Palynology of the Nanggulan Formation, Yogyakarta, Central Java, Indonesia
Eko Lelono, completed PhD project
The Nanggulan Formation, Java, Indonesia, contains an age diagnostic Eocene fauna and the richest Eocene palynomorph assemblage between the Gippsland Basin (Australia) and India. 151 samples, from four field sections, were collected and processed, and palynomorphs were studied using light microscopy. Pollen diagrams and charts were produced using Tilia and Stratabugs programmes. Diversity was assessed using Williams’ index and concentration via the aliquot method. Detrended correspondence analysis was used to investigate patterns of distribution of samples and taxa.Three hundred different palynomorph types are recorded; the 80 most abundant (>3% in any sample) taxa are described and illustrated, whilst key distinguishing features are tabulated for other taxa.
Many palynomorphs have affinity with Indian forms.This suggests plant migration into Southeast Asia following plate collision in the early Tertiary. A wider distribution of similar Middle Eocene palynomorph assemblages suggests that Sundaland extended from Java as far as southwest Sulawesi enabling migration across Wallace’s line into eastern Indonesia.
The Nanggulan Formation has been subdivided into lower, middle and upper lithological units, into 7 formal biozones (4 interval and 3 concurrent-range), and 10 informal assemblage zones. This zonation has enabled correlation between the four sections and should be applicable elsewhere in Southeast Asia. Palynological evidence indicates a Middle to Late Eocene age for the Formation.Podocarpidites pollen in the upper unit indicates cooling, probably equivalent to that near the Middle/ Late Eocene boundary recorded elsewhere. The Nanggulan Formation has been shown to be a transgressive sequence containing a series of stacked rising sea level sequences. These sequences may be comparable to the cycles (third order) from TA 3. 4 to TA 4. 1 or from 43. 0 Ma to 36.0 Ma. These sequences support palynological zones. The coastal plain setting (lower unit) changes upward into brackish or marginal marine, then into shallow marine (lower part of middle unit). The palaeoenvironment then shifts into deeper marine, characterised initially by gravity flow deposits and finally by deep water, fine-grained, volcanics and marls. Five ancient vegetation types viz. mangrove, freshwater swamp and rain forest, rattan swamp, herbaceous swamp and hinterland vegetation are shown to have existed at different times during deposition of the Nanggulan Formation.