Late Ordovician Faunal Distribution and Ecospace Partitioning in Marine Impact Craters : The Aftermath of the Lockne and Tvären Events

In the Middle to Late Ordovician a boost of marine biodiversity occurred which is regarded as the most rapid diversity in Earth’s history, and termed the Great Ordovician Biodiversification Event. This time is also unique in that at least four marine meteorite craters with a good record of post-impact sediments are preserved in Baltoscandia. Catastrophic impacts can serve as constructive events and produce wide-ranging environments providing new ecological niches for a diverse biota to occupy. Additionally, they generate distinctive patterns of biological destruction and recovery. This, and the study of distribution and ecospace utilisation of Late Ordovician faunas, has been analysed in two almost contemporary (around 455 million years ago) meteorite craters (Lockne and Tvären, Sweden). Within the confined space of the impact craters environments varied from shallow and reef-like to over 200 m in depth and from well oxygenated to hypoxic. These types of environments favored colonization of different individual groups. In Tvären rhynchonelliformean brachiopod assemblages from the shallow crater rim include a range of morphotypes, not established elsewhere in the crater. Within the crater depression rhynchonelliformean brachiopods were not established until the upper third of the remaining crater fill. Colonization of post-impact faunas varies dependent on topography, depth and susbstrate within the impact craters. This is recognised for scolecodonts in Tvären and for gastropod-like mollusks, linguliform and craniiform brachiopods in both of the craters, as they inhabit a wide range of ecospace. A succession of different taxa is observed from the deepest part of each crater and upwards towards inferably more shallow, higher energy, water settings. The development of new community types and narrowly-defined niches in the craters helped further drive both α and β biodiversity during a critical phase of the Great Ordovician Biodiversification Event

Late Ordovician Faunal Distribution and Ecospace Partitioning in Marine Impact Craters : The Aftermath of the Lockne and Tvären Events

In the Middle to Late Ordovician a boost of marine biodiversity occurred which is regarded as the most rapid diversity in Earth’s history, and termed the Great Ordovician Biodiversification Event. This time is also unique in that at least four marine meteorite craters with a good record of post-impact sediments are preserved in Baltoscandia. Catastrophic impacts can serve as constructive events and produce wide-ranging environments providing new ecological niches for a diverse biota to occupy. Additionally, they generate distinctive patterns of biological destruction and recovery. This, and the study of distribution and ecospace utilisation of Late Ordovician faunas, has been analysed in two almost contemporary (around 455 million years ago) meteorite craters (Lockne and Tvären, Sweden). Within the confined space of the impact craters environments varied from shallow and reef-like to over 200 m in depth and from well oxygenated to hypoxic. These types of environments favored colonization of different individual groups. In Tvären rhynchonelliformean brachiopod assemblages from the shallow crater rim include a range of morphotypes, not established elsewhere in the crater. Within the crater depression rhynchonelliformean brachiopods were not established until the upper third of the remaining crater fill. Colonization of post-impact faunas varies dependent on topography, depth and susbstrate within the impact craters. This is recognised for scolecodonts in Tvären and for gastropod-like mollusks, linguliform and craniiform brachiopods in both of the craters, as they inhabit a wide range of ecospace. A succession of different taxa is observed from the deepest part of each crater and upwards towards inferably more shallow, higher energy, water settings. The development of new community types and narrowly-defined niches in the craters helped further drive both α and β biodiversity during a critical phase of the Great Ordovician Biodiversification Event

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

The Siljan Meteorite Crater in central Sweden – an integral of the Swedish Deep Drilling Program (SDDP)

New drill cores from the largest known impactstructure in Europe, the Siljan crater, provide superbpossibilities to reconstruct Early Palaeozoic marineenvironments and ecosystems, and to document changes insedimentary facies, sea-level and palaeoclimate. Themeteorite crater is a major target of the project ConcentricImpact Structures in the Palaeozoic (CISP) in theframework of the Swedish Deep Drilling Program.Studies of Ordovician and Silurian strata in the SiljanDistrict have a long tradition and many scientific papersdeal with the geology of the area. The Palaeozoicsuccession starts with the Tremadocian Obolusconglomerate, the youngest pre-Caledonian strata areMiddle Silurian shales of the Nederberga Formation.However, exposures are limited, there are few continoussections, and the Early Palaeozoic sedimentary rocksresting on the Precambrian basement are incompletelyinvestigated.Detailed sedimentological and biostratigraphicalstudies of the cores and the Nittsjö trench together withanalysis of the carbon isotope chemostratigraphy will allowintra- and intercontinental correlations and the dating ofCaledonian movements. Our preliminary studies show thatdifferent and yet undefined facies belts are preserved in theSiljan District. The recent findings of palaeokarst in thearea together with similar new findings in other parts ofBaltoscandia reflect times of subaerial exposure of thebasin regionally and challange the idea that theBaltoscandian basin was a deep and tranquil depositionalenvironment.Our preliminary data provide a first base forreinterpretations of this part of Sweden, previouslyregarded as representing a stable cratonic area unaffectedby the Caledonian collision between Baltica and Laurentia.The erosional unconformity and the substantial hiatusbetween Middle Ordovician limestones and late EarlySilurian shales in the western part of the crater suggests anextended period of uplift and erosion presumably related toflexural forebulge migration toward the east due to tectonicloading by the Caledonian nappes to the west. The Lowerto Middle Ordovician carbonate succession is only about21 m thick, with a sharp flooding surface on top of theMid-Ordovician Holen Formation. The overlyingsiliciclastic succession (Upper Llandovery, based ongraptolite data) comprises a minimum thickness of about224 m. The sudden deepening after the eastward migrationof the forebulge is indicated by rapid deposition of shalesand shale/mudstones displaying unstable conditionsexpressed by megaslumps, debris flows, turbidites andseveral synsedimentary tectonic features. The intercalationof a sandstone unit reflects a strong regression in this shalebasin followed by rapid transgression and deposition ofdark, organic-rich shale and mudstone.In contrast to this development, a classicalOrdovician/Silurian carbonate/shale succession, well103 IODP/ICDP Kolloquium Kiel, 07. – 09.03.2012Figure 6: Bathymetry map of Lake Ohrid. Proposed sites aremarked by the red dots.Figure 5: Multichannel seismic line crossing the DEEP-Site inthe central basin of Lake Ohrid.known from other parts of Sweden, formed in the northern(Skattungbyn-Kallholn), northeastern (Furudal), andsoutheastern part (Boda) of the Siljan District. Detailedsampling of the cores for stable isotopes, thermal maturity,geochemistry, sediment provenance, facies and microfaciesstudies in the autumn of 2011 now helps in solvingregional problems as well as stratigraphical andpalaeogeographical questions.CISP - Concentric Impact Structures of the Palaeozoi

The Siljan Impact Structure – an important integral for reconstructing the early Palaeozoic history of Baltoscandia

CISP Concentric Impact structures of the Palaeozoi

The Siljan Meteorite Crater in central Sweden – an integral of the Swedish Deep Drilling Program (SDDP)

New drill cores from the largest known impactstructure in Europe, the Siljan crater, provide superbpossibilities to reconstruct Early Palaeozoic marineenvironments and ecosystems, and to document changes insedimentary facies, sea-level and palaeoclimate. Themeteorite crater is a major target of the project ConcentricImpact Structures in the Palaeozoic (CISP) in theframework of the Swedish Deep Drilling Program.Studies of Ordovician and Silurian strata in the SiljanDistrict have a long tradition and many scientific papersdeal with the geology of the area. The Palaeozoicsuccession starts with the Tremadocian Obolusconglomerate, the youngest pre-Caledonian strata areMiddle Silurian shales of the Nederberga Formation.However, exposures are limited, there are few continoussections, and the Early Palaeozoic sedimentary rocksresting on the Precambrian basement are incompletelyinvestigated.Detailed sedimentological and biostratigraphicalstudies of the cores and the Nittsjö trench together withanalysis of the carbon isotope chemostratigraphy will allowintra- and intercontinental correlations and the dating ofCaledonian movements. Our preliminary studies show thatdifferent and yet undefined facies belts are preserved in theSiljan District. The recent findings of palaeokarst in thearea together with similar new findings in other parts ofBaltoscandia reflect times of subaerial exposure of thebasin regionally and challange the idea that theBaltoscandian basin was a deep and tranquil depositionalenvironment.Our preliminary data provide a first base forreinterpretations of this part of Sweden, previouslyregarded as representing a stable cratonic area unaffectedby the Caledonian collision between Baltica and Laurentia.The erosional unconformity and the substantial hiatusbetween Middle Ordovician limestones and late EarlySilurian shales in the western part of the crater suggests anextended period of uplift and erosion presumably related toflexural forebulge migration toward the east due to tectonicloading by the Caledonian nappes to the west. The Lowerto Middle Ordovician carbonate succession is only about21 m thick, with a sharp flooding surface on top of theMid-Ordovician Holen Formation. The overlyingsiliciclastic succession (Upper Llandovery, based ongraptolite data) comprises a minimum thickness of about224 m. The sudden deepening after the eastward migrationof the forebulge is indicated by rapid deposition of shalesand shale/mudstones displaying unstable conditionsexpressed by megaslumps, debris flows, turbidites andseveral synsedimentary tectonic features. The intercalationof a sandstone unit reflects a strong regression in this shalebasin followed by rapid transgression and deposition ofdark, organic-rich shale and mudstone.In contrast to this development, a classicalOrdovician/Silurian carbonate/shale succession, well103 IODP/ICDP Kolloquium Kiel, 07. – 09.03.2012Figure 6: Bathymetry map of Lake Ohrid. Proposed sites aremarked by the red dots.Figure 5: Multichannel seismic line crossing the DEEP-Site inthe central basin of Lake Ohrid.known from other parts of Sweden, formed in the northern(Skattungbyn-Kallholn), northeastern (Furudal), andsoutheastern part (Boda) of the Siljan District. Detailedsampling of the cores for stable isotopes, thermal maturity,geochemistry, sediment provenance, facies and microfaciesstudies in the autumn of 2011 now helps in solvingregional problems as well as stratigraphical andpalaeogeographical questions.CISP - Concentric Impact Structures of the Palaeozoi

The Siljan Impact Structure – an important integral for reconstructing the early Palaeozoic history of Baltoscandia

CISP Concentric Impact structures of the Palaeozoi

The Siljan Meteorite Crater in central Sweden – an integral of the Swedish Deep Drilling Program (SDDP)

New drill cores from the largest known impactstructure in Europe, the Siljan crater, provide superbpossibilities to reconstruct Early Palaeozoic marineenvironments and ecosystems, and to document changes insedimentary facies, sea-level and palaeoclimate. Themeteorite crater is a major target of the project ConcentricImpact Structures in the Palaeozoic (CISP) in theframework of the Swedish Deep Drilling Program.Studies of Ordovician and Silurian strata in the SiljanDistrict have a long tradition and many scientific papersdeal with the geology of the area. The Palaeozoicsuccession starts with the Tremadocian Obolusconglomerate, the youngest pre-Caledonian strata areMiddle Silurian shales of the Nederberga Formation.However, exposures are limited, there are few continoussections, and the Early Palaeozoic sedimentary rocksresting on the Precambrian basement are incompletelyinvestigated.Detailed sedimentological and biostratigraphicalstudies of the cores and the Nittsjö trench together withanalysis of the carbon isotope chemostratigraphy will allowintra- and intercontinental correlations and the dating ofCaledonian movements. Our preliminary studies show thatdifferent and yet undefined facies belts are preserved in theSiljan District. The recent findings of palaeokarst in thearea together with similar new findings in other parts ofBaltoscandia reflect times of subaerial exposure of thebasin regionally and challange the idea that theBaltoscandian basin was a deep and tranquil depositionalenvironment.Our preliminary data provide a first base forreinterpretations of this part of Sweden, previouslyregarded as representing a stable cratonic area unaffectedby the Caledonian collision between Baltica and Laurentia.The erosional unconformity and the substantial hiatusbetween Middle Ordovician limestones and late EarlySilurian shales in the western part of the crater suggests anextended period of uplift and erosion presumably related toflexural forebulge migration toward the east due to tectonicloading by the Caledonian nappes to the west. The Lowerto Middle Ordovician carbonate succession is only about21 m thick, with a sharp flooding surface on top of theMid-Ordovician Holen Formation. The overlyingsiliciclastic succession (Upper Llandovery, based ongraptolite data) comprises a minimum thickness of about224 m. The sudden deepening after the eastward migrationof the forebulge is indicated by rapid deposition of shalesand shale/mudstones displaying unstable conditionsexpressed by megaslumps, debris flows, turbidites andseveral synsedimentary tectonic features. The intercalationof a sandstone unit reflects a strong regression in this shalebasin followed by rapid transgression and deposition ofdark, organic-rich shale and mudstone.In contrast to this development, a classicalOrdovician/Silurian carbonate/shale succession, well103 IODP/ICDP Kolloquium Kiel, 07. – 09.03.2012Figure 6: Bathymetry map of Lake Ohrid. Proposed sites aremarked by the red dots.Figure 5: Multichannel seismic line crossing the DEEP-Site inthe central basin of Lake Ohrid.known from other parts of Sweden, formed in the northern(Skattungbyn-Kallholn), northeastern (Furudal), andsoutheastern part (Boda) of the Siljan District. Detailedsampling of the cores for stable isotopes, thermal maturity,geochemistry, sediment provenance, facies and microfaciesstudies in the autumn of 2011 now helps in solvingregional problems as well as stratigraphical andpalaeogeographical questions.CISP - Concentric Impact Structures of the Palaeozoi

Terminal Ordovician stratigraphy of the Siljan district, Sweden

<div><p>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 <i>Metabolograptus persculptus</i> Biozone, at or close to the <i>Hindella</i> beds in the Upper Boda Member. The late Katian (Pirgu) age of <i>Holorhynchus</i> in the Siljan district is clear and its co-occurrence with the chitinozoan <i>Belonechitina gamachiana</i> in Estonia supports a Katian age for this zone. The base of the <i>Ozarkodina hassi</i> 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 <i>M. persculptus</i> Biozone. The <i>Hirnantia</i>–<i>Dalmanitina</i> 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 ( = <i>extraordinarius</i>) and a younger ( = <i>persculptus</i>) fauna.</p></div