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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Palaeodiversity and faunal dynamics of post-Frasnian Tabulates, Western
Palaeotethys
Hans-Georg HERBIG, Elise NARDIN & Anke MÜLLER
Universität zu Köln, Institut für Geologie und Mineralogie, Zülpicher Straße 49a, D-50674 Köln;
herbig.paleont@uni-koeln.de; enardin@uni-koeln.de; ankeira@freenet.de
Introduction: Tabulate and rugose corals, and stromatoporids were the predominating framebuilders,
bafflers and encrusters during the mid-Palaeozoic reef cycle. All were severely affected by the Frasnian-
Famennian extinction event, but had a completely different post-Frasnian history. Palaeozoic
stromatoporids never recovered sufficiently and got extinct at the Devonian-Carboniferous boundary.
Rugose corals radiated again during the latest Devonian (“Strunian”) and during the Mississippian. They
flourished in carbonate platform settings and reinvaded the reef biotope, reaching almost their Devonian
diversity (ARETZ 2010). Also tabulate corals recovered, but remained a mostly subordinate community
element (SCRUTTON 1997).
Problems and Methods: Due to relative scarceness, missing biostratigraphic value and difficult taxonomic
treatment, post-Frasnian tabulates are not sufficiently studied in the western Palaeotethys. We tried to
evaluate diversity and faunal dynamics at species level based on exhaustive bibliographic survey. Data
were cross-checked and supplemented with those from the Paleobiology Database (http://paeodb.org), to
reduce uncertainties due to unrevised faunal data. Fossil lists of that database were used, if entries are on
species level and ranges confined at least to regional stages in defined regions. Diversity was calculated for
western European regional stages in standardised regions, using the normalised diversity metric proposed
by COOPER (2004). Defined standard regions are Ireland, northern England, southern England, Belgium,
Rhenish Slate Mountains, Holy Cross Mountains, Silesia-Cracow Upland, Saxothuringia, Southern
Portugal, Catalonia, and the North African basins. Palaeogeographic relations were approached by cluster
analysis based on the Dice similarity index using PAST software.
Palaeodiversity and disparity: No tabulate corals are recorded in the lower and middle Famennian of the
western Palaeotethys except for a faunula from the lower Famennian of Moravia (HLADIL 1987). Not a
single “Strunian” or Carboniferous species is recorded from pre-Famennian strata according to our
knowledge. Thus, a completely new faunal cycle started in the “Strunian”. It ended in the Kasimovian,
comprising all together about 75 species from 33 genera and 14 families.
The diversity is relatively low in the “Strunian” but increases abruptly to reach an absolute maximum in
the Molinacian. Then the diversity decline from the Viséan to the Kasmovian is interrupted by an expressed
Brigantian peak. The low “Strunian” -Hastarian diversity reflects the slow recovery after the Frasnian-
Famennian extinction. Declining diversity during the Viséan is due to steadily increasing extinction and
decreasing origination rate, a trend only reversed during the Brigantian. The Mississippian diversity curve
for western European rugose corals (ARETZ 2010) is similar to that of tabulates. Both correlate well with
Mississippian sealevel variations. The Molinacian maximum is probably related with the Avins event, a
widely recognized transgressive event, which introduced also many rugose taxa. Of special interest is the
Brigantian peak, which introduced some Asiatic taxa to Poland, Belgium, the Betic Cordillera (own
unpublished data) and Algeria (Multithecopora, Sinopora, Verolites). The quasi-extinction of tabulates at the
end of the Viséan is related to the prograding Variscan orogeny, which caused emergence and widespread
break-down of carbonate platforms. Moscovian and Kasimovian tabulates have been described from
Cantabria and the Carnic Alps, but undescribed occurrences in the North African basins should increase
Pennsylvanian diversity.
Syringoporidae, Michelinidae and, to a lesser degree, Favositidae are the most diverse and most
abundantly occurring Carboniferous tabulate families in the western Palaeotethys (Fig. 1A). The
normalised diversity curves of the Syringoporidae and the Michelinidae parallel the general trend of
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