GeolCarp_Vol63_No2_175

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA

, APRIL 2012, 63, 2, 175—178 doi: 10.2478/v10096-012-0014-6

SHORT COMMUNICATION

Incremental growth and mineralogy of Pannonian (Late

Miocene) sciaenid otoliths: paleoecological implications

ZOLTÁN KERN

1,2,

, MIKLÓS KÁZMÉR

, MARIANN BOSNAKOFF

, TAMÁS VÁCZI

BERNADETT BAJNÓCZI

and LAJOS KATONA

Department of Palaeontology, Eötvös Loránd University, Pázmány Péter sétány 1/c, H-1117 Budapest, Hungary; mkazmer@gmail.com

Division of Climate and Environmental Physics, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland; kern@geochem.hu

MTA CsFK

Institute for Geological and Geochemical Research, Hungarian Academy of Sciences, Budapest, Hungary

Hungarian Natural History Museum, Budapest, Hungary

Department of Mineralogy, Eötvös Loránd University, Budapest, Hungary

Natural History Museum of Bakony Mountains, Zirc, Hungary

(Manuscript received September 14, 2011; accepted in revised form January 4, 2012)

Abstract: Ontogenetic age and body dimensions were studied on three extremely well-preserved sciaenid fish otoliths
from sublittoral marls of Lake Pannon from Doba, Bakony Mts, Hungary. Macroscopic and microscopic observations
offered clear evidence for the preservation of the genuine structural characteristics, for instance the bipartite incremental
features. Ontogenetic ages were assigned for the three specimens as 16, 7 and 6 years by counting the annuli of the sagittae.
Analytical results prove that the original aragonitic mineralogy has been preserved making them, and probably other Late
Miocene teleost fossils, suitable for future microchemical analysis to reconstruct the past physicochemical environment.

Key words: Lake Pannon, paleoecology, littoral environment, sagitta, cathodoluminescence, Raman microspectroscopy,
aragonite.

Introduction

Lake  Pannon,  a  long-lived,  giant  lake,  was  a  Late  Miocene
successor of the disintegrated Paratethys Sea (Kázmér 1990).
Extensive freshwater discharge by the paleo-Danube and pa-
leo-Tisza rivers into the Pannonian basins (Kuhlemann et al.
2002) altered the composition of the water-body, reducing the
marine-derived  fauna  of  the  Late  Sarmatian  brackish-water
sea into a fully endemic, lacustrine fauna. While the mollusc
fauna  is  well-documented  (e.g.  Müller  et  al.  1999  and  refer-
ences  therein),  the  fish  fauna  is  poorly  known.  Mostly  oto-
conia  (mineral  material  from  the  inner  ear  of  any  vertebrate;
see Carlström 1963) from sciaenids have been found relatively
frequently (e.g. Brzobohatý & Pana 1985; Bosnakoff 2008).

The endolymphatic organ of Sciaenidae, like in other te-

leost  fishes,  contains  three  pairs  of  small  carbonate  stones,
so-called otoliths. The largest of them are called sagittae, lo-
cated in the sacculus of the membranous labyrinth. Although
both  incremental  (e.g.  Woydack  &  Morales-Nin  2001)  and
microchemical  information  (e.g.  Carpenter  et  al.  2003)  of
fossil  otoliths  proved  to  provide  unique  information  about
the  coeval  paleoenvironment,  these  parameters  have  never
been  studied  on  the  Pannonian  otoliths.  They  are  indepen-
dent proxies for the temperature and salinity of Lake Pannon.
Water temperature and salinity estimates show a wide range
of  fluctuations  during  its  history.  A  bottom-water  tempera-
ture of ~15 °C and variable salinities (20—32 ‰) are estimat-
ed  for  the  Early  Sarmatian  sea,  while  temperature  and
salinity are estimated to have fluctuated from 15 °C to 21 °C

and from 15 ‰ to 43 ‰, respectively in the Late Sarmatian
sea  (Tóth  et  al.  2010).  These  values  are  in  range  with  esti-
mates from the composition of microfauna and molluscs. As
Lake  Pannon  hosted  many  endemic  species  (Müller  et  al.
1999;  Geary  et  al.  2000)  the  isolation  precludes  direct  esti-
mation  of  salinity  from  faunal  composition  or  from  oxygen
and  carbon  isotope  studies  of  bivalve  shells  (Geary  et  al.
1989;  Mátyás  et  al.  1996).  The  Late  Sarmatian-Pannonian
samples  have  higher  ratios  of  heavy  isotopes  (—2.11 ‰  for

O, and 1.27 ‰ for

C) than do the succeeding Pontian

Stage samples (—4.16 ‰

and —2.22 ‰, respectively). This

shift was interpreted as indicative of a basinwide drop in sa-
linity (Geary et al. 1989).

In addition, the isotope data clearly indicate that Lake

Pannon was not a huge, closed freshwater lake. Assuming a
riverine outlet somewhere along the southern margin, salini-
ty  would  have  been  lost  and  full  freshwater  conditions  ap-
pear in a couple of tens of thousands of years. In contrast, a
closed  basin  with  no  outflow  needs  evaporation  of  all  in-
flowing  water  and  rainfall  –  impossible  under  present-day
climatic conditions (Leeder 2007).

Three otolith samples have been selected for the purpose

of this pilot study. The scope was to investigate the preserva-
tion of original incremental and mineralogical structure and
decide  if  the  chemical  signature  remained  unaffected  by
post-depositional processes. The preservation of the genuine
microchemistry  of  the  fossil  otoliths  is  a  substantial  pre-
requisite  for  any  future  paleoenvironmental  or  paleoeco-
logical application.

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KERN, KÁZMÉR, BOSNAKOFF, VÁCZI, BAJNÓCZI and KATONA

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GEOLOGICA CARPATHICA, 2012, 63, 2, 175—178

Materials and methods

Fossil otolith samples

Sagittal otoliths were collected from the upper 0.9 m of a

2.6 m deep trench profile dug in a Late Miocene sequence at
Doba village, Bakony Hills, Hungary (Fig. 1). The age of the
fossiliferous  littoral  marl  layer  of  the  Lymnocardium  ponti-
cum Zone is estimated as 8.8—9.2 Ma (Magyar et al. 2007).
Twenty-nine  otoliths  were  found  after  sieving  (mesh  size:
500  micrometers)  of  ca. 300 kg  bulk  material.  Most  of  the
samples  (28)  were  determined  as  Umbrina  subcirrhosa
Schubert,  1902  based  on  the  morphological  characteristics.

For further details about the material, the reader is referred to
Bosnakoff & Katona (in print).

Three samples have been selected from the collection to

represent large (UC1) medium (UC2) and small (UC3) size
categories (Fig. 2). Basic morphological parameters have
been measured to the nearest 0.1 mm on each sagittae by a
digital caliper.

Preparation for structural analysis

Samples were embedded in epoxy resin and transverse

sections had been prepared using an IsoMet

low-speed saw

and a Buehler MiniMet grinding-polishing machine. Cut fac-
es were ground using the standard sequence of water-based
diamond suspensions (9, 6, 3, 1 µm; METADI

) and alumi-

na (0.05 µm; Gamma Micropolish

II) was used for final

polishing. Samples were placed in a distilled water bath and
agitated by an ultrasonic cleaning device for 15 min. Sec-
tioning trials were made both perpendicular to (UC1) and
parallel with (UC2, UC3) the sagittal plane to see any poten-
tial directional difference of structure or mineralogy.

Analytical methods

Cathodoluminescence microscopy

Cathodoluminescence (CL) is an electron-excited phe-

nomenon.  Upon  bombardment  by  a  high-energy  electron
beam originating from a cathode, certain materials emit pho-
tons  in  the  visible  range  of  the  electromagnetic  spectrum.
Excitation  is  generated  at  luminescence  centres  (activators)
in the material, which are crystal lattice defects and chemical
impurities. It is generally accepted that Mn

is the most im-

portant  activator  of  CL  in  carbonate  minerals  (Marshall
1988; Machel 2000). CL microscopy is a common technique
in  sedimentary  petrology  to  study  the  mineralogy,  texture
and  diagenetic  history  of  carbonate  rocks  (Machel  2000).
Biogenic carbonates (Barbin 2000) and fish otoliths (Halden
et al. 2004) are also routinely analysed.

Cathodoluminescence examination was performed using a

Reliotron cold-cathode equipment mounted on a Nikon E600
microscope. The equipment was operated at 8 to 10 kV accel-
erating voltage and 0.5 to 1.0 mA current, and a defocused
electron beam was used. Photos were taken using a Nikon
Coolpix 4500 digital camera using automatic exposure.

Raman microspectroscopy

Raman spectroscopic analysis was done using a HORIBA

JobinYvon LabRAM HR dispersive, edge-filter based confo-
cal  Raman  spectrometer  (focal  length:  800 mm)  equipped
with an Olympus BXFM microscope. Spectra were taken us-
ing the 785 nm emission of a diode laser, a 100  (N.A. 0.9)
objective,  a  grating  with  600 grooves/mm  and  a  pinhole  of
100 µm,  which  acted  also  as  the  entrance  slit  to  the  spec-
trometer. Net counting times were between 30 and 60 s. Ra-
man  spectroscopy  is  a  routinely  used  technique  to  study
small-scale  mineralogical  properties  in  fish  otoliths  (e.g.
Gauldie et al. 1997; Tzeng et al. 2007).

Fig. 1. Geographical and geological setting of the study site. Star
indicates the location of the studied Doba outcrop. Major geological
units (after Cziczer et al. 2009): 1 – pre-Late Miocene basement,
2 – sublittoral deposits of Lake Pannon, 3 – littoral to deltaic de-
posits of Lake Pannon and overlying fluvial sediments, 4 – Upper
Miocene—Pliocene volcanics. Inset map shows the location (black
square) on a map of Europe.

Fig. 2. The studied Pannonian sagittal otoliths, Umbrina cf. subcir-
rhosa Schubert, 1902. Top row shows the internal view with the
characteristic sulcus acusticus. The length of each specimen is indi-
cated. The bottom row shows the polished sections under reflected
light. Tip of the arrow points to the spot of the SEM image in
Fig. 3b. Rectangles help comparison with the CL images in Fig. 3a.

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MINERALOGY OF PANNONIAN SCIAENID OTOLITHS: PALEOECOLOGICAL IMPLICATIONS

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GEOLOGICA CARPATHICA, 2012, 63, 2, 175—178

Results and discussion

Macroscopic and microscopic incremental structures

Darker and lighter bands were clearly observed on each

polished section independently of the direction of the section-
ing plane (Fig. 2). These coupled bands were described of the
recent sciaenid otoliths to indicate an annual increment (annu-
lus) (Arneri et al. 1998; La Mesa et al. 2008; Engin & Seyan
2009). The annual periodicity of annulus deposition was con-
firmed by the edge analysis in recent sciaenids, indicating that
translucent  and  opaque  zones  are  formed  once  a  year.  The
opaque zone was laid down in summer, between June and July
while  the  dark/translucent  zone  was  found  to  be  deposited
during  the  rest  of  the  year,  starting  at  the  end  of  summer
(September) (La Mesa et al. 2008). The ontogenic age of the
specimens  can  be  assigned  on  the  basis  of  counts  of  dark/
translucent  winter  bands  (Arneri  et  al.  1998).  The  estimated
age of UC1 is 17, of UC2 is 7, while of UC3 is 6 years.

The columnar crystal fabric was also perfectly preserved

(Fig. 3b) indicating the lack of any diagenetic impact on
these fossils.

Estimated somatic parameters

A formalized experimental relationship has been pub-

lished recently describing ontogenic age vs body length and
otolith  maximum  length  vs  body  weight  relationships  for
brown meagre (Sciaena umbra Linnaeus, 1758) (La Mesa et
al.  2008),  a  possible  present-day  relative  to  the  Pannonian
Umbrina subcirrhosa. The obtained equations are thought to
be  robust  as  they  rely  on  532  specimens  of  brown  meagre

captured over a period of 11 years. Using equations obtained
on this modern dataset, somatic parameters of the Pannonian
fish specimens can be estimated as 46 cm/1470 g for UC1;
42 cm/1130 g for UC2 and 41 cm/1030 g for UC3.

It is necessary to emphasize that these estimated somatic pa-

rameters must be treated with caution. For instances the large
difference in the size of the water bodies (i.e. Modern Adriatic
Sea and Late Miocene Lake Pannon) and the lack of knowl-
edge about the food web complexity of the paleoenvironment
might introduce significant and hardly quantifiable bias.

Preserved mineralogical composition

Otolith cores showed green, yellowish green luminescence.

The intensity vanished towards the rim while faint blue lumi-
nescence was observed at the outer sectors (Fig. 3a). It is inter-
esting to note that seasonal increments showed different CL
characteristics within the annulus. Greenish and weak blue lu-
minescence bands corresponded to the opaque (summer) and
dark/translucent (winter) zones, respectively.

CaCO

minerals have characteristic CL colours caused by

the substitution of Mn

for Ca

: orange(-red) for calcite and

green to yellow for aragonite (Marshall 1988). ~ 10—20 ppm
Mn

concentration is necessary for visible Mn

activated lu-

minescence in biogenic calcite and the same or less in arago-
nite (Barbin 2000). In the case of pure carbonates or
carbonates with minor traces of substituting element, a weak
blue (so-called intrinsic) CL is detected for both polymorphs.

The observed CL features, consequently, indicate arago-

nitic mineralogy in the otolith cores but the results are still
not conclusive in the outer part. Raman microspectrometric
analyses helped to clarify the ambiguity. The Raman spectra

Fig. 3.  Structural  evidence
for the lack of recrystalliza-
tion.  a  –  Cathodolumines-
cence  (CL)  images.  White
dots mark the spots for Ra-
man

microspectrometry

(annotation  corresponds  to
the legend in c). Rectangles
help to orientate the CL im-
age  in  the  polished  section
of  Fig. 2.  b  –  Radially  ar-
ranged  columnar  aragonite
crystals  in  UC3.  c  –  Ra-
man  spectra  from  UC1.
Vertical  dashed  lines  indi-
cate  the  characteristic  Ra-
man bands of aragonite.

correspond  to  the  arago-
nite  phase  (Urmos  et  al.
1991;  Gauldie  et  al.
1997)  proving  that  the
Pannonian  otolith  un-
doubtedly  contained  ara-
gonite  crystals  at  each
analysed  spot  (Fig. 3c).
As  all  the  fossil  otolith

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KERN, KÁZMÉR, BOSNAKOFF, VÁCZI, BAJNÓCZI and KATONA

GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2012, 63, 2, 175—178

material provided only the characteristic Raman bands of ara-
gonite, regardless of the CL colour found in the otolith zone, it
is proven that the original aragonitic mineralogy has been pre-
served also in the parts with weak blue luminescence.

Incidentally, alternating greenish and weak blue CL zones

corresponding to opaque and translucent incremental zones
of annuli indicate that Mn

concentration drops below the

~10—20 ppm level in the increment laid down during the
winter season.

Conclusions

Macroscopic and microscopic observations of the three

studied  Pannonian  (Late  Miocene)  sciaenid  otoliths  offered
clear  evidence  for  the  preservation  of  the  genuine  structural
characteristics.  Ontogenetic  ages  were  assigned  for  the  three
specimens as 16, 7 and 6 years, respectively, by counting the
annuli of sagittae. Corresponding somatic parameters of the fish
specimens can be estimated as 46 cm/1470 g; 42 cm/1130 g
and  41 cm/1030 g  using  experimental  physiological  relation-
ships of the brown meager (Sciaenia umbra Linnaeus, 1758) a
modern relative of the studied Pannonian species.

Results from CL and Raman microspectrometric analyses

proved  the  preservation  of  the  original  aragonitic  mineralo-
gy. The excellent preservation of these fossils invites further
microchemical studies to reconstruct the past physicochemi-
cal  environment.  As  earlier  geochemical/paleoecological
studies concentrated exclusively on benthic organisms, these
otoliths  might  provide  the  first  geochemical  record  from
Pannonian  nektonic  organisms  related  directly  to  the  open
water marine/lacustrine conditions free from any bias due to
the benthic environment.

Acknowledgments: The European Union and the European
Social  Fund  have  provided  financial  support  to  the  Project
under  the  Grant  agreement  No. TÁMOP  4.2.1./B-09/KMR-
2010-0003. The research has been supported by Baross Gá-
bor  Fund  REG-KM-09-1-2009-0044  and  OTKA  K67583
grants.  The  authors  thank  Ágnes  Takács  for  her  help  with
sample  preparation.  Rostislav  Brzobohatý  and  Norman
Halden  are  acknowledged  for  their  constructive  reviews.
This is Budapest Tree-Ring Laboratory contribution No. 20.

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