The locality of Marsovicky Hill (N Bohemia, Czech Republic) yielded an example of a Cretaceous sea-bottom composed of Nametarhyolite. Two types of trace fossils penetrate the substrate, namely Thalassinoides isp. and ?Gastrochaenolites isp. Thalassinoides originated presumably in a firmground, i.e. the metavolcanite had to be "delithified" in some patches and subsequently rehardened again. ?Gastrochaenolites isp. is interpreted as a boring trace of decapods.La localidad de Marsovicky Hill (Norte de Bohemia, República Checa) permite estudiar un ejemplo de un fondo marino cretácico compuesto de Na-metariolitas. Dos tipos de trazas fósiles penetran el substrato: Thalassinoides isp. y ?Gastrochaenolites isp. Thalassinoides se originó probablemente en un substrato firme, es decir que la metavolcanita se habría "deslitificado" en algunas zonas y posteriormente se habría vuelto a endurecer. ? Gastrochaenolites isp. se interpreta como un traza de bioerosión de decápodos

Adamovic, Jirí

Mikulás, Radek

Nemecková, M.

The locality of Hill (N Bohemia, Czech Republic) yielded an example of a Cretaceous sea-bottom composed of Nametarhyolite. Two types of trace fossils penetrate the substrate, namely Thalassinoides isp. and Gastrochaenolites isp. Thalassinoides originated presumably in a firmground, i.e. the metavolcanite had to be "delithified" in some patches and subsequently re-hardened again. ?Gastrochaenolites isp. is interpreted as a boring trace of decapods

MIKULÁS, R.

NEMECKOVÁ, M.

ADAMOVIC, J.

Revistes CientÃ­fiques de la Universitat de Barcelona

English

Bioerosion and bioturbation of a weathered metavolcanic rock (Cretaceous, Czech Republic)

Mikulás, R.

Adamovic, J.

Secretaría de Estado de Cultura

Revistes Catalanes amb Accés Obert

21
Bioerosion and bioturbation of a weathered metavolcanic rock 
(Cretaceous, Czech Republic)
R. MIKULÁS(1), M. NEMECKOVÁ(2) and J. ADAMOVIC(3)
(1, 2, 3) Geologicky ústav Akademie ved Ceské republiky, Rozvojová 135, 165 00 Praha 6, Czech Republic. 
E-mails:  (1) mikulas@gli.cas.cz; (2) nemeckova@gli.cas.cz; (3) adamovic@gli.cas.cz
ACTA GEOLOGICA HISPANICA, v. 37 (2002), nº 1, p. 21-27
ABSTRACT
The locality of Marsovicky Hill (N Bohemia, Czech Republic) yielded an example of a Cretaceous sea-bottom composed of Na-
metarhyolite. Two types of trace fossils penetrate the substrate, namely Thalassinoides isp. and ?Gastrochaenolites isp. Thalassinoides
originated presumably in a firmground, i.e. the metavolcanite had to be "delithified" in some patches and subsequently re-hardened
again. ?Gastrochaenolites isp. is interpreted as a boring trace of decapods.
Keywords: Bioerosion. Bioturbation. Metavolcanic substrate. Cretaceous. Decapoda. Czech Republic. 
RESUMEN
La localidad de Marsovicky Hill (Norte de Bohemia, República Checa) permite estudiar un ejemplo de un fondo marino cretácico com-
puesto de Na-metariolitas. Dos tipos de trazas fósiles penetran el substrato: Thalassinoides isp. y ?Gastrochaenolites isp. Thalassi-
noides se originó probablemente en un substrato firme, es decir que la metavolcanita se habría "deslitificado" en algunas zonas y pos-
teriormente se habría vuelto a endurecer. ?Gastrochaenolites isp. se interpreta como un traza de bioerosión de decápodos.
Palabras clave: Bioerosión. Bioturbación. Substrato metavolcánico. Cretácico. Decapoda. República Checa. 
INTRODUCTION
The Glossifungites Ichnofacies represents firm but
unlithified substrates, typically dewatered chunky muds.
Crystalline rocks typically represent substrates associated
with the Trypanites Ichnofacies (e.g., Frey and Pember-
ton, 1984). 
The locality of Marsovicky Hill (northern Bohemia,
Czech Republic) exposes transgressive Upper Cretaceous
´
ˇ I (3)ˇˇ ˇ
ˇˇ
ˇ ´
ˇ ´
iˇ ´
sediments overlying a body of the ?Early Palaeozoic me-
tavolcanic rock (quartz keratophyre - e.g., Graber, 1907).
The locality has been recently studied to find possible
bioerosive traces in the Palaeozoic basement. However,
traces suggesting both bioerosion and bioturbation have
been found in the well-lithified metavolcanite rock im-
mediately below the Upper Cretaceous sediments. The
aim of the present contribution is to describe and interpret
this unusual situation.
GEOLOGICAL SETTING
In the Bohemian Cretaceous Basin (Czech Republic),
fossil rocky bottoms with cemented epibionts and bioero-
sive traces have been reported from numerous sites in the
area N and NE of Praha, and from the vicinity of towns of
Kolín and Cáslav (e.g., Zítt and Nekvasilová, 1996; Fig.
1). These fossil rockgrounds are composed mostly of La-
te Proterozoic silicites and greywackes (at Praha) and of
various crystalline and metamorphic rocks, e.g., orthog-
neisses and metaquartzites (at Kolín and Cáslav). These
hard and weathering-resistant rocks formed elevations af-
ter a long period of pre-Cretaceous denudation of the Bo-
hemian Massif; therefore, most of them functioned as
cliffs or islets in the initial phase of the transgression of
the Late Cretaceous sea. In northern Bohemia, a trans-
gression of the Cretaceous sediments over the crystalline
basement is exposed only at the foot of Marsovicky vrch
Hill 5 km N of the town of Dubá (Fig. 1). 
THE LOCALITY
The outcrop at the locality is a natural exposure in the
narrow, steeply inclined gorge ca. 250 m SE of the lonely
house of Podolec. The lower half of the outcrop is com-
posed of Na-metarhyolite (Graber, 1907), reddish-grey to
light grey in colour, showing a prominent schistosity;
pencil structure is indicated in places. More detailed pe-
trological and geochemical characteristics of the rock we-
re provided by Zrustková (1982). The rock was subjected
to extensive post-emplacement tectonism as indicated by
zones of mylonitization. At surfaces exposed to present
weathering, hardness of the Na-metarhyolite changes ra-
pidly, from a well-lithified rock to a semi-consolidated
substrate that enables, e.g., scratching by a fingernail.
The Upper Cretaceous sediments overlie a sharp ero-
sional surface of the metavolcanite body. The erosional
surface is subhorizontal, showing irregularities and small
depressions of several centimetres to decimetres in size.
Graber (1907) and Müller (1925) reported the presence of
surf pockets filled with oyster shells; however, these phe-
nomena were destroyed by fossil collectors. The basal
Cretaceous layer, about 1 m thick, is composed of well-
cemented, poorly sorted, polymictic conglomerate to
sandstone. Pebbles (usually up to 50 mm long) form 10 to
50% of the rock volume, while the remaining clasts co-
rrespond to coarse-grained sandstone. The rock yielded
rare finds of marine fauna (well preserved shells of oys-
ters). Also, angular cobbles and blocks of the underlying
metavolcanic rock are present. The basal Cretaceous layer
is overlain by medium- to fine-grained sandstone with
carbonate cement.
Biogenic (bioerosive and bioturbational) structures
are preserved at and immediately below the erosional sur-
face of the metavolcanic rock. Those visible directly on
the outcrop all belong to the type described below as Tha-
lassinoides isp. Several dozens of specimens of the same
ichnotaxon and one possible ?Gastrochaenolites isp. we-
re discovered, documented and collected on a huge (ca. 2
m) block of rock which crashed from the outcrop to the
gorge bottom probably in 1997. Another, smaller fallen
block found in debris ca. 20 m SW of the outcrop provi-
ded two specimens of ?Gastrochaenolites isp.
Seven thin sections of the metavolcanic rock were stu-
died, both from the vicinity of the burrows/borings, and at
some distance from the biogenic structures. Petrologi-
cally, the Na-metarhyolite is composed of groundmass
(quartz and feldspar), phenocrysts (K-feldspar, plagiocla-
se, quartz, weakly altered muscovite) and veinlets (mostly
quartz). In the close neighbourhood of horizontal (presu-
mably bioturbation) tunnels, the rock shows stronger alte-
ration, ?mylonitisation, fracturing of phenocrysts, and
clusters of clastic quartz grains corresponding to those of
the overlying Cretaceous sediment (evidence of  former
plasticity of the substrate). Less frequently, a suite of ot-
her minerals and petrographical features is present (iron
ore minerals, carbonates, pyrite aggregates). This points
to a complex history of the rock, including metamorp-
hism, mylonitisation of certain zones, pre-Cretaceous we-
athering, and incipient post-Cretaceous generation of mi-
nerals. However, it does not seem possible to recognise
the history in greater detail.
SYSTEMATIC ICHNOLOGY
Thalassinoides EHRENBERG, 1944
Thalassinoides isp.
Plate I, figures 1, 3, 5
22 Acta Geol. Hisp., v. 37 (2002), nº 1, p. 21-27
R. MIKULÁS et al.
rs ickyˇ ´
ˇ iˇ
áslaˇ
ˇ
Material: Five collected samples from the block ca.
1.0 x 1.8 m. On the huge fallen block, about 20 tunnels or
troughs (belonging probably to 2-3 burrow systems) were
observed and documented in situ. At least five distinctive
tunnels were observed on the outcrop.
Description: Cylindrical tunnels or troughs made in
the metavolcanic rock at or immediately below its Creta-
ceous erosive surface. Width 1.5 - 3.0 cm, preserved
length up to 30 cm. Tunnels are subhorizontal to oblique,
rarely enlarged into initial forms of chambers, occasio-
nally branching; most of the branches pointing down-
wards, showing finger-like, slightly enlarged termina-
tions. Troughs are horizontal and they may pass into
oblique tunnels. Walls of the trace fossils often show pro-
minent xenoglyph, i.e. an ornament corresponding to a
23Acta Geol. Hisp., v. 37 (2002), nº 1, p. 21-27
Figure 1. Geological sketch map of the Bohemian Cretaceous Basin. Large picture: Documented sites of Upper Cretaceous rocky sea-
floors (black points). Lower left: Overall extent of the preserved sedimentary fill of the basin (dotted).
Cretaceous Traces on Metavolcanic Rocks
Acta Geol. Hisp., v. 37 (2002), nº 1, p. 21-2724
Plate I
1, 3, 5. Thalassinoides isp.; (1) transverse section of a subhorizontal tunnel;  (3) longitudinal section of a subhorizontal tunnel; (5) part
of the outcrop at Marsovicky Hill showing basal Cretaceous layers and Thalassinoides isp. in the underlying crystalline rock. 
2. ?Gastrochaenolites isp.; natural cast of the chamber.
4. Thin section of the Na-metarhyolite bordering the tunnel of Thalassinoides isp. The tunnel fill (mostly quartz grains) on the right;
upper left, a clastic quartz grain corresponding to those of the overlying Cretaceous sediment occurs in the Na-metarhyolite.
ˇ ´
R. MIKULÁS et al.ˇ
structure (foliation or lineation) of the metavocanic rock.
Fill of the trace fossils is passive, corresponding in its
composition to the overlying basal bed of Cretaceous se-
diment.
Remarks: The "troughs" are probably collapsed or par-
tially eroded tunnels. Overall morphology of the burrow
systems is difficult to estimate but their dimensions in the
horizontal direction must have exceeded 0.5 m. Vertical
extent was probably less than 10 cm. 
Appurtenance of trace fossils of the described morp-
hology to the ichnogenus Thalassinoides follows the pa-
pers of Howard and Frey (1984), Bromley (1996), Uch-
man (1999) and many other recent publications.
Gastrochaenolites LEYMERIE, 1842
? Gastrochaenolites isp.
Plate I, figure 2
Material: One collected specimen and two additional
specimens observed at the locality.
Description: Subvertical shafts slightly enlarged at
their base to irregular, roughly drop-shaped chambers.
Dimensions of the collected specimen: depth 28 mm, dia-
meter at the presumed opening 13 mm, maximum diame-
ter 15 mm. The shafts were made in the metavolcanite and
filled passively with the Cretaceous sandstone to conglo-
merate.
Remarks: Overall shape of the trace fossils suggests
their similarity to the ichnogenus Gastrochaenolites as
defined, e.g., by Kelly and Bromley (1984).  Gastrochae-
nolites usually represents dwelling chambers (borings) of
molluscs; in such cases, the chambers show a precise re-
gularity and symmetry. However, Ekdale et al. (2000)
broadened the morphological range of Gastrochaenolites
by including irregular, roughly drop-like trace fossils of
the Ordovician age. Among the published examples of
modern traces, ?Gastrochaenolites isp. resembles traces
described by Fischer (1981), which were made by sea-ur-
chins (Diadema mexicana) and decapods (Alpheus saxi-
domus) on basalts on the Pacific coast of Costa Rica.
DISCUSSION AND CONCLUSIONS
The present outcrop and the huge fallen block below
the outcrop show a strong dominance of the ichnofossil
Thalassinoides isp. The smaller block coming from anot-
her part of the fossil sea-floor (which is not exposed at
present) bears specimens of ?Gastrochaenolites isp. This
circumstance points to a patchiness of the ichnologic re-
cord at the locality. Unfortunately, the present state of the
locality does not allow a more precise picture of the trace
fossil distribution.
To explain the differences in the occurrence of the tra-
ce fossils, we find the substrate control to be the most
probable cause. Present surfaces of the Na-metarhyolite
(on fallen blocks and boulders, natural and artificial out-
crops or in soil skeleton) retain in places a character of so-
lid rock, but in other places they weather into a semi-con-
solidated substrate. We may presume that also during the
period of the pre-transgression subaerial exposure the
metavolcanite body had weathered in a similar way
(though the climatic conditions were different). As we re-
cognized no relevant differences in mineral composition
between Na-metarhyolite tending to the "soft" weathering
and the patches of hard, less weathered rock, we presume
that a variation in degree of tectonic stress is responsible
for the differences in weathering style.
Patches of the firm sea-floor could be colonised by
the tracemakers of Thalassinoides. This trace fossil oc-
curs frequently on semi-consolidated substrates (e.g.,
Frey and Pemberton, 1984). Decapods are the usual ma-
kers of Thalassinoides-like traces in modern settings and
presumably also through the Mesozoic and Cenozoic
(e.g., Bromley, 1996). However, decapods were recogni-
sed also as the agent of bioerosion of modern non-carbo-
nate rocky bottoms (Fischer, 1981; Fischer and Meyer,
1985). The bioerosive traces of decapods do not resemble
the Thalassinoides-like networks and boxworks, but they
form irregular, finger-like, drop-like or bag-like cham-
bers. These structures have not been described in the fos-
sil record yet and therefore no ichnotaxon has been erec-
ted for them; anyway, it would be very complicated to
demarcate boundaries between these irregular traces and
Gastrochaenolites. 
Traces of decapods described by Fischer (1981) from
modern basalt coast of Costa Rica are similar to the tra-
ces described herein as ?Gastrochaenolites isp. We may
presume that ?Gastrochaenolites isp. from the above-des-
cribed locality represents bioerosive traces of decapods:
they are less regular compared with Gastrochaenolites
produced by boring bivalves. We may even suggest that
Thalassinoides isp. and ?Gastrochaenolites isp. from
Marsovicky Hill were produced by the same decapod tra-
cemaker: this possibility is supported by a similar diame-
ter of both traces and, more significantly, by the similarity
25Acta Geol. Hisp., v. 37 (2002), nº 1, p. 21-27
Cretaceous Traces on Metavolcanic Rocks
ˇ ´
of terminations of tunnels of Thalassinoides and cham-
bers of ?Gastrochaenolites. As the metavolcanite at the
Marsovicky Hill is a very fine-grained rock (in contrast to
a coarse-grained fill of the trace fossils; Plate I, fig. 4), we
cannot consider whether its individual grains were cut or
by-passed.
Besides the substrate control, patchiness of the ichno-
logical record could be influenced by some other factors,
e.g., by exposure to wave action and currents. However,
we find the following scenario for the development of the
fossil record at the locality the most probable:
1) Pre-Cretaceous tectonic deformations and a long
interval of pre-Cretaceous weathering (cf. Zítt and Nek-
vasilová, 1996) induced selective alterations of the Na-
metarhyolite body at Marsovicky Hill. As a result, some
surfaces were firm while others retained the character of
a hard rock (Fig. 2A). 
2) The transgression at Marsovicky Hill probably be-
gan with a non-sedimentation episode characterized by
the appearance of the described burrowing/boring traces.
We may presume high-energy settings, probably in a sha-
llow sublittoral zone (Fig. 2B).
3) The coarse-grained, polymictic sediment buried the
omission surface. The basal Cretaceous layer is remarka-
ble for the presence of a well-preserved oyster fauna. Al-
so the good preservation of xenoglyphs is notable on the
trough-like parts of Thalassinoides. This points to the pre-
sumption of a sudden burial of the firmground by mate-
rial accumulated nearby in the previous phase of trans-
gression (Fig. 2C).
4) The present-day hardness of the metavolcanic rock
was enhanced by the same processes as the diagenesis of
the overlying Cretaceous sediments. Effects resulting
from the considerable thickness of the Cretaceous sedi-
26 Acta Geol. Hisp., v. 37 (2002), nº 1, p. 21-27
Figure 2. Possible scenario of development of the fossil sea-floor at Marsovicky Hill. (A) the situation immediately before the Creta-
ceous transgression; (B) after the transgression; (C) after the obrution of the rocky bottom; (D) after the Tertiary magmatic activity.
Not to scale. See the text for further explanation.
ˇ ˇ
ˇ ´
iˇ ´
ˇ ´
iˇ
R. MIKULÁS et al.ˇ
Acta Geol. Hisp., v. 37 (2002), nº 1, p. 21-27 27
ments (several hundreds of metres – cf. Malkovsky, 1974)
were probably augmented by the Tertiary magmatic acti-
vity (Fig. 2D).
ACKNOWLEDGEMENTS 
We thank Tony Ekdale, Markus Bertling and Jordi M. de Gi-
bert for valuable comments to the topic during the 3rd Interna-
tional Bioerosion Workshop in Barcelona, and Richard Bromley
for his reviewer’s help. The study is a part of the Research Pro-
gramme of the Institute of Geology, AS CR, Praha (No. CEZ:
23-013-912).
REFERENCES
Bromley, R.G., 1996. Trace Fossils - Biology and Taphonomy.
London, Chapman & Hall, 361 pp.
Ehrenberg, K., 1944. Ergänzende Bemerkungen zu den seiner-
zeit aus dem Miozäan von Burgschleinitz beschrieben
Gangkernen und Bauten dekapoder Krebse. Paläontologis-
che Zeitschrift, 23, 345-359.
Ekdale, A.A., Benner, J.S., Bromley, R.G., de Gibert, J.M.,
2000. Origins of hardground bioerosion in the Early Ordo-
vician in Scandinavia and Western North America. In J.
Martinell, R. Domènech, J.M. de Gibert (eds.). Third Inter-
national Bioerosion Workshop, Barcelona, August 28- Sep-
tember 3, 2000, Barcelona, Contributions. 17-18.
Fischer, R., 1981. Bioerosion of basalt of the Pacific coast of
Costa Rica. Senckenbergiana Maritima, 13(1), 1-41.
Fischer, R., Meyer, W., 1985. Observations on rock boring by
Alpheus saxidomus (Crustacea: Alpheidae). Marine Bio-
logy, 89, 213-219.
Frey, R.W., Pemberton, S.G., 1984. Trace fossil facies models.
In R.G. Walker (ed.). Facies Models, 2nd ed., Geoscience
Canada Reprint Series. 189-207.
Graber, H.V., 1907. Der Maschwitzberg bei Habstein in
Nordböhmen. Jahresbericht der Staats-Realschule in B.-
Leipa für das Schuljahr 1906-1907, 1-43. Ceská Lípa.
Howard, J.D., Frey, R.W., 1984. Characteristic trace fossils in ne-
arshore to offshore sequences, Upper Cretaceous of east-cen-
tral Utah. Canadian Journal of Earth Sciences, 21, 20-219.
Kelly, S.R.A., Bromley, R.G., 1984. Ichnological nomenclature
of clavate borings. Palaeontology, 27, 793-807.
Leymerie, M.A., 1842. Suite du Mémoire sur le Terrain Cretacé
du Department de l’Aube. Mémoires de la Societe Geologi-
que de la France, 5, 1-34.
Malkovsky, M. (ed.), 1974. Geologie Ceské krídové pánve a je-
jího podlozí. Vydavatelství Ústredního Ústavu geologické-
ho a Academia, Praha, 262 pp.
Müller, B., 1925. Die geologische Sektion Hohlen des Karten-
blattes Böhm.Leipa-Dauba in Nord-Böhmen. Sborník Stát-
ního geologického Ústavu CSR, 5, 111-174.
Uchman, A., 1999. Ichnology of the Rhenodanubian Flysch
(Lower Cretaceous-Eocene) in Austria and Germany. Berin-
geria, 25, 67-173.
Zítt, J., Nekvasilová, O., 1996. Epibionts, their hard-rock subs-
trates, and phosphogenesis during the Cenomanian-Turo-
nian boundary interval (Bohemian Cretaceous Basin). Cre-
taceous Research, 17, 715 - 739.
Zrustková, Z., 1982. Krystalinikum a terciérní vulkanity Mars-
sovického vrchu.  M.Sc. Thesis, Faculty of Sciences, Char-
les University, Praha, 96 pp.
Cretaceous Traces on Metavolcanic Rocks
´
´ ˇ ˇ
ˇ ˇ
ˇ
ˇ


https://revistes.ub.edu/index.php/ActaGeologica/article/download/4810/6301

Bioerosion and bioturbation of a weathered metavolcanic rock (Cretaceous, Czech Republic)

Abstract

Similar works

Full text

Available Versions

Revistes CientÃfiques de la Universitat de Barcelona

Secretaría de Estado de Cultura

Revistes Catalanes amb Accés Obert

Bioerosion and bioturbation of a weathered metavolcanic rock (Cretaceous, Czech Republic)

Abstract

Similar works

Full text

Available Versions

Revistes CientÃ­fiques de la Universitat de Barcelona

Secretaría de Estado de Cultura

Revistes Catalanes amb Accés Obert

Revistes CientÃfiques de la Universitat de Barcelona