Upper Miocene-lower Pleistocene calcareous nannofossil biostratigraphy of ODP 1210, northwestern Pacific and some application
Date Issued
2012
Date
2012
Author(s)
Lin, Ho-Ya
Abstract
The conventional nannofossil standard zonations of Martini (1971) and Okada & Bukry (1980) have been prime standards for biostratigraphic correlation of Neogene sediments. Advance in biochronology in the last four decades has further calibrated the first and last occurrences of index species in those schemes. However, these two zonations were mainly based upon low-latitudes stratigraphic sections of marine sediments. The diachroniety of each bioevent needs to be evaluated when such standard schemes are employed in middle latitudes. Particularly, the first and last occurrences of warm-water Discoaster spp. tend to be diachronous between low- and mid-latitudes.
This study analyzed the upper Miocene-lower Pleistocene calcareous nannofossil assemblages from a mid-latitude ODP site in the northern Pacific to address the fore-mentioned issues. The studied site is ODP 1210 (32°13N, 158°15E; water depth of 2574 m) which located on the Shatsky Rise.
This study examined the samples at 50 cm intervals with semi-quantitative abundance of nannofossils, and prepared all slides with processed standard techniques.All slides were analyzed under the light microscope at ×1600 magnification. Moreover, the bioevents were determined by higher resolution which was 10 cm sampling interval and counting the key fossil number within a total as 500 specimens.
The age of 11 nannofossil datums is estimated by interpolation between magnetic reversals. They are: LCO of Discoaster brouweri at 1.96 Ma, LO of D. pentaradiatus at 2.51 Ma, LO of D. surculus at 2.52 Ma, LO of D. asymmetricus at 2.81 Ma, LO of D. tamalis at 2.85 Ma, LCO of Reticulofenestra pseudoumbilica at 3.82 Ma, FO of D. tamalis at 3.98 Ma, LO of Amaurolithus spp. at 4.00 Ma, FO of D. asymmetricus at 4.12 Ma, FO of Ceratolithus spp. at 5.00 Ma, LO of D. quinqueramus at 5.86 Ma. Three bioevents are evaluated to be diachronous, including LO of D. surculus, LO of D. tamalis, and LO of D. quinqueramus.
3.84 Ma for the FO of Pseudoemiliania lacunosa recorded slightly below the LCO of R. pseudoumbilica. Amaurolithus spp.and Ceratolithus spp. are presented in rare numbers, hence the LO of A. tricorniculatus and the FO of C. rugosus are unavailable in ODP 1210. Especially, that the LCOs of R. gelida and R. pseudoumbilica at 3.82 Ma are identical suggested the fates of both morphotypes were controlled by the same factor. Reticulofenestra gelida may represented a winter morphovariant of R. pseudoumbilica. The absence of a warm-water species Sphenolithus abies implies that the water masses throughout the late Miocene-early Pliocene at this location were too cold for Sphenolithus abies to live, but still warm enough for various Discoaster species.
Subjects
nannofossil biochronology
Pliocene
diachroniety
Discoaster
SDGs
Type
thesis
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