary, KT boundary in Somalia and Kenya as an additional which enhanced the catastrophic impact on the biota. evidence of this impact event. Other researchers [7] Deccan trap volcanism may have played a substan argue that the eastern surrounding segment of the cra tial role in primary destruction of the global trophic ter is located along the western coast of India, where it chain. Release of harmful substances during eruption is overlain by Deccan traps. In their opinion, the aster of large lava volumes may have destroyed the oceanic oid strike was so strong that provoked melting of biota. Several trillion tons of toxic gases (SO2, HCl, asthenospheric basalts, which formed lava lakes. СО2) and ash may have been discharged into the upper Chatterjee [14] identified the eastern surrounding atmosphere, which would have affected its global cir

OCEANOLOGY Vol. 51 No. 4 2011 FACTORS RESPONSIBLE FOR CATASTROPHIC EXTINCTION OF MARINE 647 culation and caused cooling, acid rains, and alkalinity and pH drop in surface waters, as well as reduction of the ozone layer, this being destructive for marine and ? terrestrial ecosystems [25]. The temperature fall related to sulfate aerosols was, in contrast, compen sated for by its rise caused by greenhouse gases such as СО2. Gases, except for СО2, are rapidly (from a few months to 10 years) removed from the atmosphere and may influence weather, not longterm climate [56]. The trap layers are found to contain evidence of green house conditions, which became subsequently more severe with notable seasonal fluctuations and aridity [46]. There are also other, in addition to the abovemen tioned, impact craters formed at that period. The cen tral part of the Ukrainian crystalline shield (48°45′N, 32°10′E) hosts the Boltysh crater, which is now buried under sediments, Quaternary included, 30 m thick. Its 50 km structure and composition of filling sediments are rather well known owing to many boreholes and geo Fig. 7. The ring structure of the Kara crater inferred from physical investigations. The Boltysh impact structure gravimetric data [43]. represents a 24 km across with a central rise and approximately 1 km deep. Its discharge prod ucts cover an area at least 25000 km2 in size. The shock Russian and foreign researchers [10, 53, and others]. melt forms a “lake,” i.e., a ring shield up to 220 m The sediments of the crater contain shocked glass and thick that surrounds the central rise. The melt is over quartz grains. The crater is buried under a thick cover lain by a zuevite layer 12–97 m thick. According to of glacial sediments, although river erosion locally Ar–Ar dating, the age of the melt is estimated to be recovered breccias and impact melt. According to 65.17 ± 0.64 Ma, i.e., practically analogous to that of gravimetric data, the Kara crater represents a structure the Chicxulub impact event, which corresponds to the approximately 120 km across with a positive central KT boundary. The crater was formed in subaerial con anomaly and surrounded by a negative ring anomaly, ditions. It is filled with sediments ranging from the in which outcrops were found (Fig. 7). The Paleogene–Neogene in age to Quaternary loesses and crater depression between the central rise about 10 km containing diverse faunal and floral remains [24]. across and surrounding swell is occupied by a breccias In Iowa of the United States (42°35′N, 94°33′ W), a sequence 1–2 km thick. Frankel notes that the Kara ring structure 35 km in diameters () crater is approximately 66 Ma in age [22], although the filled with intensely deformed sedimentary sequences , University of New Brun is recovered by drilling under a 100mthick layer of swick, cites the date of 70.3 ± 2.2 Ma. glacial sediments [22]. The structure is surrounded by an external ring >10 km wide composed of uplifted Analysis of seismic records obtained during oil and eroded upper sedimentary layers. Geophysical exploration work in the North Sea near the England investigations revealed that the central part of the coast revealed the Silverpit 20 km in structure is occupied by an uplift of the crystalline diameter and, possible, 60–65 Ma in age [50]. The basement 12 km across. The vertical displacement is crater exists under sedimentary cover up to 1500 m equal to approximately 4 km. The basement rocks thick at a water depth of 40 m. It is assumed that it was contain shocked quartz, and the central rise is sur formed in water depths of 50–300 m. The impact rounded by breccias. In the surrounding rim, older nature of this structure is evident from development of layers rest upon younger sediments, which is charac the central rise. The crater is approximately 3 km teristic of crater discharge products. It is thought the across near the top of Cretaceous strata. Judging from Manson crater was formed at the end of the Creta the crater size, it was formed by the strike of an asteroid ceous. The Earth Impact Database (PASSC) cites the approximately 120 m in diameter. It is assumed that the age of the crater as 73.8 ± 0.3 Ma. Frankel mentions crater is as old as 65–60 Ma, although the lastmen that shocked feldspar from this crater was dated in tioned authors infer its age from more careful analysis 1988 by the Ar–Ar method back to 65.7 ± 1.0 Ma, of seismic material to be 74–45 Ma. If its age is, in which correlates this event with the KT boundary. fact, close to 65 Ma, which approximately corre Further evidence of the impact event (Kara crater) sponds to that of the other abovementioned impact is located near the Ob estuary on the Arctic coast of events, the crater may have resulted from the strike of Russia (69.6°N, 64.9°E). It was discovered in the one of the asteroids that bombarded the Earth near the 1970s, and since that time it has been visited by many KT boundary.

OCEANOLOGY Vol. 51 No. 4 2011 648 BARASH There are other buried craters found in different explained by deterioration of climatic conditions or parts of the world. One of them, the Eagle Butte crater changes in water mass circulation. 10 km across, is in the Alberta Province of Canada (49°42′N, 110°30′W). Several impact structures have The “J” layer appeared to be vertically heteroge been recorded in Brazil. For example, the Vista Alegre neous in many aspects. Its lower part differs from the crater 9.5 km in diameter is reported from the state of upper one in higher concentrations of As, Zn, Cu, Pb, Parana (25°57′S, 52°41′W). Both these structures are Cr, Ir, Co, V, and Ni. In the opinion of the lastmen presumably <65 Ma old (Paleocene or older), i.e., tioned authors, the high As concentration cannot be approximately correlative with the KT boundary [18]. explained in the context of the asteroid hypothesis, since its content in is low. The layer Thus, this review shows that several large craters, encloses four iridium anomalies: one welldeveloped such as Chicxulub, Shiva, Boltysh, Silverpit, and, at the KT boundary, as well as below and above the lat probably, Manson, were formed near the KT bound ter. The authors believe that these anomalies may have ary. Several others resulted from an impact event that been produced by volcanism, in addition to cosmic occurred either at or near the KT boundary. Inasmuch factors. Changes in the mineral and chemical compo as the World Ocean substantially exceeds in size the sitions of sediments also reflect variations in deposi continental block of the Earth, most asteroids should tional environments during accumulation of the “J” have fallen into the oceanic realm, where searches for layer. Inasmuch as Ni spinel occurs in the cosmic dust their traces are hampered. It is undisputed that, at the and micrometeorites, its presence in the “J” layer is Cretaceous–Paleogene boundary, the Earth collided not necessarily indicative of a large impact event. Dia with many cosmic bodies. mond crystals and Ni spherules may have been formed Some researchers have analyzed oceanic and ter from cooled products of destructed meteorites. Varia restrial evidence (based on foraminifers and plant tions in 18O and 13C demonstrate a significant negative remains, respectively) of temperature variations prior shift (from 5 to 23‰ PDB for 18O) within the “J” layer to the KT boundary and shown their coincidence in below the level, which is correlated with the impact different world areas [57]. A particularly distinct ten event. The foraminiferal genera became extinct below dency for warming is characteristic of the period this layer, which may indicate contamination of waters beginning from 66.0–65.9 Ma ago with an optimum with As from volcanic aerosols against a background of approximately 65.8–65.6 Ma ago and subsequent anoxic conditions. The middle part of the boundary cooling immediately before the KT boundary. The layer barren of foraminifers is overlain by sediments, lastmentioned authors interpret these data as demon which are related, in the opinion of the authors, to the strating a global climatic shift. These results are con impact event. Eventually, these researchers arrived at sistent with the recent data on рСО2 from carbonates the conclusion that biotic changes were caused by vol of paleosoils in Canada, southern France, and other canism, while the fall of a cosmic body happened areas, which confirm almost doubling of рСО2 values 500–800 ka later. for ~0.5 Myr prior to the KT boundary and a return to low values immediately before the latter, its insignifi An alternative interpretation of these data is also cant variations or stability at the boundary between the possible. The practically global distribution of the Cretaceous and Paleogene, and again almost doubling boundary layer, its peculiar lithology, and similarity of during the period of ~1.5 Ma after the boundary. These main characteristics in different sections show that it data confirm close relations between рСO and tem was formed with specific conditions in common, 2 which were characteristic of the entire Earth’s surface. perature. One of the СО2 sources was likely repre sented by volcanism of the Indian Plate. Now (as well as in the Late Quaternary), no such sed iments are deposited and no such conditions exist, Recently, the Cretaceous–Paleogene boundary which prevents both determination of sedimentation was thoroughly studied in sections near Gams in the rates and estimating the duration of the corresponding eastern part of the northern Alps (Austria) [23]. The period based on a real comparison. Some researchers boundary layer “J” from 1 to 5 cm thick in different assert that it may have lasted from several months to outcrops was sampled every 2–3 mm with subsequent several hundreds of years. Regardless of the origin of study of the samples by paleontological, mineralogi accumulating material (volcanic or cosmic), on its way cal, granulometric, geochemical, isotopic, and petro to the bottom it should be differentiated by its “buoy magnetic methods. The adjacent uppermost Maas ancy,” which depends on the size, specific weight, and trichtian and basal Paleogene sediments were also ana shape of particles. As is known from experiments, lyzed. some siltsized (0.05–0.1 mm) mineral particles sink Analysis of foraminiferal assemblages revealed in freshwater with a velocity of approximately considerable decrease in their abundance and diversity 5 cm/min and may reach the bottom at a depth of 4 km 4 cm below the “J” layer. Immediately under this layer, (characteristic of the ocean) after 1.5–2.0 months [1]. some species, such as Contusotruncana contusa var. sin Finer materials of aerosols, which, as is assumed, sat istralis and Globotruncana rosetta, increased the abun urated the atmosphere during accumulation of the KT dance of their sinsitral specimens, which was probably boundary layer, should sink even more slowly.

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Under conditions of a normal biological trophic Regression + Volcanism+ Impact structure, the main share of finely dispersed material is Cooling concentrated by filtering zooplankton in fecal pellets and reaches the bottom substantially faster with a velocity of 40–440 m/day [4]. In the case of mass death of phyto and zooplankton at the Cretaceous– Time Paleogene boundary, the mechanism of pellet forma Т tion was, however, dysfunctional. The material sinking К Moderate Mass process was slower, and sedimentary material experi extinction extinction enced longer and stronger differentiation. Therefore, Minor it is natural that the lower and upper parts of the “J” extinction boundary layer in the Gams outcrops, as well as in other sections, differ in many characteristics. In addi Intensity tion, some researchers believe that the boundary layer was to a variable extent formed from discharge prod Fig. 8. Combination of factors responsible for extinction of ucts of the impact event that were transported during a organisms at the Cretaceous (K)–Tertiary (T) boundary [39]. long period from land [15, 47, and others]. The same scenario should also be characteristic of finely dis persed volcanic material. extinct first and more tolerant forms later. Neverthe less, mass extinction of six groups of oceanic microor As was noted, in the Gams sections, a significant ganisms (planktonic and benthic foraminifers, cocco decrease in abundance and diversity of foraminiferal liths, radiolarians, dinoflagellates, and diatoms), bra assemblages is recorded 4 cm below the “J” layer [35], chiopods, ammonites, belemnites, and marine reptiles which is explained by water poisoning with As from precisely coincides with the impact event. Drastic volcanic aerosols against a background of an anoxic changes in floral communities implying a common condition [23]. At the same time, the growth of As cause of extinction of marine and terrestrial organisms concentration is registered higher, directly at the KT are also consistent with the impact hypothesis [54]. boundary, in contrast to Ir and Sr, the content of which increased precisely 4–5 cm below the latter [23, Lethiers [39] justly considers that both factors that pp. 46–47]. Regardless of the order of volcanism and influence the biota gradually and over a relatively long the impact event or their simultaneous effect, what is time and powerful brief impacts of large asteroid falls important is the fact that, according to the available should be taken into considerations when interpreting data [23], both these phenomena took place and events at the KT boundary (Fig. 8). affected the biota. The analysis of available information shows that The harmful consequences of intense volcanic the relatively short period (hundreds of thousands to a eruptions and impact events are somewhat similar to few million years) in the terminal Cretaceous was each other, although the former, such as, for example, marked by a combined influence of several factors, trap eruptions, occur over long periods and their influ some of which were mutually independent (tectonic ence is, correspondingly, gradual and prolonged (for movement, orbital oscillations, sealevel and climatic tens to hundreds of thousands of years). Changes in fluctuations, volcanism, asteroid falls, changes in the other processes (temperature fluctuations, sealevel composition of the atmosphere and hydrosphere, and oscillations, СО2 concentrations and other compo probably others such as cosmic radiation, supernova nents of the atmosphere, structure and chemistry of explosion, magnetic reversals, and others). This water masses, tectonic movements, and others), which implies a common cause of a higher order originating distorted the ecological equilibrium, were also grad beyond the limits of the Solar System. ual. At the end of the Cretaceous Period, these factors The hypotheses of biota mass extinction on the were responsible, along with volcanism and probably Earth in response to impacts of asteroids or comets weak impact events, for gradual or stepwise degrada offer an opportunity to correlate astrophysical, global tion and even extinction of some marine organisms. In geological, and biotic evolutionary processes. Mass contrast with these factors, powerful impact events are demonstrate a periodicity of approxi very rapid. The catastrophic events at the KT bound mately 26–30 Ma. Some researchers suggest a similar ary were, consequently, determined mostly by falls of periodicity for impact crater formation as well. The large asteroids. last pulses of impact events occurred 2–3 and approx Deccan volcanism commenced prior to the impact imately 35, 65, and 95 Ma ago. The astronomical event, but an enormous bolide strike could shake the mechanism responsible for such pulses may be pro crust and mantle to increase sharply volcanic dis vided by the motion of the Earth through the Milky charges precisely at the KT boundary [11]. The large Way and periodic intersections of Galactic arms dur impact event could serve as a triggering mechanism of ing which the Earth experiences attacks of density the main phase of the ecological crisis of >10000– waves, which affect both its tectonic and biological 100000 years [28]. Less resistant organisms became evolution [52]. The rotation of the Solar System

OCEANOLOGY Vol. 51 No. 4 2011 650 BARASH around the Galactic Core causes oscillations, i.e., 14. S. Chatterjee, New Concepts in Global Tectonics, Ed. by deviations from the Galactic plane with a halfcycle of S. Chatterjee, N. Hotton, and N. Lubbock (Texas Tech. 30 ± 3 Myr. This cyclicity should result in quasiperiod Univ. Press, Texas, 1992), pp. 33–62. ical intersections of interstellar clouds and changes of 15. S. Chatterjee, “Multiple Impacts at the KT Boundary Galactic tidal forces with a peak during the intersec and the Death of the Dinosaurs,” in Proc. 30th Intern. tion with the Galactic plane. These events may be Geol. Congr. 26, 31–54 (1997). responsible for substantial perturbations in motion of 16. S. Chatterjee, N. Guven, A. Yoshinobu, et al., “The comets, producing their intermittent flow inside the Shiva Crater: Implications for Deccan Volcanism, Solar System. 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