AM.Peleo-Alampay, G.A.Mead, W.Wei:Oiigocene Braamdosphaera-rich layers.. p. 17-26. Journal of Nannoplankton Research, 21 , l, 1999.

UNUSUAL OLIGOCENE BRAARUDOSPHAERA - RICH LAYERS OF
THE SOUTH ATLANTIC AND THEIR PALAEOCEANOGRAPHICIMPLICATIONS
A lyssa M Peleo-Alampay*, GregoryA. Mead** & Wuchang Wei*National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon City 1101, Philippines;**Dept. ofGeology, University ofFlorida, Gainesvil/e, Florida 32611, USA; Scripps Institute ofOceanography,
University ofCalifornia, San Diego: La Jo/la, CA 92093-0215, USA

Abstract: The origin of the Oligocene Braarudosphaera layers over large ocean basins has remained amystery since the question was raised a lmost three decades ago by the Deep Sea Drilling Project. A
micropalaeontological study, coupled with oxygen and carbon isotope data, from Sites 363 and 522 in the
S Atlantic Ocean have shed some new light on this question. Our Braarudosphaera abunda nce data
correlate with oxygen isotope curves, suggesting that Braarudosphaera preferred cold waters. Variationsin the relative abundance of sphenoliths (warm-water taxa), and longer Coccolithus pelagicus placoliths,
also indicate colder water conditions during times of elevated Braamdosphaera deposition. Upwelling andmid-ocean overturn of cold, nutrient-rich, low-salinity water are suggested to be the most likely
palaeoceanographic mechanisms for the deposition of Braarudosphaera layers.

Introduction
The genus Braarudosphaera includes calcareous
nannoplankton species with a coccosphere of pentaliths,
each comprising with five elements of basic trapezoidal
shape. Braarudosphaera has a long stratigraphic range,from the Early Cretaceous to Recent. It is represented in
the modem oceans by the type species, Braarudosphaera
bigelowii, which is covered by twelve flat pentaliths.
Modern occurrences of braarudosphaerids(dominated by B. bigelowii) are mostly associated withnearshore, low-salinity marine waters (Bukcy, 1974; Okad.a,1992 ). High concentrations of modern representatives havebeen found in areas of relatively low salinities, such as the
GulfofMaine (31.8-32.7%o: Gran&Braarud, 1935) and Gulf
ofPanama (26.8-32.5o/oo) where it reached 1500 cells/litre ofwater (Smayd.a, 1966). Bukry (1974) noted that their affinity
for low-salinity waters is well illustrated by tl1eir abundancein the Black Sea (salinity 17-18%o) , and tl1eir absence in the
Red Sea (salinity 37-41%o). They have sometimes beenreported from open-ocean sites with normal salinities, but
only at very low abundances, e.g. Okada & Honjo, 1973.
Some braarudosphaerids have also been reported from thePersian Gulf(Martini, 1967) where surface salinities are high(34-40%o).

During Deep Sea Drilling Project (DSDP) Leg 3, in
the S Atlantic Ocean, strong seismic reflectors were foundin the Oligocene and the horizons were recovered in cores.
Detailed examination of the cores revealed chalk intervals
almost exclusively composed of Braarudosphaera(Maxwell et al., 1970). These layers immediately aroused
great interest, in geophysics as unusual extensive
acoustical reflectors, and in sedimentology because of tlleir
significance in the study of sediment lithification anddiagenesis (Wise & Hsii, 1971; Wise & Kelts, 1972). They
also posed an intriguing palaeoceanographic question as
to why this typically nearshore nannoplankton genus
became so abundant in the open ocean.

unusual Braarudosphaera horizons. Most of thesehypotheses address the problem from the standpoint of
low-salinity conditions in the S Atlantic during the
Oligocene, a view based on modern occurrences of thisgenus. Mechanisms suggested to reduce surface-watersalinities over large areas include: an increase in theregional rainfall (Bukry, 1974); periodic fluxes ofOligocene
glacial melt-waters to reduce near-surface salinity (Hsii in
Bukry, 1978); high influx of fresh water from the Orange
River into the Cape Basin, coupled with upwelling of
nutrient-rich, intermediate or deep, low-salinity water (Bolli
et al., 1978); and initiation of the Benguela Current was
postulated as the trigger for this upwelling process in thearea of Leg 40 in tl1e mid-latitude S Atlantic by Siesser(1978) and Melguen (1978).
Red tide hypotheses
Braarudosphaera blooms, analogous to modern day redtide blooms but with longer duration, have also been
proposed (Maxwell et al., 1970). This type ofinteq>retation
is supported by analogy with the Braarudosphaera
blooms from immediately above the Cretaceoustrertiaryboundary (Fischer & Arthur, 1977). In tllis context, they
are considered to be ,opportunistic disaster forms ' thattook advantage of tl1e available ecological niches andminimal competition from otl1er groups. This hypothesis,
however, does not explain the repetitive Braarudosphaera
layers witl1in normal pelagic oozes that occur in U1e
Oligocene.
Upwelling
LaBrecque et al. (1983) suggested mid-ocean upwellingas tl1e mechanism for enhanced productivity in the open
ocean that could lead to these blooms. This would also
account for their wide distribution in the S Atlantic.
LaBrecque et al. (1983) suggested further that the openingof the Drake Passage, which appears to coincide with the
Oligocene braarudosphaerid occurrence, could havecaused the S Atlantic mid-ocean upwelling. The openingof the Drake Passage is associated with tl1e start ofcircumAntarctic winds and strong latitudinal temperature-

Origin of Braarudosphaera layers
Salinity-reduction hypotheses
Several hypotl1eses have been proposed to explain these17Journal ofNannoplankton Research, 21, I, 1999. A.M.Peleo-Alampay, G.AMead,WWei:Oligocene Braarudosphaera-rich layers.. p. 17-26.

gradients that would have contributed to the upwelling.
However, this does not explain the dominance ofBraarudosphaera in the upwelling-induced blooms, nor
the repetitive and temporary nature of the oozes. Siesser
et al. (1992) suggested regional divergent upwelling,much like the Subtropical Divergence, to explain thesebraarudosphaerid occurrences. However, these divergenceareas have not yielded any Recent Braarudosphaera-richsediments (Lohman, 1986) and the present day species
diversity among these sites appears to be normal (Okada&Honjo, 1973).
Berger (1981) suggested mid-ocean overturn as
anotlter possible mechanism to explain the blooms (seeDiscussion, below). This phenomenon occurs during times
of instability in the water-column. Cyclonic circulation andwinter seasonal cooling combine to bring about overturnof surface-waters and the delivery of cold, nutrient-richwaters from below.

Redeposition
Another hypothesis centres on redeposition of thebraarudosphaerids to deeper waters. In DSDP Leg 3
reports, Maxwell et al. (1970) proposed that unusual
oceanographic conditions might have triggered thetransportation of shallow-water sediments bearing
Braarudosphaera to deeper waters over a large area. Hsti
et al. (1984), on tlte otlter hand, proposed that at Site 522
in the central S Atlantic, the braarudosphaerid pentaliths
were transported by the ancestral Benguela Current to
the open ocean from upwelling sites off the South African
margins. However, this does not explain their wide
geographical distribution and the cyclical nature of theoccurrences. Moreover, there is neither a shallow-water
source in the S Atlantic nor evidence of slumping or
turbidite flow in the sediments where they were found(Wise & Kelts, 1972).

conclude that the palaeotemperature they obtained
represented bottom-water conditions where braarudosphaerid skeletons were diagenetically altered. Carbon
isotope results by Siesser et al. (1992), from Braarudosphaera-rich bulk samples from the mid-latitude Indian
Ocean, showed no clear correlation between 13C andBraarudosphaera. Their a18o measurements showed
higher values in tl1e Braarudosphaera-bearing intervals.
Based on these oxygen isotope data, Siesser et al. (1992)
suggested significant cooling of surface-waters in the
Indian Ocean for the Braarudosphaera-bearing interval.
However, Braarudosphaera made up less than 10% of
tlte sediment in their samples. The low abundance ofBraarudosphaera may have made tlte palaeoceanographic
signal from the Braarudosphaera-bearinft intervals too
weak to be detected. Results from the o 8o and al3c
analyses ofSiesser et al. ( 1992) are difficult to interpret forpalaeoenvironment because bulk sediment samples wereused for isotope studies and changes in assemblage
composition could easily cause variations in the isotopic
records.

oDiagenetic concentration
Selective dissolution of nannofossil species was discussed
by Wise & Hsti (1971). They noted, however, that the lowamount of terrigenous material in the braarudosphaerid
chalk implies tllat minimal dissolution has taken place.
Moreover, Braarudosphaera is highly susceptible todissolution (Bukry, 1971; Wise & Kelts, 1972) and thus
selective dissolution cannot account for the enrichmentof Braarudosphaera.

Objectives of this !i1udy
This study concentrates on the Oligocene Braarudosphaera layers in the S Atlantic, where this phenomenon
is best recorded. The objective was to better understandthe palaeoceanographic conditions for the deposition oftlte braarudosphaerid layers by collecting and analysing
quantitative nannofossil data and by synthesising Ox')'gen
and carbon isotope data collected previously (Mead, 1995).
In particular, two DSDP sites were investigated indetail (Figure 1). Site 363 in tlte Angola Basin ( 19°S, 09<'E;
2248m water-depth) is a nearshore site, while Site 522 at
Walvi.s Ridge (26°S, 05°W; 444lm water-deptl1) represents
the mid-ocean occurrence of these deposits. Agedetermination was facilitated by the availability ofmagnetostratigraphy at Site 522.
Quantitative abundance patterns of key
nannofossil taxa across the Braarudosphaera layers are
documented for the first time. A census of cool(chiasmoliths, Reticu/ofenestra daviesii, Coccolithus
pelagicus) and wann-water taxa (discoasters, sphenoliths
and helicosphaerids) was used to infer surface-watertemperature fluctuations. In addition, coccolitll sizevariations downcore were examined for evidence ofchanges
in surface-water temperature.

Isotope data
Stable isotope analyses were perfonned by Lloyd & Hsti
( 1972) and by Siesser et al. (1992) on Oligocene
braarudosphaerid-bearing samples from DSDP cores.
Based on analyses of three bulk samples enriched in
Braarudosphaera rosa, Lloyd & Hsii (1972) suggested
growth of Braarudosphaera in cold surface-waters
brought by upwelling Antarctic waters. However, thepalaeotemperature of 6°C, as inferred from the o;..:ygenisotope values, were thought to be too low for Braarudosphaera growth. Modern braarudosphaerids had notbeen recorded from waters below 1ooc (Wise & Hsti, 1971 ).
This led Wise & Hsii (1971) and Lloyd & Hsti (1972) toMaterial and methods
Sediment samples were taken from across eight Braarudosphaera layers in cores 5-7 at Site 363 (Figure 2). At Site
522, samples across the thickest Braarudosphaera layer
were examined. These include samples from botll Holes
522 and 522A. As the corresponding Braarudosphaera
layer was recorded at slightly different subbottom depths
in the two holes, sample depths from Hole 522A werecorrected by adding 1.45m (Mead, 1995).
The three cores analysed from Site 363 have thefollowing ages assigned by Proto Decima et al. (1978),based on the calcareous nannofossil zones of Martini(1971): Core 363-5, NP24 (S. distentus Zone); 363-6, NP23

18

AM.Peleo-Alampay. GA.Mead,W.Wei:Oligocene Braarudosphaera-rich layers.. p. 17-26. Joumal ofNannoplankton Research. 21, 1, 1999.

60°~ :~~~~~~~~!I p~~~~~ 'i/' ;··~····\:

30°

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.
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00
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30°

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•

363\\:::

I522"· • \

•

-

.

Y:

:o

-~-:::::; : ;:;: : :-.

:::::>::::c
•

0

0

0

60°

0
0
0

0

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or

tJ

~
0

0

90°

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0

0

600 . L _ _
120°

0 0

0

oo

30°

30°

60°

0

90°

120°

150°

180°

150°

Figure 1: Location map of Oligocene Braarudosphaera occurrences as synthesised from DSDP/ODP reports. Braarudosphaera oozes
and chalks are represented by black circles. Sites with noticeable Braarudosphaera are indicated by grey circles. Open circles represent sites
with calcareous Oligocene sediments but practically no Braarudosphaera. The location of ODP Sites 363 and 522, studied in detail, aremarked.

Hole
522

I I?- I

J~l
~I

60---t-ji 6C I

80~

....
lOO

I522A
Hole I I

IHole
363

IDEPTHI~I(mbsf) U

rcEPTH(mbsf)

I

6 0~

r--Y

80 ~

(S. predistentus Zone); and 363-7, NP22 (H reticulata

Zone). Percival (1984) assigned cores 522-25 and 522A-13
to NP23. Based on the Sr-isotope age-model of Mead &Hodell (1995), cores 5-7 of Site 363 have an average age of
29.83-32.4Ma (ages converted to the timescaleofCande&
Kent, 1995). Ma!:,'Iletostratigraphy of Site 522 suggests that
cores 522-25 and 522A-13 correlate to Chron Cl Or (29Ma).
The duration of the Braarudosphaera
occurrences studied from Sites 363 and 522 were calculated
to be 7-46kyr, depending on thickness, using a constantsedimentation rate model, and 6-19kyr, assuming a nonconstant sedimentation rate model. The non-constantsedimentation rate model assumed that the sedimentation
rate of non-carbonate in the Braarudosphaera and nonBraarudosphaera intervals did not change, and used thevariation of carbonate content to vary the sedimentationrate(Mead, 1995).
Smear-slides were made from fine-fractions( <63 J.Ull) and set in Norland optical adhesive. Microscope
analyses were done at xlOOO magnification under phasecontrast a nd crossed-nicols on a Zeiss Axioscop
microscope. Nannofossil abundance counts are based ona total of300+ specimens per slide.
Oxygen and carbon isotope results and methods
are documented in detail by Mead (1995). Foraminiferal
and fine-fraction isotope data are available for Site 363.
However, foraminiferal isotope data were not generated
for Site 522 due to evidence of carbonate diagenesis andthe absence of Chiloguembelina cubensis. The following
foraminifera, representing different water-column habitats,were analysed: C. cubensis (shallow planktonic),
Catapsydrax dissimilis (deep-living planktonic) andCibicidoides spp. (benthic).

w

"'

0

u

40
-

-:l

~"j

5~
6~

7 G;I
120

sB
140

Figure 2: Cores 363, 522 and 522A sampled for this study. Arrows
i:ldicate cores used. Magnetostratigraphy of Site 522 is from Tauxe
ez aL (1984). Calcareous natmofossil zones are from Proto Decima
n aL ( 1978) and Percival (1984). Tie-lines indicate calcareous=ofossi1 zone boundaries between cores. In Site 363,
3~dosphaera ooze/chalk layers are indicated by short horizontal:!:::x:s within the core. Modified from Mead (1995).

19

Journal of Narmoplankton Re~arch, 21, I, 1999. A.M.Peleo-Aiampay, GAMead,W.Wei:Oiigocene Braamdosphaera-rich layers.. p. 17-26.

Braarudosphaera have been found in the N

SITE363

]'
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0

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c

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=

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<=l!

fu ~ fc! ~u ano

108.960 1.332 1.381

c

5-2,64-66

109. 150 0.210 1.324

5-2,69-71

109.200 1.146 1.279

c
Cl>

c
Ch
109.305 0.464 1.236 cc129.540 0.339 1.420 c
0.174 1.562 Ch
ChCH
129.845 1.644 1.918 c
Cl>
Ch
CH
129.900 1.758 2.419 c

c
c
Ch
Cl>

16-3,96-99

129.975 2.153 2.232

6-3, 104-106

130.050 2. 131 2.506 Ch
1.733 2.582 CH
130.200 1.829 2.727 c
Ch130.250 2. 189 2.710 c
130.300 1.546 2.531
cCl>

6 -3, 119-121
6-3, 124-127
6-3, 129-131

6-3, 140-142

130.410 1.034 2.085

f---6-4, 4-6

c
Cl>
Cl>
CH

f.---

6-3, 144-146cc130.450 1.997 2.464
1.568 2.519
130:550 1.481 2.38E

c
Cl>

c
c
Ch
Cl>
CH

6-4, 14-16

130.650 1.005 2.067

7- 1,49-52

145.505 0.165 1.208

c
Ch

c
Cl>
Cl>

7-1,89-91
7-1,90-93
7-1, 109-113
7-1,115- 120
7-1. 128- 133
7 -1, 133-135
7-1, 146- 149
7-CC

145 .900 0.968 2.709
145.91 5 0.827 2.152
0.681 2.404
146.110 2. 180 3.527
146 .175 2.091 3.697
146.305 2.366 3 .675
1.855 3.581
146.340 1.949 3 .663
146.450 2.45 1 3.662
146.500 2.436 3.668

p
p
c
p

p

~ Atlantic Ocean.
~t~"""El- 5 .s g -~li .!!
~ll
e ~8 :g~c " ~ -~
t. ..!!
~ Q :~"' :t:~ \.i t.
<nabundance and oxygen. Braarudosphaeraisotope data-~~

5-2, 45-47

6-3.89-91

dissimilis

Cibicidoides
spp.

=
.g

c

6-3,83-86

cuben.fi!

~'[ ,§! ..:~....~
t~ o"'
u"'~~108.845 0.841 1.447

5-2,79-82

Campsydnu

05-2,33-36

6-3,53-55

Chtlog•emMliM

d"C

d"O

auc a..od"C"' r/1.
~·0 .177r/1.~~

1.159 0.857 0.269 1.623 0.528 0 3 51 2 44
1.626 0.542-0.325 1.088 0.912 0.5 10 0.601 0.971 18 6 45 2 47
1.365 0.602-0.351 0.838 1.445 0.589 1.496 0.534 7 10 47 2 41
-0.443 0.970·0.051 1. 108 1.164 0.754 1.527 0.715 56 8 53 4 35
0.242 1.219
1.441 0.745·0.282 0.739 0.672 0.962 1.356 0.356 0 13 48 3 36
0.049 0.894
1.575 0.473
0.098 1.483 0.811 0.956 1.948 0.834 3 9 42 I 48
1.705 0.767
1.906 1.067·0.030 1.645
0.351 1.723
0 .564 1.818 1.010 1.226 1.730, 1.081 36 6 38 0 55
0.624 1.880
0.666 1.916
I
0.888 1.705
0.011 -0.137 1.014 1.371 1.193 0.976 7 1 8 37 I 55
1.411 0.750
1.322 0.844
0.154 2.006
0 .404 1.943
0 .519 1.838 1.019 1.264 1.374 1.103 7 3 12 251 62
0. 212 1.64 1
0.235 1.594 1.197 1.313 1.502 1.218 78 15 23 0 63
0.698 1.281-0.015 1.770 1.040 1.232 1.115 1.047 80 9 22 I 68
·0.294 1.779
0.167 1.787 1.247 1.168 1.533 1.296 68 7 33 00.004 1.750 1.200 1.136 0.920 0.875 59 12 38 0 50
-0 .018 1.811 1.112 1.277 1.082 0.845
1.046 0.855·0.014 1.730 1.058 1.132 1.237 0.828 48 10 3 3 I 55
1.238 0.832
0.07 1 1.907
1.055 0.909·0.027 1.784-0. 166 1.874
0.517 1.885 0.997 1.272 1.545 0.95 1 63 11 35 0 53
0.665 1.897
1.830 0.932
0.077 1.799 0.869 1.192 1.078 0.968 45 7 46 1 46
1.748
·0.001
0. 144 1.907-0.044 1.76(
0.061 1.912-0 .023 1.617 0.876 1.214 0.979 0.787 33 5 38 I 56
0. 113 1.790-0.771 1.222 0 .418 0.977 0.956 0.708 5 14 26 2 58
·0. 146 1.496.
1.301 0 .582
1.208 0.586.
·0.784 1.347-0.328 1.097
0.1 19 0.902 0.983 1.087 1.267 1.089 65 25 28 I 46
0.440 1.994 0.363 1.223 1.659 0.979 46 20 29 I 50
1.160 1.099
92 27 2 1 0 52
1.773 1.739 0 .000 1.386 1.325 1.490 96 29 15 I 56
95 34 19 0 47

\.i
7.6
7 .7
7.5
7.6
7.7

7.6

8.4

8.1

8.5
8.4
8.5

I§Q 8.3

0.458

0.441

8.3

8.3

7.3
7.9

7 .2
7.8

8.6
8.7
9.6
9.4
8.7

0.438 1.642 1.503 1.574 93 34 13 0 53 8.6
94 4 5 11 0 44 100.129 1.365 1.279 1.441 98 50 13 0 37 9.3

Table 1: Calcareous nannofossil abundances, C. pe/agicus length mcasureml!nts,[me-fraction and foraminiferal oxygen and carbon isotope data for Site 363. Isotope
data are from Mead (1995). Different size-fractions of C. cubensis were analysed
for isotopes a nd are designated by the following: c= l04-125f1m; C= J04-l50f1m;
Ch=l25- l50f1m; CH=l50-2 50 f1m; cC= l04-250Jll11; P=125-150f1m (bulk planktonic
foraminifera analysed). Discoaster, sphenolith, Helicosphaera and C. pelagicus
percentages are fractions of the total of these four nannofossil groups and do notinclude Braarudosphaera values.

Results
Distribution of Braarudosphaera chalk
An extensive survey of DSDP and ODP nannofossil
biostratigraph.ic literature revealed t11at occurrences ofBraarudosphaera oozes and chalks appear to be
distributed between -19° to 30° latitude in the S Atlantic(Legs 3, 40 and 73 ; Figure 1). These oozes and chalks are
assigned to calcareous nannofossil zones NP22-NP24(Oligocene; Parker et al., 1985). At Site 362 (Leg 40), atleast 34 cyclic Braarudosphaera beds, with an interbed
period of 100 000 years or less, were reported. Ot11er
Oligocene occurrences with lower abundances of20

Nannofossil analysis reveals that
Braarudosphaera comprises 18-98% of thena nnofossil assemblages in the
Braarudosphaera layers in Site 363 and 7989% in Site 522 (Tables l and 2). Results from
Site 363 show that higher percentages ofBraarudosphaera correspond to morepositive shallow planktonic foraminiferala l8o values (Figure 3) and, presumably, coldwater conditions. This correspondence is also
shown between the fme-fraction a l8ovalues
and Braarudosphaera abundance in both
Sites 363 and 522 (Figures 4 and 5). o,.-ygenisotope values from the deeper planktonic andbenthic foraminifera do not show any
correlation with Braarudosphaera
abundance (Speannan correlation coefficient,r' = 0.073 for tl1e deeper planktonics andr' = -0.072 for the bentltics). These resultsfrom tl1e forantiniferal a 18o data in Site 363
suggest that the Braarudosphaera
occurrence is a surface-water phenomenon.
Although Sample 363-5-2, 45-47cm(1 08. 96mbsf) was previously assumed byMead (1995) to be Braarudosphaera ooze,
quantitative analysis in this study reveals a
relatively low percentage of braarudoSQhaerids (18%). The correlation of higher
a 18o values and greater Braarudosphaera
abundance is consistent with reports from
Lloyd & Hsii (1972) and Siesser et al. (1992).
Average palaeotemperatures at Site 363 were
estimated, based on fine-fraction oxygenisotope analyses, as 5, 6 and 9°C within
Braarudosphaera layers in cores 7, 6 and 5,
respectively (Mead, 1995). Average
palaeotemperatures for the non-Braarudosphaera intervals were estimated as 10, 9
and l2°C for cores 7, 6 and 5, respectively,
based also on fine-fraction oxrygen isotope
results (Mead, 1995). Wise & Hsii (1971)
ascribed tl1eir low palaeotemperature estimate(6°C) for the braarudosphaerid layer toisotopic re-equilibration during diagenesis of thebraarudosphaerids on the sea-floor. They assumed aminimum temperature of 10•c for the growth ofBraarudosphaera, based on the fact that living
braarudosphaerids have not been found below thistemperature. A plankton study in the English Channel,
however, showed that Braarudosphaera was mostabundant during the winter months (Boalch, 1987) whentemperatures range from 5 to 10°C (Robinson et al. , 1979).
This would be consistent with the relatively low
palaeotemperatures estimated by Wise & Hsii ( 1971) andMead(l995).

AM.Peleo-Alampay. GA.Mead,WWei:Oligocene Braarudosphaera-rich layers.. p. 17-26. Journal of Nannoplankton Research, 21 , 1, 1999.

522 & 522A

5:::1. 5:::1.
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13-1 ' 63-67
25-2, 68-70
13- 1' 84-86
13- 1' 94-96
25-2, 83-85
13- I , I 04- 106
25-2,99- 101
13-1 , I 14- I 16
13-1, 124- 126
25-2, 116- I 18
13-1 , 138- 141
25-2, 137- 139
13-2, 14-16
13-2, 24-27
13-2, 34-37
13-2, 44-46?
Q! i'o

i'o

93.48
93.60
93.79
93.80
93.90
93.94
94.00
94.10
94.10
94.20
94.27
94.35
94.48
94.60
94.70
94.80
94.90

1.97 002.27 02.38 02.41 80
2.20 79
2.35 88
2.19 84
2.25 85
2.19 89
2.13 6
2.39 47
2.29 02.3 1 02.37 3
2.46 02.61 0..(0Discoasters and sphenoliths
The relative abundances of cool- and warm-waternannofossil taxa were determined to investigate possible
temperature changes across the Braarudosphaera-richlayers. Biogeographic studies have established the warmwater preference of sphenoliths and discoasters (e.g. Haq& Lohmann, 1976a, b; Haq, 1980; Backman eta/., 1986;
Wei & Wise, 1990). At Sites 363 and 522, sphenoliths
outnumber discoasters in all ofthe cores except Core 3637 (Tables l and 2). There are also more sphenoliths than
Coccolithus pelagicus in Site 522 cores and in Core 363-5.
Sphenolith abundance clearly shows ananticorrelation with Braarudosphaera abundance (Figures
6 and 7). More sphenoliths correlated with fewer
Braarudosphaeras in warmer intervals. On the other hand,
Discoaster abundance was unexpectedly higher duringcolder intervals. This difference is also shown in Discoasterand sphenolith percentage curves in Site 522 samples in
Wei & Wise (1990) but was not discussed. Consequently,
sphenoliths should be considered as better palaeotemperature indicators in these Early Oligocene S Atlantic
waters than tl1e discoasters.

I

HOLES

5:->

0.61
0.90
0.78
2.48
2.34
2.37
2.25
2.25
2.10
0.81
1.21
0.82
0.92
0.91
0.99
1.08

Q:l
~

s

00

u

~

~

u~

100 24 49 27
100 18 45 37
100 25 42 34
100 20 51 28
20 23 54 23
21 23 50 27
12 35 42 24
16 22 48 31
16 44 35 21
11 27 49 24
94 21· 49 30
53 25 53 22
100 22 153 26
100 15 53 32
97 20 56 24
100 17 45 37
100 14 58 28

10.6
9.3
9.5
9.5
10.5
11.1
13.4
13.4
13.4
11.8
9.4
10
10
8.6
10.4
8.2
8.9

0

~

~

~

~:>.8

Coccolithus pelagicus
Coccolithus pe/agicus has been shown to prefer coolwater conditions (Haq, 1980; Raffi & Rio, 1981; Wei &Wise, 1990). Other cool-water indicators, such as
Reticu/ofenestra daviesii and Chiasmo/ithus spp. are eitl1er
absent or too rare to be used effectively in tl1is study.
There is a significant difference in tl1e range of C.
pelagicus abundance between the two sites (Tables 1 and
2). At Site 522, .C. pelagicus comprises 21-37% of tl1e

Table 2 : Calcareous oannofossil abundances, C. pelagicus length
measurements, fine-fraction oxygen and carbon isotope data (from
Mead, 1995) for Holes 522 and 522A. Discoaster, spheno lith,
Helicosphaera and C. pelaglcus percentages are fractions of thetotal of these four nannofossil groups and do not include
Braarudosphaera values.

<:s-~-4-.L~I

IOOrJte 363

-0.5

]80~
c~ 60

;:s

...

~

~

40
20
0
108.8

0

0

0.5

§.. ~

1.0

.s"'

C">Q)

~

~

t -1.0

109.2

129.4

129.8

130.2

130.6

~ 0

1.5

....

L-.1:.~~..-~ ~~~......,.~~ 2.0
J4~6
146.2
145.8

145.4 T

DEPTH (mbst)
Figure 3 : % Braarudosphaera ( +) and a l 8o (open circle) of shallow planktonic foraminifer, Chiloguembelina cubensis ( I 04-125f!msize-fraction) in Site 363. Spearman 's correlation coefficient, r ' = 0.624.

.,~

100

0

80

0.5

<:!

..:::

s

~ 60

::s
1.0 '!' Q):::t' ~

i:<::S

40

1.5

Q:l
~

20

2.0

.g
~

~ 0
=
·
0

2.-

0
108.8

109.2

12M

129.8

130.2

130.6

145.4

145.8

146.2

2.5
146.6

DEPTH (mbst)
Figure 4 : % Braarudosphaera (+ ) and fine-fraction a 18o (open circ le) from S ite 363. Spearman's correlation coeffi cient, r ' = 0. 874 .

21

Journal ofNannoplankton Research, 21, 1, 1999. A.M.Peleo-Alampay, GAMead,W.Wei:Oligocene Braarudosphaera-rich layers.. p. 17-26.
100

:::

Site 522

0.5

80

"'

s

<:;

..::

~

nannofossil assemblage, excluding Braarudosphaera,
while at Site 363, it ranges from 35-68%. In addition, at Site
363 there is a general positive relationship between C.
pelagicus and Braarudosphaera abundance (Figure 8),that is, hi~her abundance of C. pelagicus corresponds tohigher al 0 (cold-water conditions). However, these tworecords show a general anticorrelation at Site 522 (Figure9). We suspect that this may be related to the significantly
lower abundance of C. pelagicus at this site compared to
Site363.

60

"'"'

~

'

CV

1.5 ~;...<:;...<:;
1:::1

40

<f.

20

::!

~ 0

c;·
2..
2

93.4

93.6

93.8

94

94.2

94.4

94.6

94.8

Coccolithus pelagicus size
Coccolith size may be related to surface-water temperature.
Baurnann (1995) docwnented an increase in the abundance,

DEPTH (mbsf)
Figu re 5: % Braarudosphaera (+) and fine-fraction a l 8o (opencircle) from Site 522. Speannan's correlation coefficient, r' = 0. 768.

<fl

20 I:)

s;·

~ 20

10

o ++~.-~~T4~~~~~~~~~~-.~~~~~~~ +~~~~~~~~~~~~~+ 0

108.8

109.2

129.4

129.8

130.2

130.6

145.4

145.8

146.2

146.6

r>

0
11>

.,!0"'"'

DEPTH (mbsf)
Figure 6: % Discoastcrs (closed circle), % Sphenoliths (closed triangle) and % Braarudosphaera (+) from S ite 363.

60

100

.c
"'
:0::
0 50
=
~
.c

80

~

40

60

~
~

;:::
....,

c?J

..."'
....

~

t:c

1:1.

00

~

30

40 ~

"'0
<.1
"' 20
~

l:l

~

;::-

~

~

20

~

~

93.4 93.6 93.8 94.0 94.2 94.4 94.6 94.8 95.0

DEPTH(mbsO
Figure 7 : % Discoasters (closed circle), % Spheno liths (closed
triangle) and% Braarudosphaera (+)from Site 522.

100

l:
~

and a marked decrease in the length, of C. pelagicus
specimens in the Norwegian-Greenland Sea during the
Holocene and Interglacial Stage 7. In this study, larger C.
pelagicus correlates with a higher abundance ofBraarudosphaera (Figures 10 and 11) at Sites 363 and 522.
This suggests colder conditions for the Braarudosphaerarich intervals.

Carbon isotope data
Braarudosphaera abundance generally correlates with
fo raminiferal carbon isotope values of Catapsydrax
dissimilis and Cibicidoides spp. at Site 363 (Figures 12
and 13). Higher al3c values accompanied by hig her
braarudosphaerid abundance may be interpreted as
evidence for increased productivity in the surface-waters,
since lighter 12c is preferentially taken up during
photosynthesis. However, the a l 3c curve of the planktonic
and benthic foraminiferal isotope values is inconclusive,

Site 363

80

60 <fl

c::s

..:::

~ 60

~
::s

..

c::s

50

~

20
0
108.8

~

~
!';'
40 t;

40

l:

l:l::l~'1:!

~~~~~~~~~~~~~~~~~+~~~~~~--~~~~r-~~ 30

109.2

129.4

129.8

130.2

130.6

145.4

145.8

146.2

DEPTH (mbsf)
Figure 8 : % Braarudosphaera (+) and % C. pelagicus (closed diamond) from Site 363.

22

146.6

AM.Peleo-Alampay, GA.Mead,W.Wei:Oligocene Braarudosphaera-rich layers.. p. 17-26. Journal ofNannoplank.ton Research, 21 , 1, 1999.
100

40

Site 522::: 80

35

\-

~

'::!

..=:

30 ~

~

... 40
::!
'::!

:::
Q:)
~

~
r:;·

l\

20
0

<;'2l
~

~ 60

!::

25

"'

I o lo o I o o o 1f o o o I o o o I o o o I 1\1 I 1-<j""j"""j>l I I I I 20
93.4 93.6 93.8 94.0 94.2 94.4 94.6 94.8 95.0
DEPTH (mbsf)

Figure 9: % Braarudosphaera (+) and % C. pelagicus (closed
diamond) at Site 522.

so the above interpretation, linking Braarudosphaera
abundance and productivity of surface-waters, cannot be
substantiated by these results.
There is a possibility that diagenesis controls thenannofossil taxa and isotopic variations. However, there
were no significant secondary overgrowths on the
Braarudosphaera pentaliths and on the forarninifera asverified by SEM examination (Mead, 1995). Moreover, thecorrelation between the size of C. pelagicus placoliths and% Braarudosphaera and, by inference, the a18o values
argues against a significant diagenetic control on theisotope signal.
Another possibility is that tl1e variation in a18o
and a13 c values in the fine-fraction could be due to vitaleffects. Analyses on individual laboratory-cultured
coccolitll species (Dudley & Goodney, 1979) and fine-I

100 lsite 363
~
] 80

I

~E 105r':l

10'1:::1

9.5

~

{5 60

9

f:

~ 40

8.5

~

8

~

20

7.5

0 I ( .. , .. " , + , I -b--.-'...;.,-~~,.........~....,~....-.~~,-~.-~-.+ +-.~....~....-,~~,....--.-,,...,-~....-,~~+ 7](J8.8.
109.2. 129.4
129.8
1:30.2
130.6
145.4
145.8
146.2
146.6

"'
~
....

1::

"'
;-

=
as.
::r

"!.-..

DEPTH (mbsf)
Figure 10: % Braarudosphaera (+) and length of C. pelagicus placoliths (open diamond) from Site 363 .

100

:::

14

Site 522

13 ~80'1:::1

"'

~

12 {.

'::!

..:::

~

....

60

!::

{5

11

::!

a 40

=
as.

A !

~
i:l:l

~

"'
;-

10 .:::

20

90 I oil I I I I I 1/ I I I I I I I I I I I I 1,1 I rc;==;==;.j I I I I 8
93.4 93.6 93.8 94.0 94.2 94.4 94.6 94.8 95.0

DEPTH (mbsf)
Figure 11 : % Braarudosphaera (+) and length of C. pelagicus
placoliths (open diamond) from Site 522.
100

~

~"'

~

~

fraction samples witll coccoliths (Paul! & Thierstein, 1987)
have shown iliat vital effects influence their isotopic
composition. Kinetic vital effects in calcareous organisms
results in l3c and 18o depletion with rapid calcification(McCo1maughey, 1989). The isotope record, however,indicates an increase ratller than a decrease during tl1e
Braarudosphaera-cich intervals, where calcite productionis the greatest, and t11erefore argues against the influenceof vital effects on tl1e fine-fraction isotope values.
The nannofossil abundance patterns and finefraction oxygen and carbon isotope variations as discussed
above are, t11erefore, probably mainly a reflection ofpalaeoceanographic conditions. One of the proposed
oceanic events discussed earlier involved a major freshwater input into tlle S Atlantic from tlle continent to reducesalinity (Bolli et al., 1978). Salinity decrease brought about
by fresh-water input would have to be accompanied by~~

I

jSite 363~

~ 1 .81.6

80

1.4 .-..
1.2 0

60

"'-

... 40'::!

1 o:;· ct:!
08§·r:5

Q;)

0.6

;:!

.

~

~

20
0

0.4
108.8

109.2

129.4

129.8

~

130.2

130.6

145.4

145.8

146.2

DEPTH (mbsf)
Figure 12:% Braarudosphaera (+) and a!3c (open circle) of Catapsydrax dissimilis ti·om Site 363.

23

.s-·

Journal ofNannoplankton Research, 21 , I, 1999. A.M.Peleo-Alampay, GAMead,WWei:Oligocene Braarudosphaera-rich layers .. p. 17-26.

1.6
1.4

0

<:>1.2 ;:;·

-·~~

"'
0.8 f}<i0.6 "'

"'

"0

109.2

129.4

129.8

•

130.2

130.6

145.4

145.8

146.2

0.4 "0.:._..
0.2
146.6

DEPTH (mbsf)
Figure 13: % Braarudosphaera (+)and a13c (open circle) of Cibicidoides spp. from Site 363.

additional cooling of the surface-waters, given that theisotopic values of planktonic foraminifera changed very
little.
Discussion
Upwelling of low-salinity water
The hypothesis of upwelling as the mechanism forincreased Braarudosphaera production in the S Atlantic
during the Oligocene is supported by the nannofossil andisotopic evidence presented above. The correspondenceof high Braarudosphaera abundances with low
abundances of warm-water taxa (sphenoliths), longer C.
pelagicus placoliths and high 818o values suggests colder
water conditions during intervals of increased
Braarudosphaera production. Modern braarudosphaerids
are generally known to prefer low-salinity waters. So, alikely scenario is upwelling of cold, nutrient-rich and lowsalinity waters into the S Atlantic, leading toBraarudosphaera blooms. The Antarctic region is the most
likely source for cold, low-salinity waters. Antarctic
Intermediate Water (AAIW) is currently formed below
the Antarctic Polar Frontal Zone from the nortllwardflowing low salinity Antarctic Surface Water, and spreads
northwards throughout the Southern Hemisphere and into
the Atlantic as a tongueoflow-salinity (34.2-34.3o/oo) waterwith its core at 800-1 OOOm depth at 40oS (Pickard & Emery,1982). There is no definitive evidence that AAIW existed
during the Oligocene, but this has been speculated(Kennett & Stott, 1990; Diester-Haass, 1995). The
presence of AAIW in the soutl1ern Indian Ocean was
postulated from changes in carbon isotope distributions
during tl1e early Oligocene by Zachos et al. (1990).

Opening of the Drake Passage
The initiation oftl1e Antarctic Circwnpolar Current, as the
Drake Passage opened and Australia continued its
northward movement away from Antarctica, could havebeen the triggering mechanism for the rich
Braarudosphaera beds in tl1e Oligocene. The increased
N-S circulation that this event has created in the Atlantic
would have enhanced upwelling conditions.
The timing of opening of the Drake Passage haslong been debated. Part of the debate centres on theinterpretation of the Western Scotia Sea magnetic
anomalies (LaBrecque & R.abinowitz, 1977). Barl<:er & Burrell( 1977) concluded that the opening of the Drake Passage
started during Chron C8 (Late Oligocene). On tl1e other

hand, LaBrecque & R.abinowitz ( 1977) placed this event
during Chrons C 10 (Early Oligocene) to C 13 (Late Eocene),coincident with the time of Braarudosphaera-ooze
deposition in the S Atlantic. However, Wright & Miller( 1992) believed that analysis of the opening of the Scotia
Sea alone may not have been sufficient because of thecomplexity of the opening of the Drake Passage. Theysuggested that a shallow opening of the Drake Passage
may have been in existence since the earliest Oligocene,
based on the relative movement between South America
and the Antarctic Peninsula (Lawver et al. , 1992). DiesterHaass & Zahn ( 1996) concluded from their isotopic study
that the Drake Passage was already open to intermediate
depths as early as 37Ma (Late Eocene). Several studies,
therefore, support the coincidence between the intervalsof increased Braarudosphaera deposition and thepresence of at least a shallow opening in the Drake Passage.

Mid-ocean overturn
The Braarudosphaera blooms may also be explained by
mid-ocean overturn. Kennett & Stott (1990) suggested iliat
the Oligocene ocean (proto-Oceanus) represented anintermediate condition between the Eocene halothermal
and tl1e Present Day tl1ermohaline oceans. Tlus type oftransition has the potential to bring about instabilities intl1e water-column. Once instability in the water-column ispresent, mid-ocean overturn can occur as a result of
seasonal cooling (Berger, 1981). This phenomenon has
been observed off Toulon, in the W Mediterranean Sea(MEDOC Group, 1970; Anati & Stommel, 1970). Here,
cyclonic circulation and winter surface-cooling combine
to reduce the surface-layer stability of the waters andpromote vertical mixing of the surface-layer. Winterstorms build on tllis instability and bring about deep,
penetrative convection in a narrow area of about 25 miles,
reaching 1400m deptl1. When the storm ceases, the mixed
water sinks quickly and spreads out horizontally. This
process of seasonal overturn brings deep, nutrient-richwaters to the surface. The sporadic nature of this type of
mid-ocean overturn process may encourage ilie growth ofopportunistic algae, such as braarudosphaerids.

Further worl<
Further work to test tl1e results from tllis study should
include isotope analysis of isolated Braarudosphaera
pentaliilis. Tllis may be possible using Paull & Thierstein's(1987) automated decanting device which separates the24

AM.Peleo-Alampay, GA.Mead,W.Wei:Oligocene Braarudosphaera-rich layers.. p. 17-26. Journal ofNannoplankton Research, 21, I, 1999.

fine-fraction particles into subfractions. The obvious size
difference between the braarudosphaerids and the othertaxa will be an advantage for such an analysis. The
possibility of wind-induced upwelling can be tested byinvestigating climate proxies along the South African
margin. Abundance changes of temperature-sensitive
calcareous nannofossil taxa in short time-intervals,
corresponding to the time ofBraarudosphaera deposition,
can also be investigated in other oceanic sites to tracewater-mass movements in the S Atlantic.
Conclusions
Quantitative calcareous nannofossil data show that hi~herabundances of Braarudosphaera correlate with high a 8ovalues and lower abundances of Sphenolithus, a warmwater genus. Increased Braarudosphaera abundance also
corresponds to longer C. pelagicus placoliths and toelevated C. pelagicus abundance. These results appear toindicate that colder water conditions prevailed during times
ofelevated Braarudosphaera deposition in the S Atlantic.
All tllis suggests that the widespread Oligocene
Braarudosphaera-rich layers are most likely tl1e result of
the upwelling ofcold, nutrient-rich, low-salinity waters via
AAIW, or seasonal overturn ofan unstable water-column.
Acknowledgements
We gratefully acknowledge the constructive and very
helpful comments that W. Berger, T. Herbert, C. Charles
and J. Young have given to improve the manuscript. AMPA would like to tllank the International Nannoplankton
Association for their financial support in enabling her topresent this paper at the 7th INA Conference. GAM would
like to thank D. Hodell and P. Ciesielski for encouragement
and assistance in this study. A class led by Dr. E.L. (Jerry)
Winterer first initiated the idea for isotopic analysis ofBraarudosphaera oozes. This research was supported inpart by a University of California President's Dissertation
Fellowship to AMP-A and National Science Foundation
grants OCD-8850 12 and DPP-8717854 to GAM.

References
Anati, D. & Stommel, H. 1970. The initial phase of deep water
formation in the northwest Mediterranean, during MEDOC'69, on the basis of observations made by Atlantis II, January
25-February 12, 1969. Cal1ier Oceanographie, 22: 343-350.
Backman, J., Pestiaux, P., Zimmerman, H. & Hermelin, 0. 1986.
Paleoclimatic and paleoceanographic development in the
P1iocene North Atlantic: discoaster accumulation and coarse
fraction data. In: C.P. Summerhayes & N. Shackleton (Eds).
North Atlantic Paleoceanography Geological Society Special
Publication, 21:231-242.
Barker, P.F. & Burrell, J. 1977. The opening ofthe Drake Passage.
Marine Geology, 25(112): 15-34.
Baumann, K.-I-1. 1995. Morphometry of Quaternary Coccolitlms
pelagicus coccoliths from northern North Atlantic and its
paleoceanographic significance. In: J.-A. Flares & F.J. Sierra(Eds). Proceedings of the 5th INA Conference, Salamanca:
11 -2 1.
Berger, W. 1981. Paleoceanography: the deep-sea record. In: C.
Emiliani (Ed.). The Sea: The Oceanic Litl10sphere, Vol.7:
1437-1519.

25

Boalch, G. T. 1987. Changes in the phytoplankton of the western
English Channel in recent years. British Phycological Journal,
22: 225-235.
Bolli, H.M., Ryan, W.B.F. et al. 1978. Initial Reports of theDSDP,40.
Bukry, D. 1971. Cenozoic calcareous nannofossils from the Pacific
Ocean. San Diego Natural History Transactions, 16: 303328.
Bukry, D. 1974. Coccoliths as paleosalinity indicators: evidence
from the Black Sea. American Association of Petroleum
Geologists, Memoir, 20: 353-363.
Bukry, D. 1978. Cenozoic silicoflagellate and coccolith
stratigraphy, southeastern Atlantic Ocean, Deep Sea Drilling
Project Leg 40. Initial Reports ofthe DSDP, 40: 635-649
Can de, S.C. & Kent, D. V. 1995. Revised calibration of thegeomagnetic polarity timescale for the Late Cretaceous andCenozoic. Journal ofGeophysical Research, 100:6093-6095.
Diester-Haass, L. 1995. Middle Eocene to early Oligocene
paleoceanography of the Antarctic Ocean (Maud Rise, ODP
Leg 113, Site 689): change from a low to a high productivity
ocean. Palaeog~ography, Palaeoclimatology. Palaeoecology,
113: 311-334.
Diester-Haass, L. & Zahn, R. 1996. Eocene-Oiigoccne transitionin the Southern Ocean: history of water mass circulation andbiological productivity. Geology. 24(2):163-166.
Dudley, W.C. & Goodney, D.E. 1979. Oxygen isotope content
of coccoliths grown in culture. Deep-Sea Research, 26A:
495-503.
Fischer, A.G. & Arthur, M.A. 1977. Secular variations in the
pelagic realm. In: H.E. Cook & P. Enos (Eds). Deep-Water
Carbonate Environments. SEPM, Special Publication, 25:
19-50.
Gran, H.H. & Braarud, T. 1935. A qualitative study of thephytoplankton in the Bay of Fundy and the Gulf of Maine.
Journal ofthe Biological Board ofCanada, 1: 279-467.
Haq , B. 1980. Biogeographic history of Miocene calcareous
nannoplankton and pa1eoceanography of the Atlantic Ocean.
Micropaleontology. 26(4): 4 14-443.
Haq, B.U. & Lohmann, G.P. 1976a. Early Cenozoic calcareous
nannoplankton biogeography of the Atlantic Ocean. Marine
M icropaleontology. 1: 119-94.
Haq, B.U. & Lohmann, G.P. 1976b. Calcareous nannoplankton
biogeography and its paleoclimatic implications: Cenozoicof the Falkland Plateau (DSDP leg 36) and Miocene of theAtlantic Ocean. Initial Reports of the DSDP, 36: 745-759.
HsU, K.J., LaBrecque, J.L. et al. 1984. Initial Reports of theDSDP, 73.
Kennett, J.P. & Stott, L.D. 1990. Proteus and Proto-Oceanus:
ancestral Paleogene oceans as revealed from Antarctic stable
isotopic results: ODP Leg 113. Proceedings of the ODP,
Scientific Results, 113: 865-880.
LaBrecque, J.L. & Rabinowitz, P.D. 1977. Magnetic anomalies
bordering the continental margin ofArgentina. AAPG, Special
Map Series.
LaBrecque, J.L. , Hso , K.J., Carman, M .F., Karpoff, A.M.,
McKenzie, J.A., Percival, S.F., Petersen, N .P., Pisciotto,
K.A., Schreiber, E ., Tauxe, L., Tucker, P., Weissert, H.J. &Wright, R. 1983. DSDP Leg 73: contributions to Paleogene
stratigraphy in nomenclature, chronology and sedimentation
rates. Palaeogeography, Palaeoclimalology. Palaeoecology,
42: 91-125.
Lawver, L.A. , Gahagan , L.M. & Coffin, M.F. 1992. The
development of paleoseaways around Antarctica. In: J.P.
Kennett & D.A. Warnke (Eds). The Antarctic
Paleoenvironment: A Perspective on Global Change, Part].
Antarctic Research Series, 56: 7-30.
Lloyd, R.M. & Hso, K.J. 1972. Stable isotope investigations of

~

l

;o

lli

I

Journal of Nannoplankton Research, 2 1, 1, 1999. A.M.Peleo-Alampay, GAMead,WWei:OJi gocene Braarudosphaera-rich layers.. p. 17-26.

sediments from the DSDP m cruise to South Atlantic.
Sedimentology, 19: 45-58.
Lohman, W.H. 1986. Calcareous nannoplankton biostratigraphyof the Southern Coral Sea, Tasman Sea, and Southwestern
Pacific Ocean, Deep Sea Drilling Project Leg 90: Neogenc andQuaternary. Initial Reports of the DSDP, 90: 763-794.
Martini, E. 1967. Nannoplankton und Umlagerungserscheinungen
im Persischen Golfund in nordlichenArabischen Meer. Neues
Jalrrbuchfor Geologie und Paliiontologie, Monatslrefte, 10:597-607.
Martini, E. 197 1. Standard Tertiary and Quaternary calcareous
nannoplankton zonation. In: A. Farinacci (Ed.). Proceedings
ofthe If Planktonic Conference, Rome, 2: 739-785.
Maxwell, A.E., von Herzen, R.P. et al. 1970. Initial Reports oftheDSDP,3 .
McConnaughey, T. 1989. Be and 18o isotopic disequilibrium
in biological carbonates: II. In vitro simulation of kinetic
isotope effects. Geochimica et Cosmochirnica A cta, 53(1):151-162.
Mead, G. 1995. Paleoccanography of the South Atlantic Ocean
from the middle Eocene through the Oligocene. Unpublished
PhD thesis, University of Florida, Gainesville.
Mead, G.A. & Hodcll, D.A. 1995. Controls on the 87srt86sr
composition of seawater during the Late Eocene to Oligocene:
Hole 689B, Maud Rise, Antarctica. Paleoceanography, 10(2):327-346.
MEDOC Group 1970. Observatio n of formatio n of deep waterin the Mediterranean Sea, 1969. Nature, 227: 1037-1040.
Melguen, M . 1978. Facies evolution, carbonate dissolution cycles
in sediments from the eastern South Atlantic (DSDP Leg 40)
since the Early C retaceous. Initial Reports ofthe DSDP, 40:
981-1024.
Okada, H . 1992. Biogeographic control of modern nannofossil
assemblages in surface sediments of Ise Bay, Mikawa Bay
and Kumano-nada, off coast of central Japan. Mem. Inst.
Geol. Mineral. Univ. Padova, 43: 43 1-449.
Okada, H. & Honjo, S. 1973. The distribution of oceanic
coccolithophorids in the Pacific. Deep-Sea Research, 20: 355374.
Parker, M .E ., C lark, M. & Wise, S.W. 1985. Calcareous
nannofossils of Deep Sea Drilling Project Sites 558 and 563,
North Atlantic Ocean: Biostratigraphy and the distribution
ofOiigocene braarudosphaerids. Initial Reports ofthe DSDP,
82: 559-589.
Paull, C .K. & Thierstein, H . R. 1987. Stable isotopic fractionation
among particles in Q uaternary coccolith-sized deep-sea
sediments. Paleoceanography, 2(4): 423-429.
Percival, S.F. 1984. Late Cretaceous to P leistocene calcareous

26

nannofossils from the South Atlantic, Deep Sea Drilling
Project Leg 73. Initial Reports of the DSDP, 73: 391-424.
Pickard, G.L. & Emery, W.J. 1982 . Descriptive Physical
Oceanography. 4th (SI) Enlarged Edition. Pergamon Press,
Oxford.
Proto Decima, F., Medizza, F. & Todesco, L. 1978. Southeastern
Atlantic Leg 40 ca.lcareo us nannofossils. Initial Reports of
the DSDP, 40: 571-634.
Raffi, I. & Rio, D. 1981. Coccolithus pelagicus (Wallich); a
palcotemperature indicator in the late Pliocene Mediterranean
deep sea record. In: F.C. Wezel (Ed.). Sedimentary basins ofMediterranean margins. Proceedings CNR International
Conference, Urbino University, Italy: 187-190.
Robinson, M .K., Bauer, R.A. & Schroeder, E.H. 1979. Atlas ofNorth Atlan tic-Indian Ocean monthl y mean s urface
temperatures and mean salinities of the surface layer. Naval
Oceanographic Office Reference Publication, 18.
Siesser, W.G. 1978. Leg 40 results in relation to continental shelfand onshore geology. Initial Reports of the DSDP , 40: 965979.
Siesser, W.G., Bralower, T.J. & De Carlo, E.H. 1992. Mid-Tertiary
Braarudosplwera-rich Sediments on the Exmouth Plateau.
Proceedings ofthe ODP, Scientific Results, 122: 653-663.
Smayda, T. J. 1966. A quantitative analysis of the ecologicalconditions and the phytopla nkton dynamics at 8°45'N,
79°23' \V from November 1954 to May 1957. lnter.-Am.
Tropical Tuna Comm. Bulletin, II: 353-612.
Tauxe, L., Tucker, P., Petersen, N.P. & LaBrecque, J.L. 1984.
Magnetostratigraphy of leg 73 sediments. Initial Reports of
the DSDP, 73: 609-621.
Wei, W. & Wise, S.W..1990. Biogeographic gradient of middle
Eocene-Oiigocene calcareous nannoplankton in the South
Atlanti c Ocean. Palaeogeography, Palaeoclimatology,
Palaeoecology, 79: 29-61.
Wise, S.W. & HsO, K.J. 1971. Genesis and lithification of a deepsea chalk. Eclogae Geologicae He/vetiae, 64: 273-278.
Wise, S.W. & Kelts, K.R. 1972. Inferred diagenetic history of a
weakly silicified deep sea chalk. Transactions of the Gulf
Coast Association ofGeologists, 22: 177-191.
Wright, J.D. & Miller, K.G. 1992. Southern Ocean influences on
Late Eocene to Miocene deepwaler circulation. In: J.P.
Kenn ett & D.A. Warnke (Eds). The Antarctic
Paleoenvironment: A Perspective on Global Change, Part 2.
Antarctic Research Series, 60: 1-25.
Zachos, J.C., Rea, D.K. & Lohmann, K.C. 1990. Late Eocene toearly Oligocene evolution of Indian Ocean thermal gradientsand intermediate water circulation: infere nces fromgeochemical and sedimentological data. EOS, Transactions,

American Geophysical Union, 71(43): 1398.