Seventy four (74) samples from three succesive formations of Late Miocene to Middle Plistocene age (Kerek, Kalibeng, and Klitik Formations) of Kendeng zone (northern part of East Java Basin) have been analyzed, showing that climate changes influenced to the growth of nannoplanktons. The diversities, abundance, and the percentage of species are lower in a cold temperature better than warm temperature. Besides, the size of Coccolithus pelagicus is smaller, and the amounts of discoaster and coccolith forms increase in a warmer temperature.
Result of the study reveals that a number of twelve alternating warm and cold zones are found. Two zones (Zone 1 and 2) of the Kerek Formation are the warm zone and the cold zone of lower part of NN12 and NN12-NN13 respectively. Kalibeng Formation. are subdivided into eight zones (Zone 3 to Zone 10), the transitional zone (Zone 3) has an age of NN13NN14, Zone 4 the warm zone (NN14-NN15), Zone 5 (cold zone, NN15), Zone 6 (warm. zone, NN16), Zone 7 (cold zone, NN16), Zone 8 (warm zone, NN16), Zone 9 (transitional zone, NN16), and Zone 10 (warm zone, NN16-NN18). The last two zones the 11 th & the 12th zones belong to Klitik Formation. The 11th zone is a cold zone of NN18, whilst the 12th zone is divided into two warm zones, the 12a & 12b zones of the NN19 and NN20. There is a barren zone occured between the 12a and the 12b zones.
AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid