GEOSCAN, résultats de la recherche


TitreContrasting paleoenvironments and paleoproductivity signals in the Upper Cretaceous Boreal Sea: a multi-fossil approach
AuteurSchröder-Adams, C J; Pugh, A T; Andrews, J; Herrle, J O; Haggart, J W; Hay, M; Harwood, D; Galloway, J M
SourceGeologic problem solving with microfossils III conference, abstracts with program; 2013 p. 102-103
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130015
RéunionGeologic Problem Solving with Microfossils III Conference; Houston, Texas; US; mars 10-13, 2013
ProvinceNunavut; Région extracotière du nord
SNRC69C/16; 69D/13; 69F; 69G/03; 69G/04; 69G/05; 79E/08; 79E/09; 79E/16; 79H/01; 79H/02; 79H/07; 79H/08
Lat/Long OENS-106.0000 -99.0000 79.3333 77.7500
Sujetspaléoenvironnement; distribution de fossiles; fossiles; microfossiles; biostratigraphie; Formation de Kanguk ; Bassin de Sverdrup ; paléontologie; Mésozoïque; Crétacé
ProgrammeBassin sédimentaire Sverdrup, GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
The Cretaceous Boreal marine system is not well understood and the resolution is hindered by taphonomic loss of proxies such as the solubility of biogenic silica under deep burial and carbonate dissolution as the result of acidic porewater. The Late Cretaceous Arctic Ocean experienced ice-free summers that resulted in high surface productivity dominated by biogenic siliceous microfossils and dinoflagellates. The Cenomanian to Campanian Kanguk Formation of Arctic Canada remains an undivided thick shale package lacking a biostratigraphic framework. This study uses a multi-fossil approach to impose stage boundaries and to contrast the Kanguk Formation and its depositional and paleoecological history as exposed on Ellef Ringnes Island with equivalent strata on Axel Heiberg Island, both part of the Queen Elizabeth Islands.
The Ellef Ringnes locality represents a central location in Sverdrup Basin during Kanguk deposition and is a bio-silica dominated system. In contrast, the Kanguk Formation as exposed on Axel Heiberg shows no bio-silica preservation. High surface productivity is evidenced at Ellef Ringnes by diatoms and radiolaria in addition to abundant dinocycts. The mix of plankton and mud and silt suggests winter sea-ice, whereas the lack of coarser clastics excludes glacial ice and floating ice as sediment transport mechanisms. Microfossil assemblages respond to transgressive/regressive sea-level phases linking the Boreal Sea to eustatic cycles. Regressions triggered radiations in radiolarian and dinocyct assemblages due to reduced oxygen minimum zones (OMZ) and fertile shelf settings. Transgressive phases provided increased rates of organic matter deposition, in part due to terrestrial flooding coupled with humid conditions and input of Type III organic matter, but also high surface productivity (type II organic matter) which resulted in an expanded OMZ. These systems are prevalent throughout the late Cenomanian to Coniacian. As temperature cooled again primary productivity and carbon flux decreased and slight bottom oxygenation returned in the upper Santonian, where rare benthic foraminifera are observed. No carbonate is preserved in this system. In contrast, at Glacier Fiord, Axel Heiberg Island, the Kanguk Formation is interpreted as an outer shelf setting within the Sverdrup Basin and therefore is more proximal than the Ellef Ringnes locality. The most distal part of this section is represented by the uppermost Cenomanian/lower Turonian interval that is characterized by the newly established OAE 2 interval in the Sverdrup Basin, which provides a reliable marker for correlation to the Ellef Ringnes section. Bottom hypoxia developed during that time and benthic foraminifera are absent in thinly bedded 'paper shale'. Biogenic silica is absent either due to high suspended sediment turbidity and therefore a limited photic zone or not preserved due to deep burial. As sea level fell during the late Turonian, the proximal setting of this locality was increasingly oxygenated, and capable of supporting abundant and diverse benthic foraminiferal communities from the late Turonian to Campanian. A late Santonian to early Campanian shelf setting at the top of the section is supported by communities of large Inoceramus shells inhabiting the sea floor. Whereas upwelling processes might have played a role at the distal setting of Ellef Ringnes, stratification did not develop in this region, with the exception of the OAE 2 interval.
Résumé(Résumé en langage clair et simple, non publié)
Durant la période géologique du Crétacé tardif il y a de cela 95 à 80 millions d'années, l'océan Arctique s'est trouvé libre de glaces en été, ce qui a entraîné la forte productivité biologique des eaux océaniques superficielles. Les animaux planctoniques unicellulaires à radiolaires étaient parmi les formes biologiques les plus courantes dans ces eaux. Cet article résume les recherches effectuées sur la succession des radiolaires qui ont vécu à cette époque dans l'Arctique et sont préservés sous forme de fossiles dans la roche sédimentaire de l'île Ellef Ringnes. Les fossiles permettent la datation à haut niveau des sédiments et aident à établir la corrélation entre ceux-ci et d'autres successions sédimentaires d'autres îles de l'Arctique.