Boda Limestone Research Articles

On Paleozoic platycerate gastropods

The platycerate gastropods Orthonychia yutaroi Ebbestad, sp. nov. (Ordovician, Boda Limestone, Sweden), O. enorme (Silurian, Sweden, Gotland), O. parva (Pennsylvanian, Finis Shale Member, USA), and Orthonychia sp. (Mississippian, Imo Formation, USA) are studied including their protoconch morphology. Orthonychia yutaroi is the oldest known species in Orthonychia. Platycerates contain species with both, openly and tightly coiled protoconchs. This is the first report that tightly coiled protoconchs occur in Orthonychia. This and previously published observations blur the diagnostic difference between orders Cyrtoneritimorpha (openly coiled protoconch) and Cycloneritimorpha (tightly coiled protoconch). We suggest to treat Cyrtoneritimorpha and Cycloneritimorpha as synonyms of Neritimorpha. The monotypic Devonian genus Pragoserpulina is morphological so close to the Orthonychia species reported herein that synonymy of both genera seems to be possible (and thus of the families Pragoserpulinidae and Orthonychiidae). Protoconch morphology and dimensions suggest that the studied platycerate species had planktotrophic larval development. By contrast, two studied Carboniferous euomphaloid species (one with an openly and the other with tightly coiled protoconch) have paucispiral, large protoconchs indicating non-planktotrophic larval development. We assume that openly and tightly coiled protoconchs were present in various Paleozoic gastropod clades and that selection acted against the openly coiled protoconch morphology. It has previously been proposed that increasing predation pressure in the plankton was the reason for the demise of openly coiled protoconchs (Paleozoic plankton revolution). The presence of larval planktotrophy in platycerates excludes the possibility that they belong to extant basal gastropod clades such as Patellogastropoda, Cocculiniformia, and Vetigastropoda. However, a previously proposed close relationship to Neritimorpha is corroborated.

Thermal Decrepitation and Thermally-Induced Cracking of Limestone Used in Quicklime Production

To produce quicklime, high calcium carbonate rocks, including limestone, are burned in industrial kilns at 1100–1450 °C. As a consequence of the high temperatures, the carbonate rock can break and decrepitate into fine material, causing operational problems and material losses. In the present paper, an industrial case study on thermal decrepitation was performed on Boda Limestone from the Jutjärn quarry in Dalarna, Sweden. We analyzed 80 limestone samples for thermal decrepitation; furthermore, the correlation with chemical composition was statistically analyzed. The experiments were complemented by a detailed analysis of thermally-induced cracking at a range of temperatures (ambient, 500 °C, 800 °C, and 1150 °C) for two limestone samples with similar chemical compositions but with very different decrepitation behaviors. Decrepitation was analyzed by an in-house method, the chemical composition by XRF, and the thermally-induced cracking was investigated by SEM and image analysis. No strong correlation was found between thermal decrepitation and the chemical composition of the limestone. For the sample with low thermal decrepitation, a dense narrow network of fractures was found after full calcination; however, this network was not observed in the sample with high thermal decrepitation. A plausible explanation for the different decrepitation behaviors is that this fracture network releases internal stress and stabilizes the calcined rock. The obtained results can help in predicting limestone thermal decrepitation, enabling increased resource efficiency in quicklime production.

A new large mound dwelling chiton (Mollusca), from the Late Ordovician Boda Limestone of central Sweden

ABSTRACT A new rare Upper Ordovician mound dwelling palaeoloricate chiton is described as Crassaplax collicola gen. et sp. nov. from three large isolated intermediate valves from the Katian carbonate mud mounds of the Boda Limestone in the Siljan district of central Sweden. Together with the previously known Spicuchelodes? sp., also from the Boda Limestone, these are the only known Late Ordovician mound dwellers so far among the palaeoloricates, adding to Ordovician environments with reported chiton remains. Crassaplax collicola is distinguished from other Ordovician palaeoloricate chitons by their thick and large valves that can be 2 cm in length, and especially the clear differentiation between the lateral and central valve areas.

The cephalopods of the Kullsberg Limestone Formation, Upper Ordovician, central Sweden and the effects of reef diversification on cephalopod diversity

The cephalopods collected from the mud mounds of the Kullsberg Limestone Formation, late Sandbian–earliest Katian(?), south central Sweden, are highly diverse and comprise 26 identifiable species of 12 families and six orders in a sample of c. 180 specimens. The assemblage is strongly dominated by orthocerids in abundance and diversity. In contrast, the time-equivalent assemblage of the reef limestone of the Vasalemma Formation of Estonia is dominated by actinocerids and less diverse. Only one-third of the species co-occur in these two palaeogeographically relatively close assemblages. The taxonomic composition of the Kullsberg assemblage is, on the order level, more similar to that of the late Katian–early Hirnantian Boda Limestone Formation of south central Sweden, which represents a similar relatively deep depositional environment. The high local differentiation of cephalopod reef faunas exemplifies the importance of the emergent Baltic reef habitats in diversification processes during the early Late Ordovician. Of the described taxa, the following are new: Beloitoceras thorslundi sp. nov., Cameroceras motsognir sp. nov., Clothoceras thornquisti gen. et sp. nov., Danoceras skalbergensis sp. nov., Discoceras amtjaernense sp. nov., D. nilssoni sp. nov., Endoceras naekki sp. nov., Furudaloceras tomtei gen. et sp. nov., Isbergoceras consobrinum gen. et sp. nov., I. niger gen. et sp. nov., Isorthoceras nikwis sp. nov., I. sylphide sp. nov., I. urdr sp. nov., I. verdandi sp. nov., Kullsbergoceras nissei gen. et sp. nov., Ordogeisonoceras uppsalaensis sp. nov. and Valkyrioceras dalecarlia gen et sp. nov.http://zoobank.org/urn:lsid:zoobank.org:pub:F5243F9B-547C-424F-895F-6CCECA8BBF11

Integrated graptolite-conodont biostratigraphy and organic carbon chemostratigraphy of the Llandovery of Kallholn quarry, Dalarna, Sweden

A revised graptolite and conodont biostratigraphy together with new organic carbon isotope data for the middle Aeronian to lower Telychian (Llandovery, lower Silurian) of Kallholn quarry, central Sweden, are presented. The base of the section is marked by an unconformity between the Ordovician Boda Limestone and Aeronian shales with limestone nodules belonging to the Pribylograptus leptotheca Biozone. These are overlain by strata assigned to the lower Lituigraptus convolutus Biozone. The Stimulograptus sedgwickii Biozone, previously recorded from the section, is absent and marked by an unconformity which is overlain by radiolarian-rich graptolitic shales belonging to the Stimulograptus halli Biozone. The overlying Telychian strata are assigned to the Spirograptus guerichi, Spirograptus turriculatus and Streptograptus crispus biozones. Conodonts indicate that the boundary between the Distomodus staurognathoides Biozone and Pterospathodus eopennatus Superzone lies within the Sp. turriculatus Biozone, as it does also in the Ohesaare core, Estonia. The δ13Corg record shows mostly minor fluctuations but with a distinct twin-peaked positive excursion in the upper Sp. turriculatus Biozone, close to the boundary with the overlying Streptograptus crispus Biozone. The excursion in the Kallholn section may correlate with the earliest positive shift in δ13C values at the onset of the excursion associated with the Valgu Event or it may represent a new excursion (provisionally named the Kallholn excursion) preceding this. Many more bentonites (36) occur in the section than previously recorded – geochemical studies are needed to confirm whether the Osmundsberg bentonite (which may or may not be equivalent to the “O” bed in Estonia and Latvia) is present.

Accretionary Mechanisms and Temporal Sequence of Formation of the Boda Limestone Mud-Mounds (Upper Ordovician), Siljan District, Sweden

Abstract Late Ordovician mud-mounds in the Boda Limestone, Siljan area, central Sweden, consist mainly of massive spiculitic stromatactis limestone similar to other well-known Paleozoic mud-mounds. The mound cores are predominantly formed by spiculite and ostracod-rich mudstone and/or wackestone, and networks of spar-filled syndepositional cavities. The mounds of the Boda Limestone are specific in two ways: (1) large parts of the lower mound cores are formed by a Palaeoporella framestone and/or bafflestone with signs of early recrystallization and cementation; and (2) the stromatactis facies is accompanied by masses of limestone with non-stromatactis cryptocrystalline patches. Cryptocrystalline patches are filled with massive, fibrous low-Mg calcite, have cloudy, transitional margins, contain randomly spaced skeletal grains and dolomitic micro-inclusions, and are interpreted as recrystallized patches of the original host lime mud. Models of formation of Paleozoic mud-mounds generally hypothesize accretionary processes that are based on sponge biomass degradation and associated diagenetic processes. In the Boda Limestone Palaeoporella skeleton disintegration, early recrystallization, and additionally, cementation were essential for the mound formation. The Boda mounds exemplify that formation of Paleozoic mud-mounds reflects a spectrum of different essentially diagenetic accretionary mechanisms. This diversity should be taken into account in future discussions about Paleozoic mud-mound formation. The new name Osmundsberget Formation is given for a Hirnantian succession of brachiopod-rich limestone above the Boda Limestone. The Osmundsberget Formation occurs only in direct geographical vicinity to the mud-mounds.

Terminal Ordovician stratigraphy of the Siljan district, Sweden

Integration of new isotopic data and earlier biostratigraphic information from eight sections through the terminal Ordovician (Pirgu and Porkuni stages) of the Siljan district, Sweden, allows a more precise correlation of sections in terms of biostratigraphy and carbon isotope dating. Four levels with positive δ13C excursions are identified (from bottom) – the Moe, an unnamed excursion, Paroveja and Hirnantian Carbon Isotope Excursion (HICE). The δ13C values through the Boda Limestone are 1–2‰ higher than usual in Baltica, only the values for the HICE remains within what is expected. Background values increase from 1.5‰ in the bottom of the core of the Boda Limestone up to 3‰ in the top of it. The HICE is identified in five of eight sections and the main peak falls according to inferred correlation within the Metabolograptus persculptus Biozone, at or close to the Hindella beds in the Upper Boda Member. The late Katian (Pirgu) age of Holorhynchus in the Siljan district is clear and its co-occurrence with the chitinozoan Belonechitina gamachiana in Estonia supports a Katian age for this zone. The base of the Ozarkodina hassi Biozone may occur within units B–C of the Upper Boda Member and in the upper part of the Loka Formation and most likely is correlated with the M. persculptus Biozone. The Hirnantia–Dalmanitina faunas reported from the lowermost part of the Loka Formation and units B–D of the Upper Boda Member seem to range through all the Hirnantian, but detailed morphological studies allow to distinguish an older ( = extraordinarius) and a younger ( = persculptus) fauna.

Conodonts in the Upper Ordovician Keisley Limestone of northern England: taxonomy, biostratigraphical significance and biogeographical relationships

AbstractThe classical fauna from the Keisley Limestone, one of the first Upper Ordovician conodont faunas described from the UK, is re‐evaluated based on relatively abundant collections of well‐preserved conodont elements representing 20 multielement taxa. Common taxa are representatives of Amorphognathus duftonus, Birksfeldia circumplicata, Eocarniodus aff. E. gracilis, Hamarodus brevirameus, Scabbardella altipes, Strachanognathus parvus and several coniform species. These occur with more rare specimens of, among others, Aphelognathus nudus, Amorphognathus aff. A. ordovicicus, Dapsilodus mutatus, Icriodella prominens, Icriodella rhodesi sp. nov. and Protopanderodus liripipus. One new species is proposed, and the concepts of Birksfeldia, Gamachignathus, Icriodella and Notiodella are discussed. It is proposed that Birksfeldia is a senior synonym of Gamachignathus and Notiodella a junior synonym of Icriodella. The described Keisley species association, which represents the A. ordovicicus Zone and is of late Katian (Ka4) age, is closely similar to those of the Boda Limestone of south‐central Sweden and some other European faunas, but coeval shallow‐water faunas from eastern North America differ in several respects from these European faunas. Biostratigraphy and carbon isotope chemostratigraphy indicate that most of the Keisley Limestone is of late Katian age.

Late Ordovician Holorhynchus succession in the Siljan district, Sweden: facies, faunas and a latest Katian event

The pentameride brachiopod genus Holorhynchus is a useful tool for correlation of the upper part of the Katian Stage in the Upper Ordovician. Holorhynchus occurs in the Boda Limestone, Siljan district, Sweden, but is generally only known from taxonomic descriptions. Here, we report in detail fossil occurrences relating morphology and sedimentary facies within the context of a major faunal turnover during the latest Katian. The specimens occur exclusively within the intercalated beds of pelmicritic mudstone and fossiliferous layers, which are down-slope storm deposits. The comparison of sedimentary features between the beds with and without Holorhynchus suggests that the animal inhabited fluid conditions on a muddy substrate, such as the channel environment reconstructed herein. The geological and autecological evidence suggests that the environmental conditions on the seabed were eutrophic. The opportunist Holorhynchus rapidly explored new habitats during a time of transition.

Origin of oil and bitumen in the Late Devonian Siljan impact structure, central Sweden

Organic geochemical assessment of seep oil from the Upper Ordovician (Hirnantian) Boda Limestone and solid bitumens from the Middle Ordovician (Darriwilian) limestone formations in the Siljan Crater, Sweden indicates their generation primarily from peak oil window maturity, clay-rich marine source rocks that contained aquatic algal organic matter and were deposited in an anoxic environment. Biomarkers indicate some significant differences between the seep oil and solid bitumens and their alteration by moderate to severe biodegradation. The Solberga quarry seep oil from the Boda Limestone and Solberga-1 solid bitumen from the Skärlöv–Seby–Folkslunda Limestone equivalents do not show signs of mixing and the similarity in their biomarker distributions indicates a genetic relationship. However, solid bitumens recovered from cavities in the underlying Segerstad and Holen limestones were derived predominantly from clay-rich source rocks that contained mixed marine and lacustrine algal organic matter and minor inputs of prokaryotic organic matter, possibly from thin beds of calcareous rocks interbedded within the main clay-rich source rocks. It is inferred that the Siljan Crater seep oil and solid bitumens were generated from the organic rich Upper Ordovician Fjäcka Shale, a source rock for economic accumulation of oil in the eastern Baltic region, and/or from Silurian shale units. The presence of various compounds of known biological origin and existence of organic rich Fjäcka Shale/Silurian Shale units are consistent with the biogenic origin of Siljan Crater petroleum. Although these seep oil and solid bitumens were generated at peak oil window maturities, the intense heat generated by meteorite impact caused secondary reactions resulting in unusual distributions of maturity sensitive aromatic hydrocarbon isomers and conflicting molecular maturities.

Palaeoecology and palaeogeography of Late Ordovician (Katian–Hirnantian) cephalopods of the Boda Limestone, Siljan district, Sweden

The carbonates associated with the Late Ordovician (Katian–Hirnantian) Boda mounds of the Siljan district, Sweden, contain a rich cephalopod fauna. Cephalopods are rare in the micritic stromatactis facies of the Katian Boda Core Member, but are concentrated together with other molluscs and trilobites in synsedimentary fillings of caves and crevices of the lithified mound limestone. More than 60 cephalopod species are known from these fillings. The assemblage is dominated in richness and abundance by small orthoconic proteoceratids of the genus Isorthoceras and by curved barrandeocerids, and is considerably less endemic than the benthic fauna of the Boda mounds. Similarities are remarkable at the species level with assemblages from elsewhere in Baltica, with Avalonia and south-western Kazakhstan. A genus-level comparison reveals affinities with Laurentia. However, the genus-level similarities are interpreted as reflecting mainly similarities of the depositional environment and of physicochemical conditions. The presence of calcareous algae in the Boda Limestone and maximum hydrostatic septal strength of cephalopods indicate a depositional depth of <100 m, well within the euphotic zone. The dominance and diversity of cephalopods with vertical migrant lifestyle and the absence of actinocerids indicate a cool, nutrient-rich deeper neritic environment. The post-Katian sediments contain a drastically reduced diversity, dominated by orthocerids. The maximum hydrostatic septal strength of the Hirnantian cephalopods and sedimentological features indicate a shallowing during the Hirnantian, but a continuation of high food availability for cephalopods in the water column.

The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden

The late Katian, Late Ordovician Boda Limestone of Dalarna, Sweden contains a rich cephalopod assemblage. The assemblage consists of 61 species, of 31 genera, comprising almost all major Ordovician cephalopod orders. Most common and diverse are the Orthocerida. The Ascocerida are also remarkably comman and diverse. The new ascocerid species, Redpathoceras bullatum sp. nov., R. depressum sp. nov., R. magnum sp. nov., and Probillingsites scandinavicum sp. nov., give reason to revise current hypotheses on the origin an evolution of this group. An ascocerid origin from barrandeoceratids or aspidoceratids is hypothesised. The absence of actinocerids in the Boda Limestone is notable, and is interpreted as an indication of relatively cool or/and deep depositional environments. The dominance of orthocerids is provisionally interpreted as evidence for nutrient-rich waters during the time of the deposition of the Boda Limestone. Additionally, the assemblage contains the new barrandeocerids Schuchertoceras fryi sp. nov., Siljanoceras varians gen. et sp. nov., Warburgoceras gen. nov. (for Cyrtoceras longitudinale Angelin in Angelin &amp; Lindström, 1880), the new endocerid Cameroceras turrisoides sp. nov., the new oncocerid Cyrtorizoceras thorslundi sp. nov., and the new orthocerids Dawsonoceras stumburi sp. nov., Isorthoceras angelini sp. nov., I. curvilineatum sp. nov., Nathorstoceras adnatum gen. et sp. nov., N. kallholnense gen. et sp. nov., Palaeodawsonocerina? nicolletoides sp. nov., Pleurorthoceras osmundsbergense sp. nov., and Striatocycloceras isbergi sp. nov.

Conodont biostratigraphy, and δ13C and δ34S isotope chemostratigraphy, of the uppermost Ordovician and Lower Silurian at Osmundsberget, Dalarna, Sweden

The previously established graptolite and chitinozoan Hirnanian-Telychian biostratigraphy in the unique Osmundsberget North outcrop in the Siljan region, south-central Sweden, is integrated with new conodont biostratigraphy and δ13Corg, δ13Ccarb and δ34Spyr chemostratigraphy. At this locality, the middle Hirnantian (latest Ordovician) topmost part of the Boda Limestone is overlain by the latest Hirnantian Glisstjärn Formation, and the late Aeronian–early Telychian (Llandovery) Kallholn Formation rests unconformably on the Glisstjärn Formation. Previous conodont work showed that the Glisstjärn Formation belongs to the lower Ozarkodina hassi Zone. New samples from calcareous interbeds in the dominantly shaly Kallholn Formation, some of which contain hundreds of condont elements, yielded Distomodus staurognathoides, Aspelundia fluegeli and other taxa indicating the D. staurognathoides Zone. In the East Baltic succession, the coeval interval, which is in the uppermost Raikküla–lowermost Adavere stages just below the geographically widespread Osmundsberg K-bentonite, has yielded a conodont fauna similar to that of the lower Kallholn Formation. A regional review of the D. staurognathoides Zone shows that there are possible equivalents to our study interval also in Norway and the Welsh Borderland, but equivalent strata are missing in large parts of North America, or have not produced diagnostic conodonts. The δ13Corg values from the study section are relatively uniform (mostly ranging between − 29‰ and − 30‰), and the late Aeronian and Valgu positive excursions have not been recognized.

Biometry and lifestyle of the Ordovician proetide trilobite Cyamella stensioei Owens, 1979

Biometric analyses of the trilobite Cyamella stensioei Owens, 1979, from carbonate mud mounds of the Upper Ordovician Boda Limestone of central Sweden, along with a comparison of closely allied rorringtoniid taxa from outside Baltoscandia, reveal important systematic and ecological information on this proetide taxon. Biometric analysis of the cephala of C. stensioei shows a number of instars, reflecting several ontogenetic stages, and a meraspis stage of this taxon is figured for the first time. C. stensioei is exclusively found in mass accumulations in the former, open cavities of the carbonate mud mound and was therefore most likely a cavity-dweller, possibly adapted to this lifestyle through chemosymbiosis. Some of the cavities are interpreted as former seepage conduits. Comparison of C. stensioei with other rorringtoniid trilobites suggests possible ancestors occurring in South China and Sibumasu terranes, determined earlier as Decoroproetus sp. and Cyamella sp., all differing from the genus Paracyamella, which is reassessed here. In wider terms of ancestry, they originate from Baltica or Laurentia, where the first rorringtoniids are known from the middle Darriwilian.

Mass concentration of Hirnantian cephalopods from the Siljan District, Sweden; taxonomy, palaeoecology and palaeobiogeographic relationships

The Hirnantian Glisstjärn Formation (&lt;i&gt;Normalograptus persculptus graptolite&lt;/i&gt; Biozone) is a succession of limestones and shales onlapping the Katian Boda Limestone in the Siljan District, Sweden. It contains a conspicuous, up to several decimeter thick bed densely packed with bipolarly oriented, orthoconic cephalopod conchs that can reach lengths of more than 120 cm. Conch fragmentation, bioereosion and the generally poor preservation of the conchs indicate time averaging and the conchs are tentatively interpreted as beached, and a result of winnowing. Ten nautiloid species were collected from the Glisstjärn Formation of which five are new: &lt;i&gt;Dawsonoceras gregarium&lt;/i&gt; n. sp., &lt;i&gt;Discoceras siljanense&lt;/i&gt; n. sp., &lt;i&gt;Isorthoceras dalecarlense&lt;/i&gt; n. sp., &lt;i&gt;Retizitteloceras rarum&lt;/i&gt; gen. et sp. n., and &lt;i&gt;Transorthoceras osmundsbergense&lt;/i&gt; gen. et sp. n. The non-endemic taxa in most cases are known from elsewhere in Baltoscandia, except one species which is known from Siberia, and North America respectively. Proteocerid orthoceridans dominate the association, of which &lt;i&gt;T. osmundsbergense&lt;/i&gt; is the predominant species. Oncocerids are diverse but together with tarphycerids very rare. Notable is the lack of many higher taxa, that are typical for other Late Ordovician shallow water depositional settings. Based on the taxonomical composition of the cephalopod mass occurrence it is interpreted as an indicator of eutrophication of the water masses in the area. &lt;br&gt;&lt;br&gt; doi:&lt;a href="http://dx.doi.org/10.1002/mmng.201000014" target="_blank"&gt;10.1002/mmng.201000014&lt;/a&gt;

Mass concentration of Hirnantian cephalopods from the Siljan District, Sweden; taxonomy, palaeoecology and palaeobiogeographic relationships

The Hirnantian Glisstjärn Formation (Normalograptus persculptus graptolite Biozone) is a succession of limestones and shales onlapping the Katian Boda Limestone in the Siljan District, Sweden. It contains a conspicuous, up to several decimeter thick bed densely packed with bipolarly oriented, orthoconic cephalopod conchs that can reach lengths of more than 120 cm. Conch fragmentation, bioereosion and the generally poor preservation of the conchs indicate time averaging and the conchs are tentatively interpreted as beached, and a result of winnowing. Ten nautiloid species were collected from the Glisstjärn Formation of which five are new: Dawsonoceras gregarium n. sp., Discoceras siljanense n. sp., Isorthoceras dalecarlense n. sp., Retizitteloceras rarum gen. et sp. n., and Transorthoceras osmundsbergense gen. et sp. n. The non-endemic taxa in most cases are known from elsewhere in Baltoscandia, except one species which is known from Siberia, and North America respectively. Proteocerid orthoceridans dominate the association, of which T. osmundsbergense is the predominant species. Oncocerids are diverse but together with tarphycerids very rare. Notable is the lack of many higher taxa, that are typical for other Late Ordovician shallow water depositional settings. Based on the taxonomical composition of the cephalopod mass occurrence it is interpreted as an indicator of eutrophication of the water masses in the area. doi:10.1002/mmng.201000014

Unravelling a Late Ordovician pentameride (Brachiopoda) hotspot from the Boda Limestone, Siljan district, central Sweden

The correlation of the uppermost Boda Core Member of the Boda Limestone is reassessed and the beds assigned to the upper Katian. This is based on the identification of the brachiopod species Brevilamnulella kjerulfi (Kiær) and Amphiplecia tardicostata Wright & Jaanusson from the highest beds in the unit. The former species is overwhelmingly abundant in the uppermost beds of the Boda Core Member in Osmundsberget quarry, forming an almost monospecific coquina. Also occurring in the coquina, is Clorilamnulella osmundsbergensis gen. et sp. nov., which ranges into the overlying Hirnantian Glisstjärn Formation. The new genus is here regarded as a transitional form between Brevilamnulella and Clorinda. The oldest occurrence of this latter genus is here revised and not found in rocks older than the Aeronian. Instead, previous Rhuddanian occurrences of ‘Clorinda’ are transferred to Clorilamnulella based on a dorsal cardinalia that differs from both that of Brevilamnulella, as well as that of Clorinda. Moreover, gigantic shells of a new species of Brevilamnulella, B. umbosulcata sp. nov, are described from the nearby Solberga quarry where the species occurs in great abundance in a local fossil pocket, that also is correlated with the upper Katian. These new virgianid and clorindoid occurrences, together with previously described occurrences of Holorhynchus and Costilamnulella, demonstrate that during the late Katian, the Boda Limestone was a virgianid hotspot crucial in the evolution of the earliest pentameroid family, the Virgianidae, as well as a possible early cradle for the evolution of the hitherto exclusively Silurian superfamily, the Clorindoidea.

Stratigraphy, carbonate facies and trilobite associations in the Hirnantian part of the Boda Limestone, Sweden

The Hirnantian (Upper Ordovician) sequence of the Boda Limestone is defined and described as a new formal Upper Boda Member. It has four petrologically distinct, bedded units containing three strikingly different trilobite faunas. These differences are thought to be caused by a sea-level lowering leading to the first Hirnantian sea-level lowstand and successive transgression as well as to shifts in sea-water chemistry. This is indicated by the occurrence of a level with botryoidal carbonate cement. On top follows the upper Hirnantian Glisstjärn Formation.

Armoured annelids and molluscs from the Upper Ordovician Boda Limestone, central Sweden

Sclerites of machaeridians (Annelida) and polyplacophorans (Mollusca) from the Upper Ordovician (Katian–Hirnantian) Boda Limestone of the Siljan district, central Sweden are described for the first time. Four taxa of machaeridians were found, but with one exception they are either known from a single isolated sclerite or only one type of sclerite. The largest taxon is represented by an inner modified sclerite of Plumulites sp. A from Osmundsberget Quarry. The complete scleritome is estimated to have reached a length of 12–15 cm. A more diverse material allows the description of Plumulites eueides sp. nov. from Kallholn Quarry. Within smaller cavities in Solberga Quarry minute sclerites of two taxa were found; Lepidocoleus sp., and Turrilepas sp. The latter record represents the third known Ordovician occurrence and the youngest from that period. Association with minute blind trilobites and concentrations of tiny articulated ostracodes suggest that these small cavities represented cryptic habitats. Two polyplacophoran sclerites are also described: one intermediate sclerite of Chelodes sp. A from Jutjärn Quarry, with only the outer surface exposed, and one intermediate sclerite of Spicuchelodes? sp. from Kallholn Quarry, with only the inner surface exposed. These represent rare examples of Ordovician chitons recorded from outside Laurentian terranes.

Isorthoceras wahlenbergi, a new Late Ordovician cephalopod from the Boda Limestone of Dalarna, Sweden

A new species of Isorthoceras (Proteoceratidae: Cephalopoda), I. wahlenbergi, is described from the Upper Ordovician Boda Limestone in Dalarna, central Sweden. The Boda Limestone consists of up to 20 isolated carbonate mounds ranging in size from a few meters to over 400 m in diameter and attaining 70 m in thickness (Jaanusson, 1982; Cocks, 2005). Each mound is divided into a micritic core facies, a pelmatozoan flank facies, and a bioclastic terminal facies (Suzuki and Bergstrom, 1999). The diverse faunas of the Boda Limestone include well documented taxonomic groups such as trilobites (e.g., Warburg, 1925; Suzuki, 2002), brachiopods (e.g., Wright, 1974, 1993; Cocks, 2005) and gastropods (e.g., Koken and Perner, 1925; Ebbestad and Peel, 1997). These faunas are suggestive of a middle Ashgillian age for these limestones. In contrast to these, taxonomic studies of cephalopods from the Boda Limestone are limited to Frye (1982, 1987), who described 18 species belonging to the orders Ascocerida, Oncocerida, Tarphycerida and Barrandeocerida.