| 1. |
- Zetterström Evins, Lena
(författare)
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Geochronology of the Oklo and Bangombé fossil natural fission reactors : tracing the effects of geological events
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thesis to be publicly defended for the degree of Doctor of Philosophy, in lecture room De Geersalen, Svante Arrhenius väg 8a, Stockholm, Friday February 1, 2002 at 10.00 am. Two billion years ago, natural fission reactions took place in the Oklo and Bangombé uranium ores in Gabon, West Equatorial Africa. Uraninite (UO 2+x) in the reactor zones is studied as a natural analogue to spent nuclear fuel. Since uraninite accumulates radiogenic Pb, U-Pb isotope systematics may be used to establish when uraninite alteration, and consequently migration of elements contained in the uraninite, occurred. The aim of this study is to establish when uraninite alteration and related radiogenic Pb loss occurred in the Oklo and Bangombé natural fission reactors.The isotopic compositions of U, Pb and S in uraninite, galena (PbS) and zircon (ZrSiO 4) were analysed using an ion microprobe. The ion microprobe technique requires the use of standards of the same mineral as the sample in order to determine instrumental fractionation. One part of this study involved describing and evaluating potential uraninite and galena standards for U and Pb isotopic analysis by ion microprobe. The galena standard analyses showed that Pb isotopic fractionation during galena analyses was ca 0.5% per atomic mass unit (a.m.u.) in favour of the lighter isotope. The uraninite standard study showed that U isotopic fractionation was ca 1.4% per a.m.u. in favour of the lighter isotope and that uraninite ion microprobe analysis may be influenced by significant amounts of hydrides. Hydride interferences during Pb isotopic analysis of uraninite were found to be of greater importance than Pb isotopic fractionation.A dolerite dyke swarm in the Francevillian basin, where the Oklo and Bangombé U deposits are located, was previously dated to sometime between ca 1000 and 700 Ma. In this study, zircon U-Pb ion microprobe analyses of one of the dolerite dykes yielded an age of 860±39 Ma (2). This age is in accordance with single-stage Pb-Pb model ages of large, mm-sized galena crystals that formed during a major Pb loss from uraninite in the reactor zones. Smaller galena crystals, ca 10 µm in diameter, are common in reactor zone 16 at Oklo. Variable Pb isotopic compositions of these crystals indicate that they formed sometime after the ca 860 Ma old major Pb loss from uraninite. An age of ca. 500 Ma is suggested for this second event of Pb loss and galena crystallisation. The existence of a second event of radiogenic Pb loss from uraninite is also indicated by the alteration of dolerite dykes that cross-cut the Oklo deposit. One of these altered dykes contains galena with Pb originating from the uranium ore as well as S from the surrounding sediment. Hence, the galena crystals in the dyke are not magmatic but a result of a later element migration. Pb-Pb and U-Pb systematics of uraninite also indicate that recrystallisation of uraninite occurred sometime between 600 to 500 Ma ago at both Oklo and Bangombé. Thus, this study has shown that at least two episodes of Pb loss from uraninite occurred after the formation of fission reactors; one at ca 860 Ma and one 600-500 Ma ago. Either one of these events might be related to regional Pb mobility in the Francevillian basin.
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| 2. |
- Blaj, Teodora, 1079-, et al.
(författare)
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A new Oligocene Triquetrorhabdulus specie: Triquetrorhabdulus longus sp. nov.
- 2009
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Tidskriftsartikel (refereegranskat)abstract
- While investigating the LO (Lowest Occurrence) of Triquetrorhabdulus carinatus at ODP Site 1218 in the paleo-equatorial Pacific, a form that resembles this species was observed and counted separately (Blaj et al., 2009). Based on differences in size, shape, and stratigraphic range compared with the typical Triquetrorhabdulus carinatus, we decided to describe this longer morphotype as a new and potentially biostratigraphically useful nannolith species, Triquetrorhabdulus longus sp. nov.
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| 3. |
- Blaj, Teodora
(författare)
-
Abundance and diversity changes among calcareous nannofossil assemblages across the early/late Oligocene boundary in the paleo-equatorial Pacific Ocean
-
Annan publikation (populärvet., debatt m.m.)abstract
- Ocean Drilling Program (ODP) Leg 199 recovered a complete Oligocene sediment sequence at Site 1218 in the paleo-equatorial Pacific Ocean. This paper presents a high-resolution study of relative abundances and diversity fluctuations of calcareous nannofossil assemblages in an Oligocene interval showing high carbonate contents. The data generated are compared with stable isotope (C, O) and sediment flux data in order establish possible relationships to changes in sea surface temperature and productivity. The nannofossil assemblage is dominated by Cyclicargolithus floridanus, Sphenolithus moriformis and Coccolithus pelagicus, which show a combined mean abundance of 84 % throughout the investigated 3.6 Myr interval (30.0 - 26.4 Ma). All component taxa show fluctuations in abundance. Variations in abundance and Shannon diversity index have been used to subdivide the 3.6 Myr long study interval into four subintervals. Intervals of highest Shannon index diversity coincide with Oi-glaciation events. However, the variations in abundance of selected nannofossil taxa do not appear to correlate with changes in either oxygen isotopes or carbon isotopes. This presumably indicates that a dynamic equilibrium did not exist between these Oligocene calcareous nannoplankton assemblages and changes in surface water temperature or productivity conditions. Observed changes in the nannofossil assemblages thus could have probably been driven by other factors, like for example, the internal evolutionary dynamics within the coccolithophore communities.
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| 4. |
- Blaj, Teodora, 1979-, et al.
(författare)
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Late Eocene to Oligocene preservation history and biochronology of calcareous nannofossils from paleo-equatorial Pacific Ocean sediments
- 2009
-
Ingår i: Rivista italiana di paleontologia e stratigrafia. - Italy : University of Milan. - 0035-6883 .- 2039-4942. ; 1, s. 67-85
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Tidskriftsartikel (refereegranskat)abstract
- A continuous late Eocene through Oligocene carbonate sequence was recovered at Ocean Drilling Program (ODP) Site 1218 in the paleo-equatorial Pacific Ocean. The preservation history of selected calcareous nannofossil species across the Eocene/Oligocene (E/O) boundary is presented together with late Eocene and Oligocene calcareous nannofossil biochronology. The astronomically calibrated timescale of Pälike et al. (2006) is used here. Across the E/O boundary, placolith preservation is controlled by variation in carbonate content. Taxa less prone to dissolution are Reticulofenestra umbilicus, Coccolithus pelagicus, Ericsonia formosa and Dictyococites bisectus, while Cyclicargolithus floridanus is more susceptible to dissolution. A biochronologic framework has been established for the following taxa: the highest occurrences (HO) of Discoaster barbadiensis (34.773 Ma), D. saipanensis (34.435 Ma), E. formosa (32.919 Ma), R. umbilicus (32.021 Ma), Sphenolithus predistentus (26.928 Ma), S. distentus (26.812 Ma), and S. ciperoensis (24.432 Ma), and the lowest occurrences (LO) of S. distentus (29.997 Ma) and S. ciperoensis (27.142 Ma). The first consistent appearance of Triquetrorhabdulus carinatus occurs at 26.556 Ma, while the onset of the peak interval of T. carinatus was determined at 24.669 Ma. Biochronological comparisons are made with other sites from the Atlantic Ocean. A Triquetrorhabdulus morphotype, labeled as T. aff. carinatus, was recorded for the first time in the studied sediments, and precedes the LO of T. carinatus by ~ 0.7 Myr. Its stratigraphic range has a duration of about 3.3 Myr. T. aff. carinatus disappears concomitantly with the beginning of a sharp increase in abundance of T. carinatus.
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| 5. |
- Blaj, Teodora, 1979-, et al.
(författare)
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The Oligocene nannolith Sphenolithus evolutionary lineage : morphometrical insights from the palaeo-equatorial Pacific Ocean
- 2010
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Ingår i: Journal of Micropalaeontology. - : Copernicus GmbH. - 0262-821X .- 2041-4978. ; :29, s. 17-35
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Tidskriftsartikel (refereegranskat)abstract
- Changes in morphology within the biostratigraphically important Oligocene nannofossil lineage, Sphenolithus predistentus-distentus-ciperoensis, were investigated in carbonate sediments from the paleo-equatorial Pacific Ocean Site 1218 in order to determine the nature of this evolutionary lineage. Using differences in their morphology and stratigraphic ranges, the aim of this study was to determine whether this set of sphenolith species represents an anagenetic evolutionary lineage or a set of discrete species with overlapping geological ranges. 1000 specimens were analysed morphometrically and the basal ratio (the ratio between the proximal cycle height and basal width), was identified as a key parameter for study of this lineage. We conclude that S. distentus and S. predistentus are intergradational species forming an anagenetic lineage but that S. ciperoensis is a discrete species which evolved relatively abruptly in the Late Oligocene.
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| 6. |
- Babcock, L.E., et al.
(författare)
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Anatomy, paleoecology, and taphonomy of the trilobite Buenellus from the Sirius Passet biota (Cambrian), North Greenland
- 2002
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Specimens of the nevadiid trilobite Buenellus higginsi from the Sirius Passet Biota (Buen Formation: Cambrian) of North Greenland show a combination of features reflecting both biomineralized and non-biomineralized anatomy, and providing direct or indirect evidence of paleoecologic associations and taphonomic history. Buenellus illustrates some key aspects of the role that trilobites played in the Early Paleozoic Marine Revolution (apparently serving as both predator and prey); its role in sediment-excavation, however, is unknown. The Sirius Passet Biota has a low diversity and low abundance of mineralizing organisms. Buenellus specimens, which account for most of the biomineralized skeletal parts, are normally preserved as decalcified, articulated exoskeletons, parallel to bedding. Their composition is dominated by clay minerals, although quartz, chlorite, muscovite, and chloritoid, are present, indicating metamorphism of shale to greenschist grade. Specimens of B. higginsi were preferentially oriented ventral-up as collected; this suggests both that minor current reorientation of remains occurred on the sea floor, and that strata at the Sirius Passet locality are overturned. Carnivory on B. higginsi is implied by the remains of anomalocaridids and other potential predators, and by sublethal predation scars. Slight disarticulation in the thoracic region of some fossils may have resulted from either decay or scavenging. Slender traces associated with various arthropod body fossils, including those of B. higginsi, suggests scavenging. Coprolites containing trilobite sclerites are unknown, and isolated, fragmentary sclerites are rare. Preserved non-biomineralized parts of B. higginsi are: 1, slender antennae projecting from under the exoskeleton; and 2, axial structures (inflated cavities lined with silica and limonite). Three types of axial structures are present: 1, a large cavity in the rear-subcentral part of the cephalon (interpreted as the stomach cavity); 2, a narrow, smooth-sided, medial tube that tapers slightly posteriorly (interpreted as the intestinal tract); and 3, metamerically divided pairs of sagitally located structures (interpreted as midgut glands). A carnivorous feeding habit is suggested by the lack of sediment-filled guts in B. higginsi.
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| 7. |
- Bassett, Michael G., et al.
(författare)
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Pedicle preservation in a Silurian rhynchonelliformean brachiopod from Herefordshire, England : soft-tissue or an artefact of interpretation?
- 2008
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Ingår i: Earth and Environmental Science Transactions of the Royal Society of Edinburgh. - 1755-6910. ; 98:3-4, s. 303-308
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Tidskriftsartikel (refereegranskat)abstract
- The interpretation of pedicle soft tissue preservation in a unique brachiopodspecimen of Wenlock (Silurian) age from Herefordshire, western England, is re-assessed. Bethia serraticulma, assigned originally to the Orthida, is more probably a member of the Strophomenida (Plectambonitoidea). The supposed pedicle structure is more plausibly a weakly mineralised pedicle sheath, which is a common morphological and functional development in the early ontogeny of a number of Palaeozoic brachiopod lineages.
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| 8. |
- Blaauw, Maarten, 1974-, et al.
(författare)
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Were last glacial climate events simultaneous between Greenland and western Europe?
- 2008
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Ingår i: Climate of the Past Discussions. - 1814-9359. ; 4, s. 1203-1217
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Tidskriftsartikel (refereegranskat)abstract
- During the last glacial period, several large abrupt climate fluctuations took place on the Greenland ice cap and elsewhere. Often these Dansgaard/Oeschger events are assumed to have been synchronous, and then used as tie-points to link chronologies between the proxy archives. However, if temporally separate events are lumped into one illusionary event, climatic interpretations of the tuned events will obviously be flawed. Here, we compare Dansgaard/Oeschger-type events in a well-dated record from south-eastern France with those in Greenland ice cores. Instead of assuming simultaneous climate events between both archives, we keep their age models independent. Even these well-dated archives possess large chronological uncertainties, that prevent us from inferring synchronous climate events at decadal to multi-centennial time scales. If possible, tuning of proxy archives should be avoided.
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| 9. |
- Elbrächter, Malte, et al.
(författare)
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Establishing an Agenda for Calcareous Dinoflagellate Research (Thoracosphaeraceae, Dinophyceae) including a nomenclatural synopsis of generic names
- 2008
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Ingår i: Taxon. - 0040-0262 .- 1996-8175. ; 57:4, s. 1289-1303
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Tidskriftsartikel (refereegranskat)abstract
- Calcareous dinoflagellates are considered to be a monophyletic group of peridinoid taxa that have the potential to produce calcified exoskeletal structures during the life cycle, or that derive from such forms. Frequently, these calcareous bodies are excellently preserved in the fossil record and have received increased attention during the past three decades with regard to their use in biostratigraphy, climate and environmental reconstruction. Fossil and extant taxa have been classified in various, partly concurring, systematic concepts, using character complexes of the theca, cyst wall ultrastructure and archaeopyle/operculum morphology. The significance of such character complexes is briefly discussed in the light of molecular data that have been accumulated during the past decade. Over the years, the number of published taxonomic names has increased, partly due to nomenclatural changes. We propose that the entirety of calcareous dinoflagellates, and non-calcareous relatives derived from them, is accommodated in a single family of the order Peridiniales, the Thoracosphaeraceae, combining the former segregated taxonomic units Calciodinelloideae, a subfamily within Peridiniaceae, and Thoracosphaerales, a separate dinoflagellate order. As a result of a meeting of calcareous dinoflagellate specialists, we outline major subjects that are in need of re-investigation and -evaluation (an Agenda for Calcareous Dinoflagellate Research). In order to contribute to a consistent and stable nomenclature and taxonomy of calcareous dinoflagellates, we list 97 published generic names assigned to known calcareous dinoflagellates in a nomenclatural synopsis, with species names indicating their types and information on type locality and stratigraphy. We evaluate the status of these names—whether validly published and, if so, whether legitimate—,a crucial first step for any revisionary work in the future.
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| 10. |
- Skinner, E.S., et al.
(författare)
-
Taphonomy of some exceptionally preserved organisms from the Lower Cambrian of Laurentia
- 2002
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Fossils of both biomineralized and non-biomineralized tissues from three lower Cambrian deposits suggest that preservation occurred along several taphonomic pathways, as indicated by a small variety of mineral compositions. Analytical studies, including microstructural analyses, energy dispersive x-ray [EDX] analyses, and elemental mapping, were performed on material from the Sirius Passet deposit of North Greenland, the Indian Springs deposit of Nevada, and the Kinzers deposit of Pennsylvania. Non-biomineralized tissues have been preserved as organic carbon, Fe-sulfides, Fe-oxides, clay minerals, and phosphates. Organic carbon is rather common in Kinzers and Sirius Passet material, principally in algal and bacterial remains, but was not detected in specimens from Indian Springs. In all three deposits, nonmineralizing organisms are commonly preserved, in whole or part, by thin films of minerals represented today by Fe-sulfides, Fe-oxides, and Fe-rich clay minerals. The Fe-oxides are probably alteration products of pyrite. For fossils composed of clay minerals, it is unclear whether the clays formed during early-stage diagenesis or late-stage alteration. A combination of processes leading eventually to clay mineral preservation is possible. Exceptional preservation of organisms by phosphate minerals is relatively rare in the studied material. Biomineralized parts of organisms in the studied deposits are commonly leached. Leaching of calcitic, aragonitic, and phosphatic hard parts has lead to moldic preservation in shale. Decalcification is more widespread than is dephosphatization. Exceptional preservation in the lower Cambrian deposits of Laurentia implies a synergistic relationship between biological, chemical, and physical conditions at the sites of deposition. Aqueous conditions must have been sufficiently inimical, at least temporarily, to exclude scavengers, bioturbators, and certain microbial biodegraders. However, development of early diagenetic mineral films on organismic remains was probably mediated in most circumstances by microbial activity. Dysoxic sediment, or reducing microenvironments within the sediment column, and relatively rapid burial rates, also must have played key roles in exceptional preservation.
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| 11. |
- Streng, Michael, 1971-, et al.
(författare)
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A Walcottella-like bradoriid (Arthropoda) from the lower Cambrian of Sweden
- 2008
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Ingår i: GFF. - 1103-5897 .- 2000-0863. ; 130:1, s. 11-19
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Tidskriftsartikel (refereegranskat)abstract
- A probable new bradoriid genus and species, represented by a single specimen, is described tentatively as Walcottella? aff. apicalis Ulrich & Bassler from lower Cambrian strata of Sweden. The specimen comes from the Bergmyrhobben section west of Storuman in Västerbotten County, northern Sweden. It was found in mudstone in the lower part of the Grammajukku Formation, co-occurring with a rich acritarch assemblage of the Skiagia ornata-Fimbriaglomerella membranacea acritarch Zone that corresponds to the Schmidtiellus trilobite Zone. The specimen represents one of the oldest bradoriids known from the paleocontinent Baltica. Characteristics of the specimen are a dorsomedian to mid-dorsal acuminate nod and a flattened shell border along the free margin, the latter feature unknown from other bradoriid taxa. The specimen occurs at the same level where the first trilobites were found in the investigated section. The biogeographic affinities of the Baltic bradoriid genera to the bradoriid fauna of Avalonia, western Gondwana and Laurentia are reviewed and discussed.
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| 12. |
- Vandergoes, MJ, et al.
(författare)
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Cooling and changing seasonality in the Southern Alps, New Zealand during the Antarctic Cold Reversal
- 2008
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 27:5-6, s. 589-601
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensively 14C AMS dated pollen and chironomid record from Boundary Stream Tarn provides the first chironomid-derived temperature reconstruction to quantify temperature change during Lateglacial times (17,500–10,000 cal yr BP) in the Southern Alps, New Zealand. The records indicate a ca 1000-year disruption to the Lateglacial warming trend and an overall cooling consistent with the Antarctic Cold Reversal (ACR). The main interval of chironomid-inferred summer temperature depression (2–3 °C) lasted about 700 years during the ACR. Following this cooling event, both proxies indicate a warming step to temperatures slightly cooler than present during the Younger Dryas chronozone (12,900–11,500 cal yr BP). These results highlight a direct linkage between Antarctica and mid-latitude terrestrial climate systems and the largely asynchronous nature of the interhemispheric climate system during the last glacial transition. The greater magnitude of temperature changes shown by the chironomid record is attributed to the response of the proxies to differences in seasonal climate with chironomids reflecting summer temperature and vegetation more strongly controlled by duration of winter or by minimum temperatures. These differences imply stronger seasonality at times during the Lateglacial, which may explain some of the variability between other paleoclimate records from New Zealand and have wider implications for understanding differences between proxy records for abrupt climate change.
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| 13. |
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| 14. |
- Conway Morris, Simon, et al.
(författare)
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New palaeoscolecidan worms from the Lower Cambrian : Sirius Passet, Latham Shale and Kinzers Shale
- 2010
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Ingår i: Acta Palaeontologica Polonica. - : Polska Akademia Nauk Instytut Paleobiologii (Institute of Paleobiology, Polish Academy of Sciences). - 0567-7920 .- 1732-2421. ; 55:1, s. 141-156
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Tidskriftsartikel (refereegranskat)abstract
- Palaeoscolecidan worms are an important component of many Lower Palaeozoic marine assemblages, with notable occurrences in a number of Burgess Shale-type Fossil-Lagerstatten. In addition to material from the lower Cambrian Kinzers Formation and Latham Shale, we also describe two new palaeoscolecidan taxa from the lower Cambrian Sirius Passet Fossil-Lagerstatte of North Greenland: Chalazoscolex pharkus gen. et sp. nov and Xystoscolex boreogyrus gen. et sp. nov. These palaeoscolecidans appear to be the oldest known (Cambrian Series 2, Stage 3) soft-bodied examples, being somewhat older than the diverse assemblages from the Chengjiang Fossil-Lagerstatte of China. In the Sirius Passet taxa the body is composed of a spinose introvert (or proboscis), trunk with ornamentation that includes regions bearing cuticular ridges and sclerites, and a caudal zone with prominent circles of sclerites. The taxa are evidently quite closely related; generic differentiation is based on degree of trunk ornamentation, details of introvert structure and nature of the caudal region. The worms were probably infaunal or semi-epifaunal; gut contents suggest that at least X. boreogyrus may have preyed on the arthropod Isoxys. Comparison with other palaeoscolecidans is relatively straightforward in terms of comparable examples in other Burgess Shale-type occurrences, but is much more tenuous with respect to the important record of isolated sclerites. These finds from Greenland provide further evidence that palaeoscolecidans possessed a complex anterior introvert directly comparable to a number of priapulid-like taxa from other Burgess Shale-type assemblages. Although these palaeoscolecidans have been allied with the nematomorphs, molecular data in conjunction with our observations suggest that this hypothesis is untenable. Palaeoscolecidans and similar priapulid-like taxa are probably primitive cycloneuralians and as such may indicate the original bodyplan of this important group of ecdysozoans. In addition, we describe another sclerite-bearing fossil from the Sirius Passet Fossil-Lagerstatte that may be related to the cambroclaves.
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| 15. |
- Daley, Allison C., et al.
(författare)
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A possible anomalocaridid from the Cambrian Sirius Passet lagerstätte, North Greenland
- 2010
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Ingår i: Journal of Paleontology. - 0022-3360 .- 1937-2337. ; 84:2, s. 352-355
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Tidskriftsartikel (refereegranskat)abstract
- The Sirius Passet biota of North Greenland is one of the oldest Cambrian lagerstätten, and although it is dominated by non-mineralized arthropods and lobopods, anomalocaridids have never been identified. Based on a single specimen, we herein describe for the first time an appendage with possible anomalocaridid affinities as suggested by an overall gross morphology similar to that of the frontal appendage of Anomalocaris from other localitites. Tamisiocaris borealis n. gen. and n. sp. has an elongated appendage with paired spines along one margin, and differs from the frontal appendage of Anomalocaris in that segment boundaries are absent and ventral spines are relatively long and spineless. These differences may be taphonomic, but the entire surface of the appendage is covered in a fine fabric, making it unlikely that this appendage was originally segmented or sclerotized. The taxon is tentatively placed within Radiodonta, but this systematic placement cannot be confirmed while complete body specimens are lacking.
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| 16. |
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| 17. |
- Henderiks, Jorijntje
(författare)
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Miocene mysteries of coccolithophore evolution
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The likely response of coccolithophores to ongoing warming and acidification of the global oceans remains difficult to predict, because (1) we know very little about climatic adaptation by this group of marine algae and (2) experimental evidence points to complex species-specific and even strain-specific sensitivities to short-term environmental perturbations. This study takes a long-term perspective to gain insights into species-specific evolutionary rates and climatic adaptation in the past, by reconstructing the phenotypic variability within two prominent coccolithophore lineages (Reticulofenestra and Coccolithus) during the late Miocene (NN9-12).The Cenozoic ancestors of all extant coccolithophores have experienced much higher temperatures, higher levels of CO2 and lower ocean pH than today, according to proxy reconstructions over the past 60 million years. However, different lineages display different levels of variation in coccolith size, a useful proxy for cellular volume-to-surface area ratios in the investigated lineages (Henderiks, 2008), and this could indicate that some species are more adaptable to climatic change than others. Time series of phenotypic variability in fossil Reticulofenestra populations are strikingly similar between the Atlantic, Indian and Pacific oceans, depicting global patterns of evolution during the late Miocene. An abrupt decrease in Reticulofenestra size and abundance, first recorded in detail by Young (1991) in the Indian Ocean, occurred ~9 million years ago (within NN9). Although globally evident, this ‘crash’ was most pronounced in the western equatorial Pacific, whereas larger sized Reticulofenestra populations persisted across the same interval in the North Atlantic. At the same deep-sea sites, time series of Coccolithus size variability and abundance reveal consistent differences between oceanographic regimes. The largest ranges in size are found in the temperate North Atlantic, whereas much tighter size distributions are recorded at the tropical Pacific site. Equatorial Pacific populations display very stable, unimodal size distributions, but at low relative abundances, for about two million years prior to their disappearance from the record ~6.5 million years ago (within NN11). This marks a habitat contraction towards higher latitudes (and coastal upwelling areas), which remain strongholds of modern Coccolithus populations today. Together, these data support that species-specific responses are evident also on longer timescales, and offer a first glance at how such phenotypic patterns may relate to both global and regional records of climatic change.References:Henderiks, J. 2008. Coccolithophore size rules - Reconstructing ancient cell geometry and cellular calcite quota from fossil coccoliths. Marine Micropaleontology, 67: 143-154.Young, J. 1990. Size variation of Neogene Reticulofenestra coccoliths from Indian Ocean DSDP cores. Journal of Micropaleontology, 9: 71-86.
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| 18. |
- Henderiks, Jorijntje, et al.
(författare)
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Phytoplankton size : Climatic adaptation and long-term evolution
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Marine phytoplankton, such as diatoms and coccolithophores, constitute the base of the marine food chain and are a fundamental component in biogeochemical cycles. The overall ecological success of marine phytoplankton, but also its taxonomic diversity and size distribution, determines the efficiency by which fixed carbon is transferred to higher trophic levels and into the deep ocean- and sedimentary carbon reservoirs. Therefore, we need a better understanding of the mechanisms and rates of adaptation within phytoplankton to evaluate marine ecosystems under present-day and future climate scenarios of rapidly rising ocean temperatures and lowering of ocean pH (‘ocean acidification’). The likely response of coccolithophores, the most prominent group of calcifying algae, in particular has provoked controversy.We have hypothesized that species-specific responses to climatic perturbations within extant members of this group are due to differences in the mechanism and rate of climatic adaptation inherent to their respective evolutionary lineages (Henderiks, J. and Rickaby, R.E.M., A coccolithophore concept for constraining the Cenozoic carbon cycle, Biogeosciences 4: 323-329, 2007). The Cenozoic ancestors of all extant coccolithophores have experienced much higher levels of CO2 and lower ocean pH than today, according to proxy reconstructions over the past 60 million years. However, we show that different lineages display different levels of variation in coccolith shape and cell size, and that this could indicate that some species are more adaptable to climatic change than others. The observed geological trends in algal cell size also have implications for long-term feedbacks in the Cenozoic carbon cycle.
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| 19. |
- Holmer, Lars Erik, 1960-, et al.
(författare)
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The Origin of the Brachiopod Body Plan
- 2009
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Ingår i: Internationl Conference on the Cambrian Explosion. - 9780981288512 ; , s. 541-541
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Konferensbidrag (refereegranskat)
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| 20. |
- Jordan, Ric, et al.
(författare)
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The ‘coastal refugia’ hypothesis – a case of the survival of the weakest?
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Throughout geological time there has been a succession of dominant nannoplankton species, which later manifested themselves as acme zones in the sediment record. Many of these dominant species disappeared from the nannofossil assemblages after their acme had finished and then seemingly became extinct. However, in the last few decades it has become evident that quite a few of these species (or their descendants) are living in coastal assemblages, perhaps as a result of being outcompeted in offshore communities and/or being forced to modify their ecological preferences. Here we explore the so-called ‘coastal refugia’ hypothesis. Studies on living nannoplankton in coastal assemblages are surprisingly few, however, there is a growing amount of biogeographic data to suggest that these coastal nannoplankton are quite widespread along today’s coasts, particularly in subtropical andtropical localities. For instance, Cruciplacolithus neohelis has been found now incoastal waters off Hawaii, France, Puerto Rico, Japan, Guam, and Palau (e.g., Konno & Jordan, 2006), while Braarudosphaera bigelowii has recently been recorded from Japan (Hagino et al., 2009) and the Bering Sea (Konno et al., 2007). The former species has a benthic life-cycle phase which suggests that it has always been a coastal species. However, the fossil record documents the dominance of this morphospecies in open ocean environments of the early Oligocene (~33-29 million years ago). Few studies have tackled this “paleobiogeographical anomaly” (Kelly et al., 2003), and all lack the crucial consideration of adaptation. Different morphospecies may not only have tracked their environmental optima (staying true to “the present is the key to the past” paradigm of paleoecology), but most likely also have changed their environmental preferences through time. The fossil record strongly supports such plasticity in relation to environmental change, as expressed in a wide variety of morphotypes. Indeed, numerous morphotypes within Gephyrocapsa spp. and Reticulofenestra spp. were previously cosmopolitan, open ocean taxa and only later on did some of them move into coastal environments. Today, G. oceanica inhabits shallow tropical waters, while G.muellerae, G. ericsonii and most Reticulofenestra spp. are often associated with upwelling conditions, although recently a Reticulofenestra sp. was found in a shallow Palauan lagoon. Yet it should also be noted that two species, G. ornata and R. sessilis, still remain in open ocean environments. Here we suggest that there are at least two components of the coastal assemblage, 1) species which have always inhabited coastal waters and may or may not have benthiclife-cycle phases such as Cruciplacolithus, Hymenomonas, Pleurochrysis, Ochrosphaera and Jomonlithus, and 2) species which appear to have taken refuge in coastal habitats after being ‘forced out’ of their open ocean niches such as Gephyrocapsa, Reticulofenestra and possibly Braarudosphaera. There is also the possibility that further genera will be discovered in coastal waters in the near future and that Emiliania huxleyi is destined to become the next coastal refugee in the more distantfuture. References Hagino, K., Takano, Y. & Horiguchi, T. 2009. Pseudo-cryptic speciation in Braarudosphaera bigelowii(Gran and Braarud) Deflandre. Marine Micropaleontology, 72: 210-221. Kelly, D. C., Norris, R. D. & Zachos, J. 2003. Deciphering the paleoceanographic significance of EarlyOligocene Braarudosphaera chalks in the South Atlantic. Marine Micropaleontology, 49: 49-63. Konno, S., Harada, N., Narita, H. & Jordan, R.W. 2007. Living Braarudosphaera bigelowii (Gran &Braarud) Deflandre in the Bering Sea. Journal of Nannoplankton Research, 29(2): 78-87. Konno, S. & Jordan, R.W. 2006. Lagoon coccolithophorids from the Republic of Palau, NW EquatorialPacific. Journal of Nannoplankton Research, 28(2): 95-110.
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| 21. |
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| 22. |
- Moczydlowska-Vidal, Malgorzata, 1951-
(författare)
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Life cycle of early Cambrian microalgae from the Skiagia-plexus acritarchs
- 2010
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Ingår i: Journal of Paleontology. - 0022-3360 .- 1937-2337. ; 84:2, s. 216-230
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Tidskriftsartikel (refereegranskat)abstract
- Light microscopy studies on new materials and museum collections of early Cambrian organic-walled microfossils, informally called acritarchs, provide the observations on phenetic features that permit a comparison to certain Modern microalgae and the recognition of various developmental stages in their life cycle. The microfossils derive from various depositional settings in Estonia, Australia, Greenland, Sweden and Poland. The exceptionally preserved microfossils reveal the internal body within the vesicle, - the endocyst -, and the process of releasing the endocyst from the cyst. Vegetative cells, cysts and endocysts are distinguished, and the hypothetical reconstruction of a complex life cycle with the alternation of sexual and asexual generations is proposed. Acritarchs from the Skiagia-plexus are cysts, and likely zygotes in the sexual generation, which periodically rested as “benthic plankton”. Some microfossils of the Leiosphaeridia-plexus are inferred to be vegetative cells, were planktonic and probably haplobiontic. These form-taxa may belong to a single biological species, or a few closely related species, and represent the developmental stages and alternating generations in a complex life cycle that are expressed by polymorphic, sphaero- and acanthomorphic acritarchs. The morphological resemblance and diagnostic cell walls ultrastructure with the trilaminar sheath structure known from earlier studies suggest that the early Cambrian microfossils are the ancestral representatives and/or early lineages to Modern Class Chlorophyceae, and the orders Volvocales and Chlorococcales.
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| 23. |
- Moczydlowska-Vidal, Malgorzata, 1951-, et al.
(författare)
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Micro- and nano-scale ultrastructure of cell walls in Cryogenian microfossils : revealing their biological affinity
- 2010
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Ingår i: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 43:2, s. 129-136
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Tidskriftsartikel (refereegranskat)abstract
- Recently established protocols and methods in advanced microscopy and spectrometry applied to studies of ancient unicellular organic-walled microfossils of uncertain biological affinities (acritarchs) provide new evidence of the fine ultrastructure of cell walls and their biochemistry that support the interpretation of some such microfossils as photosynthesizing microalgae. The micro-scale and nanoscale ultrastructure of the cell walls of late Cryogenian sphaeromorphic acritarchs from the Chichkan Formation (Kazakhstan) revealed by the advanced techniques and studied originally by Kempe et al. (2005) is here further analyzed and compared to that of modern microalgal analogues. On the basis of such comparison, we interpret the preserved cell wall ultrastructure to reflect original layering and lamination within sublayers of the fossil wall, rather than being a result of taphonomic and diagenetic alteration. The outer thick layer represents the primary wall and the inner layer the secondary wall of the cell, whereas the laminated amorphous sub-layers, 10-20 nm in thickness and revealed by transmission electron and atomic force microscopy, are recognized as trilaminar sheath structure (TLS). Because two-layered cell walls, trilaminar sheaths, and the position of the TLS within the fossil cell wall are characteristic of the mature developmental state in cyst morphogenesis in modern microalgae, we infer that the Chichkan sphaeromorphs are likely resting cells (aplanospores) of chlorophyceaen green microalgae from the Order Volvocales.
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| 24. |
- Moczydlowska-Vidal, Malgorzata, 1951-
(författare)
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Proterozoic acritarchs and divergences of green microalgae
- 2010
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Ingår i: CIMP 2010 Warsaw Abstracts. - : Institute of Geological Sciences, Polish Academy of Sciences (PAS). ; , s. 42-44
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Konferensbidrag (refereegranskat)abstract
- The morphology of microfossils with resistant cell walls, their ornamentation and functionally identifiable structures are the first source of information used to assess their biological affinities. Difficulties in relying on morphology alone due to the problem of convergent morphology may be resolved by the ultrastructure of the cell wall and its biochemistry. The cell walls of microfossils, which are acid-resistant and thus extractable by chemical processing from the host rocks, are composed of biopolymers that show the properties of the sporopollenin/algaenan classes of biomolecules synthesized by green algae, the green lineages of dinoflagellates, and the reproductive cells of higher plants (spores and pollen). These biota share primary biochemical pathways of organic synthesis of biopolymers for constructing cell walls, and show a common early lineage in their phylogeny. The geochronologic sequence of appearance of microfossils with diagnostic traits of phycoma-like cysts, zygotic cysts with ornamentation, pylomes, double-walled vesicles and endocysts, and spheroidal vegetative cells and /or aplanospores with trilaminar sheath structure (TLS), which are interpreted to be green microalgae, is aligned on the phylogenetic tree of the Viridiplantae. The radiometric datings of the first appearance datum of these taxa provide the minimum age of the origin of the classes to which they are assigned. According to the affinities of microfossils inferred herein, the sequence of evolutionary events is as it follows. The stem-group of the Viridiplantae extends in time prior to c. 1800 Ma, and the major branching nodes in a common lineage are at c. 1800 Ma for the Chlorophytes, c. 1650 Ma for the Prasinophyceae, and at c. 1450 Ma for the Chlorophyceae-Ulvophyceae lineage. The divergence of the Ulvophyceae might have occurred before c. 950 Ma. The origin of the Chlorophytes is constrained by the earliest record of the Leiosphaeridia-type microfossils from the Changzhougou Formation. The “leiosphaerid” morphology, which is recognized among the prasinophyceaen or chlorophyceaen microalgae, has deep roots in their common ancestral group and it is not only the result of a convergent morphology expressed later on. The prasinophyceaen lineage is recognized by Tasmanites rifejicus, and co-occurring species with phycoma-like, double-walled cysts: Simia, Pterospermopsimorpha, and Pterospermella, and striated Valeria. Valeria appears at c. 1650 Ma in the Mallapunyah Formation, and it marks the minimum age at which the Prasinophyceae lineage split from the basal Chlorophytes. Phycoma-like microfossils are subsequently recorded at c. 950 Ma (Octoedryxium), c. 580 Ma (Tasmanites, Simia, Octoedryxium, Pterospermopsimorpha), and since c. 540 Ma through the Cambrian (Tasmanites, Granomarginata, Pterospermella, Cymatiosphaera). The chlorophyceaen lineage is recognized by various species of Leiosphaeridia showing the TLS in their cell walls, which are likely the early members of the orders Volvocales and/or Chlorococcales. Leiosphaerids with such traits are present at c. 1450 Ma, 650 Ma and 520 Ma. The divergence of the Ulvophyceae prior to c. 950 Ma is suggested by the dasycladacean Archaeoclada and Variaclada in the Lakhanda Group, and the siphonocladacean Proterocladus from the c. 700-750 Ma Svanbergfjellet Formation. The presented minimum ages of the origin of the Viridiplantae and the divergence of the major microalgal clades differ from the molecular clocks estimates. They also suggest that previously inferred time of the origin of Chlorophytes at c. 1 Ga or 1.5 Ga is too young. The molecular clocks estimates of these events are in conflict with microfossil records, and the interpretation of some of them as being photosynthesizing biota, and seem to be delayed in time. Following the Great Oxygenation Event at c. 2.2 Ga, the oxygen pressure in the ocean-atmosphere system has been apparently increasing although with significant fluctuations through time. This was due to the variation in carbon cycles and carbonate formation, assembly and breaking off the supercontinents and weathering rate change, and hydrological cycle and stratification of the oceans. The Palaeo-Mesoproterozoic oceans were stratified with deep layers anoxic and only the surface layer oxygenated by photosynthesis within the photic zone. The late Neoproterozoic oxygenation event resulted in full oxygenation of the oceans and deep currents circulation. The increasing pressure of oxygen in marine environments is argued to have played a decisive role in the evolution of metazoans in the Ediacaran and Cambrian, yet the cause-effect relationships may be in reverse as it comes to photosynthetic organisms diversification and growing abundance observed through the Proterozoic. The recorded diversification of green microalgae (acritarchs) must have enhanced the rates of primary productivity in the surface ocean layers and organic carbon burial in shelf sediments. Photosynthesis most profoundly increased the oxygen pressure in the global ocean. Precise correlation in time of the geochemical signatures and radiations of photosynthetic biota may reveal critical relationships between biotic and environmental evolution.
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| 25. |
- Moczydlowska-Vidal, Malgorzata, 1951-
(författare)
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Proterozoic microfossils revealing the time of algal divergences
- 2010
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Ingår i: Geophysical Research Abstracts, Vol. 12, 7th EGU General Assembly 2010. - : Copernicus Publications. ; , s. 702-702
-
Konferensbidrag (refereegranskat)abstract
- Morphological and reproductive features and cell wall ultrastructure and biochemistry of Proterozoic acritarchs are used to determine their affinity to modern algae. The first appearance datum of these microbiota is traced to infer a minimum age of the divergence of the algal classes to which they may belong. The chronological appearance of microfossils that represent phycoma-like and zygotic cysts and vegetative cells and/or aplanospores, respectively interpreted as prasinophyceaen and chlorophyceaen microalgae, is related to the Viridiplantae phylogeny. These divergence times differ from molecular clock estimates, and the palaeontological evidence suggests that they are older. The best examples of unicellular, organic-walled microfossils (acritarchs) from the Mesoproterozoic to Early Ordovician are reviewed to demonstrate features, which are indicative of their affinity to photosynthetic microalgae. The first indication that a microfossil may be algal is a decay- and acid-resistant cell wall, which reflects its biochemistry and ultrastructure, and probably indicates the ability to protect a resting/reproductive cyst. The biopolymers synthesized in the cell walls of algae and in land plants (“plant cells”), such as sporopollenin/algaenan, are diagnostic for photosynthetic taxa and were inherited from early unicellular ancestors. These preservable cell walls are resistant to acetolysis, hydrolysis and acids, and show diagnostic ultrastructures such as the trilaminar sheath structure (TLS). “Plant cell” walls differ in terms of chemical compounds, which give high preservation potential, from fungal and animal cell walls. Fungal and animal cells are fossilized only by syngenetic permineralization, whereas “plant cells” are fossilized as body fossils more ubiquitously and without mineralization. Microalgae radiated quickly in the Cambrian and Ordovician; however, several morphotypes with features related to the reproductive cycle occur in the Proterozoic, although they are not always recognized as such. The assignment of Proterozoic unicellular microfossils with resistant cell walls to specific eukaryotic groups is tentative. However, we argue that the new interpretations of their functional morphology, combined with cell wall ultrastructure and biochemistry, allow their assignment to microalgal classes. Microfossils with advanced ornamentation and ontogenetically formed excystment structures or endocysts, which prove that they are cysts in a complex life cycle with sexual reproduction, are related to the basal lineage of the Chlorophytes and the class Chlorophyceae. A cell wall ultrastructure with a TLS supports the affinity of some spheroidal taxa to the Chlorophytes. The phylogeny of the Chlorophytes shows a sequence of branching nodes from a stem-group of the Viridiplantae that leads to the classes Prasinophyceae and Chlorophyceae, and then the Ulvophyceae. Based on a modern interpretation of the record, the timing of these nodes is deduced to be prior to c. 1650 Ma for the Prasinophyceae, c. 1450 Ma for the Chlorophyceae, and c. 950 Ma for the Ulvophyceae. The origin of the Chlorophytes, and in general the Viridiplantae, predates 1.8 Ga. These ages, based on microfossils, are earlier than the estimates based on molecular clocks.
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| 26. |
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| 27. |
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| 28. |
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| 29. |
- Rickaby, Rosalind E. M., et al.
(författare)
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Perturbing phytoplankton : response and isotopic fractionation with changing carbonate chemistry in two coccolithophore species
- 2010
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Ingår i: Climate of the Past. - : Copernicus Publications on behalf of the European Geosciences Union. - 1814-9324 .- 1814-9332. ; 6, s. 771-785
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Tidskriftsartikel (refereegranskat)abstract
- All species of coccolithophore appear to respond to perturbations of carbonate chemistry in a different way. Here, we show that the degree of malformation, growthrate and stable isotopic composition of organic matter and carbonate produced by two contrasting species of coccolithophore (Gephyrocapsa oceanica and Coccolithus pelagicusssp. braarudii) are indicative of differences between their photosynthetic and calcification response to changing DIC levels (ranging from 1100 to 7800 μmol kg−1) at constant pH (8.13±0.02). Gephyrocapsa oceanica thrived under all conditions of DIC, showing evidence of increased growth rates at higher DIC, but C. braarudii was detrimentally affected at high DIC showing signs of malformation, and decreased growth rates. The carbon isotopic fractionation into organic matter and the coccoliths suggests that C. braarudii utilises a common internal pool of carbon for calcification and photosynthesis but G. oceanica relies on independent supplies for each process. All coccolithophores appear to utilize bicarbonate as their ultimate source of carbon for calcification resulting in the release of a proton. But, we suggest that this proton can be harnessed to enhance the supply of CO2(aq) for photosynthesis either from a large internal HCO−3 pool which acts as a pH buffer (C. braarudii), or pumped externally to aid the diffusive supply of CO2 across the membrane from the abundant HCO−3 (G. oceanica), likely mediated by an internal and external carbonic anhydrase respectively. Our simplified hypothetical spectrum of physiologies may provide a context to understand different species response to changing pH and DIC, the species specific Ep and calcite “vital effects”, as well as accounting for geological trends in coccolithophore cell size.
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| 30. |
- Rickaby, Rosalind E. M., et al.
(författare)
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Perturbing phytoplankton : a tale of isotopic fractionation in two coccolithophore species
- 2010
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Ingår i: Climate of the Past Discussions. - : Copernicus Publications on behalf of the European Geosciences Union. - 1814-9359. ; 6, s. 257-294
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- No two species of coccolithophore appear to respond to perturbations of carbonate chemistry in the same way. Here, we show that the degree of malformation, growth rate and stable isotopic composition of organic matter and carbonate produced by two contrasting species of coccolithophore (Gephyrocapsa oceanica and Coccolithus pelagicus ssp. braarudii) are indicative of differences between their photosynthetic and calcification response to changing dissolved inorganic carbon (DIC) levels (ranging from ~1100 to ~7800 μmol kg−1) at constant pH (8.13±0.02). G. oceanica thrived under all conditions of DIC, showing evidence of increased growth rates at higher DIC, but C. braarudii was detrimentally affected at high DIC showing signs of malformation, and decreased growth rates. The carbon isotopic fractionation into organic matter and the coccoliths suggests that C. braarudii utilises a common internal pool of carbon for calcification and photosynthesis but G. oceanica relies on independent supplies for each process. All coccolithophores appear to utilize bicarbonate as their ultimate source of carbon for calcification resulting in the release of a proton. But, we suggest that this proton can be harnessed to enhance the supply of aqueous dissolved carbon dioxide (CO2(aq)) for photosynthesis either from a large internal bicarbonate ion (HCO3-) pool which acts as a pH buffer (C. braarudii), or pumped externally to aid the diffusive supply of CO2 across the membrane from the abundant HCO3- (G. oceanica), likely mediated by an internal and external carbonic anhydrase, respectively. Our simplified hypothetical spectrum of physiologies may provide a context to understand different species response to changing pH and DIC, the species-specific εp and calcite "vital effects", as well as accounting for geological trends in coccolithophore cell size.
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| 31. |
- Skovsted, Christian B., et al.
(författare)
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Hyolithellus in life position from the Lower Cambrian of North Greenland
- 2011
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Ingår i: Journal of Paleontology. - : Cambridge University Press (CUP). - 0022-3360 .- 1937-2337. ; 85:1, s. 37-47
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Tidskriftsartikel (refereegranskat)abstract
- Tubular specimens belonging to Hyolithellus from silty dolostones of the basal Aftenstjernesø Formation of North Greenland may represent the first occurrence of this widespread Cambrian fossil in life position. A high proportion of preserved specimens are oriented normal to bedding with the tapering end of the tube down. Occasional undulations in the growth of the tubes indicate that the animal actively adjusted its growth to achieve a vertical orientation in relation to the sediment surface. Increasing thickness of the tube wall towards the tapering end shifted the center of mass downwards and resulted in greater stability in the sediment. The tube remained open at both ends throughout ontogeny; it was most likely secreted by an annelid-grade animal which pumped water into the sediment through the tube. Hyolithellus and similar tubular fossils from the Lower Cambrian probably represent stem group annelids.
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| 32. |
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| 33. |
- Stein, Martin, et al.
(författare)
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Isoxys (Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte, lower Cambrian of North Greenland
- 2010
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Ingår i: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 43:2, s. 258-265
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Tidskriftsartikel (refereegranskat)abstract
- Isoxys volucris is the most commonly occurring species in the lower Cambrian Sirius Passet Lagerstatte of North Greenland. Newly identified material allows a first, limited, account of the ventral morphology of this species, hitherto known only by the morphology of its shield. The antennula is large and robust, composed of about seven articles armed with spines, and was probably not sensorial. The postantennular limbs are serially similar, biramous with a large paddle-shaped exopod fringed with setae. It is possible that the animal possessed a furca. The inner lamella, lining the ventral surface of the shield is recognised in Isoxys for the first time. Comparisons with other congeneric species of which aspects of the ventral morphology are known, show similarities with Isoxys auritus from China, reconsidered here, but indicate differences in antennular morphology with other species as currently understood. square Cambrian, Greenland, Isoxys, soft anatomy, Sirius Passet, palaeoecology.
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| 34. |
- Willman, Sebastian, et al.
(författare)
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Acritarchs in the Ediacaran of Australia — Local or global significance? : Evidence from the Lake Maurice West 1 drillcore
- 2011
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Ingår i: Review of Palaeobotany and Palynology. - : Elsevier BV. - 0034-6667 .- 1879-0615. ; 1-2:166, s. 12-28
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Tidskriftsartikel (refereegranskat)abstract
- The Lake Maurice West 1 drillhole is located in the Officer Basin in South Australia and penetrates a siliciclastic rock succession of Ediacaran age (ca 635–542 Ma). Within this succession well-preserved organic-walled microfossils called acritarchs have been recovered from the Dey Dey Mudstone and Karlaya Limestone, which constitutes a major part of the Ungoolya Group. The assemblage consists of biostratigraphically useful acanthomorphic acritarchs in addition to a diverse assemblage of unornamented leiospheres, filamentous microbiota and some undetermined taxa. Here we describe eight acanthomorphic taxa belonging to three distinctive Ediacaran genera (Cavaspina, Ceratosphaeridium and Tanarium), of which one is described as a new species (Cavaspina amplitudinis sp. nov.). Similar acanthomorphic assemblages are known from Ediacaran strata worldwide and biostratigraphic subdivision of the system based on the occurrence of cosmopolitan taxa is possible in Australia, China, Siberia and Baltica (East European Platform), and perhaps in other areas. The Lake Maurice West 1 microfossil assemblage adds to the growing record of the Ediacaran acritarchs and supports a biostratigraphic scheme for the Ediacaran System at a global scale.
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| 35. |
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| 36. |
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| 37. |
- Willman, Sebastian, et al.
(författare)
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Taphonomic analysis of Ediacaran acritarchs and its importance for taxonomy,biostratigraphy and global correlation
- 2008
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this study we analysed the taphonomic degradation history of a diverse assemblage of Ediacaran(late Neoproterozoic) acritarchs from the Centralian Superbasin and Adelaide Rift Complex inAustralia. Taphonomic features observed include compression features, folding and tearing ofvesicle walls, pitting, perforation, abrasion, exfoliation, shrinking, twisting, splitting, curling,shredding, pyritization, particle entrapment, and thermal maturation effects. The physical andchemical structure of the vesicle wall determines the degree of taphonomic damage. Consistentassociations allowed identification of degradation series which incorporate previously describedindividual species and provide a framework for taxonomic revision. Recognition of taphonomicvariants is an important first step in systematic studies, and tracking degradational pathways forparticular species resulted in more precise taxonomic identification. Other biostratigraphicallyuseful fossils are uncommon in the Neoproterozoic which means that considerable reliance willbe placed on acritarch biostratigraphy for future global correlations. It is vital, therefore, that thesignificance of taphonomic degradation, for both taxonomy and palaeoenvironmental analysis, isgiven adequate recognition. Identification of taphonomic variants is critical for taxonomic studiesand must be considered before making biostratigraphic subdivision of the Ediacaran System.
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| 38. |
- Willman, Sebastian, et al.
(författare)
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Ultrastructural Approaches to the Microfossil Record : Assessing Biological Affinities by Use of Transmission Electron Microscopy
- 2011
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Ingår i: Quantifying the Evolution of Early Life. - Dordrecht Heidelberg London New York : Springer. - 9789400706798 - 9789400706804 ; , s. 301-320
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Bokkapitel (refereegranskat)abstract
- One of the major technological advances in biological research was the invention and development of the transmission electron microscope, which enables high resolution and high magnification studies of cross-sections of specimens. As such, it has proved to be a useful tool to describe ultrastructural features of taxonomic and phylogenetic importance in modern organisms. Here we discuss how to extend the use of transmission electron microscopy (TEM) to the fossil record, with emphasis on acritarchs (organic-walled microfossils of unknown affinity). Microfossils are traditionally studied by use of transmitted light microscopy, a method that reveals details of external morphology only. TEM however, gives an additional level of detail and reveals structures that can greatly aid in interpretation of taxonomic affinity, and thus can reveal further detail on the origination and diversification of myriad eukaryotic groups in the fossil record. In this chapter we describe the preparation procedure, show advantages and shortcomings of the technique, and discuss how to interpret the results from a geobiological perspective.
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| 39. |
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| 40. |
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| 41. |
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| 42. |
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| 43. |
- Ahlberg, Per E., et al.
(författare)
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Palaeontology: A firm step from water to land
- 2006
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 440:7085, s. 747-749
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Tidskriftsartikel (refereegranskat)
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| 44. |
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| 45. |
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| 46. |
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| 47. |
- Anderson, Cajsa Lisa
(författare)
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All we need now is fossils; a new phylogenetic dating method (PATHd8) allowing thousands of taxa and multiple fossil constraints.
- 2006
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Ingår i: Ancient life and modern approaches. - 7312019560 ; , s. 45-
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Konferensbidrag (refereegranskat)abstract
- Estimation of divergence times in phylogenetic trees using sequence databecomes increasingly popular, but so far dating studies have given widely different results,and especially datings of the lower nodes within the angiosperms and metazoans, have givenmuch older ages than those obtained from the fossil record. It has been concluded in differentstudies that more taxa, and more fossils are needed for more reliable age estimates. For thisreason, a dating method that can handle very large data sets with multiple fossil constraints isnecessary.Chronograms obtained by e.g. penalized likelihood and Bayesian methods, oftenadds a large "ghost range" to the fossil record, and produces chronograms with a more or lesssmooth appearance, even if the corresponding phylograms have apparently veryheterogeneous rates. Compared to the other methods, our recently developed method,PATHd8, gives the results with the best agreement with the fossil record, which coincideswith the least smooth appearance of the chronograms. When other programs often run intocomputational problems when analysing trees with hundreds of leaves, PATHd8 has noproblems analysing thousands of taxa instantaneously. An arbitrary number of fossil ageconstraints can be specified, either as fixed-, minimum or maximum age.With our new method, the biggest problem in dating studies is that we needmore fossils, and these fossils must be well dated and assigned to the correct branches of thephylogeny. Therefore, to accomplish divergence time estimates, which hopefully approximatethe real ages, biologists now need to cooperate with palaeontologists.
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| 48. |
- Andrén, Elinor, 1966-
(författare)
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Holocene environmental changes recorded by diatom stratigraphy in the southern Baltic Sea
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sediment cores from the southern Baltic Sea and the Oder River estuary are analysed for their siliceous microfossil assemblages and organic carbon content. Long piston cores from the Bornholm and Gotland Basins provide data on the long-term Holocene history of the Baltic proper and serve as a natural background when evaluating the most recent environmental changes recorded in the short gravity cores. Corrected and calibrated 14C dates for the Holocene part, together with 210Pb and 137Cs dates for the sediments deposited during the last century, are used as a basis for constructing chronologies and age models. The main results are:The brackish phase of the Yoldia Sea stage in the Bornholm Basin is recorded by a diatom assemblage of periphytic taxa indicating a shallower water depth than today and more marine conditions than are recorded by the planktonic assemblage found in the Gotland Basin.The transition between the Yoldia Sea and the Ancylus Lake stages is distinguished in the offshore facies and recorded in the sediments in the form of a small increase in organic carbon coinciding with a peak in the diatom abundance and increased diatom diversity.The onset of the Initial Litorina Sea stage, recorded about 10,100 calendar years BP (c. 8900 14C years BP) in the Bornholm Basin, indicates a complex transition with different phases of brackish-water inflow.Six periods with major marine water inflow into the Baltic basin are recorded during the Holocene. Once an open connection was established with the North Sea, climatic influence seems to have been the most important factor controlling such inflow events.Comparison between the organic carbon content, the absolute abundance of siliceous microfossils and a regional climate proxy, the Greenland (GRIP) ice core (18O record, shows a tentative link between primary production in the Baltic proper and climate. A high temperature on Greenland corresponds to high organic carbon content and increased diatom abundance in the Baltic proper.Climate change is recorded in both the siliceous microfossil assemblages and the organic carbon content. A sediment sequence indicating high productivity c. 950-800 calendar years BP (AD 1000-1150) correlates with the Medieval warm period. An alteration in the diatom assemblage interpreted as being due to a deterioration in the climate correlates with the start of the Little Ice Age about 850-700 calendar years BP (AD 1100-1250).The effects of eutrophication are recorded AD 1850-1860 in the southwestern Baltic proper, AD 1900 in the Oder estuary and AD 1950-1960 in the Gotland Basin. These effects were probably caused by increased discharge of nutrients deriving from fertilisers, as the responding diatom species partly indicate a cold climate rather than a warm one, as would have been expected if this had been only a response to the warmer climate documented during the last 100 years or so.
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