| Popis: |
Intracontinental basins are regions located in plate interiors that usually have a long evolutionary history involving vertical motions associated with crustal-scale and mantle- related processes. These tectonic processes also result in a common type of vertical motion in intracontinental basins known as exhumation which is defined as the vertical movement of rocks toward the Earth's surface. This movement has significant implications for the tectonic evolution of intracontinental basins as well as their energy potential. However, mechanisms and factors that control the distribution of exhumation in many of these basins are poorly understood. The Early Ordovician Canning Basin, located in Western Australia is a typical intracontinental basin that has experienced several exhumation episodes and provides a natural laboratory and opportunity to investigate the mechanisms influencing the distribution of exhumation in intracontinental basins. In this study, I examined major episodes of exhumation that affected the Canning Basin to understand how mechanical factors affect the magnitude and distribution of exhumation across intracontinental basins. I also investigated the implication of exhumation distribution on the energy potential of the basin. Seismic and well data were used to establish evidence of exhumation and their magnitude and distribution across the Canning Basin during major exhumation episodes. Seismic data revealed five major unconformities interpreted as a result of exhumation episodes that affected the basin. However, I constrained the magnitude and distribution of three of these exhumation events across the basin, given the available data. These three exhumation episodes are considered the major exhumation events in the basin. They were in response to basin inversion which occurred in the Late Silurian-Early Devonian, middle Carboniferous, and Late Triassic- Early Jurassic. Thermal-based method using vitrinite reflectance data and compaction-based method using porosity data were used to constrain the magnitude and distribution of exhumation across the basin during these three exhumation periods. The uncertainty associated with exhumation estimates from these methods ranges from ± 300 m to ± 1200 m. Results indicate that the magnitude of exhumation was higher in the northern and northwestern parts of the basin and decreased steadily towards the southeastern portions of the basin during each of the three exhumation events. Exhumation decreased from 3300 ± 800 m in the northern parts of the basin to 1800 ± 800 m in the southeastern parts of the basin from the Late Silurian-Early Devonian to present-day. Also, from the Middle Carboniferous to present-day, the magnitude of exhumation decreased from 2700 ± 600 m in the northern parts of the basin to 1300 ± 600 m in the southeastern parts of the basin. Similarly, the magnitude of exhumation decreased from 1800 ± 400 in the northern parts of the basin to 800 ± 400 in the southeastern parts of the basin from the Late Triassic-Early Jurassic to the present-day. The distribution of the amount of exhumation across the Canning Basin indicates that the magnitude of exhumation is highest in areas of inherited or pre-existing basement weaknesses and lowest in regions of relatively stronger and stable basement units. These indicate that the magnitude of vertical motions in intracratonic basins caused by far-field effects of compressional stresses is strongly controlled by the distribution of basement heterogeneities in the basin. The multiple exhumation episodes and the variation in exhumation magnitudes across the basin have likely caused fracturing and faulting of salt deposits that may be targeted for hydrogen gas (H2) storage in the basin. Thus, a detailed fault and fracture analysis is required to test the suitability of these salt deposits for H2 storage. Also, the multiple exhumation episodes and higher exhumation estimates pose critical risks to the generation, accumulation, and preservation of hydrocarbon in the basin. These risks are lower in the southeastern parts of the basin that experienced relatively lower amounts of exhumation. Although there is a working petroleum system in the basin, these risks must be considered during any hydrocarbon exploration. |
