Basin Research最新文献

The traditional distinction of magma-poor and magma-rich margins is challenged by the presence of significant late-stage rift-related magmatism in certain margins, such as the South China Sea (SCS). We use numerical modelling to investigate the conditions and processes that lead to crustal melting and the formation of high-velocity lower crustal layers (HVLs) in such magma-intermediate margins. The models demonstrate that the preferential removal of the lithospheric mantle during rifting is crucial for crustal melting, as it allows the crust to receive sufficient heat from the upwelling asthenosphere. The extent and distribution of crustal melts are influenced by extension velocity and crustal rheology, and the models reveal a strong correlation between the presence of crustal melts and thin-crust domains (< 20 km thick). The study reveals a younger-oceanward trend in magmatism, attributed to the progressive exposure of the crust to the hot asthenosphere during rifting. Comparison of modelling results with seismic observations from the SCS margin suggests that both asthenospheric and crustal melts contribute to the formation of HVLs, with crustal melts estimated to constitute approximately 15%–30%. The results not only deepen our understanding of magmatic processes in magma-intermediate margins, but also provide quantitative evidence for the classification and interpretation of passive margins.

The meridional, Permo–Triassic Bowen Basin of NE Australia became a retroarc foreland basin in the late Permian, with a mapped foredeep axis (Taroom Trough) running north–south adjacent to the eastern edge of the basin. The present outline of the basin is, nonetheless, shaped by significant structural deformation along its eastern margin, and stratigraphic pinch-outs and erosional truncation in the west. The plan form of the basin thus gives a potentially misleading representation of the basin's original shape and extent. By analysing wireline log data from over 1000 drillholes, we developed isochore, net sand thickness, and net-to-gross maps, which inform a new set of palaeogeographical maps for the three upper Permian formations of the Bowen Basin (Peawaddy Formation, Black Alley Shale, and Bandanna Formation, in ascending order). These maps were further refined using palaeocurrent data from outcrops and validated against logged vertical sections from various parts of the basin. Isochore plots for the three formations indicate abrupt truncation of contour lines along the structural eastern margin, in the Taroom Trough. This pattern is interpreted as evidence of significant erosion of stratigraphy along the eastern basin margin during contractional deformation. Based on these findings, we posit that the Taroom Trough synclinal axis does not represent the original foredeep axis, which we propose was located farther east and was erosionally excised. The configurations of sand-prone depositional systems, and the preservation of upper Permian strata outside the structural basin boundaries, support the hypothesis that the original eastern depositional edge of the basin extended farther east than its current structural boundary. Similarly, truncation and westward onlap of formations along the western margin suggest that the basin's original western boundary lay beyond its present margin. Based on the truncated isochores and other criteria, we estimate that the preserved part of the basin is ~50% of its original area.

Most works propose a genetic “wide-rift” model for the northern South China Sea (SCS) rifted margin, where low-angle detachment faults accommodate significant deformation during crustal extension. However, a new seismic grid along the northern SCS shows along-strike changes in tectonics. At least two distinct tectonic domains, i.e., “wide-rift” Eastern Domain and “narrow-rift” Western Domain, have been revealed, which indicates that the current conceptual SCS rift models are likely too simplistic. Whereas, the Western Domain remains little explored because of the lack of available 3D seismic data and boreholes here. The 3D rift architecture in this tectonic domain is therefore inadequately constrained, which leads to insufficient knowledge of the syn-tectonic rift evolution in this region. Based on an unpublished 2D deep-penetration grid of seismic reflection sections, we have investigated the faulting style, sedimentary structure, and crustal architecture in the Western Domain of the mid-northern SCS. Our data display that the Western Domain contains the Changchang and Heshan Segments separated by a transfer fault zone. The aborted Changchang Segment is characterised by landward-dipping faults and younger T60 breakup unconformity. The neighbouring Heshan Segment, reaching the final continental breakup, is characterised by oceanward-dipping faults and older T70 breakup unconformity. The observations imply abrupt along-strike rifting changes not contemplated by current models, requiring unexplained crustal or mantle heterogeneity during extension.

In rifted margins or rifted basins, the structure of the basin is often complex due to the multistage development of fault systems. As we can only see the result of the basin evolution, it is difficult to judge the influence of early fault activity on the later stages. Here, we present a case study from the southern part of Qiongdongnan Basin (QDNB) where the influence of the early stage can be clearly recognised. Using newly acquired high-resolution 3D seismic datasets, we analyse the prototype and temporal evolution of the study area since the Cenozoic. Three fault systems (FS1, FS2 and FS3) were identified according to fault activities and fault strike. Observation results show a rotation of the stress field at the end of the Eocene, dividing the whole rifting into two stages. FS1 initiated in NW-SE extension at rift stage I (42.5–33.9 Ma), showing a typical basement-involved structure while FS2 and FS3 developed in N-S extension at rift stage II (33.9–23.03 Ma). The faults in FS1 were either crosscut to form a zigzag plane geometry by FS2 and FS3 faults, or became long-lived active faults throughout the rifting period, resulting in a localisation of strain and extremely thinning of the crust. It can also be compared with adjacent basins which have undergone the same regional tectonic evolution history at the northern margin of the South China Sea. The long-lived NE–SW trending faults cause significant variation in the subsidence history, basin structure, and crust thickness along strike in the study area, indicating that faults developed in rift stage I play a significant role in basin evolution at rift stage II.

The outcrops of the Panoche and Tumey Giant Injection Complexes in California have been instrumental in refining the interpretation of the sandstone intrusion reservoirs in the Volund Field, Norway. Insights from the outcrops enhanced the subsurface team's confidence and understanding of reservoir presence and connectivity during field production. This led to more accurate estimates of hydrocarbon reserves. Learnings from the Volund Field show that historical reservoir models underestimate net reservoir volume and reservoir connectivity. Outcrop data reveal step-like geometry in some intrusions, which potentially explains the lack of seismic resolution of sandstone intrusions in some areas of the field. Failure to recognise this leads to misinterpretation of parts of the field as non-reservoir. In some intervals, well logs interpreted as non-reservoir mudstone-rich units are actually mudstone-clast breccia, which, because of good connectivity within the sandstone matrix, can comprise significant reservoir volumes. The rationale for including sandstone intrusions as reservoirs, although unresolved by seismic or borehole log data in static models, is validated by reference to outcrop data and from recent drilling in the adjacent Kobra Field. Observations of outcrop analogues enhance the interpretation of subsurface data, and the knowledge acquired from outcrops helped justify the drilling of more production wells in areas where reservoir presence and quality were difficult to predict, but almost nearly doubled the hydrocarbon reserves.