GEOLOGICAL SOCIETY OF THE PHILIPPINES

Benthic foraminiferal assemblages of Balayan Bay, Calaca, Batangas

Diana M. Lopez* and Maybellyn A. Zepeda*+

*School of Earth and Materials Science and Engineering,
Mapúa Institute of Technology, Intramuros, Manila
+Petrolab Paleontology Unit, Lands Geological Survey Division,
Mines & Geosciences Bureau, North Ave., Diliman, Quezon City


Abstract

This study presents the microfauna found in Balayan Bay, Calaca, Batangas. Balayan Bay is a part of the primary bay system on Batangas Gulf Coast. It is an open bay facing the South China Sea. It is also located near a coal-fired thermal power plant and serves as recipient of domestic and industrial waste. The Balayan Bay–Calaca area has been the subject of several studies in recent years. Among the studies conducted focused on the sedimentology, geochemistry and geotechnical investigation of the area.

A total of twenty samples were collected within 10m lateral intervals between sampling points from the sea-surface sediments of the bay. These were analyzed for their microfaunal content. Microfauna identified in the samples consist mostly of Foraminifera, which are single-celled animals belonging to Protozoa, most of which are marine although few have been reported from fresh water. Few mollusks, numerous coral fragments and other unidentifiable organic forms are also present. Results of this study showed that sampling points (SP) 1-10 exhibited lower foraminiferal abundance and diversity while sampling points (SP) 11-20 displayed higher foraminiferal content as well as higher species diversity (simple and Shannon-Weaver). SP 1-10 consists of only few foraminifera, with the majority identified as Quinqueloculina seminulum (Linnaeus) and Ammonia beccarii (Linné). The faunas identified in SP 11-20 consist of abundant planktonic foraminiferal assemblage such as Globigerina bulloides (d’Orbigny), Orbulina universa (d’Orbigny) and Globigerinoides trilobus (Cushman) and benthonic assemblage of Nonion scaphum (Montfort), Elphidiononion poeyanum (d’Orbigny), Bulimina gibba (Cushman), Elphidium lessonii (Montfort) and Lenticulina convergens (Linnaeus). The most dominant benthonic species include Quinqueloculina seminulum (Linnaeus) and Ammonia beccarii (Linné). Variations in abundance and diversity of the species could probably be the result of factors such as high influx of sediments and nutrients in

the area as well as to other anthropogenic causes due to disposal of domestic and municipal wastes in the bay. In cases, where all samples were collected at depths not greater than five meters, foraminiferal occurrence is most likely determined by differences in environmental conditions and type of substrate.

 
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