QUATERNARY VOLCANISM IN THE PERªANI MOUNTAINS (ROMANIA)
GEOLOGICA CARPATHICA, 55, 4, BRATISLAVA, AUGUST 2004
SHORT-LIVED QUATERNARY VOLCANISM IN THE PERªANI
MOUNTAINS (ROMANIA) REVEALED BY COMBINED K-Ar AND
CRISTIAN G. PANAIOTU
, ZOLTÁN PÉCSKAY
, ULRICH HAMBACH
, IOAN SEGHEDI
CRISTINA E. PANAIOTU
, ITAYA TETSUMARU
, MIHAI ORLEANU
and ALEXANDRU SZAKÁCS
University of Bucharest, Paleomagnetism Laboratory, Bãlcescu 1, 70111 Bucharest, Romania; email@example.com
Institute of Nuclear Research of the Hungarian Academy of Sciences, Bem Tér 18c, 4001 Debrecen, Hungary
Geosciences University of Bayreuth, Chair of Geomorphology, 95440 Bayreuth, Germany; firstname.lastname@example.org
Institute of Geodynamics Sabba S. Stefãnescu, str. Jean-Luis Calderon 1921, 70201 Bucharest, Romania
Research Institute of Natural Sciences, Okayama University of Science, Ridai-cho11, 700-0005 Okayama, Japan
Leinberger Str. 6, 44141 Dortmund, Germany
(Manuscript received February 19, 2003; accepted in revised form October 2, 2003)
Abstract: New K-Ar ages combined with paleomagnetic data demonstrate that the basaltic volcanism in the Perºani
Mountains occurred in two relatively short phases. The first one lasted several tens of thousands of years around 1.2 Ma
and it seems that the inception of the volcanic activity took place in two isolated places and reached the maximum extent
during the Cobb Mountain Normal Polarity Subchron when larger areas were covered. The second phase started just
before 600 ka and was restricted to the central area of the volcanic field. One lava flow of this phase recorded a short-
lived reversed polarity event inside the Brunhes Normal Chron, probably the 15β reversal excursion. The duration of this
phase was less than 200 kyr, which is the best estimate according to the available radiometric data.
Key words: Carpathians, Perºani Mountains, Quaternary volcanism, alkali basalts, K-Ar data, paleomagnetism, magnetic
The alkali basaltic volcanism in the Perºani Mountains, al-
though of modest extension (ca. 22×8 km), represents an im-
portant Quaternary alkali basaltic province inside the Car-
pathians and south-eastern Europe. Previous K-Ar data
pointed to a Late Pliocene, Early and Middle Pleistocene vol-
canic activity (Casta 1980; Ghenea et al. 1981; Mihãilã &
Kreuzer 1981; Downes et al. 1995). Paleomagnetic studies
(Hambach et al. 1994; Pãtraºcu et al. 1994) showed a strong
bias towards normal polarity and intermediate directions but
only a few reversed polarities. Because this pattern cannot be
explained by a long lasting volcanic activity, a new study was
initiated to obtain more reliable K-Ar data in order to con-
strain better the timing of volcanic activity.
Geological settings and sampling
Well-preserved volcanic structures show spectacular topo-
graphic features in the Perºani Mountains: more or less eroded
conical hills and remnants of scoria cones on top of a volca-
nic plateau. Volcanological investigations revealed several
successive stages, each one starting with phreatic or
phreatomagmatic eruptions followed by a less energetic
strombolian or effusive activity (Seghedi & Szakács 1994).
Fossil soils (e.g. Bogata Quarry, Bârc Quarry) separate se-
quences of pyroclastics and lava flows (Seghedi & Szakács
1994), however, without giving exact information about dura-
tion of interruptions in volcanic activity.
The initiation of the volcanic activity is represented by thin-
ly-bedded pyroclastic deposits with plan-parallel, undulatory
or cross lamination and frequent bomb-sags indicating near
vent phreatomagmatic explosion-derived dilute density cur-
rents and co-surge fall-out deposition resulting from the inter-
action of ascending magma with the shallow water table.
These deposits are organized as a number of maar or tuff-ring
type volcanic structures (Sãrata, Racoº, Mãguricea, and Bârc).
Such structures are overlain by strombolian fall-out deposits,
which constructed volcanic cones, and by lava flows of vari-
able thickness. Thicker lavas generally display various platy,
columnar or blocky jointings inside the flow-body, breccia-
tions at the base and clinker-like features at the top. Five iso-
lated volcanic structures have been recognized, three in the
north (Sãrata, Racoº and Mateiaº) and one in the south (Coma-
na) as well as a more complex volcanic area in the central part
(between Hoghiz and Bogata Valley).
For the K-Ar measurements we sampled mostly the fresh
lava flows, however, in some cases loose fragments have been
also sampled (e.g. a fragment at the base of the upper Bârc
lava flow and a fragment of strombolian bomb belonging to
the Gruiu cone), in order to accurate the judgment of the event
succession. Each collected sample had 2 kg wt. and was mac-
roscopically free of xenoliths. The most suitable samples (free
of any alteration and xenoliths) were selected on the basis of
the examination of thin sections.
PANAIOTU et al.
Sampling sites for paleomagnetic investigations cover all
the volcanic structures, though samples are mainly derived
from lava flows. From each site at least 3 block samples or 6
cores have been collected (Table 2). Exogene alterations and
lightning areas have been avoided. Fig. 1 shows sample loca-
tions on a simplified volcanological map.
Fig. 1. Volcanological sketch-map of the Perºani Mountains Quaternary ba-
saltic province. Inset map shows location of the Perºani Mountains in Romania.
1 Prevolcanic basement (Mesozoic and Cenozoic). First phase: 2 Initial
pyroclastics (phreatomagmatic deposits); 3 Scoria cones; 4 Lava flows.
Second phase: 5 Pyroclastics (phreatomagmatic deposits); 6 Scoria cones;
7 Lava flows; 8 Holocene alluvia; 9 Sampling sites for K-Ar. Sampling
sites for paleomagnetism: 10 Normal polarity; 11 Reversed polarity; 12
The samples for K-Ar datings were crushed and
sieved to 250100 µm. Sieved fraction was
washed with distilled water and dried at 110 °C
for 24 h for Ar-analysis. A portion of the fraction
was ground using an agate mortar and the result-
ing powder was analysed for potassium. Due to
the mineralogical and petrological character of the
rock samples principally the K-Ar age determina-
tion was carried out on whole rock samples,
however, in some cases the analytical work has
been made on the groundmass rich fractions
(iron-oxides and plagioclase phenocrysts were re-
moved using a permanent magnet and an isody-
In the ATOMKI, Debrecen, conventional exper-
imental techniques were used for the argon and
the potassium analysis. Details of the procedures
are those described in Pécskay & Molnár (2002).
The results of calibration of the instruments and
the applied methods have been described else-
where (Balogh 1985). All analytical errors given
in Table 1 represent one standard deviation (i.e.
68% analytical confidence level).
In Okayama University the K-Ar dating has
been made following the methods described by
Nagao et al. (1984) and Itaya et al. (1991). Potas-
sium was analysed by flame photometry using a
2000 ppm Cs buffer. Its analytical error is within
2 % at the 2 sigma confidence level. Argon was
analysed by a 15 cm radius sector type mass spec-
trometer with a single collector system using an
isotopic dilution method with a spike of
Multiple runs of standard (JG-1 biotite, 91 Ma) in-
dicate that the error of Ar analysis is about 1 % at
the 2 sigma confidence level.
Calculations of K-Ar ages were made using the
decay constants given by Steiger & Jäger (1977).
K-Ar data from the Perºani Mountains
The new K-Ar ages are presented in Table 1.
For the sake of checking reproducibility of Ar
analysis duplicate measurements have been made
on samples No. 4390 and No. 4389 respectively.
These samples have significant importance be-
cause they belong to different lava flows. Data
show that basaltic volcanism in the Perºani Moun-
tains occurred in two phases: first phase between
1.51.2 Ma and the second phase between 0.67
0.52 Ma. Comparing these data with K-Ar ages
from Downes et al. (1995) we found a good agreement for the
age of Racoº Complex and an important difference for the age
of lava flows from Bârc Valley where they reported an age
around 1.6 Ma. This discrepancy points out the difficulties to
obtain good K-Ar ages for this type of rocks. The assumption
Ar ratio of argon trapped in volcanic rocks at
QUATERNARY VOLCANISM IN THE PERªANI MOUNTAINS (ROMANIA)
Presented data set includes 26 sites. The age of each site
was established by direct K-Ar dating or by a direct geological
relation to a dated lava flow: 19 sites belong to phase 1 and 4
sites belong to phase 2. Last four sites in Table 2 (marked with
?) still lack well established ages so they were excluded
from further analysis. Data were divided in sites with normal
polarity, reversed polarity and transitional directions accord-
ing to the virtual geomagnetic pole (VGP) latitude for each
site (latitude >45° N for normal polarity, latitude >45° S for
reversed polarity, latitude = 45° N or S for transitional direc-
tions) (Fig. 2).
Normal polarity (7 sites, probably from 45 independent
flows) and transitional directions (8 sites from 4 flows in the
Racoº Complex and 1 flow in Bogata Quarry) dominate sites
from phase 1. Only four sites (from 23 lava flows: Turzun
and Comana) have reversed polarity. From phase 2, one site
has a reversed polarity and the other two flows (3 sites) have
Correlation of magnetic polarity data and K-Ar ages
To correlate the observed magnetic polarities with the polar-
ity time scale, several histograms of K-Ar ages were computed
using the method of Vandamme et al. (1991). Each datum
from Table 1 is given unit weight and represented by a Gauss-
ian distribution with standard deviation equal to age uncer-
tainty. This flattens the large uncertainty data and emphasizes
the most precise results. The smooth histogram represents the
sum of all individual Gaussian distributions. The precise loca-
tion of the peak and duration of the tails do not reflect the tim-
ing of volcanic activity, but parameters linked to argon-loss or
argon-excess process. This would account for the asymmetric
nature of the histogram with its sharp rise, actually the most
eruption is atmospheric (295.5) often gives a large systematic
geological error in the K-Ar dating of Quaternary basaltic
rocks, especially younger than 1 Ma. There are two possible
sources of error: a) the existence of excess Ar; b) mass-frac-
tionated initial Ar. The major source of excess Ar is supposed
to be the magma itself (Balogh et al. 1994). Frequently the
mafic phenocrysts (olivine, pyroxene and amphibole) and
crustal quartz xenolith proved to be carriers of excess Ar, too
(Fuhrmann & Lippolt 1986). If mass-fractionation of initial Ar
occurred this should give a
Ar ratio different from the
atmospheric ratio, so simply determining the
Ar ratio in
samples can check this. The error sources other than those
mentioned above are uncertainty in the blank correction and
instabilities in the sensitivity of mass spectrometer. All these
factors produce overlapping of the confidence limits for ages,
which make it difficult to distinguish between lava flows.
To avoid any dubious conclusion caused by age disturbing
effects, K-Ar ages will be analysed further in combination
with paleomagnetic data.
Paleomagnetic data from the Perºani Mountains
The compilation of previous paleomagnetic results (Ham-
bach et al. 1994; Pãtraºcu et al. 1994) in conjunction with two
new sites is presented in Table 2. All data from Table 2 fulfill
the minimum criteria of McElhinny & McFadden (1997) for
data quality in secular variation studies from lava flows: (1)
there can be no suggestion that the sampling region has been
subjected to any tectonic effects; (2) a minimum N=2 samples
per lava flow (site) should have been studied; (3) stability of
the magnetization must have been tested by some demagneti-
zation method; (4) the radius of the circle of 95% confidence
) for each site must be <20°.
Fig. 2. Equal-area projection of VGPs from the Perºani Mountains: full square lower hemisphere; open triangle upper hemisphere.
Dotted circle limit of secular variation (45° north or south).
PANAIOTU et al.
significant feature with respect to true age. The width of the
histogram peak at half amplitude is probably the best estimate
of the geological age. We computed several histograms
(Fig. 3) grouping the data from Table 1 according to their
magnetic polarity and volcanic phase. The histogram for tran-
sitional directions was constructed using both data from Ta-
ble 1 and the age (1.19±0.05 Ma) reported for the Racoº vol-
cano by Downes et al. (1995).
Looking at the position of the histogram peaks for phase 1
on the polarity time scale, it is obvious that expected magnetic
polarities should be dominated by reversed polarity. On con-
trary, paleomagnetic polarities measured in lava flows belong-
ing to this volcanic phase are dominantly normal and transi-
tional. This aspect reduces dramatically the duration of
eruptions and suggests that most of volcanic activity was dur-
ing Cobb Mountain Normal Polarity Subchron (CMNS). In
order to check if our K-Ar ages are in agreement with this in-
terpretation, we computed a new histogram combining all sites
with normal and transitional directions. The width of histo-
gram peak at half amplitude suggests an age between 1.15 Ma
and 1.4 Ma. This time interval includes the age accepted for
CMNS between 1.17 and 1.24 Ma (Table 3). The combined
histogram is asymmetric with a tail toward older ages. The
asymmetry was produced by K-Ar ages obtained from sites
with normal polarity, most of them achieved from the Bogata
area and reflecting excess argon in samples. For this reason,
the symmetrical histogram for transitional directions gives a
better estimation for the age of the first phase: 1.24±0.09 Ma.
This age confirms the suggestion of Hambach et al. (1994)
that transitional directions from the lava flows of the Racoº
Complex recorded the CMNS. The new K-Ar data show that
not only the transitional directions of CMNS were recorded,
but also the normal polarity associated with this subchron. The
duration of CMNS based on paleomagnetic studies on sedi-
ments is around 88 kyr (Clement & Martinson 1992), with
normal polarity around 30 kyr (Clement & Martinson 1992) or
23 kyr (Yang et al. 2001) or even 10 kyr (Horng et al. 2002).
Fig. 3. Histograms of K-Ar ages from the Perºani Mountains: 1
phase 1 reversed polarity; 2 phase 1 normal polarity; 3 phase 1
transitional directions; 4 phase 1 combined normal and transitional
directions; 5 phase 2 normal polarity; 6 phase 2 reversed polari-
ty; 7 phase 2 combined normal and reversed polarity. Main Geo-
magnetic polarity time scale after Cande & Kent (1995): black =
normal polarity; white = reversed polarity. Full white bands are short-
lived global polarity events inside the Brunhes Normal Chron after
Langereis et al. (1997) and Quidelleur et al. (1999), 15α = Big Lost;
15β = La Palma. Position of reversal and events during the late
Matuyama Reversed Chron are after Singer et al. (1999). CMNS =
Cobb Mountain Normal Polarity Subchron.
Table 1: K-Ar ages (Ma) from basaltic lavas of the Perºani Mountains.
5.295 ´ 10
1.44 ± 0.22
5.286 ´ 10
1.53 ± 0.23
6.609 ´ 10
1.34 ± 0.18
5.552 ´ 10
1.35 ± 0.11
7.239 ´ 10
1.44 ± 0.13
7.542 ´ 10
1.36 ± 0.14
7.757 ´ 10
1.39 ± 0.13
6.384 ´ 10
1.25 ± 0.06
7.583 ´ 10
1.27 ± 0.20
3.180 ´ 10
1.21 ± 0.12
6.022 ´ 10
1.24 ± 0.06
Racoº upper (Hegheº)
6.744 ´ 10
1.39 ± 0.24
Racoº upper (Hegheº)
6.040 ´ 10
1.27 ± 0.07
4.130 ´ 10
0.668 ± 0.08
Old Bârc Quarry
4.645 ´ 10
0.679 ± 0.06
3.477 ´ 10
0.578 ± 0.12
3.682 ´ 10
0.612 ± 0.08
3.810 ´ 10
0.631 ± 0.05
3.647 ´ 10
0.524 ± 0.02
QUATERNARY VOLCANISM IN THE PERªANI MOUNTAINS (ROMANIA)
K-Ar ages of reversals recorded in Turzun and Comana are af-
fected by relatively large analytic errors and excess argon, but
we supposed that they erupted not much before the start of
CMNS. In conclusion, the total duration of the first phase of
eruption in the Perºani Mountains was in the order of ten thou-
The second phase of eruptions took place between 0.5
0.72 Ma, according to the width of total histogram peak at half
amplitude. Several eruptions occurred during this interval,
since one of them recorded one short-lived polarity event in-
side the Brunhes Normal Chron (e.g. Gubbins 1999). One lava
flow from Bârc Quarry has a paleomagnetic direction inside
Site means were computed using Fishers statistics (1953): n number of specimens; Dec paleomagnetic declination; Inc paleomagnetic in-
clination; k precision parameter; α
95% confidence circle; Lat latitude and Long longitude of paleomagnetic pole; Polarity: N nor-
mal, R reversed, T transitional directions; Ref: 1 (Hambach et al. 1994), 2 (Pãtraºcu et al. 1994), 3 (this study). Sites labeled with A, B, C were
sampled in the same lava flow.
Comana Quarry (A)
Comana Quarry (B)
Comana Old Quarry
Bogata Valley (1)
Bogata Valley (2)
Bogata Valley (3)
Bogata Valley (4)
Bogata Quarry (A)
Bogata Quarry (B)
Bârc Old Quarry
Trestia Valley (1)
Trestia Valley (2)
Table 2: Site mean paleomagnetic data from basaltic volcanism in the Perºani Mountains.
Radiometric ages (Ma)
Cobb Mountain Normal Subchron
Excursions in Brunhes Chron
Horng et al. (2002);
Singer et al. (1999) and references therein;
Downes et al. (1995);
Langereis et al. (1997) and references therein;
Quidelleur et al. (1999);
Lund et al. (2001);
Table 3: Comparison of magnetic reversal ages used in this paper.
the secular variation limits for a full reversal. The age of this
reversed polarity event is around 0.63±0.08 Ma considering
the symmetrical histogram computed from the K-Ar ages de-
termined from this quarry (Table 1). This interval includes two
reversal excursions, reported both in lava flows and sedi-
ments. The most detailed record of this sequence of excursions
was recovered from Leg 172 sediments (Lund et al. 2001).
The older excursion 15β has an astronomical age around
604 ka and strongly negative inclinations and significant dec-
lination variability. According to this age estimation, 15β ex-
cursion can be correlated with an excursion of the geomagnet-
ic field characterized by strongly abnormal directions
PANAIOTU et al.
associated with a field intensity as low as 7 µT identified in a
lava flow sequence from La Palma, Canary Islands
(602±12 ka obtained by K/Ar dating, using the Cassignol
technique, Quidelleur et al. 1999). This age is concordant with
a minimum observed in the global SINT800 composite
record, derived from worldwide deep-sea records of relative
paleointensity (Guyodo & Valet 1999). Taking into account
this directional behaviour, 15β can be defined as a short dura-
tion of the altered polarity according to the definition of Gub-
bins (1999) or a reversal excursion (e.g. Langereis et al.
1997). The younger excursion, 15α, has an age of 573 ka and
less directional variability with minimum inclinations reach-
ing only 0°. It can be classified as a large secular variation
event. Both the age and the directional behaviour of 15α are
similar to the event CR3 found in an eastern Mediterranean
piston core (Langereis et al. 1997). Langereis and co-workers
correlated it with the Big Lost Event. Since the direction re-
corded in the Bârc Quarry look like a full reversal, we sup-
posed that the best correlation is with 15β which is also a full
reversal and not with Big Lost.
The new K-Ar data combined with paleomagnetic data
demonstrate that the basaltic volcanism in Perºani Mountains
took place in two relatively short phases. The first one lasted
about ten thousand years around 1.2 Ma, however, not as con-
tinuous activity but showing in this interval several short term
volcanic pulses. At the actual level of knowledge, it seems
that the volcanic activity started in two isolated places (Tur-
zun and Comana) and reached the maximum extension and
volume during CMNS. The duration of volcanic activity in
different parts of the Perºani Mountains can be estimated on
the basis of the length of CNMS from marine sediments: 1.
Racoº volcano, with transitional directions, consists of several
eruptions, suggesting its generation in less than 5 kyr; 2. The
lava flow from Bogata Quarry, with a different transitional di-
rection than the Racoº directions, was not erupted simulta-
neously with the Racoº lavas; 3. The lavas with full normal
polarity (Sãrata, Hoghiz, Bogata Valley, Bârc Valley) were
emplaced in less than 1020 kyr.
The second phase started just before 600 ka and was re-
stricted to both sides of the Bogata Valley. The duration of
this phase was less than 200 kyr, which is the best estimate ac-
cording to the available radiometric data. Paleomagnetic data
and K-Ar ages give evidence for three independent lava flows
belonging to this second phase. Additional evidence for the
long lasting gap between the two eruption phases is given by
a paleosol complex between the lavas from the Bârc Valley
(phase 1) and Bârc Quarry (phase 2). This fossil soil devel-
oped on a wind blown volcanogenic detrital sediment and not
directly on the lava flows. Such successions indicate at least
one glacial/interglacial cycle between the volcanic phases.
Our analyses demonstrate that by combining paleomagnetic
and K-Ar data with magnetic polarity time scale, it was possi-
ble to obtain more detailed and accurate information about the
age of volcanic activity in the Perºani Mountains. This ap-
proach overcame analytical difficulties in using K-Ar dating
methods on young basaltic rocks and it helped to remove the
effect of a perturbing factor, such as excess argon. Moreover,
these results not only contributed with additional constraints
and information to the knowledge about the volcanological
evolution of the Perºani Mountains in the last 1.2 Ma, but also
demonstrated the potential for studying the behaviour of the
past geomagnetic field. More analytical (paleomagnetic and
more precise Ar-Ar dating) and volcanological work in this
area to benefit from this unique feature of the basaltic lava
flows from the Perºani Mountains to record both the Cobb
Mountain Normal Subchron and reversal excursions inside
the Brunhes Chron.
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