Carbonates in Skeleton-poor Seas: New Insights From Cambrian and Ordovician Strata of Laurentia

Calcareous skeletons evolved as part of the greater Ediacaran–Cambrian diversification of marine animals. Skeletons did not become permanent, globally important sources of carbonate sediment, however, until the Ordovician radiation. Representative carbonate facies in a Series 3 (510–501 Ma) Cambrian to Tremadocian succession from western Newfoundland, Canada, and Ordovician successions from the Ibex area, Utah, USA, show that, on average, Cambrian and Tremadocian carbonates contain much less skeletal material than do post-Tremadocian sediments. Petrographic point counts of skeletal abundance within facies and proportional facies abundance in measured sections suggest that later Cambrian successions contain on average <5% skeletal material by volume, whereas the skeletal content of post-Tremadocian Ordovician sections is closer to ~15%. A compilation of carbonate stratigraphic sections from across Laurentia confirms that post-Tremadocian increase in skeletal content is a general pattern and not unique to the two basins studied. The long interval (~40 myr) between the initial Cambrian appearance of carbonate skeletons and the subsequent Ordovician diversification of heavily skeletonized organisms provides an important perspective on the Ordovician radiation. Geochemical data increasingly support the hypothesis that later Cambrian oceans were warm and, in subsurface water masses, commonly dysoxic to anoxic. We suggest that surface waters in such oceans would have been characterized by relatively low saturation states for calcite and aragonite. Mid-Ordovician cooling would have raised oxygen concentrations in subsurface water masses, establishing more highly oversaturated surface waters. If correct, these links could provide a proximal trigger for the renewed radiation of heavily skeletonized invertebrates and algae

Lipid biomarker and stable isotopic profiles through Early-Middle Ordovician carbonates from Spitsbergen, Norway

One of the most dramatic episodes of sustained diversification of marine ecosystems in Earth history took place during the Early to Middle Ordovician Period. Changes in climate, oceanographic conditions, and trophic structure are hypothesised to have been major drivers of these biotic events, but relatively little is known about the composition and stability of marine microbial communities controlling biogeochemical cycles at the base of the food chain. This study examines well-preserved, carbonate-rich strata spanning the Tremadocian through Upper Dapingian stages from the Oslobreen Group in Spitsbergen, Norway. Abundant bacterial lipid markers (elevated hopane/sterane ratios, average = 4.8; maximum of 13.1), detection of Chlorobi markers in organic-rich strata, and bulk nitrogen isotopes (delta N-15(total)) averaging 0 to -1 parts per thousand for the open marine facies, suggest episodes of water column redox-stratification and that primary production was likely limited by fixed nitrogen availability in the photic zone. Near absence of the C-30 sterane marine algal biomarker, 24-n-propylcholestane (24-npc), in most samples supports and extends the previously observed hiatus of 24-npc in Early Paleozoic (Late Cambrian to Early Silurian) marine environments. Very high abundances of 3 beta-methylhopanes (average = 9.9%; maximum of 16.8%), extends this biomarker characteristic to Early Ordovician strata for the first time and may reflect enhanced and sustained marine methane cycling during this interval of fluctuating climatic and low sulfate marine conditions. Olenid trilobite fossils are prominent in strata deposited during an interval of marine transgression with biomarker evidence for episodic euxinia/anoxia extending into the photic zone of the water column. (C) 2019 Elsevier Ltd. All rights reserved.Peer reviewe

The Ordovician succession adjacent to Hinlopenstretet, Ny Friesland, Spitsbergen

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Records of carbon and sulfur cycling during the Silurian Ireviken Event in Gotland, Sweden

Field and stable isotope work was supported by an Agouron Institute grant to DAF and WWF as well as a Packard Fellowship and a Hanse-wissenschaftskolleg Fellowship awarded to DAF.Early Silurian (∼431 Ma) carbonate rocks record a ca. 4.5‰ positive excursion in the stable isotopic composition of carbonate carbon (δ13Ccarb). Associated with this isotopic shift is a macroevolutionary turnover pulse known as the ‘Ireviken Event’. The onset of this carbon isotope excursion is commonly associated with a shallowing-upward facies transition that may have been accompanied by climatic change, as indicated by a parallel positive shift (∼0.6‰) in the stable isotopic composition of carbonate oxygen (δ18Ocarb). However, the relationships among carbon cycle perturbations, faunal turnover, and environmental changes remain enigmatic. Here we present a suite of new isotopic data across the Ireviken Event from multiple sections in Gotland, Sweden. These samples preserve no systematic change in δ18Ocarb but show positive excursions of equal magnitude in both carbonate (δ13Ccarb) and organic (δ13Corg) carbon. In addition, the data reveal a synchronous perturbation in sulfur isotope ratios, manifest as a ca. 7‰ positive excursion in carbonate-associated sulfate (δ34SCAS) and a ca. 30‰ positive excursion in pyrite (δ34Spyr). The increase in δ34Spyr values is accompanied by a substantial, concomitant increase in stratigraphic variability of δ34Spyr. The relatively constant offset between the δ13Ccarb and δ13Corg excursions throughout the Ireviken Event could be attributed to increased organic carbon burial, or possibly a change in the isotopic composition of CO2 sources from weathering. However, a positive correlation between carbonate abundance and δ13Ccarb suggests that local to regional changes in dissolved inorganic carbon (DIC) during the shallowing-upward sequence may have been at least partly responsible for the observed excursion. The positive excursion recorded in δ34SCAS suggests a perturbation of sufficient magnitude and duration to have impacted the marine sulfate reservoir. An inverse correlation between CAS abundance and δ34SCAS supports the notion of decreased sulfate concentrations, at least locally, consistent with a concomitant increase in pyrite burial. A decrease in the offset between δ34SCAS and δ34Spyr values during the Ireviken Event suggests a substantial reduction in the isotopic fractionations (εpyr) expressed during microbial sulfur cycling and pyrite precipitation through this interval. Decreased εpyr and the concomitant increase in stratigraphic variation in δ34Spyr are typical of isotope systematics observed in modern shallow-water environments, associated with increased closed-system behavior and/or oxidative sedimentary reworking during early sediment diagenesis. While the isotopic trends associated with the Ireviken Event have been observed in multiple locations around the globe, many sections display different magnitudes of isotopic change, and moreover, are typically associated with local facies changes. Due to the stratigraphic coherence of the carbon and sulfur isotopic and abundance records across the Ireviken Event, and their relationship to changes in local depositional environment, we surmise that these patterns more closely reflect biogeochemical processes related to deposition and lithification of sediment than global changes in carbon and sulfur burial fluxes.PostprintPeer reviewe

A high-resolution record of early Paleozoic climate

The spatial coverage and temporal resolution of the Early Paleozoic paleoclimate record are limited, primarily due to the paucity of well-preserved skeletal material commonly used for oxygen-isotope paleothermometry. Bulk-rock δ¹⁸O datasets can provide broader coverage and higher resolution, but are prone to burial alteration. We assess the diagenetic character of two thick Cambro–Ordovician carbonate platforms with minimal to moderate burial by pairing clumped and bulk isotope analyses of micritic carbonates. Despite resetting of the clumped-isotope thermometer at both sites, our samples indicate relatively little change to their bulk δ¹⁸O due to low fluid exchange. Consequently, both sequences preserve temporal trends in δ¹⁸O. Motivated by this result, we compile a global suite of bulk rock δ¹⁸O data, stacking overlapping regional records to minimize diagenetic influences on overall trends. We find good agreement of bulk rock δ¹⁸O with brachiopod and conodont δ¹⁸O trends through time. Given evidence that the δ¹⁸O value of seawater has not evolved substantially through the Phanerozoic, we interpret this record as primarily reflecting changes in tropical, nearshore seawater temperatures and only moderately modified by diagenesis. Focusing on the samples with the most enriched, and thus likely least-altered, δ¹⁸O values, we reconstruct Late Cambrian warming, Early Ordovician extreme warmth, and cooling around the Early–Middle Ordovician boundary. Our record is consistent with models linking the Great Ordovician Biodiversification Event to cooling of previously very warm tropical oceans. In addition, our high-temporal-resolution record suggests previously unresolved transient warming and climate instability potentially associated with Late Ordovician tectonic events

The Magnitude and Duration of Late Ordovician–Early Silurian Glaciation

Understanding ancient climate changes is hampered by the inability to disentangle trends in ocean temperature from trends in continental ice volume. We used carbonate “clumped” isotope paleothermometry to constrain ocean temperatures, and thereby estimate ice volumes, through the Late Ordovician–Early Silurian glaciation. We find tropical ocean temperatures of 32° to 37°C except for short-lived cooling by ~5°C during the final Ordovician stage. Evidence for ice sheets spans much of the study interval, but the cooling pulse coincided with a glacial maximum during which ice volumes likely equaled or exceeded those of the last (Pleistocene) glacial maximum. This cooling also coincided with a large perturbation of the carbon cycle and the Late Ordovician mass extinction

BioDeepTime : a database of biodiversity time series for modern and fossil assemblages

We thank the Paleosynthesis Project and the Volkswagen Stiftung for funding that supported this project (Az 96 796). M.C.R. acknowledges the German Research Foundation (DFG) for funding through the Cluster of Excellence ‘The Ocean Floor – Earth's Uncharted Interface’ (EXC 2077, grant no. 390741603). E.E.S. acknowledges funding from Leverhulme Trust grant RPG-201170, the Leverhulme Prize and the National Science Research Council grant NE/V011405/1. Q.J.L. and L.N. acknowledge support from the Youth Innovation Promotion Association (2019310) and the Chinese Academy of Sciences (CAS-WX2021SF-0205). A.M.P. acknowledges funding from the Leverhulme Trust through research grant RPG-2019-402. M.D. acknowledges funding from Leverhulme Trust through the Leverhulme Centre for Anthropocene Biodiversity (RC-2018-021) and a research grant (RPG-2019-402), and the European Union (ERC coralINT, 101044975). L. H. L. acknowledges funding from the European Research Council (macroevolution.abc ERC grant no. 724324). K.H.P acknowledges funding from the National Science Foundation Graduate Research Fellowship Program (DGE-2139841). H.H.M.H. acknowledges support from Peter Buck Postdoc Fellowship, Smithsonian Institution. A.T. acknowledges funding from the Slovak Research and Development Agency (APVV 22-0523) and the Slovak Scientific Grant Agency (VEGA 02/0106/23).Motivation We have little understanding of how communities respond to varying magnitudes and rates of environmental perturbations across temporal scales. BioDeepTime harmonizes assemblage time series of presence and abundance data to help facilitate investigations of community dynamics across timescales and the response of communities to natural and anthropogenic stressors. BioDeepTime includes time series of terrestrial and aquatic assemblages of varying spatial and temporal grain and extent from the present-day to millions of years ago. Main Types of Variables Included BioDeepTime currently contains 7,437,847 taxon records from 10,062 assemblage time series, each with a minimum of 10 time steps. Age constraints, sampling method, environment and taxonomic scope are provided for each time series. Spatial Location and Grain The database includes 8752 unique sampling locations from freshwater, marine and terrestrial ecosystems. Spatial grain represented by individual samples varies from quadrats on the order of several cm2 to grid cells of ~100 km2. Time Period and Grain BioDeepTime in aggregate currently spans the last 451?million years, with the 10,062 modern and fossil assemblage time series ranging in extent from years to millions of years. The median extent of modern time series is 18.7?years and for fossil series is 54,872?years. Temporal grain, the time encompassed by individual samples, ranges from days to tens of thousands of years. Major Taxa and Level of Measurement The database contains information on 28,777 unique taxa with 4,769,789 records at the species level and another 271,218 records known to the genus level, including time series of benthic and planktonic foraminifera, coccolithophores, diatoms, ostracods, plants (pollen), radiolarians and other invertebrates and vertebrates. There are to date 7012 modern and 3050 fossil time series in BioDeepTime. Software Format SQLite, Comma-separated values.Publisher PDFPeer reviewe

Measurement-Based Automatic Parameterization of a Virtual Acoustic Room Model

Modernien auralisaatiotekniikoiden ansiosta kuulokkeilla voidaan tuottaa kuuntelukokemus, joka muistuttaa useimpien äänitteiden tuotannossa oletettua kaiutinkuuntelua. Huoneakustinen mallinnus on tärkeä osa toimivaa auralisaatiojärjestelmää. Huonemallinnuksen parametrien määrittäminen vaatii kuitenkin ammattitaitoa ja aikaa. Tässä työssä kehitetään järjestelmä parametrien automaattiseksi määrittämiseksi huoneakustisten mittausten perusteella. Parametrisaatio perustuu mikrofoniryhmällä mitattuihin huoneen impulssivasteisiin ja voidaan jakaa kahteen osaan: suoran äänen ja aikaisten heijastusten analyysiin sekä jälkikaiunnan analyysiin. Suorat äänet erotellaan impulssivasteista erilaisia signaalinkäsittelytekniikoita käyttäen ja niitä hyödynnetään heijastuksia etsivässä algoritmissa. Äänilähteet ja heijastuksia vastaavat kuvalähteet paikannetaan saapumisaikaeroon perustuvalla paikannusmenetelmällä ja taajuusriippuvat etenemistien vaikutukset arvioidaan kuvalähdemallissa käyttöä varten. Auralisaation jälkikaiunta on toteutettu takaisinkytkevällä viiveverkostomallilla. Sen parametrisointi vaatii taajuusriippuvan jälkikaiunta-ajan ja jälkikaiunnan taajuusvasteen määrittämistä. Normalisoitua kaikutiheyttä käytetään jälkikaiunnan alkamisajan löytämiseen mittauksista ja simuloidun jälkikaiunnan alkamisajan asettamiseen. Jälkikaiunta-aikojen määrittämisessä hyödynnetään energy decay relief -metodia. Kuuntelukokeiden perusteella automaattinen parametrisaatiojärjestelmä tuottaa parempia tuloksia kuin parametrien asettaminen manuaalisesti huoneen summittaisten geometriatietojen pohjalta. Järjestelmässä on ongelmia erityisesti jälkikaiunnan ekvalisoinnissa, mutta käytettyihin suhteellisen yksinkertaisiin tekniikoihin nähden järjestelmä toimii hyvin.Modern auralization techniques enable making the headphone listening experience similar to the experience of listening with loudspeakers, which is the reproduction method most content is made to be listened with. Room acoustic modeling is an essential part of a plausible auralization system. Specifying the parameters for room modeling requires expertise and time. In this thesis, a system is developed for automatic analysis of the parameters from room acoustic measurements. The parameterization is based on room impulse responses measured with a microphone array and can be divided into two parts: the analysis of the direct sound and early reflections, and the analysis of the late reverberation. The direct sounds are separated from the impulse responses using various signal processing techniques and used in the matching pursuit algorithm to find the reflections in the impulse responses. The sound sources and their reflection images are localized using time difference of arrival -based localization and frequency-dependent propagation path effects are estimated for use in an image source model. The late reverberation of the auralization is implemented using a feedback delay network. Its parameterization requires the analysis of the frequency-dependent reverberation time and frequency response of the late reverberation. Normalized echo density is used to determine the beginning of the late reverberation in the measurements and to set the starting point of the modeled late field. The reverberation times are analyzed using the energy decay relief. A formal listening test shows that the automatic parameterization system outperforms parameters set manually based on approximate geometrical data. Problems remain especially in the precision of the late reverberation equalization but the system works well considering the relative simplicity of the processing methods used