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Materials and methods

Micropaleontological analyses

I analyzed the upper ~14 m sedimentary section for ostracode fauna characterization and IRD content. Samples (2 cm thick slices) were taken at 10 cm intervals using two 10 cm3 plastic scoops. Sampling resolution was increased to 5 cm at selected intervals where more detailed examination was desired. The obtained 20 cm3 samples were washed with deionized water over a 63 µm sieve and dried and later dry sieved into subfractions of 125–250 µm and >250 µm. All ostracodes from the >125 µm size fraction were picked, identified, and counted. This method assured that all adults and, for most species, two to three prior molt stages were attained. Ostracodes were characterized exclusively by the morphology of the valves following descriptions and SEM images provided by Joy and Clark (1977), Whatley and Coles (1987), Whatley et al. (1996, 1998), Rodriguez-Lazaro and Cronin (1999), Swanson and Ayress (1999), Didié and Bauch (2001), and Stepanova (2006). Most specimens were identified to species level, but some were only identified to genus level. Ostracode assemblages were characterized by calculating the total ostracode abundance, species diversity (number of species and Shannon Weaver index), and relative abundance of individual taxa (percent). These results and their interpretation are presented in Alvarez Zarikian et al. (2009).

Ostracodes were imaged using JEOL JSM-6400 and FEI Quanta 600 FE scanning electron microscopes at the Texas A&M University Microscopy and Imaging Center.