Entity

Time filter

Source Type


Dera G.,University Paul Sabatier | Prunier J.,University Paul Sabatier | Smith P.L.,University of British Columbia | Haggart J.W.,University of British Columbia | And 10 more authors.
Gondwana Research | Year: 2015

The breakup of Pangea and onset of growth of the Pacific plate led to several paleoenvironmental feedbacks, which radically affected paleoclimate and ocean chemistry during the Jurassic. Overall, this period was characterized by intense volcanic degassing from large igneous provinces and circum-Panthalassan arcs, new oceanic circulation patterns, and changes in heat and humidity transports affecting continental weathering. Few studies, however, have attempted to unravel the global interactions linking these processes over the long-term. In this paper, we address this question by documenting the global changes in continental drainage and surface oceanic circulation for the whole Jurassic period. For this purpose, we present 53 new neodymium isotope values (εNd(t)) measured on well-dated fossil fish teeth, ichthyosaur bones, phosphatized nodules, phosphatized ooids, and clastic sediments from Europe, western Russia, and North America. Combined with an extensive compilation of published εNd(t) data, our results show that the continental sources of Nd were very heterogeneous across the world. Volcanic inputs from a Jurassic equivalent of the modern Pacific Ring of Fire contributed to radiogenic εNd(t) values (-4ε-units) in the Panthalassa Ocean. For the Tethyan Ocean, the average surface seawater signal was less radiogenic in the equatorial region (-6.3), and gradually lower toward the epicontinental peri-Tethyan (-7.4), western Russian (-7.4) and Euro-Boreal seas (-8.6). Different Nd sources contributed to this disparity, with radiogenic Nd influxes from westward Panthalassan currents or juvenile volcanic arcs in open oceanic domains, and substantial unradiogenic inputs from old Laurasian and Gondwanan shields for the NW Tethyan platforms. Overall, the εNd(t) values of Euro-Boreal, peri-Tethyan, and western Russian waters varied quite similarly through time, in response to regional changes in oceanic circulation, paleoclimate, continental drainage, and volcanism. Three positive shifts in εNd(t) values occurred successively in these epicontinental seas during the Pliensbachian, in the Aalenian-Bathonian interval, and in the mid-Oxfordian. The first and third events are interpreted as regional incursions of warm surface radiogenic currents from low latitudes. The Aalenian-Bathonian shift seems linked to volcanic outbursts in the NW Tethys and/or circulation of deep currents resulting from extensional events in the Hispanic Corridor and reduced influences of boreal currents crossing the Viking Corridor. In contrast, the εNd(t) signals decreased and remained very low (<-8) during the global warming events of the Toarcian and Late Oxfordian-Early Tithonian intervals. In these greenhouse contexts, a latitudinal expansion of humid belts could have extended the drainage pathways toward boreal Nd sources of Precambrian age and increased the supply of very unradiogenic crustal-derived inputs to seawater. Finally, a brief negative εNd(t) excursion recorded in parallel with regional drops in seawater temperature suggests that southward circulation of cold unradiogenic Arctic waters occurred in the NW Tethys in the Callovian-Early Oxfordian. All these results show that changes in surface oceanic circulation resulting from the Pangean breakup could have regionally impacted the evolution of seawater temperatures in the NW Tethys. © 2014 International Association for Gondwana Research. Source


Cuny G.,The Natural History Museum of Denmark | Liard R.,Sirindhorn Museum | Deesri U.,Mahasarakham University | Liard T.,Sirindhorn Museum | And 2 more authors.
Palaontologische Zeitschrift | Year: 2013

A revision of the freshwater shark fauna from the Phu Kradung Formation in NE Thailand allows the recognition of a new species of Acrodus, which represents the youngest occurrence of the genus and confirms its displacement in freshwater environments after the Toarcian. The rest of the shark fauna includes teeth of Hybodus sp., aff. Hybodus sp., hybodontid dermal denticles, Jiaodontus sp., Lonchidion sp. A, Lonchidion sp. B, Heteroptychodus cf. H. kokutensis and dorsal fin spines. The presence of Jaiodontus and of unusual hybodontid dermal denticles suggests a Jurassic age for most of the Phu Kradung Formation, whereas the presence of Heteroptychodus suggests an Early Cretaceous age for the top of the Formation. However, the age of the Phu Kradung Formation is still uncertain, with contradictory signals coming from palynology, detrital zircon thermochronology and vertebrate palaeontology. In any case, it appears that this is the oldest occurrence of the genus Heteroptychodus, and suggests a Thai origin for this genus, which may have replaced Acrodus in the Thai freshwater palaeoecosystems. Together with Acrodus, the presence of Lonchidion sp. A suggests some European affinities for the shark fauna from the Phu Kradung Formation. © 2013 The Author(s). Source


Cuny G.,The Natural History Museum of Denmark | Liard R.,Sirindhorn Museum | Deesri U.,Mahasarakham University | Liard T.,Sirindhorn Museum | And 2 more authors.
Palaontologische Zeitschrift | Year: 2014

A revision of the freshwater shark fauna from the Phu Kradung Formation in NE Thailand allows the recognition of a new species of Acrodus, which represents the youngest occurrence of the genus and confirms its displacement in freshwater environments after the Toarcian. The rest of the shark fauna includes teeth of Hybodus sp., aff. Hybodus sp., hybodontid dermal denticles, Jiaodontus sp., Lonchidion sp. A, Lonchidion sp. B, Heteroptychodus cf. H. kokutensis and dorsal fin spines. The presence of Jaiodontus and of unusual hybodontid dermal denticles suggests a Jurassic age for most of the Phu Kradung Formation, whereas the presence of Heteroptychodus suggests an Early Cretaceous age for the top of the Formation. However, the age of the Phu Kradung Formation is still uncertain, with contradictory signals coming from palynology, detrital zircon thermochronology and vertebrate palaeontology. In any case, it appears that this is the oldest occurrence of the genus Heteroptychodus, and suggests a Thai origin for this genus, which may have replaced Acrodus in the Thai freshwater palaeoecosystems. Together with Acrodus, the presence of Lonchidion sp. A suggests some European affinities for the shark fauna from the Phu Kradung Formation. © 2013, The Author(s). Source


Romero M.L.J.,Bureau of Fisheries and Aquatic Resources | Kotaki Y.,Kitasato University | Lundholm N.,The Natural History Museum of Denmark | Thoha H.,Indonesian Institute of Sciences | And 9 more authors.
Harmful Algae | Year: 2011

Nitzschia navis-varingica is a diatom that is known to produce significant levels of amnesic shellfish poisoning (ASP) toxins. A total of 33 N. navis-varingica strains were isolated from four brackish water localities in the Philippines and Indonesia, and cultured to characterize the toxins produced. The isolates were analyzed for domoic acid (DA) and isodomoic acids A (IA) and B (IB) by HPLC with fluorescence detection. Two toxin composition types were detected that have not been previously described: strains producing only IB and strains producing DA-IA-IB. These two types were isolated from two different localities. Eighteen strains were isolated from the Philippines (northern Luzon Island). Among them, 10 isolates from Alaminos produced only IB with an average toxin content of 3.05pgcell-1, seven isolates from Bulacan produced DA and IB with average toxin contents of 0.68pgcell-1 and 1.18pgcell-1, respectively. One isolate from Cavite produced DA, IA, and IB with a toxin content of 0.58, 0.20, and 0.92pgcell-1, respectively. Fifteen isolates from Indonesia (Bone, South Sulawesi) produced only DA (four isolates) or DA with trace amounts of IB (eleven isolates), with an average toxin content of 2.38pgcell-1 and 0.06pgcell-1, respectively. Sub-strains were established from strains producing either of the three toxin types: IB, DA-IA-IB, and DA-trace IB. Results showed that the toxin composition type was the same for parent and sub-strains, indicating that the toxin composition is a stable character for a strain. © 2011 Elsevier B.V. Source


Mols-Mortensen A.,University of New Hampshire | Neefus C.D.,University of New Hampshire | Nielsen R.,The Natural History Museum of Denmark | Gunnarsson K.,Iceland Marine Research Institute | And 3 more authors.
European Journal of Phycology | Year: 2012

Foliose species of the Bangiales (Porphyra sensu lato) have a long history of study in the N Atlantic, but there are still regions, especially in the northern parts of the N Atlantic that need more attention. A molecular study using rbcL and cox1 sequences was undertaken to assess the diversity of foliose Bangiales species in Iceland and the Faroe Islands. Herbarium collections from the intertidal and subtidal of Iceland (summer and winter) and the Faroe Islands (all seasons) revealed a total of 13 species (11 common to both areas), which were referred to four of the genera recognized in a recent two-gene global phy-logeny. Boreophyllum birdiae, Porphyra dioica, P. linearis, P. purpurea, P. umbilicalis, Pyropia 'leucosticta' A, Pyropia njordii Mols-Mortensen, J. Brodie & Neefus, sp. nov., Wildemania amplissima and W. miniata were common to both areas, while Pyropia thulaea and Wildemania abyssicola (Kjellman) A. Mols-Mortensen & J. Brodie, comb. nov. (=Porphyra abyssicola Kjellman) were reported from Iceland but not from the Faroe Islands; Porphyra sp. FO and Pyropia elongata were reported from the Faroe Islands but not from Iceland. Boreophyllum birdiae is reported for the first time for Iceland and Porphyra sp. FO is reported for the first time for the Faroe Islands. Pyropia njordii is described from the Faroe Islands and is also recorded for Iceland, Greenland, New England, USA and Nova Scotia, Canada. A total of 25 foliose Bangiales species are now reported from the N Atlantic and these results demonstrate the importance of investigating as many areas as possible to reach a more complete understanding of species diversity and distribution. © 2012 British Phycological Society. Source

Discover hidden collaborations