Authors: Wolfe, Alexander P.; Edlund, Mark B.

Source: Canadian Journal of Earth Sciences, Volume 42, Number 2, February 2005 , pp. 243-257(15)

Publisher: NRC Research Press

Abstract:

A new centric diatom genus is described from laminated freshwater sediments of Middle Eocene age near Horsefly, British Columbia, Canada. This diatom, Eoseira wilsonii gen. et sp. nov., grew in filaments that constitute dense monospecific sub-horizons within the white couplets that represent summer deposition in the varved sequence. Although Eoseira clearly belongs within the Family Aulacoseiraceae, several features distinguish its valve structure from Aulacoseira. Gigantism of spines and the lack of geometric relationships between spine position and mantle areolae are the most conspicuous features of the genus. Eoseira is among the oldest freshwater diatoms known and one of relatively few extinct freshwater genera. In addition to serving as a potential biostratigraphic marker, Eoseira is a cornerstone to undertanding the evolutionary trajectory of the Aulacoseiraceae, likely the oldest family of freshwater diatoms. As such, it refines our understanding of early radiations from the marine realm in western North America. Furthermore, paleoecological inferences based on Eoseira life strategy pertain directly to limnological conditions during early Cenozoic hot-house conditions.

Un nouveau genre de diatomée centrique est décrit à partir de sédiments laminés d'eau douce (datant de l'Éocène moyen) à proximité de Horsefly, Colombie-Britannique, Canada. Cette diatomée, Eoseira wilsonii gen et sp. nov., croissait dans des filaments qui constituent des sous-horizons denses monospécifiques à l'intérieur des couplets blancs, lesquels représentent la dépôt estival dans la séquence varvée. Bien que Eoseira appartienne clairement à la famille Aulacoseiraceae, plusieurs caractéristiques distinguent la structure de sa valve de celle d'Aulacoseira. Le gigantisme des épines et le manque de relations géométriques entre la position des épines et des pores aréolaires du manteau sont les caractéristiques les plus remarquables du genre. Eoseira est parmi les plus anciennes diatomées d'eau douce connues et l'un des relativement peu nombreux genres d'eau douce disparus. En plus de servir comme indicateur biostratigraphique potentiel, Eoseira précise nos connaissance de comprendre la lignée des Aulacoseiraceae, probablement la plus ancienne famille de diatomées d'eau douce. En tant que tel, cela affine nos connaissances des premiers retraits du domaine marin dans l'ouest de l'Amérique du Nord. De plus, les inférences paléo-écologiques basées sur la stratégie de vie d'Eoseira réfèrent directement aux conditions limnologiques durant les conditions de serre au Cénozoïque intérieur.[Traduit par la Rédaction]

Document Type: Research article

Publication date: 2005-02-01

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• Published since 1963, this monthly journal reports current research in climate and environmental geoscience; geoarchaeology and forensic geoscience; geochronology and geochemistry; geophysics; GIS and geomatics; hydrology; mineralogy and petrology; mining and engineering geology; ore deposits and economic geology; paleontology, petroleum geology and basin analysis; physical geography and Quaternary geoscience; planetary geoscience; sedimentology and stratigraphy; soil sciences; and structural geology and tectonics. It also publishes special issues that focus on information and studies about a particular segment of earth sciences.
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