(k/t) boundary. a 15-m section

PALEOCEANOGRAPHY, VOL. 1, NO. 2, PAGES 97-117, JUNE 1986

THE CRETACEOUS/TERTIARY BOUNDARY EVENT IN THE NORTH PACIFIC:

PLANKTONIC FORAMINIFERAL RESULTS

FROM DEEP SEA DRILLING PROJECT

SITE 577, SHATSKY RISE

Jennifer Gerstel and Robert C. Thunell

Department of Geology, University of South Carolina, Columbia

James C. Zachos and Michael A. Arthur

Gr-aduate School of Oceanography, University of Rhode Island, Kingston

Abstract. A detailed micropaleontologic analysis of sediments from Deep-Sea Drill- ing Project site 577 from the Shatsky Rise, North Pacific, was undertaken to describe extinction and radiation patterns of planktonic foraminifera in a continuous carbon-

ate sequence spanning the Cretaceous/ Tertiary (K/T) boundary. A 15-m section containing the boundary was closely sampled and contained planktonic foraminiferal assemblages characteristic of the late Maastrichtian Abathomphalus mayaroensis zone through the Danian Globorotalia uncinata zone. The Cretaceous/Tertiary boundary was placed at the abrupt disappearance of almost all Maastrichtian planktonic foraminifera. Coincident with these

extinctions was the presence of a large number of "microtektitelike" spherules. The most important faunal change in the late Maastrichtian was an abrupt increase in the relative abundance of the high- latitude species Hedbergella monmouthensis, together with the appearance of diminutive populations of Guembelitria cretacea and Globigerina eugubina approximately 20,000 years before the boundary. These changes are interpreted as indicating a cooling of surface water conditions. Globigerina

Copyright 1986 by the American Geophysical Union

Paper number 5P0863. 0883-8305 / 86/005?-8306510.00

eugubina and G. cretacea were the only planktonic foraminiferal species to survive the Cretaceous/Tertiary boundary event at this locality. The 60-18 and •C-13 values of G. eugubina from below the K/T boundary are nearly the same as those from above the boundary, but in both cases the 60-18 values indicate relatively cooler paleotemperatures than those from other coexisting planktonic foraminiferal species. In addition, the •C-13 values of G. eugubina are lighter than those of the other planktonic foraminifera. Such a relationship might suggest that G. eugubina lived in cooler, shallow intermediate water masses advected from higher latitudes during a latest Maastrichtian cooling episode. Better preservation of planktonic foraminifera, a progressive change in the •C-13 of benthic foraminifera, and a brief positive excursion in •C-13 of the carbonate fine fraction and of planktonic foraminifera within 20 to 30 cm below the K/T boundary all suggest important paleoceanographic changes that preceded the extinction event. A large population of aberrant G. eugubina and Eoglobigerina was observed in the earliest Danian. These forms are charac-

terized by the development of secondary apertures, bullae, and abnormal final chambers. These abnormal morphotypes are considered to be ecophenotypic variants reflecting ecologic stress or instability in the earliest Cenozoic marine environ-

ment.

98 Gets tel et al.- Cretaceous/Tertiary Boundary Planktonic Foraminifera

INTRODUCTION

The rapid faunal and floral changes that occurred near the Cretaceous/Tertiary (K/T) boundary represent the most dramatic bio- logical turnover that can be studied in deep-sea sediments. It has been well documented that planktonic foraminifera and coccolithophorids underwent rapid and widespread extinction at the K/T boundary [Loeblich and Tappan, 1957; Bramlette, 1965; Tappan and Loeblich, 1973; Tappan, 1982], although Perch-Nielsen et al. [1982] and Smit and Romein [1985:] have suggested that the mass extinctions of these two

groups were not simultaneous. Toward the. end of the Cretaceous, planktonic foraminiferal diversity was very high, perhaps higher than at any other time• in the past [Cifelli, 1969]. Many multichambered, morphologically ornate forms as well as a diverse stock of serial forms have been

described from shelf and deep marine sections of this age [Bolli, 1957; Blow, 1979]. Stable isotopic studies [Saito and Van Donk, 1974; Douglas and Savin, 1975; Boersma et al., 1979; Boersma and Shackleton, 1981] suggest that this diverse Late Cretaceous assemblage lived in a warm, stable habitat and that the different mor-

phologic forms occupied discrete depth- stratified niches.

While the massive extinction of planktonic foraminifera that occurred at the K/T

boundary was by far the most severe in the history of Globigerinacean evolution, it was by no means unique in character. The ecologic and evolutionary significance of the selective extinction and survival of

certain morphologic forms has been recog- nized for many years [œifelli, 1969]. Iterative evolution, the repetition of evolutionary trends, which• often results in diachronous homeomorphy, is a well- documented phenomenon of planktonic foraminiferal phylogeny [Cifelli, 1969; Steineck and Fleisher, 1978; Caron and Homewood, 1983]. Recent theories have suggested that this repeated occurrence of certain morphotypes is attributable to successive attempts to invade deeper water habitats [Douglas and Savin, 1978; Hart, 1980]. Periods of stress are characterized by oligotaxic assemblages [Fischer and Arthur, 1977] composed of primitive, oppor- tunistic species. The heartlest group of planktonic foraminifera are the simple globigerine morphotypes [Cifelli, 1969]. Highly ornate forms tend to be associated with tropical provinces in the modern

ocea•n, while globigerine forms are characteristic of boreal or higher-latitude regions [Cife!!i, i969]. •us the extinction of tropical forms and invasion of boreal forms may be associated with climatic instability or cooling. The extinctions at the end of the Cretaceous, which included all Globotruncanidae and most Hetero-

,

heliCidae, illustrate the selectivity of extinction in planktonic foraminifera. Selectiwe survivals have been reported for the boreal species Hedbergella monmouthensis [01ss•n, !964; smit, 1982; Bøersma, i984], for Glo.botruncane!la caravacaensis and Globigerinelloides

'• 1982] and for Guembe- mess•nae ISmit, , litria cretacea, a simple, diminutiv e species 'ismit, 1982].

Many scenarios as to the nature of the event which may have ended the Mesozoic era have been proposed, including (1). global coo.ling [Hay, I960; Saito and Van Donk, 1974], (2)• rapid temperature increase [Emiliani et al , 198I; Romein and Smit, 1981], (3) injection of fresh water into the world ocean [Gartner and Keany, 1978; Thierstein and Berger, 1977], (4) rise of the carbonate compensation depth (CCD)into the photic zone [Worsley, 1974], (5) in- tense volcanic activity [Vogt, 1972; McLean, !982; Officer and Drake, 1985], and (6) the impact of a large extraterrestrial body such as an asteroid with the earth [Alvarez et al., 1980].

Alvarez et al. [1980] proposed their asteroid impact theory after the discovery of anomalously high concentrations of iridium and other platinum group elements in the K/T boundary section at Gubbio, Italy. Since these elements are depleted in the earth's crust and mantle in relation to

their concentrations in average solar mate- rial, the high concentrations at the boundary can be attributed to an extraterrestrial source. Excursions in iridium concentrations have since been found in at

least 48 boundary sections [Alvarez et al., 1984], but the source of the high iridium concentrations has been questioned [Officer and Drake, 1985].

PLANKTONIC FORAMINIFiE•L BIOSTRATIG•HY OF

THE LATE MAASTRICHTIAN AND DANIAN

Many workers have contributed to the development o.f globally correlative planktonic foraminiferal biostratigraphic zona- tions for the time period surrounding the Cretaceous/Tertiary boundary (Figure 1). Many of these zones were originally de-

Gerstei et al.: Cretaceous/Tertiary Boundary Planktonic Foraminifera 99

• SPAIN & TRINIDAD ITALY GERMANY TUNI SIA SCANDINAVIA

AGE (Bolli, 1957 (Luterbacher & Premoli Silva, (Herm et al,, 1981) (Smit, 1982) (Malmgren, 1982) and 1966) 1964)

G. uncinata G. uncinata G uncinata G. uncinata •

G. trinidadensis G. trinidadensis G. trinidadensis G. trinidadensis •

•' G. compressa G, pseudo- • • Z G. pseudo- G. pseudo- . . . bulloides • • • bulioides bulloideS • •" Z G. edita • E. •

'UJ t,-t • ' ' " ' t a u r i c a • G. eugubina G. eugubina G, eugubina '•

.• . G. frin , • G. cretacea •

G. stuarti . P. elegans-

•.• •'• R fructicosa • A mayaroensis A mayaroensi s A. mayaroensis

• ½• A. mayaroensis 0 • R. fructicosa

I I I

Fig. 1. Comparison of various planktonic foraminiferal biostratigraphic zones for the late Maastrichtian and Danian.

scribed and defined by Bolli [1957, 1966] from various sections in Trinidad. Subse-

quent workers have documented differences in late Maastrichtian planktonic foraminiferal faunas from boreal and temperate regions [Blow, 1979; Malmgren, 1982]. The latest Maastrichtian is generally recog- nized by the Abathomphalus mayaroensis range zone [Bolli, 1966], but correlations

[1964] first described the Globigerina eugubina zone from the Central Apennines of Italy and interpreted this interval as representative of the basal Tertiary. Since that time, Herm et al. [1981] have identified an "earlier" Tertiary zone, the Globigerina fringa zone, which occurs just below the G eugubina zone. In contrast, Smit [1977, 1982] concluded from studies of

between high- and low-latitude sections are the E1 Kef section in Tunisia and the often difficult because of the frequent absence of both the nominate taxa and

Globotruncana spp. in high latitudes [Berggren, 1962; Olsson, 1964; Malmgren, 19821.

The zonation of the earliest Danian has

been subject to many emend•ations and modi- fications due to refinements in chrono-

stratigraphic correlations and detailed biostratigraphic studies of more complete

Gredero section in southeast Spain that the basal Tertiary consists of a zone containing G. cretacea and perhaps G. messinae and H. monmouthensis. This G. cretacea zone of

Smit [1982] occurs below the G. fringa zone of Herm et al. [1981].

There has been a great deal of specula- tion as to which Late Cretaceous planktonic foraminifera survived the boundary event and gave rise to the various Cenozoic

geographically widespread boundary sections lineages. Olsson [1964] concluded that (Figure 1). Luterbacher and Premoli Silva H. monmouthensis, a boreal form, may have

100 Gerstel et al.: Cretaceous/Tertiary Boundary Planktonic Foraminifera

50 ø

40 ø

30 ø

20 ø

10 ø

130 ø 140 ø 150 ø 160 ø 155 ø 165 ø

HOKKA

RISE

165 o

40 ø

30 ø

• N.W. PACIFIC OCEAN

40 ø

30 ø

Fig. 2. Site location map showing the position of the Shatsky Rise it: the northwest Pacific and the location of DSDP site 577 on the southeastern flank of the rise [modified from Douglas and Savin, 1975].

survived the boundary crisis and given rise to the Cenozoic species. Smit [1982] contends that the cosmopolitan species G. cretacea, a small, hispid, high-spired form, may have been the sole Maastrichtian species from which all Cenozoic planktonic foraminifera evolved.

In the present study the large-scale extinction and subsequent radiation of planktonic foraminifera during the late Maastrichtian to Danian are described on

the basis of a detailed analysis of sediments from Deep-Sea Drilling Project (DSDP) site 577, located on the Shatsky Rise in the North Pacific.

SITE DESCRIPTION

The Shatsky Rise is a large aseismic plateau located in the northwest Pacific (Figure 2). While most areas of the Pacific basin generally lack a thick sequence of carbonate sediments, the Shatsky Rise is capped by 1000 m of Late Jurassic to Recent calcareous sediments [Matter et al., 1975].

DSDP site 577 (32ø26.1'N, 157ø43.40'E) was hydraulically piston cored three times during leg 86 with the objective of obtain- ing an undisturbed sequence from across the

Cretaceous/Tertiary boundary. Hole 577 was cored in a water depth of 2675 m and a total of 111 m of calcareous nannofossil

ooze was recovered. The core penetrated to 118.8-m subbottom depth, and an undisturbed record of the Late Cretaceous-early Tertiary is contained in the bottom 20 m of this sequence.

The Danian sequence at hole 577 is interrupted by an 80-cm section of displaced upper Maastrichtian sediments, ex- tending from 105.0-m to 105.8-m subbottom depth. Danian sediments are found above this interval, with no discernible temporal interruption in sediment accumulation. The Cretaceous sediments probably represent a slump deposit originating from a topograph- ically higher area on the Shatsky Rise.

METHODS

Hole 577 was sampled at intervals rang- ing from 10 cm to 2 cm, providing us with a sample spacing of 10,000 years or less. In preparation for micropaleontologic analysis, samples were dried, weighed, disag- gregated with a hot calgon solution, and wet sieved through a 63-Bm screen. The >63-Bm portion of the sample was reweighed and dry sieved on a 150-Bm screen.

Gerstel et al.: Cretaceous/Tertiary Boundary Planktonic Foraminifera 10I

Relative abundances of planktonic foraminiferal species were calculated from ran- dom splits of 300 or more specimens ob- tained from the >150-Bm size fraction. Specimens of individual planktonic foraminiferal species were identified and coun- ted from each of a total of 99 samples. We realize that counting the 150-Bm fraction results in biasing toward the larger species, but this is the standard size fraction'used in most quantitative micropaleon- tological studies. The 63-Bm to 150-Bm fraction of each sample was scanned to check for the presence of diminutive species which did not occur in the larger size fraction. Relative abundances of the dif-

ferent planktonic foraminifera in this smaller size fraction were not calculated.

In addition, the number of "microtektitelike" spherules [Smit and Romein, 1985] and the presence of "micarb" particles were determined for each sample. Smit and Romein [1985] have shown that the microtektitelike spherules found at site 577 are composed primarily of glauconite and magnetite. The micarb particles consist of aggregates of subhedral to euhedral micritic particles and are produced through dissolution and reprecipitation of carbonate [van der Lingen and Packham, 1975].

Carbonate accumulation rates were calcu-

lated using the gamma ray attenuation porosity evaluator (GRAPE) wet bulk density and porosity data provided by DSDP for the core, and percent carbonate data. Absolute ages were assigned to stratigraphic levels from hole 577 using the available paleo- magnetic stratigraphy [Bleil, 1985] and the polarity time scale of Berggren et al. [1985]. Sedimentation rates were assumed to be constant between paleomagneticdatums.

Using this time framework the Danian planktonic foraminiferal data were used to calculate the rate of faunal turnover (Rt) as defined by Sepkoski [1978]. The rate of faunal turnover is a a function of speciation and extinction and can be used as a

measure of relative stability in faunal assemblages.

This rate is calculated as

1 •t 1 E Rt = ( 5X ) + (•X•) where D is the number of taxa, S is the number of speciations that occurred during a time intervalAt, and E is the number of extinctions during that time interval. A duration of 100,000 years was selected for At.

Stable isotopic analyses were carried out using the techniques described by Zachos et al. [1985]. All isotopic results are reported as per mil deviations from Pee Dee Belemnite (PDB) standard. Precision of isotopic analyses is better than +0.11 per mill for oxygen and +0.08 per mil for carbon.

RESULTS

Faunal Results

Fifty-two species of planktonic foraminifera were identified from 15.2 m of late

Maastrichtian and Danian sediments from

site 577. Twenty-nine of these species are typical of the upper Maastrichtian A. mayaroensis zone, with the other 23 species being characteristic of the Danian G. eugubina through Globorotalia uncinata zones [e.g. Luterbacher and Premoli Silva, 1964; Bolli, 1966; Stainforth et al., 1975]. The biostratigraphic ranges of these taxa are shown in Figure 3. Except for those of G. cretacea and G. eugubina, these ranges are based on the presence or absence of a species in the >150-•m fraction. The ranges for G. cretacea and G. eugubina are based on their occurrence in the >63-Bm fraction. The Cretaceous/ Tertiary boundary was placed at 109.09 m on the basis of a complete species turnover in the >150-Bm portion of the samples. Spe- cifically, all species from the genera Globotruncana, Heterohelix, Pseudo- textularia, Pseudoguembelina, and Prae- globotruncana, which flourished in the late Maastrichtian, as well as the genera Hed- bergella, Abathomphalus, Trinitella, Racemiguembelina, and Rugoglobigerina, which occurred in lesser abundances, last appeared at this particular level (Figures 3 and 4). The K/T boundary was placed at the same level by Monechi [1985] on the basis of an abrupt increase in the frequen- cy of Thoracosphaera and the first occurrence of small Biscutum romeinii, a nannofossil described from the lowermost Paleo-

cene of the E1 Kef section [Perch-Nielsen, 1981]. However, as was demonstrated by Perch-Nielsen et al. [1982], many Creta- ceous coccoliths survived the K/T boundary event and persisted into the early Danian.

The most significant changes in the Maastrichtian assemblage prior to the boundary extinctions are a sudden increase in the abundance of H. monmouthensis about

16 cm below the boundary (Figure 4), and the simultaneous introduction of diminutive


SUBBOTTOM DEPTH, meters

I I I I I I I I I I i I I I I , I

o o o o ß o ß ß o o o ß o o o o o o o o o o ooooooo©ooeeoeIelee eee© •©©eeeeeee© eee ooooo oooe eeeee eee e-©©© ©ee©eee.eeee© •

Zto.

o • •

o

•Rugoglobigerina fugosa Rugoglobigefina r.otundata Pra e glo b o truncan a p e t a Io id e a

- - Praeglobotruncana havenensis Praeglobotruncana citae

-- Ventibrella glabrata -- Ventibrella eggeri

Pseudo,rex tularia elegans -- Pseudotext•ularta carseyae

Pseudot.extularia brown• Pseudoguembelina polypleura Pseudoguembelina palpebra Pseudoguembelina excotata Pseudoguembelina costellifera Pseudoguembelina costara Gl•obotruncana stuart• stuartiform•s Globotruncana stuart• stuarti

Globotru.ncana rosetta

Globotruncana ganserr• • Giobotruncana gagnebin•

- - Globotruncana contusa

- - .• Heterohelix carinata Heterohelix globulosa --- Heterohelix moreman•

Heterohelix str•ata

.... Racemiguernbelina fruct•cosa - - Trinitella scott•

-- - Abathomphalus mayaroens•s Hedbergella monrnouthens•s _ _ _

Guembehtrla cretacea

G!ob•gerina eugubina .... aberrant G. eugubina ....

Globigerlna tetragona -- - Eoglobigerina eobulloides •

Eoglobigerina edita Chiloguembelina taurica r. . _ Guembehtria irregularis ........

Chiloguernbelina rnidwayensis - - Chdoguembelina hornerstownens•s •

Globigerina triloculinoides Globorotalia pseudobulloides

Globorotalia trinidadensts - - - Globigerina •'nconstans ............

Globigerina rninutula - - Globorotalia compressa --

Globorotalia uncinata .. -

Globorotalia prae cursoria - Globorotalia angulata

Globorotalia ehrenbergi Globigerina daubiergensis - --

Globorotalia praequa Globigerina trivialis _

A. mayaroensls G. trlnidadensls

Late Maastr•½htlan G. eugubina L . pseudobulloides

G. unclnata

Dania•

Fig. 3. Late Maastrichtian. Danian planktonic foraminiferal range chart for site 577. The ranges for all species except G. eugubina and G. cretacea are based on occurrence in the greater than 150-Bm size fraction. The ranges for these two particular species are based on their occurrence in the greater than 63-Bm size fraction. Subbottom depth, sample position, and foraminiferal preservation are indicated on the left.

populations (<150-Bm) of •, eugubina and truncana, members of the family Globotrunc- G. cretacea (Figure 3). N ø other "Danian" anidae, tended to decrease in abundance foraminifera were observed below the bound• relative to Heterohe!icidae (including ary. Globige•ina eugubina and G. cretacea Pseudotextularia, Heterøhelix, and Pseudo- were the ønly pianktønic foraminifera t ø guembelina) as the boundary was approached. survive the boundary extinction event at Many samples from below the boundary show this North Pacific locality. signs of severe dissolution, and as a re-

Changes in the relative abundances of sult, some of the Maastrichtian faunal the dominant genera within the Cretaceous fluctuations may be attributed to preferen- interval of the core are shown in Figure 4. tial preservation of certain taxa, as sug- The most abundant members of the Maas- gested by Smit and Romein [!985]. For trichtian assemblage were the genera Globo- example, Praeglobotruncana, Pseudoguembe- truncana, Praeglobotruncana, and Pseudo- lina, Globotruncana stuarti and GlobotrUnc - guembe!ina. praegløbøtrUncana and G10bo- a na stuartiformis are solution-resistant

Gerstel et al.: Cretaceous/Tertiary Bo•und•ary Planktonic Foraminifera 103

p • ee g .t3t o•ø t; • e c • • • B :øgø gt :• e dbe • • 20 10 0 10 20 30 20 10 •0 10 :2:0 30 5 0 5 10 0 10

• • • i • I ,, I ,, , I ,I , • •. • • I • I . , -',1 I

109 -

I 10 -

111 -

112 -

113 -

I 1•4 -

1 15 -

116 -

117 -

118 -

pseCd ote• t4etefo bet%• 10 0 10 10 0 10

I, • I I I I

p seødøgø 20 10 0 10 20

I , I I I i

109-

110 -

'• 111 -

:• 112--

LU 113 --

• 114-- 0

•-- 115-- 0

o3 116 --

117 --

118 --

Fig. 4. Downcore changes in the relative abundances of the most common Maastrichtian planktonic foraminiferal genera in the greater than 150-Bm size fraction. Poorly preserved assemblages (see Figure 3) are not included in this analysis.

forms and occur more commonly in the poorly 109.09-m subbottom depth. These forms are preserved samples. Samples which displayed characteristic of the first 30 cm of DanJan severe dissolution were not included.

The sequential changes in the abundance of the most common DanJan species are il- lustrated in Figure 5. Globigerina eug,u:, bind and Eoglobigerina eobulloides (normal and aberrant morphotypes) were •øund together with the last Cretaceous fauna at

sediments, at which point they rapidly decrease in abundance and Chiloguembelina taurica becomes the dominant species. This form is subsequently replaced bY GlOb i- geri.na pseudobul!•oides, and the other nominate taxa of the biostratigraphic zones of Bolli [1966]. Most of the important early

104 Gerstel et al..' Cretaceous/Tertiary Boundary Planktonic Foraminifera

o•

• o-

Ol

O•

o oO

o o •0

o o o o o c• o

•.•e•ew 'Hld3O •o•.•.o88n•

•.•e•ew 'H.Ld:IO •oA•.oeens

o

o

6• 0 0 u•

0 0•

Gerstel et al.: Cretaceous/Tertiary Boundary Planktonic Foraminifera 105

Rt 13

67-•

0 0.2 0.4 0.6 0.8 1.0 0.6 1.0 1.4 1.8 2.2 2.6 3.0 I I I I I I I I . I I I I I • i • • I •

68 4 - o fine fraction carbonate

,, Aragonia

Fig. 6. Turnover rate (Rt) of Danian planktonic foraminifera calculated according to Sepkowski [1978] and the carbon isotope records for the benthic foraminifera Aragonia and fine-fraction carbonate. An absolute timescale is indicated by a dotted line.

Tertiary zonal indicator species occur in low abundances when they initially appear and then gradually increase in abundance until they become the dominant species of the assemblage.

The sequential evolution and extinction of planktonic foraminifera during the Danian (Figure 5) resulted in a high rate of faunal turnover (Rt) (Figure 6). As is expected, there is nearly a complete turnover associated with the K/T boundary event. This is followed by an interval

tures as secondary apertures, bullae, and distorted final chambers. These changes in test form are considerably different from those associated with evolutionary change, such as those described by Cifelli [1969] and Hart [1980]. Instead, intra- specific variation of this nature has been attributed to ecological or environmental factors [Steineck and Fleisher, 1978]. These forms of G. eugubina and Eoglobiger- ina are considered to be ecophenotypic variants and are not assigned to a new

approximately 1.3 m. y. in duration that is genus or species. Samples from the G. marked by rapid large-scale changes in the makeup of the total assemblage. Between approximately 64 and 65 Ma (within the G. uncinata zone) the fauna remained rela--- tively stable; there were few speciations and extinctions. The rate of turnover is

plotted next to the 6C-13 records for the benthic foraminifera Aragonia and fine- fraction carbonate from Zachos et al.

eugubina zone of DSDP site 524 in the Cape basin of the South Atlantic were also exam-

ined and found to contain similar aberrant

forms.

Microtektitelike Spherules

An abundance of reddish spheroids were found at the K/T boundary (Figure 9d). These spheroids are composed of glauconite

A relatively abundant and diverse assem- and magnetite [Smit and Romein, 1985] and blage of morphologically complex aberrant are similar in texture to the spherules forms of G. eugubina and Eoglobigerina was described by Smit and Kyte [1984] in the found in association with normal morpho- boundary sections in Umbria, Italy. Smit types in the early Danian (Figures 7 and and Romein [1985] have recently proposed 8). The aberrant forms exhibit such fea- that these spherules, which are commonly


.a

Fig. 7. Aberrant morphotypes of G. eugubina and Eoglobigerina. Panel 1 shows the spiral side of G. eugubina showing a secondary aperture, 12-5-108, 160X. Panel 2 shows the umbilical side of the G. eugubina specimen shown in figure l, 12-5-108, 160X. Panels 3-6 show aberrant Eoglobigerina. Panel 3 is a side view, 12-5-129, 173X; Panel 4 shows the spiral, 12-5-129, 173X; Panel 5 shows the spiral side of the form shown in Panels 3 and 6,12-5-108, 200X; and Panel 5 shows the umbilical side of E. eobulloid6s with a secondary aperture, 12-5- 108, 200X. Panels 7 and 8 show an aberrant transitional form with a bulla, 12-5--98, 173X. Panel 9 shows aberrant G. eugubina with an areal aperture, 12- 5-98, 200X.

found at the K/T boundary, be referred to the extent of bioturbation and mixing with- as "microtektitelike" spherules. At site in the core. The spherules are mixed to a 577 the spherules occur over an interval of subbottom depth of 109.15-m, or 6 cm below less than 25 cm, with a dramatic peak of over 800 spherules per cubic centimeter of sediment in the boundary sample (Figure 9d). If these spherules were deposited instantaneously, as has been suggested by several authors [Montanari et al., 1983; Smit and Kyte, 1984], their distribution over the boundary interval should reflect

the boundary, and extend 15 cm above the boundary.

Sediment Preservation and Accumulation

Carbonate dissolution was far more se-

vere in the Cretaceous sediments than in

the Paleocene sediments. Many authors have

Gerstel et al.: Cretaceous/Tertiary Boundary Planktonic Foraminifera

.

- .:...-.'¾

2

Fig. 8. Aberrant morphotypes of G....eugubina and Eoglobigerina. Panel 1 shows G. eugubina with a secondary aperture in large, distorted final chamber, 12-5- 98, 200X. Panels 2 and 3 show side views of forms with large final chambers (panel 2, 12-5-108, 166X; panel 3, 12-5-129, 173X). Panel 4 shows a morphotype with a final chamber encompassing a large portion of the test, 12- 5-108, 176X. Panels 5-8 show a morphotype with various bullae. Panel 5 is a form showing several bullae and secondary apertures, 12-5-98, 200X. Panel 6 shows bulla encompassing a large portion of the test, 12-5-108, 173X. Panel 7 is a side view of E. edita with flanged primary aperture and bulla, 12-5-129, 215X. Panel 8 is a side view of Eoglobigerina with a bulla parallel to the primary aperture imparting a planispiral appearance, 12-5-129, 190X. Panel 9 shows what may be a streptospirally coiled morphotype, 12-5-129, 160X.

107

used the ratios of planktonic to benthic because in many Maastrichtian samples the foraminifera as an index of preservation in benthic foraminifera are also broken and calcareous sediments [Matter et al., 1975; dissolved. Instead, variations in plank- Thunell, 1976]. This is based on the fact tonic foraminiferal number (number of that planktonic foraminifera are less planktonic foraminifera per cubic centi- solution-resistant than benthic foram- meter of sediment) were used to monitor inifera, since the planktonics generally changes in preservation (Figure 9a). This have thinner, more porous test walls. This index clearly illustrates the overall approach could not be used in this case better preservation of the Danian assem-


A. FORAMINIFERAL NUMBER B. CARBONATE ACCUMULATION RATE (¾ planktonics Icm 3 sediment) (gm/cm2/Ky) 10 100 103 104 105 10 e 0.2 0.4 0.6 0.8 1.0 1.2

102.0 L , ,,h,d , ,,I,,a , ,,h,,t , ,,I,,,d , ,,I,,,J , lalitJ I I I I J I I I I I _

103.0 --

104.0 --

_

105.0-- _

_ • Cret Slump Cret. Slump 106.0 -

_

107.0 -

_ 108.0 -

-T T 109.0 --

-K • • K 11o.o- • _ 111.0-½ _

112.0- -- L 113.0. --

,

114.0 - _

_

115.0- _ _

116.0- _

_

117.0- _

C.

1 lO.O -

- 111.o-

- 112.o -

- 113.0 -

•3C PDB

1.8 2.0 2.2 2.4 2.6 2.8 I I I I I I I I I I I I

104.0

105.0

Cret. slump

106.0

107.0

108.0

109.0

K

114.0 -

115.0 -

116.0 -

D. 'Microtekrite-Like' Spherules (•/cm 3 sed.)

200 400 800 800 1000 I I I I I I I I I I

108.90 -

108.95 --

109.00 -

109.05 -

117.0 -

109.10

109.15

109.20

109.25

109.30

T

Fig. 9. Downcore changes in (a) foraminiferal number, (b) carbonate accumulation rate, (c) abundance of microtektitelike spherule•, and (d) the carbon isotopic composition of fine fraction carbonate. The isotopic data are from Zachos et al. [1985].

Getstel et al.: Cretaceous/Tertiary Boundary Planktonic Foraminifera 109

blages compared with to those of the Maas- trichtian. The most severe dissolution

occurs between 110.0- and 114.5-m sub-

bottom depth (Figure 9a). Approximately 50 cm below the K/T boundary, foraminiferal preservation begins to improve and is very good throughout the DanJan (except for within the Cretaceous slump deposit).

Samples containing only a few poorly preserved planktonic foraminifera are primarily composed of unusual agglomerations of micritic crystals or "micarb" particles. These sand-sized particles comprise a large proportion of the >63- m fraction of many of the Cretaceous samples and are interpreted as having recrystallized from calcium carbonate dissolved in situ. Similar

carbonate aggregations were described from the Cretaceous/Tertiary boundary section of DSDP site 465 on the Hess Rise [Vallier et al., 1981]. Since foraminiferal calcite is more susceptible to dissolution than nannofossil calcite [Schlanger and Douglas, 1974], most of the reprecipitated calcite is probably derived from the solution of foraminifera and consists of overgrowths on calcareous nannofossils. Sediment accumu-

lation rates also change significantly at the K/T boundary (Figure 9b). The average sedimentation rate calculated for the late

Maastrichtian is approximately 1.0 cm/kyr, while in the Danian, sedimentation rates range from 0.1 to 0.3 cm/kyr. Likewise, carbonate accumulation rates below the

boundary are greater than 1.1 g/cm2/kyr and are only 0.1 to 0.3 g/cm2/kyr in the DanJan (Figure 9b).

DISCUSSION

Cretaceous/Tertiary Boundary Event at Site 577

At site 577 in the North Pacific a num-

ber of distinct faunal, sedimentological, and geochemical events occur in close proximity to the K/T boundary (109.09-m depth). These events include (1) an improvement in carbonate preservation at approximately 109.6 m, (2) the first appearances of G. eugubina and G. cretacea at 109.25 m, and at 109.09-m, respectively, (3) the last occurrence of nearly all Cretaceous planktonic foraminifera, (4) the first occurrence of Paleocene nannofossils [Monechi, 1985], (5) the abundant occurrence of microtektitelike spherules, (6) a decrease in carbonate accumulation, and (7) a deple- tion in the carbon isotopic composition of fine-fraction carbonate [Zachos et al.,

1985]. The first two changes occur below the boundary in the latest Maastrichtian, whereas the last five occur simultaneously and mark the K/T boundary.

The presence of G. cretacea in the latest Maastrichtian and its persistence into the early DanJan has previously been reported for the Gredero section in Spain and the E1 Kef section in Tunisia [Smit, 1977, and 1982]. However, the cooccurrence of G. cretacea and G. eugubina below the K/T boundary at site 577 has not been observed at other localities. Globigerina eugubina is considered by most workers to have evolved at the base of the DanJan

[Luterbacher and Premoli Silva, 1964; Smit, 1982]. The question then arises as to whether the occurrence of these two

species, and in particular that of G. eugubina, below the boundary at site 577 is real or an artifact of either mixing or burrowing.

Ruddiman et al. [1980] have demonstrated that mixing due to bioturbation is neither size-dependent nor shape-dependent. The deposition of the microtektitelike spherules found at site 577 should represent an "instataneous" geologic event, and therefore the distribution of these spherules should be an accurate measure of how much

sediment mixing has occurred. Officer and Drake [1985] have estimated that if the rate of bioturbation at the K/T boundary was similar to that of today, mixing would occur through depth intervals of approximately 5 to 6 cm. Figure 9d shows that the spherules are in fact mixed only to a depth of 6 cm below the K/T boundary, suggesting that the presence of G. eugubina 16 cm below the boundary is not due to normal mixing. A number of other lines of evidence also support this conclusion. Globi- gerina eugubina is the only "Paleocene" species found below the boundary, and if mixing had occurred to this level (16 cm below the boundary), we would expect other early DanJan species to be present. Simi- larly, Monechi [1985] reported that no Paleocene nannofossils were mixed below the

K/T boundary. These findings seem to suggest that G. eugubina evolved in the latest Cretaceous and together with G. cretacea survived the K/T boundary event at this locality.

The presence of G. eugubina below the boundary could also be explained by a different scenario. J. Smit (personal communi- cation, 1985) has suggested that the G. eugubina specimens found below the K/T boundary may be displaced within a discrete burrow. While this remains a possibility,

110 Gerstel et al.: Cretaceous/Tertiary Boundary Planktonic Foraminifera.

it is difficult to explain why no other "Danian" species or microtektitelike spherules are similarly displaced.

Smit and Romein [1985] have recently suggested that "planktonic foraminifera and nannoplankton apparently show a different extinction-recovery pattern at the K/T boundary" and specifically that the final extinction of all Cretaceous nannoplankton occurred up to 10,000 years after the massive extinction of the Cretaceous planktonic foraminifera. Such a scenario im-

plies a differential response of these two groups of plankton to the change in the marine environment that accompanied the K/T boundary event. The "asteroid impact theory" of Alvarez et al. [1980] hypothe- sizes that dust thrown up into the atmos- phere would have blocked out sunlight and suppressed photosynthesis, the net result being a progressive breakdown of the food chain. The fine-fraction 6C-13 and carbonate accumulation records for site 577

clearly show that there was a major decrease in plankton productivity at the K/T boundary (Figure 9). If such a decrease in productivity did occur, it seems unlikely that the higher trophic level zooplankton (foraminifera) would have been affected before the photosynthetic nannoplankton which they are dependent upon. According to the model of Milne and McKay [1982], the hypothesized global atmospheric darkening at the end of the Cretaceous would have

stopped phytoplankton production within a matter of weeks and shortly thereafter resulted in starvation of zooplankton. Within the resolution of the geologic record, the impact of this event on both groups of plankton should appear coincident. Our planktonic foraminiferal results and the nannoplankton results of Monechi [1985] indicate that the major faunal and floral changes do occur simultaneously at site 577, in association with the peak in microtektitelike spherules.

Late Cretaceous-Early Tertiary Paleoenvironments

The faunal, sedimentological, and geochemical records for site 577 indicate that

in addition to the "catastrophic" event at the K/T boundary, there were other significant changes in the marine environment during the late Maastrichtian and Danian.

Numerous workers [Monechi, 1977; Hofker, 1978; Thierstein, 1982; Hsu et al., 1982; Smit and Romein, 1985] have made the gene- ral observation that the preservation of

calcareous plankton was substantially poorer during the late Maastrichtian than during the Danian. This same observation had previously led Worsley [1974] to hypothesize that the CCD rose into the photic zone at the end of the Cretaceous. The results of our work at site 577 may indicate that the change from poor p.reser- vation to good preservation did. not occur instantaneously at the K/T boundary but began at least 50,000 years earlier (Figure 9a). Such a change in preservation in- dicates that a change in the physical- chemical properties of deep waters must have occurred at this time, making these waters less corrosive. This change in preservation was not induced by whatever phenomenon occurred at the boundary.

Likewise, we find evidence at site 577 for a change in surface water conditions prior to the boundary event. The Globo- truncanidae and Heterohelicidae are the

dominant groups of planktonic foraminifera found at site 577 during the late Maas- trichtian (Figure 4), with their abundances varying inversely through time. In gene- ral, the tropical Globotruncanidae are dominant throughout the Maas t•ichtian at site 577 until approximately 30,000 years prior to the K/T boundary. At this point there is an increase in abundance of the

more temperate Heterohelicidae, followed by the introduction of the boreal genus Hed- bergella approximately i5,000 years bef'øre•

,,

the boundary. This sequence of fa. unai events at site 577 is indicative of a cool-

ing of surface waters in this region of the North Pacific in the latest Maastrichtian.

As with the change in carbonate preservation, these faunal changes occur prior to, and therefore cannot be attributed to, the K/T boundary event.

The stable isotopic composition of G. eugubina was determined for three samples from below and two samples from above the K/T boundary (Table 1 and Figure 10).. The 60-18 and 6C-13 values of all samples are not significantly different, although the 60-18 values of the G. eugubina just below the boundary are slightly heavier and the 6C-13 values are slightly lighter than those of G. eugubina at or above the boundary. The 60-I. 8 and 6C-I3 values of G. eugubina below the K/T boundary are also significantly heavier and lighter, respectively, than those of coexisting late Maas trichtian planktonic foraminifera. SUch a relationship could. be used. to argue that the G. eugubina that occur in samples below the boundary were burrowed down from above


TABLE 1. Stable Isotopic Compositions of Selected Planktonic Foramanifer Species

Across the K/T Boundary at Site 577

Core/ Section/ • O-18 o/oo, In terra 1 Species (PDB)

• C-13 o/oo, (PDB)

13/4/19-21 G. ganserri -0.45 13/4/19-21 P. petaloidea -0.06 12/6/69-71 R. rotundata -1.02 12/6/69-71 G. contusa -0.56 12/6/69-71 P. petaloidea -0.41 12/6/69-71 G. s tuarti -0.27 12/5/144-145 G. eugubina -0.28 12/5/139-140 G. eugubina -0.63 12/5/134-136 G. eugubina -0.69 12/5/131-132 P. palebra -1.19 (-1 12/5/131-132 T. scotti -1.14 12/5/131-132 R. rotundata -1.02

12/5/131-132 P. elegans -1.01 12/5/131-132 H. carinata -0.95 12/5/131-132 P. browni -0.74 12/5/131-132 P. varians -0.65 12/5/131-132 G. stuarti -0.64 12/5/131-132 P. petaloidea -0.42 12/5/125-126 G. eugubina -0.86 12/5/108-109 C. taurica -1.00

G. eugubina (large) -1.07

G. eugubina (normal) -0.83

G. eugubina (normal) -0.79

G. eugubina (with aperture)

.20)

+2.70

+2.15

+2.82

+2.62

+2.25

+2.55

+1.73

+1.57

+1.49

+2.52 (+2.42) +3.02

+2.85

+3.03

+2.70

+3.00

+3.43

+2.72

+2.45

+1.67

+2.12

+1.72

+2.01

+1.70

-0.76 +1.75

and therefore have earliest Tertiary isotopic signals. However, because of the relatively slow sedimentation rates and the thin G. eugubina zone above the boundary, we would expect to also see downward mixing of the spherules that mark the boundary, as was previously discussed. In addition, there are none of the aberrant forms of

G. eugubina below the boundary that are relatively abundant at and above it. Therefore we still conclude that the first

occurrence of G. eugubina below the K/T boundary, as supported by several other criteria, is real and not due strictly to bioturbational mixing. Such an interpreta- tion suggests that marked paleoceanographic changes occurred prior to what has been termed the "K/T boundary event".

The combination of better preservation of latest Maastrichtian planktonic foram-

inifera, the progressive positive •C-13 trend in benthic foraminifera, and the brief positive excursion in the •C-13 of the carbonate fine fraction and planktonic foraminifera below the K/T boundary support the inference of paleoceanographic changes as discussed above. One possible interpre- tation of the data is that cooling began at high latitudes during the latest Maastrich- tian and progressively affected lower- latitude regions, thereby explaining the floods of heterohelicids and hedbergellids just below the boundary. Cooling at high latitudes could have produced surface waters that were more dense than warmer sub-

tropical waters. The high-latitude surface waters could therefore have served as a

source for shallow intermediate water mas-

ses that were advected into subtropical regions. Planktonic foraminifera such as


108.90-

108.95-

109.00-

109.05-

109.10-

109.15-

109.20-

109.25-

109.30-

•13C PDB 1.6 1.8 2.o 2.2 2.4 2.6 2.8 3.0

I I I I I I I I I I I I I I I I

ß

'% 'Pa .C

ß Various Planktonic Foram.

G. eugubina

• • -normal • - large m - wl aperture

(this paper) & Aragonia

ß Fine Fraction(•3pm) (Zachos et al., 1985)

Fig. 10. Carbon isotopic composition of fine fraction carbonate, the benthic foraminifera Aragonia, and various planktonic foraminifera across the K/T boundary in hole 577. The lettered symbols represent the following species: T, Chiloguembelina taurica; Pe, Praeglobotrunana petaloidea; Pa, Pseudoguembelina palebra; C, Heterohelix carinata; R, Rug0globigerina rotundata; B,Pseudetextularia browni; S, Trinitella scotti; and E, Pseudotextularia elegans.

G. eugubina and other heterohelicids and These rapid faunal changes may reflect Hedbergella could have lived in the shallow repeated attempts to colonize an unstable intermediate water masses in the subtropics or stressful marine environment. for a period prior to the K/T boundary The benthic foraminiferal and fine- while a more normal late Maastrichtian fraction carbon isotope records for this subtropical planktonic fauna persisted in a site [Zachos et al., 1985] indicate that warmer water mass above. Such a model the surface water to deepwater carbon iso- would explain the cooler isotopic paleo- tope gradient was virtually nonexistent for temperatures and lighter carbon isotopic the first 300,000 years of the Danian and composition of G. eugubina below the boun- then was gradually reestablished throughout dary. the remainder of the Danian (Figure 6). A

The Danian faunal record is character- similar observation was made at DSDP sites

ized by a very distinctive pattern in which 465 in the North Pacific [Boersma and new species evolve, become dominant and Shackleton, 1981] and 524 in the South then give way to other newly evolving forms Atlantic [Hsu et al., 1982]. Surface water (Figure 5). This pattern, which has been previously observed [Smit, 1982; Smit and Romein, 1985], results in a high rate of turnover (Rt) in the assemblage, particu- larly during the early Danian (Figure 6). The high turnover rates reflect high rates of speciation and extinction and are not significantly affected by diversity, which is relatively constant (8-11 species) at this site throughout this time interval.

to deepwater carbon isotope gradients in the modern ocean are controlled by primary productivity in surface waters and carbon oxidation in deep waters [Broecker, 1974; Kroopnick, 1974, 1980]. The low surface water and high bottom water •C-13 values observed in the early Danian at site 577 suggest that photosynthesis was greatly reduced and that there was little oxidation

of organic matter in bottom waters [Zachos


and Arthur, 1985]. Globigerina eugubina, E. eobulloides, and C. taurica became dominant and then declined during this interval of very low surface productivity (Figure 5), resulting in the high turnover rates (Figure 6).

The surface to bottom carbon isotope gradient began to be reestablished approximately 300,000 years after the K/T boundary, indicating an increase in surface productivity (Figure 6). At this time, G. pseudobulloides and G. trinidadensis become the dominant components of the assemblage. By approximately 65 Ma a surface to bottom carbon isotope gradient (1.5 0/00) was reestablished at site 577 that is comparable in magnitude to the present-day gradient in the North Pacific [Boersma and Shackleton, !981]. This may signify the point at which a more normal, stable marine environment developed following the K/T boundary event. Globorotalia uncinata becomes the dominant member of the planktonic foraminiferal fauna at this time and re-

mains so throughout the rest of the Danian (Figure 5). This faunal stability is re- flected by the low rates of faunal turnover above 65 Ma.

Early Danian Planktonic Foraminiferal Morphologic Variability

Morphologically complex, aberrant forms of G. eugubina and forms evolving toward and including E. eobulloides and Eoglobi- gerina edita occur in high abundances in the basal Danian section of site 577.

The morphologic variation exhibited by these forms includes the development of secondary apertures and areal bullae as well as distorted final chambers (Figures 7 and 8). In the past, this type of morphologic variability has been used to distin- guish globigerinids at the generic level [Bolli et al., 1957]. However, as under- standing of the phylogenetic relationships between foraminiferal groups has improved, it has become apparent that the iterative development of certain biocharacters is controlled not by common ancestry but by functional adaptations which are often convergent [Steineck and Fleisher, 1978]. The misinterpretation of ecophenotypic variants as phyletically significant species has led to overcomplication of planktonic foraminiferal taxonomy, while the ecologic significance of these traits has usually been overlooked [Be, 1965; Berger, 1969; Kennett, 1976]. For example, the Neogene genus Globigerinoides is distin-

guished from Globigerina by the presence of secondary apertures. However, the indepen- dent evolution of supplementary apertures in unrelated lineages has occurred at least four times during the Neogene [Steineck and Fleisher, 1978] and twice each in the Paleogene and the Cretaceous [Frerichs, 1971]. Morphologic characters which do not reflect evolutionary descent cannot be used in a phylogenetically significant scheme of taxonomic classification.

Secondary apertures are present on the spiral side of both normal and inflated forms of G. eugubina, as well as on forms of Eoglobigerina (Figure 7, panels 1-8). Most of these secondary apertures occur on the basal sutures of chambers in the last

whorl, although some tests exhibit areal apertures on the final chamber as well (Figure 7, panel 9). Aberrant final chambers and sutural bullae appear only on inflated forms, most of which more closely resemble E. edita and E. eobulloides than

G. eugubina (Figure 7, panel 7; Figure 8, panels 1-4). In some cases the final chamber embraces a large portion of the test, resulting in some tests having no discernible primary or secondary apertures. In such extreme cases it becomes very difficult to identify the normal species affini- ty of the specimen (Figure 8, panel 6).

Where bullae occur, they usually cover or partially cover secondary apertures, which may be visible through an infralaminal aperture (Figure 7, panel 7; Figure 8, panels, 5, 7, and 8). In addition, some specimens have infralaminal apertures parallel to the primary umbilical aperture, resulting in a symmetric or almost planispiral appearance and producing a form which could easily be mistaken for the Cretaceous species G. messinae (Figure 8, panel 8). In some extremely distorted forms, chamber addition becomes so irregu- lar that it is difficult to identify the dorsal and ventral sides of the test (Fig- ure 8, panel 9).

The forms described above are considered

morphologic variants of the primitive early Danian species from which they are derived. The occurrence of these aberrant forms

immediately above the Cretaceous/Tertiary boundary is a good example of the high degree of genetic plasticity that exists in the morphologic development of planktonic foraminifera [Kennett, 1976]. According to Be [1965] the formation of aberrant terminal structures may be related to environmental or reproductive factors. The question of greatest significance to paleocean-


ographers regarding the development •of these aberrant test forms is, what is the adaptational significance of such morphologic structures? Unfortunately, little is kno• about the evolutionary biology and functional morphology of planktonic foraminifera [Lipps, 1981]. Be [1965] suggested that •the formation of abnormal terminal structures in several modern-day spe- •cies could be related to the occupation of relatively deeper depth habitats than their "normal" counterparts. Likewise, Berger [197t] found abundant kummerforms associated with a tongue of advected intermediate water in an oceanic front off Baja California. He attributed this abnormal

3. An increase in the abundance of the

temperate Heterohelicidae approximately 30,000 years (30cm) before the K/T boundary, followed by the introduction of the boreal genus Hedbergella approximately

,

t5,000 years later (15 cm below the K/T boundary), is indicative of a cooling of surface waters in this region during the latest Maas trichtian.

4. The oxygen and carbon isotopic composition of G. eugubina from above and below the K/T boundary are not significantly different. Although this could be interpreted as indicating reworking of specimens with early Tertiary isotopic signals into uppermost Maastrichtian strata

growth of final chambers to the submergence by burrowing organisms, other available of typically shallow-dwelling forms.

The aberrant forms described above are

also present in great abundances in earliest Danian samples from DSDP site 47.2, which was drilled in close proximity to site 577. Morphologically similar forms were also found in early Danian samples from DSDP site 524, located in the South Atlantic. It is difficult to determine

whether or not they occurred in large abundances at the latter site, because tur- bidite deposition has significantly reduced the CaCO3 content and foraminiferal abun-

dance at this site [Hsu et al., 1982]. It would appear that these morphologic variants are not present in significant num- bers in any of the commonly studied sections such as Gubbio and E1 Kef, since these sections have been described in de-

tail by many authors [e.g., Luterbacher and Premoli Silva, 1964 and Smit, 1982], but these aberrant forms have not been reported.

CONCLUSIONS

1. Globigerina eugubina first appears approximately 20,000 years below the K/T boundary at site 577. The distribution pattern of microtektitelike spherules and the lack of reworked Danian nannofossils

below the boundary indicate that this appearance is not the result of core distur- bance or biotuzbation. Globigerina eugubina and G. cretacea were the only planktonic foraminifera to survive the K/T boundary event at this locality.

2. There is a gradual improvement in foraminiferal preservation beginning approximately 50,000 years (50 cm) before the K/T boundary. This change in preservation is interpreted as reflecting a change in the physicochemical properties of deep waters during the latest Maastrichtian.

evidence supports a primary first occurrence of G. eugubina below the boundary. The occurrence of G. eugubina below the boundary region requires explanation. The 60-18 and 6C-13 values of this species are heavier and lighter, respectively, than those of the other Cretaceous planktonic species from the same intervals. One possibility is that cooling began at higher latitudes several tens of thousands of

years prior to the K/T boundary and that cool, high-latitude surface waters sank to become shallow intermediate water masses

that were then advected into subtropical regions. The overlying subtropical surface waters would have been warmer and charac-

terized by a normal late Maastrichtian planktonic foraminiferal and nannofossil assemblage. These shallow intermediate water masses carried with them a high- latitude planktonic foraminiferal fauna that included G. eugubina. Globigerina eugubina therefore would record cooler oxygen isotopic paleotemperatures and lighter carbon isotope values than the near-surface Maastrichtian forms. The

disappearance of the latest Cretaceous forms was accompanied by further cooling of surface waters and less thermal and

carbon isotopic differentiation above the thermocline.

5. Carbonate accumulation rates and the

fine-fraction carbonate 6C-13 record indicate a major decrease in surface water productivity at the K/T boundary. Within the resolution of the record, calcareous nannoplankton and planktonic foraminifera were influenced simultaneously by this decrease in productivity.

6. The rapid speciation and high turnover rate of planktonic foraminifera in the early DanJan may be related to a highly unstable marine evironment. In particular, the surface to bottom 6C-13 gradient indi-


cates that surface productivity was greatly Bliel, U., The magnetostratigraphy of diminished at the K/T boundary and was only gradually reestablished during the early DanJan.

7. Aberrant forms of G. eugubina and Eoglobigerina are abundant in the earliest Danian. These forms exhibit a high degree of morphologic variability including such structures as secondary apertures, bullae, and distorted final chambers. Variations of this nature can be attributed to

ecologic or environmental stress and have no phyletic significance.

Acknowledgments. We appreciate the com- ments of Gerta Keller, Hans Thierstein and Douglas Williams on this manuscript. We also acknowledge and appreciate a stimula- ting conversation with Jan Smit on this work. We thank K. Gruenhagen, L. Sautter, and E. Tappa for drafting the figures and L. Henderson for editing and typing the manuscript. The samplies were provided by the Deep-Sea Drilling Project, which is funded though the U.S. National Science Foundation. This research was supported by NSF grant EAR-8306561.

REFERENCES

Alvarez, L. W., W. Alvarez, F. Asaro, and

northwest Pacific sediments, Deep Sea Drilling Project Leg 86, Initial Rep. Deep Sea Drill. Pro•., 86--•"441'458, !985.

Blow, W. H., The Cainozoic Globigerinida, E. J. Brill, p. 1409, Leiden, Nether- lands, 1979.

Boersma, A., Campanian through Paleocene paleotemperature and carbon isotope sequence and the Cretaceous-Tertiary boundary in the Atlantic Ocean, in Catastro- phes and Earth History: The New uniform - itarianism, edited by W. A. Berggren and A. A. Van Couvering, pp. 274-277, Prince- ton University Press, Princeton, N.J., 1984.

Boersma, A., and N.J. Shackleton, Oxygen and carbon isotope variations and planktonic foraminiferal depth habitats, Late Cretaceous to Paleocene, Central Pacific, DSDP sites 463 and 465, leg 62, Initial Rep. of the Deep Sea Drill. Pro•., 6__2, '513-52-•, 1981. ' •

Boersma, A., and N.J. Shackleton, M. Hall, and Q. Given, Carbon and oxygen isotope records at DSDP site 384 (North Atlantic) and some Paleocene paleotemperatures and carbon isotope variations in the Atlantic Ocean, Initial Rep. Deep Sea Drill. pro•., 43, 695-717, 1979.

H. Michel, Extraterrestrial cause for the Bolli, H. M., The genera Praeglobotruncana, Cretaceous-Tertiary extinctions, Science, Rotalipora, Globotruncana, and Abatho m- 208, 1095-1108, 1980. phalus in the Upper Cretaceous of Trindad

Alvarez, W., E.G. Kauffman, F. Surlyk, A. B. W. I., Bull. U.S. Natl. Mus., 215, 51- W. Alvarez, F. Asaro, and H. Michel, 60, 1957. Impact theory of mass extinctions and the Bolli, H. M., Zonation of Cretaceous to invertebrate fossil record, Science, 223, 1135-1141, 1984.

Be, A. W. The influence of depth on shell growth in Globigerinoides sacculifer (Brady), Micropaleontology, 11, 81-97, 1965.

Berger, W. H., Planktonic foraminifera: Basic morphology and ecotogic implications, J. of Paleontol., 43, 1369-1383, 1969

Berger, W. H., Planktonic foraminifera: Sediment production in an oceanic front, J. of Foraminiferal Res., 1, 95- 118, 1971.

Berggren, W. A., Stratigraphic and taxonomic-phylogenetic studies of 'Upper Cretaceous and paleogene planktonic foraminifera, Stockholm Contrib. Geol., 9, 108-129, 1962.

Berggren, W. A., D. V. Kent, and J. J. Flynn, Paleogene geochronology and chro- nostratigraphy, in Geochronology and the geological record, Geological Society of London, in press, 1985.

Pliocene marine sediments based on planktonic foraminifera, Asoc. Venez. Geol., Min. Pet. Bol. Inf., 9, 3-3'2, 1966

Bolli, H.M., A. R. Loeb!ich, Jr., and H. Tappan, Planktonic foraminiferal families Hantkenenidae, Orbulinidae, Globorotali- da e and GlobotrUnCanidae, U S. Natl. Mus., Bull., 215, 3-50, 1957.

Bramlette, M. N., Massive extinctions in biota at the end of Mesozoic time, Sci- ence, 148, 1696-1699, 1965.

Broecke r, W. S., Chemical Oceanography, 214 pp., •rcourt, Brace, Jovanovich, New York, 1974.

Caron, M., and P. Homewood, Evo!ution of early planktic foraminifers, Mar, Micro- paleonto!., 7, 453-461, 1983.

Cifelli, R. J., Radiation of Cenozoic planktonic foraminifera, Syst. Zoo!., 18, 154-!68, 1969.

Douglas, R. G., S. M. and Savin, Oxygen and carbon isotope analyses for Tertiary and •Cretaceous micro'fossils from Shatsky Rise and other sites in the North Pacific


Ocean, Initial Rep. Deep Sea Dril. Proj., 32, 509-521, 1975.

Douglas, R. G. and S. M. Savin, Oxygen isotopic evidence for the depth stratifi- cation of Tertiary and Cretaceous planktonic foraminifera, Mar. Micropaleontol., 3, 175-196, 1978.

EmTliani, C., E. B. Kraus, and E. M. Shoemaker, Sudden death at the end of the Mesozoic, Earth Planet. Sci. Lett., 55, 317-334, 1981.

Fischer, A. G., and M. A. Arthur, Secular variations in the pelagic realm, Spec. Pub. Soc. Econ. Paleontol. Mineral., 25, 19-50, 1977.

Frerichs, W. E., Evolution of planktonic foraminifera and paleotemperatures. J. Paleontol., 45, 963-968, 1971.

Gartner, S., and J. Keany, The terminal Cretaceous event: A geologic problem with an oceanographic solution, Geology, 6, 708-712, 1978.

Hart, M. B., A water depth model for the evolution of the planktonic foramini- feridae Nature, 286, 252-254, 1980.

Hay, W. W., The Cretacous-Tertiary boundary in the Tampico embayment, Mexico, Inter- national Geologic Congr., Rep. Sess. Norden, 21st, 5, 70-77, 1960.

Herm, D., A. V. Hillebrandt, and K. Perch- Nielsen, Die Kriede/Tertiar-Grenze im Lattenbirge (Nordliche Kalkalpen) in mikropalaontologischer Sicht, Geologica Bavarica, 82, 319-344, 1981.

Hofker, J., Analysis of a large succession of samples through the upper Maastrich- tian and the lower Tertiary of drill-hole 47-2, Shatsky Rise, Pacific, Deep Sea Drilling Project, J. Foraminiferal Res., 8, 46-75, 1978.

Hsu, K. J., J. A. McKenzie, H. Weissert, K. Perch-Nielsen, H. Oberhansli, K. Kelts, J. LaBrecque, L. Tauxe, N. Peterson, P. Tucker, R. Z. Poore, A.M. Gombos, K.

paleontology?, Paleobiology, 7, 167-199, 1981.

Loeblich, A. R., Jr., and H. Tappan, Corre- lation of the Gulf and Atlantic coastal

plain Paleocene and lower Eocene forma- tions by means of planktonic foraminifera, J. Paleontol., 31, 1109-1137, 1957.

Luterbacher, H. P., and I. Premoli Silva, Biostratigrafia del Limite Cretaceo- Terziario nell Appennino centrale, Riv. Ital. di Paleontol. Stratigr., 70, 67-88, 1964.

Malmgren, B. A., Biostratigraphy of planktic foraminifera from the Maas trichtian

white chalk of Sweden, Geol. Foeren. Stockholm Forh., 103, 357-375, 1982.

Matter, A., R. G. Douglas, and K. Perch- Nielsen, Fossil preservation, geochemistry and diagenesis of pelagic carbonates from Shatsky Rise, North Pacific, Initial Reports Deep Sea Drill. Proj., 32, 891- 907, 1975.

McLean, D., Deccan volcanism: The Cretaceous-Tertiary marine boundary timing event, Abstr. Programs, Geol. Soc. Am., 14, 562, 1982.

Milne, D. H. and C. P. McKay, Response of marine plankton communities to a global atmospheric darkening, Spec. Pap. Geol. Soc. Am., 190, 297-303, 1982.

Monechi, S., Upper Cretaceous and early Tertiary nannoplankton from the Scaglia Umbra Formation (Gubbio, Italy), Riv. Ital. Paleontol., 83, 759-802, 1977.

Monechi, S., Campanian to Pleistocene calcareous nannofossil stratigraphy from the northwest Pacific Ocean, Deep Sea Drill- ing Project Leg 86, Initial Reports of the Deep Sea Drill. Pro•., 86. 301-336, 1985.

Montenari, A., et al. Spheroids at the Cretaceous-Tertiary boundary are altered impact droplets of basaltic composition, Geology, 11, 668-671, 1983.

Pisciotto, M. F. Carmam, and E. Schreiber, Officer, C. B., and C. L. Drake, Terminal Mass mortality and its environmental and Cretaceous environmental events, Science, evolutionary consequences, Science, 216, 227, 1161-1166, 1985. 249-256, 1982. Ols$on, R. K., Late Cretaceous planktonic

Kennett, J.P., Phenotypic variation in foraminifera from New Jersey and Dela- some Recent and late Cenozoic planktonic ware, Micropaleontology, 10, 157-188,1964. foraminifera, in Foraminifera, vol. 2, Perch-Nielsen, K., Les .coccolithes du edited by R. H. Hedley and C. G. Adams, pp. Paleocene pres de E1 Kef, Tunisie et 111-170, Academic, 1976.

Kroopnick, P., Modelling the dissolved CO2- •C-13 system in the eastern equatorial Pacific, Deep Sea Res., 21, 211-229, 1974.

Kroopnick, P., The distribution of •C-13 in the Atlantic Ocean, Earth Planet. Sci. Lett., 49, 469-484, 1980.

Lipps, J. H., What, if anything, is micro-

leurs ancetres, Cah. Micropaleontol., 3, 7- 23, 1981.

Perch-Nielsen, K., J. McKenzie, and Q. He, Biostratigraphy and isotope stratigraphy and the catastrophic extinction of calcareous nanno plankton at the Cretaceous/ Tertiary boundary, Spec. Pap. Geol. Soc. Am., 190, 353- 371, 1982.


Romein, A. J. T. and J. Smit, The Cretaceous/Tertiary boundary: calcareous nannofossils and stable isotopes, K. Ned. Akad. Wet. Proc. Ser. B, 84, 295-314, 1981.

Ruddiman, W. F., G. A. Jones, T. H. Peng, L. K. Glover, B. P. Glass, and P. J. Liebertz, Tests for size and shape depen- dency in deep-sea mixing, Sediment. Geol., 25, 257-276, 1980.

Saito, T., and J. V. Van Donk, Oxygen and carbon isotope measurements of Late Cre- taceous and Early Tertiary foraminifera, Micropaleontology, 20, 152-177, 1974.

Schlanger, St O., and R. G. Douglas, The pelagic ooze-chalk-limestone transition and its implications for marine stratigraphy, Spec. Publ. Int. Asoc. Sedimen- tol., 1, 117-148, 1974.

tivity and causes for the Phanerozoic crises, Spec. Pap. Geol. Soc. Am., 190, 265-276, 1982.

Tappan H., and A. R. Loeblich, Evolution of the ocean plankton, Earth Sci. Rev., 9, 207-240, 1973.

Thierstein, H. R., Terminal Cretaceous plankton extinctions: a critical asses- sment, Spec. Paper Geol. Soc. Am., 190, 385-399, 1982.

Thierstein, H. R., and W. H. Berger, Injec- tion events in ocean history, Nature, 276, 461-466, 1977.

Thunell, R. C., Optimum indices of calcium carbonate dissolution in deep-sea sediments, Geology, 4, 525-528, 1976.

Vallier, T. L., et al., Site 465: Southern Hess Rise, Initial Rep. Deep Sea Drill. Pro•., 62, 199-283, 1981.

Sepkoski, J. J., A kinetic model of Phaner- Van der Lingen, G. J., and G. H. Packham, ozoic taxonomic diversity, I., Analysis of marine orders, Paleobiology, 4, 223- 251, 1978.

Smit, J., Discovery of a planktonic forami- nifeal association between the Abathom-

phalus mayaroensis Zone and the Globiger- ina eugubina Zone at the Cretaceous/ Tertiary boundary in the Barranco del Gredero (Cavavaca, Spain), K. Ned. Akad. Wet. Proc., Ser. B, 80, 280-301, 1977.

Smit, J., Extinction and evolution of planktonic foraminifera at the Cretaceous/Tertiary boundary after a major impact, Spec. Pap. Geol. Soc. Am. 190, 329-352, 1982.

Smit, J., and G. Klaver, Sanadine spherules at the Cretaceous-Tertiary boundary indicate a large impact event, Nature, 292, 47-49, 1981.

Smit, J., and F. T. Kyte, Siderophile-rich magnetic spheroids from the Cretaceous- Tertiary boundary in Umbria, Italy, Nature, 310, 403-405, 1984.

Smit, J., and A. J. T. Romein, A sequence of events across the Cretaceous-Tertiary boundary, Earth Planet. Sci. Lett. 74, 155-170, 1985.

Stainforth, R. M., J. L. Lamb, H. Luterbacher, J. H. Beard, and R. M. Jeffords, Cenozoic planktonic foraminiferal zonation and characteristics of

index forms, Univ. Kans. Paleontol. Con- trib. pap., 62, 425 pp., 1975.

S teineck, P. L., and R. L. Fleischer,

Relationships between diagenesis and physical properties of biogenic sediment of the Ontong-Java Plateau (sites 288 and 289, Deep Sea Drilling Project), Initial Rep. Deep Sea Drill. Pro•., 30, 443-481, 1975.

Vogt, P. R., Evidence for global synchro- nism in mantle plume convection, and possible significance for geology, Nature, 240, 338, 1972.

Wei, K. Y., and J. P. Kennett, Taxonomic evolution of Neogene planktonic foraminifera and paleoceanographic relations, Paleoceanography, _1, 67-84, 1986.

Worsley, T., The Cretaceous-Tertiary boundary event in the ocean, Spec. Publ. Soc. Econ. Paleontol. Mineal., 20, 94-125, 1974.

Zachos, J. C., and M. A. Arthur, Paleocean- ography of the Cretaceous-Tertiary boundary event: Inferences from stable isotopic and other data, Paleoceanography, _1, 5-26, 1986.

Zachos, J.C., M. A. Arthur, R. C. Thunell, D. F. Williams, and E. J. Tappa, Stable isotope and trace element geochemistry at DSDP hole 577, leg 86. Initial Rep. Deep Sea Drill. Pro•., 86, 513-532, 1985.

M. A. Arthur and J. C. Zachos, Graduate School of Oceanography, University of Rhode Island, Kingston, RI 02882

J. Gerstel and R. C. Thunell, Department of Geology, University of South Carolina,

Towards the evolutionary reclassification Columbia, SC 29208. of Cenozoic Globigerinacea (Foraminifer- ida), J. Paleontol. 52, 618-635, 1978. (Received September 23, 1985;

Tappan, •., Extinction or survival: selec- accepted November 22, 1985.)

(k/t) boundary. a 15-m section

Documents