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Sökning: L773:0031 0182 > (2020-2024)

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1.
  • Agic, Heda, et al. (författare)
  • Life through an Ediacaran glaciation : Shale- and diamictite-hosted organic-walled microfossil assemblages from the late Neoproterozoic of the Tanafjorden area, northern Norway
  • 2024
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 635
  • Tidskriftsartikel (refereegranskat)abstract
    • New organic-walled microfossil (OWM) assemblages are reported from upper Neoproterozoic glacial and interglacial siliciclastic deposits in Finnmark, northern Norway. A nearly continuous sedimentary succession of the Vestertana Group contains two glaciogenic units, the Smalfjorden and Mortensnes formations, interpreted as end-Cryogenian Marinoan and Ediacaran glaciations, respectively. We investigated the OWM record in the Nyborg, Mortensnes, and St ' ahpogieddi formations to assess the impact of a glacial interval on the diversity of microscopic eukaryotes. A modified acid-extraction technique was applied to recover OWM from the diamictite matrix. The upper Nyborg Formation contains morphologically complex Doushantuo-Pertatataka acritarchs (DPA), restricting the age of the Nyborg Formation to early-mid Ediacaran. DPA occur below the dolostones that record a negative carbon isotope excursion correlated with the Shuram anomaly and below a glacial diamictite. A decline in species richness and compositional change is observed in the Mortensnes glacial assemblage. DPA are replaced by bacterial filaments and cell aggregates. The overlying Indreelva Member, St ' ahpogieddi Formation contains Ediacara-type biota and palaeopascichnids, but only a depauperate OWM assemblage of leiosphaerids and flask-shaped microfossils characteristic of the late Ediacaran.The succession of assemblages in the Vestertana Group demonstrates a turnover from large eukaryotic OWM to a microbial community in the glacial interval, to a low diversity post-glacial assemblage during the rise of macroscopic life. We compared the Vestertana record to global DPA occurrences. Although one DPA assemblage zone postdates the Shuram excursion, no DPA occur above Ediacaran glacial diamictites in successions where those deposits are present. Considering this, and the community changes in the Vestertana succession, we suggest that DPA were affected by the onset of an Ediacaran glaciation. Lastly, we combined the biostratigraphic markers in the Vestertana Group to constrain the age of the Mortensnes diamictite.
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2.
  • Andrén, Elinor, et al. (författare)
  • Medieval versus recent environmental conditions in the Baltic Proper, what was different a thousand years ago?
  • 2020
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 555
  • Tidskriftsartikel (refereegranskat)abstract
    • A sediment record from the western Gotland Basin, northwestern Baltic Proper, covering the last 1200 years, was investigated for past changes in climate and the environment using diatoms as a proxy. The aim is to compare the environmental conditions reconstructed during Medieval times with settings occurring the last century under influence of environmental stressors like eutrophication and climate change. The study core records more marine conditions in the western Gotland Basin surface waters during the Medieval Climate Anomaly (MCA; 950–1250C.E.), with a salinity of at least 8 psu compared to the present 6.5 psu. The higher salinity together with a strong summer-autumn stratification caused by warmer climate resulted in extensive long-lasting diatom blooms of Pseudosolenia calcar-avis, effectively enhancing the vertical export of organic carbon to the sediment and contributing to benthic hypoxia. Accordingly, our data support that a warm and dry climate induced the extensive hypoxic areas in the open Baltic Sea during the MCA. During the Little ice Age (LIA; 1400–1700C.E.), the study core records oxic bottom water conditions, decreasing salinity and less primary production. This was succeeded during the 20th century, about 1940, by environmental changes caused by human-induced eutrophication. Impact of climate change is visible in the diatom composition data starting about 1975C.E. and becoming more pronounced 2000C.E., visible as an increase of taxa that thrived in stratified waters during autumn blooms typically due to climate warming.
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3.
  • Bicknell, Russell D. C., et al. (författare)
  • Cambrian carnage : Trilobite predator-prey interactions in the Emu Bay Shale of South Australia
  • 2022
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 591
  • Tidskriftsartikel (refereegranskat)abstract
    • The Cambrian explosion represents the rapid emergence of complex marine ecosystems on Earth. The propagation of predator-prey interactions within these systems was almost certainly one of the major drivers of this evolutionary event, sparking an arms race that promoted the proliferation of biomineralised exoskeletons and shells, and the evolution of the first durophagous (shell-crushing) predators. The most commonly documented evidence of Cambrian durophagous predation comes from injured trilobites. However, quantitative analysis based on multiple specimens from single localities is lacking. Such studies are required to reveal the dynamics of ancient predator-prey systems at fine ecological scales (e.g. at the population or community level). This study documents injured specimens of two trilobite species, Redlichia takooensis and Redlichia rex, from the Emu Bay Shale Konservat-Lagersta center dot tte (Cambrian Series 2, Stage 4) on Kangaroo Island, South Australia. A total of 38 injured specimens exhibiting various healed cephalic and thoracic injuries are documented, in addition to the mangled remains of two individuals that probably resulted from the activities of a durophagous predator or scavenger. Specimens of both species show that most injuries are located on the posterior portion of the thorax, indicating that predators preferentially attacked from behind and/or prey individuals presented the posterior of the trunk towards the predator when threatened or fleeing. The larger sample of injured R. takooensis shows that while unilateral injuries are more common than bilateral ones, there is no evidence for a left-or right-side bias, contrasting with previous suggestions that Cambrian trilobites exhibit right-sided injury stereotypy. Comparing the position of injured and non-injured R. takooensis and R. rex in bivariate space, we illustrate that injured specimens of both species typically represent some of the largest individuals of these taxa. This suggests that smaller individuals were completely consumed during an attack and/or larger individuals were more likely to survive an attack and thus record a healed injury. We argue that R. rex, rather than radiodonts, was likely the chief producer of exoskeletal injuries and large shelly coprolites in the Emu Bay Shale biota, and represents one of the earliest cannibalistic trilobites.
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4.
  • Blaesild, Paulina, et al. (författare)
  • Early Holocene vegetation development at Mesolithic fen dwelling sites in Dagsmosse, south-central Sweden, and its implications for understanding environment–human dynamics at various scales
  • 2024
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182. ; 641
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent discoveries of several Mesolithic sites within the Dagsmosse Basin, south-central Sweden, offer an opportunity to study the lifestyle and skillsets of Mesolithic hunter-gatherer-fishers operating in wetland environments. In this paper, we present a combined archaeological and palaeoecological analysis of a Mesolithic fenland environment using Repetitive-Proxy Pollen Analysis (RPPA) of early Holocene sequences. Based on comparison of stratigraphic profiles from two cores within the basin, we infer that the variance in pollen composition and anthropogenic signals reflect variability in human/vegetation interactions in the fenland, at different distances to the main human dwelling at Jussberg (9.0–8.2 ka cal BP). Our study describes the socio-environmental relations within the wetland and adjacent terrestrial areas, providing a basis for tracking changes in forager interactions with their surroundings during the Mesolithic. Pollen analysis is consistent with the previously established sequence of settlement phases and extent as well as providing new data concerning the anthropogenic impacts on plant communities within the wetland including the use, reuse, and management of vegetation taxa. Correlations between palaeoecological and archaeological data demonstrate that forager communities (i) prevailed in the open fenland landscape between 9.3 and 8.2 ka cal BP, (ii) actively altered taxa composition through small-scale clearings of pine (Pinus), birch (Betula) and sedges (Cyperaceae) and (iii) reduced canopy cover, possibly to intentionally encourage the growth of taxa such as hazel (Corylus), but that also promoted the establishment of pioneer plants such as mugwort (Artemisia) and bracken (Pteridium).
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5.
  • Blaesild, Paulina, 1994, et al. (författare)
  • Early Holocene vegetation development at Mesolithic fen dwelling sites in Dagsmosse, south-central Sweden, and its implications for understanding environment–human dynamics at various scales
  • 2024
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182. ; 641
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent discoveries of several Mesolithic sites within the Dagsmosse Basin, south-central Sweden, offer an opportunity to study the lifestyle and skillsets of Mesolithic hunter-gatherer-fishers operating in wetland environments. In this paper, we present a combined archaeological and palaeoecological analysis of a Mesolithic fenland environment using Repetitive-Proxy Pollen Analysis (RPPA) of early Holocene sequences. Based on comparison of stratigraphic profiles from two cores within the basin, we infer that the variance in pollen composition and anthropogenic signals reflect variability in human/vegetation interactions in the fenland, at different distances to the main human dwelling at Jussberg (9.0–8.2 ka cal BP). Our study describes the socio-environmental relations within the wetland and adjacent terrestrial areas, providing a basis for tracking changes in forager interactions with their surroundings during the Mesolithic. Pollen analysis is consistent with the previously established sequence of settlement phases and extent as well as providing new data concerning the anthropogenic impacts on plant communities within the wetland including the use, reuse, and management of vegetation taxa. Correlations between palaeoecological and archaeological data demonstrate that forager communities (i) prevailed in the open fenland landscape between 9.3 and 8.2 ka cal BP, (ii) actively altered taxa composition through small-scale clearings of pine (Pinus), birch (Betula) and sedges (Cyperaceae) and (iii) reduced canopy cover, possibly to intentionally encourage the growth of taxa such as hazel (Corylus), but that also promoted the establishment of pioneer plants such as mugwort (Artemisia) and bracken (Pteridium).
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6.
  • Bowman, Chelsie N., et al. (författare)
  • Integrated sedimentary, biotic, and paleoredox dynamics from multiple localities in southern Laurentia during the late Silurian (Ludfordian) extinction event
  • 2020
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 553
  • Tidskriftsartikel (refereegranskat)abstract
    • The Silurian was a time of major climatic transition punctuated by multiple biotic crises and global carbon cycle perturbations. The most severe of these biotic events was the late Silurian (Ludfordian) Lau/Kozlowskii extinction event (LKE) and the associated Lau carbon isotope excursion (CIE). Although the extinction event and Lau CIE are globally documented, the only records thus far of local and global marine paleoredox conditions through this interval are from a single region in Scandinavia. Here we examine four sections along a bathymetric transect of mixed carbonate-siliciclastic sediments from western Tennessee, USA. A novel approach using a multi-proxy dataset combining high-resolution geochemical data and microfacies analyses from multiple localities explores the possibilities of local/regional-scale redox heterogeneities during a time of widespread environmental upheaval on a global scale. Paired positive excursions recorded in carbonate carbon isotopes and carbonate-associated sulfate sulfur isotopes support recent work from carbonate and siliciclastic successions from Scandinavia, suggesting a global enhancement of organic carbon and pyrite burial driven by an expansion of euxinic (anoxic and sulfidic water column) conditions in the oceans during the mid-Ludfordian. Furthermore, positive excursions in organic carbon isotopes and pyrite sulfur isotopes reflect the global changes in redox. Stratigraphic trends in I/Ca ratios imply a local expansion of low-oxygen conditions, with low, but non-zero values during the rising limb and peak of the CIE. The fossil assemblages vary across the shelf and through the CIE interval. Stratigraphic changes in fossil assemblages and I/Ca are closely associated with local and global changes in oxygenation and sea level during the mid-Ludfordian. The collective data indicate significant biotic reorganization in response to changes in marine redox conditions and in conjunction with sea-level variation during the LKE interval, but detailed macroscopic biodiversity is currently unconstrained for this region.
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7.
  • Bradák, Balázs, et al. (författare)
  • Magnetic susceptibility in the European Loess Belt : New and existing models of magnetic enhancement in loess
  • 2021
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 569
  • Tidskriftsartikel (refereegranskat)abstract
    • Magnetic susceptibility measurements play a key role in Quaternary studies. Magnetic proxies, such as low field and frequency-dependent magnetic susceptibility, are widely applied in the reconstruction of terrestrial paleoclimate, e.g., in the study of loess-paleosol successions. In general, the interpretation of loess magnetic susceptibility signals is based on two commonly accepted models: the pedogenic magnetic enhancement and wind-vigour models. However, there are an increasing number of cases where such models cannot be used. These cases show unusual relationships between the two common loess magnetic susceptibility proxies: low field and frequency-dependent magnetic susceptibility. Such relationships have been attributed to various phenomena including the dissolution of fine-grain minerals and the formation of ultrafine magnetic rims on the surface of coarser grains by weathering. Despite the growing number of these exceptional cases of magnetic enhancement, our knowledge about the occurrence and potential causes of the unusual behaviour of magnetic susceptibility parameters is still limited. This, in turn, hinders the wider application of magnetic susceptibility parameters in loess. To fill this knowledge gap, magnetic susceptibility data of various profiles from the European Loess Belt were collected and compared to reveal various enhancement trends in loess. Along with the analysis of magnetic susceptibility parameters, combined scanning electron microscopy (SEM) and rock magnetic analyses were applied to samples from the Paks loess sequence in Hungary to describe some of the irregular cases, notably the cause of increasing frequency-dependent susceptibility in non-altered sediments. Analysis of loess, paleosol and common mineral samples separated from loess (e.g., muscovite) revealed that various features may be responsible for these increasing frequency-dependent susceptibility values: i) surface weathering (maghemitization) of coarser detrital grains, ii) nanofragmentation by physical weathering and iii) the appearance of significant amounts of ultrafine magnetic inclusions in micas. These special modes of magnetic enhancement of loess do not undermine the importance of the basic theories suggested above, but rather provide three mechanisms that account for some of the increasing number of unusual cases. To aid in the wider and more accurate use of magnetic susceptibility parameters in loess, we review the current magnetic enhancement models with special emphasis on the identification of unusual trends in magnetic enhancement and understanding their drivers.
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8.
  • Bradák, B., et al. (författare)
  • Potential drivers of disparity in early Middle Pleistocene interglacial climate response over Eurasia
  • 2022
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 585
  • Tidskriftsartikel (refereegranskat)abstract
    • Poor understanding of the differential evolution of interglacial climate over various regions in Eurasia greatly limits our ability to predict the specific local impacts of future climate change. Here we demonstrate starkly opposing trends in interglacial intensities in Asia and Europe over the early Middle Pleistocene and Mid-Brunhes Transitions based on the study of various climate proxies in the Paks loess record (Hungary), a key profile in the European Loess Belt. These contrasting climate trends imply major but unexplained differences in the regional response of Quaternary climate to shifts in forcing mechanisms during two major reorganizations of Earth's climate across Eurasia. Using new rock magnetic datasets from the Paks record we suggest that the changing dominance of Mediterranean, Atlantic (Westerlies) and continental air masses under the influence of the quasi permanent high pressure centres over the Fennoscandian ice sheet played a key role in the observed differences in the evolution of early Middle Pleistocene climate. We also propose that the intensification of the early Middle Pleistocene glaciation of Central Asian mountains may have strengthened and shifted the Siberian High west-ward on multi-millennial/orbital timescales, which in turn forced geographically contrasting expressions of the MIS 19 to 11 interglacials in Eurasia. This is the first coherent explanation for the geographically diverse response of regional climate to the early Middle Pleistocene climate transitions and points to the clear role of global cooling and expanded mid-latitude glaciers in driving these events.
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9.
  • Brylka, Karolina, et al. (författare)
  • Biogenic silica accumulation and diatom assemblage variations through the Eocene-Oligocene Transition : A Southern Indian Ocean versus South Atlantic perspective
  • 2024
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182. ; 636
  • Tidskriftsartikel (refereegranskat)abstract
    • It is widely interpreted that there is a significant link between climate cooling at the Eocene-Oligocene Transition(EOT; ~34 Ma) and subsequent diatom proliferation in the world’s oceans during the mid to late Cenozoic. Yet,our understanding of biogenic silica flux through the EOT interval is based on limited data from a few sites, andthere are many complications in making a meaningful comparison based on biogenic silica concentration datagenerated using different techniques. Here, we present new biogenic opal flux and diatom assemblage recordsacross EOT from Ocean Drilling Program Site 748 (Southern Kerguelen Plateau, southern Indian Ocean), inaddition to new biogenic opal flux records from the South Atlantic (Deep Sea Drilling Project Site 511, FalklandPlateau and Ocean Drilling Program Site 1090, Agulhas Ridge). Observed opal flux shifts and variability at Site748 are consistent with published data from nearby Site 744; both sites show considerable shifts in biogenic opalaccumulation rates corresponding to shifts in published benthic oxygen isotope records through the EOT. Incontrast, our new opal flux record for Site 511, derived from biogenic opal concentration measurements viaspectrophotometry, differs from the published record derived from insoluble residues, whereas new datagenerated for Site 1090 are generally consistent with previously published flux reconstructions. The SouthAtlantic biogenic opal flux records, however, are dissimilar from one another, and both are dissimilar from theSouthern Indian Ocean records. Also, the taxonomic composition of the diatom assemblages from Sites 511, 748and 1090 display considerable differences, with hemiauloids and rhizosolenids – generally inferred as indicativeof oligotrophic conditions – being the dominant diatoms at the Southern Kerguelen Plateau (Site 748). Publishedrecords show that hemiauloid taxa are absent from the earliest Oligocene interval at Site 1090, which is widelyseen as a record of deposition from nutrient-rich waters sustaining abundant diatom assemblages. These differencesin diatom assemblages testify to regional differences in nutrient concentrations. In particular, the timingof biogenic opal flux pulses between Sites 1090 and 748 imply a shift in the locus of opal deposition to areasfurther south in the Southern Ocean across the EOT, likely related to proto-ACC development and strengtheningof frontal boundaries. Thus, combined geochemical and micropaleontological evidence points to a regionallyvariable rather than a global, unified opal flux response to climate cooling through the Eocene-OligoceneTransition.
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10.
  • Byrne, Hannah, et al. (författare)
  • Coprolite diversity reveals a cryptic ecosystem in an early Tournaisian lake in East Greenland : Implications for ecosystem recovery after the end-Devonian extinctio
  • 2022
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 605
  • Tidskriftsartikel (refereegranskat)abstract
    • The early Tournaisian (Carboniferous) stage represents a key episode in the evolution of vertebrates. It follows the end-Devonian Hangenberg extinction event, which led to a major perturbation to both terrestrial and aquatic vertebrate ecosystems, and resulted in a significant restructuring of assemblages. However, few faunal associ-ations of this age have been described, and our understanding of faunal turnover across the Devonian -Carboniferous boundary remains poor. In this paper, we present an analysis of coprolite material from early Tournaisian lacustrine facies at Celsius Bjerg on Ymer o in East Greenland, which overlies the world-famous latest Devonian tetrapod-bearing localities. Fifty-five coprolite specimens (defined as a single coprolite or a piece of shale containing coprolites) were analysed using propagation phase-contrast synchrotron micro -tomography (PPC-SR mu CT). Through a study of external morphology, shape and size combined with information about internal structures, we categorise coprolite morphotypes, and interpret their origin. Notably, we identify a greater number of coprolite morphotypes compared to vertebrate taxa known from skeletal material, indicating the existence of a cryptic ecosystem that has not yet been recovered as body fossils. Vertebrate diversity in the immediate aftermath of the end-Devonian extinction is inferred to have been higher than expected, and might have included transient faunal elements within an open system, perhaps involving marine basin connections. Our results show that coprolites offer an alternative fossil data source, revealing diversity that is otherwise not always captured by the skeletal record.
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11.
  • Dong, Jiang, et al. (författare)
  • Millennial-scale interaction between the East Asian winter monsoon and El Niño-related tropical Pacific precipitation in the Holocene
  • 2021
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 573
  • Tidskriftsartikel (refereegranskat)abstract
    • Both the East Asian winter monsoon (EAWM) and El Niño (EN) activities are vital climate modes that regulate the Pacific hydrologic cycle. However, the Holocene interactions among the EAWM, EN activities, and tropical Pacific precipitation remain unclear due to the lack of appropriate EAWM proxies. Here, we present high-resolution grain size records from the East China Sea shelf along with a transient climate model simulation to study the Holocene EAWM evolution and compare the findings with paleo-EN precipitation-related proxies records. The millennial-scale oscillations of grain size records, which are indicative of the intensity of the EAWM-driven coastal current, reveal an anti-phase coupling between the EAWM and EN-related tropical Pacific precipitation on a millennial timescale since 5.8 ka. These results, which are consistent with simulation results, indicate that the intensified EAWM could not only reduce equatorial western Pacific precipitation by reducing the sea surface temperature but also likely change boundary conditions in the tropical Pacific (i.e., the east-west Pacific temperature gradient and westerly anomaly) to favor the formation of subsequent intensive EN activities. The enhanced EN activities, inferred by the positive tropical eastern Pacific precipitation anomalies, could subsequently suppress the EAWM through anomalous low-level anticyclones and associated southerly anomalies, thereby generating intensified tropical western Pacific (mainly tropical monsoon areas) precipitation. Our study highlights these intrinsic interactions during the mid- to late Holocene and has useful implications for understanding this millennial-scale climate oscillation, which may represent periodic atmospheric exchange between high- and low-latitude climate systems by mediating the EAWM.
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12.
  • Emmanouilidis, Alexandros, et al. (författare)
  • Holocene paleoclimate variability in the eastern Mediterranean, inferred from the multi-proxy record of Lake Vouliagmeni, Greece
  • 2022
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 595
  • Tidskriftsartikel (refereegranskat)abstract
    • This study presents a Holocene multi-proxy record from Lake Vouliagmeni, eastern Gulf of Corinth, Greece. The lake is subjected to intense climatic and tectonic forces causing stratigraphic variations with laminated sediments frequently interrupted by homogenous sections and event deposits. Lamination couplets consist of aragonite layers alternating with detrital and organic residues formed during periods of seawater intrusion and stratification of the lake water. The discontinuous occurrence of laminated deposits excludes a varve based chronology from being established but highlights the susceptibility of the lake to record environmental and climatic changes. Our synthesis model for regional climatic reconstruction and local environmental changes derives from δ18O and δ13C data from laminated and homogenous sediments studied separately and depending on the dominant carbonate mineral. This is further strengthened by high-resolution geochemical proxies, diatom and sedimentological data. Regional climatic signals from key sites and possible links to the Lake Vouliagmeni record are explored in response to atmospheric circulation patterns. Phases of overall humid conditions are recorded by increased inflow of siliciclastic material to the lake and negative δ18Obulk values. In contrast, periods of marine intrusion and enhanced evaporation are recorded by aragonite precipitation, positive δ18OAr values and laminations. The laminations formed in the lake seem to occur during periods of sea water intrusion into the lake, which led to pycnocline stabilization and stratified lake waters.
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13.
  • Fielding, Christopher R., et al. (författare)
  • Environmental change in the late Permian of Queensland, NE Australia: The warmup to the end-Permian Extinction
  • 2022
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - Amsterdam : Elsevier. - 0031-0182 .- 1872-616X. ; 594, s. 110936-110936
  • Tidskriftsartikel (refereegranskat)abstract
    • The upper part of the upper Permian succession in the Bowen Basin of Queensland, NE Australia, was investigated to ascertain the timeline and character of environmental changes in this high southern palaeolatitudinal setting leading up to the End-Permian Extinction (EPE). The study focused on (in ascending order) the Peawaddy Formation, Black Alley Shale, and Bandanna Formation, and laterally correlative units. In the western Bowen Basin, the base of the Peawaddy Formation (257 Ma) records the onset of thrust loading and volcanic activity associated with the Hunter-Bowen contractional orogeny. The Peawaddy Formation comprises a series of coarsening-upward, terrigenous clastic intervals interpreted as the product of repeated progradation of deltas into shallow, open marine environments. The overlying Black Alley Shale also comprises multiple deltaic coarsening-upward cycles, which accumulated in stressed, restricted marine environments. The uppermost Bandanna Formation and equivalents formed in extensive coastal plain to estuarine environments. All three formations accumulated under the influence of explosive volcanic activity from the emerging continental volcanicarc to the east of the foreland basin. Volcanism peaked during deposition of the Black Alley Shale around the Wuchiapingian–Changhsingian transition. Abundant dispersed gravel and glendonites (calcite pseudomorphs after ikaite) indicate that the Peawaddy Formation formed under the influence of cold conditions and possible glacial ice (P4 Glaciation; Wuchiapingian Stage). Direct evidence of cold conditions ends at the top of the Peawaddy Formation (254.5 Ma); however, Chemical Index of Alteration (CIA) data suggest that surface conditions remained cold through the accumulation of the Black Alley Shale, and the lower Bandanna until c. 253 Ma, before gradually rising through the upper Bandanna Formation. The end of P4 glaciation is also characterized by a major spike in the abundance of marine acritarchs (Micrhystridium evansii Acme Zone), reflecting the development of a regional restricted basin of elevated nutrient concentrations but reduced salinity. In contrast to this short interval of stressed marine conditions, the fossil floras indicate remarkably consistent terrestrial ecosystems throughout the late Lopingian until the EPE. The terrestrial EPE is recorded by adistinctive, laminated mudrock bed (‘Marker Mudstone’) that records a palynological ‘dead zone’ above the uppermost coal seam or equivalent root-penetrated horizon followed by spikes in non-marine algal abundance. Overall, the time interval 257–252 Ma represented by the studied succession does not record a simple monotonic change in palaeoenvironmental conditions, but rather a series of intermittent stepwise changes towards warmer, and more environmentally stressed conditions leading up to the EPE in eastern Australia.
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14.
  • Gill, Benjamin C., et al. (författare)
  • Redox dynamics of later Cambrian oceans
  • 2021
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 581
  • Tidskriftsartikel (refereegranskat)abstract
    • A growing body of evidence suggests that the deep oceans during the early Paleozoic Era were widely oxygen deficient, despite evidence for increased marine oxygenation during the Neoproterozoic. However, the temporal and geographic extents and dynamics of reducing marine conditions within these oceans are not well understood. Here, we investigate marine redox history during the Drumian through the earliest Jiangshanian International Stages of the Cambrian Period, using concentrations of redox-sensitive metals (vanadium, uranium, and molybdenum), iron speciation, and Mo isotope stratigraphy of the Alum Shale Formation of Scandinavia. These data suggest a major perturbation occurred in trace metal cycling during the later Cambrian Period that was linked to a transient change in marine redox conditions coincident with the well-known Steptoean Positive Isotope Excursion or SPICE. The δ98Mo measurements of the Alum shale show systematic variations during the interval that contains the SPICE which are broadly consistent with a transient expansion of sulfidic, reducing marine environments — indicating a significant exacerbation of an already-common condition during the Cambrian Period. Additionally, iron speciation data record a local transition from predominantly anoxic, ferruginous (Fe+2 containing) to anoxic, euxinic (sulfide containing) water column conditions near the initiation of the SPICE. Trace metal abundances, however, appear to decline well before the start of the SPICE, suggesting an earlier initiation of the global expansion of reducing environments. More broadly, our data and modeling support the notion that significant portions of the oceans remained oxygen deficient throughout the later portion of the Cambrian, and that these oceans were also prone to transient intervals of more reducing conditions similar to the Oceanic Anoxic Events of the Mesozoic.
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15.
  • Hu, Yazhou, et al. (författare)
  • Burrows filled with faecal pellets from the Cambrian (Stage 4) Guanshan biota of South China and their palaeoecological implications
  • 2021
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 567
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent excavations of the Guanshan biota at the Shijiangjun section in the eastern Yunnan Province, South China, have revealed many well-defined faecal pellets and related trace fossils. These can be assigned to three morphotypes, which have affinities with the ichnogenera Tomaculum, Alcyonidiopsis and Tubulichnium. Morphotype 1 is an unbranched burrow filled with randomly distributed faecal pellets. Morphotype 2 is a string-shaped burrow without branching, containing intensely compacted faecal pellets. Morphotype 3 comprises unbranched burrows with a fill of faecal pellets and a central cavity. The ellipsoidal faecal pellets in morphotype 1 and 2 can be assigned to Coprulus oblongus. They are morphologically similar to the excrements produced by modern deposit-feeding polychaetes, as well as the gut content of early Cambrian polychaete worms (Guanshanchaeta felicia) from the Guanshan biota and priapulid worms (Selkirkia) from the Xiaoshiba Lagerstätte. This analogy suggests polychaetes and priapulid worms as potential producers of these burrows and that a diverse range of digestive methods had already been established in the Cambrian Stage 4 ca. 510 Ma ago. Morphotype 3 is interpreted to be related to the storage of faecal pellets and possibly for cultivation of bacteria, which would represent an early case of this behaviour. The discovery of this diverse suite of burrows with faecal pellets indicates that the origin of diverse deposit-feeding strategies in worms can be traced back to at least the Cambrian Stage 4.
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16.
  • Kaal, Joeri, et al. (författare)
  • Reconstruction of 7500 years of coastal environmental change impacting seagrass ecosystem dynamics in Oyster Harbour (SW Australia)
  • 2020
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 558
  • Tidskriftsartikel (refereegranskat)abstract
    • Seagrass ecosystems, which have important functions such as coastal protection and blue carbon sequestration, are threatened by anthropogenic pressure including climate change. Long-term data series from seagrass sedimentary archives (mats) can be used to understand natural cycles of environmental change and answer key questions related to contemporary management. A 7500 yr sediment record from Posidonia australis meadows in Oyster Harbour (Albany, SW Australia) was subjected to multiproxy reconstruction by means of pigment analysis (UHPLC), analytical pyrolysis (Py-GC-MS), carbonate content, delta C-13 and delta N-15 stable isotope ratios, organic C (C-org) content, C-org/N ratio and glomalin-related soil proteins (GASP). The study revealed a brackish lagoon (7500-7000 cal yr BP) that was transformed in an open marine environment (7000-4100 cal yr BP) due to Holocene transgression. Earliest evidence of seagrass establishment was detected around 4500 cal yr BP, and meadow extension accelerated between 4100 and 3700 cal yr BP. The meadow environment was surprisingly resistant against environmental perturbations, as the mat, composed of P. australis seagrass fibres embedded within a siliciclastic mineral matrix containing biogenic carbonates, continued to develop steadily until 190 cal yr BP (1830 CE). Then, shifts in several proxies (pigments, GASP) showed evidence of terrestrial runofftriggered eutrophication/turbidity (likely driven by forest clearance and agricultural activities after European settlement), but the seagrass showed resilience (no decline of the proportion of seagrass-derived C-org). By contrast, since similar to 1930 CE seagrass retreat is evident in the biogeochemical record: lighter delta C-13 values, lower lignin abundance and shifts in pigment abundance and types, affecting the balance between seagrass inputs and alternative sources, as was observed in previous studies of the area. The findings show that pigment proxies are useful early indicators of shifts in seagrass ecosystem condition, while lignocellulose and other pyrolysis products are useful proxies of more profound ecosystem alterations that influence seagrass abundance. The record indicates that the climax seagrass ecosystem condition, which prevailed for several millennia, had been impacted over the last century. Management of seagrass and coastal ecosystems should aim to avoid crossing ecological thresholds and diminish local impacts aggravating those of global change.
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17.
  • Katrantsiotis, Christos, et al. (författare)
  • Late quaternary hydroclimate variability in Madagascar and its connection to atmospheric circulation patterns
  • 2024
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 649
  • Tidskriftsartikel (refereegranskat)abstract
    • Large uncertainties still exist about the long-term mechanisms influencing the hydroclimate variability of southeast Africa where proxy data and model simulations indicate rainfall dipoles between subtropical and tropical areas. The topography of Madagascar, located off the southeastern coast of Africa, modulates these dipoles while its climate is influenced by the position of the Intertropical Convergence Zone (ITCZ) and the Subtropical High as well as the sea surface temperature (SST) of SW Indian Ocean. The island can thus be considered a key location for the understanding of the tropical SE African climatic variability and the interplay between atmospheric patterns. However, the scarcity of continuous records from Madagascar has made the evolution of regional late Quaternary climate and its driving mechanisms difficult to assess. Here, we present a 26-kyr record of the deuterium/hydrogen isotope ratio (δD) of biomarkers (n-alkanes) from the central eastern part of the island at Antananarivo at around 1250 m a.s.l. Preliminary summary pollen data are also presented as a comparison. The δD profiles of aquatic plant and terrestrial plant-derived n-alkanes generally exhibit similar trends implying that they all record changes in the isotope composition of source water, namely meteoric water that recharges soil and lake waters. In this tropical region, the δD variability of precipitation is mainly influenced by the amount effect reflecting the intensity of precipitation associated with the monsoon. We observe: (i) stable and wet conditions during the Last Glacial Maximum, (ii) drier conditions from 18.5 to 15 ka (ka before present) during the Heinrich Stadial 1 (iii) high humidity after 15 ka culminating at the Younger Dryas (YD), (iv) drier conditions from 11.7 ka to 8.2 ka, (v) a return to humid climate until 2.8 ka, and (vi) an arid phase followed by increased wetness after 0.9 ka, although the record is likely influenced by human-induced vegetation changes the last 1.2 ka. This climate signal is similar to other records from the Mozambique Channel but opposite to records from the East African mainland and the subtropical southern Africa, especially between 20 and 25°S. Although there is a good correspondence of our record with insolation- driven migrations of ITCZ during the LGM and the early Holocene, the dipoles are largely consistent with the modern rainfall anomaly and are best explained by the interlinked effects of the SST changes and the variability of the Mozambique Channel Trough.
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18.
  • Kiel, Steffen, et al. (författare)
  • A thyasirid-dominated methane-seep deposit from Montañita, southwestern Ecuador, from the Oligocene-Miocene boundary
  • 2021
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - Amsterdam : Elsevier. - 0031-0182 .- 1872-616X. ; 575
  • Tidskriftsartikel (refereegranskat)abstract
    • A mass occurrence of the thyasirid bivalve Thyasira montanita in a limestone bed, exposed at Punta Montañita on the northern side of the Santa Elena peninsula in southeastern Ecuador, is here identified as an ancient methane-seep deposit. The massive to nodular limestone shows carbonate phases and microfabrics typical of seep limestones, such as banded and botryoidal cements. Its δ13 Ccarbonate values, as low as −52.6‰, suggest a biogenic methane source. Furthermore, the carbonate microfabrics and biomarkers typical of ANME-2 archaea indicate high seepage rates. Tubular fossils previously interpreted as worm tubes show cone-shaped projections and an internal structure consistent with that of crustacean cuticle and are here interpreted as crustacean fragments. Seep deposits with mass occurrences of thyasirid bivalves have so far only been reported from the Cretaceous, making the Montañita seep deposit the first such example from the Cenozoic. The faunal and biomarker inventories of this deposit indicate deposition on an open shelf; the oysters on the upper surface of the limestone are likely secondary encrusters that arrived only after the emergence of this deposit in shallower water.
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19.
  • Kiel, S., et al. (författare)
  • Brachiopods in early Mesozoic cryptic habitats: Continuous colonization, rapid adaptation, and wide geographic distribution
  • 2021
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - Amsterdam : Elsevier. - 0031-0182 .- 1872-616X. ; 583, s. 110668-110668
  • Tidskriftsartikel (refereegranskat)abstract
    • Late Triassic and early Jurassic dikes and fissures in the Dachstein Limestone in the Northern Calcareous Alps harbor mass occurrences of the rhynchonellide brachiopods Sulcirostra juvavica and Halorella amphitoma. To test recent hypotheses about their paleoecology, we characterized these habitats using petrography, carbon stable isotopes, and trace element patterns, and found no evidence for hydrocarbon seepage or hydrothermal venting. Thus the brachiopods lived under normal-marine conditions, in darkness and absence of local photosynthetic primary production, hence relying on the supply of limited and presumably small-sized food washed into the dikes and fissures. Because Halorella and Sulcirostra occur in dikes and fissures since the beginning of their stratigraphic ranges, these rhynchonellides are not relics of formerly widely distributed taxa, but instead are two genera that rapidly adapted to these habitats. Both Halorella and Sulcirostra occur also in late Triassic and early Jurassic deep-water settings such as deep-marine sills and hydrocarbon seeps, indicating that close phylogenetic relationships between submarine cave faunas and deep-sea faunas, as seen today, existed also in the early Mesozoic, albeit among very different taxa. Another analogy to the modern cave fauna is the wide but disjunct geographic distribution of Sulcirostra and Halorella, both found throughout the Tethys and Panthalassa oceans. Our findings support the view that submarine cave habitats were continuously colonized by new taxa throughout Earth’s history.
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20.
  • Li, Liqin, et al. (författare)
  • Palaeovegetation and palaeoclimate changes across the Triassic–Jurassictransition in the Sichuan Basin, China
  • 2020
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - Amsterdam : Elsevier. - 0031-0182 .- 1872-616X. ; 556
  • Tidskriftsartikel (refereegranskat)abstract
    • The Triassic–Jurassic transition interval is marked by enhanced biotic turnover rates in both marine and terrestrial realms. However, limited data from Asia hampers the understanding of global ecosystem response to the end-Triassic mass extinction event. Here, we present significant vegetation and climate changes across the Triassic–Jurassic transition in the eastern Tethys region (southern China). A detailed palynological study was performed from the Qilixia section of the Sichuan Basin, China, spanning the Upper Triassic (Norian–Rhaetian) (Xujiahe Formation) to the Lower Jurassic (Hettangian–Sinemurian) (lower Zhenzhuchong Formation). Five palynological assemblages reveal significant ecosystem fluctuations across the Triassic–Jurassic transition. Our study indicates a lowland fern flora and a warm and humid climate in the Late Triassic (Norian to Rhaetian), interrupted by a cooler interval at the Norian–Rhaetian transition, and followed by a mixed mid-storey forest under cooler and drier condition in the latest Rhaetian. This is followed by a fern-dominated lowland vegetation and a warmer and drier climate during the Triassic–Jurassic transition, and a flora with abundant cheirolepid conifers in the Hettangian–Sinemurian. These long term changes in vegetation and inferred climatic conditions are comparable with records from the western Tethyan realm, and possibly reflect global terrestrial environmental changes associated with Central Atlantic Magmatic Province volcanism during the Triassic–Jurassic transition.
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21.
  • Li, Luoyang, et al. (författare)
  • Qingjianglepas from the Qingjiang biota, an evolutionary dead-end of Cambrian helcionelloid mollusks?
  • 2021
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 575, s. 110480-110480
  • Tidskriftsartikel (refereegranskat)abstract
    • A minute limpet-shaped shell, Qingjianglepas elegans n. gen. n. sp., is reported from the 518 million-year-old Qingjiang biota in Hubei, China. The new shell exhibits a typical limpet morphology with a shell sculpture of strongly developed radial ribs, an anterior shell fold, and distinctive shell shape shift. Feature combinations such as in Qingjianglepas are unique among Cambrian mollusk assemblages, but strikingly resemble that of some modern fissurellids (keyhole and slit limpets; Vetigastropoda). The biological affinity of Qingjianglepas is discussed, but temporarily remains uncertain. Regardless, the heavily sculptured and limpet-shaped Qingjianglepas represents a previously unrecognized shell form, and hence significantly extends the morphological diversity of Cambrian mollusks. The abrupt ontogenetic change in shell morphology suggests that Qingjianglepas might change microhabitat throughout the growth of the animal. This study reveals that the phenomenon of limpetization occurred within early Cambrian total-group conchiferans. Furthermore, Qingjianglepas might represent an evolutionary dead-end in course of helcionelloid mollusk evolution, which marks the end of the Cambrian explosion of animals at the beginning of Cambrian Series 2.
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22.
  • Li, Nannan, et al. (författare)
  • Phytolith and simulation evidence for precipitation-modulated vegetation dynamics along the East Asian monsoon margin
  • 2022
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 590
  • Tidskriftsartikel (refereegranskat)abstract
    • An improved understanding of past interactions between terrestrial vegetation and various forcings, such as climate change, human impact, and paleofire, is crucial for assessing impacts of future global change on terrestrial ecosystems. This study seeks to find the key factor or factors that have driven Holocene vegetation change along the East Asian monsoon margin. Several high-resolution pollen records are reviewed and new phytolith-based paleovegetation reconstructions and physical geochemical datasets are presented from a peatland in northeastern China. Using 108 modern topsoil samples as a training set, canopy cover and vegetation composition are estimated for the period since 5100 cal. yr BP. Variation partitioning analysis (VPA) is used to determine the relative importance of climate change, human impacts, and paleofire disturbance. The generalized dynamic vegetation model LPJ-GUESS is forced with climate anomaly output from an atmospheric general circulation model to simulate vegetation dynamics during the mid-Holocene and the pre-industrial era. The proxy-based estimates are compared to modelling output. Results indicate that regional tree cover varied from 10% to 40% during the past five millennia. The single-core, phytolith-based reconstructions are generally consistent with stacked tree pollen z-scores calculated from different records along the East Asian monsoon margin, implying that mid-Holocene tree cover decrease was persistent and almost synchronous over extensive areas. VPA demonstrates that long-term monsoon marginal vegetation successions were mainly caused by climate effects. Numerical modelling suggests that since the mid-Holocene the retreat of forests along the monsoon margin was primarily associated with precipitation deficits. Our investigation highlights that the precipitation associated with the East Asian monsoon system has exerted a stronger influence than the westerlies on the monsoon margin climate and vegetation change. With ongoing global change, close attention to variations in precipitation patterns and amounts should be especially helpful in efforts aimed at ecological monitoring, change prediction, and restoration.
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23.
  • Licht, Alexis, et al. (författare)
  • Decline of soil respiration in northeastern Tibet through the transition into the Oligocene icehouse
  • 2020
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 560
  • Tidskriftsartikel (refereegranskat)abstract
    • Soil respiration (Rs), the production of carbon dioxide in soils, increases dramatically from deserts to forested ecosystems. Rs values thus provide a potential tool to identify past ecosystems if recorded in sedimentary archives. Here, we propose a quantitative method to reconstruct past Rs values from paleosols. This method reverses the soil paleobarometer, a proxy that estimates past atmospheric CO2 concentration values (CO2atm) from paleosols while considering a narrow range of variation for Rs. We use past CO2atm values from marine proxies to reconstruct soil respiration from a 20 million year-long isotopic record from northeastern Tibet covering the transition from the Eocene greenhouse to the Oligocene icehouse. We show that Rs dropped at least 4-fold through the transition into the Oligocene icehouse, marking the spread of boreal desert-steppes of Central Asia. We show that increasing aridity and the decline of monsoonal rainfall, in parallel with global cooling, caused the fall of soil respiration. These highly dynamic Rs emphasize the need for a systematic screening of paleosol isotopic data before using the soil paleobarometer to reconstruct CO2atm.
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24.
  • Lindskog, Anders, et al. (författare)
  • Coupled biostratigraphy and chemostratigraphy at Lanna, Sweden : A key section for the Floian–lower Darriwilian interval (Lower–Middle Ordovician)
  • 2023
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 615
  • Tidskriftsartikel (refereegranskat)abstract
    • The Lanna area in the province of Närke, south-central Sweden, hosts a succession of cool-water carbonate strata that are largely devoid of tectonic and diagenetic alteration, and span the Floian through lower Darriwilian Global stages (Ottenbyan–Kundan Regional stages). In this study we assess the integrated biostratigraphic and chemostratigraphic framework for the Ordovician sequence at Lanna, utilizing trilobites and conodonts coupled with bulk-rock carbon and oxygen isotopes (δ13Ccarb and δ18Ocarb). The local succession is thin but relatively complete; biostratigraphic details are similar to coeval successions in Baltoscandia. The new high-resolution δ13C and δ18O data are broadly consistent with other chemostratigraphic records at the regional scale, but notable differences in δ13C are obvious compared to global records. δ13C trends diverge markedly in the Dapingian and intra- and inter-regional differences become increasingly pronounced through younger strata. This may largely be explained by an overall low eustatic sea level, which led to more widespread oceanic restriction of epeiric seas. As a result, δ13C records became more influenced by local variables, muddling the global δ13C signal. This, in turn, suggests that sea level played a larger role than long-term changes within the global carbon cycle for regulating local–regional δ13C gradients in the Middle Ordovician. Regardless of the underlying cause(s), the documented variability poses significant challenges for using δ13C as a tool for detailed stratigraphic correlations. The limited expression of many named ‘carbon isotope excursions’ (CIEs) in the studied interval indicate that they are artefacts of local overprinting rather than reflective of changes to the global carbon cycle. Thus, these CIEs are of questionable correlative importance and validity. Although the scatter in numeric values is relatively large, long-term δ18O trends are overall consistent at the global scale, tentatively supporting the notion that climate cooled during the studied time interval.
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25.
  • Liu, Fan, et al. (författare)
  • Soft part preservation in hyolithids from the lower Cambrian (Stage 4) Guanshan Biota of South China and its implications
  • 2021
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 562, s. 110079-110079
  • Tidskriftsartikel (refereegranskat)abstract
    • Hyoliths, known globally from the Cambrian to the Permian are generally recognized as early lophotrochozoan animals of uncertain phylogenetic position. The calcareous exoskeleton of hyolithids, one of the two subgroups of hyoliths, consist of four elements including a conical conch, an external operculum, and a pair of curved enigmatic helens, but their ecology and internal morphology have long been considered controversial. Here we present for the first time, remarkably preserved hyolithids with helens and interior soft tissues from the Guanshan Biota (Cambrian, Stage 4) of Shijiangjun section, Wuding County in eastern Yunnan Province of South China. Preserved soft tissues and organs encompass the digestive tract, muscle scars and connective tissues between the operculum and conch. Three modes of soft part preservation in hyolithids from the Guanshan Biota are described: (1) preservation through pyritization, (2) sediment-infilling of guts, and (3) bacterial biofilm pseudomorphs (expressed as large internal hollow cavities), resulting from endogenous bacterial decay of soft parts. Such differential preservation of hyolith guts indicates different taphonomic modes for the soft parts of Cambrian animals in the Guanshan Biota. The newly collected material yields the oldest preserved guts in hyolithids from Konservat-biotas, and reveals new evidence for reconstructing hyolithid anatomy, such as the articulation mechanism of the opercula and the internal structures in the conch. Comparisons with younger wellpreserved hyolithid specimens indicate that the gut anatomy of hyolithids was evolutionarily conservative from the early Cambrian through to at least the Ordovician. 
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26.
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27.
  • Niedzwiedzki, Grzegorz, 1980-, et al. (författare)
  • Non-tetrapod trace fossils from the Middle Devonian tetrapod tracksite at Zachelmie Quarry, Holy Cross Mountains, Poland
  • 2020
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 553
  • Tidskriftsartikel (refereegranskat)abstract
    • The Middle Devonian (Eifelian) dolomites exposed in the Zachelmie Quarry (Holy Cross Mountains, southern Poland) contain the earliest fossil record of tetrapods. Low-diversity, but unique assemblages of trace fossils characterize the track-bearing interval within the Lower Complex of the Wojciechowice Formation. The reconstructed environment of the trace fossil-rich beds includes ephemeral lakes and/or shallow-water lagoons separated from an open marine area by sparsely vegetated islands and spits. The most abundant non-tetrapod trace fossils from these beds are large, horizontal-to-vertical burrows, and dish-, circular- to oval-shaped, shallow depressions. The burrows are abundant on the upper surfaces of thick dolomicritic beds, especially in some palaeosol levels, but they are also associated with tetrapod trackways. Large, semi-aquatic or terrestrial animals (e.g., arthropods or vertebrates) most likely produced these burrows. The circular- to oval-shaped depressions observed on a large surface and other smaller, isolated blocks from the same stratigraphical level are interpreted as fish feeding/nesting/resting traces. Piscichnus sanctacrucensis isp. nov. is proposed as a new ichnospecies of the oval-shaped fish trace fossil from the Middle Devonian of Poland. A single, medium-sized Undichnia specimen, a fish swimming trace, is associated with the Piscichnus traces. The described trace fossils provide new insight into the palaeoecology and taphonomy of the Middle Devonian tetrapod tracksite from Poland and clarify remaining controversies regarding the interpretation of some poorly preserved trace fossils from the Zachelmie Quarry.
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28.
  • Njagi, Dennis, et al. (författare)
  • A multi-proxy reconstruction of the late Holocene climate evolution in the Kapsabet Swamp, Kenya (East Africa)
  • 2021
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 574
  • Tidskriftsartikel (refereegranskat)abstract
    • Multi-proxy high-resolution records relating to climate and dominant vegetation cover have been obtained from a peat deposit retrieved from the Kapsabet swamp in western Kenya. The 4-m long peat sequence provided a continuous sedimentation record spanning ca. 3023 cal yr BP to the present and is representative of the late Holocene changes in the relatively high-altitude part of the Lake Victoria catchment. Paleoenvironmental factors influencing peat formation and organic matter (OM) source inputs in Kapsabet were reconstructed based on total organic carbon, carbon accumulation rate, delta C-13, delta N-15, C/N ratio, and specific biomarker-based n-alkane ratios. The Kapsabet peat sequence was divided into five stages based on different climatic conditions: Stage 1 (3023-1670 cal yr BP) represents a progression from cool dry to wet conditions. Stage 2 (1670-1187 cal yr BP) is a relatively warm and wet period with increased productivity and high OM input. Stage 3 (1187-625 cal yr BP) represents gradual warming coeval to the late Holocene Medieval Warm Period. Stage 4 (625-188 cal yr BP) is a cool and wet period with high variability in precipitation and hydrological conditions representing the Little Ice Age. Stage 5 (188 cal yr BP to present) represents a relatively cool and wet period that coincides with the expansion of agriculture, particularly in the lowlands. The proxies indicate a progressive change from a forested landscape to an open woodland coeval to a decline in terrigenous inputs and the advent of more wet conditions. The climate on the highlands was less variable than in the lowlands, which underwent several periods of drought and intermittent wet conditions. The changes in the catchment coincided with the expansion of agriculture and land clearance marking increased human activities in the lowlands. Overall, the Kapsabet peat sequence tracks the regional climatic changes in East Africa and marks a promising sedimentary archive for palaeoclimate reconstruction from a region with a paucity of palaeoenvironmental and palaeovegetation histories.
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29.
  • Olempska, Ewa, et al. (författare)
  • Phosphatic bromalites and microfossils from the Furongian (Cambrian) of northern Poland (Baltica) and palaeobiological implications
  • 2023
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 610
  • Forskningsöversikt (refereegranskat)abstract
    • The Furongian Słowińska Formation in Poland yielded minute three-dimensionally preserved, phosphatic fossils. Based on shape and structure, two distinct types are identified. The first type comprises sinuously folded, coiled, or spiral string-shaped specimens, interpreted as faecal material, coprolites. The specimens measure between less than one and two mm, the strings being long and against their subcircular to circular cross-section (60–150 μm). Many strings are folded in few to more than 30 regular loops, in this exceptional complexity unknown from any comparable fossil or extant faeces. Fully stretched, such strings may have an estimated length of more than three cm, suggesting continuous production of such faeces and resistance very a longer period after defecation until fossilization. Modelling similar strings indicates that the loops were produced by sidewards swinging of the body end of the producer during forward move. EDS analysis of the strings revealed low silica content, but high amounts of phosphate pointing to a organic-rich muddy bottom, which the producers swallowed and eventually became phosphatized as faeces. The producers of this faeces might have been few millimeter long and benthic, not infaunal worms, yet, none of the putative coprolites can be unquestionably ascribed to a particular animal group. The second type of fossils comprises between 100 and 220 μm long ellipsoidal to spherical forms with a smooth but wrinkled surface. They are interpreted as collapsed and deformed eggs or embryos lacking the egg shell, rather than coprolites made of digested and squeezed remains of possibly phosphatocopid crustaceans, the most abundant component of the Polish and Baltoscandian Orsten-type fossil assemblages. The spheres also have a smooth surface, which in all cases is partly broken off, uncovering an internal mass. This ranges from a small hump of possibly embryonic material in a large void, to a completely round body possibly presenting a late shield-bearing embryo filling the entire space underneath the egg shell. We interpret this second type of fossils as the first evidence of eggs in Orsten-type preservation, most likely belonging to phosphatocopid crustaceans.
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30.
  • Pujalte, Victoriano, et al. (författare)
  • A rapid sedimentary response to the Paleocene-Eocene Thermal Maximum hydrological change : New data from alluvial units of the Tremp-Graus Basin (Spanish Pyrenees)
  • 2022
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 589
  • Tidskriftsartikel (refereegranskat)abstract
    • A massive emission of light carbon about 56 Ma, recorded in marine and terrestrial sediments by a negative carbon isotope excursion (CIE), caused a short-lived (~170 kyr) global warming event known as the Paleocene–Eocene Thermal Maximum (PETM). The onset and core of this event is represented in the south Pyrenean Tremp-Graus Basin by two successive alluvial units, the Claret Conglomerate (CC) and the Yellowish Soils, which represent laterally juxtaposed depositional environments. It is generally agreed that these units record a dramatic increase in seasonal rain and an increased intra-annual humidity gradient during the PETM, but the timing of the sedimentary response to this hydrological change is a matter of debate. Some authors maintain that the CC was developed during the early, most intense phase of the carbon emission, others that its formation lagged by 16.5 ± 7.5 kyr behind the onset of the PETM. The latter claim was mainly based on the assumption that in two sections of this basin, Claret and Tendrui, the onset of the CIE occurs 3 and 8 m below the base of the CC, respectively. Here we show that in some zones between these two sections the CC was not deposited and the Yellowish Soil unit rests directly and conformably on the underlying Esplugafreda Formation. New δ13Corg data from this intervening zone provide evidence that the onset of the CIE is situated just ~1 m below the Yellowish Soils. In adjacent sections the CC erosional base cuts down deeper than 5 m, thus removing or obscuring the chemostratigraphically-defined base of the PETM. A tentative estimate based on averaged sedimentation rates indicates that ~3.8 kyr, or less, may have elapsed from the onset of the CIE to the arrival of PETM alluvium into the Claret-Tendrui study area, less than half of the lowest estimate of previous authors. Since the study area was situated about 15 km from the source area, our new estimate supports a rapid response of the sedimentary system to the hydrological change at the onset of the PETM.
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31.
  • Rosengren, Erika, et al. (författare)
  • Ungulate niche partitioning and behavioural plasticity of aurochs in Early Holocene southern Scandinavia revealed by stable isotope analysis of bone collagen
  • 2024
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182. ; 648, s. 1-12
  • Tidskriftsartikel (refereegranskat)abstract
    • This study examines the impact of the extensive climatic and environmental changes associated with the Early Holocene on the feeding ecology of aurochs, European bison, red deer, and Eurasian elk in southern Scandinavia from radiocarbon dates and analysis of stable carbon and nitrogen isotopes. Molecular sex information is utilised in the study of aurochs to understand the underlying reasons behind observed intraspecific differences. Asynchronous diachronic changes in dietary palaeoecology were observed between the included taxa. The observed trends in foraging and habitat use among herbivores in our dataset can be attributed to the directional vegetation change from open landscape to forest. Our findings imply that environmental changes and/or interspecific competition contributed to the local extinction of European bison and impacted the niches of remaining speciesthrough niche overlap (cervids) and partitioning (between cervids and aurochs). Thus, our observations are consistent with the influence of multiple mechanisms that acted concurrently.
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32.
  • Sha, Longbin, et al. (författare)
  • Diatom-reconstructed summer sea-surface temperatures and climatic events off North Iceland during the last deglaciation and Holocene
  • 2022
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 602
  • Tidskriftsartikel (refereegranskat)abstract
    • Lateglacial and Holocene summer sea-surface temperature (SST) variability in the northern North Atlantic was reconstructed based on diatom records from two sediment cores from the North Icelandic shelf. The temperature changes are discussed in relation to palaeoceanographic circulation patterns and past climatic changes. Modern diatom data from surface sediments from around Iceland and Southeast and West Greenland, with known modern environmental variables, were used as the basis for the quantitative reconstruction of summer SST. The results show that summer SSTs varied during both the Lateglacial and the Holocene, but the amplitude of SST variations during the Lateglacial was greater than that during the Holocene. No pronounced warm or cool events were recorded on the North Icelandic shelf during the GI-1e to GI-1a events (Bølling-Allerød) and the GS-1 event (Younger Dryas). The changes in SST were possibly caused by major changes in the ocean circulation pattern around Iceland, and by minor variations in the interaction between the cold and warm currents in the region. Comparison of the reconstructed summer SSTs with other marine records from the North Atlantic suggests an antiphase relationship between the oceanic climatic responses off North Iceland and in the eastern North Atlantic during the Lateglacial and the earliest part of the Holocene (the Preboreal).
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33.
  • Skovsted, Christian, 1974-, et al. (författare)
  • On the origin of hyolith helens
  • 2020
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 555
  • Tidskriftsartikel (refereegranskat)abstract
    • Helens, the curved lateral spines inserted between the conch and operculum of some hyoliths, are a unique morphological adaptation characterizing the order Hyolithida. These structures are paired, movable and had a mechanical function, probably related to orienting the hyolith conch and lifting its aperture above the sea floor. We show that helens are intimately associated with the hyolith opercula and are structurally comparable to the rod like units that constitute the clavicles, internal wall-like structures of the hyolithid operculum that probably evolved to secure the operculum from lateral displacement in the conch aperture. In some early Cambrian hyolith taxa that lack helens, such as Paramicrocornus, new clavicle rods are added in the gap separating the clavicles from the cardinal processes, the same position where helens are inserted in later hyolithids. We also show that the size of incipient helens at the earliest ontogenetic stage matches the size of the clavicles in associated opercula. We propose that helens are modified clavicle rods that were detached from the operculum and developed into lateral spines through allometric growth during early ontogeny. Further, we suggest a four-step model for the evolution of hyolithid hyoliths from orthothecid ancestors: 1, Externally fitting operculum; 2, Stabilizing, radially arranged structures on the inside of the operculum; 3, Ligula and folded operculum; 4, Detachment of clavicle rods and origin of helens.
  •  
34.
  • Slodownik, Miriam, et al. (författare)
  • Fossil seed fern Lepidopteris ottonis from Sweden records increasing CO2 concentration during the end-Triassic extinction event
  • 2021
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - Amsterdam : Elsevier. - 0031-0182 .- 1872-616X. ; 564
  • Tidskriftsartikel (refereegranskat)abstract
    • The end-Triassic event (ETE), a short global interval occurring at the end of the Triassic Period (~201.5 Ma), was characterized by climate change, environmental upheaval, as well as widespread extinctions in both the marine and terrestrial realms. It was associated with extensive perturbations of the carbon cycle, principally caused by the volcanic emplacement of the Central Atlantic Magmatic Province in relation to the break-up of Pangea. The correlated change in atmospheric CO2 concentrations (pCO2) can be reconstructed with the stomatal proxy, which utilizes the inverse relationship between stomatal densities of plant leaves (here stomatal index (SI), which is the percentage of stomata relative to epidermal cells) and pCO2. Fossilized Lepidopteris leaves are common and widespread in Triassic strata, thus offering great potential for high-resolution pCO2 reconstructions. A dataset of leaf cuticle specimens belonging to the seed fern species Lepidopteris ottonis from sedimentary successions in Skåne (Scania), southern Sweden, provided the possibility of pCO2 reconstruction at the onset of the ETE. Here, we tested the intra- and interleaf variability of L. ottonis SI, and estimated the pCO2 during the onset of the ETE. Our findings confirm L. ottonis as a valid proxy for palaeo-pCO2, also when using smaller leaf fragments. Importantly, the statistical analyses showed that the SI values of abaxial and adaxial cuticles are significantly different, providing a tool to distinguish between the two sides and select cuticles for analysis. Reconstructed pCO2 increased from ~1000 pre ETE to ~1300 ppm at the onset of the event, a significant increase of ~30% over a relatively short time period. The pCO2 recorded here is similar to previously published estimates, and strongly supports the observed pattern of elevated pCO2 at the onset of the ETE.
  •  
35.
  • Tang, Wanru, et al. (författare)
  • Drought variations in the southeastern Tibetan Plateau region since 1704 and their link to the Atlantic Multidecadal Oscillation
  • 2023
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182. ; 630
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding the long-term history of drought in the Tibetan Plateau region is important to improve understanding of drought frequency in response to future global warming. Although the Tibetan Plateau has become generally wetter recently, the southeastern part of the Tibetan Plateau has become drier since the 2000s. To place this drying trend in a historical context, we conducted tree-ring studies for Abies spectabilis and Tsuga dumosa at three sites in the southeastern Tibetan Plateau, and developed tree-ring width (TRW), earlywood width (EWW), and latewood width (LWW) chronologies to permit local drought reconstruction. Based on correlation between these tree-ring parameters and instrumental meteorological data, the EWW chronologies were identified as suitable variables for reconstructing the average April–July self-calibrating Palmer Drought Index (scPDSI). The reconstruction accounted for 45.86% of the variance in the instrumental record and allowed us to extend the drought record back to 1704 CE. Based on this new dataset, the driest interval was from 1907 to 1919 CE during which time agricultural production fell by about 70% according to written historical records, leading to severe famine. Our findings suggest that this early twentieth century drought was in phase with the previously known drought over the northern Daxing'an Mountains. However, the southeastern Tibetan Plateau drought occurred one decade earlier than the known widespread drought event in North China during the 1920s–1930s. We show that this spatial drought pattern may have been modulated by the Atlantic Multidecadal Oscillation.
  •  
36.
  • Vajda, Vivi, et al. (författare)
  • Confirmation that Antevsia zeilleri microsporangiate organs associated with latest Triassic Lepidopteris ottonis (Peltaspermales) leaves produced Cycadopites-Monosulcites-Chasmatosporites- and Ricciisporites-type monosulcate pollen
  • 2024
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182. ; 640
  • Tidskriftsartikel (refereegranskat)abstract
    • In reply to the commentary by N. Zavialova (Rev. Palaeobot. Palynol. 322, 105,065), we provide additional data and illustrations reaffirming that the Triassic peltaspermalean ‘seed-fern’ Lepidopteris ottonis produced the abnormal pollen Ricciisporites tuberculatus, solving a long-standing mystery in palaeobotany. The microsporangiate organ Antevsia zeilleri linked to Lepidopteris ottonis foliage produced polymorphic pollen ranging from smooth-walled monads that would normally be attributed to Cycadopites, Monosulcites and Chasmatosporites to strongly ornamented Ricciisporites tuberculatus-type grains occurring in permanent tetrads. Multiple microscopy techniques reveal that these in situ and associated dispersed pollen are represented by a complete continuum in exine ornamentation. Moreover, scanning electron microscopy and ultrastructural analyses reveal variation in the wall architecture between these pollen types that can be explained by aberrant developmental pathways within the pollen sac. Finally, the occurrence of Ricciisporites tuberculatus in at least 15 Antevsia zeilleri sacs and their co-occurrence with smooth-walled monosulcate pollen in an additional five pollen sacs, in the absence of any other palynomorphs, plant detritus or mineral matter, demonstrates their co-production by the parent plant and excludes the possibility of taphonomic mixing.
  •  
37.
  • Vajda, Vivi, et al. (författare)
  • The ‘seed-fern’ Lepidopteris mass-produced the abnormal pollen Ricciisporites during the end-Triassic biotic crisis
  • 2023
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 627
  • Tidskriftsartikel (refereegranskat)abstract
    • The end-Triassic mass extinction (ETE; ~201.6 million years ago) led to dramatic changes in terrestrial eco­ systems including the extinction of several seed-plant groups. Among the most intriguing features in the vege­ tation signal is the dominance of the peculiar pollen, Ricciisporites tuberculatus Lundblad, across large areas of the Northern Hemisphere immediately prior to and during the ETE. The parent plant of this pollen has remained unknown for 70 years. Here, we demonstrate that the ‘seed-fern’ Lepidopteris ottonis (Go¨ppert) Schimper (Pel­ taspermales) produced R. tuberculatus in permanent tetrads. We show that R. tuberculatus is a large, abnormal form of the small smooth-walled monosulcate pollen traditionally associated with L. ottonis, which disappeared at the ETE, when volcanism induced cold-spells followed by global warming. We argue that the production of aberrant R. tuberculatus resulted from ecological pressure in stressed environments that favoured asexual reproduction in peltasperms. The expansion of dry environments led to the dominance of drought-tolerant plants in the Early Jurassic of northern middle latitudes.
  •  
38.
  • Wang, Jing, et al. (författare)
  • Impact of centennial-scale solar activity reduction on the weakened Asian monsoon event at 9.2 ka BP
  • 2023
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182. ; 628
  • Tidskriftsartikel (refereegranskat)abstract
    • The weakened Asian monsoon event at 9.2 ka has been documented in many proxy-based reconstructions, but its underlying causes are uncertain. In this study, we investigated this event from a regional monsoon perspective by analysing simulations of Holocene transient solar activity forcing using the Community Earth System Model and high-resolution proxies. Our results revealed two separate periods of decreasing precipitation in the western North Pacific (WNP) and South Asian (SA) monsoons from 9.5 to 9.2 ka, each lagging behind two remarkable weakening events (0.38 and 0.21 W m−2) in solar forcing. However, there was no significant change in East Asian summer monsoon precipitation at 9.2 ka based on our experiment. Moisture budget analysis indicated that the dynamic effects term (i.e., anomalous descending motion) figured prominently in decreasing WNP and SA monsoon precipitation. Such a change was affected by an anomalous WNP anticyclone, which was maintained by the ‘wind-evaporation-sea surface temperature’ feedback during the decay phase of the centennial-scale El Niño-like event. The development of centennial El Niño-like conditions was caused by a reduction in solar irradiance. Reduced solar irradiance induced cooling over northern Australia, generating anomalous zonal sea level pressure gradients and westerlies over the tropical Pacific, ultimately resulting in the development of an El Niño-like pattern.
  •  
39.
  • Weber, Katrin, et al. (författare)
  • Dental microwear texture analysis on extant and extinct sharks : Ante- or post-mortem tooth wear?
  • 2021
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 562
  • Tidskriftsartikel (refereegranskat)abstract
    • Sharks are apex-predators that play an important role in past and present aquatic food webs. However, their diet - especially in extinct species - is often not well constrained. Dental microwear texture analysis (DMTA) has been successfully applied to reconstruct diet and feeding behaviours of different aquatic and terrestrial vertebrates. However, unlike in mammals, food-to-tooth contact in sharks is rather limited because only larger prey is manipulated before swallowing. Together with a fast tooth replacement rate, this reduces wear on individual teeth. Here, we present an explorative study of dental microwear texture on extant and extinct sharks to test whether ante-mortem wear is related to ingested diet or habitat preferences and resistant to post-mortem alteration processes. Shark teeth from 24 modern species and 12 fossil species from different localities were measured. As an additional comparison, extant shark teeth of Carcharhinus plumbeus were tumbled in sediment-water suspensions to simulate post-mortem mechanical alteration by sediment transport. Only three of the twelve extant shark species with three or more specimens had significantly different dental surface textures. Furthermore, no clear relation between food or habitat preferences and ante-mortem dental wear features was detected for this sample set. Tumbling modern shark teeth with siliciclastic sediment of four different grain size fractions led to increasing complexity of the dental surface. Fossil specimens resemble these experimentally altered shark teeth more in complexity and roughness. Thus, fossil shark teeth seem to display either very different (e.g. harder) diet-related wear or a strong degree of post-mortem alteration. Based on our restricted sample size, dental wear of shark teeth does overall not seem to simply reflect dietary differences; hence, it is difficult to use DMTA as reliable dietary reconstruction, in either extant nor extinct sharks.
  •  
40.
  • Witkowski, Jakub, et al. (författare)
  • Early Paleogene biosiliceous sedimentation in the Atlantic Ocean : Testing the inorganic origin hypothesis for Paleocene and Eocene chert and porcellanite
  • 2020
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 556
  • Tidskriftsartikel (refereegranskat)abstract
    • The widespread occurrence of lower Eocene chert and porcellanite has been viewed as a major paleoceanographic issue since the advent of ocean drilling, and both biotic and abiotic forcings have been proposed to explain it. We present a reconstruction of indurated siliceous sediment (ISS) and preserved biosiliceous sediment (PBS) occurrences in the Atlantic Ocean through the Paleocene and Eocene (~66 through 34 Ma). ISS and PBS distributions reveal dissimilar temporal trends, with the peak of ISS occurrences coinciding with the Early Eocene Climatic Optimum, in line with previous studies. PBS occurrences show a generally increasing trend culminating between 44 and 43 Ma. The common co-occurrence of ISS and PBS, and their coherent geographic distribution lends strong support to the biogenic origin of the precursor to the widespread Paleogene ISS, and argues against an inorganic mode of early Cenozoic chert and porcellanite precipitation. Weight per cent biogenic opal records and trends in linear sedimentation rates indicate two plausible modes of silicification: 1) silicification due to prolonged exposure of biogenic opal-rich sediments to corrosive bottom waters; and 2) silicification due to elevated pressures and temperatures caused by rapid burial of biogenic opal-rich deposits. The confinement of ISS and PBS to proximal sites along continental margins points to the reliance of siliceous sedimentation through the Paleocene and Eocene on terrestrial supply of dissolved silicon. Consistent with this, quantitative siliceous microfossil assemblage records from the Blake Nose in the NW Atlantic indicate that the nutrient-rich marginal rather than oligotrophic pelagic settings hosted the majority of siliceous plankton production through the early Paleogene. The inorganic SiO2 precipitation model is unlikely to have been the dominant mechanism responsible for ubiquitous occurrences of early Paleogene ISS. We favor the biogenic ISS precursor scenario and reconcile it with the low-productivity early Cenozoic oceans by showing that large volumes of biogenic silica were supplied to the western North Atlantic Ocean from the North American margin through the Paleocene and Eocene. Dissolution of this surplus silica was facilitated by an early southwestward flow of young, SiO2-depleted waters from the North Atlantic. All these factors contributed to ISS and PBS focusing in the western North Atlantic through the early Paleogene.
  •  
41.
  • Xian, Xiaofeng, et al. (författare)
  • Reassessment of Archaeooides based on new material from the Fortunian (early Cambrian) of China infers algal affinity
  • 2024
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182. ; 637
  • Tidskriftsartikel (refereegranskat)abstract
    • Archaeooides originally refers to a group of early Cambrian globular microfossils with regularly arranged nodular surface ornaments, and of a diameter ranging from less than 400 μm to more than 2 mm. The traditional taxonomy assigns all Archaeooides-like microfossils to a single morphotaxon, Archaeooides granulatus, irrespective of their differences in size and surface ornamentation. Archaeooides has been interpreted as a possible diapause embryo because of its inferred palintomical cell division and thick wall with vesicular structures. However, this interpretation needs further testing based on an updated taxonomy and differentiation of taphonomic artifacts from biological structures. Here, we report new, three-dimensionally phosphatized, Archaeooides-like microfossils from the Fortunian of China. In addition to A. granulatus with nodular ornaments, we recognized three new taxa, i.e., Shaanisphaera spinosa gen. et sp. nov. with spine-like ornaments, Qinlingisphaera conica gen. et sp. nov. with cone-like ornaments, and Dahisphaera plana gen. et sp. nov. with oblate ornaments. Each taxon has a wide size interval, ranging continuously from several hundred micrometers to one or two millimeters, which is different from animal eggs that generally have a narrow and conservative size interval. Micro-CT analyses and thin sections reveal that the vesicular structures may be taphonomic in nature, and that the wall thickness is specimen-dependent. Collectively, the evidence at hand does not support an embryo interpretation for Archaeooides. Instead, the wide size interval probably represents ontogenetic variations that are common in many fossil and modern algae, and thus further suggests an algal affinity for Archaeooides as well as the other Archaeooides-like microfossils.
  •  
42.
  • Yan, Guanzhou, et al. (författare)
  • The record of early Silurian climate changes from South China and Baltica based on integrated conodont biostratigraphy and isotope chemostratigraphy
  • 2022
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 606
  • Tidskriftsartikel (refereegranskat)abstract
    • New conodont and stable isotope data are presented from the classical Baizitian section in the Yanbian County of Sichuan Province, South China. The Telychian to Sheinwoodian strata were sampled and studied for carbon isotope stratigraphy and conodont biostratigraphy. The paired δ13Ccarb and δ13Corg data reveal a pronounced positive excursion, the Manitowoc carbon isotope excursion (Manitowoc CIE, ‘Manitowoc Excursion’) spanning the upper Pterospathodus eopennatus Zone and the lower Pterospathodus amorphognathoides amorphognathoides Superzone, with an increase of ca. 2‰ in δ13Ccarb and ca. 5‰ in δ13Corg. Well-bracketed by conodont biostratigraphy, the Manitowoc CIE is an essential tie-point for correlation between the Baizitian succession and the Telychian strata of Baltica and Laurentia. Our new δ13Ccarb and δ13Corg data imply that the carbon isotope excursion previously recognized as the ‘Ireviken Excursion’ (Early Sheinwoodian Carbon Isotope Excursion) at Baizitian should be revised as being the Manitowoc CIE. The Δ13C data presented in this study further suggest a slight concurrent drop of atmospheric CO2, and thus add evidence for a perturbation of the global carbon cycle during the middle Telychian. Based on the combined information from the conodont apatite oxygen isotope records from Estonia and the significant stratigraphic gaps recognized at the Baizitian section, we propose that the latter stratigraphic gaps should correlate with the Telychian Valgu and the early Sheinwoodian glaciation.
  •  
43.
  • Zhang, Lei, et al. (författare)
  • Diverse cuticular remains in Cambrian (Series 2) SSF assemblages from China and the pioneer metazoan colonization of offshore environments
  • 2021
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 567
  • Tidskriftsartikel (refereegranskat)abstract
    • Our understanding of the early Cambrian bioradiation is largely driven by the contrasting information obtained from small skeletal fossils (SSF) and various types of exceptionally preserved fossils from different parts of the world. In this study, a new ‘Orsten’-type fossil Lagerstätte is reported from the Cambrian Series 2 upper Shuijingtuo Formation in the eastern Three Gorges area, South China. The Shuijingtuo Formation yielded a range of microscopic fragments of metazoan cuticles as well as fragments of possible epithelial tissue. Seventeen different types of micro-ornamentation patterns are recognized on the surface of these cuticular fragments. Based on comparisons with fossil organisms recorded from coeval strata elsewhere, as well as extant relatives, possible affinities with arthropods, palaeoscolecids, acrotretid brachiopods and mollusks are discussed. This ‘Orsten’-type fossil assemblage was deposited in offshore environments, and the lack of evidence for long-distance transportation indicates that a highly diverse fauna was present in, or very close to, the relatively deep shelf settings in the Three Gorges area during the early Cambrian (Epoch 2, Age 3). The invasion of metazoans into deeper, offshore environments could have closely followed, or even been coeval, with their radiation in relatively shallow water settings. Thus, albeit highly fragmented, such cuticular fossils can aid in providing a more complete picture of the Cambrian bioradiation.
  •  
44.
  • Zhang, Z. Y., et al. (författare)
  • From Tethyan subduction to Arabia-Eurasia continental collision: Multiple geo-thermochronological signals from granitoids in NW Iran
  • 2023
  • Ingår i: Palaeogeography Palaeoclimatology Palaeoecology. - 0031-0182. ; 621
  • Tidskriftsartikel (refereegranskat)abstract
    • NW Iran, situated between the Arabian and Eurasian plates, carries a record of both Paleo-Tethyan and Neo-Tethyan tectonic evolution. During the Wilson Cycle of Tethys Ocean opening and closing, several episodes of magmatism from Late Paleozoic to latest Cenozoic generated a massive volume of intrusive rocks. These in-trusives, which record cooling histories from high-temperatures to final exhumation, are ideal for multiple geo-thermochronological studies. Our new zircon and apatite U-Pb results suggest three regional magmatic events in the Late Carboniferous, mid-Cretaceous and middle Eocene, which could be related to Paleo-Tethys subduction, Neo-Tethys subduction and Neo-Tethyan ridge subduction, respectively. New apatite fission track and (U-Th)/He data reveal post-magmatic cooling and differential exhumation related to subduction and collision. By inte-grating published regional thermochronological data from northeastern part of the Middle East, a broader tectono-thermal framework is outlined as follows: 1) Cretaceous cooling signals are most pronounced in the Alborz and Caucasus, and reflect back-arc extension during Neo-Tethyan subduction; 2) diachronous Neo-Tethyan evolution led to the Paleocene assemblage of Anatolia in the west, and subduction associated with a late Paleocene-Eocene magmatic flare-up in Iran. Subsequent westward escape of Anatolia and extensive surface uplift were driven by propagation of Arabia-Eurasia collision in the Miocene; 3) Continuous northward inden-tation of Arabia into Eurasia triggered late Miocene-Pliocene fast exhumation of the Zagros, Alborz and the Caucasus.
  •  
45.
  • Zigaite, Zivile, 1979-, et al. (författare)
  • Trace and rare earth element compositions of Silurian conodonts from the Vesiku Bone Bed : Histological and palaeoenvironmental implications
  • 2020
  • Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 549
  • Tidskriftsartikel (refereegranskat)abstract
    • In-situ minor, trace and rare earth element (REE) compositions have been measured in conodonts from the lower Silurian Vesiku Bone Bed (Estonia), with the aim to visualize and to quantify conodont apatite elemental geochemistry, to evaluate compositional differences between conodont histologies, and to evaluate the use of conodont chemistry as a palaeobiological or palaeoenvironmental proxy. Tissue-selective analyses of minor, trace and rare earth element compositions of albid, hyaline, and basal tissues demonstrated significant chemical offsets among these histologies. The albid tissue had the lowest REE and trace element concentrations, suggesting crystallinity-determined better resilience to diagenetic alteration as documented in previous studies. Conversely, the basal tissue had highest concentrations of REEs and many trace elements, except for Sr that showed an opposite trend. The higher concentrations in albid and hyaline tissues supports the in-vivo Sr incorporation by conodont crown. Nonetheless, the obtained SN-normalized REE patterns were uniform through all the analyzed conodont taxa and different tissues, implying common diagenetic history. Absence of a Ce anomaly, and defined negative Eu anomaly indicate reducing conditions during early burial. These results validate current interpretations of the palaeoenvironmental conditions during the deposition of Vesiku Bone Bed and bolsters the use of REEs in Palaeozoic marine vertebrates as an important palaeoenvironmental proxy.
  •  
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