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
The widespread growth of reefs formed by a framework of biogenic constructors and frame-lacking carbonate mounds began on Baltica during Ordovician time. Previously, Ordovician reef and mound ...development on Baltica was considered to be sporadic and local. A review of all known bioherm localities across the Baltic Basin reveals a more consistent pattern. Ordovician bioherms grew in a wide E–W-aligned belt across the Baltic Basin and occur in several places in Norway. Substantial reef development began simultaneously across the region during the late Sandbian – early Katian interval and climaxed during the late Katian Pirgu age. The current spatiotemporal distribution of bioherms is a result of interdependent factors that involve original drivers of reef development such as relative sea level, climate during the time of deposition and effects of post-depositional erosion. Oceanographic conditions were likely more favourable during times of cooler global climates, low sea level and glacial episodes. At the same time, the likelihood that bioherms are preserved from long-term erosion is higher when deposited during low sea level in deeper parts of the basin. A main factor controlling the timing of the reef and mound evolution was Baltica's shift toward palaeotropical latitudes during Late Ordovician time. The time equivalence between initial reef growth and the Guttenberg isotope carbon excursion (GICE) suggests that global climatic conditions were important.
The Great Ordovician Biodiversification Event (GOBE) involved a remarkable rise of skeletal reefs during the late Middle Ordovician. A new type of skeletal patch reef built by labechiid ...stromatoporoids is reported from the Yeongheung Formation (Darriwilian) of the Korean Peninsula, part of the eastern North China Block, a hot-spot for late Middle Ordovician diversification of early labechiids. The attachment of laminar labechiids, subordinate peloidal micritic crusts and spiculate sponges, and minor bryozoans on peloidal–intraclastic packstone to grainstone substrates, and upward growth of these organisms by repeated encrustation, resulted in the construction of centimeter-scale domal tight frame structures. These skeletal frames were in turn veneered by larger labechiids, forming sub-meter-scale laminar skeletal reefs with primary cavities. Such skeletal reefs that formed by the encrustation and binding of labechiid stromatoporoids are analogous to the bindstone frameworks of coeval Laurentian reef mounds and skeletal reefs, though they differ markedly in composition, as is apparent in the absence of tabulate corals and markedly lower contribution of bryozoans, both of which were key elements of the Chazy reefs of Laurentia. The Yeongheung reefs described herein represent some of the oldest labechiid skeletal reefs known to date, and formed mainly by the aggregation of early stromatoporoids prior to the arrival of corals and other robust constructors in the region. This discovery provides new information on the evolutionary trends of early skeletal reefs in response to the appearance of new reef-building organisms and their regional distributions during the Ordovician radiation.
•One of the oldest Middle Ordovician stromatoporoid skeletal reefs is reported from Korea.•The reef is primarily built by laminar labechiid stromatoporoid, which differs from coeval Chazy skeletal reefs composed of bryozoan-coral-stromatoporoid.•Such disparity might represent regionally variable trend of skeletal reef evolution during GOBE.
Penha Garcia Ichnological Park is the most important fossil site and one of the most significant geosites of international relevance, in the territory of Naturtejo UNESCO Global Geopark. This ...municipal protected area is a key site for the study of trace fossil diversity at high paleolatitudes in the early stages of the Great Ordovician Biodiversification Event. Most famous among 21 ichnotaxa is Cruziana, interpreted as foraging burrows of trilobites, present in high abundance and excellent preservation. They are among the largest fossils found anywhere in the Lower Paleozoic, not uncommonly several meters long and over 20 cm wide, covering large bedding planes almost completely. The birthplace of Naturtejo Geopark is now a nature school, one of the most visited outdoor sites by schools in Portugal. It also became a reference for geotourism in this country because of the Fossil Trail that allows visitors to access a natural fossil art gallery in the Variscan-folded cliffs of the Ponsul Gorge. The Fossil Home provides the interpretation of the local geoheritage, and additional attractions are the Templar castle and church viewpoints, the climbing school, the secular watermills, the views over the lake in the heart of the syncline, and the Pego river pool. This is a major geotourism destination in the center of Portugal. The in situ conservation of fossils in this ‘outside museum’ is a challenging subject, which is being monitored using 3D high-resolution modeling of the whole gorge and the main fossil sites there to an mm-scale precision.
Massive-bedded Thalassinoides ichnofacies occurs pervasively in widely separated areas on the vast Upper Ordovician carbonate platforms along the palaeoequator of Laurentia, from the Børglum River ...Formation in North Greenland, through the Red River Formation and Bighorn Dolomite of the Williston Basin (Manitoba, Canada to Wyoming, USA), to the Ely Springs Dolomite and equivalent strata of the eastern Great Basin (Utah and Nevada, USA). The Late Ordovician Thalassinoides is characterised by complex, three-dimensional, anastomosing or multi-level galleries that are consistent in size, pattern and density, with preserved depth of 1m or greater. In addition to the similar Thalassinoides burrows, the ichnofacies across the palaeocontinent also contains typical taxa of the Red River biota, such as the soccer-ball sized receptaculitid Fisherites, large-shelled, diverse and abundant nautiloids, the distinctively planispiral gastropod Maclurina, as well as diverse tabulate and rugose corals. The consistent characteristics of the Red River biofacies and Thalassinoides ichnofacies suggest a palaeogeographically homogeneous and temporally stable depositional environment along the palaeoequatorial belt of Laurentia during the pre-Hirnatian Late Ordovician. The Thalassinoides ichnofacies marked the first phase of mega-scale invasion of burrowers into relatively deep-water platform and shelf environments by successively creating a well-oxygenated deep burrow system for protection and deposit feeding. Such substrate tiering expansion constituted an important aspect of the Great Ordovician Biodiversification Event.
The “backfill” model for dolomite mottling of Thalassinoides borrows. Display omitted
► Massive-bedded Thalassinoides facies was confined to Late Ordovician palaeoequator. ► Burrow mottle was formed by dolomitization of cleaned matrix by burrowers. ► Burrow inside dolomite mottle was the remain of active tunnel of deposit feeder.
The current study presents new bed‐by‐bed brachiopod δ13C and δ18O records from Öland, Sweden, which together with previously published data from the East Baltic region, constitutes a high‐resolution ...paired brachiopod and bulk rock carbon and oxygen isotope archive through the Lower to Upper Ordovician successions of Baltoscandia. This new data set refines the temporal control on the global Ordovician δ18O‐trend considerably, improving paleoenvironmental reconstructions through the main phase of the Great Ordovician Biodiversification Event (GOBE). The new brachiopod carbon and oxygen isotope records from Öland display strong similarity with the East Baltic records, elucidating the regional consistency as well as global correlation utility of the ensuing composite Baltoscandian Lower to Middle Ordovician carbon and oxygen isotope record. The carbon isotope record from Öland indicates that the widely reported Middle Ordovician carbon cycle perturbation—MDICE (Mid‐Darriwilian Carbon Isotope Excursion)—is recorded in both brachiopods and bulk carbonates. The oxygen isotope record reveals a long‐term Lower to Upper Ordovician trend of increasingly heavier brachiopod δ18O values, with a pronounced increase during the Middle Ordovician Darriwilian Stage. We interpret this trend as dominantly reflecting a paleotemperature signal indicating progressively cooler Early to Middle Ordovician climate with glacio‐eustasy. Our Baltic δ18O values are therefore consistent with postulations that the biotic radiations during the GOBE and climatic cooling during the Darriwilian were strongly linked.
Plain Language Summary
Oxygen isotope values obtained from fossil brachiopod shells have traditionally been used as a faithful paleoclimatic proxy to shed light on temperature trends in ancient oceans. However, because brachiopod shells are susceptible to diagenetic overprint after burial, secular oxygen isotope trends derived from these fossils are often questioned—notably the farther one goes back in geological time. This study presents temporally well‐resolved oxygen isotope data from Lower–lower Upper Ordovician sedimentary rocks of Öland, Sweden, tied precisely to conodont biostratigraphy on the bed‐by‐bed scale. This interval is important in Earth history as it brackets the greatest marine biodiversification event known in the fossil record and coincides with a global climatic cooling phase (determined based on proxies other than oxygen isotopes). The current study therefore provides an excellent test of the spatial and temporal consistency of the secular Ordovician oxygen isotope trend. We find that although our data is probably affected by diagenetic modification, primary paleoclimatic signals are preserved. Furthermore, as current global Ordovician oxygen isotope records lack sufficient resolution because they comprise data from geographically widely distributed low‐paleolatitude localities, our new high‐resolution data set from one mid‐paleolatitude region, provides significant temporal insights that considerably improves our understanding of the Ordovician climate.
Key Points
New paired Baltic carbonate data set improves Ordovician 18O‐ and 13C‐record
The new data supports a Middle Ordovician sea surface temperature cooling
Regional/intra‐basinal consistency of oxygen isotope trends indicate primary nature of paleoenvironmental changes
Attribution of Ordovician climate forcing to explosive volcanism and the potential global importance of volcanism in Ordovician biodiversification suggest the necessity of evaluating the ...relationships between K-bentonite deposition and increasingly high-resolution records of marine biogeochemical change. Globally, Ordovician strata preserve an extensive record of explosive volcanism — including the widely recognized Lower to Middle Ordovician Famatina K-bentonite suite in Argentina and the Upper Ordovician Millbrig–Deicke–Kinnekulle suite of North America and Europe. Here, we present high-resolution ID-TIMS U–Pb zircon ages of K-bentonites from measured sections of the San Juan Formation (Talacasto and Cerro La Chilca section) of the Argentine Precordillera. K-bentonites from the Argentine Precordillera provide stratigraphically consistent (i.e., younging upward) ages that range from 473.45±0.70Ma to 469.53±0.62Ma, and constrain the age of a low-magnitude (2‰), globally recorded, negative carbon-isotope excursion. Evaluation of the timing of K-bentonite deposition in the Argentina Precordillera relative to marine biostratigraphic and biogeochemical records provides insight into relationships between explosive volcanism and regional to global environmental change. From a regional standpoint, these ages provide critical direct evidence for a Dapingian to earliest Darriwilian age of the upper San Juan Formation at sampled localities. These ages are consistent with carbon-isotope data suggesting that the San Juan Formation in the region of its type section is coeval with only the base of the often-correlated Table Head Group of western Newfoundland. This data thus highlights the difficulties in using regional biostratigraphic data – particularly within erosionally truncated or otherwise diachronous units – to define the timeframe of carbon-isotope chemostratigraphy. New geochronological data also indicate that a discrete negative carbon-isotope excursion within the San Juan and Table Head formations is correlative to a globally recognized pre-MDICE negative excursion, and indicates that this aspect of the marine carbon isotope record can be used as a discrete chronologic marker. San Juan Formation bentonites, however, cannot be discretely correlated with observed, environmentally significant changes in the Middle Ordovician marine geochemical records of carbon, sulfur, strontium, or sea surface temperature. These results suggest that the extent of volcanism represented by the Famatina bentonite suite was insufficient to affect global surface environments and that the relationship between explosive volcanism and environmental change may not be straightforward as previously suggested.
► We provide new, high-resolution U–Pb ages for Middle Ordovician K-bentonites. ► Data permits detailed calibration of biostratigraphic and chemostratigraphic record. ► Chronology confirms diachroneity of the uppermost San Juan Formation, Argentina. ► We report a distinct, though environmentally variable, pre-MDICE negative excursion. ► Volcanism cannot be linked to change in Earth's biological or geochemical records.
The Great Ordovician Biodiversification Event (GOBE) was a time of pronounced radiation within the Paleozoic and Modern evolutionary faunas. Despite increases in metazoan diversity during both the ...Cambrian and the Ordovician, recent geochemical evidence suggests that the Early Paleozoic may have experienced recurring deep ocean euxinia. The dynamic connections between deep ocean redox and fossil-rich shelf environments remain unclear, but one way to elucidate these relationships is to study rocks formed during the GOBE using both long-term global and short-term local redox proxies. Here we report geochemical results from the Middle Ordovician Juab Formation and Kanosh Formation at Fossil Mountain, Utah. The Kanosh Formation has been interpreted by different workers either as an anoxic restricted basin or as a well-oxygenated normal marine basin based on sedimentological and paleontological characteristics.
Here we employ the sulfur isotopic composition of carbonate associated sulfate (CAS) as a proxy for long-term, whole-ocean redox changes during the Middle Ordovician. We use the abundances of organic carbon and total sulfur as proxies for short-term, localized changes in redox during the deposition of the Fossil Mountain sediments. Organic carbon abundances are low overall (average=0.7wt.%, maximum=1.2wt.% using the most conservative estimate), although some units may have had considerably higher organic content before burial. Total sulfur is uniformly low, with an average value of 0.02wt.% and a maximum value of 0.07wt.%. The total sulfur and organic carbon abundance results suggest that anoxia was not prevalent in the depositional environment of the Juab and Kanosh Formations. Similarly, the sulfur isotopic results correlate well with those reported from time-equivalent strata in Newfoundland, suggesting that the Fossil Mountain sediments were not deposited in a restricted basin. Even though the total sulfur and organic carbon data suggest that the local environment was not anoxic, our sulfur isotopic results support the hypothesis that the global ocean was likely euxinic during the Middle Ordovician.
•Kanosh Formation was deposited under aerobic conditions.•Kanosh Formation sediments have a low abundance of organic carbon and total sulfur.•Sulfur isotopes of CAS suggest global deep ocean anoxia.•Sulfur isotopes of CAS from Fossil Mountain can be correlated to Newfoundland.•GOBE may have proceeded with little impact from deep ocean redox changes.
The Great Ordovician Biodiversification Event (GOBE) represented the largest increase in diversity in the marine biosphere during the Phanerozoic Eon, yet its causes and consequences remain poorly ...understood. Patterns of isotopic variation in high-resolution
δ
13C
carb and
δ
13C
org records from a well-exposed section at Honghuayuan in South China may provide important insights regarding the GOBE. The Honghuayuan isotopic profiles, which can be correlated with C-isotopic records from contemporaneous sections globally, reveal large perturbations to the global carbon cycle during the Ordovician. A +
8‰ increase in
δ
13C
org values in the Floian implies a large, albeit transient increase in the burial rate of organic matter during the mid-Early Ordovician that may have contributed to climatic cooling and played an important role in triggering the GOBE. A +
4‰ increase in
δ
13C
carb and high-frequency variation in
δ
13C
org in the Darriwilian to Sandbian suggest a second episode of elevated organic carbon burial rates accompanied by substantial instability in the global carbon cycle during the late Middle and early Late Ordovician. This pattern may mark the onset of climate changes culminating in the end-Ordovician Hirnantian glaciation and mass extinction event that terminated the GOBE.
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