Excursion Guidebook - Geoloogia Instituut

EsthoniaCryptolichenariaEocateniporaRabdotetradiumPriscosoleniaProporaAcidolitesPlasmoporaParastriatoporaSubalveolitesAuloporaSyringolitesMastoporaTheciaCladopora?RiphaeolitesMesosolenia10 th International Symposium on Fossil Cnidaria and Porifera. Excursion B2: Field GuideTabulate coralsThe East Baltic and Dniestr River basins are the areasof the Baltica plate with abundant, well preserved andwell known tabulate corals. The largest taxonomicalstudies in Estonian tabulate corals were carried out byKlaamann (1962a,b, 1964, 1966) and Sokolov (1951,1952, 1955). Estonia and Gotland together comprisethe most complete section with diverse tabulate faunaknown throughout the Silurian. The Ordovician coralsare exposed in outcrops of Estonia. The best tabulatebearing Ludlow sections are in the Dniestr River basin.Tabulate corals are distributed predominantly inthe shallow part of the basin and occur mainly in thehigh-energy, shoal facies, although they also occurless frequently in all other facies belts except the depression.The corals are rare in tidal flats and transitionfacies belts and achieve maximum diversity inthe belts of shoal to open platform (Klaamann et al.1980).The changes in composition of tabulate faunas ofthe East Baltic at the Ordovician and Silurian boundarywere mainly expressed at the generic level (Fig.14). The Ordovician tabulate taxa did not disappearsimultaneously. Some taxa disappeared much earlierthan the beginning of the Silurian. In total, 16 UpperOrdovician genera disappeared towards the end of theperiod and 5 genera continued into the Silurian (Fig.14) in the Estonian sequence. The Upper Ordovicianlichenarids, tetradiids, sarcinulids and heliolitids disappeared,but several species of paleofavositids con-tinued into the Silurian and became more diverse thanthe extinct cateniporids (Klaamann 1964, 1966). Afew heliolitid genera also continued from the Ordovicianinto the Silurian.The widespread transgressions and amelioratingclimates at the beginning of the Silurian induceda rapid emergence of the cosmopolitan species andgenera among corals (Copper 1994). In East Baltic,small bioherms are known in Estonia in the HillisteMember of the Juuru Stage, Rhuddanian. In the earlyLlandovery the tabulate faunas in Estonia are characterisedby low generic diversity, although the speciesdiversity of Paleofavosites increased. The early-middleLlandovery macrocycle began with the glacioeustaticsea level rise and ended with the denudationin marginal areas of the basin (Nestor and Einasto1997).According Johnson (1996) and Johnson et al. (1998),the first Silurian sea-level rise took place at approximatelythe beginning of the Aeronian. The renewal offaunas in the upper part of the Raikküla Stage occurredat this time in Estonia (Fig. 14); the genera Parastriatopora,Multisolenia, Syringopora, Vacuopora andSinopora appeared. Favosites is more abundant thanPaleofavosites in the Raikküla Stage than in the JuuruStage. The Adavere Stage (Rumba Member) displaysthe highest diversity of tabulates and the highest ratioof cosmopolitan taxa for the whole Llandovery. Thisis the beginning of stabilisation stage in the basin development(Nestor and Einasto 1997). The upper partOhesaareKaugatumaKuressaarePaadlaRootsikülaJaagarahuJaaniAdavereRaikkülaJuuruPorkuniPirguVormsiNabalaRakvereOanduStageGenusEoflecheriaSaffordophyllumLyoporaCalapoeciaSarcinulaProheliolitesProtaraeaPragnelliaPorkunitesCateniporaHeliolitesPaleofavositesHalysitesFavositesVacuoporaSinoporaMultisoleniaSubalveolitellaRomingeriaAdaverinaPlacocoenitesAngoporaSaaremolitesThamnoporaBarrandeolitesStriatoporaRomingerellaCoenitesLaceriporaTrochiscolithusWormsiporaSyringoporaFig. 14. Ranges of tabulate coral genera in the sequence of Estonia (Mõtus 2005).24