Late Pliocene Paleoceanography in the Subpolar North Atlantic (IODP site U1314) deduced from Calcareous Nannofossil Observation

• Main Author: RESTI SAMYATI JATININGRUM
• Format: Thesis
• Language: English
• Published: 秋田大学 2018
• Subjects: North Atlantic
• Online Access: http://hdl.handle.net/10295/00003566; https://air.repo.nii.ac.jp/?action=repository_uri&item_id=3206; https://air.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3206&item_no=1&attribute_id=46&file_no=1; https://air.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3206&item_no=1&attribute_id=46&file_no=2

Calcareous nannofossils were observed to reconstruct surface water conditions during the late Pliocene sediments (2.55 to 2.88 Ma) from the southern Gardar Drift, in the subpolar North Atlantic IODP Site U1314 (56°21.9’1N, 27°53.3’W) at an average resolution of 3 kyr. Based on quantitative analyses twenty-four species belonging to fourteen genera are identified and are rare to very abundant with moderate to good preservation. One calcareous nannofossil datum event is found within the samples interval, which is the Last Occurrence (LO) of Discoaster tamalis in sample B28H-2A, B at 272.81 mcd. It correlates with Datum A discussed by Sato et al. (2004) which is considered strongly related to the heavy glaciation in the Northern Hemisphere. The datum event dates to an age 2.756 Ma, situated within upper Gauss Chron or just below MIS G7. Based on the nannofossil event that is found at IODP Site U1314, the studied interval belongs to Zone NN16 (Martini, 1971). However, referring to Okada and Bukry (1980) the studied interval is included within two Subzones, which are Subzones CN12b and CN12a as defined by the LO of D. tamalis. In general, the coccolith assemblages are dominated by species belonging to genus Reticulofenestra with different (sized-defined) morphotype. Thus the significant changes in paleoceanographic condition are mainly shown by the ratio of Reticulofenstra morphometry.Calcareous nannofossil assemblage, magnetic susceptibility (MS) and natural gamma radiation (NGR) records in the IODP Site U1314 indicate that the surface ocean condition was very stable with a warm and oligotrophic condition prior to ~2.76 Ma. It is characterized by the dominance of medium and large Reticulofenestra with low detrital input to the site area (low NGR values). The size variations of Reticulofenestra are uni-modal indicated by coccolith size of 3 to 4μm. This suggests an extension of Mid-Pliocene warm influence and the final closure of Central American Seaway (CAS) was incomplete. The warm current originates in eastern ...