Late Cretaceous-Eocene nannofossil and magnetostratigraphic correlations near Gubbio, Italy

Abstract

Using a modified sample preparation technique, we have been able to establish a detailed lower Campanian to upper Eocene nannofossil stratigraphy in the Bottaccione and Contessa Highway sections near Gubbio. Appearance and extinction levels of virtually all the commonly used calcareous nannofossil zonal markers have been recognized and can now be closely correlated with the planktonic foraminifera zonation and the magnetic reversal stratigraphy previously established in these sections. Comparisons with the nannofossil calibrations of the oceanic magnetic anomaly sequence in Deep Sea Drilling Project (DSDP) sites suggest that magmetic Subchrons C17N and C25N are missing in the Bottaccione section. The observed variability of the relative stratigraphic position of most plankton events is confirmed to less than one magnetic subchron. Absolute abundance, paleobiogeographic restriction, and differential preservation render some of the traditionally used biostratigraphic events less reliable than others.

Full text

Marine Micropaleontology, 9 (1985): 419--440 419
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
LATE CRETACEOUS--EOCENE NANNOFOSSIL AND MAGNETOSTRATIGRAPHIC
CORRELATIONS NEAR GUBBIO, ITALY
SIMONETTA MONECHI 1 and HANS R. THIERSTEIN 2
I Dipartimento di Scienze della Terra, Universit~ di Firenze, Via La Pira 4, 50121 Firenze (Italy)
2Scripps Institution of Oceanography, University of California, San Diego, La JoUa, CA 92093 (U.S.A.)
(Revised version accepted December 31, 1984)
Abstract
Monechi, S. and Thierstein, H.R., 1985. Late Cretaceous--Eocene nannofossil and magnetostratigraphic cor-
relations near Gubbio, Italy. Mar. Micropaleontol., 9: 419--440.
Using a modified sample preparation technique, we have been able to establish a detailed lower Campanian to
upper Eocene nannofossil stratigraphy in the Bottaccione and Contessa Highway sections near Gubbio.
Appearance and extinction levels of virtually all the commonly used calcareous nannofossil zonal markers have
been recognized and can now be closely correlated with the planktonic foraminifera zonation and the magnetic
reversal stratigraphy previously established in these sections. Comparisons with th e nannofossil calibrations of the
oceanic magnetic anomaly sequence in Deep Sea Drilling Project (DSDP) sites suggest that magmetic Subchrons
C17N and C25N are missing in the Bottaccione section. The observed variability of the relative stratigraphic
position of most plankton events is confirmed to less than one magnetic subchron. Absolute abundance, paleo-
biogeographic restriction, and differential preservation render some of the traditionally used biostratigraphic
events less reliable than others.
Introduction
With the realization by a broad spectrum of
earth scientists, that our planet in its geolog-
ical history may have been subject to large
and possibly very rapid changes of environ-
mental conditions (e.g., Berggren and
Hollister, 1977; Thierstein and Berger, 1978;
Herman, 1981; Watts, 1982), has come a new
appreciation of the importance of high strati-
graphic resolution in any analyses of the
processes responsible for these changes.
Recent advances in high-resolution bio-,
chemo- and magneto-stratigraphy (e.g.,
Shackleton and Opdyke, 1973; Ryan et al.,
1974; Alvarez et al., 1977; Thierstein et al.,
1977; Lowrie et al., 1982; Napoleone et al.,
1983) have been instrumental in such analyses
(e.g., Hays et al., 1976; Van Couvering et al.,
1976; Silver and Schultz, 1982; Keller et al.,
1983). The fact that we can now recognize
with confidence more than 26 nannofossil
events in continuously exposed sections with
established magnetic stratigraphies will help in
identifying hiatuses, in correlating magnetic
reversals in notoriously incomplete DSDP
cores, and after appropriate radiometric
calibrations, in calculating changes in sedi-
mentation rates in sections spanning the
Cretaceous--Tertiary boundary.
The published stratigraphic studies of the
well-exposed and apparently continuous
pelagic sequences of the Umbrian Apennines
have contributed greatly to a refinement and
consolidation of late Cretaceous to early
Tertiary bio- and magneto-stratigraphies. The
0377-8398/85/$03.30 © 1985 Elsevier Science Publishers B.V.

420
stratigraphic distribution of planktonic
foraminifera in the Bottaccione section as
described by Luterbacher and Premoli Silva
{1962, 1964), Luterbacher (1964), and
Premoli Silva (1977), allowed Lowrie and
Alvarez (1977) and Roggenthen and
Napoleone {1977) to correlate the magnetic
stratigraphy in that section with the seafloor
anomaly time-scale of Heirtzler et al. (1968).
Their results led to the proposal that the
Bottaccione section should become the type
section for the late Cretaceous--Paleocene
geomagnetic reversal time scale (Alvarez et al.,
1977). The proposed Paleocene planktonic
foraminiferal and magnetostratigraphic cor-
relation was subsequently confirmed and
extended upwards to the lowermost Miocene
in the nearby Contessa section, and at the
same time numerous late Paleocene to early
Miocene calcareous nannofossil events were
recognized (Lowrie et al., 1982). The paleo.
magnetic and planktonic foraminiferal strati-
graphies of the Bottaccione section have also
,
ik=
CONTESSA L~
n
HIGHWAY~ "'~,''
SECTION ~ /
)- "\ Scheqqia
)i I ~-x\
'
BOTTACCIONE~
/
/
,
SECTION .
;ubbio
Fig. I. Location of Bottaccione and Contessa High-
way
sections.
been extended recently from the Paleocene to
the upper Eocene (Napoleone et al., 1983).
We report here the results of our detailed
light-microscopic study of the calcareous
nannofossils in the upper Cretaceous through
Eocene sequence of the Bottaccione and
Contessa Highway sections, both located near
the town of Gubbio (Fig. 1). More detailed
descriptions of the locations of the
Bottaccione and Contessa sections were given
by Alvarez et al. (1977) and Lowrie et al.
(1982).
Methods
The upper Cretaceous--Eocene Scaglia For-
mation of the Umbrian Apennines consists
dominantly of indurated, micritic, pelagic
limestones devoid of any macrofossils. Because
it has been difficult to isolate the pelagic mi-
crofossils from the limey sediment matrix with
traditional micropaleontological preparation
techniques, most of the previous biostrati-
graphic studies were carried out using thin
sections and broken sediment surfaces (e.g.,
Renz, 1936; Luterbacher and Premoli Silva,
1964; Monechi and Pirini Radrizzani, 1975).
By carefully crushing small, clean limestone
pieces with a mortar and pestle, suspending
the resulting fine rock powder, and repeatedly
decanting, we have been able to recover
adequate amounts of strongly overgrown but
still recognizable calcareous nannofossils. Our
samples were taken from the rock specimens
collected by Luterbacher and Premoli Silva
(1964), Premoli Silva (1977), and from the
drilled paleomagnetic samples taken by
Lowrie and Alvarez (1977) and Roggenthen
and Napoleone (1977). We have made a spe-
cial effort during our light-microscopic exam-
inations to reliably establish the first and last
occurrences of those taxa which have pre-
viously been used to define zonal boundaries
by Martini (1971), Bukry (1973, 1975),
Thierstein (1976), Roth (1978), Perch-Nielsen
(1979) and Okada and Bukry (1980). The
nannofossil taxa which we have identified are
listed in Table I.

421
TABLE I
Calcareous nannofossils recorded in the Umbrian sections
Paleogene
Sphenolithus anarrhopus
Discoaster aster
Discoaster barbadiensis
Chiasmolithus bidens
Braarudosphaera bigelowii
Zygrhablithus b~ugatus
Dictyococcites bisectus
Prinsius bisulcus
Heliolithus cantabrme
Ericsonia cava
Neochiastozygus concinnus
Heliolithus conicus
Chiasmolithus consuetus
Tribrachiatus contortus
Coccolithus crassus
Toweius craticulus
Coccolithus cribeUum
Chiasmolithus danicus
Discoaster diastypus
Prinsius dimorphosus
Bmarudosphaera diseula
Ellipsolithus distichus
Toweius eminens
Coccolithus formosus
Nannotetrina fulgens
Calcidiscus gammation
Chiasmolithus grandis
Rhabdosphaera inflata
Markalius inversus
Triquetrorhabdulus inversus
Heliolithus kleinpellii
Discoasteroides kuepperi
Discoaster lenticularls
Discoaster Iodoensis
Elllpsolithus macellus
Discoaster mohleri
Sphenolithus moriformis
Discoaster multiradiatus
Discoaster nobilis
Thoracosphaera operculata
Tribrachiatus orthostylus
Coccolithus pelagicus
Toweius petalosus
Fasciculithus pileatus
Cruciplaeolithus primus
Thoracosphaera prolata
Cyclicargolithus pseudogammation
Sphenolithus peeudoradians
Sphenolithus radlans
lsthmolithus reeurvus
Heliolithus riedelii
Discolithina rimosa
Discoaster saipanensis
Reticulofenestra samodurovii
Thoracosphaera saxea
Bramletteius serraculoides
Zygodiscus simplex
Zygodiscus sigmoides
Bian th ol ithus sparsus
Blackites spinulus
Discoaster su blodoensis
Ericsonia se bpertuse
Cruciplacolithus tenuis
Rhabdosphaera tenuis
Fasciculithus tympaniformis
Fasciculithus ulii
Reticulofenestra umbilica
Cretaceous
Ceratolithoides aculeus
Reinhardtites anthophorus
Watznaueria barnesae
Lithraphidites carniolensis
Bukry and Bramlette, 1969
Bramlette and Riedel, 1954
Tan, 1927
(Bramlette and Sullivan, 1961) Hay and Mohler, 1967
(Gran and Braarud, 1935) Deflandre, 1947
(Deflandre, 1954)Deflandre, 1959
(Hay, Mohlar and Wade, 1968) Bukry and Percival, 1971
(Stradner, 1963) Hay and Mohler, 1967
Perch-Nielsen, 1971
(Hay and Mohler, 1967) Perch-Nielsen, 1969
(Martini, 1961)Perch-Nielsen, 1971
Perch-Nielsen, 1971
(Bramlette and Sullivan, 1961) Hay and Mohler, 1967
(Stradner, 1958) Bukry, 1972
Bramlette and Sullivan, 1961
Hay and Mohler, 1967
(Bramlette and Sullivan, 1961) Stradner, 1962
(Brotzen, 1959) Hay and Mohier, 1967
Bramlette and Sullivan, 1961
(Perch-Nielsen, 1969) Perch-Nielsen, 1977
Bramlette and Riedel, 1954
(Bramlette and Sullivan, 1961) Sullivan, 1964
(Bramlette and Sullivan, 1961) Gartner, 1971
(Kamptner, 1963) Wise, 1973
(Stradner, 1960) Achutan and Stradner, 1969
(Bramlette and Sullivan, 1981) Loeblich and Tappan, 1978
(Bramlette and Riedal, 1954) Radomski, 1968
Bramlette and Sullivan, 1961
(Deflandre, 1964) Brarnlette and Martini, 1964
Bukry and Bramlette, 1969
Sullivan, 1964
(Stradner, 1959) Bramlette and Sullivan, 1961
Bramlette and Sullivan, 1961
Bramlette and Riedel, 1954
(Bramlette and Sullivan, 1981) Sullivan, 1964
Bukry and Percival, 1971
(Bronnimann and Stradner, 1960) Bramlette and Wilcoxon, 1967
Bramlette and Riedel, 1954
Martini, 1961
Bramlette and Martini, 1964
Shamrai, 1963
(Wallich, 1967) Schiller, 1930
Ellis and Lohmann, 1973
Bukry, 1973
Perch-Nielsen, 1977
Bukry and Bramlette, 1989
(Bouche, 1962) Bukry, 1973
Bramlatte and Wilcoxon, 1967
Deflandre, 1952
Deflandre in Deflandre and Fert, 1954
Bramlette and Sullivan, 1961
(Bramlette and Sullivan, 1961) Levin and Joerger, 1987
Bramlette and Riedel, 1954
(Hay, Mohler and Wade, 1988) Roth, 1970
Stradner, 1961
Gartner, 1969
(Bramlette and Sullivan, 1961) Hay and Mohler, 1967
Bramlette and Sullivan, 1981
Bramlette and Martini, 1984
(Levin, 1965) Roth, 1970
Bramlette and Sullivan, 1961
Nay and Mohler, 1967
Hay and Mohlar, 1967
Brernlette and Sullivan, 1981
Hay and Mohler, 1967
Perch-Nielsen, 1971
(Levin, 1968) Martini and Ritzkowski, 1968
( Stradner, 1961) Gartner, 1968
(Deflandre, 1969) Perch-Nielsen, 1968
(Black, 1959)Perch-Nielsen, 1968
Deflandre, 1963

422
TABLE I (continued)
Lucianorhabdus cayeuxii
Biacutum constans
Prediacosphaera cretacea
Arkhangelskiella cymbiformis
Microrhabdulus decoratus
Zygodiscus diplogramrnus
Cribrosphaerella ehreabergii
Parhabdolithus embergeri
Broinsonia enormis
EiffeUithus eximius
Tetralithus gothicus
Lithastrinus grillii
Chiastozygus litterarius
Micula taurus
Gartnerago obliquurn
~Xcanolithus orionatus
Broinsonia parca
Manivitella pemmatoidea
Micula praemurus
Lithraphidites quadratus
Parhabdolithus regularis
Discorhabdus rotatorius
Zygodiscus spiralis
Micula staurophora
Microrhabdulus stradaeri
Vagalapina stradneri
Cretarhabdus surirellus
Tetralithus trlfidus
Eiffellithus turriseiffeli
Deflandre, 1959
(Gbrka, 1957)Black, 1967
(Arkhangelsky, 1912)Gartner, 1968
Vekshina, 1959
Deflandre, 1959
(Deflandre, 1954) Gartner, 1968
(Arkhangelsky, 1912) Deflandre, 1952
(No~|, 1958) Stradner, 1963
(Shumenko, 1968)Manivit, 1971
(Stover, 1966) Perch-Nielsen, 1968
Deflandre, 1959
Stradnar, 1962
(G6rka, 1957) Manivit, 1971
(Martini, 1961) Bukry, 1973
(Stradner, 1963) No~l, 1970
(Reinhardt, 1966a) Reinhardt, 1966b
(8tradner, 1968) Bukry, 1969
(Deflandre ex Manivit, 1985) Thierstein, 1971
(Bukry, 1973) Stradner and Steinmetz, 1984
Brarnlette and Martini, 1964
(G6rka, 1957) Bukry, 1969
(Bukry, 1969)Thierstein, 1973
Bramlette and Martini, 1964
(Gardet, 1955) Stradner, 1963
Bramlette and Martini, 1964
(Rood, Hay and Barnard, 1971) Thierstein, 1973
(Deflandre, 1954) Reinhardt, 1970
(Stradner, 1961 )Bukry, 1973
(Deflandre, 1954) Reinhardt, 1965
Our stratigraphic terminology usage fol-
lows the International Stratigraphic Guide
(Hedberg, 1976; Anonymous, 1979) and
Tauxe et al. (1983). The zonal numbering
scheme we have used for the calcareous
nannofossils is after Roth (1978) and Okada
and Bukry (1980), and for the planktonic
foraminifera after Berggren (1971) and Sigal
(1977).
Bottaccione section
A summary of the stratigraphic evidence is
given in Fig. 2. The lithologies of the Scagiia
Rossa (115--440 m above the top of the
Maiolica limestone) and the Scaglia Variegata
(440--464 m above the top of the Maiolica
limestone) have been described in detail by
Arthur and Fischer {1977), Arthur (1979)
and Napoleone et al. {1983). We report in the
following on the calcareous nannofossils from
limestones in the interval of 185--505 m
above the top of the Maiolica limestone
(Fig. 2). This sequence includes, from bottom
to top, 35 m of yellow-gray, cherty, thin-
bedded limestones (185-220 m), 7 m of red-
brown marlstone (220-227 m), 120 m of
thin bedded, pink to dark red-brown lime-
stones (227--347 m) interrupted by 2 inter-
vals of thicker, bedded limestones (298--312 m
and 340--342 m), the 1-cm thick Cretaceous--
Tertiary boundary clay, 57 m of thin-bedded
pink to red-brown limestones {347--404 m)
interrupted by 3 maristone sequences (marl I:
348--356 m, marl II: 370-375 m, marl III:
382--387 m), 34 m of variably bedded red,
pink and gray cherty limestone (404--438 m).
and over 170 m of red, gray, greenish, well-
bedded limestone of the Scaglia Variegata
(438--510 m), interrupted by a "white
marker" bed (449 m) and a recessed marly
bed (463 m).
Most of the standard late Cretaceous and
Paleogene planktonic foraminiferal zones
were recognized in the Bottaccione section by
Luterbacher and Premoli Silva (1962, 1964)
prior to any magnetic studies and have since
been refined by Premoli Silva (1977) and
Napoleone et al. (1983).
The magnetic stratigraphy of the
Bottaccione section has been established by
Premoli Silva et al. (1974), Lowrie and
Alvarez {1977), Roggenthen and Napoleone
(1977), and Napoleone et al. (1983). A cor-
relation of the observed magnetic stratigraphy
of the Bottaccione section with the oceanic
magnetic anomaly sequence A-18 through
A-34 has been proposed by Premoli Silva et
al. {1974) and by Napoleone et al. (1983).

423
These correlations were based on planktonic
assemblages recovered from pelagic sediments
overlying basaltic basement in eight DSDP
holes.
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NANNOFOSSIL FORAMINIFER AGE
LOGY I RITYI EVENT ZONE, ZONE EVENT
~se I r~u,v~
/5olin)
CPISb ~ lop 6
sem,,nvomro (499 5m) ~
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~nvol~o (489m)
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f484 m)
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/uY~'ns (445m)--
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(sse D
/417~m) ~o~e .G" po/meroe (4185m(
e C CfO~US (414m) "~Fll P8
~ O /odoe~s (402m)
CPtO~
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bo~ T~lho~yl~ (398m)
CP9
-- bose
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P6
~se O dYosty~s f~m) ~ ~ f°D M ~y (~ mJ
se
0 ~/hr~Yl~ofus(378 5m)/~'~7 -/top P pse~omenen~rd,,(37Z~/~
-~oseDmohler, (37~m)--;P5
p]J~po$~ /if onpJlofo (.~9 m/
~ bo~ef~.wnoo~o~m~s(3615m(--~j',~bo
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~,~to(356.~m) --
= bose E moce#u~ (354my__ 2
- top Cre/oceous (3476m)
NC2] =C$11
~se G e~g~l~no (3476 m) --
NC~I ¥CslO ~c~
top T lr, f,dus (JO~m) -- --~s~ a ~ons~, /JO~m) -- O~_
NCZC MCs9
--~op 6
coycom~o (2~o2m)
- bose T /~#,dus (264my- --
MCs8
~ose G ca/~om (264 my -
-
lop E exlmlus (ZSJm)
NCl9~ z
- y)o~
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goYh~cus (~50mf -- ~_
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+
Fig. 9. Correlation of biostratigraphic events with
magneto- and lithostratigraphy in the Bottaccione
section. Redrawn in part from Alvarez et al. (1977)
and Napoleone et al. (1983). Short tick marks to
right of polarity pattern are nannofossfl sample
levels.
Calcareous nannofossil stratigraphy
The stratigraphic distribution of the cal-
careous nannofossil taxa is documented in
Figs. 3-5. We have included the detailed
range-charts because they are crucial in eval-
uating the reliability and accuracy of the
appearance and extinction levels of the cal-
careous nannofossil taxa. The relative abun-
dance of nannofossils and their preservation
in the processed fractions of the sample are
given in the left part of Figs. 3--5. The esti-
mated abundance descriptors refer to the
logarithmic frequency of nannofossils among
the observed micarb and clay particles on a
slide, as indicated in the figure explanations.
Assemblage abundances listed as rare there-
fore indicate that more than one thousand
micarb particles were encountered in the light
microscope per nannofossil specimen.
Recrystallization susceptibility and identifi-
ability of recrystailized specimens in various
orientations may vary between species arid
produce apparent abundance changes between
samples. At the particle densities and magni-
fications we used, this is equivalent to about
one nannofossil per one to three fields of
view. Despite the scarcity and strong re-
crystallization of most nannofossil assem-
blages, we have been able .to recognize most
of the biostratigraphically important taxa.
The relative abundances of individual taxa are
given as logarithmic estimates of their fre-
quency among the identified nannofossils.
The statistical reliability of all biostratigraphic
events can therefore be estimated directly
from the range charts. The first occurrence of
Micula murus
for instance (Fig. 3) means that
at 337.9 m of the Bottaccione section at least
one specimen was encountered per few thou-
sand nannofossils screened or per every few
tens of thousands of particles examined,
which at the particle" densities we used would
be equivalent to approximately 50-100 fields
of view. The next lower sample at 340.2 m
did not contain a single specimen of
M. murus
in several thousand nannofossils screened,
which required several hundred fields of view
to be examined.
The following is a summary of our bio-
stratigraphic interpretation of the nannofloras
shown in Figs. 3-5. The lowermost assem-
blages (186--204 m) are poorly preserved and
lack upper Cretaceous marker species, such as
M. furcatus, B. parca, C. aculeus and T.
gothicus.
The lowest biostratigraphic event
observed is the appearance of
B. parca,
which
defines the base of zone NC18 of Roth
(1978), at 209 m. The widely recognized

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30 T contertus
L~

426
)i : -- ! ::-- --.. _:---,:.i.=-.: -:=.=-:::
•
605>0 A P C C C F C F F R FA R
5040 A p C F F C F C
C C F C F FRFAR
5000 A P C C
502,0 A P R C F C C F F (~ (~
6010 A P C C C F C FR R FARR
500,0 A P C F F F F A
0P15 4070 A P C F C F C RRi~l
406.0 A P C C C C F C R C C R
O iilil ! 4540 A P C C F C F C F C R C
)llllll
4016 C P R C R C R C C F F C
4000 A P R C C R F C C F FR RC
---- 4000 A P R C C F R C C C F F F. C
4660 C P F F F F C C F F R C
4140 A P F F F FC C
46. ,, c ; ;, ,",c ,cC ,,"" c
,360
c.
; ~ ,c~ ,c . ,
,~
4780 C P
4760 A P R C C F FCC CR F F RF
4730 C P F F C F
4720 A P C F F RC F
CPI4 4700 A P A F R R FFF RCR FRFR F
0 umtlhcl 4500 A P C F F FRR RC FF FR
4675 A p R ¢ ,F F RC F(~F F
4660 C P R C F C C C
4645 C P R C F R F F F C CF
4630 A P A F F C FCR RC CFF F
4§2,5 A P A (~ F F~; RCF CFF RF
4610 A p A C F C FCF RC CC R
4600 A P F C C F F C F AC
= 4500 iA P R ¢ C F R FCF RCF CCF
: 4570 A P C C F FCF FC CCF
- 4560 A P ¢ C FFF FCF CF
• 4550 C P A C F F F F RC F A F
CPI3 4530 A P C C FCF CF
CC R
N. ilUHilit I
4510 A A P C F C F FCF FC AFC,F R
w 4505 P C C F F FFF C CFFFF
a¢ 4460 A P C C F CCF C CCC FF
446'; i P C C F F FCF C CCCIFR
445,0 P R F C C FF CCF C FFIFR
¢= 4450 P A C C F F FC C I,F
¢= 439,0 A P A C F CC C F
4310 i P C C F F CC F
400.0 P C C
4350 P C F C C
4340 P C C F F F
4330 P C C FCF C C F
4210 M ~ C C F FC~ F C F
4ooo
IAA PP A ~ c F ~ c_F
c,,2 42,5 ,, c c , ,c, .,,
0 suili
4200 C C C C F A F
lllllll 4200 P C C F F F
4275 P C C A F AF C F
4250 P C
A
C AF F FCF R
4230 P
C
F F F
C
F A F R?
4210 P R C A F RCC FA R C
4206 A P C F F F A F
4100 A P C A C R A F
4136 A P C A C F AR F R
4~76
A r c C R F¢ ccF F c F R
4111 C P C C R F C F F¢ R
0P31 4153 pi C C F R F CC F FC
LIJLIIUItiJ. 4140 A P A RC F C CCF F F¢ R
4130 ~ PI C C F R FFRCCF F
4120 p C C C
4416 P F C C F F FFFRCC FF
4101 A P C A F FCAF F
4100
i P C R~;
FF :CC
4065 P' C R C F FFCCF
4,70 p F C C C F F C F F
CPIO 4066 P C C A F F RF FF FCA R R
F
lirthlitl
4000 A P F C C RA F R FF FFAF r'R
los 4040 ~ P C C R FFC
4030 P C C C F FCCF
4020 P C C C F F F F F C FCcC F FF
4111 P F C C F F C FC R F
3000 i ; F c'
3ill C C F
A
CFCFR
)07,6 p, F C C F F C F F I~
Fig. 5. Stratigraphic distribution of middle Paleogene calcareous nannofossils in the Bottaccione section. Symbols
as in Fig. 3.
sequence oI latest cretaceous calcareous
nannofossil events in oceanic environments is
as follows: base C. aculeus (NC19a) at 222 m,
base T. gothicus (NC19b) at 250 m, top E.
eximius at 253 m, base T. trifidus (NC20) at
264 m, top T. trifidus (base of NC21) at
302 m, base L. quadratus (NC22) at 326 m,
and base M. taurus (NC23) at 337.9 m. Above

427
the Cretaceous--Tertiary boundaiT the se-
quence of Paleocene nannofossil appearances
traditionally used in zonal boundary defini-
tions are found at the following levels: base C.
tenuis (CPlb of Okada and Bukry, 1980) at
349 m, base C. danicus (CP2) at 350.5 m,
base E. rnacellus (CP3) at 354 m, base F.
tympaniformis (CP4) at 361.5 m, base H.
kleinpellii (CP5) at 371 m and base D.
mohleri at 372 m. D. nobilis, the marker for
zone CP7, could not be recognized in any of
the recrystallized samples of the Bottaccione
section, possibly because of its delicacy. A
questionable, poorly preserved specimen of
D. multiradiatus was found at 374 m, but the
species is absent from any sample from the
next higher 4 m. Unequivocal but rare D.
multiradiatus (base of CP8) occur at 378.5 m,
immediately above a minor angular uncon-
formity. The base of zone CP8 was therefore
placed at the 378.5 m level. The next higher
nannofossil event is the lowermost occurrence
of D. diastypus (base CP9) at 386 m. Within
zone CP9 we recognized the following se-
quence of first occurrences: base D.
barbadiensis at 389 m, base T contortus at
391 m and base C. grandis at 402 m. The first
occurrence of D. lodoensis (base of T.
orthostylus Zone CP10) is also at 402 m, the
first occurrence of rare C. crassus (base of D.
lodoensis Zone CPll) is at 414 m, and the
first occurrence of rare D. sublodoensis is at
417.5 m. Within the D. sublodoensis Zone we
observed the appearance of D. saipanensis at
437 m and of R. inflata at 443 m. The first
occurrence of N. fulgens at 445 m defines the
base of the N. quadrata Zone (CP13). The
base of the overlying R. umbilica Zone
(CP14) is identified by the appearance of R.
umbilica at 462.5 m, and the base of the D.
barbadiensis Zone (CP15) is at 486 m, 2 m
above the extinction level of C. grandis. The
lowermost rare occurrence of I. recurvus is at
501 m, indicating a latest Eocene age for the
youngest nannofossil assemblages we have
studied. The continuous outcrop along the
south side of the Bottaccione Gorge ends at
this level.
Contessa Highway section
A summary of the stratigraphic evidence in
the Contessa Highway section is given in
Fig. 6.
The close lithostratigraphic similarity of
the Paleogene Contessa Highway section with
the Bottaccione section has been pointed out
by Lowrie et al. (1982) in their detailed
lithologic, magnetic and foraminifera] strati-
graphic descriptions. We studied the cal-
careous nannofossils in the 160-m thick
Paleogene sequence, beginning at the
Cretaceous--Tertiary boundary (Fig. 6). The
upper Cretaceous part of the Scaglia Rossa
tl #IGNETIC CALCAREOUS PLANKTON IC
LITHO LNOMALy/I NANNOFOSSIL FORAMINIFER AGE
E LOGY ~OLARITY I EVENT ZONE ZONE EVENT
5 ,,I ,,,:"5
)PI--3 #ose o beckman, M35m)
3 19~t~ cP~'! P~2
2°I
boseRumb,l,ca(MO2ml
"'~11
top M atao~ens,s fll2m)
--
'i
C
CPI3
9 ~ 21 I l base N/u/~ens/9oral
- ---Cpl2
PlOp8
~
•
"l 2 ~ose o ~aaoe~s.% -- b ~ * p Y .
' ~J P9
E
~loprocthos,¥1us(60m )
CPll
2 °Z; ~
~,::Z///:;/,
i base Tor1~oscvlus(39m)
CP9 P6
aose Odtastyp~J$(35m] ~
--
~o~e M edqOr, /J4 Sin)
b°se
O~'f°d'°tu$iJOm) --
P7
; ~ base D mo~/e¢l (23
5m
)~
I
2B~l~
............
<4 ....
CP~ .......................
bose
C d~,cus (m) ~
PI
~9~mp cretaceous/odin)
CP 1
__
oase S ~,seudobuu~de~
(07~;
Fig. 6. Correlation of biostratigraphic events with
magneto- and lithostratigraphy in the Contessa High-
way section. Redrawn in part from Lowrie et al.
(1982). Short tick marks to right of polarity pattern
are nannofossil sample levels.

~'~
~ .,--J
<° it. _.. il =,
~.o ® ~-
O
"-" O" C~ Oo
't2 Co ~ '~
"< <~ ~
• El
o_
i
PALEOCENE
i
I
I
l , i
II ,
x ~
I
EOCENE
I
E
ADUNOANCE
PRESERVATION
REWORKING
B. bilelewi
Thara¢esphaera S!
O. sparius
T iaxea
T |etalesus
B,discula
T iparculata
Z sillIeides
M+lnlersls
C.priIu|
C.tlneis
C pelagicus s impi
[. auipier tusa
Cyclageiespkaers sp,
Creliidelitkls sp
li,cencinaas
p diiier pllosu s,
C datiicus
Pbisll¢is
Fasciculithus sp
E macallvs
C censietus
0 filRiSa
F tympanifermls
F pileatos
l ullii
S mlrlier RIIS
0 mehleri
T. craticulis
O noiiNs
O multiradialvs
S. radians
Okispperi
O diastypus
Z bijvgatus
~
.barbidiensis
urtkostylus
C lameation
~
lodeensls
folmesus
C crlbellum
C crassus
C. iraniis
T inversus
O. svblodoensll
C pseudaoammation
N fuloens
R. samudlro¥11
~
saipiaensis
umbillca
0 tisectus
R tenuis
recursul
L~
(3O

marker bed at 99 m and by recessed clayey
beds at 110 m (bed K) and128 m (beds L, M,
N). The reversed polarity zone between
Anomaly 28 and 29, magnetic Subchron 29R,
has not been recognized, whereas three re-
versed polarity zones within Chron 26 and
one each within Chrons 23 and 21 have been
resolved in the Contessa Highway section by
Lowrie et al. {1982).
Degpite the fact that the planktonic
foraminifera stratigraphy of the Contessa
Highway section was established independent-
ly on washed residues and thin sections, poor
preservation allowed only approximate deter-
minations of zonal boundary levels (Lowrie et
al., 1982). Poor fossil preservation was im-
plied as an explanation for the discrepancies
observed in the detailed correlation of
Paleocene magnetic chrons and foraminifera
zonal boundaries between the Contessa
Highway section (Lowrie et al., 1982) and the
Bottaccione section (Premoli Silva, 1977;
Napoleone et al., 1983). Our nannofossil
results will shed more light on the causes for
these discrepancies.
Calcareous nannofossil stratigraphy
A complete succession of the well-known
first occurrences of Paleocene nannofossils is
observed in the Contessa Highway section at
the following levels {Fig. 7):
C. tenuis
defin-
ing the base of nannofossil zone CPlb at 2 m,
base
C. danicus
(CP2) at 4 m, base
E. macellus
(CP3) at 10 m, base
F. tympaniformis
(CP4) at
15 m, base
H. kleinpellii
(CP5) at 21 m, base
D. mohleri
(CP6) at 23.5 m, and base D.
nobilis
(CP7) at 28 m. The lowermost ap-
pearance of
D. rnultiradiatus,
defining the
base of nannofossil zone CP8 is at 30 m.
Continuing upwards we identified the fol-
lowing marker events: base
D. diastypus
(CP9) at 35 m, and within that zone a suc-
cession of first occurrences of
Z. bi]ugatus
at
38
m, D. barbadiensis and T. orthostylus
at
39 m. The traditionally used succession of
rather delicate marker species in the lower
and middle Eocene could be recognized, but
429
marginal preservation and low relative abun-
dances led to rather intermittent occurrences
of these taxa and therefore only moderately
reliable determinations of appearance and
extinction levels. The observed succession
consists of: base
D. lodoensis
(CP10) at 48 m,
base
C. crassus
(CPll) at 51.5 m, base D.
sublodoensis
(CP12) at 55 m, base
N. fulgens
{CP13) at 90 m, base
R. umbilica
(CP14) at
110.2 m, and top
C. grandis
(base CP15)at
138.5 m. Rare/.
recurvus
at 160 m suggest an
age of latest Eocene, rather close to the
Eocene--Oligocene boundary. The sequence
of Eocene nannofossil events we observed in
the Contessa Highway section is very similar
to the one reported from the nearby Contessa
Road section by Lowrie et al. {1982).
Bio- and magneto-chronologic correlation
Reliability
Because individual magnetostratigraphic
units have non-unique, repetitive properties,
their identification depends on biostratigraph-
ic evidence and on the similarity of relative
thicknesses of several sequential polarity
zones in sedimentary sequences with the
widths of magnetic anomaly patterns as
preserved in oceanic crust. We will therefore
first discuss the independent correlations
between magnetic and biostratigraphic units
and then address the consistency of these
units in various sedimentary sequences.
The independent correlations between bio-
and magnetostratigraphic units are derived
from microfossfl assemblages found in basal
sedin~ents recovered in DSDP holes. For this
purpose we have compiled a list of a total of
17 DSDP Sites {Table II) which were drilled
on previously identified, numbered magnetic
anomalies. Such a calibration attempt is based
on the assumption that sediment deposition
followed emplacement of extrusive basalts
without long delay. The appropriateness of
this assumption has been discussed previously
by Van Andel {1972). A comparison of the
bio- and magneto-stratigraphic correlation

430
TABLE II
Biostratigraphic ages of oldest sediments overlying oceanic crust in DSDP sites drilled on known magnetic
anomalies
Magnetic chron DSDP Site Calcareous nannofossil Zone Reference
C17N 573 CP15
D. barbadiensis
Zone
C17N 574 CP15
D. barbadiensis
Zone
C20N (top) 221 CP14a
D. bifax
Subzone
C21N 19 CP13
N. quadratus
Zone
C21N 523 CP13b C.
gigas
Subzone
C22N 38 CPll
D. lodoensis
Zone
C23N 343 CP10
I. obscurus
Interval
C24N 39 CP10
T. orthostylus
Zone
C26N 213 CP6
D. mohleri
Zone
C29N 245 CP2
C. danicus
Zone
C30N 20 NC23
M. taurus
Zone
C31N 527 NC21
A. cymbiformis
Zone
C31R 239 NC23
M. murus
Zone
C31R 528 NC21
A. cymbiformis
Zone
C32N 525A NC20
T. trifidus
Zone
C33N (base) 10 NC19b T.
gothicus
Zone
C33R (near top) 355 NC18
B. parca
Zone
A. Pujos (1984)
A. Pujos (1984)
Bukry (1974a); Whitmarsh et al. (1974)
Maxwell et al. (1970)
Poore et al. (1983)
Bukry and Bramlette (1970), McManus et al.
(1970)
Bukry (1976), Miiller (197 6), Talwani
(1978)
Bukry and Bramlette (1970), McManus et al.
(1970)
Gartner (1974); Von der Botch, Sclater et al.
(1974)
MLiller (1974), Schlich (1974)
Maxwell, Von Herzen et al. (1970)
Manivit (1984), Moore, Rabinowitz et al.
(1984)
Bukry (1974b), Schlich (1974)
Manivit (1984), Moore, Rabinowitz et al.
(1984)
Manivit (1984), Moore, Rabinowitz et al.
(1984)
Cita and Gartner (1971), Cande and
Kristo ffersen (1977)
Supko and Perch-Nielsen (1977)
based on evidence from DSDP Sites on one
hand and the pelagic sediment outcrops on
the other provides a convenient test for the
accuracy of these correlations.
In Fig. 8 we have plotted 17 DSDP Sites
from Table II in their appropriate positions
on the marine magnetic anomaly sequence
(horizontal axis) versus the relative bio-
stratigraphic age of the oldest nannofossil
assemblage encountered above basement
(vertical axis). We have chosen the geomagnet-
ic polarity time scale of Mankinen and
Dalrymple (1979), who recalibrated the
polarity time scale of LaBrecque et al. (1977)
with the new constants used in K--At dating
(Steiger and J~ger, 1977). The geomagnetic
polarity time scale of LaBrecque et al. (1977)
required the smallest changes in spreading
rates in various ocean basins between magnet-
ic anomalies A-24 and A-34 (Cande and
Kristoffersen, 1977). The calibration of the
relative geomagnetic polarity scale with radio-
metric age dates was done by assuming a
K--At age of 3.41 Ma for anomaly 2A and an
age of 66.7 Ma for the Cretaceous--Tertiary
boundary (Mankinen and Dalrymple, 1979).
The latter date, however, is not firmly estab-
lished yet and more definite assignments of
absolute age estimates for bio- and magneto-
stratigraphic events will require further scru-
tiny of the radiometric and stratigraphic
evidence. The derivation of such a geochro-
nologic time scale will be the topic of a forth-
coming paper. The relative biostratigraphic
ages of the standard calcareous nannofossil
zonal sequence in Fig. 8 are scaled to the
thickness of these zones in the Bottaccione
section. The horizontal bars are estimates of

431
THICK
CALC. NANNOFOSSIL MAGNETIC
NESS EVENT
rn
500-
480 -
460
440
420 -
Z
0 4OO
(-.)
580
ILl
0'3
360-
;;~
340-
C) 320-
0
<~ 500
F--
F-
0 280-
rn 260 -
240
-
220 -
200 -
ZONEPOLARITY
16
18
20
2]
22
25
24
DEEP SEA DRILLING PROJECT SITE
27
29
5]
527
/ I 528
52 ~25
33
")O
573
~ -523
54
ANOMALY 54 35 32 51 3(3 292~ 27 26 25 24 23 22 21 20 19 18 ]7 16
Uo
80 75 70 65 60 55 50 45 40
MARINE MAGNETIC ANOMALY TIME SCALE
Fig. 8. Biostratigraphic correlation of magnetic stratigraphy of the Bottaccione section with the marine magnetic
anomaly time scale, as calibrated by Mankinen and Dalrymple (1979) at 17 DSDP sites. For details see text.
the uncertainties of locating the DSDP sites
on the magnetic profiles and were obtained
from the respective Initial Reports of the
Deep Sea Drilling Project. The vertical bars
cover the extent of overlap of the biostrati-
graphic zone corresponding to the oldest
nannofossil assemblage in the DSDP site and a
magnetozone in the Bottaccione section
which has the same polarity as the oceanic
crust underlying the respective DSDP site.
The similarity of the two magnetic field
reversal records and the good biostratigraphic
match allow accurate correlations of identical
chrons, in their true geochronological sense,
in both records (Fig. 8). At two of the seven-
teen sites listed in Table II, however, a dis-
crepancy exists between the expected age
(from the correlations in Umbria) and the
observed age of the oldest nannofossil as-
semblages. At DSDP Site 239 there appears to
be a recognizable time delay between the
cooling of the presumably extrusive basaltic
crust and the deposition of pelagic sediments
(Simpson, Schlich et al., 1974). Such an
interpretation is strongly supported by in-
dependent correlations established at DSDP
Site 527 (Manivit, 1984), Site 530A (Stadner
and Steinmetz, 1984), and in the Bottaccione
section. The paleontological age of the oldest
sediments recovered at DSDP Site 10 is
younger than expected from the correlations
observed in the Bottaccione section, especial-
ly when linear sedimentation rates are as-
sumed between magnetic reversals (thin line

432
on Fig. 8}. The fact that basal sediments
recovered at DSDP Site 10 were baked sug-
gests that an intrusive basalt sill, rather than
true oceanic basement was recovered
(Peterson et al., 1970). The remaining cor-
relations, based on calcareous nannofossil
evidence in fifteen DSDP Sites confirm and
refine previous correlations based on plank-
tonic foraminifera in seven of these sites
(Napoleone et al., 1983).
Accuracy
What is the currently obtainable accuracy
of stratigraphic correlation in the upper
Cretaceous through Paleocene interval? One
can address this question by comparing the
consistency of the relative succession of, and
the measured stratigraphic thicknesses be-
tween, the recognized bio- and magneto-
stratigraphic events in the sections available.
Previous studies have established the suit-
ability of the magnetic properties of the
Umbrian and certain DSDP sediment se-
quences for magnetic stratigraphy (e.g.
Lowrie et al., 1982; Tauxe et al., 1983;
Chave, 1984). The observed stratigraphic
variability of the magnetic reversal patterns
between individual sections is therefore most
likely caused by differences in sediment
depositional processes such as accumulation-
rate changes, redeposition and erosion. Such
processes will affect all sediment particles and
thus will also be recognizable micropaleonto-
logically. For instance, in the entire upper
Cretaceous sequence of the Bottaccione
section we have investigated, no pre-
Campanian or post-Maastrichtian nannofossil
taxa were detected. If there was any re-
deposition of sediment, it could only have
been from nearby penecontemporaneous
sources. Since our smear-slides were made of
sediment from the inside of rock-samples, we
did not find evidence for surficial contamina-
tion with younger material, as had been re-
ported by Coccioni {1978) and Premoli Silva
and Luterbacher {1978). In numerous
Tertiary assemblages of the Bottaccione and
the Contessa Highway sections, however,
reworked Cretaceous nannofossils were ob-
served, but their relative abundances were
always less than 0.1% of all nannofossils
encountered {Figs. 4, 5, 7). The relative
abundances of these reworked taxa are very
comparable to those of Pliocene discoasters
and middle Pleistocene P.
lacunosa
observed
occasionally in deep-sea sediment cores with
well-established latest Pleistocene and
Holocene isotope stratigraphies (CLIMAP,
unpublished data). In none of the samples
studied have we found any larger proportion
of reworked older nannofossils, that might
indicate significant lateral influx of sediment
particles from nearby outcrops, presence of
turbidites, or slumping, as has been suggested
(e.g., Wezel, 1979).
Even cursory examination of the stratigraph-
ic evidence currently available from the
Umbrian and other sections indicates that there
is a considerable degree of internal strati-
graphic variability (Fig. 9). Because we have
studied the Bottaccione, Contessa Highway,
and DSDP 577 sections ourselves, we can
evaluate the stratigraphic variability among
these sections more reliably than the variabil-
ity observed among the other sections shown
in Fig. 9, because the latter is based on the
evidence published in the literature. This, of
course, also applies to our interpretation of the
planktonic foraminifera stratigraphies. In ad-
dition, because many planktonic foraminifera
events have not been established from several
of the known sections, the foraminifera
successions cannot yet be correlated as reli-
ably with the magnetic reversal sequence as
can the nannofossils.
Chronology
We will discuss in the following paragraphs
the relative chronologic sequence of early
Campanian to late Eocene nannofossil, plank-
tonic foraminifera and magnetostratigraphic
events as observed in the sections near Gubbio
and reported from elsewhere, with reference
to Fig. 9.

433
PLANKTIC FORAM- CALCAREOUS NANNOFOSSIL
INIFERA EVENT EVENT ZONE
Dose I recurvus
top G semnnvoluto
bose
G semnnvoluto
C
P 15
top C
grahamS
top 0
bec~monn,
- -
Dose
0 beclfmannl
CP14
bose
R
utah,hoe
to o M ora~onens,s CPI3
base Hont~enmo s# bose N fulqens
CP~2
bose G ~olmeroe
bose
O
sublodoens~s
r offbostylus-- CPII--.-~
top
Dose O tarouboens, s bose C crossus P
Dosed /odoens~s
CPIO
bose M ovoqonensxs bose r orlhos(#/us --
CP 9
top
M ed~ort
Dose
0
dxostypus-
bose M edqom Dosed muH~rod~otus
CP8
Io~ G
veloscoens~s beseO nabobs
GP7
"" _~
Dose D mohlem CP 6 - -"
bose P pseudomenord, bose H kletnpel/s, CP 5
base M uncmato bose F tympemformls
CP4
bose E mocellus
CP ~
Dose S tmmdodens/s CP
Dose u pseudobullotdes bose C domcu~
CP I
C / T - boundory
NC 23
bose M mucus
Do$e
A
moyaroensls NC
22
bose C~ contuse Dose L quadro~us--____--
bose O
gonssem
ted O coscuroto
bose G colcarota
NC21
top T trJxdus
NC20
bose T trthdus
top E exlrnlus --
NCI9b
bose T
qoth~cus --
NC190
beset oculeus
NC18
boseB
porto NC17
CONTESSA
BOTTACCIONE HIGHWAY DSDP DSDP DSDP DSDP DSDP DSDP
524 525A 527 530A 577 577A
, :7,
Fig. 9. Biostratigraphic correlations of the Bottaccione and Contessa Highway sections, and of DSDP Site 524
(Poore et al., 1983), DSDP Sites 525A and 527 (Boersma, 1984; Chave, 1984; Manivit, 1984), DSDP Site 530A
(Stradner and Steinmetz, 1984), and DSDP Sites 577 and 577A (Monechi et al., 1984)• Vertical scale: 20 m be-
tween arrows. Solid lines = calcareous nannofossil correlations; dotted lines = planktonic foraminifera correla-
tions; dashed lines = correlations inferred.
The first occurrence of
B. parca
is observed
in the middle part of magnetic Subchron
C33R in the Bottaccione section which is
consistent with previous reports from western
Pacific DSDP Sites 462 and 462A (Steiner,
1981; Thierstein and Manivit, 1981) and
South Atlantic DSDP Site 530A (Stradner
and Steinmetz, 1984). The first occurrence of
B. parca
is within the
G. elevate
foraminifera
Zone (Premoli Silva, 1977). Six biostrati-
graphic events occur during Subchron C33N:
its older end correlates with the first oc-
currence of
C. aculeus,
in its middle part base
T. gothicus,
top
E. eximius,
base
T. trifidus
occur in rapid succession and in its youngest
third the total range of the foraminifer G.
calcarata
is observed. Although the base of T.
trifidus
coincides with the base of
G. calcarata
in the Bottaccione section, there are several
other sections known, where the lowest T.
trifidus
clearly precede the lowest G.
calcarata,
such as at DSDP Site 146 (Edgar,
Saunders et al., 1973), DSDP Site 167
(Winterer, Ewing et at., 1973), DSDP Site 305
(Larson, Moberly et at., 1975), DSDP Site
356 (Supko, Perch-Nielsen et al., 1977), and

434
El Kef (Verbeek, 1977). The last occurrence
of T.
trifidus
is consistently observed near the
top end of Subchron C32N. The first oc-
currence of the foraminifer
G. gansseri
co-
incides with the last occurrence of T.
trifidus
in the Bottaccione section. At DSDP Site 146,
the first
G. gansseri
precede the last
T. trifidus
(Edgar, Saunders et al., 1973), at DSDP Sites
305 and 357 the reverse is observed (Larson,
Moberly et al., 1975; Supko, Perch-Nielsen et
al., 1977), and at DSDP Site 167 the two
events coincide (Winterer, Ewing et al., 1973).
The appearance of foraminifer
G. contusa in
the Bottaccione section occurs just below the
base of Subchron C31N (Premoli Silva, 1977),
which is immediately followed by the ap-
pearance of
L. quadratus.
The first occurrence
of the foraminifer
G. contusa
in the South
Atlantic is reported from the lowest fossil-
iferous sample at DSDP Site 524 which lies
near the base of Subchron C31N (Poore et al.,
1983), but its lowest occurrence is known
only from mid-Subchron C30N sediments at
DSDP Sites 525A and 527, apparently be-
cause of poor preservation (Boersma, 1984).
The first occurrence of
L. quadratus,
how-
ever, is observed in the upper part of Sub-
chron C31N in three of the South Atlantic
sites (Poore et al., 1983; Manivit, 1984) and
in Subchron C30N at DSDP Site 530A,
possibly because of dissolution of nannofossil
assemblages (Stradner and Steinmetz, 1984).
Similar displacements upwards in some of the
South Atlantic sites are observed for the ap-
pearance of
M. murus
and of the foraminifer
A. mayaroensis. Base A. mayaroensis
occurs
in Subchron C31N in the Bottaccione section
and at DSDP Site 524, but only in Subchron
C30N at DSDP Sites 525A and 527. Base M.
taurus
occurs near the base of Subchron
C30N in the Bottaccione section and at
DSDP Site 524, but only in mid-Subchron
C30N at DSDP Sites 525A and 527. These
compilations also confirm the revision of the
magnetic stratigraphy interpretation of the
uppermost Cretaceous sediments at DSDP
Site 384 (Larson and Opdyke, 1979)pro-
posed by Thierstein (1982).
The paleontological Cretaceous--Tertiary
boundary is consistently found in a reversed
polarity interval, which has previously been
identified as Subchron C29R by Sclater et al.
(1974) and Alvarez et al. (1977). The relative
stratigraphic level of the paleontological
Cretaceous--Tertiary boundary within Sub-
chron C29R is also variable as pointed out
previously (Thierstein, 1982), but appears to
occur most frequently in the upper half of
Subchron C29R. The appearance of the
foraminifer
S. pseudobulloides
is observed
near the younger end of Subchron C29R in
the Bottaccione section and near the base of
Subchron C29N in the Contessa Highway
section and at DSDP Sites 524, 525A, and
527. The lowest C.
danicus
(inclusive of C.
edwardsii)
occur in the first normal subchron
above the Cretaceous--Tertiary boundary in
all Tethyan, Atlantic, and Pacific sections.
The appearance of foraminifer
S. trinidadensis
during Subchron C28N is documented in the
Bottaccione and Contessa Highway sections
and at DSDP Sites 524 and 527. This inter-
pretation implies that Subchron C28R is not
present or has not been sampled magnetically
in the Contessa Highway section (Lowrie et
al., 1982). The lowest occurrence of E.
macellus
is observed in Subchron C27R in the
Bottaccione and Contessa sections, and at
DSDP Sites 525A and 527 (Manivit, 1984).
At DSDP Sites 524, 577 and 577A the earliest
g. macellus
have been reported from some-
what younger sediments thought to have been
deposited during Subchron C26R time (Poore
et al., 1983; Monechi and others, 1984). Since
the identifications of magnetic chrons at these
sites is usually based on counting the number
of discrete, normally magnetized sedi-
ment intervals above the paleontological
Cretaceous--Tertiary boundary, any minor
coring or recovery gap, or any short, reversely
magnetized interval within a traditionally
recognized magnetic chron, may lead to an
incorrect identification of a chron. It is there-
fore possible, for instance, that the third
normally magnetized interval above the
Cretaceous--Tertiary boundary at DSDP Site

577A represents the upper part of a bipartite
Subchron C28N, and is not Subchron C27N,
as assumed by Monechi et al. (1985). In
addition,
E. macellus
is a dissolution sus-
ceptible taxon and is usually rare, and thus
could have been eliminated, because these
assemblages show poor to moderate pre-
servation. An additional stratigraphic problem
is encountered at DSDP Site 524, where the
first occurrence of the foraminifer M.
uncinata is
already in Subchron C27R (Poore
et al., 1983) and not only in Subchron C26R
as in the Bottaccione section (Premoli Silva,
1977). The first occurrence of
M. uncinata
at
this site is anomalously early, when compared
to other sections. This would be so even if the
overlying normal interval (in Cores 12 and 13)
were Subchron C25N, although the nan-
nofossil stratigraphy suggests it to be Sub-
chron C28N. The next higher nannofossil
event, base
F. tympaniformis
consistently
occurs in all sections in what has been iden-
tified as Subchron C26R. In the same sub-
chron the first occurrence of the foraminifer
P. pseudomenardii
has been recognized in the
Bottaccione section (Premoli Silva, 1977) and
at DSDP Site 527 (Boersma, 1984). At DSDP
Site 524, however, the lowermost P.
pseudomenardii are
reported from Subchron
C25R only (Poore et al., 1983). The suc-
cession of first appearances of
H. kleinpellii
and D. mohleri
occurs in the Bottaccione
section in what was considered to be Sub-
chron C25N by Alvarez et al. (1977)and
Napoleone et al. (1983). As discussed previ-
ously, both of these events occur in the
Contessa Highway section in what Lowrie et
al. (1982) identified as a tripartite C26N. The
former Subchron C25N of the Bottaccione
section therefore must be considered as the
middle normal zone of the tripartite Sub-
chron C26N. This interpretation is necessary
because we have established the sequential
first occurrence of
D. nobilis and D.
multiradiatus
in Subchrons C25R and C25N,
respectively, in the Contessa Highway section.
The synchroneity of
D. nobilis
with Subchron
C25R and of
D. multiradiatus
with Subchron
435
C25R in various DSDP sites strongly supports
our contention. The lowest occurrence in the
Bottaccione section of
D. multiradiatus
in a
long, reversely magnetized interval below
Subchron C24N and immediately above a
minor angular unconformity suggests that the
sediments equivalent to the later part of
Subchron N25R, all of Subchron C25N, and
the early part of Subchron C24R are missing.
The missing chrons imply that the uppermost
Paleocene (and possibly the Paleocene--
Eocene boundary itself) is not preserved along
the road of the Bottaccione section. A de-
tailed revision of the planktonic foraminifera
stratigraphy near the Paleocene--Eocene
boundary is currently underway by I. Premoli
Silva (personal communication, 1984).
Only three of the numerous Eocene bio-
stratigraphic events (i.e., base
D. lodoensis,
base
C. crassus,
and base
D. sublodoensis)
have been recognized at DSDP Sites 577 and
577A in the Pacific. Neither of these holes has
yielded a very continuous Eocene record, and
thus they add little independent evidence. All
other Eocene events have already been dis-
cussed with the respective sections.
Discussion
The majority of recognizable Campanian--
Eocene nannofossil events occur in consistent
stratigraphic succession relative to each other,
relative to planktonic foraminifera events, and
relative to the magnetic polarity sequence.
The correlation of rmnnofossil events with the
magnetic polarity sequence is established in
sedimentary sections and in DSDP sites,
which were drilled on known crustal magnetic
anomalies. With the growing data base, it is
becoming apparent, however, that consider-
able small-scale stratigraphic variability exists
among the individual sections. A comparison
between the independently established nan-
nofossil and planktonic foraminifera bio-
stratigraphies and the magnetostratigraphy
allows us to evaluate and verify inconsis-
tencies between the two biostratigraphic
schemes, and to identify the most reliable
biostratigraphic events.

436
Differences in the relative thicknesses of
polarity zones between various sections are
commonly caused by changes in sedimenta-
tion processes (rate of sediment accumula-
tion, erosion, slumping, etc. ), but may also be
influenced by sampling density or differences
in the acquisition processes of the remanent
magnetization. These processes appear to
lead to stratigraphic variability on rather
local scales, as a comparison between the
Bottaccione and Contessa Highway sections,
which are located only about 2 km apart from
each other, readily demonstrates. In this
particular case minor tectonic disturbances
introduced during the late-Cenozoic folding
of the Apennine mountain belt may also have
contributed to the observed magnetostrati-
graphic differences.
Stratigraphic variability, which is unrelated
to tectonic or physical sedimentation pro-
cesses, is most evident in the occasionally
observed stratigraphic reversals of nannofossil
and planktonic foraminifera events (Fig. 9).
In most cases the magnetostratigraphic data,
often in combination with multiple bio-
stratigraphic events, allow us to identify the
time-transgressive biostratigraphic event.
Some of these are related to differential
preservation of individual taxa {such as base
L. quadratus
and base
E. macellus),
while
others appear to be caused by biogeographic
restrictions. Such chronologic inconsistencies,
large enough to lead to potentially erroneous
magnetic chron identifications, are observed
for the planktonic foraminifera events base G.
contusa,
base
M. uncinata,
and base P.
pseudomenardii
and for the nannofossil
events base L.
quadratus
and base
E. macellus.
In the currently available data set consider-
able variability of stratigraphic position with-
in a particular magnetic subchron is shown by
the planktonic foraminifera events base A.
mayaroensis and M. aragonensis,
and by the
nannofossil events base
M. taurus,
base H.
kleinpellii,
base
D. lodoensis,
base
C. crassus,
and base
1). sublodoensis.
The remaining biostratigraphic events have
been established quite reliably in two or more
sections and occur consistently in relative
succession to each other, and to the magnetic
reversal patterns. The currently available
evidence indicates that accuracy of cor-
relation, as well as stratigraphic resolution in
most intervals is satisfactory to about the
duration of one magnetic subchron.
Acknowledgments
We thank I. Premoli Silva and G. Napoleone
for making their samples available to us for
study, and A. Chave, H. Manivit, J. Steinmetz
and L. Tauxe for sharing information on the
magneto- and biostratigraphy of South
Atlantic DSDP sites. We acknowledge
T. Bralower, D. Bukry and I. Premoli Silva for
reviewing early drafts of this manuscript.
Research supported through grants from the
National Science Foundation (OCE76-
22150), UCSD and ARCO Oil Company, and
through M.P.I. (60%) grant and a fellowship
to S. Monechi from the CNR.
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