Abstract
Conventional studies of petroleum basins associate oil generation with the gradual burial of organic-rich sediments. These classical models rely on the interplay between pressure, temperature, and the time required for organic matter transformation to oil and gas. These processes usually occur over geological timescales, but may be accelerated by rapid reactions when carbon-rich sediments are exposed to migrating magmatic fluids. The spectacular Lusi eruption (north-east Java, Indonesia) is the surface expression of the present-day deep interaction between volcanic and sedimentary domains. Here we report the ongoing generation of large amounts of hydrocarbons induced by a recent magmatic intrusion from the neighbouring Arjuno-Welirang volcanic complex. We have investigated a unique suite of oil and clast samples, and developed a detailed conceptual model for the complex hydrocarbon migration history in this part of the basin by integrating multidisciplinary techniques. Our results show that palynology, organic petrology, and chlorite microthermometry are the most sensitive geothermometers for basins affected by recent magmatic activity. These findings further our understanding of the driving mechanisms fueling the world’s largest active mud eruption and provide a unique dataset to investigate modern hydrocarbon generation processes.
Highlights
Hydrocarbons (HCs) stored in the sedimentary basins are predominantly of biotic origin, i.e. they are derived through the alteration of buried organic matter (OM)[1]
The dataset was gathered from a suite of samples collected during yearly sampling campaigns conducted in the study area since the beginning of the Lusi activity
Organic geochemical analyses of the oil films collected from the Lusi crater (Supplementary Table S1) reveal that they are composed of 53–64% of saturated HCs, 13–15% of aromatic HCs, and 21–34% of polar compounds. n-Alkane distributions demonstrate the predominance in high-molecular-weight zone (n-C23 − n-C27) (Fig. 3), Pristane/Phytane (Pr/Ph) ratios vary from 2.6 to 3.9
Summary
Hydrocarbons (HCs) stored in the sedimentary basins are predominantly of biotic origin, i.e. they are derived through the alteration of buried organic matter (OM)[1]. Regardless the burial history and temperature conditions, rapid oil generation can be triggered if the source rocks are exposed to anomalously high heat induced by magmatic/hydrothermal activity. This phenomenon has been documented at several localities worldwide including the Guaymas Basin, Escanaba Trough, Lake Tanganyika, Neuquén Basin, Rockall Trough, Vøring-Møre basins, Salton Sea, and Faroe-Shetland basins[6,7,8,9]. Lusi is surrounded by three hydrocarbon fields: Wunut, Tanggulangin, and Carat (Fig. 1b) These fields contain oil and gas accumulations within the shallow (200–1000 m depth) volcaniclastic reservoirs of the Pleistocene Pucangan Formation (Fm.). The major HC source rock is the Ngimbang Fm., consisting of organic-rich shales, coals and coaly shales[22,25]
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