GEOLOGICAL SOCIETY OF THE PHILIPPINES
LATE CRETACEOUS BIOSTRATIGRAPHY AND ENVIRONMENTAL CONDITIONS ALONG THE SAMPALOC/CAPINPIN – DARALITAN ROAD SECTION, TANAY, RIZAL
Maybellin Zepeda, Elsa Mula, Raymond Thaddeus Ancog, and Dilson Montano
This paper presents the preliminary results of the biostratigraphic studies of Late Cretaceous sediments in the Sampaloc/Capinpin-Daraitan road section, Tanay, Rizal. The succession consists of rhythmic sequence of sandstone and shale capped by a series of thin bedded limestone. A Late Santonian to Maastrictian age is given based on planktonic foraminifera.
Most of the plantonic forms identified belong to the genera Globotruncana, Heterohelix, Globigerinelloides, Hedbergella, Rugoglobigerina, and Archaeoglobiregina. Single and double keeled globotruncanids are common to abundant. Heterohelicids are also present in varying abundance whereas, rugoglobigerinids, globigerinellids, hedbergellids and archaeoglobigenerids occur sporadically.
Four planktonic foraminiferal zones are established. Namely; in strtigraphic order, the Concavatotruncana asymetrica (Late Santonian), Globotruncana ventricosa (Middle Campanian to Late Campanian), Globutruncana tricarinata (Late Campanian to Early Maastrichtian) and Gansserina gansseri (Middle Maastrichtian) Zones. In addition, an unzoned interval (Early Campanian) and three local zones are defined for this sequence: the Globotruncanita subspinosa, Globotruncanita stuarti, and Globotruncanella citae Partial Range Zone. These approximately correspond to the Globotruncana ventricosa, Globotruncana tricarinata and Gansserina gansseri Zones respectively; the marker species for these zones occur too sporadically in the section to be used for regional and worldwide correlation. Major faunal events are discussed in terms of the boundaries of Cretaceous stages.
Generally, environmental conditions during the Late Santonian to Maastrichtian showed deposition in an open marine, warm Tethyan outer shelf environment for the sequence. This isindicated by plantonik foramineferal assemblages characterized by igh species richness and P/B ratio, and the presence of warm and typical Tethyan species represented by the single and double keeled forms of Globotruncana. Nonetheless, shallower conditions prevailed in the Middle Maastrichtian Ganserina gansseri Zoned based on the low P/B ratio and the presence of abundant mollusks. The absence of the Late Maastrichtian Abathompalus mayaroensis Zone in the section could probably be due to several factors such as the worldwide phenomenon of biotic and environmental changes preceeding the Cretaceous/Tertiary boundary and/or to some tectonic and geologic events which occurred in the area before, during and after the Late Cretaceous.
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