Neogene Basin Evolution in a Volcanic Arc Setting
Lanu Cross, completed PhD project
The volcanic island of Java is located within the Indonesian archipelago at the Eurasian margin. To the south of Java there has been subduction of the Indo-Australian Plate beneath the Eurasian Plate along the Java Trench since the Middle Eocene. During the Middle Miocene there was a lull in volcanism followed by a Late Miocene renewal of activity along the axis of the modern arc. Contemporaneous with, or after, this resumption of volcanism the basins and the ancient arc were deformed and became elevated. The timing and cause of this deformation event is poorly constrained and not well understood. This study will involve the examination of the sedimentary and volcanic rocks deposited during the Neogene to better understand the timing and nature of deformation.
Java contains the products of ancient (Eocene-Miocene) and young volcanism (Late Miocene-Present). In addition to the volcanic rocks there are a number of sedimentary basins on and around Java, several of which contain abundant hydrocarbons. These basins developed above an accreted basement, in a variety of settings, during the Early Cenozoic and contain thick sequences of carbonate, siliciclastic, volcaniclastic and volcanic rocks. A volcanic arc was active throughout the Eocene to Early Miocene and provided abundant sediment to the basins. In addition, in West Java sediment was transported from the north by major rivers.
During the Neogene several events are postulated to have occurred that have shaped Java. The focus of volcanism shifted ~50 km north from its Paleogene position, and the old arc itself has been tilted and deformed. Large scale, possibly island wide compression has led to the uplift and inversion of the palaeo-depocentres to the north of the old island arc, forming new topographic highs. The East Java Basin in now a succession of anticlinoria as a result of this compression and rocks in West Java have been thrust northwards.
This event/succession of events are poorly constrained, primarily because of the lack of accurate chronostratigraphic data. Much of the sediment generated during these tectonic events contains abundant reworked material, meaning that chemical and biostratigraphical analyses often yield conflicting results. This project aims to acquire new stratigraphic and structural information from fieldwork in Java, integrated with existing information, in order to develop a viable and chronologically accurate model for the tectonic evolution of Java during the Neogene. It aims to build upon the previous studies by the SE Asia Research Group in order to develop a clearer understanding of the tectonic factors that have shaped Java and the surrounding regions between the Miocene and Recent.