| 1. |
- Bercovici, Antoine, et al.
(författare)
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Palynostratigraphy of John's Nose, a new Cretaceous-Paleogene boundary section in southwestern North Dakota, USA
- 2012
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Ingår i: Palynology. - : Informa UK Limited. - 1558-9188 .- 0191-6122. ; 36, s. 36-47
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Tidskriftsartikel (refereegranskat)abstract
- This study documents the terrestrial palynological record at the John's Nose section, a new Cretaceous-Paleogene (K-Pg) boundary site in North Dakota, USA. In addition to Mud Buttes and Pyramid Butte, John's Nose represents the third K-Pg section in southwestern North Dakota that preserves direct evidence of the Chicxulub asteroid impact, allowing for direct comparison over the timing and trends of the palynological record in respect to this event. The palynological analysis of John's Nose section reveals the presence of 68 pollen and spore taxa. Immediately above the boundary clay, a high abundance of fern spores of the genera Cyathidites and Laevigatosporites is recorded (with 59% of the assemblage being represented by Cyathidites). This very distinctive K-Pg 'fern spike' event is correlated with the devastation of land plants immediately following the asteroid impact and matches the composition generally reported from other sites in southwestern North Dakota. Palynostratigraphy demonstrates that the placement of the K-Pg boundary based upon the identification of the Last Appearance Datum (LAD) of typical Maastrichtian taxa (K-taxa) may be misleading. The presence of occasional K-taxa up to a few meters above the boundary clay at John's Nose represents an important difference when compared to previous reports. In light of this observation, LADs should be used cautiously as the primary criteria to identify the boundary; some K-taxa may have a short-term presence in the earliest Paleogene, or be reworked. In the John's Nose section, major changes and extinction in the palynological record occur at the geochemical K-Pg boundary, indicating that a catastrophic turnover took place over a short time.
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| 2. |
- Bercovici, Antoine, et al.
(författare)
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Palynostratigraphy of the cretaceous-paleogene mass-extinction interval of the Northern Hemisphere
- 2012
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Ingår i: Dìcéngxué zázhì. - 0253-4959. ; 36:2, s. 165-178
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Tidskriftsartikel (refereegranskat)abstract
- For a long time debate has taken place regarding the trends and extinction rates associated with the Cretaceous- Paleogene (K-Pg) mass extinction event on land. While mainly focussed on vertebrates and more especially non-avian dinosaurs, the dynamics of the plant cover remains nonetheless a major component for the understanding the biological response across the K-Pg interval and associated ecosystem destabilization. In this paper, we present a review of the late Cretaceous to Paleogene pollen and spore stratigraphy within the Northern Hemisphere Aquilapollenites paleophytogeographic province. In the United States of America, Late Cretaceous assemblages are marked by the appearance of a series of key-taxa, the Santonian-Campanian transition is characterized by the appearance of Aquilapollenites and associated triprojectate genera, while the base of the Maastrichtian is marked by the appearance of the oculate genus Wodehouseia as well as Kurtzipites sp. The K-Pg extinction event remains easily identifiable in the palynological record with the disappearance of a series of angiospermous taxa part of the Wodehouseia spinata Assemblage Zone, which are characterized by relatively large size and complex wall structure. The recovery palynoflora in the Paleocene is represented by assemblages dominated by porate grains, with key-species from the Momipites and Caryapollenites genera. As current data covers mostly the North American terrestrial record, more research efforts are needed within Chinese,European and Southern Hemisphere localities to provide for a better understanding of the global response of the terrestrialbiosphere to the K-Pg impact event.
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| 3. |
- Bercovici, Antoine, et al.
(författare)
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Permian continental paleoenvironments in Southeastern Asia: New insights from the Luang Prabang Basin (Laos)
- 2012
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Ingår i: Journal of Asian Earth Sciences. - : Elsevier BV. - 1367-9120. ; 60, s. 197-211
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Tidskriftsartikel (refereegranskat)abstract
- In Laos (Southeastern Asia), Late Paleozoic sediments were identified by early French explorations across Indochina during the late 19th century (Pavie missions), but little work was undertaken to characterize the sedimentological and stratigraphical context until now. From detailed sedimentological and paleontological studies, we propose an interpretation of the depositional environment and of the stratigraphic context of series located on the right bank of the Mekong River in the Luang Prabang Basin where three main formations were described. The silicoclastic Red Claystone Formation, attributed to alluvial plain environment, contains large fragments of unidentified dicynodonts. The Limestones and Sandstones Formation preserves a new macrofloral assemblage displaying affinities with Middle to Late Permian Cathaysian floras of South China. This assemblage occurs as an intercalation within marine calcareous sandstones that have yielded a marine fauna, including the ammonoid Pseudotirolites sp. which indicates a Late Permian (Changhsingian) age. The well-developed Purple Claystones Formation yielded an abundant and well preserved Late Permian fauna composed of a carnivorous amphibian and numerous Dicynodon cranial and postcranial elements. This formation shows a vertical evolution from braided river to alluvial plain with sheet-flood sand bed and bed-load rivers, with a constant supply of volcanic clasts. Results from the analysis of the paleontological associations in the Luang Prabang Basin suggest that a continental communication between Laurussia and the Indochina Block existed during the Permian, allowing for migration of the terrestrial Dicynodon fauna. (C) 2012 Elsevier Ltd. All rights reserved.
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| 4. |
- Bercovici, Antoine, et al.
(författare)
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Terrestrial paleoenvironment characterization across the Permian-Triassic boundary in South China
- 2015
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Ingår i: Journal of Asian Earth Sciences. - : Elsevier BV. - 1367-9120 .- 1878-5786. ; 98, s. 225-246
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Tidskriftsartikel (refereegranskat)abstract
- Well-preserved marine fossils in carbonate rocks permit detailed studies of the end-Permian extinction event in the marine realm. However, the rarity of fossils in terrestrial depositional environments makes it more challenging to attain a satisfactory degree of resolution to describe the biotic turnover on land. Here we present new sedimentological, paleontological and geochemical (X-ray fluorescence) analysis from the study of four terrestrial sections (Chahe, Zhejue, Mide and Jiucaichong) in Western Guizhou and Eastern Yunnan (Yangtze Platform, South China) to evaluate paleoenvironmental changes through the Permian-Triassic transition. Our results show major differences in the depositional environments between the Permian Xuanwei and the Triassic Kayitou formations with a change from fluvial-lacustrine to coastal marine settings. This change is associated with a drastic modification of the preservation mode of the fossil plants, from large compressions to small comminuted debris. Plant fossils spanning the Permian-Triassic boundary show the existence of two distinct assemblages: In the Xuanwei Formation, a Late Permian (Changhsingian) assemblage with characteristic Cathaysian wetland plants (mainly Gigantopteris dictyophylloides, Gigantonoclea guizhouensis, G. nicotianaefolia, G. plumosa, G. hallei, Lobatannularia heinanensis, L. cathaysiana, L. multifolia, Annularia pingloensis, A. shirakii, Paracalamites stenocostatus, Cordaites sp.) is identified. In the lowermost Kayitou Formation, an Early Triassic (Induan) Annalepis-Peltaspermum assemblage is shown, associated with very rare, relictual gigantopterids. Palynological samples are poor, and low yield samples show assemblages almost exclusively represented by spores. A similar to 1 m thick zone enriched in putative fungal spores was identified near the top of the Xuanwei Formation, including diverse multicellular forms, such as Reduviasporonites sp. This interval likely corresponds to the PTB "fungal spike" conventionally associated with land denudation and ecosystem collapse. While the floral turnover is evident, further studies based on plant diversity would be required in order to assess contribution linked to the end-Permian mass extinction versus local paleoenvironmental changes associated with the transition between the Xuanwei and Kayitou formations. (C) 2014 Elsevier Ltd. All rights reserved.
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| 5. |
- Blanchard, Sebastien, et al.
(författare)
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Late Triassic volcanic activity in South-East Asia: New stratigraphical, geochronological and paleontological evidence from the Luang Prabang Basin (Laos)
- 2013
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Ingår i: Journal of Asian Earth Sciences. - : Elsevier BV. - 1367-9120. ; 70-71, s. 8-26
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Tidskriftsartikel (refereegranskat)abstract
- In South-East Asia, sedimentary basins displaying continental Permian and Triassic deposits have been poorly studied. Among these, the Luang Prabang Basin (North Laos) represents a potential key target to constrain the stratigraphic and structural evolutions of South-East Asia. A combined approach involving sedimentology, palaeontology, geochronology and structural analysis, was thus implemented to study the basin. It resulted in a new geological map, in defining new formations, and in proposing a complete revision of the Late Permian to Triassic stratigraphic succession as well as of the structural organization of the basin. Radiometric ages are used to discuss the synchronism of volcanic activity and sedimentation. The Luang Prabang Basin consists of an asymmetric NE-SW syncline with NE-SW thrusts, located at the contact between Late Permian and Late Triassic deposits. The potential stratigraphic gap at the Permian-Triassic boundary is therefore masked by deformation in the basin. The Late Triassic volcaniclastic continental deposits are representative of alluvial plain and fluvial environments. The basin was fed by several sources, varying from volcanic, carbonated to silicic (non-volcanic). U-Pb dating of euhedral zircon grains provided maximum sedimentation ages. The stratigraphic vertical succession of these ages, from ca. 225, ca. 220 to ca. 216 Ma, indicates that a long lasting volcanism was active during sedimentation and illustrates significant variations in sediment preservation rates in continental environments (from similar to 100 m/Ma to similar to 3 m/Ma). Anhedral inherited zircon grains gave older ages. A large number of them, at ca. 1870 Ma, imply the reworking of a Proterozoic basement and/or of sediments containing fragments of such a basement. In addition, the Late Triassic (Carnian to Norian) sediments yielded to a new dicynodont skull, attributed to the Kannemeyeriiform group family, from layers dated in between similar to 225 and similar to 221 Ma (Carnian). (C) 2013 Elsevier Ltd. All rights reserved.
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| 6. |
- Blois, Jessica L., et al.
(författare)
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A framework for evaluating the influence of climate, dispersal limitation, and biotic interactions using fossil pollen associations across the late Quaternary
- 2014
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Ingår i: Ecography. - : Wiley. - 1600-0587 .- 0906-7590. ; 37:11, s. 1095-1108
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Tidskriftsartikel (refereegranskat)abstract
- Environmental conditions, dispersal lags, and interactions among species are major factors structuring communities through time and across space. Ecologists have emphasized the importance of biotic interactions in determining local patterns of species association. In contrast, abiotic limits, dispersal limitation, and historical factors have commonly been invoked to explain community structure patterns at larger spatiotemporal scales, such as the appearance of late Pleistocene no-analog communities or latitudinal gradients of species richness in both modern and fossil assemblages. Quantifying the relative influence of these processes on species co-occurrence patterns is not straightforward. We provide a framework for assessing causes of species associations by combining a null-model analysis of co-occurrence with additional analyses of climatic differences and spatial pattern for pairs of pollen taxa that are significantly associated across geographic space. We tested this framework with data on associations among 106 fossil pollen taxa and paleoclimate simulations from eastern North America across the late Quaternary. The number and proportion of significantly associated taxon pairs increased over time, but only 449 of 56 194 taxon pairs were significantly different from random. Within this significant subset of pollen taxa, biotic interactions were rarely the exclusive cause of associations. Instead, climatic or spatial differences among sites were most frequently associated with significant patterns of taxon association. Most taxon pairs that exhibited co-occurrence patterns indicative of biotic interactions at one time did not exhibit significant associations at other times. Evidence for environmental filtering and dispersal limitation was weakest for aggregated pairs between 16 and 11 kyr BP, suggesting enhanced importance of positive species interactions during this interval. The framework can thus be used to identify species associations that may reflect biotic interactions because these associations are not tied to environmental or spatial differences. Furthermore, temporally repeated analyses of spatial associations can reveal whether such associations persist through time.
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| 7. |
- Cui, Ying, et al.
(författare)
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Carbon cycle perturbation expressed in terrestrial Permian–Triassic boundary sections in South China
- 2015
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Ingår i: Global and Planetary Change. - : Elsevier. - 0921-8181 .- 1872-6364.
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Tidskriftsartikel (refereegranskat)abstract
- Stable isotopes of inorganic and organic carbon are commonly used in chemostratigraphy to correlate marine and terrestrial sedimentary sequences based on the assumption that the carbon isotopic signature of the exogenic carbon pool dominates other sources of variability. Here, sediment samples from four Permian–Triassic boundary (PTB) sections of western Guizhou and eastern Yunnan provinces in South China, representing a terrestrial to marine transitional setting, were analyzed for δ13C of organic matter (δ13Corg). These values were subsequently compared to published δ13C values of carbonates (δ13Ccarb) from the Global Stratotype Section and Point at Meishan and many other marine and terrestrial sections. A similar isotopic trend evident through all four sections is characterized by a negative shift of 2–3‰ at the top of the Xuanwei Formation, where we tentatively place the PTB. This negative shift also corresponds to a turnover in the vegetation and the occurrence of fungal spores, which is generally interpreted as a proliferation of decomposers and collapse of complex ecosystems during the end-Permian mass extinction event. Moreover, the absolute values of δ13Corg are more extreme in the more distal (marine) deposits. The δ13Corg values for the studied sediments are more variable compared to coeval δ13Ccarb records from marine records especially in the interval below the extinction horizon. We contend that the depositional environment influenced the δ13Corg values, but that the persisting geographic δ13Corg pattern through the extinction event across the four independent sections is an indication that the atmospheric δ13C signal left an indelible imprint on the geologic record related to the profound ecosystem change during the end-Permian extinction event.
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| 8. |
- Cui, Ying, et al.
(författare)
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Carbon cycle perturbation expressed in terrestrial Permian–Triassic boundary sections in South China
- 2017
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Ingår i: Global and Planetary Change. - Amsterdam : Elsevier. - 0921-8181 .- 1872-6364. ; 148, s. 272-285
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Tidskriftsartikel (refereegranskat)abstract
- Stable isotopes of inorganic and organic carbon are commonly used in chemostratigraphy to correlatemarine andterrestrial sedimentary sequences based on the assumption that the carbon isotopic signature of the exogenic carbon pool dominates other sources of variability. Here, sediment samples fromfour Permian–Triassic boundary (PTB) sections ofwesternGuizhou and eastern Yunnan provinces in South China, representing a terrestrial tomarine transitional setting,were analyzed for δ13C of organic matter (δ13Corg). These valueswere subsequently compared to published δ13C values of carbonates (δ13Ccarb) from the Global Stratotype Section and Point at Meishan and many other marine and terrestrial sections. A similar isotopic trend evident through all four sections is characterized by a negative shift of 2–3‰ at the top of the Xuanwei Formation, where we tentatively place the PTB. This negative shift also corresponds to a turnover in the vegetation and the occurrence of fungal spores, which is generally interpreted as a proliferation of decomposers and collapse of complex ecosystems during the end-Permian mass extinction event. Moreover, the absolute values of δ13Corg are more extreme in the more distal (marine) deposits. The δ13Corg values for the studied sediments aremore variable compared to coeval δ13Ccarb records from marine records especially in the interval below the extinction horizon. We contend that the depositional environment influenced the δ13Corg values, but that the persisting geographic δ13Corg pattern through the extinction event across the four independent sections is an indication that the atmospheric δ13C signal left an indelible imprint on the geologic record related to the profound ecosystem change during the end-Permian extinction event.
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| 9. |
- Field, Daniel J, et al.
(författare)
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Early Evolution of Modern Birds Structured by Global Forest Collapse at the End-Cretaceous Mass Extinction
- 2018
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Ingår i: Current Biology. - Amsterdam : Elsevier. - 0960-9822 .- 1879-0445. ; 28, s. 1825-1831
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Tidskriftsartikel (refereegranskat)abstract
- The fossil record and recent molecular phylogenies support an extraordinary early-Cenozoic radiation of crown birds (Neornithes) after the Cretaceous-Paleogene (K-Pg) mass extinction [1–3 ]. However, questions remain regarding the mechanisms underlying the survival of the deepest lineages within crown birds across the K-Pg boundary, particularly since this global catastrophe eliminated even the closest stem-group relatives of Neornithes [4 ]. Here, ancestral state reconstructions of neornithine ecology reveal a strong bias toward taxa exhibiting predominantly non-arboreal lifestyles across the K-Pg, with multiple convergent transitions toward predominantly arboreal ecologies later in the Paleocene and Eocene. By contrast, ecomorphological inferences indicate predominantly arboreal lifestyles among enantiornithines, the most diverse and widespread Mesozoic avialans [5–7 ]. Global paleobotanical and palynological data show that the K-Pg Chicxulub impact triggered widespread destruction of forests [8, 9 ]. We suggest that ecological filtering due to the temporary loss of significant plant cover across the K-Pg boundary selected against any flying dinosaurs (Avialae [10 ]) committed to arboreal ecologies, resulting in a predominantly non-arboreal postextinction neornithine avifauna composed of totalclade Palaeognathae, Galloanserae, and terrestrial total-clade Neoaves that rapidly diversified into the broad range of avian ecologies familiar today. The explanation proposed here provides a unifying hypothesis for the K-Pg-associated mass extinction of arboreal stem birds, as well as for the post-K-Pg radiation of arboreal crown birds. It also provides a baseline hypothesis to be further refined pending the discovery of additional neornithine fossils from the Latest Cretaceous and earliest Paleogene.
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| 10. |
- Miguel Sender, Luis, et al.
(författare)
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A new uppermost Albian flora from Teruel province, northeastern Spain
- 2012
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Ingår i: Geodiversitas. - : Museum National d'Histoire Naturelle, Paris, France. - 1638-9395 .- 1280-9659. ; 34:2, s. 373-397
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports a new Early Cretaceous flora discovered recently near the village of Estercuel (Teruel province, northeastern Spain). The plant bearing beds belong to the uppermost part of the Early Cretaceous succession, at the top of the fluvial deposits of the Utrillas Formation. The site has yielded a diverse assemblage of plant compressions including lycopods and ferns, various gymnosperms as well as terrestrial and aquatic angiosperms. Leaves of aquatic lycopods (Isoetites sp.) constitute a minor component of the palaeobotanical assemblage. Filicales are not very common, with Dicksoniales (Onychiopsis sp.) and a few specimens of Cladophlebis type fronds. The gymnosperms are represented by fragmented remains of long parallel veined Desmiophyllum leaves as well as a great abundance of conifer axis corresponding to the form-genus Pagiophyllum and female cones. Terrestrial angiosperms include pinnately lobed leaves of the genus Myricompia, simple leaves with spatulate lamina and some petiolate leaves both corresponding to angiosperms of uncertain affinity. Aquatic angiosperms consist of Nelumbo-like floral receptacles (Nelumbonaceae, Proteales) and Aquatifolia cf: fluitans (Nympheales). The palynological assemblage is dominated by pollen of gymnosperms (mainly Taxodiaceaepollenites hiatus, Classopollis major and Araucariacites australis). It also includes many angiosperm grains (Afropollis jardinus, Clavatipollenites spp., Di-chastopollenites spp., Liliacidites doylei, Monosulcites chaloneri, Penetetrapites mollis, Pennipollis spp., Phimopollenites augathellaensis, Retimonocolpites textus, Rousea spp., Senectotetradites varireticulatus, Stellatopollis barghoornii, Striatopollis spp., Transitoripollis sp. cf. T similis, Tricolpites spp., Tricolporoidites sp.) and records the first occurrence of tricolporate forms in the uppermost part of the Utrillas Formation. Both macroflora and microflora assemblages present taxa similar to those of the uppermost Albian Shaftesbury Formation in northwestern Alberta in Canada, the uppermost Albian Denton Shale Member of Bokchito Formation in southern Oklahoma, the lower part of the Upper Albian Dakota Formation from the mid-west of North America, and Subzone II C of the Potomac Group, eastern United States. Both macro- and microflora assemblages display boreal influence with some similar taxa to those of the Upper Albian Kome Formation in western Greenland and some taxa as Afropollis jardinus and Stellatopollis barghoornii more frequently found in the tethyan and gondwanan realms. A gondwanan affinity is also indicated by the presence of Klitzschophyllites leaves.
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