2-1) UNDERSTANDING THE INDONESIAN OROGENY : A Basement Geology Perspective
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Orogeny
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Orogeny
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This paper reviews our current understanding of basement play in the Malay basin, offshore Peninsular Malaysia. Of more than the fifty basement penetrations, most were secondary drilling objectives. The wells revealed a variety of lithologies in the pre-Tertiary basement, including igneous, metamorphic and sedimentary rocks. The first basement oil discovery was made in the Anding area in the southwestern part of the basin. This has been used as the basis of a basement play concept in further exploration. In this study, a basin-wide seismic interpretation was carried out to identify and rank prospective areas for fractured basement play. The use of high-quality 3D seismic has enabled the recognition of potential fractured zones in the basement. Seismic recognition of fractures is a key factor in finding new prospects in fractured basement. Based on detailed mapping, potential areas of fractured basement reservoirs have been identified for further analysis.
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Lithology
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Neogene
Orogeny
Alpine orogeny
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Tectonometamorphic zones were defined within the lower Paleozoic basement of the NW Argentine Andes in a transitional zone between two Andean segments of different geotectonic evolution. In the Cambrian, the Pacific edge of Gondwana changed from a passive to an active continental margin. This event began with folding of a Vendian/Eocambrian sediment wedge (Puncoviscana Formation and equivalents). The effects can be traced progressively over all structural levels with exposed depth increasing from north to south. Phenomena of a second deformation are of different nature and age but mostly characterized by shear belts causing large-scale crustal imbrication. In the lower tectonic levels this phase coincides with subduction-related magmatism of Ordovician age. A flat subduction slab is supposed, somewhat steeper in the northern than in the southern segment. The following anatectic-granitic magmatism and weak deformation in the Devonian may have marked a new change to passive margin conditions.
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Continental Margin
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The Vancouver region is underlain by three different basements, which form the Coast Mountains to the north, the Vancouver Island Ranges to the west, and the Cascade Ranges to the southeast. These elevated areas are separated by Georgia Depression and Fraser Lowland, low regions in which the Late Cretaceous and younger sedimentary cover is preserved. The basements contain much of the record of the crustal evolution of the region, which can be divided into three stages. (1) During the pre-accretion stage (>100 Ma), the crustal block forming Vancouver Island and southwestern Coast Mountains was in uncertain paleogeographic relationship to the North American plate margin, and separated from it by basinal terranes in southeastern Coast Mountains. (2) The syn- and postaccretion stage (100-40 Ma) was initiated when the western block was accreted to the plate margin, an event accompanied and followed by crustal thickening, uplift, and erosion centred in southeastern Coast Mountains. (3) During the last 40 million years, the continental Cascade magmatic arc formed on the North American plate margin above a subduction zone, the surface trace of which was, and is west of Vancouver Island. The regional physiography, probably formed in the last 10 Ma, may be related to stress distribution in the plate margin and thermal expansion in the magmatic arc; it was also influenced by the basements, as topographic depressions coincide with basement boundaries.
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Detritus
Rodinia
Orogeny
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Exploring for hydrocarbons in mature basins as well as in frontier areas have specific challenges but<br>require a common approach. In mature areas, easy and obvious objectives have already been targeted<br>whereas in frontier basins, choices and decisions have to be made on very little data. In both scenarios<br>de-risking plays and polarizing a portfolio of opportunities should be based on a good knowledge of the<br>entire geological evolution and its impact on the various play elements. At the base of this knowledge<br>lies the understanding the plate tectonic development that requires reviewing a region in a wider context.<br>Specifically for this conference, two important plate tectonic events and their implications for Arabian<br>geology and play concepts will be reviwed:<br>1. The basement and the early, ‘Pan-African’ amalgamation history<br>2. The Pangea break-up and Mesozoic to Cenozoic plate history<br>This second contribution summarises the break up history of Pangea in the Mediterranean and Middle<br>East regions and the subsequent collision of the resultant parts with Eurasia during the Tertiary. The<br>impact of plate processes and changes in plate kinematics on high level play parameters of some key<br>mature and frontier plays will be illustrated with examples from Morocco to Oman.
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