GEOLOGICA CARPATHICA, 50, 2, BRATISLAVA, APRIL 1999
125144
CORRELATION OF MAGNETOSTRATIGRAPHY
AND CALPIONELLID BIOSTRATIGRAPHY
OF THE JURASSIC/CRETACEOUS BOUNDARY STRATA
IN THE WESTERN CARPATHIANS
VÁCLAV HOUA, MIROSLAV KRS, OTAKAR MAN,
PETR PRUNER and DANIELA VENHODOVÁ
Geological Institute, Academy of Sciences of the Czech Republic, Rozvojová 135,
165 02 Praha 6-Lysolaje, Czech Republic
(Manuscript received February 25, 1998; accepted in revised form September 1, 1998)
Abstract: A short reverse polarity magnetosubzone, herein defined as the Brodno Subzone, was detected in the upper
part of the magnetozone M19n at the locality of Brodno near ilina (Western Carpathians) using high-resolution
magnetostratigraphy. An analogous short reverse polarity magnetosubzone, herein defined as the Kysuca Subzone
occurs in the middle part of the magnetozone M20n. Both the magnetosubzones are known from marine profiles but
have been detected only sporadically and documented insufficiently in continental outcrops. These two subzones have
not yet been detected together in one and the same continental section. Their stratigraphic position in the Brodno
section is defined and their interpretation in the other studied section at tramberk is inferred. In the Brodno section, the
Kysuca Subzone represents the basal part of the calpionellid Remanei Subzone of the Crassicollaria Standard Zone
(early late Tithonian), its base lies at the level of 55 % of the local thickness of the magnetozone M20n. The Brodno
Subzone lies within the calpionellid Alpina Subzone of the Calpionella Standard Zone (earliest Berriasian) and its base
in the Brodno section lies at the level of 82 % of the local thickness of the magnetozone M19n. In both the studied
sections, the Jurassic/Cretaceous boundary based on calpionellids (base of the Calpionella Standard Zone) lies ap-
proximately at the end of the lowermost third of the magnetozone M19n (at the level of 34 % of the local thickness of
the magnetozone M19n in the Brodno section). Magnetostratigraphic calibration of calpionellid events proved their
isochronous character in the localities of Brodno and tramberk. The interval of ca. ±5000 years, during which a
transition occurred from normal (reverse) to reverse (normal) polarity of magnetic field of the co-axial geocentric
dipole of the Earth, can be determined from an analysis of paleomagnetic directions inferred from samples with inter-
mediate polarity collected from normally and reversely polarized boundary strata at the locality of Brodno and with
respect to the sedimentation rate. This value represents the relative accuracy of possible correlations of the boundaries
of the detected magnetosubzones with boundaries of analogous subzones at other localities on the Earth using the above
given synchronous global event.
Key words: Jurassic/Cretaceous boundary strata, Tethyan Realm, Brodno and tramberk sections, high-resolution
magnetostratigraphy, two magnetosubzones, calpionellid and magnetostratigraphic correlation.
units in the two realms using indirect methods. The most
precise of these methods is magnetostratigraphy. For the
Tethyan Realm, magnetostratigraphic profiles of the J/K
boundary strata were worked out for a number of localities,
however with imprecise or no correlation with the biostratig-
raphy of these sections. Only a single magnetostratigraphic
profile was published from the Boreal Realm (Ogg et al.
1991), unfortunately containing numerous hiatuses and pro-
viding insufficient correlation with the biostratigraphic zo-
nation.
Imprecise and indefinite taxonomic and biostratigraphic
interpretations of fossil calpionellid associations recorded in
magnetostratigraphically analysed sections in the Tethyan
Realm resulted in the placing of the biostratigraphic J/K
boundary into different magnetozones by different authors at
different localities. The variation was also caused by chang-
es in the general position of the J/K boundary in biostrati-
graphic scales (see below). Most frequently, the J/K bound-
ary was placed in the M19n (e.g. Channell & Grandesso
Introduction
The possibilities of biostratigraphic correlations of chronos-
tratigraphic units of the Jurassic/Cretaceous (J/K) boundary
strata between the Tethyan and Boreal realms are very limited
due to the practically complete divergence between their fossil
associations. This fact hinders the establishment of a J/K
boundary acceptable on a global scale, although the biostrati-
graphic zonation of the J/K boundary strata is elaborated in
much detail both in the Tethyan and Boreal realms. Biostrati-
graphic zones between the Tethyan and Boreal realms unfor-
tunately cannot be correlated directly as they share no com-
mon taxa at specific and even generic levels. Consequently,
provisional boundaries defined at the boundaries of regional
stages are used in both realms, independently of each other.
These provisional J/K boundaries in the Tethyan and Boreal
realms are not isochronous.
Nevertheless, there are several possibilities to correlate the
biostratigraphic scales, and hence also chronostratigraphic
126 HOUA, KRS, MAN, PRUNER and VENHODOVÁ
1987: Fig. 12), on the base of the M18r (e.g. Lowrie & Ogg
1986, p. 342; Manivit et al. 1986, p. 117; Galbrun et al.
1990: Fig. 8), in the M19r (e.g. Channel & Grandesso 1987:
Figs. 4, 17), but also in the M17r (e.g. Cirilli et al. 1984: Fig.
8) or in the M16 (e.g. Márton 1982: Fig. 9) magnetozones.
However, as magnetostratigraphic events represent chro-
nologically very precise correlation horizons, the biostrati-
graphic events if expected to have relevant correlation
significance should not occupy different positions rela-
tive to magnetostratigraphic events at different localities. J.
Kirschvink (in Lowrie & Channell 1984, p. 47) noted that
the marine biological changes were probably not synchro-
nous at the Jurassic-Cretaceous transition. This fact was the
main motive of the present authors for an attempt to cali-
brate the biostratigraphic scales of the J/K boundary strata
using magnetostratigraphy, preferably high-resolution
magnetostratigraphy, first in the Tethyan Realm and later
also in the Boreal Realm. This would allow their precise cor-
relation and test the degree to which isochronous biostrati-
graphic events are used for chronostratigraphic purposes.
First, it is necessary to define the herein applied bio-
stratigraphic, taxonomic and methodological criteria. The J/K
boundary based on ammonites was defined in LyonNeuchâ-
tel in 1973 (published in 1975) as the base of the Jacobi-
Grandis Zone. This decision was confirmed on all the
following meetings of the Working group on J/K boundary
(Munich 1982; Moscow 1984; Sümeg 1984 and others) and
has recently been universally accepted. However, the precise
determination of this boundary by means of ammonites in
the whole Tethyan Realm is possible at several localities
only. It is due to the presence of stratigraphically significant
species of ammonites being strictly limited only to sublit-
toral facies. Unfortunately, the sublittoral facies are also
characterized by frequent hiatuses. Moreover, ammonite fau-
nas do not allow determination of the J/K boundary with the
precision required here (down to several centimetres, see be-
low). On sections without ammonites (and in the Tethyan
Realm such sections are more than 99 %), the J/K boundary
can be determined only if some other group of organisms is
used, which, in the majority of cases, are calpionellids. In con-
tradiction to ammonites, calpionellids are common in the J/K
boundary strata in the whole Tethyan Realm and their associa-
tions occur not only in sublittoral facies but are especially
abundant in deeper basinal facies with less frequent hiatuses.
The position of the J/K boundary based on calpionellids was
agreed upon in Sümeg in 1984 (Remane et al. 1986) as the
base of the Calpionella Standard Zone. In sections, the posi-
tion of this boundary defined on calpionellids can be deter-
mined very precisely, usually within several centimetres.
Therefore, we use the J/K boundary defined on calpionellids,
basic distinguishing characteristics of this boundary along
with criteria used for its precise determination were published
in detail elsewhere (Houa et al. 1996b, p. 137).
According to Remane et al. (1986, p. 10), the boundary
at the base of the Jacobi-Grandis Zone is practically identi-
cal with the base of the Calpionella Standard Zone. Howev-
er, Tavera et al. (1994) proved that in the Puerto Esca
ñ
o sec-
tion (S Spain), both limits are different and that the
ammonite J/K boundary is slightly older than the calpionel-
lid one. In our opinion, the J/K boundary defined by calpi-
onellids is more precise, well determinable and much more
universally usable because of the presence of calpionellids
in the majority of outcrops, than the boundary defined by a
group, which occurs in sufficient composition at only a few
localities in the whole Tethyan Realm (ammonites).
With respect to taxonomy, we prefer to use the denomina-
tion of the big Tithonian variety of Calpionella alpina sensu
lato as Calpionella grandalpina Nagy 1986 and the prolon-
gated one as Calpionella elliptalpina Nagy 1986 (see Houa
1990, p. 362). Below the denomination of Calpionella alpi-
na Lorenz 1902 we understand a short, spherical, middle-
size form only, which is characteristic for the explosion
of the species on the base of the Calpionella Zone (see
Houa 1990, p. 361). This explosion must be distin-
guished from the increase in the abundance of Calpionella
by the end of the Tithonian (see Houa et al. 1996b, p. 138).
From the methodological point of view, extremely dense
sampling was carried out both in paleomagnetic study
(high-resolution magnetostratigraphy) and in biostrati-
graphic study, particularly in intervals with important bound-
aries. The positions of magnetostratigraphic boundaries, i.e.
horizons of change of the paleomagnetic polarity in rocks,
were only provisionally determined through interpolation
between two closest samples with different polarity (as is a
common practice so far) and localized with maximum possi-
ble precision by means of additional sampling of the section
(generally 12 cm; the boundary was sometimes lying direct-
ly in the measured sample showing intermediate polarity of
remanence). In sampling, precise mutual positions of bios-
tratigraphic and magnetostratigraphic samples were recorded
as well as their exact positions in lithological sections. The
sampling points were marked in the sections to allow verifi-
cation sampling or additional sampling aimed at higher sam-
Fig. 1. Location map of the Brodno locality.
CORRELATION OF MAGNETOSTRATIGRAPHY AND CALPIONELLID BIOSTRATIGRAPHY 127
ple density any time in the future. Such precision was ap-
plied to magnetostratigraphic study at the locality of Brodno
near ilina (Fig. 1). Magnetostratigraphic study in a similar
detail was carried out at the locality of the Bosso Valley,
Umbria, central Italy. The present study also refers to magne-
tostratigraphic profile at the locality of tramberk, northern
Moravia, which was subjected to a synoptic study with no
demands for high resolution.
Terminology
In the terminology of magnetostratigraphic polarity units,
we follow the International Stratigraphic Guide (Salvador
1994, p. 6975). For the classic magnetostratigraphic units
we use common informal numerical designation (e.g. M19;
the numbers are given from a certain arbitrary level on the
Barremian/Aptian boundary in the order from the youngest
unit to the oldest one). Every such numbered classic mag-
netostratigraphic unit has two parts, the older (lower) part
with reverse paleomagnetic direction, and the younger (up-
per) one with normal paleomagnetic direction. For each part
we use the term zone (we follow the more advanced no-
menclature of Quaternary magnetostratigraphic units see
l.c., p. 75, Fig. 12). Magnetostratigraphic polarity zone
(magnetozone) is the basic formal unit in the classification
of magnetostratigraphic polarity units (l.c., p. 71, paragraph
C). Magnetostratigraphic polarity zones may consist of (1)
rock bodies with a single polarity of paleomagnetization
throughout, (2) an intricate alternation of normal and reverse
units (mixed polarity), or (3) an interval of dominantly either
normal or reverse polarity, containing minor subdivisions of
the opposite polarity. (Thus, a zone of dominantly normal
polarity may include lesser-rank units of reverse polarity.)
(l.c., p. 71). Examples of the magnetozones are M19n, or
M19r, etc. So, every classic magnetostratigraphic unit has
two magnetozones, reverse (older) and normal (younger). If
a magnetozone includes a short part with the opposite polari-
ty, we designate it with the term magnetostratigraphic polari-
ty subzone (magnetosubzone, subzone). By magnetostrati-
graphic polarity subzone (magnetosubzone, subzone), we
understand a rock body with a single polarity of paleomag-
netization throughout and within a magnetozone with domi-
nantly opposite paleomagnetic polarity.
Magnetozone or magnetosubzone are terms of magneto-
stratigraphic classification. In chronostratigraphic terminolo-
gy every magnetozone (magnetosubzone, respectively) cor-
responds to a chronozone (subchronozone), in geo-
chronological terminology it corresponds to a chron (sub-
chron), see also Ogg & Lowrie (1986). Chrons and subchrons
are time units and their reflection in rocks are zones. Speaking
about rock units delimited by their paleomagnetic polarity, we
consider it correct to use the terms magnetozone and magneto-
subzone, instead of incorrect magnetochron (or magnetosub-
chron), which must be conserved for designation of the time
unit with certain paleomagnetic polarity only.
In the terminology of magnetostratigraphic polarity units
during the last 3.5 million years of the Earths history, every
magnetozone and every magnetosubzone is named (see l.c.,
Fig. 12) in accordance with the general rules for naming
stratigraphic units (l.c., section 3.B.3). In Mesozoic
magnetozones, we prefer to respect their numerical designa-
tion combined with the letter n or r according to their
polarity (e.g. M20n). (This system is firmly entrenched in
the literature and is being usefully employed. l.c., p.73).
However, for naming magnetosubzones (subzones) we pre-
fer to avoid numbers and letters and we use the general rules
valid for the naming of stratigraphic units (see l.c., section
7.H, last paragraph) because the numerical designation of
magnetosubzones is more complicated and inappropriate for
practical use. Short reverse magnetosubzone in M19n was
designated by Ogg et al. (1991) M19n-1. The use of this des-
ignation e.g. in linguistic expressions is unnecessarily com-
plicated or difficult and it does not solve the denomination
of parts of a magnetozone divided by a magnetosubzone.
Therefore we propose naming magnetozones with simple
geographically derived names as more practical. For this rea-
son, we use the individual geographically derived names
with a clearly designated standard (name-bearing standard)
for recognition of the unit named.
Standards in magnetostratigraphy fulfil a different role in
comparison to standards in chronostratigraphy. Every chro-
nostratigraphic unit is an artificial one, it does not exist in re-
ality, it must be defined (by means of a standard, which is its
type section) and delimited (by its boundary stratotypes).
This is not the case with magnetostratigraphic polarity units.
The pattern of polarity reversals preserved in sea-floor-
spreading anomalies or in the sequential record of reversals
in rocks everywhere on the continent, reflect the real history
of the Earth´s magnetic field. Its units really exist indepen-
dently of an observer who studies them. If an observer
names one such unit, he must only determine exactly which
unit he named, nothing more. He can do it simply on an out-
crop, where the named unit is preserved, by a permanent ar-
tificial marker. Such a stratotype is the standard of the name
applied, not the standard of the magnetostratigraphic unit,
because the unit needs no stratotype for its exact determina-
tion and delimitation.
Magnetostratigraphic studies in the Tethyan
Realm
Most of the magnetostratigraphic studies of J/K boundary
strata were carried out with the aim of setting out a synoptic
scheme of normally and reversely polarized magnetozones or
possibly magnetosubzones not aspiring to their detailed de-
limitation. Synoptic sampling was naturally insufficient for
determination of the so-called polarity transition zones where
rocks are classified as having intermediate polarity. The J/K
boundary was placed at different levels in different magneto-
stratigraphic studies, ranging between the magnetozones M19
and M17. A synoptic magnetostratigraphic profile of Upper
Mesozoic rocks was published from northern Tunisia (Nairn
et al. 1981); however, whereas late Jurassic limestones were
mostly suitable for paleomagnetic study, Cretaceous rocks
generally displayed secondary components of remanence.
Magnetostratigraphic studies of the early Cretaceous Maiolica
128 HOUA, KRS, MAN, PRUNER and VENHODOVÁ
Fm. pelagic limestones from the Bosso Valley, Umbria, cen-
tral Italy, resulted in the detection of the magnetozones M20
to M14, and probably to M13 (Lowrie & Channell 1984). In
the last mentioned study, the J/K boundary was placed within
the lowermost part of the magnetozone M17. Pelagic white
limestones rich in ammonites from southern Spain were mag-
netostratigraphically studied in two sections: in Carcabuey
and Sierra Gorda. The detected magnetozones ranging from
M15 to M19 were well correlable with magnetic marine M-
anomalies and, in a narrower range, also with magnetozones
at the locality of Foza, northern Italy. The presence of a re-
verse subzone was also detected in the normal part of the
magnetozone M20 (Ogg et al. 1984). The Umbrian Maiolica
Formation was studied by combined biostratigraphic and pale-
omagnetic methods using samples of white pelagic limestones
collected from the locality of Fonte del Giordano (Cirilli et al.
1984). The detected magnetozones were correlated with the
magnetic marine M-anomalies M19 to M14 for a lower calpi-
onellid section and above a hiatus also for an upper ra-
diolarian section. The critical section around the magnetozone
M19 could not be studied due to the occurrence of hiatuses.
Determination of the J/K boundary based on the correlation of
magnetozones and calpionellid zones was discussed by Már-
ton (1986) who proposed placing this boundary within the
magnetozone M17. Lowrie & Channel (1984) placed this
boundary close to the base of M17, while the authors of earli-
er papers placed it above the magnetozone M19. Further mag-
netostratigraphic studies of pelagic limestones of the Berria-
sian stratotype in Ardéche, France (Galbrun 1985), and of
Berriasian/Valanginian boundary strata in Cehegín, southern
Spain, province Murcia (Ogg et al. 1988), also indicate appli-
cability of this method to global correlation. Pelagic lime-
stones in all the above mentioned studies proved to have re-
corded the paleomagnetic field. However, in other localities of
pelagic limestones, paleomagnetic directions could not be de-
termined; samples of Mesozoic limestones displayed syn-tec-
tonic and post-tectonic components of remanence (Villalaín et
al. 1996; Parés & Roca 1996; Hoedemaeker et al. 1998). The
importance and interpretation aspects of magnetostratigraphy
of the J/K boundary interval in the Tethyan and Boreal realms
were discussed in the paper of Ogg et al. (1991).
Pilot samples of the Tithonian-Berriasian limestones were
magneto-mineralogically and paleomagnetically studied
originally at five localities in the Western Carpathians, out of
which two lie in northern Moravia and three in western Slo-
vakia. In the first stage, a synoptic magnetostratigraphic
study was done at the localities of tramberk, N. Moravia,
and Brodno near ilina, W. Slovakia (Houa et al. 1996a). A
detailed sampling at Brodno followed by paleomagnetic and
micropaleontological study resulted in high-resolution mag-
netostratigraphy (Houa et al. 1996b, 1997). Interpretation
of data including the results from samples collected in 1997
are presented in the submitted paper.
Short reverse polarity magnetosubzones
Dense sampling for paleomagnetic studies allowed detec-
tion and precise delimitation of two short reverse magneto-
subzones in the sections studied. One of them lies in the up-
per part of the magnetozone M19n, the other one lies imme-
diately above the middle (i.e. in the upper) part of the mag-
netozone M20n. Both these reverse magnetosubzones were
previously known from marine profiles (see Ogg et al. 1991)
and one of these magnetosubzones was found in fossil sec-
tions in two cases (see Ogg et al. 1984; Lowrie & Channell
1984). However, both of these magnetosubzones have never
been found in a single section yet, except in the Brodno sec-
tion, described in this paper.
Ogg et al. (1991) designate these magnetosubzones with
symbols derived from the symbols of the magnetozones in
which they are located, such as M19n-1 and M20n-1. This no-
menclature is, however, considered impractical by the present
authors. Instead, one-word nomenclature is herein proposed
for these magnetosubzones, following the guidelines set out
by the International Stratigraphic Guide for the nomenclature
of stratigraphic units. The reverse magnetosubzone in the up-
per part of the magnetozone M19n is designated as Brodno;
the name is derived from the name of a village, in the vicinity
of which the thoroughly studied section containing the name-
bearing type of this subzone is located (Fig. 2). The reverse
magnetosubzone in the middle part of the magnetozone M20n
is designated as Kysuca; the name is derived from the name
of a river in the valley of which the Brodno locality containing
the name-bearing type of this magnetosubzone is situated
(Fig. 3). A detailed delimitation including the required formal
specifications related to the establishment of these names are
given in the text below.
The geographical names of Kysuca and Brodno have al-
ready been used by other authors in the past for the designation
of lithostratigraphic units: Brodno Member (Scheibner 1967,
AptianAlbian) and Kysuca Member (Scheibner & Scheibner-
ová 1958, CenomanianTuronian). None of these units occur at
the stratotype of the described magnetosubzones (Brodno Quar-
ry). With respect to the fact that no other suitable geographical
names usable in the international scale are available (i.e. simple
names easily pronounced in world languages), both of the
above mentioned names are herein used for the designation of a
different kind of formal stratigraphic units than those they have
been used as there is no risk of any misunderstanding.
The presence of a magnetosubzone in a magnetozone, di-
vides this magnetozone into three parts, i.e. into the magne-
tosubzone proper and parts of the magnetozone before (be-
low) and after (above) the magnetosubzone. For example,
the Kysuca reverse magnetosubzone divides the normal
magnetozone M20n into (1) the older (lower) part of the nor-
mal zone, (2) the Kysuca reverse magnetosubzone and (3)
the younger (upper) part of the normal zone. We prefer to de-
rive the informal designation of both parts of the normal mag-
netozone from the designation of the reverse magneto-
subzone, by prefix pre- (for the older part of the normal
magnetozone) and post- (for the younger part of the normal
magnetozone). So, the magnetozone M20n is divided into
three parts: the pre-Kysuca part (the older normal part), the
Kysuca reverse magnetosubzone and the younger normal
post-Kysuca part. Analogically, the M19n magnetozone is di-
vided by presence of the Brodno magnetosubzone into the
normal pre-Brodno part, the Brodno reverse magnetosubzone
CORRELATION OF MAGNETOSTRATIGRAPHY AND CALPIONELLID BIOSTRATIGRAPHY 129
and the normal post-Brodno part. This nomenclature can be
effective until both parts of the normal magnetozones receive
their individual designations.
Brodno near ilina, W. Slovakia
Basic information
The locality of Brodno near ilina (Western Carpathians,
NW Slovakia, Fig. 1; see Michalík et al. 1990; Houa et al.
1996a,b) was selected for a detailed magnetostratigraphic study
of the Tithonian-Berriasian limestone strata among
five previously considered localities (Houa et al.
1996a; Fig. 1) for its (1) favourable geological set-
ting (relatively continuous sedimentation in a quiet
basinal environment, favourable lithology), (2)
favourable physical properties of the rocks en-
abling us to infer primary paleomagnetic directions
with a high degree of reliability, using multi-com-
ponent remanence analysis combined with fold
tests, and (3) rich calpionellid associations. With
respect to the relatively low sedimentation rate of
the limestones, the original collecting of orientated
samples was realized with short sampling intervals
and the inferred data were related to limestone stra-
ta numbered by Michalík et al. (1990). The in-
ferred magnetozones M21r to M17r could be cor-
related with analogous sections in the Tethyan
Realm (Foza, Bosso, tramberk) and with marine
M (Mesozoic) anomalies. A narrow subzone with
reverse polarity was first detected in the upper part
of the magnetozone M19n. This state of knowl-
edge has been published by Houa et al. (1996a).
Later, the Brodno section was labelled with new,
more detailed numbering in order to detect another
expected reverse subzone within the magnetozone
M20n and to meet the needs of high-resolution
magnetostratigraphy, particularly to specify more
exactly the positions of the determined magneto-
stratigraphic and biostratigraphic boundaries
(Houa et al. 1996b). The older, synoptic number-
ing was also preserved.
In 1996 and 1997, very dense (locally even
continuous) collecting of orientated paleomagnet-
ic samples was performed in several consecutive
phases at this locality. Therefore, the profile can
be characterized as a high-resolution one. Rela-
tively extensive laboratory paleomagnetic, petro-
magnetic and micropaleontological analyses were
realized due to the financial support of the Grant
Agency of the Academy of Sciences of the CR in
Prague and of the Dionýz túr Geological Insti-
tute in Bratislava. Detailed sampling of the sec-
tion (averaging 20 to 35 orientated samples per 1
m of true thickness) allowed a more precise iden-
tification of boundaries of the individual magne-
tozones and of both reverse subzones within the
magnetozones M19 and M20 (Houa et al. 1997).
Fig. 3. The Kysuca Subzone, the width of which is marked by two aluminium
cylinders (of 1 inch diameter) cemented into the drill holes. The two aluminium
cylinders bear the name Kysuca.
Fig. 2. The Brodno Subzone, the width of which is marked by two aluminium
cylinders (of 1 inch diameter) cemented into the drill holes. The two aluminium
cylinders bear the name Brodno.
In 1997, collection of additional samples was aimed primarily
at identification of the boundaries of both reverse polarity
subzones. In consequence, these subzones are defined with a
high precision today. A new procedure in magnetozone and
subzone interpretation was also proposed during the detailed
processing of magnetostratigraphic data from the Brodno lo-
cality: it is based on analysis of the angle deviation of the sep-
arated fossil component of remanence from the most probable
paleomagnetic direction considered for the whole studied sec-
tion. A procedure providing estimated mean values as well as
standard deviations of the smoothed interpolated course of the
given quantities was also applied.
130 HOUA, KRS, MAN, PRUNER and VENHODOVÁ
Magnetostratigraphy
Altogether 360 orientated hand samples were collected for
the construction of a high-resolution profile with the maximum
sampling density between the base of the magnetozone M21r
and the base of the magnetozone M18r. In geological cross-sec-
tion, this interval represents only 10 metres of the true thickness
of strata.
The volume magnetic susceptibility k and the remanent
magnetization J of samples were measured by means of the
KLY-2 A.C. bridge and the JR-5 spinner magnetometer
(Jelínek 1973, 1966), respectively. A part of the set of samples
was subjected to demagnetization by alternating field using
the Schonstedt GSD-1 apparatus. Demagnetization in thermal
fields generally proved to be more effective; consequently,
each sample of the whole set was subjected to progressive
thermal demagnetization up to 590
o
C in eleven to thirteen
thermal fields on average using the MAVACS apparatus
(Pøíhoda et al. 1989). The measured values of remanent mag-
netization of thermally demagnetized samples were subjected
to multi-component analysis of remanence following the
method of Kirschvink (1980), paleomagnetic directions were
subjected to fold tests and, after correction for dip of strata,
used for construction of the magnetostratigraphic profile. In
addition, diagrams of normalized values of M
t
/M
n
vs. demag-
netizing temperature t [
o
C] were constructed for all samples,
M
t
being the modulus of the moment of remanent magnetiza-
tion of the thermally treated sample after cooling, M
n
being
the modulus of the moment of remanent magnetization of the
sample in its natural state. These diagrams were used for esti-
mation of the values of unblocking temperatures in all sam-
ples from the given set. A more precise determination of un-
blocking temperatures was derived on pilot samples following
the methods described in Houa et al. (1996a, p. 186188).
All the samples, with no exception, displayed large compo-
nents of secondary magnetization, corresponding to the vis-
cous component and to chemo-remanent magnetization condi-
tioned by weathering. The stable component of remanence
was separated with an unblocking temperature of 520 to
580
o
C linked with the content of magnetite as a carrier of the
primary paleomagnetic directions. These results are in accor-
dance with the results of combined magneto-mineralogical
and X-ray diffraction analyses of the pilot samples. Diagrams
showing the correlation of normalized values of volume mag-
netic susceptibility k
t
/k
n
vs. temperature were constructed for
all the studied samples to assess the influence of possible
phase changes of magnetically active minerals during thermal
treatment of the samples (Krs & Pruner 1997).
The studied limestones are ranked among medium to weakly
magnetic rocks. The scatter of J
n
and k
n
values is relatively
wide, with a marked decrease in magnetization from older to
younger rocks. Statistics for the quantities J
n
and k
n
for both
medium magnetic late Tithonian and weakly magnetic early
Berriasian limestones are given in Table 1. The table also im-
plies that the paleomagnetic polarity of the samples is not re-
flected in the changes of basic magnetic parameters.
The magnetostratigraphic profile shows the values of
moduli of natural remanent magnetization J
n
in [10
6
A/m]
units, the values of volume magnetic susceptibility of sam-
ples in natural state k
n
in [10
6
SI] units, paleomagnetic dec-
lination D
p
and inclination I
p
in degrees and the so-called
discrimination function first introduced into the interpretation
of magnetostratigraphic data (Figs. 5 and 9).
A newly proposed procedure for evaluating
magnetostratigraphic data
An innovation to the hitherto used method of data process-
ing and graphic presentation of results (cf. Houa et al. 1996a,
1997) was applied to the herein submitted processing of mag-
netostratigraphic data from the locality of Brodno near ilina.
This innovation (by O.M.) employed some of the procedures
described in the monograph of Fisher et al. (1987).
The essential purpose of magnetostratigraphy is to continu-
ously, if possible, subdivide the studied stratigraphic section
into intervals corresponding to normal (N) and reverse (R) po-
larity of the paleomagnetic field. Accordingly, data processing
comprises two steps: the first step is the construction of a dis-
crimination function, the direction of remanent magnetization
being its independent variable. On the basis of the discrimina-
tion function, the detected direction can be classified, i.e.
placed into one of two classes N or R. The second step in-
cludes the interpolation and smoothing of the detected direc-
tions, and the constructed discrimination function as well,
along the magnetostratigraphic profile. The applied procedure
provides continuous estimates of both the mean value and
standard deviation of a studied quantity thereby providing the
required subdivision of the section or, where appropriate, the
designation of intervals where the quality of input data does
not allow a reliable classification. Both these steps will be dis-
cussed separately in the two paragraphs below.
Age
Number
of samples
Normal (N)
Reverse (R)
magnetozone
Modulus of natural
remanent magnetization
J
n
[10
-6
A/m]
Volume magnetic susceptibility
k
n
[10
-6
SI]
Mean
value
Standard
deviation
Mean
value
Standard
deviation
Early
50
N
678
343
9.8
4.2
Berriasian
71
R
452
386
5.5
8.9
Late
159
N
1068
474
19.5
8.7
Tithonian
88
R
1274
791
22.0
10.0
Table l: Brodno near ilina, basic magnetic parameters of limestone samples.
CORRELATION OF MAGNETOSTRATIGRAPHY AND CALPIONELLID BIOSTRATIGRAPHY 131
Construction of the discrimination function
The directions
s
i
, i = 1, ..., n (1)
of remanent magnetization of all the samples from the mag-
netostratigraphic profile are plotted using the Lambert equal-
area projection in Fig. 4. This sample of directions corre-
sponds to a hitherto unknown distribution, which should be
(in an ideal case only the paleomagnetic component of rema-
nent magnetization, which originated at the time of sedimen-
tation is involved):
1) bimodal, with modes corresponding to opposite directions,
a normal mode and a reverse mode, herein referred to as s
normal
,
and s
reverse
,
2) isotropic with respect to the axis intersecting both
modes.
The above idea may be confronted with the qualitative
features of the data set (1), enhanced by non-parametric esti-
mate of the true probability density f (s) giving rise to the
data. The estimate, being a modification of Parzen estimate
(Parzen 1962), has the form (Fisher et al. 1987):
$( )
( , )
f
W
i
i
n
s
s s
=
=
∑
1
, (2)
where
W
C
n
C
C
i
n
n
n
i
( , )
/ (
sinh(
) exp(
cos( , ))
s s
s s
=
4
π
and C
n
is a parameter, whose value C
n
= 28.5 was found using
the maximum probability method. The estimated density, be-
ing displayed in Fig. 4, is not in evident contradiction to the
presumed properties of the distribution. The estimate implies
the values of s
normal
(inclination 37
o
, declination 263
o
) and
s
reverse
(inclination 41
o
, declination 65
o
), which are in a rath-
er good agreement with each other.
Although the decision on the assignment of a direction to
the class N or R may be based immediately on the quantities
of declination and inclination, such an approach is not the
best one. In order to avoid ambiguity, the classification
should be based on a single scalar quantity discrimination
function d(s
i
). Providing that the distribution has the above
given properties, an optimum choice for this function is the
angle between directions s
i
and s
normal
. Then, inequality d(s
i
)
<
π
/2 or d(s
i
) >
π
/2 implies the classification of direction s
i
to class N or R, respectively.
After the classification, polarity in the class R may be re-
versed and the two classes may be grouped together again to
estimate the mean direction of magnetization regardless of
its polarity. In this way, mean direction s
mean
(inclination
38.7
o
, declination 250.9
o
) was found. Providing that the dis-
tribution has the above given properties, this direction can
be regarded as a better approximation of s
normal
than that pre-
viously derived from the estimate of probability density.
The graphic presentation of results includes the diagrams of
declination and inclination of the paleomagnetic directions for
the individual samples. The values s
normal
, and s
reverse
may be
seen in the diagrams, too. The values of the discrimination
function computed for individual samples are also plotted.
Interpolation and smoothing
The samples are obviously not distributed continuously
along the section. Besides, the paleomagnetic directions of
remanent magnetization show a relatively high dispersion
even in the same stratum. This is understandable as the stud-
ied component of remanent magnetization is usually very
low if compared with natural remanent magnetization, the
values of which are typically of the order of 1 mA/m. These
two reasons suggest a need for interpolation and smoothing
of the detected direction or the discrimination function de-
rived from it. Several approaches to the solution of this prob-
lem were tested, mostly mentioned in the monograph of Fish-
er et al. (1987), such as the use of smoothing splines (Reinsch
1967). Among these, a relatively simple technique of moving
average seems to be the most advantageous. The algorithm is
described below.
Each sample is characterized by the coordinate t
i
, cor-
responding to its position normal to stratification or to the
time of sedimentation, and by the direction described by a
unit vector s
i
.
i) A weight function w(t), e.g.,
or
an integer value constant c, e.g. c = 6, and a real parameter
step are chosen.
ii) The following operations are performed for a chosen
coordinate t = t
0
: the weights
w
i
= w ((t
i
- t
0
)/h), i = 1,.., n,
where the parameter h is chosen so as to meet the condition
w
c
i
i
n
=
∑
=
1
, (6)
are assigned to individual samples. Then the weighted mean
direction s
0
is calculated using the formulas
r
s
r
s
r
=
=
=
=
∑
w
r
r
i
i
n
i
1
0
,
,
/
, (7)
and so is the angular standard deviation of direction
δ
0
= arrccos (r / c) . (8)
The quantities s
0
and
δ
0
are assigned to the coordinate t
0.
iii) The coordinate t
0
is substituted by t
0
+ step and the
process is repeated from step ii).
The essence of the algorithm can be described very simply.
A window whose shape, position, and width are given by the
function w(t), the coordinate t
0
, and the parameter h, respec-
(3)
1 for
|
t
|
≤
½ ,
w(t) =
〈
0 for
|
t
|
>
½
(4)
w(t) = exp (- ½ t
2
) for arbitrary real t,
(5)
$f (s)
132 HOUA, KRS, MAN, PRUNER and VENHODOVÁ
Fig. 5. Brodno locality. Kysuca Reverse Polarity Subzone. D
p
paleomagnetic declination; I
p
paleomagnetic inclination; discrimina-
tion function expressing total angular deviation of paleomagnetic direction; normal, reverse normal (N), reverse (R) polarity of paleo-
magnetic direction for respective parts of the magnetozone or magnetosubzone.
Fig. 4. Brodno locality. Paleomagnetic directions and hence derived probability density function, Lambert equal-area projection.
CORRELATION OF MAGNETOSTRATIGRAPHY AND CALPIONELLID BIOSTRATIGRAPHY 133
tively, is moving along the magnetostratigraphic profile as-
signing a weight w
i
to the individual samples. While its shape
is kept firm, its width varies according to the local density of
samples, so that the sum of all weights is constant. The
weighted mean direction and its angular standard deviation
are found for each window position. The discriminating func-
tion introduced in the preceding paragraph may be treated in a
similar way.
In the graphic presentation, the diagram of a studied quanti-
ty, e.g. declination, inclination, or discriminating function,
shows both the estimate of its mean value (depicted by full
line) and the zone
mean value ± standard deviation
(see Figs. 5 and 9). For declination, the standard deviation is
defined by expression
δ
/cos(inclination).
Definition of the Kysuca and Brodno
magnetosubzones
The Kysuca reverse magnetosubzone is situated above the
middle of the normal magnetozone M20n. The reverse paleo-
magnetic direction of this magnetosubzone at locality Brodno
is represented by limestone bed No. 99, only 15 cm in total
true thickness, i.e. 6 % of the total thickness of the normal
zone M20n (2.37 m, covering the pre- and post-Kysuca nor-
mal parts as well as the Kysuca reverse magnetosubzone), see
Figs. 5 and 6. The base of the Kysuca reverse magnetosub-
zone in Brodno lies at a level of 55 % of the local thickness of
the magnetozone M20n. Samples collected from the Kysuca
magnetosubzone were subjected to progressive thermal de-
magnetization in the fields of 100
o
, 150
o
, 200
o
, 250
o
, 300
o
,
350
o
, 400
o
, 450
o
, 500
o
, (520
o
), (540
o
) up to 590
o
C.
Figures 7 and 8 show Zijderveld diagrams of samples from
the Kysuca magnetosubzone indicating moduli of natural re-
manent magnetization (NRM) and of remanent magnetization
after the final step of thermal demagnetization (RM). Graphs
showing dependence of k
t
/k
n
vs. temperature of demagnetiza-
tion field are drawn below the Zijderveld diagrams. Symbols
N or R indicated with each of the Zijderveld diagrams denote
normal (N) or reverse (R) polarity of the primary paleomag-
netic component of remanence. This component was inferred
using multi-component analysis (Kirschvink 1980) and sub-
jected to combination with fold test. The proportion of the in-
tensity of secondary components is high in all samples, reach-
ing from 80 to 90 % of J
n
. Unblocking temperature of
minerals carriers of primary components of remanence
vary between 560
o
and 590
o
C thus indicating the presence of
magnetite. The results of the multi-component analysis have
proved that J
n
consists of three components: The A-compo-
nent of remanence was inferred in the temperature interval of
20100
o
C, undoubtedly being of viscous origin; the B-com-
ponent of secondary origin was inferred in the temperature in-
terval of ca. 100350
o
C, whereas the C-component corre-
sponding to the primary (paleomagnetic) component of
remanence was determined in the temperature interval of ca.
300
o
C (350
o
C) to 500
o
C (590
o
C), cf. Houa et al. (1996a).
The results of thermal demagnetization are presented in this
paper as examples only for some samples on the basis of
which the Kysuca reverse subzone was interpreted. In sample
No. 7550, the C-component displays both normal polarity (in
the temperature interval of 350500
o
C) and reverse polarity
(in the temperature interval of 520590
o
C). This sample
comes from the boundary interval separating the uppermost
part of the Kysuca reverse subzone from the post-Kysuca part
of the magnetozone M20n. With respect to the thickness of
the sample (2 cm) having two polarities of primary compo-
nents of remanence and to the presumed low value of the sedi-
mentation rate of the boundary interval claystones, it can be
concluded that the transition from reverse to normal polarity
of the geocentric co-axial magnetic dipole of the Earth oc-
curred within a time span of ca. ±5000 years (cf. also Butler
1992, p. 191). The boundary sample No. 7554 seems to dis-
play intermediate polarity direction.
The Brodno reverse magnetosubzone was detected in the
upper (late) part of the normal magnetozone M19n and con-
stitutes the uppermost part (8 cm) of the bed 24A, the whole
bed 24B and also the whole overlying bed 24C. Its complete
thickness is 24 cm. The Brodno reverse magnetosubzone
represents only 8 % of the total thickness of the normal mag-
netozone M19n (3.13 m, covering the pre- and post-Brodno
normal parts as well as the Brodno reverse magnetosub-
zone), see Figs. 9 and 10. The base of the Brodno reverse
magnetosubzone in Brodno lies at a level of 82 % of the local
thickness of the magnetozone M19n. This subzone was de-
fined on the basis of an analysis of paleomagnetic parame-
ters carried out in the same manner as for the preceding sub-
zone. Analogically, J
n
consists of three components of
remanence, the C-component corresponding to the primary
(paleomagnetic) component of remanence was determined
in temperature interval of ca. 300
o
C (400
o
C) to 500
o
C
(540
o
C) in the process of progressive laboratory thermal de-
magnetization. The results of thermal demagnetization of
only 12 samples from the Brodno magnetosubzone and its
vicinity are shown as examples in Figs. 11 and 12, out of
which six have normal (N) paleomagnetic polarity and six
have reverse (R) paleomagnetic polarity. The high propor-
tion of secondary components of remanent magnetization
frequently reaching 90 % of J
n
is visible in figures again. A
transition between reverse (normal) and normal (reverse) po-
larity of the magnetic field of the dipole of the Earth was not
detected in this subzone.
Correlation of paleomagnetic events
and calpionellid biostratigraphy
The oldest calpionellids, i.e. the first species of genus
Chitinoidella (Ch. slovenica Borza, Ch. colomi Borza, Ch.
dobeni Borza) characterizing the oldest calpionellid Dobeni
Subzone of the Chitinoidella Zone, were found in high num-
bers in the late part of the magnetozone M20r. The first rep-
resentatives of these species appear in the bed 84 and the last
ones were recorded in the uppermost part of the bed 86, i.e.
at the very base of the overlying magnetozone M20n.
The base of the pre-Kysuca part of the magnetozone M20n
lies in the upper part of the bed 86. The earliest portion of
the pre-Kysuca part still belongs to the calpionellid Dobeni
134 HOUA, KRS, MAN, PRUNER and VENHODOVÁ
Fig. 6. Brodno locality. Kysuca Reverse Polarity Subzone. Paleomagnetic sample Nos, strata Nos and palentological sample Nos. Ch.
Chitinoidella; Pr. Praetintinnopsella; Cr. Crassicollaria; T. Tintinnopsella.
CORRELATION OF MAGNETOSTRATIGRAPHY AND CALPIONELLID BIOSTRATIGRAPHY 135
Subzone; the Boneti Subzone starts in the bed 87 (i.e. in ap-
prox. one tenth of the local thickness of the pre-Kysuca
part). The acme of the species Ch. boneti Doben was record-
ed in the late portion of the pre-Kysuca part. The top of the
Boneti Subzone, hence also the top of the Chitinoidella
Zone, is defined by the first appearance of small Tintinnop-
sella (Remane et al. 1986) first recorded at Brodno in the
bed 98, i.e. below the Kysuca magnetosubzone. Thus, the
pre-Kysuca part of M20n comprises the late portion of the
calpionellid Dobeni Subzone, the whole calpionellid Boneti
Subzone and the earliest portion of the Remanei Subzone of
the Crassicollaria Standard Zone (the bed 98).
In terms of calpionellid biostratigraphy, the Kysuca Polari-
ty Subzone is situated in the section at Brodno at the very
base of the Crassicollaria Standard Zone. The lowermost
subzone of the Crassicollaria Standard Zone, i.e. the calpi-
onellid Remanei Subzone, in the Brodno section has a thick-
ness of 100 cm, stretching from the topmost bed of the pre-
Kysuca part (the bed 98) across the Kysuca magnetosubzone
(i.e. the bed 99) and almost the whole overlying post-Kysuca
part (except for its latest portion the bed 4B; bed numbers
see Houa et al. 1996b: Fig. 12). The top of the Remanei
Subzone is marked by a major event representing the base of
the overlying calpionellid Intermedia Subzone. This event is
the appearance of species Calpionella grandalpina Nagy.
The first (oldest) representatives of this species in the Brod-
no section were recorded in the middle of the limestone bed
4B, i.e. immediately below the top of the post-Kysuca part
(lying between the beds 4B and 5 and in fact representing
the boundary between the magnetozones M20n and M19r).
Thus the base of the calpionellid Intermedia Subzone coin-
cides with the latest portion of the post-Kysuca part.
The whole magnetozone M19r is constituted by the calpi-
onellid Intermedia Subzone. This subzone also extends to
the overlying magnetozone M19n. Here, its top is defined as
the base of the Calpionella Standard Zone, herein considered
as the J/K boundary. In the studied section, the J/K boundary
lies at the level of 40 % of the thickness of the pre-Brodno
part, i.e. at approx. 35 % of thickness of the whole magneto-
zone M19n. The last Tithonian calpionellid Intermedia Sub-
zone therefore starts in the topmost part of the post-Kysuca
part and corresponds to the whole magnetozone M19r and
approximately the lowermost one-third of the magnetozone
M19n; the rest of the magnetozone M19n is included into
the Calpionella Standard Zone, i.e. the basal part of the Ber-
riasian.
This implies that the boundary between the Crassicollaria
and Calpionella Standard Zones (i.e. the J/K boundary in the
present concept as recognized in the sections studied) lies
within the pre-Brodno part of the magnetozone M19n. No
magnetoevents lie in the immediate proximity of this boundary.
There is another event important for the verification of the
position of the J/K boundary based on calpionellids: a short
acme of species Cr. parvula Remane lying in the earliest part
of the Calpionella Zone. This acme is well defined in the
section at Brodno, being confined to the beds 20 and 21.
This calpionellid event also lies within the pre-Brodno part,
at approx. one half of the interval between the J/K boundary
and the base of the Brodno reverse magnetosubzone.
The whole Brodno magnetosubzone lies within the Calpi-
onella Standard Zone (Alpina Subzone). The interval occu-
pied by this magnetosubzone in the section at Brodno is in-
cluded in the monotonous part of the calpionellid Alpina
Subzone and so is the whole overlying post-Brodno part.
The boundary between the magnetozones M19n and M18r
lies between the limestone beds 25B and 26A. In the opinion
of Michalík et al. (1990), this level corresponds to the top of
the calpionellid Alpina Subzone (i.e. the base of the calpi-
onellid Cadischiana Subzone), but it has not proved possible
for the present authors to confirm this with the required de-
gree of accuracy. Accordingly, the whole magnetozone M18r
should be included in the calpionellid Cadischiana Subzone.
Definition of the Jurassic/Cretaceous boundary
according to calpionellids
According to calpionellids, the J/K boundary (i.e. the Titho-
nian/Berriasian boundary) is placed at the base of the Calpi-
onella Standard Zone as defined by Remane et al. (1986). The
basic diagnostic features for the identification of the base of
the calpionellid zone Calpionella were already defined by Re-
mane (1964). The problem of the position of J/K boundary in
the Brodno section was discussed in more detail by Houa et
al. (1996b, p. 137139) who placed this boundary in the
Brodno section between the beds 15A (the latest Tithonian)
and 15B (the earliest Berriasian). The reasons for the errone-
ous placement of this boundary in the Brodno section at a dif-
ferent level by other authors (to a stratigraphically lower level
approx. to the level of the upper portion of the bed 8 in the
present, more detailed numbering) were also explained.
The base of the Calpionella Standard Zone represents one
of the most prominent events in the relatively short history of
calpionellid evolution. A great advantage of the Brodno sec-
tion is that no hiatuses, slumps or washouts occur either at the
level of this event or in its close proximity. According to all
indicators, the limestone sedimentation at this horizon and in
its close proximity at Brodno was quiet, relatively slow and
continuous, and characterized by conditions very favourable
for the fossilization of calpionellid loricae. Gradual changes
associated with this event can be, therefore, studied in consid-
erable detail (see Houa et al. 1996b; Fig. 6).
tramberk, northern Moravia
Basic information
The tramberk Limestone represents a complex of peri-reef
accumulations of fine or coarser organic debris with an almost
complete absence of terrigenous admixture. In some intervals,
grain-sized particles disappear and the rock passes into finer
varieties, to micritic limestones. This fact probably reflects
sea-level fluctuations but may also result from the position of
the given site of sedimentation with respect to the main axes
of detrital material transport in a debris talus around Tithonian-
Berriasian reefs. Sedimentation rates in the tramberk peri-reef
accumulation must have been variable in space and in time as
136 HOUA, KRS, MAN, PRUNER and VENHODOVÁ
CORRELATION OF MAGNETOSTRATIGRAPHY AND CALPIONELLID BIOSTRATIGRAPHY 137
Fig. 7. Brodno locality. Kysuca Reverse Polarity Subzone. Results
of progressive thermal demagnetization of samples by means of the
MAVACS apparatus. Only selected samples are demonstrated to
show typical examples, see Fig. 6. R (reverse), N (normal) polarity
of the paleomagnetic remanence component derived by multi-com-
ponent analysis is indicated for respective samples. The Zijderveld
diagrams represent orthogonal projection onto the horizontal X,Y
plane (full circles) and the vertical X,Z plane (empty circles). NRM
natural remanent magnetization. Beneath the Zijderveld dia-
grams, the normalized values of k
t
/ k
n
in relation to temperature t
[
o
C] are plotted; k
t
is the volume magnetic susceptibility of the
sample demagnetized at temperature t and cooled to room tempera-
ture; k
n
is the volume magnetic susceptibility of the sample in its
natural state (prior to thermal treatment).
well. The occurrence of washouts must also be considered
probable in such shallow-water depositional environments.
Larger blocks of limestones (several metres in size), represent
olistoliths in detrital material, they are probably derived from
eroded reef bodies emerged during temporary eustatic sea-lev-
el falls.
The studied section was therefore chosen outside the coarse
to blocky facies, in a deeper part of the original peri-reef accu-
mulation farther from the source of materials, where a lower
incidence of hiatuses, washouts or secondary olistoliths can
be anticipated. The section was situated on the 6th level of the
Kotouè Quarry where rather finer varieties of biofragmental
limestones occur in a suitable position, at some levels passing
into micritic limestones several metres thick.
The studied section begins at the edge of the limestone body
of the Homole Hill and stretches along the 6th level northern
wall to the central part of the Kotouè Quarry, where it ends
on the opposite side of the body of the Homole Hill (close
to the Mendocino Fault). The section is 620 m long, being in-
tersected by no major fault. Stratigraphically, it covers approx-
imately the same time interval (between the magnetozones
M21n and M18n) as the above discussed part of the Brodno
section, which is only 11 m thick (extending between the mag-
netozones M21r and M18r).
Magnetostratigraphy
Magnetostratigraphic study of the J/K boundary limestone
strata at the locality of tramberk was started in 1992 in two
sections. Priority was given to the section on the 6th level of
the Kotouè Quarry. Altogether 342 orientated drill samples
were collected from the northern wall of the 6th level. The
limestone samples are exceptionally weakly magnetic with
moduli of J
n
ranging between several tens to several hundred
[10
6
A/m]. The values of k
n
are mostly negative, dia-
magnetism of the limestone mass prevails over weak para-
magnetism and ferrimagnetism. Tithonian limestones were
measured from 94 samples in the first stage. The mean value
of 78.1 µA/m and standard deviation 72.4 µA/m were ob-
tained for J
n
of samples with normal polarity, while the mean
value of 56.0 µA/m and standard deviation 45.2 µA/m were
obtained for J
n
of samples with reverse polarity. The mean
value of 12.7
×
10
6
SI and standard deviation 2.6
×
10
6
SI
were obtained for k
n
(Houa et al. 1992, 1993). The procedure
described for the Brodno locality was used for the precise de-
termination of unblocking temperatures and for the X-ray dif-
fraction determination of ferrimagnetic minerals in exception-
ally weakly magnetic limestones. Unblocking temperatures of
540560
o
C corresponding to magnetite were determined.
Analogous unblocking temperatures were determined in all
samples used for construction of the magnetostratigraphic
profile. Magnetite content determined in pilot samples is ap-
prox. 0.3 g.t
1
. Irregular, less commonly isometric and
spherolitic magnetite particles range between 3 and 20 µm in
size.
All samples collected were subjected to progressive thermal
demagnetization using the MAVACS apparatus. The results
clearly demonstrate that, in spite of the very weak magnetiza-
tion of the limestones studied and a higher proportion of sec-
ondary components of remanence, the samples are suitable for
inferring paleomagnetic directions (see Houa et al. 1996a,b).
A magnetostratigraphic profile constructed on the basis of
samples collected in 1992, indicated the basic positions of
magnetozones, but proved to be rather complicated in some
intervals due to tectonic deformations and the generally dy-
namic sedimentation of limestones deposited in the peri-reef
zone. In 1993 and 1994, additional sampling was carried out
to reach a sampling point density of ca. 3 samples per 10 m
of true thickness and in other intervals of ca. 8 sam-
ples per 10 m. Documentation of paleomagnetic samples is
included in the report of Houa et al. (1994) as well as a
magnetostratigraphic profile with values of J
n
, k
n
, D
p
, I
p
and with interpreted normal and reverse magnetozones and
magnetosubzones.
In the submitted study, the essential results from the tram-
berk section are shown only in the form of a comparative
scheme of hitherto studied magnetostratigraphic profiles for
the localities of Brodno and tramberk in Fig. 13. The basic
magnetozones were proved in the tramberk section, howev-
er, the reverse magnetozone M19r and the Kysuca reverse
magnetosubzone were indicated with a lesser degree of con-
clusiveness. Two reverse subzones were recorded in the late
part of the normal magnetozone M19n at the level of the
Brodno reverse subzone. The above mentioned shortcomings
of the magnetostratigraphic profile at tramberk may be
caused by the complicated tectonic setting and possibly also
by the extremely dynamic sedimentation. This section should,
therefore, be regarded as an orientational one, not reaching the
accuracy and reliability of the section at the Brodno locality.
Calpionellid associations
Considering the character of sedimentation in a peri-reef ta-
lus of calcareous detritus and its close vicinity (see above), the
preservation of calpionellid associations itself in the tram-
berk Limestone is remarkable. Loricae of calpionellids were
most probably transported by water flow into interstices
among detrital particles of calcareous organic remains along
with other allochthonous material forming the matrix of the
rock. Calpionellids are generally less abundant in bio-
v
138 HOUA, KRS, MAN, PRUNER and VENHODOVÁ
Fig. 8. Brodno locality. Kysuca Reverse Polarity Subzone. See caption to Fig. 7.
CORRELATION OF MAGNETOSTRATIGRAPHY AND CALPIONELLID BIOSTRATIGRAPHY 139
Fig. 9. Brodno locality. Brodno Reverse Polarity Subzone. See caption to Fig. 5.
Fig. 10. Brodno locality. Brodno Reverse Polarity Subzone. See
caption to Fig. 6.
fragmental varieties of the tramberk-type limestones, which
most probably originated close to the source of the biofrag-
mental material, i.e. probably in shallow marine conditions
not far from the reefs as such. In contrast, calpionellids are
more abundant in finer, micritic tramberk-type limestones,
which probably represent a more distal, deeper-water environ-
ment possibly originating during periods of sea-level rise. The
abundance of calpionellids in the tramberk Limestone is
generally low and only exceptionally (e.g., in thin sections of
micrite fills of ammonite shells) comparable with the calpi-
onellid abundances in limestones from basinal localities (such
as Brodno).
No material sufficient for the definition of the oldest
calpionellid Dobeni Subzone was obtained anywhere at
tramberk. Occasional finds of species of the Dobeni Sub-
zone association are absolutely insufficient for delimitation
of the Subzone. On the contrary, the following calpionellid
Boneti Subzone was recorded in all larger bodies of the
tramberk-type limestones. The occurrence of the species
Chitinoidella boneti Doben in the tramberk Limestone in
fact corresponds to the interval of its maximum abundance
(acme). In the studied section, this species was found in
samples from the late portion of the pre-Kysuca part of the
magnetozone M20n. Ch. boneti thus occurs at the same
stratigraphic position here as does the acme of this species at
Brodno. The last occurrence of Ch. boneti at tramberk co-
incides with the first appearance of calpionellids with hya-
line lorica walls. This event lies immediately below the top
of the pre-Kysuca part in the studied section.
The pre-Kysuca part in the section at tramberk is 62 m
thick (sic!, only 90 cm at Brodno) and the interval of occur-
rence of Ch. boneti is 20 m thick here (acme of this species is
restricted to ca. 50 cm at Brodno).
The base of the Crassicollaria Standard Zone in the studied
section was localized at the very top of the pre-Kysuca part.
140 HOUA, KRS, MAN, PRUNER and VENHODOVÁ
Fig. 11. Brodno locality. Brodno Reverse Polarity Subzone. See caption to Fig. 7.
CORRELATION OF MAGNETOSTRATIGRAPHY AND CALPIONELLID BIOSTRATIGRAPHY 141
Fig. 12. Brodno locality. Brodno Reverse Polarity Subzone. See caption to Fig. 7.
142 HOUA, KRS, MAN, PRUNER and VENHODOVÁ
Fig. 13. Resultant magnetostratigraphic profiles across the Tithonian/
Berriasian boundary strata at Brodno and tramberk.
This situation exactly corresponds to that at Brodno. The
Crassicollaria Zone (its lowermost calpionellid Remanei Sub-
zone) also includes the overlying Kysuca magnetosubzone,
the thickness of which is still difficult to assess precisely (a
thickness of 3 m can be estimated from interpolation). The
above given lowermost subzone of the Crassicollaria Standard
Zone also includes the overlying post-Kysuca part having a
thickness of some 30 m here (as opposed to 90 cm at Brodno).
The base of the calpionellid Intermedia Subzone should coin-
cide with the base of the magnetozone M19r, however, this
magnetozone is only insufficiently documented up to now. Its
thickness was assessed at only 3.5 m by interpolation, which
may be caused by primary reduction of sedimentary record at
this level. Datable calpionellid samples from this level are
also missing up to now and, consequently, the first specimens
of Calpionella grandalpina Nagy (base of the Intermedia
Subzone) are known from the earliest part of the magnetozone
M19n.
The most important calpionellid event the base of the
Calpionella Standard Zone (i.e. the J/K boundary) is well de-
fined in the tramberk section and its position was determined
more precisely on the basis of a denser sampling. It lies within
the magnetozone M19n, 22 m above its base, i.e. approxi-
mately at 30 % of the local thickness of the whole magneto-
zone (at 35 % at Brodno). This implies that the last Tithonian
calpionellid subzone Intermedia Subzone also corre-
sponds here approximately to the lowermost one-third of the
magnetozone M19n (the pertinence of the magnetozone M19r
to this calpionellid subzone in tramberk has still not been
shown by any fossiliferous sample).
An interesting point about the tramberk section is the
presence of two reverse magnetosubzones in the late part of
the magnetozone M19n. The Brodno magnetosubzone corre-
lates either to one or to both of them. This cannot be decided
on the basis of biostratigraphic criteria, as the Brodno mag-
netosubzone lies in the monotonous part of the Alpina Sub-
zone of the Calpionella Standard Zone. The position of the
short acme of species Cr. parvula has still not been deter-
mined more precisely within the tramberk section, due to
sparse sampling.
Discussion of results
The positions of the Kysuca and Brodno magnetosubzones
are also confirmed by our preliminary results obtained from
the section at Bosso (Italy). Lowrie & Channell (1984, p. 45)
have speculated that A single reversed sample at the base of
the section in the top of the more slowly deposited Calcari Di-
asprigni may represent the short reversed interval between
M19 and M20, i.e. the herein described Kysuca Subzone.
This occurrence of reverse magnetization was not confirmed
by detailed sampling at the level of 304.15 m or in its vicinity.
The equivalent of the Kysuca Subzone itself was recorded in
the Bosso section rather at the level of 299.2 to 299.55 m, i.e.
4.5 m lower. It is represented by bed 28 in our numbering.
Calpionellids are unfortunately completely absent from this
basal interval of the Bosso section.
The only equivalent of the magnetosubzones in M19n, i.e.
the Brodno Subzone, in the Bosso section corresponds to the
level of 318.90319.55 m (it is represented by the beds 100
103 of our numbering). Its base lies at the level of 80 % and
its top at the level of 85 % of the local thickness of the magne-
tozone M19n. As at Brodno, it lies within the monotonous
part of the calpionellid Alpina Subzone of the Calpionella
Standard Zone.
From the geophysical point of view, the magnetostratigraphic
profile at the locality of Brodno near ilina can be considered
absolutely unique among all the hitherto studied sections across
the J/K boundary strata in the Tethyan Realm. This is the first
section on the continent, where two reverse subzones were very
precisely detected within the magnetozones M20n and M19n at
positions corresponding to marine M (Mesozoic) anomalies.
Although the paleomagnetic components of remanence are very
low in comparison with natural remanence, they were easily in-
ferred with the use of progressive thermal demagnetization by
the MAVACS apparatus and subsequent multi-component anal-
ysis of remanence. Samples with intermediate polarity were de-
tected at the boundaries of the Kysuca Subzone localized within
CORRELATION OF MAGNETOSTRATIGRAPHY AND CALPIONELLID BIOSTRATIGRAPHY 143
the magnetozone M20n in the zones of transition from N to R
and R to N polarities. Time interval within the limits of ca.
±5000 years can be assumed for a transition from normal (re-
verse) to reverse (normal) polarity of magnetic field of the co-
axial geocentric dipole of the Earth with respect to the thickness
of the samples (2 cm) and the assumed sedimentation rate (ca.
2 mm/ka). This figure depends on the estimation of the sedi-
mentation rate of the studied pelagic sediments, but is in agree-
ment with data obtained from other localities (Butler 1992). A
similar sedimentation rate (2.27 mm/ka) may be obtained
from the Brodno profile if the magnetozones of total thickness
from the base of M21 to the base of M18 (10 m) and the cor-
responding time interval (4.4 Ma) are considered. An analo-
gous figure was also obtained from the Miocene sediments of
the Sokolov Basin, western Bohemia (Krs et al. 1991).
Ackowledgements: The authors wish to thank Dr. J. Michalík,
Dr. D. Reháková and two anonymous referees for reviewing the
paper and some helpful suggestions.
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