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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Coral facies of a Burdigalian rocky-shore fringing reef (Bonifacio Basin,
South Corsica)
Laura TOMASSETTI 1 , Marco BRANDANO 1 , Francesca R. BOSELLINI 2 & Andrea
MAZZUCCHI 3
1 Dipartimento di Scienze della Terra, Università di Roma “La Sapienza”, Roma, Italy;
laura.tomassetti@uniroma1.it, marco.brandano@uniroma1.it
2 Dipartimento di Scienze della Terra, Università di Modena e Reggio Emilia, Modena, Italy;
francesca.bosellini@unimore.it
3 Piazza Marianna Benti Bulgarelli 20, 00139 Rome, Italy; andrea.mazzucchi@gmail.com
In the Cenozoic, especially during the Miocene, the Mediterranean region was characterized by the
prolific development of different types of coral bioconstructions that occurred in a wide variety of
structural and depositional settings.
In this study we investigate a peculiar coral bioconstruction developed on the southern margin of the
Bonifacio Basin (southern Corsica) where, in the Burdigalian, mixed carbonate-siliciclastic sediments were
deposited in a coastal environment during the Sardinia-Corsica block rotation. The marine transgression is
represented by the Cala di Labra Formation (FERRANDINI et al. 2002; BRANDANO et al. 2009) characterized
by a coral bioconstruction unconformably lying on the granitic basement.
Based on depositional attitude and geometrical relationship with the granitic substrate, the investigated
coral episode is interpreted as a fringing reef and represents one of the few known fossil example of a
fringing reef attached to a granitic rocky shore (JOHNSON et al. 2006).
Two main reef facies can be distinguished based on their depositional attitude with respect to the
substrate, type of coral fabric and sedimentary textures: (1) coral domestone and (2) coral platestone. The
coral domestone is characterized by dense massive coral colonies forming a lens-shape framework with
development of a concave-upward and planar-top profile filling the largest cavities among granitic blocks.
The coral platestone is characterized by dominant growth of platy corals that drape and mantle the flat
portion of the granitic substrate and overlay the coarse debris infilling smaller cavities. The domestone
facies formed under moderate hydrodynamic energy, while the platestone facies indicates high
hydrodynamic energy at water depth intervals between the SWB and FWWB and limited siliciclastic input
during the coral growth.
The coral fauna is not very diversified at the generic level and dominant reef-builders are Porites,
Tarbellastrea, Thegioastrea, Favites and Favia, together with subordinate Astreopora. Massive colonies with
globous-domal shape and platy (encrusting and tabular) colonies are the dominant coral growth forms.
Coral colonies are mostly in growth position, although a coral rubble associated with granitic cobbles and
pebbles may be present at the base of the bioconstruction. Intercoral sediment is mainly represented by a
bioclastic wackestone to packstone matrix with larger benthic foraminifera, red algae nodules and debris.
Other components are articulated red algae fragments, bivalves and oysters, echinoids fragments, rotaliids,
textularids, barnacles and bryozoan fragments.
The coral bioconstruction is overlain by a 10 m-thick fine conglomerate changing to coarse bioclastic
quartz sandstone deposited in coastal settings near fluvial point sources. The C-isotope curve obtained
from the Cala di Labra section does not show a significant shift in δ 13 C values at the boundary between the
coral facies and the siliciclastic-rich unit. This suggests that nutrification was not responsible for the demise
of the fringing reef, while sudden burial by terrigenous sediment was a more likely factor. The increase of
terrigenous input had various effects: increase of turbidity with consequent decrease of light in the water
column, damage to coral tissue by abrasion and disruption of coral foundations because the high clastic
accumulation formed a mobile substrate.
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