GeolCarp_Vol65_No6_471

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, DECEMBER 2014, 65, 6, 471—479 doi: 10.1515/geoca-2015-0006

Identification of a buried Late Cenozoic maar-diatreme

structure (North Moravia, Czech Republic)

VOJTĚCH ŠEŠULKA

, IVA SEDLÁKOVÁ

, ONDŘEJ BÁBEK

1,2

and ANTONÍN PŘICHYSTAL

Department of Geological Sciences, Masaryk University, Kotlářská 267/2, 611 37 Brno, Czech Republic;

vsesulka@seznam.cz; ivased@sci.muni.cz; babek@prfnw.upol.cz; prichy@sci.muni.cz

Department of Geology, Palacký University of Olomouc, Křížkovského 8, 771 47 Olomouc, Czech Republic

(Manuscript received December 22, 2013; accepted in revised form October 7, 2014)

Abstract: The maar-diatreme volcanic structure in the vicinity of the village of Lomnice near the town of Bruntál
(North Moravia, Czech Republic) has been investigated using a set of geophysical methods including ground magne-
tometry, gravimetry and electrical resistivity tomography. The structure was detected by an aerial magnetic survey in
the second half of the 20

century. Since its discovery only limited information about this buried structure has been

available. The coherence of the magnetic anomaly of 190 nT and Bouguer anomaly of —4.7 mGal indicates a volcanic
origin of the structure. The funnel-shaped maar-diatreme structure is filled with lacustrine clay and colluvium of Car-
boniferous greywacke, which forms the country rock. The surface diameter of the structure is about 600 m, the depth is
more than 400 m. The spatial association with other volcanic centers in the surroundings of the town of Bruntál infers
the relative dating of the Lomnice maar. The phreatic eruption and maar-diatreme formation could be an indirect conse-
quence of effusive activity of the nearby Velký Roudný volcano. The Lomnice structure is the first Plio-Pleistocene
maar-diatreme ever described in North Moravia and Silesia.

Key words: applied geophysics, ground magnetometry, gravimetry, electrical resistivity tomography, maar-diatreme,
Plio-Pleistocene, Central European Volcanic Province, Bohemian Massif.

Introduction

The Late Cenozoic volcanic activity in the eastern part of the
Bohemian Massif (North Moravia) belongs to the Central
European Volcanic Province (CEPV), which includes the
Rhenish Massif and Eifel area, Germany and the Eger (Ohře)

Rift  in  the  Bohemian  Massif,  Czech  Republic  (Kopecký
1964; Schreiber & Rotsch 1998; Ulrych et al. 2011) (Fig. 1).
The anorogenic volcanism (Ulrych et al. 2011) in the prov-
ince is linked to the development of a major intracontinental
rift  system  and  to  domal  uplift  of  the  Variscan  basement.
Mantle  processes  such  as  the  diapiric  upwelling  of  small-

Fig. 1. Simplified tectonic map showing the position of the studied area in the CEVP (based on Ulrych et al. 2011).

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scale convective instabilities from the base of the upper man-
tle (Wilson & Downes 2006) or episodic rising of mantle
plumes (Wedepohl & Baumann 1999) are considered as the
driving mechanisms for the volcanic activity.

While the time constraints and tectonic models for the de-

velopment  of  the  Eger  Rift  and  its  volcanism  are  frequently
discussed  in  the  literature  (Babuška  &  Plomerová  2008;
Ulrych et al. 2011), little is known about the easternmost part
of the volcanic province in North Moravia and Silesia (Fediuk
&  Fediuková  1985;  Birkenmajer  et  al.  2007;  Lustrino  &
Wilson  2007).  The  Plio-Pleistocene  (5.5  to  0.8 Ma)  anoro-
genic volcanic activity in North Moravia is aligned with the
Sudetic fault system and it is spatially and temporally  associ-
ated  with  increased  CO

fluxes, development of geomorphic

faults, present-day seismic activity and active graben-like sed-
imentary basins (Grygar & Jelínek 2003; Špaček et al. 2009).

The Cenozoic volcanic rocks in North Moravia have been

known and mapped since the end of the 19

century (Ma-

kowsky 1882; Klvaňa 1893), but information about their age
and  geochemistry  is  scarce  (Marek  1973;  Šmejkal  1980;
Šibrava & Havlíček 1980; Birkenmajer et al. 2002a,b, 2004,
2007;  Pécskay  et  al.  2009).  The  existing  geophysical  re-
search was focused mainly on the regional magnetic surveys
(Gruntorád  &  Lhotská  1973;  Šalanský  &  Gnojek  2002;
Šalanský 2004) and only a few shallow geophysical data are
available  for  specific  volcanic  features  such  as  diatremes
(Šalanský & Gnojek 2002).

Shallow geophysical imaging, including magnetometry,

gravimetry  and  electric  conductivity  (resistivity)  surveys
proved  to  be  a  useful  approach  in  the  mapping  of  diatreme
volcanoes (Macnae 1995; Schulz et al. 2005; Matthes et al.
2010).  Recently,  Cenozoic  maars  and  diatremes  were  geo-
physically  imaged  in  the  western  and  northern  parts  of  the
Bohemian  Massif  (Schulz  et  al.  2005;  Lindner  et  al.  2006;
Mrlina et al. 2009; Skácelová et al. 2010).

The aim of this paper is to provide information on the

shape  and  subsurface  structure  of  a  maar-diatreme  volcano
near  Lomnice,  North  Moravia  based  on  detailed  magneto-
metric  and  gravimetric  mapping  combined  with  electrical
resistivity tomography. The geophysical image of the maar-
diatreme can be useful for subsequent dating and tectonic in-
terpretation  of  the  Plio-Pleistocene  volcanic  activity  in  the
easternmost part of the CEVP.

Geological setting

The North Moravian Cenozoic volcanism represents the

easternmost part of the Odra tectono-volcanic zone (Ko-
pecký 1978; Ulrych et al. 1999). It is traditionally subdivided
into two groups, which differ in location and age (Pacák
1928). The outer group (in the concept of a Variscan orogene
zonation) is of Tertiary age and is related to the Sudetic Mar-
ginal Fault. Major volcanic structures are hosted in the Fore-

Fig. 2. Geological and tectonic sketch of the Cenozoic volcanic field in the surroundings of the town of Bruntál with a possible shoreline of
the paleolake according to the present-day topography.

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Sudetic block and the North Sudetic Depression (Birkenmajer
et  al.  2004,  2007)  in  Lower  Silesia,  Poland.  A  number  of
volcanic outcrops (e.g. volcanic plugs, lava flows and  cinder
cones)  have  been  described  and  dated  by  the  K-Ar  method.
The age range of the volcanic activity is since Late Oligocene
until Miocene (Birkenmajer et al. 2002a,b, 2004, 2007). The
inner  Plio-Pleistocene  volcanic  rocks  are  concentrated
around a crossing of the Bělá and Klepáčov deep fault sys-
tems (Sudetic fault system of the Bohemian Massif – Buday
et al. 1995) and the Šternberk—Horní Benešov Belt (a tectonic
zone  with  Devonian  submarine  volcanic  belt).  Nevertheless
this  conventional  subdivision  is  not  well  constrained.  The
spatial and time correlation is not verifiable as suggested by
recent studies at the site Pohoř (Šešulka et al. 2012; Ulrych
et al. 2013).

The inner volcanic group in the surroundings of the town

of Bruntál comprises several types of volcanic structures, in-
cluding the Velký Roudný scoria cone with associated lava
flows (Cajz et al. 2012), the feeder vent in Břidličná or the
Razová subaquatic tuffs (Barth 1977; Cajz et al. 2012). The
effusive rocks are mostly represented by olivine basalt,
nephelinite basanite and olivine nephelinite (Barth 1977).

The surveyed locality is situated between the village of

Lomnice and its subdivision of Tylov (Bruntál district, North
Moravia) in a side valley of the Lomnice Brook (Fig. 2). The
slopes  of  the  valley  are  carved  in  Lower  Carboniferous
(Visean)  greywacke  with  shale  interbeds  (Horní  Benešov
Formation,  Nízký  Jeseník  Culm  Basin),  which  provide  the
country  rock  for  the  diatreme  structure.  The  central  part  of
the  valley  is  filled  with  Quaternary  colluvial  and  alluvial
sediments  with  underlying  lacustrine  clays  and  colluvium.
Although the shape of the valley might suggest the presence
of the maar, geological mapping fails to detect any evidence
of  the  volcanic  structure.  No  outcrop  or  piece  of  volcanic
rock has been found at the site. The Lomnice maar as well as
the  other  buried  volcanic  structures  in  the  vicinity  of  the
town  of  Bruntál  (e.q.  Tylov  structure)  were  identified  only
by  airborne  magnetic  surveys  (Gruntorád  &  Lhotská  1973;
Šalanský 2004).

During the 1970s, three shallow boreholes were drilled by

geologists of the Czech Geological Survey in the area of air-
borne  magnetic  structure  at  Lomnice  (drill  holes  Lomnice
MV-1 – depth 94.5 m, Lomnice MV-2 – depth 86.2 m and
Lomnice-Tylov  B-1  –  depth  52 m).  According  to  the  field
description of cores (Fig. 3) by J. Dvořák & M. Růžička (un-
published reports), the rock record between  ~ 11 and  ~ 83 m
depth  consists  of  an  alternation  of  light  green  or  grey  silt-
stones  with  emerald  green  clays,  in  places  with  small  char-
coals,  vivianite  coatings  (Lomnice  MV-1  –  43.7 m),  a  big
piece  of  wood  (70.2 m)  and  possibly  volcanoclastic  admix-
ture (89.20 m). The clays and silts are typically finely lami-
nated, with individual laminae 2 to 3 mm thick. That is why
they can be interpreted as deposits of a maar lake. Unfortu-
nately, no rock samples are retained, as all samples were lost
during the moving of the Czech Geological Survey in 1993.
The location of the collars is also unclear. The approximate
position of the B-1 drill hole is shown in Růžička’s detailed
but unpublished geological map. The coordinates of the other
two holes are unknown.

Fig. 3. Lithological log of the historic drill holes B1 and MV1
(modified from Dvořák & Růžička, unpublished data).

Methodology

The combination of several geophysical methods was ap-

plied in the survey of the Lomnice maar structure.

The ground magnetic survey was carried out using the ce-

sium  magnetometer  SM-5  NAVMAG  (Scintrex,  Canada).
The instrument enables a continuous measuring of total mag-
netic  field  and  records  data  with  frequency  of  two  points
per second. The position is measured by built-in GPS antenna
with a precision of about 5 meters. The accuracy of position
was  checked  by  hand-held  GPS  Trimble  Juno  ST.  Fifteen

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profiles were measured, each 0.5 km long, running in
NE-SW direction. Based on this data we have interpolated a
contour map of magnetic anomalies, which covers an area of
0.73 km

The gravimetric survey was done along 2.8 km long

NNE-SSW profile, with 100 m station spacing. The profile
crosses the center of the Bouguer gravity anomaly found for-
merly by Váca & Šutor (1968) during the older areal gravity
survey of 4.4 points per sq km (the distance between points
of this older measurement was ~ 500 m, accuracy 0.04 mGal,
reduction density 2.67 g.cm

—3

). For the new gravimetric sur-

vey we used a SODIN 410 (Sodin W Gravity Ltd, Canada).
Terrain elevations were gauged by levelling and the posi-
tions of points were checked up with a hand-held GPS. The
accuracy of the gravity measurements was 0.02 mGal.

Preliminary shape and depth assessment of the extent of

the  diatreme  body  was  done  in  PotentQ  software,  the  final
modelling was carried out using the GM-SYS (Oasis Montaj,
Canada). The parameters of the magnetic field (total intensity
48982 nT, declination 3.67°, inclination 66°) were taken from
the  World  Magnetic  Model  2010  Calculator  of  the  British
Geological  Survey  (http://www.geomag.bgs.ac.uk/data_ser-
vice/models_compass/wmm_calc.html).

Due to lack of geological information from the historic drill

holes,  three  general  bodies  were  considered  in  the  model:
country  rock  (Lower  Carboniferous  greywacke),  maar  filling
(lacustrine  sediments)  and  volcanic  rocks  of  the  diatreme  in
the deeper part of the modelled structure. The Quaternary de-
posits in the uppermost part of the maar are inconsequential.
The magnetic susceptibility of basalts from surface samples at
other North Moravian localities is 15—40

×10

—3

SI (Foltýnová

2003) and depends on the weathering state of the rock (Mülle-
rová & Müller 1972). For the model purposes we have used
the value 33

×10

—3

SI for the basalt breccia. The susceptibility

of greywacke (0.15

×10

—3

) was measured by hand-held kap-

pameter KT-6 (Satisgeo, Czech republic). The susceptibility
of the lacustrine sediments (mostly clays) usually tends to zero
(Schulz et al. 2005; Mrlina et al. 2009). Remanent magnetiza-
tion was not considered in the magnetic data processing.

The density of the surrounding upper Paleozoic rocks is

2.71 g.cm

—3

(Čejchanová 1981). For maar sedimentary fill-

ing (sheet washes of greywackes and Plio-Pleistocene sedi-
ments) we used a density of ~ 2 g.cm

—3

. Volcanic breccias

and relicts of basalt volcanism are expected to have the high-
est density with up to 3 g.cm

—3

. The input parameters of

magnetic susceptibility and density are shown in Table 1.

Two electrical resistivity tomography (ERT) sections were

made  using  the  ARES  automatic  geoelectrical  system  (GF
Instruments, Czech Republic) with the Wenner-Schlumberger
array and 5 m electrode spacing. The first section with a total
length  of  890 m,  running  in  a  NE-SW  direction  across  the
diatreme  was  measured  using  the  roll-along  method  of  a
32-electrode (155 m) array. Based on the results from the first
survey, another section overlapping the first one, with a total
length  of  1155 m  was  gauged  in  a  NE-SW  direction  using
the roll-along method of 104 electrodes (515 m) in a single
array. In order to reduce total measurement time with multiple
(eight) repetitions of the roll-along method, we used the Wen-
ner-Schlumberger  array.  Although  it  is  not  the  best  method

for imaging of vertical structures, we chose it as a relatively
rapid and simple compromise, which is suitable for imaging
of layered structure of the maar-diatreme sedimentary fill.

Two 2D inverse models of resistivity were generated from

the  measured  apparent  resistivity  data  using  least-square  in-
version method by RES2DINV software (Geotomo Software,
Malaysia). The first section (Fig. 6 – top) encompassed 2172
data  points  in  15  data  levels.  The  inverse  model  has  1522
blocks in 9 layers with the maximum pseudodepth of 31.3 m
below the surface. The block uncertainty of the inverse model
ranges from <1 % (near surface) to ~10 % (maximum depth)
of the model resistivity values. The root mean square (RMS)
error of model iteration 5 is 1.8 %, which indicates high-quality
data.  The  second  section  (Fig. 6  –  bottom)  was  measured
along the same line but it was extended further to the NW and
SE in order to detect the wall and the deeper structure of the
diatreme.  The  inverse  model  has  8,360  blocks  in  20  layers
with  the  maximum  pseudodepth  67.4 m  below  the  surface.
However, probably due to large variations in surface resistivi-
ties the iteration process became relatively unstable after three
iterations, with the resulting large RMS error of 23.7 %. Low-
quality  data  as  indicated  by  low  sensitivities  of  the  model
blocks are distributed especially in the lower half of the sec-
tion between 50 and 500 m along the section (Fig. 6). In order
to enhance the vertical structure of the diatreme walls, we ap-
plied three different weights (1, 1.5 and 2) of vertical-to-hori-
zontal flatness filter in the RES2DINV software. However, the
inversion  models  were  almost  identical  for  any  of  the  three
values. The inversion model on Fig. 6 was generated with the
vertical-to-horizontal flatness filter weight of 1.0.

Results

New magnetic and gravity measurement detected a deep

funnel-shaped  structure,  which  is  interpreted  as  a  maar-dia-
treme. Joint gravity and magnetic modelling of the structure
was done along a 2.8 km long gravity profile. There is an ob-
vious  ~ 250 m  shift  between  the  tops  of  the  main  positive
magnetic  anomaly  and  negative  gravity  anomaly  (Fig. 4).
Most likely it reflects the different distribution of sources of
the  magnetic  and  gravity  anomalies.  The  maar  filling  base
should not be at the same level. In the NW part the thickness
of the filling may be larger, and this would cause the gravity
minimum.  At  the  place  of  the  magnetic  maximum,  the  sur-
face of the diatreme filling seems to be shallower.

The magnetic survey revealed a ring structure with a posi-

tive magnetic anomaly > 100 nT (local peaks even up to

Rock

Magnetic

susceptibility (SI)

Density (g.cm

–3

)

Lower Carboniferous
greywacke

0.15

× 10–3

2.71

Lacustrine sediments

× 10–3

Basalt, basalt breccia

× 10–3

2.8

Table 1: Input values of magnetic susceptibility and density for the
geophysical model. Fig. 5 – Gravity model of the maar-diatreme
structure.

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190 nT). The vertical magnetic model on Fig. 5 shows a more
than 500 m deep funnel-shaped structure, which is interpreted
as a maar-diatreme. The maar is filled with lacustrine clay and
colluvial sediments and in the lower part of the maar-diatreme
structure, we assume a highly magnetic body, probably a
lava intrusion (whole diatreme is a volcanic vent). The top
surface of the highly magnetic rock (basalt breccia, basalt) is
at the depth of more than 200 m.

The Bouguer anomaly of the Lomnice maar structure shows

a  value  of    —4.7 mGal.  The  regional  trend  of  0.19 mGal/km
was subtracted from the Bouguer gravity along the profile and
residual  gravity  values  represented  input  into  the  modelling
process.  Furthermore,  with  the  horizontal  dimension  of  the
maar structure of about 600 m in diameter (according to mag-
netic survey), it was necessary to restrict the gravity model in
the  vertical  direction.  Thereby  the  2.5D  model  was  created.
The outcome of the gravity modelling is a maar structure more

Fig. 4. Gravity (from Váca & Šutor 1968) and magnetic anomalies with location of gravity and ERT profile.

than 500 m in diameter and with a depth of 400 m. The SSW
side dips gently, while the northeast slope is steeper (Fig. 4).

According to magnetic and gravity data, colluvial sedi-

ments  and  sheet  washes  of  Lower  Carboniferous  rocks  are
present in the uppermost part of the maar structure. Beneath
them  Plio-Pleistocene  lacustrine  sediments  and  volcanic
breccias  with  relicts  of  the  basalt  volcanism  are  expected.
This is consistent with results of ERT measurement.

Two zones of high resistivity values ( ~ 200 to a maximum

of 14,003

Ω.m) are visible at both margins of the two inverse

model  sections  (0  to  ~ 70 m;  ~ 980  to  1155 m  distance  on
surface). They are interpreted as country rock comprising the
Lower  Carboniferous  succession  of  greywackes  alternating
with  siltstones.  The  boundaries  of  these  high-resistivity
zones are sharp and delineate a concave, bowl-shaped body
of  low  resistivity  values  ( < 20  to  ~ 130

Ω.m) located in be-

tween, and interpreted as the diatreme fill. The resistivity

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boundaries  interpreted  as  the  maar-diatreme  walls  are  dip-
ping  steeply  in  the  NW  but  much  more  gently  in  the  SE,
which  very  well  correlates  with  the  magnetic  and  gravity
survey  data  (Figs. 4,  5,  6).  The  zone  of  very  low  resistivity
values ( < 20 to  ~ 50

Ω.m), confined to the central part of the

maar body (Fig. 6, top part), may represent the maar lake fill
(presumably  mudstones).  This  low  resistivity  zone  reaches
up to the surface between  ~ 200 and  ~ 500 m distance, giving
some  thickness  constraints  to  the  lacustrine  sediments  (be-
tween  ~ 20  and  ~ 45 m).  However,  the  lower  limit  of  this
zone is uncertain due to the low block sensitivity of the in-
verse model (see above). The low-resistivity zone is in places
overlain by near-surface zones of medium resistivity values
( ~ 80  to  ~ 160,  rarely  up  to  ~ 400

Ω.m), which thicken to-

wards the walls of the diatreme. Their shape and resistivity
ranges may indicate the presence of colluvial sediments de-
posited at the margins of the former maar (Fig. 6).

Discussion

The coherence of magnetic and gravity anomalies indicates

a volcanic origin of the structure. The magnitude of  the Lom-
nice gravity and magnetic anomalies are comparable to some
of  the  West  Bohemia  and  Western  Saxony  maar-diatreme
structures (Mrlina et al. 2009; Matthes et al. 2010). Magnetic
and gravity surveys proved to be suitable methods for detec-
tion  of  maars  elsewhere  (Macnae  1995;  Schulz  et  al.  2005;
Lindner  et  al.  2006;  Cassidy  et  al.  2007).  The  filling  of  the
maar near the Lomnice village (based on the geophysical sur-
vey  and  historic  drill  holes  in  the  western  part  of  the  maar
structure)  is  also  very  similar  to  other  known  maars  of  the
CEVP. The upper part (lacustrine clays and colluvium) corre-
sponds to the D lithozone of maar crater sediments (laminated
silt  and  clay,  sandy  and  gravel  layers)  described  in  the  Eifel
area by Pirrung et al. (2003). The lower parts are comparable
to  the  C  (pyroclasts  and  wallrock  fragments),  B  (debris  of
wallrocks and pyroclasts) and A (diatreme breccia) lithozones.
However no tephra ring is present at the Lomnice locality.

According to a study of lacustrine tuffites of the Razová

pyroclastic  complex  (altitude  530 m a.s.l.),  very  significant
changes  of  hydrological  regime  in  the  area  occurred  in  the
late  Pliocene  to  early  Pleistocene  (Barth  &  Zapletal  1978).
Lava  flows  from  the  Velký  Roudný  volcano  dammed  the
paleo-Moravice River valley, while the water level rose to at
least  550 m a.s.l.  creating  a  large  lake.  A  part  of  the  lake
very probably extended up to the maar area (present-day alti-
tude  ~ 570 m a.s.l. – Fig. 1). This might have caused a sub-

Table 2: Summary of K-Ar dating at the Velký Roudný volcano.

stantial bedrock water saturation followed by phreatic erup-
tion and birth of the Lomnice maar structure. The initiation
of  the  eruption,  which  created  the  maar-diatreme  structure,
can  thereby  be  related  to  the  activity  of  the  nearby-located
Velký Roudný volcano. Several effusive phases were docu-
mented  based  on  radiometric  dating  (Table 2),  with  at  least
two main episodes (Cajz et al. 2012).

The assumed Plio-Pleistocene age of the Lomnice maar

contrasts with similar maar structures of the Eger Rift (West
Bohemia) or the Guttau Volcano Group (Upper Lusatia),
which are of the Oligocene-Miocene age (Suhr et al. 2006;
Skácelová et al. 2010). On the other hand, the Ar-Ar age of
the Mýtina maar in the Cheb Basin (western part of the Eger
Rift) is only 288 ± 17 ka (Mrlina et al. 2009).

Conclusion

The combination of detailed magnetic and gravity survey

with  electrical  resistivity  tomography  (ERT)  proved  to  be
very  suitable  to  describe  the  shape  and  origin  of  the  previ-
ously detected geophysical anomaly near the village of Lom-
nice. The combination of magnetic and gravity anomalies as
well  as  topographical  data  points  to  the  presence  of  a  ring
structure of volcanic origin, which can be explained best as a
maar-diatreme  structure.  The  detailed  geophysical  survey
data and their inversion modelling enabled the definition of
the lateral distribution and vertical structure of the diatreme.

The maar-diatreme structure is funnel-shape and about

600 m in diameter near the surface. It extends to a depth of at
least 500 m below the present-day surface and it is filled pre-
dominantly with lacustrine clays and colluvium. This filling
causes the negative gravity anomaly. On the basis of a posi-
tive magnetic anomaly, the presence of volcanic rock in the
lower part of the diatreme is assumed.

According to other volcanic centers in the surroundings of

the town of Bruntál, the Lomnice maar-diatreme is assumed
to be of Plio-Pleistocene age (3.4 to 1.5 Ma). The formation
of the structure could be related to the water regime variations
caused by effusive activity of the Velký Roudný volcano.

The Lomnice structure is the first maar-diatreme ever de-

scribed in the Moravian-Silesian part of the CEVP.

Acknowledgments: This research was supported by the
Czech Science Foundation GAČR Project P210/12/0573 and
by the institutional research plan MSM0021622427 provided
by the Ministry of Education, Youth and Sport of the Czech
Republic.

Locality

Age

Source

Velký Roudný — Bílčice quarry

3.31 ± 0.24 Ma

Pécskay et al. (2009)

Velký Roudný — Bílčice (nepheline basanite lava)

2.4 ± 0.12 Ma

Ulrych et al. (2013)

Bílčice — Leskovec (Velký Roudný lava flow)

3.4 ± 0.9 Ma

Šibrava & Havlíček (1980)

Chřibský les lava flow (nephelinite basanite)

1.46 ± 0.15 Ma (USGS)

Chřibský les lava flow (nephelinite basanite)

2.2 ± 0.9 Ma (TI)

Chřibský les lava flow (alkaline olivine basalt)

1.28 ± 0.4 Ma (USGS)

Chřibský les lava flow (alkaline olivine basalt)

1.6 ± 0.6 Ma (TI)

478

ŠEŠULKA, SEDLÁKOVÁ, BÁBEK and PŘICHYSTAL

GEOL

EOL

EOLOGICA CARPA

OGICA CARPA

OGICA CARPATHICA

THICA

THICA, 2014, 65, 6, 471—479

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