Aretz et al_2011.pdf - ORBi - Université de Liège

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Kölner Forum Geol. Paläont., 19 (2011)
M. ARETZ, S. DELCULÉE, J. DENAYER & E. POTY (Eds.)
Abstracts, 11th Symposium on Fossil Cnidaria and Sponges, Liège, August 19-29, 2011
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Barremian–Aptian coral facies from Romania
Bogusław KOŁODZIEJ 1 , Ioan I. BUCUR 2 , Daniel LAZAR 2 & Emanoil SĂSĂRAN 2
1 Institute of Geological Sciences, Jagiellonian University, Oleandry str., 2a, 30-063 Kraków, Poland;
boguslaw.kolodziej@uj.edu.pl;
2 Babeş-Bolyai University, Department of Geology, M. Kogălniceanu str., 1, 400084 Cluj-Napoca, Romania;
ioan.bucur@ubbcluj.ro
Barremian–Aptian carbonate platforms occur in several geotectonic units in Romania: Eastern and
Southern Carpathians, Apuseni Mts., Moesian Platform and Dobrogea (BUCUR 2008). Corals are known in
some areas, but there is only one detailed taxonomic paper on Lower Cretaceous corals from Romania
(MORYCOWA 1971). The present studies are focused on Aptian coral reefs and the coral facies representing
different geotectonic and sedimentary settings: (1) Rarău Mts. (Transilvanian Nappe, Eastern Carpathians,
NE Romania), (2) Reşiţa–Moldova Nouă zone (Getic Nappe, Southern Carpathians, SW Romania), and (3)
Pădurea Craiului Massif (Apuseni Mts., NW Romania).
Rarău Mts. 54 scleractinian species, mostly small colonies, with well preserved skeletal microstructures,
were described by MORYCOWA (1971) from Lower Aptian marls of the Rarău Mts. These marls occur
throughout the Wildflysch of the Bucovinian nappe. The wildflysch is partly covered by huge thrust sheet
fragments of Urgonian (Late Barremian–Early Aptian) limestones (Transilvanian nappe). The locality
described by MORYCOWA (1971) was not found during recent studies, but numerous and diversified corals
were revealed in the Urgonian limestones. They contain Calamophylliopsis spp. including C. fotisaltensis
(BENDUKIDZE); Microsolena sp. and other microsolenids, Latiastraea sp., Latusastraea sp., Eohydnophora sp. and
related hydnophoroid-meandroid genera, Columnocoenia ksiazkiewiczi MORYCOWA, Clausastraea spp.
including C. alloiteaui MORYCOWA and Thecosmilia sp. Associated biota include benthic orbitolinids,
dasycladalean algae, chaetetid sponges and molluscs. Corals are commonly encrusted by the
microproblematicum Lithocodium aggregatum, while microbial encrustations are moderately common. The
skeletons of some microsoleninian corals from the Lower Aptian contain spectacularly preserved (redstained
and iron-enriched) assemblage of microbial euendoliths representing algae similar to the modern
siphonalean chlorophyte Ostreobium, and possible also fungi. They penetrated into skeletons during coral’s
growth (Fig. 1A–B). Microeuendoliths inhabiting skeletons of modern corals during their life are common,
however their fossil record is surprisingly poor. Dissolution cavities that occur locally within limestone,
filled with reddish-brown siliciclastic sediments (possibly terra rossa) may represent evidence of
synsedimentary emersion of the carbonate platform or younger processes.
In the Reşiţa-Moldova Nouă zone corals are present in Valea Nerei Limestones (Lower Barremian), but
spectacular coral limestone occurs within the Valea Minişului Limestone Formation of Late Aptian
(Gargasian) age. Thick bioconstructions composed of coral platestones occur along the Valea Minişului
river over the distance of approx. 1100 m. They are grouped in two lithosomes with thickness 16-17 m and
38-42 m, separated by 15-30 m thick limestones generally devoid of corals. Coral density is high: 50–90 %
(Fig. 1G–I). The individual colonies have platy to dish-like shapes, attain 8-50 cm in diameter, and are 1-15
cm thick. Corals are poorly diversified and dominated by the suborder Microsolenina: Fungiastraea crespoi
(FELIX), Latiastraea cf. kaufmanni (KOBY), Microsolena sp., and a heterocoenid Latusastraea sp. (suborder
Heterocoenina or Pachythecaliina). Phototrophic organisms include red algae: coralline Sporolithon rude,
peysossonneliacean Polyastra alba (Fig. 1I), rarely problematic microencrusters Lithocodium
aggregatum/Bacinella irregularis; dasycladalean algae are lacking. Coral-bearing sediment consists
predominantly of dark gray wackstones to grainstones, subordinately clayey calcimudstones and marls.
Bioerosion of corals is moderate to high. Coral assemblages, associated biota and inter-colony sediment
suggest environment of the outer carbonate platform. The studied platy coral assemblages can be attributed
to lithosomes formed in at the depth calculated as 20-80 m, with a low background sedimentation rate. In
respect of thickness the described coral platestones represent one of the most spectacular fossil example
among platy coral assemblages (ROSEN et al. 2002).
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