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Description and Microscale Analysis of Some Enigmatic Palynomorphs from the Middle Devonian (Givetian) of Libya

Description and Microscale Analysis of Some Enigmatic Palynomorphs from the Middle Devonian (Givetian) of Libya
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  See discussions, stats, and author profiles for this publication at: Description and Microscale Analysis of SomeEnigmatic Palynomorphs from the MiddleDevonian (Givetian) of Libya  Article   in  Palynology · November 2009 DOI: 10.2113/gspalynol.33.1.101 CITATIONS 11 READS 92 6 authors , including:Philippe SteemansUniversity of Liège 249   PUBLICATIONS   2,245   CITATIONS   SEE PROFILE Pierre BreuerSaudi Arabian Oil Company 72   PUBLICATIONS   231   CITATIONS   SEE PROFILE Alain Le HérisséUniversité de Bretagne Occidentale 86   PUBLICATIONS   1,304   CITATIONS   SEE PROFILE Frédéric de Ville de GoyetPetrostrat Ltd 7   PUBLICATIONS   34   CITATIONS   SEE PROFILE All content following this page was uploaded by Philippe Steemans on 06 January 2017. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the srcinal documentand are linked to publications on ResearchGate, letting you access and read them immediately.  P. Steemans, E. Javaux, P. Breuer, A. Le Hérissé, C.P. Marshall, F. de Ville de Goyet: Devonian palynomorphs from Libya101   DESCRIPTION AND MICROSCALE ANALYSIS OFSOME ENIGMATIC PALYNOMORPHS FROM THEMIDDLE DEVONIAN (GIVETIAN) OF LIBYA PHILIPPE STEEMANSALAIN LE HÉRISSÉEMMANUELLE J. JAVAUXUniversité de Brest CNRSPalaeobotany–Palaeopalynology–MicropalaeontologyUMR 6538 Domaines OceaniquesDepartment of GeologyInstitut Universitaire Européen de la MerUniversity of Liège6 Avenue Le Gorgeu, Batiment GB-18 Sart Tilman9238 Brest cedex 34000 Liège 1FranceBelgiume-mail: P. MARSHALLDepartment of GeologyPIERRE BREUERThe University of KansasGeological Technical Services DivisionLawrence, Kansas 66045-7613Saudi AramcoU.S.A.DhahranSaudi ArabiaFRÉDÉRIC de VILLE de GOYETRue Rioul 46B-4500 HuyBelgium Abstract Large acritarchs were recovered from the Awaynat Wanin II Formation in the A1-69 borehole, western Libya at 394.4 m. This sample hasbeen dated by acritarchs and spores as Givetian (Middle Devonian). Two species of acanthomorph acritarchs were recovered that areunusually large for the Paleozoic. The first type, represented by a single specimen, is a new occurrence of a previously described butunnamed form from the Middle Devonian of the Sahara. The second type, which is more abundant, is named as Vanguestainidiumcucurbitulum  gen. et sp. nov. Biogeochemical analysis using infrared microspectroscopy shows that the   wall composition of this new taxonis close to algaenans isolated from   the green alga  Botryococcus braunii Kützing 1849 although these forms are not morphologically similar.The presence of well-preserved fragile palynomorphs, abundant terrestrially-derived palynomorphs including large megaspores, and raremarine palynomorphs suggests deposition in a low-energy nearshore environment such as a coastal swamp. Key words : acritarchs; spores; taxonomy; microscale analysis; Middle Devonian (Givetian); Libya. Palynology 33 (2009): 101–112 © 2009 by AASP FoundationISSN 0191-6122 INTRODUCTION The majority of enigmatic palynomorphs, which are notclearly attributed to miospores or extant protistan groupssuch as specific algal groups (e.g. prasinophycea,zygnematacea), are usually assigned to the Group Acritarcha.Acritarchs are defined as palynomorphs of unknown bio-logical affinities. Although they are generally assumed torepresent algal cysts, some are clearly vegetative cells andothers may represent animal eggs, fungi, parts of multicel-lular organisms (Butterfield, 2005), and prokaryotes suchas cyanobacterial envelopes. Spherical cysts could belongto a wide range of organisms, many of which are not marinephytoplankton (Strother, 2007).During the revision of Givetian palynolofloras from theA1-69 borehole in the Ghadamis Basin, western Libya(Text-Figure 1), an assemblage of acritarchs, chitinozoans,large megaspores, and miospores was discovered. Fol-lowing gentle laboratory treatment, examination of theresidue revealed intriguing large palynomorphs approxi-mately 1 mm in diameter including processes. A newmonospecific genus is described herein for one of theseforms. A single specimen of another acritarch is placed inopen nomenclature. This form was previously recorded  102PALYNOLOGY, VOLUME 33 — 2009 from the Middle Devonian of the Sahara by Doubinger(1966).The isolation of these delicate, large acritarchs from theMiddle Devonian of Libya using gentle processing tech-niques may result in the discovery of a greater diversity of palynomorphs from the Early and Middle Paleozoic. Theseputative new finds will improve the understanding of theevolution of the eukaryotes. MATERIALS AND METHODS Samples collected from cores from the A1-69 boreholedrilled by Shell in 1959 were provided by D. Massa to thepalynology laboratory of the University of Liège, Belgium.The borehole is located on the southern flank of the GhadamisBasin, western Libya (Text-Figure 1). The Devonian strataoccur within an essentially conformable package that issubdivided into the Tadrart, Ouan-Kasa, Awaynat Wanin I,Awaynat Wanin II, and Awaynat Wanin III formations(Text-Figure 2). These units were redescribed by BenRahuma et al. (2007). Massa (1988) discussed ages usingsubsurface data. The formations are dominantly siliclasticsand the facies varies from continental to nearshore. Theyare part of the transgressive-dominated succession thatfollowed the uplifting and erosion of the southern flank of the basin by Caledonian tectonic activity during the LateSilurian. A vast, regionally continuous fluvial system,thinning to the north developed during the Devonian in theGhadamis Basin. The sediments were derived from thesoutheast.Previous palynological studies from this borehole areLoboziak and Streel (1989), Streel et al. (1990), Loboziaket al. (1992), and de Ville de Goyet et al. (2007). In thesestudies, some sandy intervals were not studied because theywere believed to be less favorable for palynology. Twentysamples, from 486.8 to 294.3 m have subsequently beenstudied or restudied during postgraduate research on me-gaspores and miospores (Breuer, 2007). All samples con-tain miospores (and nine samples contain megaspores),together with marine palynomorphs such as acritarchs,chitinozoans, and prasinophycean phycomata. The horizoncontaining the enigmatic palynomorphs described here is at394.4 m and is within the Awaynat Wanin II Formation(Text-Figure 2).In order to recover megaspores, the samples were sub- jected to gentle laboratory treatment that is less damagingto the palynomorphs than the standard technique usingcentrifugation and heavy liquids. The samples were gen-tly teased (not crushed) into small fragments. The sampleswere then immersed in 40% hydrofluoric acid for 5 to 13days. This dissolution was helped by a 0.5–1.0 cm sieveplaced under the sample. Consequently, the fragmentswere continuously bathed in acid, with the insolubleresidue dropping through the mesh during processing.The sample material was hence not coated in acid-in-soluble material. The residues were then washed througha 150 µ m sieve. No oxidation was applied. Palynomorphswere picked using a pipette under a dissecting microscopeat relatively high magnification, and then placed on amicroscope slide for examination using transmitted lightmicroscopy. Other specimens were mounted on stubs andcoated using gold for scanning electron microscope (SEM)study.All sample materials and slides, including those with theholotype, paratypes, and figured specimens (Plates 1–3),                                                                                           Text-Figure 1.Location of the A1-69 well in Libya.1–7 Vanguestainidium cucurbitulum  gen. et sp. nov.163069, K36/2.2A paratype, 63070, S35/1.3, 463069, R46/3. 4 - detail of a process on Figure 3. PLATE 1 All photomicrographs were taken using brightfield illumination. The scale bar represents 200 µ m and the slide number and England Findercoordinate are quoted for each specimen.5, 763046, M49/0. 5 - detail of a process on Figure 7 withframboids of pyrite.6The holotype, 62974, K42/0.8Genus A sp. A, 63046, N45/3.  P. Steemans, E. Javaux, P. Breuer, A. Le Hérissé, C.P. Marshall, F. de Ville de Goyet: Devonian palynomorphs from Libya103  104PALYNOLOGY, VOLUME 33 — 2009 are housed in the palynology collections of the Laboratoirede Paléobotanique, Paléopalynologie, et Micropaléon-tologie, University of Liège, Belgium. The specimens areidentified by their individual slide numbers and the loca-tions on the slide defined by England Finder coordinates.The upper edge of the slides should be aligned with the edgeof the England Finder marked ‘left’. Specimens studiedwith the SEM were not formally curated. The geochemical LOCHKOVIANPRAGIANEMSIANEIFELIANGIVETIANFRASNIANFAMENNIAN      D     E     V     O     N     I     A     N      S     Y     S     T     E     M STAGES Tadrart  Awaynat Wanin IV Awaynat Wanin IIIOuan-Kasa Awaynat Wanin II Awaynat Wanin IFormationsSamples A1-69 394.4 m* 431.9 m 453.2 m 486.8 m 296.2 m Text-Figure 2.The ages of the formations in the A1-69well and the sample positions of the material of Breuer(2007). The sample studied herein at 394.4 m is asterisked.1–7 Vanguestainidium cucurbitulum  gen. et sp. nov.1General view of a specimen.2Detail of the “pad-like” ornament.3, 4Details of Figure 1 illustrating the processes and the“pad-like” ornamentation. PLATE 2 The scale bars are in µ m.5Enlargement of Figure 1 illustrating the vesicle surface.6General view of a specimen illustrating processes of varying length.7Framboidal pyrite invading a process. techniques used are described in the section on Fouriertransform infrared microspectroscopy below. AGE AND PALEOECOLOGY Numerous miospores enable the recognition of a succes-sion of biostratigraphic markers in the A1-69 borehole . Grandispora velata  (Eisenack 1944) McGregor 1973 wasobserved from 486.8 to 431.9 m (Text-Figure 2). Geminospora lemurata Balme 1962   first appears at 453.2m, and Samarisporites triangulatus  Allen 1965 at 394.4 m;this is the sample from which the large acritarchs wereencountered. Chelinospora concinna  Allen 1965 was onlyobserved in the uppermost sample, at 296.2 m. Thosebiostratigraphically useful species, in association with othermiospores, are characteristic of the biozones of Streel et al.(1987). These are the Vel Interval Zone of the AP OppelZone from the base of the borehole overlain by the LemInterval Zone of the AD Oppel Zone from 454.5 m, the TAOppel Zone from 394.4 m, and the TCo Oppel Zone from296.2 m. Those results are similar to those of Loboziak andStreel (1989), and confirm a Givetian age for 394.4 m.The sample of blue–gray shale at 394.4 m contains a richassemblage of well-preserved palynomorphs which areyellow in color. It includes numerous miospores, rarermegaspores, numerous phytodebris of various sizes, well-preserved colorless acritarchs, large Tasmanites (250–300 µ m in diameter), and some chitinozoans. Such an assem-blage, rich in continental palynomorphs and plant remains,and low diversity acritarchs, represents a nearshore envi-ronment (Traverse, 2007). Large megaspores, >1 mm indiameter (de Ville de Goyet et al., 2007), are extremelywell-preserved, indicating reduced transport by water cur-rents. This is confirmed by the presence of other delicatecocoon-like enigmatic palynomorphs (Steemans, 2006).The environment was probably a coastal swamp periodi-cally inundated by the sea.Numerous miospores were identified, including  Archaeozonotriletes variabilis  (Naumova 1953) Allen 1965, Camarozonotriletes ?  concavus  Loboziak & Streel 1989, Camarozonotriletes rugulosus  Breuer et al. 2007, Craspedispora ghadamisensis  Loboziak & Streel 1989, Cymbosporites asymmetricus  Breuer et al. 2007,
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