BRITISH SILURIAN STROMATOPOROIDS. FAUNAS, PALAEOBIOLOGY, AND PALAEOGEOGRAPHICAL SIGNIFICANCE

ABSTRACT

Recommended reference to this publication:

Kershaw, S., Da Silva, A.-C. & Sendino, C. 2021. British Silurian stromatoporoids. Fauna, palaeobiology, and palaeogeographical significance. Monograph of the Palaeontographical Society, London: 1-92; pls 1-22. (Publ. No. 660, part of Vol. 175 for 2021.)

British Silurian stromatoporoids occur in carbonate rocks, mostly in the Wenlock Series, together with a small number in the Llandovery Series and very few in the Ludlow Series. Using field and museum material (408 samples) and literature, this study identifies 15 stromatoporoid genera, doubling the previously known generic diversity, so the British Isles holds the third highest genera-diversity Wenlock assemblage after Gotland/Estonia (23 genera) and the Siberian Platform (20 genera). Remarkably, nearly all samples come from the small (100 × 100 km) Much Wenlock Limestone Formation (MWLF) (Homerian Stage, uppermost Wenlock Series) in the Midland Platform of central England (Avalonia), surrounded, underlain, and overlain by siliciclastics. On the Midland Platform one sample is Llandovery age; 11 samples are Ludlow age (Aymestry Limestone). Other samples from the Isle of Man (Wenlock age, six samples) and south-west Scotland (Llandovery age, three samples) are in transported material, with associated corals and they indicate unpreserved carbonate platforms in northern Britain. A few Llandovery Series stromatoporoids are also reported from Ireland, both north and south of the Iapetus Suture; published reports of Wenlock stromatoporoids from Ireland are shown to be misidentified trace fossils. In the MWLF stromatoporoids (together with the more abundant rugose corals, tabulates, heliolitids, and some microbial carbonates) occur in small patch reefs and in bedded bioclastic grainstones, packstones, and nodular wackestones; stromatoporoids are more common in and near patch reefs. The MWLF stromatoporoid fauna has 15 confirmed low-level taxa: Labechia conferta (Lc), Lophiostroma schmidti (Ls), Ecclimadictyon macrotuberculatum (Em) and E. astrolaxum (Ea), Petridiostroma simplex (Ps) and P. linnarssoni (Pl), Actinostromella vaiverensis (Av), Araneosustroma fistulosum (Af), Densastroma pexisum (Dp), Plectostroma intertextum (Pi), Simplexodictyon yavorskyi (Sy), Eostromatopora impexa (Ei), ‘Stromatopora’ venukovi (‘S’v), Syringostromella borealis (Sb) and Parallelostroma typicum (Pt). No new taxa were found. The five most abundant taxa (Lc, Av, Dp, Px, and Sb) total 230 specimens, 64.2% of the MWLF assemblage, consistent with taxa proportions in other Palaeozoic stromatoporoid assemblages. The stromatoporoids have limited growth forms: Lc grew laminar frames, mostly in patch reefs; the other taxa range from laminar to high domical, maximum sizes around 40 cm basal diameter. They almost completely lack the complexities and diversities of form of their contemporaries in nearby large carbonate platforms of Baltica (Gotland/Estonia) and Laurentia (eastern USA and Canada); only two samples contain intergrown corals. Overall, British Silurian stromatoporoids may be viewed as a relatively limited shallow marine assemblage that took advantage of suitable conditions in a short time-and-space window in an episode of raised sea level with low siliciclastic input. The MWLF has the largest assemblage in the Avalonia microcontinent at the end of the Wenlock Epoch. Palaeogeographically, the Avalonia assemblage of stromatoporoids lay in an important location between Laurentia, Baltica and other Silurian continents and may have aided distribution pathways of stromatoporoids that presumably had planktonic forms for migration. Stromatoporoids were likely not affected by the mid-Silurian extinction event, but data are insufficient to be certain.

Les stromatoporoïdes de Silurien de Grande-Bretagne. Faunes, paléobiologie et signification paléogéographique

RÉSUMÉ

Les stromatoporoïdes du Silurien de Grande-Bretagne sont présents dans les roches carbonatées, principalement dans la série Wenlock, ainsi qu’un petit nombre dans la série Llandovery et très peu dans la série Ludlow. En utilisant du matériel de terrain et de musée (408 échantillons) et la littérature, cette étude identifie 15 genres de stromatoporoïdes, doublant la diversité générique connue auparavant. Les Îles Britanniques détiennent donc le troisième plus grand assemblage de Wenlock en termes de diversité des genres après Gotland/Estonie (23 genres) et la Plate-forme sibérienne (20 genres). Fait remarquable, presque tous les échantillons proviennent de la petite (100 × 100 km) Formation calcaire de Much Wenlock (MWLF) (Stage Homérien, dernière série du Wenlock) de la plate-forme du Midland du centre de l’Angleterre (Avalonia), entourée de sédiments siliciclastique sus- et sous-jacents. Sur la plate-forme du Midland, un échantillon est d’âge Llandovery; 11 échantillons sont d’âge Ludlow (calcaire Aymestry). D’autres échantillons provenant de l’île de Man (âge Wenlock, six échantillons) et du sud-ouest de l’Écosse (âge Llandovery, trois échantillons) se trouvent dans des matériaux transportés, avec des coraux associés et ils indiquent des plates-formes carbonatées non préservées dans le nord de la Grande-Bretagne. Quelques stromatoporoïdes de la série Llandovery sont également signalés en Irlande, tant au nord qu’au sud de la suture de Iapetus; les stromatoporoïdes metionnés dans des publications concernant le Wenlock d’Irlande se révèlent en fait être des bioturbations fossiles mal identifiées. Dans le MWLF, les stromatoporoïdes (ainsi que les coraux rugueux, les tabulés, les héliolitides et certains carbonates microbiens plus abondants) sont présents dans les petits “patch reefs” et également dans les grainstones bioclastiques lités, les packstones et les wackestones nodulaires; les stromatoporoïdes sont plus fréquents dans et près des récifs isolés ou “patch reefs”. La faune de stromatoporoïdes du MWLF compte 15 taxons de faible niveau confirmés: Labechia conferta (Lc), Lophiostroma schmidti (Ls), Ecclimadictyon macrotuberculatum (Em) et E. astrolaxum (Ea), Petridiostroma simplex (Ps) et P. linnarssoni (Pl), Actinostromella vaiverensis (Av), Araneosustroma fistulosum (Af), Densastroma pexisum (Dp), Plectostroma intertextum (Pi), Simplexodictyon yavorskyi (Sy), Eostromatopora impexa (Ei), ‘Stromatopora’ venukovi (‘S’v), Syringostromella borealis (Sb) et Parallelostroma typicum (Pt). Aucun nouveau taxon n’a été trouvé. Les cinq taxons les plus abondants (Lc, Av, Dp, Px et Sb) totalisent 230 spécimens, soit 64,2 % de l’assemblage MWLF, ce qui correspond aux proportions des taxons des autres assemblages de stromatoporoïdes du Paléozoïque. Les stromatoporoïdes ont des formes de croissance limitées: Lc a développé des formes laminaires, principalement dans les “patch reefs”; les autres taxons vont du laminaire à la forme en dôme haute, avec des tailles maximales d’environ 40 cm de diamètre basal. Ils n’ont pas la complexité et la diversité de formes de leurs contemporains des grandes plates-formes carbonatées voisines de Baltica (Gotland/Estonie) et Laurentia (est des États-Unis et du Canada); seuls deux échantillons contiennent des intercroissances avec des coraux. Dans l’ensemble, les stromatoporoïdes du Silurien britannique peuvent être considérés comme un assemblage marin peu profond et relativement limité qui a profité de conditions favorables durant une courte fenêtre spatio-temporelle lors d’un épisode d’élévation du niveau de la mer avec un faible apport silicico-clastique. Le MWLF possède le plus grand assemblage du microcontinent Avalonia à la fin de l’ère Wenlock. Sur le plan paléogéographique, l’assemblage de stromatoporoïdes d’Avalonia se trouvait à un endroit important entre les Laurentides, la Baltique et d’autres continents du Silurien, ce qui pourrait avoir favorisé les voies de distribution des stromatoporoïdes qui avaient vraisemblablement des formes planctoniques pour la migration. Les stromatoporoïdes n’ont probablement pas été affectés par l’extinction du milieu du Silurien, mais les données sont insuffisantes pour être totalement concluantes.

Britische Silurian Stromatoporen. Fauna, Paläobiologie und paläogeographische Bedeutung

KURZFASSUNG

Britische silurische Stromatoporen kommen in Karbonatgesteinen vor, überwiegend in der Wenlock-Serie, vereinzelt auch in der Llandovery-Serie und selten in der Ludlow-Serie. Aus eigenen Aufsammlungen und Museumsmaterial (408 Proben), sowie aus der Literatur wurden 15 Stromatoporen-Gattungen identifiziert, wodurch sich die zuvor bekannte Gattungs-Diversität verdoppelt. Damit hat die Wenlock-Vergesellschaftung Britische Inselne die dritthöchste Diversität auf Gattungsebene, nach Gotland/Estland (24 Gattungen) und der Sibirischen Plattform (20 Gattungen). Bemerkenswerterweise kommen fast alle Stücke aus der eng begrenzten (100 × 100 km) Much Wenlock Limestone Formation (MWLF) (Homerium, oberste Wenlock-Serie) auf der Midland-Plattform in Mittel-England (Avalonia), die von Siliziklastika umgeben, unterlagert und überlagert ist. Ein Exemplar von der Midland-Platform hat ein Llandovery-Alter, 11 Proben haben ein Ludlow-Alter (Aymestry-Kalk). Weitere Stücke von der Isle of Man (Wenlock-Alter, sechs Proben) und aus dem Südwesten Schottlands (Llandovery-Alter, drei Proben) stammen aus transportiertem Material, wo sie zusammen mit Korallen vorkommen, und weisen auf die Existenz nicht überlieferter Karbonat-Plattformen im Norden Grossbritanniens hin. Auch aus der Llandovery-Serie Irlands sind einige Stromatoporen nachgewiesen, sowohl nördlich als auch südlich der Iapetus-Sutur. Bei publizierten Nachweisen von Wenlock-Stromatoporen aus Irland handelt es sich um fehlbestimmte Spurenfossilien. In der MWLF kommen Stromatoporen (zusammen mit den häufigeren rugosen Korallen, Tabulaten, Heliolitiden und mikrobiellen Karbonaten) sowohl in kleinen Fleckenriffen als auch in geschichteten bioklastischen grainstones, packstones und wackestones vor. Am häufigsten sind Stromatoporen in und in der Nähe von Fleckenriffen. Auf Artebene sind 15 Taxa aus der MLWF belegt: Labechia conferta (Lc), Lophiostroma schmidti (Ls), Ecclimadictyon macrotuberculatum (Em) and E. astrolaxum (Ea), Petridiostroma simplex (Ps) und P. linnarssoni (Pl), Actinostromella vaiverensis (Av), Araneosustroma fistulosum (Af), Densastroma pexisum (Dp), Plectostroma intertextum (Pi), Simplexodictyon yavorskyi (Sy), Eostromatopora impexa (Ei), ‚Stromatopora‘ venukovi (‚S‘v), Syringostromella borealis (Sb) und Parallelostroma typicum (Pt). Neue Arten wurden nicht gefunden. Die fünf häufigsten Taxa (Lc, Av, Dp, Px und Sb) umfassen insgesamt 230 Exemplare, 64.2% der MWLF Vergesellschaftung, was ihren Anteilen an anderen paläozoischen Stromtoporen-Vergesellschaftungen entspricht. Die Variabilität der Stromatporen-Wuchsformen ist begrenzt. Lc bildete laminare Gerüste, überwiegend in Fleckenriffen. Die anderen Arten variieren von laminar bis hoch-kuppelförmig, mit maximalen Durchmessern von 40 cm an der Basis. Die Komplexizität und Formenvielfalt zeitgleicher Vorkommen auf benachbarten Karbonatplattformen Balticas (Gotland/Estland) und Laurentias (östliche USA und Kanada) fehlt fast vollständig. Nur zwei Exemplare sind mit Korallen verwachsen. Zusammenfassend sind britische silurische Stromatoporen als eine relativ limitierte flachmarine Vergesellschaftung zu betrachten, die die günstigen Bedingungen auf kleiner Fläche in einem kurzen Zeitfenster ausnutzte, die sich während einer Episode mit erhöhtem Meeresspiegel und niedrigem Eintrag von Siliziklastika boten. Die MWLF beherbergt die größte Vergesellschaftung auf dem Avalonia Mikrokontinent gegen Ende der Wenlock-Epoche. Paläogeografisch gesehen befand sich die Stromatoporen-Vergesellschaftung Avalonias an einem wichtigen Punkt zwischen Laurentia, Baltica und anderen silurischen Kontinenten, und trug dadurch wohl zur Expansion der Stromatoporen bei, die vermutlich planktonische Verbreitungsstadien hatten. Wahrscheinlich wurden die Stromatoporen nicht vom Mittel-Silurischen Aussterbeereignis beeinträchtigt. Die Datenlage dazu ist jedoch nicht ausreichend um das abzusichern. [Translation by Simon Schneider.]

Британские силурианские строматопороиды. Фауна, палеобиология и

палеогеографическое значение

АБСТРАКТ

Британские силурийские строматопороиды встречаются в карбонатных породах, в основном в венлокском отделе, а так же в небольших количествах в лландоверийском отделе и в очень малых количествах в лудловском отделе. Используя полевые и музейные материалы (408 образцов) и литературные данные, в настоящей работе определяются 15 родов строматопороидов, удваивая ранее известное родовое разнообразие. Таким образом, Британские острова занимают третье место по родовому разнообразию венлокских групп после Готланда/Эстония (24 родов) и Сибирской платформы (20 родов). Примечательно, что почти все образцы взяты из небольшой (100 × 100 км) Мач Венлоксой Известняковой формации (MWLF) (гомерский ярус, поздний венлок) с платформы Мидленд в центральной Англии (Авалония), окруженной, подстилаемой и перекрытой силикокластическими породами. На платформе Мидленд, один образец имеет лландоверийский возраст; 11 образцов лудловский возраст (Айместры известняк). Другие образцы с острова Мэн (венлоксий возраст, шесть образцов) и юго-запада Шотландии (лландоверийский возраст, три образца) найденные из переотложенного матерала в ассоциациях с кораллами, указывают на несохранившиеся карбонатные платформы на севере Британии. Несколько лландоверийских строматопороид были найдены в Ирландии, к северу и к югу от Япетской сутуры. Опубликованные отчеты по венлокским строматопороидам Ирландии указывают на неверное определение последних, как ихнофоссилий. В MWLF, строматопороиды (вместе с более многочисленными ругозовыми кораллами, табулятами, гелиолитидами и некоторыми микробиальными карбонатами) встречаются в малых изолированных рифах, а также в слоистых биокластических грейнстоунах, пакстоунах и гнездовых вакстоунах; строматопороиды наиболее часто встречаются, как в самих изолированных рифах, так и неподалеку от них. В MWLF, фауна строматопороидов имеет 15 подтвержденных таксонов низкого порядка: Labechia conferta (Lc), Lophiostroma schmidti (Ls), Ecclimadictyon macrotuberculatum (Em) и E. astrolaxum (Ea), Petridiostroma simplex (Ps) и P. linnarssoni (Pl), Actinostromella vaiverensis (Av), Araneosustroma fistulosum (Af), Densastroma pexisum (Dp), Plectostroma intertextum (Pi), Simplexodictyon yavorskyi (Sy), Eostromatopora impexa (Ei), ‘Stromatopora’ venukovi (‘S’v), Syringostromella borealis (Sb), и Parallelostroma typicum (Pt). Новые таксоны не найдены. Пять наиболее распространенных таксонов (Lc, Av, Dp, Px и Sb) насчитывают 230 особей или 64,2% фауны MWLF, что соответствует пропорциям таксонов в других палеозойских строматопоридных группах. Строматопороиды имеют ограниченные формы роста: Lc формировал ламинарные каркасы, в основном на небольших изолированных рифах. У других таксонов каркасы варьируются от ламинарных до высоких куполообразных с максимальным диаметром до 40 см. По сравнению с одновозрастнами фаунами из карбонатных платформы Балтики (Готланд, Эстония) и Лаврентии (восточный США и Канада), строматопороиды из MWLF не обладают разнообразием и сложностью форм. Только в двух образцах найдены сросшиеся кораллы. В целом, британские силурийские строматопороиды можно рассматривать, как относительно ограниченную мелководную морскую группу, которая, воспользовавшись коротким интервалом роста уровня моря, развилась на ограниченной территории с обедненным привносом силикокластики. MWLF предславляет самую большую фауну Авалония микроконтинента конца венлокского отдела. В палеогеографическом отношении, авалонская фауна строматопороидов имела важное геогафическое расположение между Лаврентийским, Балтийским и другими силурийскими континентами и могла содействовать распространанию строматопороидов, предположительно мигрировавших планктонным путем. Строматопороиды, вероятно, не были затронуты средне-силурийским вымиранием, однако из-за недостаточности данных, этот вопрос остается открытым. [Translation by Davit Vasilyan and Sergei Lazarev.]

Edited by Y. Candela, B. Moon and P. Crowther

Published by Taylor & Francis Group

View correction statement:

Correction Notice

Stephen Kershaw Department of Life Sciences

Brunel University

Kingston Lane

Uxbridge, UB8 3PH

United Kingdom

[email protected]

Sedimentary Petrology

Liège University

Allée du Six Août

12, Quartier Agora

B20, Sart Tilman

4000 Liège

Belgium

[email protected]

Consuelo Sendino

Earth Sciences Department

The Natural History Museum

Cromwell Road

London, SW7 5BD

United Kingdom

[email protected]

INDEX

Numbers in bold type indicate a page on which a description or diagnosis is given or commences; numbers in italics indicate pages where a text-figure occurs. Plate numbers are included.

Abberley Hills, 5, 8–10, 75, 76, 86

Acanthochaetetes, 16, 60, 87, 89

Actinostroma, 3, 8, 42, 55, 76, 77, 83, 87, 88

Actinostroma intertextum (= Plectostroma intertextum), 3, 13, 14, 37, 41, 42, 55, 56, 59, 68, 76, 77; Pl. 17, figs 1–8

Actinostromella vaiverensis, 14, 27, 32, 36, 37, 37, 45, 57, 59, 63, 64, 68, 75; Pl. 13, figs 1–6

Alexander Terrane (Silurian of Alaska), 58, 87

Anticosti Island, Canada (Silurian stromatoporoids), 17, 54, 85, 88

Aragonite (mineralogy of stromatoporoids), 50, 62

Araneosustroma fistulosum, 12, 27, 29, 33, 49, 50, 68, 75; Pl. 14, figs 1–4

astroites, Stromatopora, 3, 76

astrolaxum, Ecclimadictyon, 17, 68, 72; Pl. 9, figs 1–6

Astrosclera willeyana (calcified living stromatoporoid-type sponge), 16, 89

Avalonia, 1, 1, 6, 8, 9, 43, 52, 53, 55, 56, 58, 59, 63, 66, 82, 83, 85

Aymestry Limestone (Ludlow Series), 3, 5, 9, 82

Bacteria in sponges, 8, 60, 87

Balclatchie (Balcletchie), 9, 42

Baltica, 1, 1, 6, 43, 45, 47, 52, 53, 56, 58, 59, 63

Benthall Edge, 8

Bioclaustration, 45

Blakeway Hollow Quarry, Wenlock Edge, 57

borealis, Syringostromella, 16, 32–37, 37, 40, 40, 42, 54, 55, 59, 60, 62, 64, 68, 79, 80; Pl. 21, figs 1, 2

Calcarea sponges, 17

Calcimicrobes, 8, 61, 62

Calcite (mineralogy of stromatoporoids), 48, 48, 50, 51, 62

Caldwell, Elizabeth, 3, 82

Caledonian Orogen, 1, 5, 6, 27, 88

Canada, 7, 8, 17, 43, 54, 58, 66, 82, 83, 85, 86, 89

carteri, Stromatopora, 3, 4, 36, 37, 37, 60, 80

‘caunopores’ (symbiotic syringoporid tabulates in stromatoporoids), 61, 89

Ceratoporella nicholsoni (calcified living chaetetid-type sponge), 57, 87

Chair of Kildare (Ireland), 43, 83, 86

China, 55, 66

Clathrodictyon, 3, 8, 35, 53, 54, 58, 59, 72–75, 78, 87

Clathrodictyon fastigiatum, 3, 72, 73

Clathrodicyton striatellum, 3, 35, 37, 59, 75

Coates Quarry, Wenlock Edge, 2, 10, 13, 14, 20, 23, 38, 41, 48, 57, 58, 69

Colonograptus ludensis Graptolite Zone (ludensis Zone), 2, 5, 63

Colter, Victor, 3, 58

concentrica, Stromatopora, 3, 43

conferta, Labechia, 11, 13, 18, 19, 19, 20, 21, 21, 23, 37, 38, 41 41, 42, 47, 51, 57, 59, 64, 68, 69, 70; Pl. 1, figs 1–5

Conodonts, 63, 65, 66

Coralline sponges, 4, 83, 88

Craton/cratonic/intracratonic, 6, 7, 40, 55, 67, 85

Cyrtograptus lundgreni Graptolite Zone (lungreni Zone), 5, 63

Demospongiae, 4, 60, 84, 85, 87, 88

Densastroma pexisum, 8, 28, 31, 33, 35, 40, 59, 63, 68, 76; Pl. 15, figs 1–5; Pl. 16, figs 1–6

dentata, Stromatopora, 3

Devonian Period/System, 1, 1, 3, 9, 15, 16, 34, 41, 42, 55, 56, 58, 60, 62, 66, 70–72, 75, 77, 80–85, 87, 88

Diagenesis (of stromatoporoids), 23, 33, 38, 48, 50, 52, 62, 84, 87, 89; Pl. 14, figs 1–4

Dingle Peninsula, western Ireland, 1, 8, 9, 32, 43, 66, 78, 81, 84, 88

discoidea, Stromatopora, 3, 54

Dunquin Group, 9, 43, 81, 84

Ecclimadictyon astrolaxum, 17, 68, 72; Pl. 9, figs 1–6

Ecclimadictyon macrotuberculatum, 14, 17, 21, 22, 23, 38, 41, 42, 54, 56, 59, 68, 72, 73; Pl. 8, figs 1–8; Pl. 9, figs 1–4

Eke Formation (Ludlow Series, Gotland), 65, 78

elegans, Stromatopora, 3

Ellesmere Island, Arctic Canada, 8

Elton Formation (Ludlow Series), 9, 12, 40

Endobionts, 43, 45, 61, 88

Eostromatopora impexa, 31, 68, 79; Pl. 20, figs 1–4

Epibionts, 43, 45, 61, 78, 87

Estonia, 56, 59, 65, 82, 84–87

Extinction, 1, 5, 7, 52, 63–66, 63, 86, 88

Farley Member, 7, 32, 61, 78

fastigiatum, Clathrodictyon, 3, 72, 73

Favosites, 17, 82, 85

fistulosum, Araneosustroma, 12, 27, 29, 33, 49, 50, 68, 75; Pl. 14, figs 1–4

Florida (modern coral banks), 57

Gaspé Peninsula, eastern Canada, 54, 66, 83, 86

Geopetal infills (in stromatoporoids), 20, 20, 21, 21, 23, 25, 34, 35, 50, 52, 51, 62

Girvan, southwest Scotland, 1, 9, 42, 43, 52, 55, 56, 66, 72, 83, 84, 86, 88

Girvanella, 8, 61, 84

Goldfuss, 3, 9, 43, 83

Gondwana, 55

Gotland (Silurian of Sweden), 6, 7, 17, 19, 36, 40, 42, 47, 54, 57, 58, 59, 61, 63–67, 63, 69–89

Graptolites, 7, 63, 64, 66, 89

Greenland (early Silurian stromatoporoids), 55, 87

Halla Formation (Wenlock Series, Gotland), 7, 57, 64–66

Hamra Formation (Ludlow Series, Gotland), 65

Haven conglomerate, 43

Heliolitids, 3, 11, 16, 17, 18, 19, 41, 50, 57, 58, 83

Heliolites interstinctus, 57

Heliolites parvistella (= Stelliporella parvistella), 19, 41

Hemse Group (Ludlow Series, Gotland), 65, 78

Hill Top, Wenlock Edge, 4

Hobb’s Quarry (May Hill), 64

Hypercalcified sponges, 4, 16, 17, 67, 71, 89

Iapetus Ocean, 6, 9, 42, 52

Iapetus Suture, 1, 9, 43, 56

Illinois, 7, 85

impexa, Eostromatopora, 31, 68, 79; Pl. 20, figs 1–4

intertextum, Plectostroma, 3, 13, 14, 37, 41, 42, 55, 56, 59, 68, 76, 77; Pl. 17, figs 1–8

Ireviken Event (lower Silurian System), 65, 87

Isle of Man, 1, 9, 42, 43, 47, 47, 55, 56, 61, 77, 83; Pl. 18, figs 1–8

Johnston, Mary, 69

Katri (Ludlow Series, Saaremaa Island, Estonia), 65

Kildare Inlier (Ireland), 43, 83, 86

Klinte Secundo episode, 7

Klinteberg Formation (Gotland), 6, 7, 54, 63–66, 78, 83

Labechia conferta, 11, 13, 18, 19, 19–21, 21, 23, 37, 38, 41, 41, 42, 47, 51, 57, 59, 64, 68, 69, 70; Pl. 1, figs 1–5

Labechia rotunda, 3, 36, 68, 71, 84; Pl. 2, figs 5–8; Pl. 4, figs 1, 2; Pl. 6, figs 1, 2

Labechia scabiosa, 3, 36, 68, 71; Pl. 2, figs 5–8; Pl. 7, figs 1, 2

Lau Event (Ludlow Series), 65, 89

Laurentia, 1, 1, 40, 43, 47, 52, 53, 56, 58, 63, 82

Lea Quarry, Wenlock Edge, 48, 76

Lea Quarry South, Wenlock Edge, 9, 50

Leiolite (microbial fabric in reefs), 58

linnarssoni, Petridiostroma, 54, 55, 68, 74; Pl. 11, figs 1–3; Pl. 12, fig. 3

Lithistid sponges (Demospongiae), 7, 60

Llandovery Series/Epoch, 2, 6, 7, 9, 10, 17, 42, 43, 52, 54–56, 65, 72, 75, 80

Lophiostroma schmidti, 3, 22, 36, 67, 70, 71; Pl. 2, figs 1–8; Pl. 4, figs 1, 2; Pl. 5, figs 1, 2; Pl. 6, figs 1, 2; Pl. 7, figs 1, 2

Lophiostroma ?schmidti, 36, 71; Pl. 3, figs 1-4; Pl. 4, figs 1, 2; Pl. 5, figs 1, 2; Pl. 6, figs 1, 2; Pl. 7, figs 1, 2

Lower Quarried Limestone Member (LQLM), 2, 4, 15, 18, 20, 31, 34, 34, 40, 63, 64

ludensis Zone (Colonograptus ludensis Graptolite Zone), 2, 5, 63

Ludlow Series/Epoch, 4, 6, 7, 8, 9, 11, 23, 36, 42, 54–56, 61, 65, 66, 70, 71, 74, 76, 77, 79, 80, 82–84, 87

lundgreni Zone (Cyrtograptus lundgreni Graptolite Zone), 5, 63

macrotuberculatum, Ecclimadictyon, 14, 17, 21, 22, 23, 38, 41, 42, 54, 56, 59, 68, 72, 73; Pl. 8, figs 1–8; Pl. 9, figs 1–4

Malvern Hills, 1, 5, 8, 9, 29, 30, 31, 42, 63, 64, 76, 86

May Hill Inlier, 4, 8, 9, 64, 72, 83

Merlia, 18, 59

Microbia/microbial fabrics/microbial carbonates, 8, 18, 20, 21, 58, 62, 79, 83, 85, 86, 87

Microreticulate microstructure, 75, 76, 80, 81

Mid-Homerian extinction, 63

Midland Platform, 1, 2, 5, 6, 7, 9, 10, 21, 38, 40, 42, 43, 52, 54–56, 61, 66, 67, 82–84

Morocco (Devonian mounds), 34, 82, 85

Much Wenlock Limestone Formation (MWLF), 2, 4, 5, 5, 6, 7–10, 10, 11–16, 17–21, 18, 19–34, 33, 34, 36, 37, 38–40, 40–43, 45, 45–50, 47, 53, 54–67, 63, 69, 70, 72–74, 76, 78–81, 83, 86

Mulde Beds (Gotland), 57, 64, 65

Mulde Event, 7, 63–66, 63, 82, 86

New Brunswick, 53, 83, 86

Nicholson, H. Alleyne, 69

nicholsoni, Ceratoporella (calcified living chaetetid-type sponge), 57, 87

Nodular Member, 4, 15, 16, 40, 57, 64

Old Red Continent, 55

Ordovician, 1, 42, 43, 56, 60, 70–73, 83–89

Oslo area, 43, 52, 52, 54, 85, 67, 82, 85

Palaeogeography, 1, 4, 9, 52, 67

Papillae (on Labechia conferta), 19, 21, 69

Parallelostroma typicum, 42, 44, 46, 48, 54, 55, 61, 64, 68, 80; Pl. 22, figs 1–4

Parkwood Quarry (Malvern Hills), 9, 31, 42

parvistella, Stelliporella, 19, 41

Peel Sandstone, 1, 9, 42, 55, 83

Petridiostroma linnarssoni, 54, 55, 68, 74; Pl. 11, figs 1–3; Pl. 12, fig. 3

Petridiostroma simplex, 3, 23–25, 32–35, 35, 37, 42, 54, 55, 59, 64, 68, 73, 74, 78; Pl. 10, figs 1–4; Pl. 12, figs 1–3

pexisum, Densastroma, 8, 28, 31, 33, 35, 40, 59, 63, 68, 76; Pl. 15, figs 1–5; Pl. 16, figs 1–6

Philip structures, 19, 83, 85

Pinnacle reefs (Silurian of Arctic Canada), 7, 82

Plectostroma intertextum, 3, 13, 14, 37, 41, 42, 55, 56, 59, 68, 76, 77; Pl. 17, figs 1–8

Powell, John, 3, 71, 79

Pridoli Series (upper Silurian System), 54, 66, 76, 88

Queensland, Australia (Silurian stromatoporoids), 55, 60, 82, 83, 84, 85, 87

rotunda, Labechia, 3, 36, 68, 71; Pl. 2, figs 5–8; Pl. 4, figs 1, 2; Pl. 6, figs 1, 2

Rugose corals, 3, 19, 46, 47, 57, 77

scabiosa, Labechia, 3, 36, 68, 71; Pl. 2, figs 5–8; Pl. 7, figs 1, 2

Scania (Sweden), 54, 85

schmidti, Lophiostroma, 3, 22, 36, 67, 70, 71; Pl. 2, figs 1–8; Pl. 4, figs 1, 2; Pl. 5, figs 1, 2; Pl. 6, figs 1, 2; Pl. 7, figs 1, 2

?schmidti, Lophiostroma, 36, 71; Pl. 3, figs 1–4; Pl. 4, figs 1, 2; Pl. 5, figs 1, 2; Pl. 6, figs 1, 2; Pl. 7, figs 1, 2

schmidti, Stromatopora, 3

Sclerospongiae, 4

Siberia, 58, 59, 84

simplex, Petridiostroma, 3, 23–25, 32–35, 35, 37, 42, 54, 55, 59, 64, 68, 73, 74, 78; Pl. 10, figs 1–4; Pl. 12, figs 1–3

Simplexodictyon yavorskyi, 55, 60, 61, 68, 73, 78; Pl. 19, figs 1–9

Spicules, 4, 7, 15, 17, 18, 60, 67, 82, 83, 84

Stelliporella parvistella, 19, 41

striatellum, Clathrodicyton, 3, 35, 37, 59, 75

Stromatopora astroites, 3, 76

Stromatopora carteri, 3, 4, 36, 37, 37, 60, 80

Stromatopora concentrica, 3, 43

Stromatopora dentata, 3

Stromatopora discoidea, 3, 54

Stromatopora elegans, 3

Stromatopora schmidti, 3

Stromatopora typica, 3, 80

‘Stromatopora’ venukovi, 42, 55, 61, 68, 77; Pl. 18, figs 1–8

Sundre Formation (Ludlow Series, Gotland), 65

swinderniana, Thecia (tabulate in Wenlock reefs), 57

Symbiotic intergrowths in stromatoporoids, 33, 42, 43, 44, 45, 46, 47, 47, 57, 61, 62, 88; Pl. 13, figs 3–6; Pl. 22, figs 1–8

Syringoporid tabulates (symbiotic), 42, 47, 61, 77, 89; Pl. 18, figs 1–8

Syringostromella borealis, 16, 32–37, 37, 40, 40, 42, 54, 55, 59, 60, 62, 64, 68, 79, 80; Pl. 21, figs 1, 2

Tabulates, 3, 8, 11, 16, 17, 18, 19, 22, 41–43, 47, 50, 57, 58, 60, 61, 64, 71, 77, 84, 86, 87

Telychian Stage, lower Silurian, 43, 74, 75

Thecia swinderniana (tabulate in Wenlock reefs), 57

Trypanites, 26, 86

Turbidites (Silurian System, Scotland), 56

typica, Stromatopora, 3, 80

typicum, Parallelostroma, 42, 44, 46, 48, 54, 55, 61, 64, 68, 80; Pl. 22, figs 1–4

Upper Quarried Limestone Member, 2, 4, 16

Usk Inlier, 1, 4, 8, 9, 42, 80, 82, 86, 88

vaiverensis, Actinostromella, 14, 27, 32, 36, 37, 37, 45, 57, 59, 63, 64, 68, 75; Pl. 13, figs 1–6

venukovi, ‘Stromatopora’, 42, 55, 61, 68, 77; Pl. 18, figs 1–8

Virginia (Silurian and Devonian stromatoporoids), 54, 88

Wales, 2, 5, 10, 71, 83, 84, 86

West Point Formation (upper Silurian System, eastern Canada), 66, 86

Whitman’s Hill Quarry (Abberley Hills), 9, 10, 42, 64, 86

willeyana, Astrosclera (calcified living stromatoporoid-type sponge), 16, 89

Wisconsin (Silurian reefs), 54, 56, 88

Woodland Point, 9, 42, 72, 88

Woodland Point Formation, 42

Woolhope Inlier, 1, 8, 9, 22, 64, 70, 80, 81, 82, 86, 87; Pl. 2, figs 1–4

yavorskyi, Simplexodictyon, 55, 60, 61, 68, 73, 78; Pl. 19, figs 1–9

Zoophycos, 8, 43

PLATE 1

Labechia conferta (Lonsdale, 1839)

Middle Silurian, Much Wenlock Limestone Formation

Wren’s Nest, Dudley, West Midlands

1–5 CAMSM X.50347.187; 1, 2, whole thin section views showing major features in vertical and transverse section respectively. 3, 4, details of vertical section (1) showing robust pillars and curved dissepiments defining the structure of this taxon. 5, detail of transverse section (2), oblique in places, showing even distribution of pillars in the sample.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 1

PLATE 2

Lophiostroma schmidti (Nicholson, 1886)

Middle Silurian, Much Wenlock Limestone Formation

Haugh Wood, Woolhope, Herefordshire

1–4 NMW 99.35G.2582; vertical (1, 3) and transverse (2, 4) sections showing partly altered skeletal structure. The skeleton is penetrated by a large boring (1, 2) filled with shell debris and micritic sediment. Equally spaced growth interruptions (1) contain sparite cement (3). Shows poorly-preserved state in both transverse and vertical views.

Upper Silurian, Hemse Group

Kuppen peninsula, near Östergarn, eastern Gotland, Sweden

5–8 CAMSM X.50347.37.2; vertical plane-polarized (ppl) (5) and cross-polarized light (xpl) (6) sections; transverse ppl (7) and xpl (8) sections. This is a comparative example from the middle Ludlow Hemse Group stromatoporoid biostrome at Kuppen, Gotland, Sweden, presented as evidence that Labechia rotunda and Labechia scabiosa illustrated in Plates 3–7, are junior synonyms of L. schmidti.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 2

PLATE 3

Lophiostroma ?schmidti (Nicholson, 1891)

(Labechia rotunda Johnston, 1915; Holotype)

Middle Silurian, Much Wenlock Limestone Formation

Bradwell Rock Quarry, Wenlock Edge, Shropshire

1–4 NHMUK PI H969; 1, 2, whole thin section of laminar growth form, vertical section in plane-polarized and cross-polarized light, respectively. 3, 4, enlargements of 1 and 2, of area in green box in 2, showing detail of solid columnar structure, particularly well shown in 4, where the structure is also shown as recrystallized.

Compare with enlargements in Plate 4 and transverse section in Plate 5.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 3

PLATE 4

Lophiostroma ?schmidti (Nicholson, 1891)

(Labechia rotunda Johnston, 1915; Holotype)

Middle Silurian, Much Wenlock Limestone Formation

Lilleshall Quarry, Wenlock Edge, Shropshire

1, 2 NHMUK PI H969; Enlargement of central part of laminar growth form shown in Plate 2, vertical section in plane-polarized (1) and cross-polarized light (2). The base of the stromatoporoid is composed of the same recrystallized structure of the skeleton as the rest of it, and thus there is no epithecal layer at the base, consistent with all other specimens of L. schmidti observed by the authors.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 4

PLATE 5

Lophiostroma ?schmidti (Nicholson, 1891)

(Labechia rotunda Johnston, 1915; Holotype)

Middle Silurian, Much Wenlock Limestone Formation

Lilleshall Quarry, Wenlock Edge, Shropshire

1, 2 NHMUK PI H969; transverse section in plane-polarized (ppl) (1) and cross-polarized light (xpl) (2). Both ppl and xpl views show approximately rounded transverse sections through the pillars. Compare with Plate 2 for comparison with Lophiostroma schmidti from Gotland and Plates 3 and 4 for vertical section.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 5

PLATE 6

Fig. Page

Lophiostroma ?schmidti (Nicholson, 1891)

(Labechia scabiosa Nicholson, 1891; Holotype)

Middle Silurian, Much Wenlock Limestone Formation

Wenlock Edge, Shropshire

1, 2 NHMUK PI P6145 vertical section in plane-polarized (1) and cross-polarized light (2), showing its structure of large pillars that are recrystallized. The base of the specimen lacks an epitheca. The upper part of the specimen shows two prominent growth interruption events where sediment lies between layers of stromatoporoid skeleton. In the lower part of the thin section there are two areas of recrystallized structure, left and right, where the stromatoporoid skeleton has been replaced.

See Plate 2 for comparison with Lophiostroma schmidti from Gotland and Plates 3–5 for comparison with Labechia rotunda.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 6

PLATE 7

Fig. Page

Lophiostroma ?schmidti (Nicholson, 1891)

Labechia scabiosa Nicholson, 1891

Middle Silurian, Much Wenlock Limestone Formation

Wenlock Edge, Shropshire

1, 2 NHMUK PI P6145 (holotype of Labechia scabiosa Nicholson, 1891) transverse thin section views in plane-polarized (1) and cross-polarized light (2) show approximately rounded transverse sections through the pillars. See Plate 2 for comparison with Lophiostroma schmidti from Gotland and Plates 3–5 for comparison with Labechia rotunda.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 7

PLATE 8

Ecclimadictyon macrotuberculatum (Riabinin, 1951)

Middle Silurian, Much Wenlock Limestone Formation

Lea South Quarry, Wenlock Edge, Shropshire

1–8 CAMSM X.50347.99; 1, vertical thin section of a large area of stromatoporoid skeleton. The base is the bottom of the stromatoporoid that grew either on sediment or as a primary cavity and shows overlapping growth of laminae, that grew upwards and laterally from right to left. 2, 3, enlargements of 1, showing details of skeletal structure and overlapping growth of laminae. The lower part shows oblique downward development of the skeleton from right to left, possible evidence that the specimen grew to form a primary cavity. Former growth surfaces are shown by the three slightly darker horizontal lines (centre and upper), evidence that growth did not progress evenly through the life of this stromatoporoid. 4, detail of 3 showing the crumpled laminae architecture with circular to elongate galleries. 5–8, transverse sections at increasing scale showing character of astrorhizae and pillars.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids

Plate 8

PLATE 9

Ecclimadictyon astrolaxum (Nestor, 1966)

Middle Silurian, Much Wenlock Limestone Formation

Lea South Quarry, Wenlock Edge, Shropshire

1–6 CAMSM X.50347.95; 1–3, vertical thin sections at different scales, showing the crumpled laminae architecture characteristic of taxa classed traditionally as Ecclimadictyon, and the consistently finer scale of structure, indicative of E. astrolaxum, different from E. macrotuberculatum illustrated in Plate 8. 4–6, transverse thin sections at different scales. Note difference in structure from E. macrotuberculatum in Plate 8.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 9

PLATE 10

Petridiostroma simplex (Nestor, 1966)

Middle Silurian, Much Wenlock Limestone Formation

Lea South Quarry, Wenlock Edge, Shropshire

1–4 CAMSM X.50347.47; 1, 2, vertical sections showing continuous laminae and the downward reflection of laminae to form pillars, characteristic of this taxon. 3, 4, transverse sections of skeletal architecture of continuous laminae and distinct rounded pillars present in this taxon.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 10

PLATE 11

Petridiostroma linnarssoni (Nicholson, 1887)

Middle Silurian, Much Wenlock Limestone Formation

Coates Quarry, Wenlock Edge, Shropshire

1–3 CAMSM X.50347.37; 1, vertical thin section of the only sample available; there is no transverse section of this specimen. Large area of thin section, showing the stromatoporoid in the lower one third of the photograph. 2, 3, enlargements of lower right part of 1, showing the poorly preserved structure that is somewhat recrystallized, but contains a recognizable architecture that is not consistent with any other taxon. The stromatoporoid is also affected by pressure solution between the three pieces of skeleton illustrated.

Lower Wenlock, Upper Visby Formation

Kneippbyn, Gotland, Sweden

4 CAMSM X.50347.37.1; vertical thin section view at the same scale as 3 that confirms the identification.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 11

PLATE 12

Petridiostroma simplex (Nestor, 1966)

Middle Silurian, Much Wenlock Limestone Formation

Lea South Quarry, Wenlock Edge, Shropshire

1 CAMSM X.50347.47; vertical thin section showing prominent lamina and pillar structure; compare with 2.

2 NMW 99.35G.EDG-3.23; vertical acetate peel showing an architecture the same as 1, but laminae spacing is less, reflecting the variation of the skeleton within this taxon.

Petridiostroma linnarssoni (Nicholson, 1887)

Middle Silurian, Upper Visby Formation

Kneippbyn, Gotland, Sweden

3 CAMSM X.50347.37.1; vertical thin section to emphasize the differences in physical appearance of the architecture from P. simplex in 1 and 2 above, but with similar laminae spacing as 2.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 12

PLATE 13

Actinostromella vaiverensis (Nestor, 1966)

Middle Silurian, basal Elton Formation

Lea South Quarry, Wenlock Edge, Shropshire

1, 2 CAMSM X.50347.64; vertical (1) and transverse (2) views of whole thin sections. This taxon is characterized by an open network structure with narrow vertical spaces that develop as continuous vertical spaces appearing as tubes, visible as small white circles in transverse section (2, 6). Patches of sparite in the central area of 1 are interpreted as recrystallization of sediment in a sediment-interruption layer, because this photograph shows the correct way up to the top of the image.

Middle Silurian, Much Wenlock Limestone Formation

Major’s Leap, Wenlock Edge, Shropshire

3–6 CAMSM X.50347.165; 3, 4, enlargements of vertical sections of the network structure. Light-coloured wavy horizontal lines in 3, enlarged in 4, show growth layers of the stromatoporoid. 5, 6, transverse sections of the network structure, showing astrorhizae. Symbiotic possible worm tubes are present as spar-filled circles; the continuous vertical spaces shown in 3 and 4 are here seen as small circles (6). Sample donated by David Walker, West Midlands, UK.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 13

PLATE 14

Araneosustroma fistulosum Lessovaya, 1970

Middle Silurian, Much Wenlock Limestone Formation

Crews Hill Quarry, Abberley Hills, Worcestershire

1–4 CAMSM X.50347.258; 1, 2, vertical (1) and transverse (2) views of whole thin sections. They are partly stained with a combination of Alizarin Red S and potassium ferricyanide, producing a purple stain (darker shade in monochrome) that indicates presence of ferroan calcite, evidence of diagenesis in burial below the redox boundary. 3, 4, partial enlargement in vertical (3) and transverse (4) views. In 3 the laminate structure is more clear but even at this magnification the detail of the structure comprises narrow skeletal elements. 4 shows detail of an astrorhiza.

Compare with Plate 15. See also Text-figs. 48–51 of diagenetic change in stromatoporoids.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 14

PLATE 15

Araneosustroma fistulosum Lessovaya, 1970

Middle Silurian, Much Wenlock Limestone Formation

Crews Hill Quarry, Abberley Hills, Worcestershire

1–6 CAMSM X.50347.258; 1–3, successive enlargements of vertical sections. In 3 the structure is revealed as an irregular network composed of non-aligned fine vertical and horizontal elements characteristic of this taxon, with scattered small spaces shown as pale areas. 4–6, successive enlargements of transverse sections showing the elements with tiny spaces represented as pale areas.

This structure contrasts with the aligned structures of Densastroma pexisum, that lack the small spaces, displayed in Plate 16.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 15

PLATE 16

Densastroma pexisum (Yavorsky, 1929)

Middle Silurian, Much Wenlock Limestone Formation

Crews Hill Quarry, Abberley Hills, Worcestershire

1–6 CAMSM X.50347.257; 1, vertical thin section showing fine structure of this taxon, dominated by coenosteles (vertical elements), connected together by horizontal processes, so the skeleton lacks pillars and laminae. Several growth interruption events have left sediment layers in the structure, some of which pass laterally to areas lacking sediment. 2, transverse thin section showing part of a growth interruption in plan view and branched borings penetrating the sediment. 3, 5, enlargements of vertical section showing aligned horizontal processes and short vertical pillars. 4, 6, enlargements of transverse thin sections showing the uniform dense structure of the arrangement of coenosteles.

See Plate 15 for comparison with Araneosustroma, noting the more uniform structure of Densastroma. Thin sections from sample donated by Margaret Rodway, Malvern, Worcestershire.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 16

PLATE 17

Plectostroma intertextum (Nicholson,1886)

Middle Silurian, Much Wenlock Limestone Formation

Coates Quarry, Wenlock Edge, Shropshire

1–8 CAMSM X.50347.163; 1–4, vertical thin sections with increasing magnification, to show skeletal architecture of this taxon comprising long narrow pillars and short horizontal processes. 5–8, transverse thin sections showing transverse sections through pillars; the horizontal processes are rods.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 17

PLATE 18

‘Stromatopora’ venukovi Yavorsky 1929

Middle Silurian clast in Devonian Peel Sandstone

Either Whitestrand Beach or Peel Bay, north-west coast, Isle of Man

1–8 CAMSM X.50347.283; 1–4, vertical sections at increasing scale of the single available sample, showing the amalgamate skeletal architecture, with cyst plates in the galleries, consistent with this taxon described by Mori (1970) from Gotland. It is not assigned completely to a genus-level taxon, but is regarded here as a distinct low-level taxon distinct from all other taxa in this study. 5–8, transverse sections at increasing scale, of the amalgamate structure.

Numerous lined tubes in this specimen are syringoporid tabulate symbionts, common in this taxon in Upper Silurian limestones of Gotland (Mori 1970). Unlined tubes with dissepiments (3) are part of the stromatoporoid skeleton.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 18

PLATE 19

Simplexodictyon yavorskyi (Nestor, 1966)

Middle Silurian, Much Wenlock Limestone Formation

Farley Quarry, Wenlock Edge, Shropshire

1–9 NMW 99.35G.853; 1–5, vertical thin sections at increasing scale, to show skeletal architecture of this taxon comprising tripartite lamina, visible particularly in 3, 4 and 5 show variations of structure in closely located portions of the skeleton in 2; such variations are common in stromatoporoids but this is clearly within one specimen that is a single taxon. 6–9, transverse sections at increasing scale, showing the prominent pillars characteristic of this taxon.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 19

PLATE 20

Eostromatopora impexa (Nestor, 1966)

Middle Silurian, basal Elton Formation

Lea South Quarry, Wenlock Edge, Shropshire

1–4 CAMSM X.50347.57; 1, vertical section showing typical structure of this taxon. 2, transverse section showing prominent astrorhizae in this taxon. 3, 4, vertical and transverse sections respectively, showing the dense structure dominated by vertical elements but with sufficient transverse gallery space to form a layered skeletal appearance.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 20

PLATE 21

Syringostromella borealis (Nicholson, 1891)

Middle Silurian, Much Wenlock Limestone Formation

Lea South Quarry, Wenlock Edge, Shropshire

1–8 CAMSM X.50347.91. 1, 2, vertical (1) and transverse (2) views of large areas of thin sections showing the broad variation of structure across a sample. In 1 note the layering reflecting numerous growth interruptions common in stromatoporoids. 3, vertical thin section enlargement of left centre portion of 1, showing encrusting bryozoan on a growth interruption surface. 5, 7, vertical thin section enlargements, to show skeletal architecture of this taxon comprising thick verical pillars and short transverse elements. 4, 6, 8, transverse sections at increasing scales showing transverse cuts through pillars and the curved connecting elements.

In 7 and 8 the heterogenous microstructure is visible, showing what may be partial preservation of an original structure.

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 21

PLATE 22

Parallelostroma typicum (Rosen, 1867)

Middle Silurian, Much Wenlock Limestone Formation

Lea South Quarry, Wenlock Edge, Shropshire

1–8 CAMSM X.50347.77; 1–4. Vertical sections at increasing scale, showing the reticulate structure with gallery spaces and some symbiotic intergrown tubes. 5–8, transverse sections at increasing scale, showing the reticulate structure with gallery spaces and some symbiotic intergrown tubes.

In samples of this taxon in the British suite, the microstructure is not well-preserved. P. typicum is generally characterized by orthoreticulate microstructure that is not well displayed in material from Britain.

Page

Page

KERSHAW, DA SILVA & SENDINO, British Silurian stromatoporoids Plate 22