East Java – Southeast Asia Research Group Skip to main content Home Research Research By Region Borneo Java Thailand Peninsular Malaysia Sumatra Sulawesi Seram West Papua Banda Arc Philippines Vietnam Myanmar Sorong Fault Zone Regional Projects Research By Topic Plate Tectonics Provenance Studies Thermochronology Carbonates Tomography Isotopic Ages Geochemistry Heat Flow Biostratigraphy Companies Membership Information Members Only Biogeographers Publications Papers Books Personnel Contact Us Home Research Java Geology and Evolution East Java East Java Eocene to Miocene basin history and volcanic activity in East Java, Indonesia Helen Smyth, completed PhD project East Java is located on the SE margin of the Mesozoic continental core of SE Asia (Sundaland). In this study the region is divided into four east-west trending zones. The Southern Mountains Zone contains the eruptive products of an Eocene to Miocene volcanic arc. North of this arc is an (?Eocene) Oligocene to Early Miocene depocentre, the Kendeng Zone, now a fold-thrust belt. The most northerly zone, on the edge of the Sunda Shelf, is the Rembang Zone where Eocene to Miocene shelf and slope clastic and carbonate rocks dominate. About 50 km north of the Eocene to Miocene volcanic arc is the modern (Late Miocene to Recent) volcanic arc, products of which cover many older Cenozoic deposits. SRTM DEM of East Java This field-based study, aims to understand the Cenozoic development of East Java, particularly the basement character, nature of overlying sedimentary and volcanic sequences and their relationships to one another, and timing and causes of basin formation. A range of field techniques were utilised, including detailed section logging, palaeocurrent analysis and sampling. Samples have been studied using petrographic, SEM, XRD, and heavy mineral analytical methods. Isotopic dating has been carried out in collaboration with CSIRO, Australia. Geophysical data sets and remotely sensed images have been used to complement field and laboratory studies. The exposed basement in East Java includes rocks of arc and ophiolitic character accreted during the Cretaceous; there are no outcrops of continental rocks. However, the new field observations and U-Pb SHRIMP analysis of zircons indicate the presence of continental crust at depth beneath SE Java. View of Mount Merapi, East Java In the Early Paleogene, basins developed on the Cretaceous and older East Java basement. Sedimentary rocks in the East Java basins have previously been interpreted to be continental clastic sediments. However, there has been subduction at the Sunda-Java Trench since the Early Cenozoic and volcanic activity in East Java was important. This study shows that Eocene-Miocene explosive Plinian-type volcanic activity was much more important and more acidic than previously recognised. New provenance studies show that many of the sediments have a volcanic origin or a significant volcanic component. There is no evidence to suggest sediment transport from Sundaland. Many of the sedimentary rocks previously thought to be “mature” have a major volcaniclastic component, and their “mature” character reflects pyroclastic processes and tropical weathering. This study shows that maturity or discriminant diagrams should be used with caution in tropical volcanic settings. New U-Pb SHRIMP analysis of zircons has enabled precise dating of volcanic events. A potential super-eruption has been identified within the Southern Mountains (19 Ma ±1), likely to be a Toba-scale event. This previously unrecognised eruption may have had a significant influence on global climate during the Early Miocene. The U-Pb SHRIMP analysis also identified the presence of inherited zircons, which reveal basement structure and indicate the presence of Gondwanan continental crust beneath SE Java. Basin development appears to be closely related to volcanism. Modelling in this study suggests that the Kendeng Zone depocentre was a flexural response to loading by the volcanic arc. Search the Site Content Home Research Companies Members Only Publications Biogeographers Personnel Contact Us Recent News Recent Papers – Max Webb et al., 2020. Isotopic mapping reveals the location of crustal fragments along a long-lived convergent plate boundary. Lithos. https://doi.org/10.1016/j.lithos.2020.105687 Max Webb et al., 2020. The history of Cenozoic magmatism and collision in NW New Guinea – New insights into the tectonic evolution of the northernmost margin of the Australian Plate. Gondwana Research. https://doi.org/10.1016/j.gr.2019.12.010 Amy Gough et al., 2020. Mid-Cenozoic fluvio-deltaic to marine environments of the Salin Sub-basin, Central Myanmar. Journal of Asian Earth Sciences. https://doi.org/10.1016/j.jseaes.2019.104143 Recent News – Amy Gough and Max Webb attended the Restech 2.0 Virtual Reservoir Conference. Amy Gough presented new SEARG research on the pitfalls of light mineral studies for sedimentary provenance in tropical climates. Amy Gough was awarded an honorary research fellowship of the British Geological Survey and continues to foster collaborative relationships between SEARG and the BGS. © Southeast Asia Research Group 2016
