|
The Centenary of the Netherlands Indies Geological Survey was commemorated by the publication of a synthesis of the geology of Indonesia by van Bemmelen (1949). In his account of the geology of Sumatra van Bemmelen (1949) described three distinct, but continuous, cycles of volcanic activity during the Tertiary and Quaternary: Old Neogene (Late Oligocene-Mid-Miocene); Young Neogene (Mid-Miocene-early in the Quaternary); and Young Quaternary. The first cycle began with the 'Old Andesites', and ended with the Mid-Miocene uplift of the Barisan Mountains. The second cycle commenced with the eruption of basic igneous products and concluded with an acidic phase which coincided with a second episode of uplift of the Barisan Mountains.
Subsequently, knowledge of the Tertiary volcanic rocks in Sumatra has been refined as the result of programmes of geological mapping in the early 1970s by the Geological Survey of Indonesia and the United States Geological Survey, and between 1975 and the mid-1990s by the Geological Research and Development Centre, the Directorate of Mineral Resources and the British Geological Survey. Exploration by oil and mineral companies has also provided data concerning the distribution of Tertiary plutonic rocks in the Pre-Tertiary basement and in the Tertiary sedimentary basins, of volcanic units interbedded with sediments. Further contributions to the understanding of Tertiary volcanicity in Sumatra and its forearc islands have been made by academic researchers and post-graduate students from the Institute of Technology, Bandung and the University of London, in collaboration with the Geological Research and Development Centre, LIPI and LEMIGAS, and the
