GEOLOGICAL SOCIETY OF THE PHILIPPINES

 

 

Response of Calcareous Nannofossils to Sedimentological and Paleoceanographic Variations in Core Sediments Off Vietnam, South China Sea

 

Alyssa M. Peleo-Alampay, Deborah N. Tangunan and Rikki Pamela L. Pineda

National Institute of Geological Sciences,
University of the Philippines, Diliman, Quezon City;
ampanigs@yahoo.com

 

Abstract

 

Calcareous nannofossils (coccolithophores) are marine haptophyte algae which have been very useful both as biostratigraphic and paleoenvironmental indicators for marine sediments. The offshore area off Vietnam is an ideal area to study the use of these calcareous nannofossils to determine past oceanic events because of the strong upwelling that occurs today during the summer months in the southwest monsoon. This study attempts to trace the extent of this upwelling signal and changes in depositional history through time using indicator nannofossil species.

 

This research investigates sediment cores collected during Sonne cruises SO-140 and SO-187 on the offshore continental shelf and slope of Vietnam. Core SO140-58 is 383 cm long and was retrieved from 1908 m water depths, closer to the shore. Core SO-187-61 is longer (927 cm) and was collected in deeper waters (2226 m) on the continental slope. The cores are subsampled at 10-cm intervals and analyzed for nannofossil distribution and abundance. This study presents analyses from the entire length of these two cores. The nannofossil assemblage in the cores is characteristic of marginal sea environments. It is of low diversity, dominated by Gephyrocapsa oceanica, Florisphaera profunda and Emiliania huxleyi. G. oceanica is the most abundant species in the nearshore core (SO-140) while F. profunda dominates in the deeper cores (SO-187). Variations in the distribution of F. profunda are interpreted in terms of possible changes in the upwelling intensities in the area. F. profunda has been used widely as a productivity/upwelling indicator in core sediments. The downcore distribution and abundance of other environmentally-sensitive species such as Helicosphaera carteri, Umbellosphaera irregularis and Umbilicosphaera sibogae are also compared among the studied cores.

 

 
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