Change in the degree of catagenesis and hydrocarbon generation in the sedimentary rocks of the South Sumatra Basin, Indonesiaстатья
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Аннотация:Temperature and catagenetic history of the South Sumatra Basin in Indonesia is considered by the
example of the sedimentary sequence of the Limau graben during its subsidence from the Oligocene to the
present time. GALO system for basin modeling was applied for numerical reconstruction of six sedimentary
successions in the area of holes Pandan81, Petanang1, Tepus2, Tepus1, Gambir1, and Lembak8 located
along the profile cutting across the Limau graben. Modeling suggests significant cooling of the basemen for
the last 15–20 Ma from the high initial heat flow of 105 mW/m2, which is typical of axial zones of continental
rifting, and significant heating of the basin lithosphere during the last 2–5 Ma. Examination of variations in
tectonic subsidence of the basin confirms the possible extension of the lithosphere in the Oligocene–
Miocene with an amplitude β increasing from 1.12 on the flanks of the Limau graben (Hole Lembak8) to
1.32 in the central part of the graben (Tepus1 and 2), Tectonic analysis indicates also the notable thermal
activation of the basin in the Pliocene, Pleistocene, and Holocene. This activation is consistent with the high
temperature gradient typical of the presentday sedimentary cover of the basin. Numerical modeling of the
evolution of the organic matter maturity and hydrocarbon generation by main source formations of the basin
confirms good prospects of the inferred source formations (Lemat, Talang Akar, and Gumai) of the South
Sumatra basin for the generation of liquid hydrocarbons (HC) in the Limau Graben. It is also demonstrated
that the source rocks of the Lemat Formation are oregenerating rocks in the main part of the Limau graben
and are gasgenerating rocks only in the deepest portions of the graben. The rocks at the base and roof of the
Talang Akar Formation could be considered as highly oilgenerating rocks, probably except for the upper
horizons of the formation in the shallowest portions of the graben (Hole Lembak8). Oil generation reached
peak in the last 5–10 Ma. Modeling showed that intense oil generation by the Gumai Formation may be sig
nificant in the most part of the Limau graben and negligible only in the distant flanks of the graben (Hole
Lembak8).