Distribution of Benthic Foraminifers of Parts of Iligan Bay

Edward S. Lucero and Liza Soccoro J. Manzano

Mines and Geosciences Bureau-Reg. X
email address: cguwapo@yahoo.com

Abstract

This study investigates the present-day distribution of benthic foraminifers of parts of Iligan Bay, particularly the coastal areas of Lugait and Initao, Misamis Oriental. Results of the benthic foraminiferal data are correlated with sedimentologic parameter to better understand its environmental implication and significance (i.e., characterizing the different environment, sedimentation rate). A total of 15 surface sediment samples were used for foraminiferal and sedimentological analyses.

Two major Rivers characterized the study area, namely the Lugait and Initao Rivers. Lugait River is situated not far from an active quarry area while Initao River is located in close proximity to the future quarry area. Benthic foraminiferal data indicate that samples situated near and at the mouth of these Rivers exhibit low foraminiferal abundance, species diversity and high species evenness. This may possibly result from depressed salinity and/or rapid sedimentation, which diluted the concentration of foraminiferal tests.

Interestingly, tributaries of Lugait River are the receiving water bodies of the effluents of siltation ponds of Cement Corporation. During high runoff and prior to its better mine environmental plan, the mine wastes seem to sludge down unto the River and ultimately drained in Iligan Bay. As consequence, the sediments have been build-up parallel the coastal strip near the River mouth. The samples at the estuary of this River show low amount of silt-clay sized sediments.

Samples within Lugait River show high occurrence of Ammonia beccarii and high frequency of family Nonionidae (i.e., Pseudononion granuloumbaticum, Nonion subturgidum). These assemblage are typical of estuarine species, however, the high abundance of Ammonia, Bolivina and Nonion suggest the presence of opportunistic species.

Two distinct environments characterized the coastal areas of Initao. A probable transitional type of environment, both siliclastic and carbonate type of environments, is best described the samples situated near at Initao River. This is most likely the high occurrence of lithogenic components and more importantly, the high abundance of biogenic component, particularly Calcarina that strongly links to a carbonate type of environment. On the other hand, a shallow carbonate reef type of environment characterized the rest of the samples. These samples support high standing crop of benthic foraminifers and low species evenness. This is the result of the abundance and dominance of a few species (Calcarina spp.). These species are most likely highly specialized and uniquely adapted to this type of settings. However, of the samples belonging to this type of environment, one site shows the most diverse benthic foraminiferal assemblage. This suggests that the combination of coarse- and relatively high amount of fine-grained sediments is favorable to benthic foraminiferal proliferation.