15 research outputs found
The dinoflagellate cyst genera Achomosphaera Evitt 1963 and Spiniferites Mantell 1850 in Pliocene to modern sediments: a summary of round table discussions
Source at https://doi.org/10.1080/01916122.2018.1465739. We present a summary of two round-table discussions held during two subsequent workshops in Montreal (Canada) on 16 April 2014 and Ostend (Belgium) on 8 July 2015. Five species of the genus Achomosphaera Evitt 1963 and 33 of the genus Spiniferites Mantell 1850 emend. Sarjeant 1970 occuring in Pliocene to modern sediments are listed and briefly described along with remarks made by workshop participants. In addition, several holotypes and topotypes are reillustrated. Three species previously assigned to Spiniferites are here considered/accepted as belonging to other genera: Impagidinium inaequalis (Wall and Dale in Wall et al.1973) Londeix et al. 2009, Spiniferites? rubinus (Rossignol 1962 ex Rossignol 1964) Sarjeant 1970, and Thalassiphora balcanica Baltes ̧ 1971. This summary forms the basis for a set of papers that follows, where points raised during the workshops are explored in greater detail
Paléocéanographie et variabilité climatique sur le talus du Mackenzie (Mer de Beaufort, Arctique canadien) au cours de l'holocÚne récent
Une séquence sédimentaire prélevée sur le talus du Mackenzie (station CASES
2004-804-803, mer de Beaufort, Arctique canadien) Ă 218 m de profondeur a pennis de
documenter la variabilité hydroclimatique au cours des derniers 4600 ans à cet
emplacement clé de l' Arctique occidental. La sédimentation y est à la fois influencée par
la gyre de Beaufort (impliquée dans le transport des glaces et dans les principaux modes
de variabilité hydroclimatiques telle l' Oscillation arctique) et la décharge sédimentaire du
Mackenzie, de loin le plus important tributaire de l'Océan Arctique.
La chronologie de la carotte à piston (longueur: ~ 6 m) a été détenninée sur la base
de quatre datations AMS-!4C sur des coquilles de bivalves. Le taux de sédimentation
rĂ©sultant est extrĂȘmement similaire Ă celui estimĂ© Ă partir de mesures d'activitĂ© de 2 10Pb
sur les premiers 20 cm de la carotte boßte. La carotte à gravité ayant été corrélée
stratigraphiquement à la carotte à piston, on obtient une séquence composite complÚte
couvrant les derniers 4600 ans, avec un taux d'accumulation constant de 140 cm.ka-!.
Les reconstitutions quantitatives des paramÚtres océaniques de surface (température
et salinité de surface en août, durée du couvert de glace) ont été estimées à partir des
assemblages de kystes de dinoflagellés dans les sédiments en utilisant des fonctions de
transfert (méthode des meilleurs analogues modernes). Celles-ci indiquent des conditions
de surface relativement stables au cours des derniers 4600 ans. Cependant, des
refroidissements épisodiques d'environ l ,SOC sous la valeur actuelle (5 ,9°C) sont
enregistrés entre 700 et 1820 AD, possiblement reliés à l'advection d'eau pacifique froide
(valeurs négatives de l' index PDO - Pacifie Decadal Oscillation). Nous associons
le dernier et le plus long de ces refroidissements (1560-1820 AD) avec le Petit Ăge
Glaciaire. De 1920 à 2004 AD, des variations récurrentes de salinité de surface (oscillant
entre ~21 et 27) peuvent ĂȘtre associĂ©es au mĂ©canisme d'accumulation d' eau douce par la
gyre de Beaufort pendant les régimes de circulation atmosphérique anticyclonique.
Nos données indiquent également que des accumulations d'eau douce similaires
(qui précÚdent les anomalies de salinité documentées dans l' Atlantique Nord) ont pu
survenir vers 1790 et 1860 AD.
Les donnĂ©es isotopiques (Ă 13C et Ă15N) indiquent une lente augmentation de
l' influence marine (vs terrestre) dans l'origine de la matiĂšre organique au cours de
l ' HolocÚne récent. Cette variation est attribuable au rehaussement du niveau marin relatif
dans la rĂ©gion du delta du Mackenzie, une rĂ©gion cĂŽtiĂšre particuliĂšrement vulnĂ©rable Ă
l'érosion. Nos données suggÚrent également que le taux de transgression marine s'est
intensifié depuis 1820 AD. Entre 4600 et 1300 cal avant aujourd'hui, des variations
séculaires de l'Oscillation arctique sont enregistrées par les mesures de Î! 5N qui mettent
en Ă©vidence des modifications de l'influence de l'eau pacifique au site d'Ă©tude.
Ainsi, cette étude à haute résolution a pennis de documenter la variabilité
hydroclimatique arctique au-delà des mesures instrumentales récentes. Des changements
hydrographiques importants ont pu ĂȘtre mis en Ă©vidence au sein de la stabilitĂ© climatique
relative de l' HolocÚne récent
Devonian palynoevents in the circum-Arctic region
Devonian strata of the present-day Arctic contain abundant and diverse assemblages of terrestrial palynomorphs, particularly from Middle and Upper Devonian sections; few intervals of Lower Devonian and Silurian strata have been palynologically studied, and these demonstrate strong palynofloral similarities across the region. Based on published records, we present a compilation of six last occurrence events (LOs), 44 first occurrence events (FOs) and one acme event that have proven of value in correlation in the present-day Arctic. Although their chronostratigraphic resolution is relatively low, and a scarcity of independent age control hampers precise age assignments, palynology is the only biostratigraphic discipline available for confident chronostratigraphic correlation of most Arctic Devonian strata
PalynophénomÚnes dévoniens dans la région circumarctique
Devonian strata of the present-day Arctic contain abundant and diverse assemblages of terrestrial palynomorphs, particularly from Middle and Upper Devonian sections; few intervals of Lower Devonian and Silurian strata have been palynologically studied, and these demonstrate strong palynofloral similarities across the region. Based on published records, we present a compilation of six last occurrence events (LOs), 44 first occurrence events (FOs) and one acme event that have proven of value in correlation in the present-day Arctic. Although their chronostratigraphic resolution is relatively low, and a scarcity of independent age control hampers precise age assignments, palynology is the only biostratigraphic discipline available for confident chronostratigraphic correlation of most Arctic Devonian strata.Les strates dĂ©voniennes de lâArctique dâaujourdâhui abritent des assemblages abondants et diversifiĂ©s de palynomorphes, terrestres, en particulier des sections du DĂ©vonien moyen et supĂ©rieur. Quelques intervalles de strates du DĂ©vonien infĂ©rieur et du Silurien ont fait lâobjet dâĂ©tudes palynologiques et celles-ci ont rĂ©vĂ©lĂ© des similaritĂ©s palynoflorales marquĂ©es Ă lâĂ©chelle de la rĂ©gion. Nous basant sur des documents publiĂ©s, nous prĂ©sentons une compilation des six derniĂšres occurrences (DO), des 44 premiĂšres occurrences (PO) et dâun phĂ©nomĂšne dâabondance sâĂ©tant avĂ©rĂ©s utiles pour la corrĂ©lation dans lâArctique dâaujourdâhui. MĂȘme si leur rĂ©solution chronostratigraphique est relativement faible et que la raretĂ© des contrĂŽles indĂ©pendants de la datation gĂȘne lâattribution dâĂąges prĂ©cis, la palynologie est la seule discipline biostratigraphique dont nous disposons pour lâĂ©tablissement dâune corrĂ©lation chronostratigraphique sĂ»re de la majoritĂ© des strates dĂ©voniennes arctiques
Process length variation of Operculodinium centrocarpum in the North Pacific and its relation to salinity and temperature
Jurassic palynoevents in the circum-Arctic region
Successions of Jurassic strata located in the Arctic region normally yield rich assemblages of terrestriallyderived and marine palynomorphs, reflecting relatively warm air and sea-surface temperatures. The land plant floras were prone to the development of local communities and regional provincialism, whereas the marine biotas thrived across extensive open marine areas with high productivity, resulting in the rapid evolution of dinoflagellate cysts (dinocysts) following their earliest fossil record in the Triassic. Dinocysts exhibit low taxonomic richness and provide low biostratigraphic resolution throughout the Lower Jurassic sections. By contrast, they are diverse in Middle and Upper Jurassic strata where they provide excellent biostratigraphic markers for correlating and dating both surface and subsurface sections. Over twenty formal and informal biozonations based on the first
and last occurrences of dinocysts have been erected in Alaska, Arctic Canada, the Barents Sea region, Greenland and northern Russia, many of which are correlated with macrofossils, including ammonites, that occur in the same sections. This paper presents a compilation of 214 Jurassic palynostratigraphic events (118 first occurrences and 96 last occurrences) that have regional chronostratigraphic value in the Circum-Arctic, based on their published records. Each event is correlated with the base of a chronostratigraphical unit (including formal stages and sub-Boreal ammonite zones), or as an estimated percentage above the base of the chronostratigraphical unit relative to the entire unit. The relationships of each event to stages and key fossil zonal schemes is shown on chronostratigraphic plots using the 2020 version of TimeScale Creato
PalynophénomÚnes jurassiques dans la région circumarctique
Successions of Jurassic strata located in the Arctic region normally yield rich assemblages of terrestriallyderived and marine palynomorphs, reflecting relatively warm air and sea-surface temperatures. The land plant floras were prone to the development of local communities and regional provincialism, whereas the marine biotas thrived across extensive open marine areas with high productivity, resulting in the rapid evolution of dinoflagellate cysts (dinocysts) following their earliest fossil record in the Triassic. Dinocysts exhibit low taxonomic richness and provide low biostratigraphic resolution throughout the Lower Jurassic sections. By contrast, they are diverse in Middle and Upper Jurassic strata where they provide excellent biostratigraphic markers for correlating and dating both surface and subsurface sections. Over twenty formal and informal biozonations based on the firstand last occurrences of dinocysts have been erected in Alaska, Arctic Canada, the Barents Sea region, Greenland and northern Russia, many of which are correlated with macrofossils, including ammonites, that occur in the same sections. This paper presents a compilation of 214 Jurassic palynostratigraphic events (118 first occurrences and 96 last occurrences) that have regional chronostratigraphic value in the Circum-Arctic, based on their published records. Each event is correlated with the base of a chronostratigraphical unit (including formal stages and sub-Boreal ammonite zones), or as an estimated percentage above the base of the chronostratigraphical unit relative to the entire unit. The relationships of each event to stages and key fossil zonal schemes is shown on chronostratigraphic plots using the 2020 version of TimeScale CreatorÂź.Les successions de strates jurassiques dans la rĂ©gion de lâArctique recĂšlent normalement de riches assemblages de palynomorphes dâorigine terrestre et marins reflĂ©tant les tempĂ©ratures relativement chaudes de lâair et Ă la surface de la mer.  Les flores de plantes terrestres Ă©taient susceptibles de favoriser lâĂ©panouissement de communautĂ©s locales et dâun provincialisme rĂ©gional, alors que les biotes marins se dĂ©veloppaient sur de vastes secteurs marins ouverts Ă un rythme de productivitĂ© Ă©levĂ©, ce qui a entraĂźnĂ© lâĂ©volution rapide de kystes de dinoflagellĂ©s (dinokystes) dâaprĂšs leur plus rĂ©cents enregistrements fossiles au cours du Trias. Les dinokystes affichent une faible richesse taxonomique et produisent une faible rĂ©solution biostratigraphique dans toutes les sections du Jurassique infĂ©rieur. Par contre, ils se diversifient dans les strates du Jurassique moyen et supĂ©rieur, oĂč ils reprĂ©sentent dâexcellents repĂšres biostratigraphiques pour la corrĂ©lation et la datation de sections de surface et de subsurface. Plus dâune vingtaine de biozonations officielles et officieuses basĂ©es sur les premiĂšres et derniĂšres manifestations de dinokystes ont Ă©tĂ© Ă©tablies en Alaska, dans lâArctique canadien, dans la rĂ©gion de la mer de Barents, au Groenland et dans le nord de la Russie, lesquelles sont dans de nombreux cas corrĂ©lĂ©es avec des macrofossiles, notamment des ammonites, prĂ©sents dans les mĂȘmes sections. Le prĂ©sent article prĂ©sente une compilation de 214 phĂ©nomĂšnes palynostratigraphiques du Jurassique (118 premiĂšres manifestations et 96 derniĂšres manifestations) ayant une valeur chronostratigraphique rĂ©gionale dans la rĂ©gion circumarctique, dâaprĂšs les documents pertinents publiĂ©s. Chaque phĂ©nomĂšne est corrĂ©lĂ© avec la base dâune unitĂ© chronostratigraphique (notamment les stades et les zones dâammonites subborĂ©ales officielles), ou sous forme dâun pourcentage estimatif au-dessus de la base de lâunitĂ© chronostratigraphique par rapport Ă lâensemble de lâunitĂ©. Les liens entre chaque phĂ©nomĂšne et les stades et principaux mĂ©canismes zonaux fossiles sont illustrĂ©s dans les schĂ©mas chronostratigrapiques des figures 1 Ă 9 au moyen de la version de 2020 de TimeScale CreatorÂź
Process length variation of the cyst of the dinoflagellate Protoceratium reticulatum in the North Pacific: a new density proxy and first evidence of pseudo-cryptic speciation
Unravelling the molecular taphonomy of organic-walled dinoflagellate cysts via infrared spectroscopy
Dinoflagellates are an extant group of unicellular, eukaryotic microalgae occurring in a wide range of aquatic environments. They can form resistant, organic-walled resting stages (dinocysts); the earliest body fossils appear in the Middle Triassic. Dinocyst walls are composed of a heavily cross-linked, nitrogenous, cellulose-like carbohydrate, âdinosporinâ, which is compositionally distinct from other resistant biomacromolecules such as sporopollenin (pollen and spores) and algaenan (green algae). Macromolecular analyses of modern dinosporin via attenuated total reflection micro-Fourier transform infrared (ATR micro-FTIR) spectroscopy revealed a variable compound: sometimes strongly influenced by the presence of brown colour-inducing (possibly eumelanin) pigments, or with additional aromatic (âsporopollenin-likeâ) or aliphatic (âalgaenan-likeâ) moieties.
Here, ATR micro-FTIR spectroscopy was used to collect a large dataset from a wide range of Meso- and Cenozoic dinocysts, to investigate their molecular taphonomy. These data reveal an expected increase in the aliphaticity of dinosporin over time, likely related to early-diagenetic in situ polymerization of lipids. Furthermore, modern dinosporin variability was detected in fossil dinocysts up to the late Paleocene, highlighting the palaeoecological and taxonomical value of these chemospecific signatures. Finally, it is hypothesised that some dinosporin types might be better suited for low-salinity (aliphatic type) or high-UV (pigmented and aromatic types) aquatic environments