2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 41-25
Presentation Time: 9:00 AM-5:30 PM


BORGO, Giovanni, ITT Fossil, Unisinos, Sao Leopoldo, Brazil and GRADSTEIN, Felix M., Geology Museum, University of Oslo, Sarsgate 1, Oslo, N0318, Norway, felix.gradstein@gmail.com

The cosmopolitan genus Turrilina Andreae (1884) is a component of bathyal to abyssal and deep neritic benthic foraminiferal assemblages. It ranges from earliest Ypresian into Aquitanian.

Traditionally, the genus includes two species: a stubby and older (Eocene) form called Turrilina brevispira (senior syn. T. robertsi), and a more slender and younger (Oligocene) form called Turrilina alsatica (syn. T. andreae). The former shows a random pattern of calcite crystals that compose the test, rendering a granular texture under polarized light. Conversely, the latter generally (?) possesses a well-defined wall arrangement, with the c-axis of the calcite crystals disposed perpendicularly to the test surface, creating a cross-shaped polarization pattern.

In the classification of Loeblich &Tappan (1986), such situation (species of different wall-structure assigned to the same genus) is taxonomically problematic. This stable character has been considered useful in the distinction of taxa at a supra-generic level, posing doubt on the validity of the genus Turrilina, as currently understood.

The present research tries to better define Turrilina, and refine the unusual paleoecologic and stratigraphic record of the genus through a comprehensive appraisal and specimens study from many sites.

The genus Turrilina has its first stratigraphic occurrence as a component of the re-colonization benthic taxa post-BEE (P/E transition) in shallow marine deposits from the eastern U.S. Coastal Plain. At about the same time it appears also in deep marine southern Alpine deposits. This unusual scenario suggests two possible interpretations for its evolution: I) An event of speciation in one location followed by a rapid radiation of a single lineage (e.g. Turrilina), which comes to thrive in an wide range of paleobathymetric settings; II) two distinct events of speciation giving rise to nearly homeomorphic, albeit paleoecologically distinct lineages. We are evaluating both scenarios.