| IODP Expedition 334 drilled west of the Costa Rican coast just offshore of the Osa Peninsula with Hole U1381A being the focus for this study. The preservation of the calcareous nannofossils at this hole ranges from moderate to good, while the total abundance ranges from very rare to very abundant. The nannofossil assemblages fall into two different zones, NN19 of the Pleistocene and NN5 of the Miocene. There are about 12 million years missing between these two zones. This hiatus is believed to be the result of erosion based on reworked Pliocene specimens in Pleistocene samples. A scheme by de Kaenel (1999) was used to further subdivide Zone NN19, and it was determined that Core 6H fell into de Kaenel's datum 18. An article by Anthonissen and Ogg (2012) was used to define Zone NN5 and to determine the relative age.;IODP Expedition 352 drilled west of the Izu-Bonin-Mariana system, just east of the fore-arc of the subduction zone. Hole U1439A is the focus for this study. The preservation of the nannofossils from Cores 5H to 7H ranges from moderate to good while preservation in Cores 9H to 14X ranges from moderate to poor. The latter is due to an increase in diagenesis below the lysocline where some nannofossils begin to dissolve or become overgrown. The total abundance for all of these slides ranges from very rare to very abundant, similar to Expedition 334. These slides fall into seven different zones, CN12a, NN14, CN10b, NN11a, NN7, NN6, NN5, and NN3. Anthonissen and Ogg (2012) was used to define the majority of these zones while Perch-Nielsen (1989) was used for the remainder. The 12 million year hiatus is not observed at this site; only small intermittent gaps between zones were noted. |
