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Integrated study of the uppermost Ordovician Porkuni Stage in the Stirnas-18 core, western Latvia, has revealed one of the most complete Hirnantian successions in the eastern Baltic region. The interval is characterized by two shallowing upwards depositional sequences that correspond to the Kuldiga and Saldus formations. The whole-rock carbon stable isotope curve indicates a long rising segment of the Hirnantian carbon isotope excursion, with the highest peak in the upper part of the Kuldiga Formation. The bioclast carbon and oxygen curves fit well with the whole-rock carbon data. Micro- and macrofossil data enabled seven combined associations to be distinguished within the Hirnantian strata. The early Porkuni fauna of the Spinachitina taugourdeaui Biozone, with pre-Hirnantian affinities, is succeeded by an interval with a Hindella–Cliftonia brachiopod association, a specific polychaete fauna, the chitinozoan Conochitina scabra, and the conodont Noixodontus girardeauensis. The middle part of the Kuldiga Formation is characterized by a low-diversity Dalmanella testudinaria brachiopod association, high diversity of scolecodonts, and the occurrence of the chitinozoan Lagenochitina prussica. From the middle part of the Kuldiga Formation the youngest occurrence yet known of the conodont Amorphognathus ordovicicus is reported. Also typical of the Kuldiga Formation is the occurrence of the trilobite Mucronaspis mucronata. The uppermost Hirnantian Saldus Formation contains no shelly fauna, but yields redeposited conodonts and at least partly indigenous chitinozoans and scolecodonts. Palaeontological criteria and stable isotope data enable correlation of the Stirnas section with other Hirnantian successions in the Baltic region and elsewhere.

The trilobite order Proetida forms a minor but important faunal element within the Ordovician strata of Baltoscandia. This review follows the current systematic, taxonomic, and stratigraphical usage and discusses the distribution of these trilobites within the context of the Confacies Belt model. A database of species-level information was derived from numerous publications relating to the Scandinavian and Baltic states and relevant neighbouring regions. Important additional information on stratigraphical occurrences of genera has been derived from glacial erratic boulders (geschiebe) from northern Germany and adjacent areas. The representatives from Baltoscandia of three superfamilies, Bathyuroidea, Aulacopleuroidea, and Proetoidea, are listed. The genus level was chosen as the most practicable to plot on the maps, one showing the time interval for the Kukruse Regional Stage (or Global Stage Slice Sa1), the other that for the Pirgu and Porkuni stages (or stage slices Ka4 and Hi1–Hi2). These intervals each show a diversity peak within the ranges of about 30 genera of Proetida and over 70 species from the Ordovician successions of Baltoscandia. Out of these a total of nine genera cross the Ordovician–Silurian boundary.The regional comparisons from within Baltoscandia show differences in facies dependency of certain genera, with possibly also a latitudinal component. During the late Ordovician the faunal resemblance appears to be closest to the neighbouring palaeocontinent Avalonia, suggesting a faunal exchange between or pathways to both continents from elsewhere. Besides climatic and geographical proximity of palaeocontinents, sea-level changes also have to be considered in explaining the distribution of Proetida in Baltoscandia.

The composition, diversity and distribution of various groups of organisms in the late Llandovery (Telychian) and early Wenlockian (Sheinwoodian) interval of the Pahapilli 675 and Kõrkküla 863 sections (western Estonia) were studied. Due to the small size, fragmentation and disarticulation of the specimens, the studied paleontological material could, in the major part, be tentatively considered as “biodetritus” or “bioclast material” occurring in the carbonate and siliciclastic lithologies. The recognized conodont biozonation provides a detailed stratigraphic framework for this study. The brachiopod fauna is represented by two different Dicoelosia–Skenidioides communities, comprising diverse associations of non-brachiopod fauna, whose composition changes over time. Successive associations of trilobites are based on dominating taxa among odontopleurids, encrinurids, calymenids and aulacopleurids. The distribution and taxonomic composition of Silurian echinoderms (cyclocystoids, bothriocidarid echinoids, pisocrinid crinoids) in the East Baltic area are documented for the first time. New data on bryozoans, corals, sponges and other fossils are provided, improving the knowledge of the whole biota of the open shelf and transition to basinal environments. The distribution of faunas is affected by different changes in the ecosystem. The highest diversity was recorded in the Upper Pterospathodus a. amorphognathoides Conodont Zone, before the main faunal turnover caused by the Ireviken Event, which was associated with rapid sea-level fall and climate changes. The faunal recovery started at the early Wenlockian in the second half of the Ireviken Event, above the base of the Lower Kockelella ranuliformis Conodont Zone. [ABSTRACT FROM AUTHOR]

Trace fossils of the ichnogenera Cruziana and Rusophycus are described for the first time from the Lower Ordovician of Baltica. These specimens were found from the upper Tremadocian−lower Floian glauconite sandstone of the Leetse Formation in the Leetse and Uuga cliffs on the Pakri Peninsula, North-West Estonia. The one from the Leetse locality was collected already in the 19th century but was hidden in museum collections. On this piece of rock, together with the Rusophycus, brachiopods Leptembolon lingulaeformis and Thysanotos siluricus occur. They indicate that the sample comes from the strata corresponding to the Thysanotossiluricus Brachiopod Biozone of the Hunneberg Stage. Different lithology of the two newly discovered loose slabs with trace fossils found under the Uuga cliff indicates that, most probably, they originate from different levels of the glauconite sandstone exposed in this section. One of them is heavily pyritized and yields a contact surface with the underlying beige argillite of the Varangu Stage with fragments of the graptolite Kiearograptus supremus and some undescribed acrotretid and other linguloid brachiopods. The second, less strongly lithified slab contains abundant fine debris of thin-shelled unidentifiable linguloid brachiopods and probably comes from a higher level. Earlier studies of conodonts revealed that the Prioniodus elegans Conodont Zone is missing in the Uuga section, thus narrowing down the possible interval of origin of these ichnotaxa to the Paroistodus proteus zone. Interestingly, these two slabs preserve the dissimilar pattern of grouping and orientation of the multiple Rusophycus/Cruziana traces giving some idea about the ethology of trilobites who probably left these traces. The earliest trilobites in the Ordovician succession of Estonia are recorded from the Mäeküla Member, the uppermost part of the Leetse Formation, from an interval where calcareous component first appears in the sediment and thus also the trilobites with their calcitic exoskeleton are preserved. The only trilobites recorded from the Mäeküla Member of the Leetse Formation in these two localities are specimens of Paramegistaspisleuchtenbergi who could have been the trace maker with its macropygidium being of similar size to its cephalon if the second slab would come from the same interval. However, there are more candidates, mainly isoteline trilobites with similar characteristics which are preserved in older but calcareous succession in Sweden and Norway. [ABSTRACT FROM AUTHOR]

Baltica except for Baltoscandia was subject to an early Tremadocian immigration of trilobites similar to that on other plates. In Baltoscandia the Olenid biofacies lingered on until it was replaced by the late Tremadocian Ceratopyge biofacies. For the rest of the time (Floian to mid-Darriwilian), Baltoscandia had fairly monotonous lithologies and faunas, constituting a single Asaphid biofacies with lateral variations expressed as differences largely in the relative abundance of species. In the South Urals immigration started in the earliest Tremadocian with fairly rich deep-water faunas. A poorer fauna is known from the Polar Urals. A slightly younger, sparse fauna is known from Paj-Khoj. Over most of the Ural border north of the South Urals there was a further development of first a Ceratopyge biofacies, then an eastern Asaphid biofacies, together with more siliciclastic input to the lithofacies and with fewer asaphids than in Baltoscandia. In the South Urals there was a development in the Darriwilian of a Cheirurid biofacies following the Ceratopyge biofacies. By contrast, the shelf part of the South China Plate shows a development of fifteen biofacies distinguished on the genus level, and the number of species for each biofacies is notably small. The major difference in the pattern of distribution of the biofacies probably reflects the faunal development in rather different climatic conditions, suggesting that the Yangtze block is supposedly positioned rather distant from Baltica, but still close enough to share genera inhabiting the outer shelf. [ABSTRACT FROM AUTHOR]

The lower boundary of the Second Stage of the Lower Ordovician Series, the Floian Stage, is defined by the first appearance of the graptolite Tetragraptus approximatus. In the stratotype section of Diabasbrottet at Hunneberg, southern Sweden, the boundary falls within the Megistaspis planilimbata trilobite Zone and within the Oelandodus elongatus-Acodus deltatus deltatus conodont Subzone of the Paroistodus proteus Zone, and within the Hunneberg Regional Stage. Graptolites, including the index species T. approximatus, are missing in the terrigenous sediment of Estonia. The earliest trilobites are poorly preserved in this terrigenous succession. They represent an interval older than the Megalaspides dalecarlicus Zone but probably younger than the M. planilimbata Zone, and are correlative to the Prioniodus elegans conodont Zone. Thus the lower boundary of the Second Stage can be detected using mainly conodonts. In accordance with conodont occurrence, the base of the Floian (i.e. somewhat higher than the base of the O. elongatus-A. d. deltatus Subzone) falls within the Joa Member of the Leetse Formation. Probable levels have been suggested in some localities. Thus the lower part of the Leetse Formation belongs to the Tremadoc Stage, and to the Hunneberg Regional Stage. [ABSTRACT FROM AUTHOR]

The brachiopod Hirnantia sagittifera (M.Coy) and trilobite morphs of the genus Mucronaspis from the topmost Ordovician Porkuni Stage of the central East Baltic are described and compared with those from the Hirnantian Stage of other regions. These important Hirnantian taxa occur in the Livonian Tongue of the Central Baltoscandian Facies Belt of the Baltic Basin, where the Porkuni Stage is represented by the non-graptolitic Kuldiga and Saldus formations. Hirnantia sagittifera appears in the lowermost part of the Porkuni Stage and is rather widely distributed in the basin in spite of its rare finds in each locality. Our study of trilobites of the genus Mucronaspis has enabled us to observe morphological changes in its exoskeleton in time and to identify a succession of five morphotypes (morphs). In some characteristics these morphs are similar to those of different alleged species of the genus Mucronaspis (M. olini, M. danai, M. ganabina, M. mucronata) but they cannot be definitely assigned to any of these species due to some variances. However, here for the first time a stratigraphically ordered collection is presented, which deserves attention in revising the taxonomy of highly variable Mucronaspis. The described brachiopods and trilobites occur mainly in the strata correlated with the Normalograptus extraordinarius graptolite Biozone. However, the uppermost finds of both taxa come from strata correlated with the N. persculptus Biozone. [ABSTRACT FROM AUTHOR]

The earliest known representative of the subfamily Encrinurinae, Encrinuroides regularis sp. nov., is described from the glauconitic sandstone of the Mäeküla Member, Billingen Stage (Arenig), from localities in the Baltic-Ladoga Clint area. Cybele (subfamily Cybelinae) has its earliest appearance at about the same level, but at different localities, probably indicating their facies dependence. The predominant developing area of the pygidial axis and the general array of spines on the exoskeleton serve to distinguish the Encrinurinae and Cybelinae, but resolve the Staurocephalidae and Dindymeninae within the Encrinuridae. A reassessment of Encrinuroides and the genera recently excluded from it ( Frencrinuroides, Physemataspis and Walencrinuroides) sustains the utility of an Encrinuroides sensu lato grouping and endorses Strusz's evolutionary lineages. Encrinuroides uncatus Evitt and Tripp, E. neuter Evitt and Tripp and probably Encrinuroides lapworthi Tripp belong in Erratencrinurus Krueger. [ABSTRACT FROM AUTHOR]