Late Miocene Calcareous Nannofossils from Danao, Bohol (Visayan Basin)

Allan Gil S. Fernando¹, Adrian Raymund C. Fernandez¹, Yolanda Maac-Aguilar²,
Yukito Kurihara³, Tomoki Kase³

¹National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon City 1101
²Petrolab, Mines and Geosciences Bureau, North Ave., Diliman, Quezon City, Philippines
³Department of Geology and Paleontology, National Museum of Nature and Science, Hyakunin-cho, 3-23-1, Shinjyuku, Tokyo, 169-0073 Japan

Abstract

This paper presents the results of the calcareous nannofossil investigation of 29 samples collected from an unnamed shallow marine, mollusk-bearing clastic formation in the Danao Basin of central Bohol, Philippines. The study was conducted in order to refine the stratigraphy and age of the Neogene formations in the island. Calcareous nannofossils in the samples range from rare to abundant and are generally moderately-preserved. The most common species are Discoaster spp., Helicosphaera carteri, Reticulofenestra spp. (R. haqii, R. pseudoumbilicus), Sphenolithus abies and Umbilicosphaera spp. (U. jafari, U. rotula; Figure 1). Based on the occurrence of Discoaster quinqueramus and Discoaster berggrenii, the NN11 nannofossil zone of Martini (1971) is recognized (=CN9 of Okada and Bukry [1980]). This suggests a Late Miocene age for the sandstone-siltstone sequences with calcarenite interbeds exposed in Danao, which have been previously mapped as part of the Middle Miocene Carmen Formation (e.g., Porth et al., 1989).

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