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Page 1: M Acritarchs and E - DiVA portal166094/FULLTEXT01.pdf · Dissertation presented at Uppsala University to be publicly examined in Lecture Theatre, Palaeontology Building, Uppsala,

MAcritarchs and E

Page 2: M Acritarchs and E - DiVA portal166094/FULLTEXT01.pdf · Dissertation presented at Uppsala University to be publicly examined in Lecture Theatre, Palaeontology Building, Uppsala,

Dissertation presented at Uppsala University to be publicly examined in Lecture Theatre,Palaeontology Building, Uppsala, Friday, April 29, 2005 at 13:00 for the degree of Doctor ofPhilosophy. The examination will be conducted in English.

AbstractStockfors, M. 2005. Cambro-Ordovician microorganisms: acritarchs and endoliths. 29pp. Uppsala. ISBN 91-506-1798-2

Organic-walled microfossils are abundant and taxonomically diverse in Cambrian-Ordovicianstrata; some are important for biostratigraphy and for the correlation of geological succes-sions. New assemblages of Cambrian-Ordovician acritarchs from Kolguev Island, ArcticRussia and Middle Cambrian ichnofossils of endoliths from Peary Land, North Greenland arestudied. Twenty-seven acritarch species are described in detail and 10 taxa are left under open nomenclature. The diagnosis of one genus is restricted, and two other are emended. Newcombinations are proposed for three species and one new species is recognised. The studiedacritarch assemblages are taxonomically rich and age-diagnostic and used to recognise UpperCambrian and Tremadoc strata on Kolguev Island. The sedimentologically continuous succes-sions provide for the first time palaeontological evidence of Cambrian strata in the north-eastern sector of Europe. The exact level of the Cambrian-Ordovician boundary was distin-guished together with stratigraphic intervals equivalent to the Peltura and Acerocare zones ofthe Upper Cambrian of Baltica. The newly established relative age of the lowermost sedimen-tary succession overlying the Timanian unconformity allows verification of the minimum ageof the Timanian deformation and the time-span of the hiatus bound to this unconformity.Endoliths occur in the fossil record from the Early Archean and they played an important rolein the formation of stromatolites and the process of bioerosion and biodegradation. Endolithsthat have actively bored into brachiopod shells or carbonate grains (euendoliths), and some that inhabited the cavities inside brachiopod shells (cryptoendoliths) are described. Borings within the carbonate grains extended with a dentritic pattern, whereas those within the brachiopod shells were formed by a multifilamentous euendolith which produced characteris-tic longitudinally ridged galleries. The cryptoendolithic morphologies include indeterminatecoccoid masses and at least two filamentous forms. However, considerable variation in thedimensions of the currently phosphatised diagenetic crusts of the cryptoendoliths hindersdiscrimination.

Keywords: Cambrian. Ordovician, acritarch, endolith, Kolguev Island, North Greenland,stratigraphy

Martin Stockfors, Department of Earth Sciences, Palaeobiology, Norbyvägen 22, Uppsala University, SE-75236 Uppsala, Sweden

DISCLAIMERThis manuscript is printed only for public examination as a doctoral thesis.

© Martin Stockfors 2005

ISBN 91-506-1798-2

Printed in Sweden by Geotryckeriet, Uppsala 2005

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Tillmin familj

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List of Publications

I. Moczyd owska, M., Popov, L.E. & Stockfors, M., 2004: Upper Cam-brian-Ordovician successions overlying Timanian complexes: new evidence of acritarchs and brachiopods from Kolguev Island, Arctic Russia. Geobios 37, 239-251.

II. Moczyd owska, M. & Stockfors M., 2004: Acritarchs from the Cam-brian-Ordovician boundary interval on Kolguev Island, Arctic Russia. Palynology 28, 15-73.

III. Moczyd owska, M., Stockfors, M. & Popov, L.E., 2004: Late Cam-brian relative age constrains by acritarchs on the post-Timanian deposi-tion on Kolguev Island, Arctic Russia. In D. Gee & V. Pease (eds.):The Neoproterozoic Timanide Orogen of Eastern Baltica. GeologicalSociety, London, Memoirs 30, 159-168.

IV. Stockfors, M. & Peel, J.S., 2005: Endolithic Cyanobacteria from the Middle Cambrian of North Greenland, GFF, submitted manuscript.

V. Stockfors, M. & Peel, J.S., 2005: Euendoliths and cryptoendolithswithin late Middle Cambrian brachiopod shells from North Greenland. GFF, submitted manuscript.

Reproduction of papers I-III was made with permission of the copyrightholder.

Paper I © 2004 Elsevier Paper II © 2004 AASP FoundationPaper III © 2004 The Geological Society of London Paper IV-V © 2005 by the authors, submitted to GFF

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Contents

List of Publications .........................................................................................v

Introduction.....................................................................................................1Early life and microorganisms ...................................................................1The Cambrian Explosion and diversification of microorganisms..............3Aims ...........................................................................................................4

Acritarchs........................................................................................................5Geology of Kolguev Island and the Pechora Basin....................................7Palaeogeography ........................................................................................9

Endolithic microorganisms ...........................................................................11Euendoliths...............................................................................................11Cryptoendoliths ........................................................................................12Bioerosion ................................................................................................13North Greenland.......................................................................................14

Results & Discussion ....................................................................................16The Acritarch Study .................................................................................16The Endolith Study...................................................................................17

Sammanfattning på svenska:.........................................................................19Kambro-ordoviciska mikroorganismer: acritarcher och endoliter ...........19

Tidigt liv och mikroorganismer ...........................................................19Den kambriska explosionen och diversifieringen av mikroorganismer.............................................................................................................21

Acknowledgements.......................................................................................23

References.....................................................................................................24

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Introduction

Early life and microorganisms

Life has existed on Earth for almost four billion years. Until recently its his-tory has been recognised exclusively from the study of fossils but is nowalso supported by molecular data, geochemical signatures and isotopic frac-tionations of some organic compound. The earliest known microfossils, ofprobable cyanobacterial origin, are from the Apex Cherts, Western Australiaand of Early Archean age, approximately 3.5 Ga (Schopf & Packer 1987,Schopf et al. 2002; see discussion in Brasier et al. 2002). Fossils of mi-croborers from the same period have also been found in pillow lava fromSouth Africa (Furnes et al. 2004). The degree of complexity of the earliest microorganisms probably required a substantial period to develop, suggest-ing that life must have existed for a long time before its first appearance inthe geological record. Crustal rocks older than 3.5 Ga are intensely meta-morphosed, hence lacking recognisable organic remains and fossils once preserved in them. However, biotic activity is inferred from geochemicalsignatures of carbon isotopes preserved in the approximately 3.8 Ga meta-sediments from the Isua Formation exposed on Akilia Island, southwest Greenland (Mojzsis et al. 1996; see also Whitehouse et al. 2001; Fedo & Whitehouse 2002). In rocks younger than 3.5 Ga, in particular after the ap-pearance of eukaryotic organisms at 2.7 Ga (Brocks et al. 1999), the increas-ing amount of microfossils provides evidence of progressive evolution and diversification of the biota.

The earliest microbiota known from the geological record was unicellular prokaryotes, lacking a cell nucleus and advanced organelles, and inhabiting marine environments. They have been described as photosynthesizingcyanobacteria that used sunlight as the source of energy for their metabolicprocesses. The cyanobacteria, together with other bacteria, could form mi-crobial mats (stromatolites) in near-shore tidal environments, or live a plank-tonic mode of life in the oceans. They probably occupied various marineenvironments down to a maximum depth dependent on the availability ofsunlight. Today cyanobacteria and other bacteria also thrive in lacustrine andother fresh water environments, but such ancient environments are poorly

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preserved in the geological record and the time of bacterial colonisation of land is uncertain.

The first evidence of eukaryotes, i.e. cells with a differentiated and mem-brane-bound cell nucleus, comes from molecular fossils of biological lipids, approximately 2.7 Ga (Brocks et al. 1999, see also Javaux et al. 2004),whereas morphological fossils appeared in the geological records at 2.1 Ga (Runnegar 1994). One group of single celled marine organisms which is among the earliest and most common microfossils from 1.9-1.8 Ga (Hof-mann & Schopf 1983; Zhang 1986; Jankauskas 1989; Mendelson andSchopf 1992), is referred to as acritarchs. This is a group of microfossilsnamed and taxonomically defined by their uncertain origin. Acritarchs are considered to be resting cysts of phytoplankton which accumulated in the bottom sediments where they may be buried and fossilised. Since the affinity of most acritarchs is now related to eukaryotic photosynthesising plankton,the status as a group of ‘uncertain origin’ has diminished. Although not so ancient, the Cambrian-Ordovician acritarchs of an approximate age of 500-480 Ma are the major subject of the present studies.

This thesis also describes endoliths, a group of microorganisms which may be representative of various biological clades, such as bacteria, cyano-bacteria, algae and fungi that are characterised by their mode of life, i.e. living within rocks by inhabiting small cavities in carbonate substrates either by boring actively or using existing cavities. It is well known that endolithspenetrate shells of metazoans and they are recorded from the Cambrian pe-riod onwards (Golubic & Seong-Joo 1999). Nonetheless, they appeared long before the shell secreting metazoans in the geological record. The earliestendolithic microorganisms have been described by Furnes (2004) from Ar-chaean pillow lava in South Africa, but they are more commonly found fromthe Late Proterozoic (700-800 Ma) onwards (cf. Knoll et al. 1986).

From our own ‘homocentric’ point of view, the species Homo sapiens is often alleged to be the most prominent creature on Earth. However, the mi-crobes (e.g. archea, bacteria, cyanobacteria and algae) exhibit the greatestspecies diversity on Earth and constitute the frontiers of the biosphere ex-pansion, inhabiting an enormous array of environments down to depth of several kilometres into the hydrosphere and the lithosphere. The unicellularorganisms exhibit far more complex metabolic processes and this is becausethey perform all their life functions in a single cell, whereas true multicellu-lar organisms have specialised cells and tissues for different life functions.The latter cells are not capable of a surviving on their own.

The biosphere has a profound influence on the Earth system and generates driving mechanisms for a global environmental change (Lovelock 1979;Lenton 1998). The most significant effect of the early microbial life on Earth was the gradual oxidation of the initially reducing atmosphere through a continuous release of free oxygen as the by-product of photosynthesis thathas evolved among cyanobacteria in the early Proterozoic. The release of free oxygen into the atmosphere was a prerequisite for the development of

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eukaryotes and subsequently the ‘higher’ organisms, and the colonisation of land. The Earth’s continual environmental change is the result of the interac-tion between living organisms, and underlying tectonic processes, all com-bining to create the Dynamic Earth we know today.

The Cambrian Explosion and diversification of microorganisms

The Cambrian Period (543-490 Ma) is known for a remarkable diversifica-tion of marine shelly metazoans, also known as The Cambrian Explosion.Several distinct clades of protoctists (unicellular eukaryotes) both organicwalled and with mineralised tests or skeletons, such as algae (including acri-tarchs), foraminiferans and radiolarians also radiated rapidly throughout the Cambrian (Vidal & Moczyd owska 1997; Moczyd owska 1998; Won & Below 1999; McIlroy et al. 2001; Moczyd owska 2002) forming an inte-grated part of this evolutionary event.

Most Cambrian metazoans were suspension feeders and grazers depend-ant on organic matter provided by the photosynthesising microbiota, pre-dominantly algal acritarchs at this time. Thus they are tightly linked to theprimary producers in the trophic web. The coeval evolution of autotrophicmicrobiota and heterotrophic metazoans established complex marine ecosys-tems and was a result of the interplay between genetic and environmentalfactors, among which the nutrient-generating phytoplankton played a signifi-cant role (Moczyd owska 2002).

The studies of endolithic microborers is still at an initial stage, althoughthe first endolithic trace fossils have been found as far back as the Early Ar-chean (Furnes et al. 2004). The endoliths are also experiencing selective pressure from grazers, feeding on endolithic and epilithic (inhabiting the surface of shells, corals and other carbonate substrates) cyanobacteria, greenalgae and fungi. A strong selective pressure may also produce a great diver-sification among primary producers, suggesting that many new forms of microphytoplankton and cyanobacteria appear in conjunction with the Cam-brian Explosion.

The fossils studied here are neither closely related biologically nor be-longed to the same biocenosis, but they were a part of the extended and di-verse community of single celled biota that rapidly radiated in the Cambrianand showed a variety of modes of life and ecological adaptations. This wasone of the signs of the Cambrian evolutionary and ecological explosion.

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Aims

The aim of this thesis is to document two interesting and distinct groups of microorganisms from the late Middle Cambrian to Early Ordovician periods: the algal acritarchs and cyanobacterial endoliths. Although differing in manyways, they evolved through the Cambrian and were a part of the great diver-sification event. The thesis is based on two separate studies. The first study deals with the group Acritarcha, which is defined by the uncertain origin ofthe fossil organisms. Well preserved acritarch assemblages from Kolguev Island, Arctic Russia, are described in detail and referred to valid and revised taxa and higher systematic ranks. The Cambrian-Ordovician boundary isalso identified for the first time in this region. The second study constitutes a group of microorganisms with an endolithic mode of life, fossilised in rock cavities and brachiopod shells. Well preserved material associated with hardgrounds from the Henson Gletscher Formation and Holm Dal Formationof North Greenland consists of trace fossils of a diverse flora of endolithsfrom an area that so far has a poorly known microfossil record.

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Acritarchs

As early as in the nineteenth century palaeontologists developed an interestin organic-walled microfossils, but it took more than half a century before amore systematic research was undertaken. The first palynomorphs classified as acritarchs are almost certainly those described by White (1862) from the Ordovician to Devonian strata of New York State, U.S.A. The term acri-tarch originates from the Greek words acros and tarchos, and simply meansuncertain origin. In the 1930’s, Eisenack described many acritarch speciesand eventually he regarded them to be of phytoplanktonic origin (Eisenack1969). Together with co-authors, he produced a monumental taxonomiccatalogue (Eisenack et al. 1973, 1976). At the same time Wetzel (1933) as-signed many Mesozoic microfossils to the group Hystrichosphaera that con-sisted both of acritarchs and dinoflagellates. This was later divided into twodifferent groups by Evitt (1961) to distinguish fossil cysts of dinoflagellatesfrom fossil cysts of unknown origin. Subsequently, Evitt (1963) proposedthe group Acritarcha that today is defined principally as organic walled cystsof uncertain origin. Consequently, any acritarch of which the biological af-finity has been determined should be transferred from the group Acritarchato their true systematic group (Tappan 1980). Certain taxa of the former acritarchs have also been transferred, e.g. the genus Tasmanites and Pteros-permella, and are today referred to the Family Prasinophyceae of the algal Phylum Prasinophyta. The group Acritarcha is a polyphyletic and informalgroup (Deflandre 1947; Downie et al. 1963; Evitt 1963), and its taxonomy isentirely phenetic and based on morphological features. Despite the acri-tarch’s uncertain biological affinity and they are all classified under the In-ternational Code of Botanical Nomenclature (Downie 1961). Acritarchs ex-hibit many different morphologies (Fig. 1) and are classified primarily by their vesicle shape, the shape and size of the processes.

Acritarchs and many other microfossils have become very important toolsin biostratigraphic correlation. The application of microfossils to biostrati-graphic correlation was developed by researchers in the petroleum industryat an early stage of micropalaeontological studies. Improved modern micro-scopes enable better interpretations of morphological features of the micro-fossils. Scanning Electron Microscopes (SEM) improved the possibilities to distinguish ultrastructures and recently acritarchs were studied in Transmis-sion Electron Microscope (TEM) (e.g. Talyzina & Moczyd owska 2000).The Laser Confocal Microscope enables studies of the internal structures of organic walled fossils, but also allows creation of three dimensional images.

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This permits more precise classifications of microfossils and to improve the systematic and biostratigraphical interpretations.

Figure 1. Acritarchs from the Upper Cambrian-Tremadocian strata in Kolguev Island illustrat-ing the diversity of cyst morphologies. 1. Vulcanisphaera britannica Rasul, 1976. 2. Polygo-nium sexradiatum (Timofeev, 1959) Volkova, 1990. 3. Eliasum llaniscum Fombella, 1977. 4.Saharidia fragilis (Downie, 1958) Combaz, 1967. All specimens are from Kolguev Island,Arctic Russia. Scale bar in 1 is 12 µm for 1, 2; 15 µm for 3; 20 µm for 4.

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Geology of Kolguev Island and the Pechora Basin

Kolguev Island is located on the Barents Sea shelf near the northern coast of Arctic Russia and geologically it is a part of the Pechora Basin (Fig. 2). ThePechora Basin extends between the Timan Range and the Polar Urals, whichare the two fold belts amalgamated to the East European Craton during theEdiacaran (formerly Vendian) Timanian and the late Palaeozoic Uralianorogenies, respectively (see review by Gee et al. 2000). The Pechora Basin is a crustal block defined by deep faults and it consists of a pre-Ediacaranbasement of deformed and metamorphosed sedimentary and volcanic rocks, intruded by igneous bodies, approximately 620 and 560 Ma, and the overly-ing terminal Neoproterozoic-Phanerozoic platform cover (Bogatsky et al.1996; Olovyanishnikov 1998; Gee et al. 2000).

Figure 2. Right: Sketch map of the Arctic Russia showing the location of Kolguev Island(insert map), the extension of the Pechora Basin on the Barents Sea coast and shelf (shadedarea), and left: the simplified map of Kolguev Island with marked localities of the North-Western 202 and Bugrino 1 boreholes. (From Moczyd owska & Stockfors 2004; modifiedafter Gee et al. 2000).

The angular, so-called Timanian unconformity that separates basement and sedimentary cover is a major tectonic feature in the region, yet the timeinterval of the hiatus is not accurately recognized because of the deficiencyof reliable fossil records and/or isotopic datings. The maximum age of the platformal succession has been estimated roughly to be late Neoproterozoicin the Timan Range and early Ordovician in the Pechora Basin (Preobraz-henskaya et al. 1995; Olovyanishnikov 1998; Melnikov 1999). However, the supposed Neoproterozoic age of the strata in the Timan Range (Bogatsky etal. 1996; Olovyanishnikov 1998) lacks supporting evidence. Recent studies

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of acritarchs from Kolguev Island have proved the existence of Upper Cam-brian rocks (Moczyd owska et al. 2004).

The Phanerozoic sedimentary strata on Kolguev Island are almost 5000 m

Figure 3. Sedimentary successions in the Bugrino 1 and North-Western 202boreholes with sample locations and proposed biostratigraphic subdivision.

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thick and logged in several boreholes. However, the lowermost part of thesuccession is recognised exclusively in the Bugrino 1 and North-Western202 boreholes, although the basement rocks are not yet reached (Preobraz-henskaya et al. 1995; Fig. 3). This succession is composed predominantly offine-grained siliciclastic rocks with thin interbeds of conglomerates and it underlies the pre-Devonian regional paraconformity. The strata are almosthorizontal, un-metamorphosed and consist of laminated organic-rich clay-stones and siltstones with a maximum thickness of 1280 m in the Bugrino1borehole. Formations are not yet distinguished in the two studied successionsand only brief descriptions of the lithology and sedimentary structures areavailable (Bro et al. 1988; Preobrazhenskaya et al. 1995; Moczyd owska etal. 2004). Fossil records of acritarchs, brachiopods and phyllocarid arthro-pods have been interpreted previously to indicate an early Ordovician age (Rudavskaya & Popov in Preobrazhenskaya et al. 1995), whereas the newstudies of acritarchs reveal assemblages which are diagnostic for both the late Cambrian and Tremadocian time intervals. These Upper Cambrian-Lower Ordovician sediments accumulated in open marine environments on a stable shelf flooded by a transgression prograding over the peneplanedbasement (Preobrazhenskaya et al. 1995; Malyshev 2000; Moczyd owska etal. 2004). The deposition of platformal sediments on the passive marginextending along the northern and north-eastern (in present day coordinates) edge of the Baltica palaeocontinent has been interrupted by several episodes of regional uplift and submergence as well as some volcanic activity, but it continued throughout the Palaeozoic.

PalaeogeographyAcritarchs play an important role in global palaeogeographic reconstruc-tions. Based on palaeontological, palaeomagnetic, palaeoclimatic, tectonicand stratigraphic evidence, several models of Cambrian and Ordovician pa-laeogeography are available today. The Cambrian model by Scotese andMcKerrow (1990) has been used (Moczyd owska 1997) to plot the fossil records and to test the possible bioprovincial distribution of acritarchs. Moretime restricted Ordovician palaeomaps have recently been published byCocks (2001) and Li & Powell (2001). Bergström (1990) presented an oce-anic current circulation model for the Early Ordovician whereas Christiansenand Stouge (1999) published a palaeo-oceanographic model for theArenigian epoch. Servais et al. (2003) summarised different palaeobio-geographical distribution of Ordovician organic-walled microphytoplankton,such as acritarchs, prasinophytes and related microorganisms.

Cramer (1968) made the first bioprovincial interpretation of two majoracritarch assemblages to be dependent on palaeo-latitudes. Cramer & Díez(1977) distinguished two acritarch ‘provinces’ in the Ordovician; one con-trolled by cold water regimes and the other of warm water regimes. During

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the Late Cambrian and Early Ordovician, the supercontinent Gondwana (in-cluding South Africa, America, Antarctica, Australia, India and several mi-cro-continents) occupied higher palaeolatitudes and was dominated by cold water provinces, whilst Laurentia (including North America and Greenland)was located in the equatorial zone and was dominated by warm water as-semblages. Vavrdová (1974) distinguished two other provinces; the Mediter-ranean province dominated by diacromorphic acritarchs and the Baltic prov-ince dominated by acanthomorphic acritarchs. Studies on recent marinephytoplankton show that ocean currents play an important role for theirglobal distribution (Matthiessen 1995; Mudie and Harland 1996), suggesting that palaeo-ocean currents must have played an important role for the distri-bution of acritarchs (Vidal & Moczyd owska 1996; Servais et al. 2003).

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Endolithic microorganisms

Cyanobacteria form a very diverse group of Eubacteria (true bacteria) and its constituent members range in morphology from minute unicellular to large multicellular organisms. Most cyanobacteria are photosynthesising, produc-ing oxygen as a by-product and most of them contain chlorophyll a, together with various proteins called phycobilins, which give the cells a typical blue-green colour. Cyanobacteria have a known geological record from the Ar-chaean, approximately 3.5 Ga (Schopf & Packer 1987, Schopf et al. 2002;see discussion in Brasier et al. 2002), to the present day. Certain cyanobacte-ria are characterised by an endolithic mode of life. Such endoliths may be classified as chasmoendoliths that colonize existing cracks and fissures,cryptoendoliths that occupy structural cavities in the rock and euendolithsthat actively penetrate the interior of rocks (Golubic et al. 1981).

The earliest described endolithic microorganisms have been found in Ar-chean pillow lava from South Africa (Furnes 2004) but cyanobacteria appear more frequently from the late Proterozoic (Knoll et al. 1986) onwards.

EuendolithsA variety of names has been applied to fossils and ichnofossils of euen-dolithic organisms (e.g. Green et al. 1988; Guoxiang 1997). One such form,with branching linear cell series, has been described as Eohyella Zhang &Golubic, 1987, emend. Green et al., 1988 and it is a morphological counter-part of the recent living genus Hyella Bornet & Flahault, 1888 (Fig. 4).Hyella has been described as one of the morphologically most complex gen-era of coccoid cyanobacteria (Golubic et al. 1987), combining properties of both unicellular and multicellular organisms (LeCampion-Alsumard &Golubic 1985). Cyanobacterial taxonomy has been based mainly on mor-phology, which is also the only parameter applicable to fossil specimens.Several attempts to compare boring patterns and cell shapes of fossil en-dolithic morphospecies with recent living Hyella species have been made to find modern morphological counterparts to the fossil Eohyella and other early ichnofossils (e.g. Campbell 1982; Knoll et al. 1986; Green et al. 1988; Al-Thukair & Golubic 1991a; Golubic & Seong-Joo 1999). However, it is also possible to reconstruct palaeoenvironments by comparing fossil cyano-bacteria with their modern counterparts (Golubic & Seong-Joo 1999). Re-

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cently, our understanding of the fossil endoliths has been improved by thedescription of many new euendolithic Hyella species, especially from theArabian Gulf (Al-Thukair & Golubic 1991a, 1991b, 1996; Al-Thukair et al.1994).

Figure 4. FEG SEM images of different endoliths from North Greenland. A. Etched out“mould” of a euendolithic organism actively bored into a carbonate grain and resemblingthe modern genus Hyella. B. Cryptoendolith, with long encrusted filament that inhabit theinside of a brachiopod shell. Scale bars = 100µm.s

CryptoendolithsAnother group of endoliths is the cryptoendoliths (Golubic et al. 1981),which inhabit a cavity, e.g. the inside of shells or cracks and fissures in therocks (Fig 4). Schroeder (1972) described the growth of calcareous crusts on algal filaments in cavities within present day Bermuda reefs, recognising its contribution to synsedimentary submarine cementation. The cavity-dwellingfilaments, or cryptoendoliths in the terminology of Golubic et al. (1981),formed the locus for deposition of a crust of radiating bladed or fibrous cal-cite crystals, such that individual cavities were crossed with a mesh of calci-fied fibres. Schroeder (1972) also recognised algal borings within shellfragments, euendoliths in the sense of Golubic et al. (1981), noting that these euendolithic filaments extended from their galleries to form the cryptoen-dolithic meshworks. Schroeder (1972) attributed his modern endolithic algal threads to the green alga Ostreobium, although this was not previouslyknown to change between euendolithic and cryptoendolithic life styles. Rid-ing & Voronova (1985) stressed that the true affinities of Cambrian so-called‘algae’ are often contentious, giving as examples the familiar Renalcis, Epi-

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phyton and Chabakovia which were interpreted as Rhodophyta by Vologdin(1962) and Cyanobacteria by Luchinina (1975). Riding (2001) noted thattwo thirds of the 30 principal genera of calcified Cambrian microbes weremost likely cyanobacteria, while only 3 genera were interpreted as calcifiedalgae.

Unlike the modern Bermudan examples described by Schroeder (1972)and the Greenland forms described in this thesis, many of these Cambrianmicrobes described by Riding (2001) developed calcification of the enclos-ing sheath during life.

Figure 5. Multifilamentous, bundle forming euendolith from the samples of Holm Dal For-mation. The endolithic galleries may show very acute angles or soft bends in the brachiopodshell. The bundles vary greatly in diameter. The individual filaments also vary in diameter in concordance with the diameter of the bundle. Scale bar = 5µm.

BioerosionEndolithic organisms are commonly and widely known to play a major role in bioerosion and biodegradation (e.g. Mao Che et al. 1996; Vogel et al.1996; Radtke et al. 1997; Vogel et al. 2000; Tribollet & Payri 2001). Bydissolving and perforating carbonate rocks, endoliths have a great impact on micritization in shallow marine and intertidal environments. Vogel et al.(2000) studied the rate of bioerosion due to endolithic activity and pointed out its palaeoecological importance. Metazoans grazing on endoliths notonly increase coastal destruction (Torunski 1979), but also enhance the mic-ritization process immensely. Nevertheless, it has been suggested that en-dolithic Cyanobacteria not only destroy original grain textures, but also playa constructional role in stromatolite growth by forming lithified layers of welded grains (Macintyre et al. 2000). Present day endolithic Cyanobacteriaare restricted to the upper photic zone, whereas the lower photic zone is in-habited by green and red algal endoliths. Thus, endolithic Cyanobacteria canbe important bathymetric indicators (Budd & Perkins 1980) and may con-

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tribute to the recognition of palaeodepth zonation (LeCampion-Alsumard etal. 1982; Budd & Perkins 1982).

North Greenland. The endolithic material treated in this thesis comes from two separate areas and three different localities in Peary Land, North Greenland. The first study reported in Paper IV is based on material collected from one locality in the Løndal area, marked locality 1 in Figure 6, belonging to the Henson Glet-scher Formation. The Henson Gletscher Formation forms part of the Brønlund Fjord Group of late Early-Middle Cambrian age (Ineson & Peel 1997) which represents the development of a carbonate platform on the cur-

rently southern margin of the mainly Lower Palaeozoic Franklinian Basin of the Canadian Arctic Islands (Peel & Sønderholm 1991). Off-platform strata of the Brønlund Fjord Group show an alternation of pale, carbonate-dominated units (Aftenstjernesø and Sydpasset Formations) with darker,mixed siliciclastic and carbonate units (Henson Gletscher and Ekspedition Bræ Formations). The former represent extensive sheets of carbonates shedfrom the strongly prograding platform during highstands of sea level (Surlyk & Ineson 1987; Ineson & Surlyk 1992, 1995). The mixed siliciclastic-carbonate sediments of the Henson Gletscher and Ekspedition Bræ Forma-

Figure 6. Sampled localities in Peary Land, North Greenland. 1. The area where the euen-dolithic fossils in paper IV were sampled, from the Cambrian Henson Gletscher Formation. 2.Area around Gustav Holm Dal, where the cryptoendolithic and euendolithic fossils in paper Vwere collected, from the late Middle Cambrian Holm Dal Formation.

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tions were deposited during lowstands of sea level during which much of thecarbonate platform was exposed. The phosphatised sediments forming the upper few metres of the Henson Gletscher Formation in Løndal represent a lowstand wedge of wackestones which accumulated prior to the ensuing highstand represented by the Sydpasset Formation.

The samples in Paper V were all collected from two localities around Holm Dal, marked locality 2 in Figure 6, and are all from the Gustav HolmDal Formation of central North Greenland (Peel 1988). The formation was defined by Ineson (1988) as part of the Tavsens Iskappe Group which is fully described by Ineson & Peel (1997); see also Peel & Sønderholm(1991). The formation is about 155 m thick in its type section (Fig. 6, local-ity 2) but pinches out entirely some 5 km to the south in Fimbuldal. In thearea around Gustav Holm Dal, the formation typically forms recessive, dark-weathering outcrops of mainly thin, parallel and wavy bedded argillaceous lime mudstones and grey laminated dolomites that are interbedded with thinbedded packstones and grainstones. The latter dominate the upper third ofthe formation where they are frequently dolomitised. Beds of carbonate breccia and slumped horizons occur sporadically throughout the formation.

A hardground composed of a finely laminated phosphatised surface, a few millimetres in thickness, is conspicuous on frost-heaved slabs derived fromthe lower 10 m of the formation at the type locality at Holm Dal. The same,or a similar surface, was also located at one of the Holm Dal localities, some11 m above the base of the formation. The hardground is encrusted withminute, crater-like, echinoderm holdfasts and is associated with winnowed shell lags of phosphatic brachiopods, which also display the currently de-scribed endolith associations.

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Results & Discussion

The thesis is based on two separate studies on different groups of microor-ganisms from late Middle Cambrian to the earliest Ordovician. The firststudy is based on fossil acritarchs from late Cambrian-early Ordovician ma-terial from Kolguev Island in Barents Sea in the Arctic region of Russia andcomprises three papers. The second study deals partly with euendoliths that extends with dendritic patterns into carbonate grains, partly with Bundle-forming euendoliths penetrating brachiopod shells with complex galleries incombination with encrusted filaments of cryptoendoliths inhabiting brachio-pod shells. All associated with the late Middle Cambrian hardground pre-served in geological successions in Peary Land, central North Greenland.

The Acritarch Study Moczyd owska, M., Popov, L.E. & Stockfors, M., 2004: Upper Cambrian-Ordovician successions overlying Timanian complexes: new evidence of acritarchs and brachiopods from Kolguev Island, Arctic Russia. Geobios 37,239-251. (Paper I)

Moczyd owska, M. & Stockfors M., 2004: Acritarchs from the Cambrian-Ordovician boundary interval on Kolguev Island, Arctic Russia. Palynology28, 15-73. (Paper II)

Moczyd owska, M., Stockfors, M. & Popov, L.E., 2004: Late Cambrian rela-tive age constrains by acritarchs on the post-Timanian deposition on KolguevIsland, Arctic Russia. In D. Gee & V. Pease (eds.): The Neoproterozoic Ti-manide Orogen of Eastern Baltica. Geological Society, London, Memoirs 30,159-168. (Paper III)

The first paper (Paper I) ‘Upper Cambrian-Ordovician successions overlyingTimanian complexes: new evidence of acritarchs and brachiopods from Kol-guev Island, Arctic Russia’ focuses on new material from the Kolguev Is-land. The studies on acritarch microfossils from the lowermost part of thePalaeozoic succession (c. 4500 m depth) revealed diverse assemblages that are biostratigraphically very significant. The position of the Cambrian-Ordovician boundary is recognised in the off-shore marine sedimentological

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succession at a level where the age-diagnostic Ordovician taxa appeared.The Upper Cambrian strata of the Peltura and Acerocare trilobite zones are distinguished on the basis of taxa known from adjacent areas in the East European Platform, in general from Baltica and other palaeocontinents, Ava-lonia and Gondwana. Invertebrate faunas, including brachiopods, problem-atic mollusc and phyllocarid arthropods, are revised taxonomically and theyare indicative for the Tremadocian and Arenigian stages in the upper part of the succession.

The second paper (Paper II) ‘Acritarchs from the Cambrian-Ordovicianboundary interval on Kolguev Island, Arctic Russia’ is a major taxonomicrevision of the diverse fossil association from the Bugrino 1 and North-western 202 boreholes. Age-diagnostic acritarchs were used to identify Up-per Cambrian and Lower Ordovician (Tremadocian) strata and were evalu-ated in the context of regional stratigraphy and interregional correlation. Theboundary between Cambrian and Ordovician is established in a sedimen-tologically continuous succession, as are the Peltura and Acerocare trilobite Zones of Cambrian from Baltica. In this paper we describe the acritarch as-sociation from Kolguev Island in great detail, its taxonomy and biostrati-graphic interpretation. We propose several new combinations and emenda-tions of species and genera commonly known from Cambrian-Ordoviciansuccessions. The aim of the revision is also to verify and establish a moreconsistent morphological key to identify acritarchs taking into considerationtheir intraspecific variations and their morphologically evolutionary diversi-fication.

The third paper (Paper III) ‘Late Cambrian age constrains on the post-Timanian deposition on Kolguev Island, Arctic Russia’ summarizes the re-cently established acritarch dating of the relative age of the lowermost sedi-mentary succession known on Kolguev Island (Moczyd owska & Stockfors2004) and re-evaluates the microfossil record by Rudavskaya (in Preobraz-henskaya et al. 1995) deriving from the same section as well as the inverte-brate faunas. The newly documented relative age of the base of the post-Timanian platform succession is significant for interpreting the timing of theTimanian orogeny (its minimum age) and establishing the passive marginsetting and onset of deposition. The previous assessment on the age of the post-Timanian unconformity in the context of the regional occurrence of Cambrian rocks is also summarized and critically reviewed.

The Endolith StudyStockfors, M. & Peel, J.S., 2005: Endolithic Cyanobacteria from the Middle Cambrian of North Greenland, GFF, submitted manuscript. (Paper IV)

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Stockfors, M. & Peel, J.S., 2005: Euendoliths and cryptoendoliths within late Middle Cambrian brachiopod shells from North Greenland, GFF, submittedmanuscript. (Paper V)

Two papers describe endolithic microorganisms from the Henson GletscherFormation and the Holm Dal Formation. Two different kinds of endolithswere present in the study; 1 euendoliths that actively penetrates the substrate or shell by boring (chemically dissolving calcium carbonates), obtainingcomplex boring patterns and galleries that, in recent studies on living cyano-bacterial endoliths, suggest that they are species specific; 2 cryptoendolithsinhabiting cracks and fissures, or any other cavity in the rock, e.g. cavities between brachiopod shells.

In the first paper (Paper IV) ‘Endolithic Cyanobacteria from the MiddleCambrian of North Greenland’, we describe borings in carbonate grains,attributed to the euendolithic cyanobacteria Eohyella, from the Middle Cam-brian Henson Gletscher Formation of North Greenland. Four morphotypesare recognised, both in thin section and as three-dimensional phosphaticreplicas etched from the host rock with acetic acid. While comparisons aremade with living species of Hyella and fossil Eohyella, the lack of details concerning the cell shape and size allows description under open nomencla-ture only.

The second paper (Paper V) ‘Euendoliths and cryptoendoliths within late Middle Cambrian brachiopod shells from North Greenland’ is focused ondescribing both euendoliths and cryptoendoliths. At least in same cases it is possible to infer a combination of the two living modes for some of the de-scribed ichnofossils. Traces of an association of microscopic endoliths aredescribed within the shell wall and internal cavity of phosphatic brachiopodswith conjoined valves from the Holm Dal Formation (late Middle Cambrian)of Peary Land, central North Greenland. Ridged galleries which also pene-trate early diagenetic, phosphatised, fibrous crusts on the shell interior are borings excavated by a multifilamentous euendolith. Meshworks of strands crossing the shell interiors are phosphatised encrustations seemingly origi-nally deposited as radiating, acicular, aragonite crystals on cryptoendolithicfilaments prior to their degradation. The identity of the endoliths from the Holm Dal Formation is unknown, but they were probably cyanobacteria.

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Sammanfattning på svenska:

Kambro-ordoviciska mikroorganismer: acritarcher och endoliter

Tidigt liv och mikroorganismerLiv har existerat på jorden i nästan fyra miljarder år. Det tidiga livet har främst beskrivits genom fynd av fossila organismer vilka på senare tid även kompletteras av moleylära och geokemiska data. De äldsta kända mikrofossilen har man funnit i Apex Cherts, västra Australien, och vartroligtvis cyanobakterier och av tidigarkeisk ålder, ca. 3,5 Ga (Schopf & Packer 1987, Schopf et al. 2002; se även diskussion i Brasier et al. 2002).Nyligen har dessutom fossila spår av borrande mikroorganismer av sammaålder upptäckts i kuddlava från Sydafrika (Furnes et al. 2004). De äldsta kända organismerna måste haft en längre tid att utveckla den komplexitet depåvisar, vilket också innebär att livet är mycket äldre än dessa. Allberggrund äldre än 3,5 Ga har utsatts för så kraftig metamorfos och deformation att inga fossil finns bevarade. Däremot visar geokemiska fynd(av kolisotop 13C) på biologisk aktivitet i 3,8 Ga metasediment från IsuaFormation, Akiliaön, sydvästra Grönland (Mojzsis et al. 1996; se ävenWhitehouse et al. 2001; Fedo & Whitehouse 2002). I berggurnd yngre än 3,5 Ga, framför allt efter eukaryoternas första uppträdande omkring 2,7 Ga (Brocks et al. 1999), visar den ökande mängden mikrofossil på en progressiv evolution och större diversitet bland mikroorganismer.

De tidigaste mikroorganismerna var prokaryota och levde i marina miljöer. De flesta fossil har beskrivits som fotosyntetiserande cyanobakt-erier, men även andra fototrofa, såväl som heterotrofa bakterier existeradevid denna tid. Cyanobakterier kunde forma strandnära stromatoliter (algmattor) eller leva ett planktiskt liv i alla marina miljöer ner till ett djupsom endast begränsades av tillgången på solljus. Idag florerar cyanobakterieroch andra bakterier även i sötvattensmijöer. Emellertid är sådana miljöerdåligt bevarade i den geologiska lagerföljden och tidpunkten förmikroorganismernas kolonisation av landområden är därför osäker.

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De tidigaste bevisen för eukaryota organismer kommer från molekylärarester av biologiska fetter med en ålder av 2,7 Ga (Brocks et al. 1999, se även Javaux et al. 2004), medan riktiga fossil uppträder först 2,1 Ga(Runnegar 1994). En grupp av fossila marina organismer, som är bland detidigaste och vanligaste mikrofossilen från 1,9-1,8 Ga (Hofmann & Schopf 1983; Zhang 1986; Jankauskas 1989; Mendelson and Schopf 1992), kallas acritarcher (av grek. akritos 'osäker', 'tvivelaktig' och arch 'ursprung'). Dettaär en grupp mikrofossil utan närmare släktskapsband men sammanhållna av praktiska skäl. De har ett motståndskraftigt hölje av organiskt material.Idag anses dock de flesta i princip vara vilocystor av fotosyntetiserandeplankton. Eftersom acritarchernas ursprung numer anses tillhöra eukaryotafytoplankton bör de också föras till deras rätta taxonomi (se Tappan 1980).Denna avhandling fokuserar huvudsakligen på 500-480 miljoner år gamla acritarcher av kambro-ordoviciska ålder.

En annan grupp av mikroorganismer som behandlas i avhandlingen ärendoliter, vilka representerar olika biologiska klader, t.ex. Archea, bakterier,cyanobakterier, alger och svampar. Endolitiska organismer karakteriseras avatt de ”lever i berg” och då främst i hårda karbonatsubstrat, i spickor ochhåligheter, antingen genom att aktivt borra sig in, alternativt att bebo redan exiterande håligheter (t.ex. mellan brachiopodskal). Endoliter finns, som redan nämnts, beskrivna från 3,5 Ga, men återfinns mer frekvent från sen-proterozoikum, 800-700 Ma, (Knoll et al. 1986) och är väl kända som skal-borrande organismer från kambrium och framåt (Golubic & Seong-Joo1999).

Oftast ser vi livets mångfald främst bland de högre djuren och växterna.Men faktum är att mikroberna (Archea, bakterier, cyanobakterier, alger ochsvampar) påvisar den största diversiteten bland alla organismer på jorden. De utgör de yttersta gränserna av biosfären och existerar på flera kilometersdjup i hydrosfären och litosfären, samt lever i de mest extrema miljöer. De encelliga organismerna består av mer komplexa celler på grund av att alla deras livsfunktioner måste inrymmas i en enda cell, emedan de flercelliga organismerna har specialiserade celler för olika funktioner i organismen.

Biosfären har en grundläggande påverkan på systemet jorden och generar drivmekanismer för globala miljöförändringar (Lovelock 1979; Lenton 1998). Den mest påtagliga effekten som det tidiga livet hade på jorden, varatt det påbörjades en oxidation av den tidigare reducerande atmosfären,främst p.g.a. av att fritt syre släpptes ut i atmosfären. Syret var en biproduktav fotosyntesen som utvecklades hos cyanobakterier under tidig-protero-zoikum. Tillförseln av syre till atmosfären blev också förutsättningen för den utveckling av eukaryoter och sedemera ”högre liv” som följde och därmedäven förutsättningen för kolonisationen av landmassorna.

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Den kambriska explosionen och diversifieringen avmikroorganismerKambrium (543-490 Ma) är bland annat känt för den snabba utvecklingenoch diversifieringen av skalbärande marina djur, den sk. ”kambriskaexplosionen”. Parallellt med denna skedde dock även en anmärkningvärddiversifiering av encelliga mikroorganismer från olika framträdande grupper,dels de som är inneslutna endast av organiska cellväggar, såsom alger (inkl. acritarcher), cyanobakterier och andra bakterier, dels de som utsöndrar etthårt skal utanför cellmembranet, t.ex. foraminiferer (skalamöbor) och radiolarer och kalkalger.

Syftet med denna avhandling är att beskriva två av dessa intressanta och distinkta grupper av mikroorganismer från sen-mellankambrium till tidig-ordivicium, nämligen de planktiska acritarcherna och de cyanobakteriellaendoliterna. Trots att de skiljer sig avsevärt åt i många avseenden har de gemensamt att de är encelliga (cyanobakterierna visar dock ”primitivflercellighet” med celler i serie) och fotosyntetiserande organismer.Dessutom var de en del av den stora evolutionshändelsen under kambrium.Avhandlingen baseras på två separata studier.

Den första handlar om gruppen Acritarcha, där välbevarade acritarcher från Kolguevön, arktiska Ryssland systematiskt beskrivits i detalj. Från den sedimentologiskt kontinuerliga lagerföljden på Kolguevön presenteras förförsta gången paleontologiska bevis för kambriska strata i den nordöstra sektorn av Europa. I lagerfölden som omsluter övergången mellan kambriumoch ordovicium har många tidsdiagnostiska acritarcher blivit identifierade. Likaså har de stratigrafiska intervallen vilka motsvarar Peltura- och Acerocare- zonerna i Baltica identifierats, vilket gjort det möjligt att peka utgränsen mellan kambrium och ordovicium. En stor diversitet av acritarcher har urskiljts, men inga tydliga utdöendemönster kan noteras vid övergången kambrium-ordovicium, vilket stämmer väl överens med undersökningar frånandra paleokontinenter (Laurentia, Gondwana och Avalonien). Istället ses engradvis förändring av acritarchernas diversitet, snarare än en abrupt, vilket normalt associeras med större utdöendehändelser.

Den andra studien behandlar mellankambriskt, tidigare obeskrivetmaterial från Peary Land i norra Grönland och handlar om endolitiska mikroorganismer. I två olika artiklar beskrivs dels euendoliter som aktivt borrar sig in i skal av brachiopoder och/eller karbonatkorn genom att kemiskt lösa upp karbonater. De tidigare skapar komplexa mönster ochnätverk av gångar inuti skalet, medan de senare sprider ut sig i ett trädlikt mönster. Dels beskrivs kryptoendoliter vilka utnyttjar de redan existerande håligheterna mellan brachiopodskalen och som fossilt består av långa kalcifierade filament med radiell kristallpåväxt.

Endoliter spelar bland annat en viktig roll för bildningen av stromatoliter (Macintyre et al. 2000) såväl som för bioerosionen och biodegradation (t.ex. Mao Che et al. 1996; Vogel et al. 1996; Radtke et al. 1997; Vogel et al.

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2000; Tribollet & Payri 2001). Den taxonomiska identiteten är osäker för de beskrivna fossilen från Holm Dal Formation och Henson Gletscher Formation, men de var sannolikt cyanobakterier, såsom beskrivits från annatmaterial (jmf Runnegar 1985; Bengtson et al. 1990; Guoxiang 1997; Seong-Joo & Golubic 1998).

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Acknowledgements

Thanks to all the members of the Palaeobiology Program at the Departmentof Earth Sciences, Uppsala University. Special thanks to my supervisors Ma gorzata Moczyd owska-Vidal and John S. Peel for help, guidance and cooperation in my quest to complete this work. My co-authors Ma gorzataMoczyd owska-Vidal and Leonid Popov who provided the Kolguev Islandmaterial for the acritarch study and John S. Peel, apart from co-authorship,also provided the Greenland material for the endolith study. Thanks to Sebastian Willman for variable comments and coffee-break discussions;Jonas Ahnesjö and Joakim Eriksson for recreational debates on natural sci-ence during weeks of fishing and sailing etc. I would also like to thank myfamily, Jenny and Malte for great support as well as my mother Birgitta forentertaining Malte.

Scanning electron microscoping was carried out in the microscopy centre, Evolutionary Biology Centre, Uppsala University. Financial support from The Swedish Research Council (Vetenskapsrådet) to Ma gorzata Moc-zyd owska-Vidal and John S. Peel and scholarship from The Royal Swedish Academy of Sciences (Kungl. Vetenskapsakdemien) is gratefully acknowl-edged, as is the award of a faculty postgraduate research scholarship.

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