Some Encrusted Hardgrounds from the Ordovician of Estonia (Baltica)

Carnets de Géologie [Notebooks on Geology] - vol. 15, n° 7

Some encrusted hardgrounds from the Ordovician of Estonia (Baltica)

1 Olev VINN

2 Ursula TOOM

Abstract: The Ordovician hardground faunas of Estonia are not diverse. They include echinoderm holdfasts (i.e., eocrinoids and crinoids), edrioasteroids, bryozoans (both hemispherical trepostomes and stalked ptilodictyids) and cornulitids. The earliest hardground faunas appeared in the Dapingian (i.e., bryozoans and echinoderms). The Estonian hardground faunas are less diverse than the North Ame- rican ones. North American hardgrounds seem to be more heavily encrusted than the Estonian ones. These differences may be due to the paleogeographic distances, different climates and different sedimentation environments of the paleocontinents. Key Words: Hardground; Cornulites; Bryozoa; echinoderms; Ordovician; Baltica. Citation : VINN O. & TOOM U. (2015).- Some encrusted hardgrounds from the Ordovician of Estonia (Baltica).- Carnets Géol., Madrid, vol. 15, nº 7, p. 63-70. Résumé : Quelques fonds durcis et encroûtés de l'Ordovicien d'Estonie, bouclier balte (Baltica).- La faune des fonds durcis ordoviciens est peu diversifiée. On y observe des structures d'ancrage d'échinodermes (d'éocrinoïdes et de crinoïdes), des édrioasteroïdes, bryozoaires (à la fois des trépostomes hémisphériques et des ptilodictyidés pourvus de tiges) et des cornulitidés. Les pre- miers peuplements de fonds durcis apparaissent au Dapingien : il s'agit alors de bryozoaires et d'échinodermes. La faune des fonds durcis estoniens est moins diversifiée que celle d'Amérique du Nord. Les fonds durcis nord-américains semblent être plus fortement encroûtés que ceux d'Estonie. Ces différences tiennent peut-être aux distances entre ces deux paléocontinents ou à des conditions climatiques ou d'environnements de dépôt distinctes. Mots-clefs : Fond durci ; Cornulites ; bryozoaires ; échinodermes ; Ordovicien ; bouclier balte ; Baltica.

the occurrence of Trypanites borings and the 1. Introduction edrioasteroid Cyathocystis. Another hardground is Carbonate hardgrounds are synsedimentarily located above the reef bodies in the Vasalemma cemented carbonate layers that have been quarry. This hardground is remarkable for its exposed on an ancient seafloor (WILSON & PAL- numerous cornulitid encrusters. MER, 1992). Hardgrounds form excellent attach- This paper attempts to: 1) identify encrusted ment surfaces for encrusting and bioeroding hardgrounds in the Ordovician of Estonia, 2) (i.e., boring) organisms (PALMER, 1982). These identify hardground encrusters in the Ordovician organisms otherwise dwell on carbonate of Estonia, 3) find trends in the record of hard- cobbles or exoskeletons of various inverte- ground encrustation in the Ordovician of Estonia, brates. Carbonate hardgrounds are more com- 4) find possible controls on the hardground en- mon in calcite sea conditions, such as in the crustation in the Ordovician of Estonia, 5) com- Ordovician, than in aragonite seas. Calcite seas pare hardground encrustation in Baltica with that favored early cementation of carbonate of North America. sediments in the seafloor (WILSON & PALMER, 1992). Ordovician hardground faunas are 2. Geological background and locality relatively well documented. They are among The area of Estonia (Fig. 1) was covered by a the best studied hardground faunas in general, shallow epicontinental sea in the Ordovician. The especially the North American examples. Much Ordovician sequence of northern Estonia is rela- less is known of Ordovician hardground faunas tively complete (Fig. 2) and represented mostly in Baltica and the eastern Baltic. The earliest by carbonate rocks, except for the terrigenous hardground ichnofaunas of Baltica include Lower Ordovician part. Ordovician carbonate Trypanites and Gastrochaenolites? from the rocks are exposed in northern Estonia as a wide latest Early Ordovician (VINN & WILSON, 2010). belt from the Narva River in the east to Hiiumaa Ripple marks associated with the hardground in Island in the west (MÕTUS & HINTS, 2007). The the Vasalemma quarry were described in detail drift of Baltica from the southern high latitudes by HINTS & MIIDEL (2008). They also mentioned (i.e., temperate climate zone) to the tropical

1 Department of Geology, University of Tartu, Ravila 14A, 50411 Tartu (Estonia) [email protected] 2 Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, Tallinn, 19086 (Estonia) [email protected] Published online in final form (pdf) on June 11, 2015 [Editor: Bruno GRANIER; language editor: Phil SALVADOR]

63 Carnets de Géologie [Notebooks on Geology] - vol. 15, n° 7

W Figure 1: Map with locations of encrusted Ordovician hardgrounds in Estonia (modified after MÕTUS, 2006). 1 - Väike-Pakri Island, 2 – Pakri Cliff at Cape Pakri, 3 – Vasa- lemma quarry, and 4 – Suhkrumägi outcrop.

realm caused a drastic climatic change (SCOTESE & MCKERROW, 1990; TORSVIK et al., 1992). Sedimentation rate of carbonates increased during the warming of the climate. Due to climatic change deposits that are characteristic of an arid and tropical climate appeared in the Estonian Ordovician sequence (MÕTUS & HINTS, 2007). In the Early and Middle Ordovician, when the Baltic sedimentation basin was situated in a temperate climate zone, these types of tropical deposits were completely lacking (JAANUSSON, 1973). The first signs of a warm climate in the early Katian include the appearance of tabulate corals, stromatoporoids and reefs, but it was not until the Hirnantian that they became prevalent (MÕTUS & HINTS, 2007). The large Vasalemma quarry is situated in Vasalemma settlement in northwestern Estonia (Fig. 1), west of the Keila-Riisipere railway. Limesto- nes of the quarry are excavated by Nordkalk AS down to the rippled upper surface of the Pääsküla Mem- ber of the Kahula Formation (HINTS & MIIDEL, 2008). The Vasalemma For- mation consists of a succession of biodetrital grainstones up to 15 m thick with numerous intercalated reef bodies, composed of bryozoan framestone-bindstone, echinoderm bindstone, receptaculitid-bryozoan-microbial framestone, and tabulate bafflestone. The reef bodies reach diameters of more than 50 m (KRÖGER et al., Figure 2: Stratigraphy of the Middle and Upper Ordovician of 2014). The studied hardground surfa- Estonia (modified after HINTS et al., 2008). Location of encrusted ces are located above the reef bodies hardgrounds marked. and at the base of Vasalemma For- mation (Fig. 3).

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3. Material and methods Hardground cobbles from Väike-Pakri Island – Two large cobbles from Toila Formation (Volkhov Regional Stage, Dapingian) of Väike-Pakri Island have a total area of 40.8 cm2. Studied material came from the collections of Institute of Geology, Tallinn University of Technology. Hardground pebbels from Suhkrumägi – Two large pebbles from Suhkrumägi, Toila Formation (Volkhov Re- gional Stage, Dapingian) with total area 21.5 cm2. Studied material came from the collections of Institute of Geology, Tallinn University of Technology. Vasalemma 1 hardground – Nine hardground samples with total area 818 cm2 from Vasalemma quarry. This hardground forms a boundary between Kahula and Vasalemma Formation of the Keila Regional Stage (early Katian). Studied material came from the collections of Institute of Geology, Tallinn University of Technology. Vasalemma 2 hardground - Three hardground slabs collected from the Vasalemma quarry were studied for encrustation and bioerosion using the collections of Institute of Geology, Tallinn University of Technology. The studied hardground area was 562 cm2. Only the hardground upper surface was exposed for the study. This hardground forms the upper surface of Vasalemma Formation (early Katian). Sample orientation was marked during collecting. Samples were manually cleaned with water and soft brushes. Maximal number of Trypanites borings was counted in 4cm2 using a cm grid drawn on a transparent film (TAPANILA et al., 2004). A centimeter grid was also used to measure the area of the studied hardground surface. A millimeter grid drawn on a transparent film was used to measure the area covered by cornulitid and bryozoan encrusters. An Olympus B 061 binocular micro- scope equipped with caliper (accuracy 0.1 mm) was used to measure cornulitid specimens. The hardground samples were photographed using Nikon 7000 digital camera.

Figure 3: Stratigraphic locations of hardgrounds in the Vasalemma quarry. This section is modified after KRÖGER et al. (2014).

Figure 4: Ptilodictyid bryozoan (Br) (TUG 1681-2) cemented to the hardground from Pakri Formation (Darriwilian) of Pakri Cliff, Cape Pakri, NW Estonia. Small disc below the bryozoan belongs possibly to echinoderms (TUG 1681-3).

65 Carnets de Géologie [Notebooks on Geology] - vol. 15, n° 7

Figure 5: Discoid echinoderm holdfast cemented to the hardground from Volkhov Regional Stage (Dapingian) of Suhkrumägi outcrop, northern Estonia Figure 6: Two domical trepostome bryozoans and a (GIT 156-356). possible ptilodictyid cemented to the hardground from Volkhov Regional Stage (Dapingian) of Väike-Pakri Island, NW Estonia (GIT 381-595).

Previously studied hardgrounds (RAUKAS & MIIDEL, 1997). Cape Pakri hardground (VINN, pers. obs.) – Vasalemma 1 hardground The encrusters compose of discoidal echi- The surface of hardground has a dark noderm holdfasts and a ptilodictyid bryozoan brownish-grey colour due to mineralization by holdfasts (Figs. 2 & 4; Table) cemented to the pyrite, contrasting to the grey limestone matrix. hardground surface within the Pakri Formation The surface is eroded and cuts the bioclasts in (Darriwilian). The encrusters cover only 4.65 the hardground. We found just a single eroded 2 cm (0.37%) of the total hardground sample cornulitid cemented to the hardground upper 2 studied (1260 cm ). Sample represents sandy surface. The encrustation area of the studied limestone of relatively shallow water and hardground samples is 0.2 cm2 of 818 cm2 nearshore origin (RAUKAS & MIIDEL, 1997) (0.02%). HINTS and MIIDEL (2008) reported also encrustation by edrioasteroid echinoderm Cya- 4. Results thocystis, which we did not find. The sample The hardground cobbles from Väike-Pakri represents relatively shallow water and near Island shore sediments (RAUKAS & MIIDEL, 1997) (Ta- The Dapingian hardground cobble studied ble). (Toila Formation of Volkhov Regional Stage) is Vasalemma 2 hardground (above reefs) formed of pure grey limestone and has a slight- The hardground surface has a darker grey ly lens-shaped profile. Its surface is strongly colour than the rest of rock matrix, which is mineralized by pyrite and has a much darker light grey in colour (Figs. 2 - 3 & 7; Table). The coluor than the matrix. The surface of cobble is hardground occurs on the upper surface of a relatively smooth and has numerous Trypanites reef limestone layer. Its surface is relatively borings. A discoidal echinoderm holdfast is smooth, with possible marks of microbio- cemented to upper surface of the cobble (Figs. erosion. Bioclasts in the hardground are 2 & 5; Table). The total encrustation area is abraded on the hardground surface. Its ledges 2 2 0.07 cm of 40.8 cm (0.2%). Sample repre- have rounded edges. Crypts are formed under sents limestone of relatively shallow water and the hardground ledges. The hardground ledges near shore origin (RAUKAS & MIIDEL, 1997). are 2 to 9 mm thick. The top surface of Hardground pebbles from Suhkrumägi - hardground is encrusted by cornulitids and Studied Dapingian (Toila Formation of Volkhov branching bryozoans (Fig. 8). The total Regional Stage) limestone pebbles have an encrustation area is 7.4 cm2 (1.3% of the total irregular shape and slightly lens-shaped profile. hardground surface studied). Their surface is slightly bumpy and is strongly Numerous Cornulites sp. tubes occur on the mineralized by pyrite and has a dark colour that upper surface of the hardground (area 562 cm2, contrast to the grey colour of the matrix. There N=18) (Fig. 5). These tubes lack preferred are numerous Trypanites borings in the orientation. Their maximal diameters vary from pebbles. Three small bryozoans (possibly 1.1 mm to 3.5 mm (mean 2.59 mm, sd=0.64, trepostomes) are cemented to the pebble (Figs. N=18). Most tubes are of similar large size, but 2 & 6; Table). There is an indication (i.e., good juveniles also occur. Some tubes were broken preservation) that the eroded cobbles were off from the hardground and their bases were secondary colonized by bryozoans. The total subsequently overgrown by other cornulitids. 2 2 encrustation area is 0.16cm of 21.5 cm Overgrowth occurs between four specimens of (0.7%). Sample represents limestone of cornulitids. Weathered and broken off tubes relatively shallow water and near shore origin 66 Carnets de Géologie [Notebooks on Geology] - vol. 15, n° 7

Figure 7: Upper surface of the hardground, Figure 8: Cornulites sp. encrusted by a branching Vasalemma Formation, early Katian, Vasalemma bryozoan, with Trypanites borings in the hardground, quarry, NW Estonia (GIT 362-96). Vasalemma Formation, early Katian, Vasalemma quarry, NW Estonia (GIT 362-96). (tube bases) occur on the hardground (N=4). rest of rock matrix is probably due to slight Distribution of cornulitids on the hardground is pyritization during diagenesis. The hardground patchy. Cornulitids cover 1.3% of the studied was most likely cemented under sediment cover hardground surface (562 cm2), but in some and exposed later to winnowing, which also places they may encrust up to 4% of the exposed the cryptic surfaces. The occurrence of hardground surface. abraded bioclasts of reef origin in the Cornulites sp. tubes are straight to mode- hardground indicate that the hardground was rately curved, up to 1.7 mm long, and with abraded before the cornulitid and bryozoan diameters ranging from 1.1 mm to 3.5 mm encrustation. The sediment layer below the (mean 2.59). The divergence angle of the tubes hardground may have still been soft or less is 10.5o. The tubes are externally covered with cemented than the hardground during the very faint and dense longitudinal striation and abrasion; this conclusion is supported by the moderately developed perpendicular annulation. occurrence of crypts. Their bases are not widened to slightly The relatively low bioerosion density on the widened, especially at annular crests. The studied Vasalemma hardground for the Late lumen of the tubes is covered with prominent Ordovician (VINN’s pers. obs.) could indicate a and regular annulation. The distance between relatively short exposure time for the hard- annular crests at the tube diameter 3 mm is 0.7 ground, before it was buried by sediments, or a to 1.0 mm. Cornulites sp. resembles most relatively low number of bioeroding organisms closely Cornulites? sp. D (VINN, 2013) from the in the Vasalemma hardground community. Vasalemma Formation by its moderately conical However, considering the small size of the shell and prominent annulation in the tube studied hardground sample and the usual pat- lumen. It differs from C.? sp. D by presence of chy distribution of Trypanites borings, it is likely external faint longitudinal striation and less that the samples do not represent the most developed perpendicular ornamentation. The bioeroded part of the hardground. tube divergence angle is also slightly smaller in Cornulitid tubeworms form an important and o C. sp. than in C.? sp. D (12 ). primitive group of the encrusting tentaculitoids. One branching trepostome bryozoan en- Cornulitids are presumably phylogenetically crusts a cornulitid tube (Fig. 8). The bryozoan closely related to free-living tentaculitids (VINN, encrustation area is 2.5 cm2 (0.45% of the total 2010). The biological affinities of cornulitids hardground area). have long been debated. They most likely re- In addition to cornulitids and bryozoans, a present Lophothrochozoa (VINN & ZATOŃ, 2012) few Trypanites borings occur in the upper and could belong to stemgroup phoronids (TAY- surface of the hardground. Trypanites borings LOR et al., 2010). Their palaeoecology is range from 0.2 to 2.1 mm in diameter. There is relatively well documented and understood as a maximum five Trypanites borings per 4 cm2 they generally retain their original position on of the hardground upper surface, but some the substrate after fossilisation (TAYLOR & areas (up to 10 cm2) have no borings. WILSON, 2003). In contrast to their close rela- tives, the microconchids that lived in waters of 5. Discussion various salinities, cornulitid tubeworms are found only in normal marine sediments (ZATOŃ Vasalemma 2 hardground et al., 2012). Shallow marine sediments, We interpret the palaeoenvironment of the especially those associated with carbonate Vasalemma hardground community as a platforms, are usually rich in cornulitid fossils. shallow sea floor of normal salinity below the Cornulitids were most abundant in the Late tidal zone on the basis of fauna and sediments Ordovician to Devonian, but their fossils are (KRÖGER et al., 2014). The relatively dark color known also from the Carboniferous (VINN, of the hardground surface as compared to the 2010). Six adaptive strategies have thus far 67 Carnets de Géologie [Notebooks on Geology] - vol. 15, n° 7 been described in cornulitids, indicating a diver- There seems to be no remarkable stratigra- se ecology (VINN, 2010). phic trend in encrustation intensities in the Cornulitids show that hardground was Ordovician of Estonia, which is surprising consi- exposed to encrusters long enough to allow at dering the great climatic change in Baltica least two generations of cornulitids to colonize (SCOTESE & MCKERROW, 1990; RAUKAS & TEEDU- it, and then bryozoans to encrust the MÄE, 1997) while moving from the temperate cornulitids. The numerical dominance of large zone to tropics and the diversification of faunas sized Cornulites sp. specimens resulted presu- during the Great Ordovician Biodiversification mably from colonization event/s where most of Event (GOBE) (WEBBY et al., 2004). specimens reached adult size after the settling The hardground encrusters of the Ordovician on the hardground. High juvenile mortality is of Estonia compared to the other regions common in many modern invertebrates. The The Middle Ordovician hardgrounds of Esto- situation with the Vasalemma hardground nia are very sparsely encrusted (<1% of the cornulitids can either be explained by low hardground area) as compared to known North juvenile mortality or weaker preservation American analogues. 10.5% of the Kanosh potential of juvenile specimens. The empty Shale hardground area is covered by encrusters juvenile tubes could have been destroyed by (WILSON et al., 1992) which is a magnitude the hydrodynamic activity of the waters above more than any known Middle Ordovician the hardground. The random orientation of the example from Estonia. Similar to Estonian tubes indicates the lack of unidirectional water (Baltica) faunas, North American Middle Ordo- current or random settlement of larvae or lack vician hardground faunas contain bryozoans of larvae reorientation after settlement. If there and echinoderms (WILSON et al., 1992). was unidirectional water current, the cornulitids The Late Ordovician Vasalemma 2 hard- would have oriented their apertures up current ground has a relatively small number (N=1) of to achieve better position for suspension branching bryozoans in the association, which feeding. Oriented cornulitids have been repor- usually cover the largest area on the other ted from Ordovician to Carboniferous brachio- Ordovician hardgrounds, especially North Ame- pods (SCHUMANN, 1967; VINN, 2010) where they rican ones (BRETT & LIDDELL, 1978; TAYLOR & presumably took advantage of the feeding WILSON, 2003). The Vasalemma 2 hardground currents of brachiopods. fauna is unique for its numerical dominance by Middle Ordovician hardgrund encrusters Cornulites sp. What is the reason for the high The Middle Ordovician hardground faunas of abundance of Cornulites sp. in this association? the Estonia are not diverse. They include only They may have been opportunistic suspension bryozoans and echinoderms. Among the bryo- feeding encrusters, successful in conditions of zoans both domical colonies and stalked colo- low competition with other suspension feeders. nies (possible ptilodictyids) occurred. Echino- Similar opportunistic behavior has been descri- derms were represented at least by three bed in microconchids (ZATOŃ & KRAWCZYŃSKI, different stemmed forms (i.e., eocrinoids or 2011; ZATOŃ et al., 2012, 2013), a group of crinoids). spirorbiform tubeworms descended from the Trends in the hardground encrustation in the same ancestor as the cornulitids (VINN & ZATOŃ, Ordovician of Estonia 2012). All samples derive from relatively shallow The relatively low skeletal coverage (1.3%) water environments and no obvious bathy- of the Vasalemma 2 hardground and an metric or sedimentological trends can be esta- extremely low skeletal coverage (0.02%) of the blished for the Ordovician of Estonia (RAUKAS & Vasalemma 1 hardground contrast with the TEEDUMÄE, 1997). However, there is a stratigra- higher coverage of Late Ordovician analogues phical trend in the taxonomic composition of from North America (BRETT & LIDDELL, 1978; hardground encrusters in the Ordovician of BRETT & BROOKFIELD, 1984). This could represent Estonia. a paleobiogeographic difference caused by a slightly colder climate in Baltica and possibly In the Dapingian the first hardground differences in faunal composition and sedimen- encrusters appeared in the Ordovician of Esto- tation (RAUKAS & TEEDUMÄE, 1997). It can also be nia. They included bryozoans (possibly trepo- explained by low nutrient levels in the local sea stomes), and echinoderm holdfasts (i.e., eocri- water of Baltica (low productivity, e.g., LESCIN- noids or crinoids). During the Darriwilian, SKY et al., 2002; WILSON et al., 2015; ZATOŃ et ptilodictyid bryozoans appeared, but in general al., 2015) or by a large area of hardground the early Middle Ordovician and late Middle being occupied by soft-bodied organisms in the Ordovician hardground faunas of Estonia were community, which did not preserve as fossils. similar. In the Late Orodovician (early Katian) Alternatively, low skeletal coverage may indi- edrioasteroids (i.e., Cyathocystis) and cornu- cate a short exposure time of the hardground litids (i.e., Cornulites) appeared. Most notable is (LESCINSKY et al., 2002). the late appearance of edrioasterioids in the Ordovician hardground communities of Estonia. The North American Middle Ordovician and Similarly, cornulitids are known from the late Late Ordovician hardground faunas (BRETT & Darriwilian of Estonia (VINN, 2013), but they LIDDELL, 1978; BRETT & BROOKFIELD, 1984; WILSON colonized hardgrounds later in the early Katian. et al., 1992) seem to be more diverse than the 68 Carnets de Géologie [Notebooks on Geology] - vol. 15, n° 7

Estonian ones (Baltica). This may be due to a experiments in the Java Sea, Indonesia.- different faunal composition caused by paleo- Palaios, Lawrence, vol. 17, p. 171–191. geographic distance. During the Ordovician MÕTUS M.-A. & HINTS O. (2007).- Excursion B2: North America was located in a tropical zone Lower Paleozoic geology and corals of while Baltica was located in a temperate zone Estonia. In: Excursion Guidebook. 10th until the earliest Katian. Thus, most likely the International Symposium on Fossil Cnidaria lower diversity of Estonian Ordovician hard- and Porifera (August 18-22, 2007).- ground faunas was mostly caused by the diffe- Institute of Geology at Tallinn University of rent climates of the paleocontinents. It is a Technology, p. 54–55. general trend that tropical faunas are more di- PALMER T. (1982).- Cambrian to Cretaceous verse than temperate ones (BARNES & HUGHES, changes in hardground communities.- Le- 1999). thaia, Oslo, vol. 15, p. 309–323. RAUKAS A. & TEEDUMÄE A. (1997).- Geology and Acknowledgments Mineral Resources of Estonia.- Estonian Aca- Financial support to O.V. was provided by demy Publishers, Tallinn, 436 p. the Palaeontological Association Research SCHUMANN D. (1967).- Die Lebensweise von Grant, Estonian Research Council projects Mucrospirifer GRABAU, 1931 (Brachiopoda).- ETF9064 and IUT20-34. This paper is a Palæogeography, Palæoclimatology, Palæo- contribution to IGCP 591 "The Early to Middle ecology, vol. 3, p. 381–392. Palaeozoic Revolution". We are grateful to G. SCHLOTHEIM E.F. von (1820).- Die Petrefak- tenkunde auf ihrem jetzigen Standpunkte BARANOV, Institute of Geology, Tallinn University of Technology for photographing the specimens. durch die Beschreibung seiner Sammlung versteinerter und fossiler Überreste des We are also grateful to M.A. WILSON, College of Wooster, for comments on the manuscript. Thier- und Planzenreichs der Vorwelt erläu- tert.- Becker'sche Buchhandlung, Gotha, 436 Bibliographic references p. SCOTESE C.R. & MCKERROW W.S. (1990).- Revised BARNES R.S.K. & HUGHES R.N. (1999).- An intro- world maps and introduction. In: MCKERROW duction to marine ecology.- Blackwell Scien- W.S. & SCOTESE C.R., eds., Palaeozoic ce, Oxford, 3rd Edition, 286 p. palaeogeography and biogeography.- The BRETT C.E. & BROOKFIELD M.E. (1984).- Mor- Geological Society of London, Memoirs, phology, faunas and genesis of Ordovician London, vol. 12, p. 1–21. hardgrounds from southern Ontario, Cana- TAPANILA L., COPPER P. & EDINGER E. (2004).- da.- Palæogeography, Palæoclimatology, Environmental and substrate control on Palæoecology, vol. 46, p. 233–290. Paleozoic bioerosion in corals and stroma- BRETT C.E. & LIDDELL W.D. (1978).- Preservation toporoids, Anticosti Island, Eastern Canada.- and paleoecology of a Middle Ordovician Palaios, Lawrence, vol. 19, p. 292–306. hardground community.- Paleobiology, TAYLOR P.D., VINN O. & WILSON M.A. (2010).- Washington, vol. 4, p. 329–348. Evolution of biomineralization in "lophopho- FISHER D.W. (1962).- Small conoidal shells of rates".- Special Papers in Palaeontology, uncertain affinities. In: MOORE C.D., ed., Oxford, vol. 84, p. 317–333. Treatise on Invertebrate Paleontology.- TAYLOR P.D. & WILSON M.A. (2003).- Palaeo- Geological Society of America, New York; ecology and evolution of marine hard sub- University of Kansas, Lawrence, Part W, p. strate communities.- Earth Science Reviews, 130–143. vol. 62, p. 1-103. HINTS L., AINSAAR L., MÄNNIK P. & MEIDLA T., eds. TORSVIK T.H., SMETHURST M.A., VOO R. van der, (2008).- The Seventh Baltic Stratigraphical TRENCH A., ABRAHAMSEN N. & HALVORSEN E. Conference: Abstracts and Field Guide.- (1992).- Baltica. A synopsis of Vendian– Geological Society of Estonia, Tallinn, 46 p. Permian palaeomagnetic data and their HINTS L. & MIIDEL A. (2008).- Ripple marks as palaeotectonic implications.- Earth-Science indicators of Late Ordovician sedimentary Reviews, vol. 33, p. 133–152. environments in Northwest Estonia.- Esto- VINN O. (2010).- Adaptive strategies in the nian Journal of Earth Sciences, Tallinn, vol. evolution of encrusting tentaculitoid tube- 57, p. 11–22. worms.- Palæogeography, Palæoclimatology, JAANUSSON V. (1973).- Aspects of carbonate Palæoecology, vol. 292, p. 211–221. sedimentation in the Ordovician of Balto- VINN O. (2013).- Cornulitid tubeworms from the scandia.- Lethaia, Oslo, vol. 6, p. 11–34. Ordovician of eastern Baltic.- Carnets Géol., KRÖGER B., HINTS L. & LEHNERT O. (2014).- Age, Madrid, Letter 2013/03 (CG2013_L03), p. facies and geometry of the Sandbian/Katian 131-138 (Upper Ordovician) pelmatozoan-bryozoan- VINN O. & WILSON M.A. (2010).- Early large receptaculitid reefs of the Vasalemma borings from a hardground of Floian- Formation, northern Estonia.- Facies, Erlan- Dapingian age (Early and Middle Ordovician) gen, vol. 60, p. 963–986. in northeastern Estonia (Baltica).- Carnets LESCINSKY H.L., EDINGER E. & RISK M.J. (2002).- Géol., Madrid, Letter 2010/04 (CG2010_ Mollusc shell encrustation and bioerosion L04), 4 p. rates in a modern epeiric sea: taphonomy VINN O. & ZATOŃ M. (2012).- Phenetic phy-

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logenetics of tentaculitoids - extinct proble- ZATOŃ M., BORSZCZ T., BERKOWSKI B., RAKOCIŃSKI matic calcareous tube-forming organisms.- M., ZAPALSKI M.K. & ZHURAVLEV A.V. (2015).- GFF, Stockholm, vol. 134, p. 145–156. Paleoecology and sedimentary environment WEBBY B.D., DROSER M.L., PARIS F. & PERCIVAL I., of the Late Devonian coral biostrome from eds. (2004).- The Great Ordovician Bio- the Central Devonian Field, Russia.- Palæo- diversification Event.- Columbia University geography, Palæoclimatology, Palæoecology, Press, New York, 484 p. vol. 424, p. 61–75. WILSON M.A. & PALMER T.J. (1992).- Hardgrounds ZATOŃ M. & KRAWCZYŃSKI W. (2011).- and hardground faunas.- University of Microconchid tubeworms across the upper Wales, Aberystwyth, Institute of Earth Stu- Frasnian – lower Famennian interval in the dies Publications, Aberystwyth, vol. 9, p. 1– Central Devonian Field, Russia.- Palaeon- 131. tology, Oxford, vol. 54, p. 1455–1473. WILSON M.A., PALMER T.J., GUENSBURG T.E., FINTON ZATOŃ M., TAYLOR P.D. & VINN O. (2013).- Early C.D. & KAUFMAN L.E. (1992).- The develop- Triassic (Spathian) post-extinction microcon- ment of an Early Ordovician hardground chids from western Pangaea.- Journal of community in response to rapid sea-floor Paleontology, Lawrence, vol. 87, p. 159– calcite precipitation.- Lethaia, Oslo, vol. 25, 165. p. 19–34. ZATOŃ M., VINN O. & TOMESCU M. (2012).- WILSON M.A., BOSCH S. & TAYLOR P.D. (2015).- Invasion of freshwater and variable marginal Middle Jurassic (Callovian) cyclostome bryo- marine habitats by microconchid tubeworms zoans from the Tethyan tropics (Matmor – an evolutionary perspective.- Geobios, Formation, southern Israel).- Bulletin of Villeurbanne, vol. 45, p. 603–610. Geosciences, Prague, vol. 90, p. 51–63.

Table Table: Encrusted hardgrounds in the Ordovician of Estonia.

Total hardground Total hardground Hardground Taxa Area encrusted area encrusted area studied Hardground cobbles Discoidal echinoderm 0.07 cm2 (0.2%) 0.07 cm2 (0.2%) 40.8 cm2 from Väike-Pakri Island holdfast Hardground pebbles Trepostome bryozoans 0.16 cm2 (0.7%) 0.16cm2 (0.7%) 21.5 cm2 from Suhkrumägi Cape Pakri Discoidal echinoderm 4.65 cm2 (0.37%) 4.65 cm2 (0.37%) 1260 cm2 hardground holdfasts and bryozoans Vasalemma 1 Cornulites sp. 0.2 cm2 (0.02%) 0.2 cm2 (0.02%) 818 cm2 hardground

Cornulites sp. 7.4 cm2 (1.3%) 7.4 cm2 (1.3%) 562 cm2 Vasalemma 2 hardground Branching bryozoans 2.5 cm2 (0.45%)