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(A) A representative seismic profile shows troughs below polygonal faults and fluidized sediments within incised valleys above polygonal faults in southeast direction in the Qiongdongnan Basin, South China Sea (modified from Sun et al. (2010)); (B) A seismic profile through a polygonal fault system and buried pockmark field in the Canterbury Basin, New Zealand (modified from Hoffmann et al. (2019)).
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Polygonal faults (PFs) have been widely found in over 100 sedimentary basins worldwide, mainly in marine setting on continental margins and intracratonic sedimentary basins. PFs are characterized by layer-bound minor normal faults arranged in polygonal patterns and multi-direction strikes, most of which were developed in fine-grained sediments rich...
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Timor Island, Indonesia has complex geological structures related to its tectonic history. There is an existing subsurface geological model that is based on geophysical data. It is limited to the regional crustal scale and has a relatively low spatial resolution. The objective of our study was to delineate the sedimentary basin configuration of the...
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... The fault pattern in the Val d'Agri Basin is very complex and has been explained through various tectonic evolutionary models. Our data improve and advance these previous models by providing evidence for deformation processes hitherto not described in the study area, such as re-activation of the pre-orogenic forebulge extensional faults (Doglioni, 1995;Vitale et al., 2012;Tavani et al., 2023) and polygonal-like faulting (i.e., layer-bound normal faults arranged in polygonal patterns and multi-direction strikes; Xia et al., 2022). These results may be useful for the exploitation of natural fluids and the mitigation of seismic hazard. ...
... Accordingly, we propose that a polygonal-like style of faulting occurred above this unit within the competent carbonate rocks cut by the EAFS. Indeed, the not-systematic orientation of fault strikes and the radial pattern of slip directions documented for the EAFS meso-scale faults are fully consistent with typical features described in well-recognized polygonal fault systems worldwide (e.g., Cartwright, 2011;Elmahdy et al., 2020;Xia et al., 2022). In fact, polygonal faults are often composed of a network of minor normal faults confined to a specific stratigraphic interval by an overpressured and plastic horizon, such as the Irpinia mélange underneath the allochthonous units in the study area, and result in the isotropic collapse of the overlying competent rocks radially spreading above the flattening plastic unit. ...
The Val d’Agri Basin is a Quaternary sedimentary basin topping multiple tectonic units of the southern Apen
nines fold-and-thrust belt and a giant oilfield within deeper Apulian Platform carbonates. This basin is bounded
by the seismically active East Agri (EAFS) and Monti della Maddalena (MMFS) extensional fault systems. The
reservoir rocks are sealed and separated from shallower thrust sheets by a clay-rich and overpressured m´ elange.
The role of this m´ elange during fault evolution at shallow crustal levels is widely debated and perhaps under
estimated. Here, through multi-scale structural analyses and U–Pb dating of syn-tectonic calcite mineralizations,
we gain new insights into the Val d’Agri fault system architecture, their structural maturity, and their relations
with both natural and induced seismicity. Consistent with present-day NE-SW crustal stretching, the macro-scale
structural architecture of both EAFS and MMFS is controlled by NW-SE and NE-SW fault sets, which displaced
and in part re-sheared inherited pre- and syn-orogenic structures. The lack of evident clustering of meso-scale
faults and the radial pattern of related slickenlines suggest that polygonal-like faulting occurred, particularly
along the EAFS, due to lateral spreading of the Irpinia m´ elange in the subsurface. Structural data show that the
MMFS is characterized by a higher structural maturity (slip longevity), with calcite U–Pb ages indicating the
onset of long-lasting extensional tectonics in Early-Middle Miocene time. The original results are discussed in
terms of seismotectonic setting of the study area, emphasizing the role played by both the thickness and spatial
distribution of plastic m´ elange in modulating fluid pressure and seismic faulting.
... A large, laterally extensive, polygonal fault field in the SU12 unit of the NW Guinea margin slope domain (Figs. 4,9) indicates biosiliceous sediments, with polygonal faults forming due to volume loss during dewatering and compaction (Cartwright, 1993;Xia et al., 2022). ...
The Guinea Plateau contains a ~200-million-year stratigraphic record, encompassing the mid-Cretaceous opening of the Equatorial Atlantic Gateway (EAG). Here we present new 2D seismic data to constrain the structural and stratigraphic evolution of the plateau. Seismic stratigraphic analysis reveals five megasequences of ~25-65 My duration: M1, a Jurassic syn-rift sequence with prominent seaward-dipping reflections; M2, a late Jurassic- Early Cretaceous post-rift carbonate platform; M3, a late Early Cretaceous syn-transform clastic-dominated sequence; M4, an Albian-Maastrichtian post-transform sequence; and M5, a Maastrichtian-Recent passive margin sequence with low sedimentation rates. These megasequences also contain prominent transgressive-regressive cycles of 5-10 My duration, interpreted to be the result of dynamic topography.The boundary between M3 and M4 is a major erosional unconformity documenting final continental breakup during the opening of the EAG. Above this, a pronounced Albian to Cenomanian/Turonian marine transgression resulted in marine inundation of the plateau. Structural deformation continued into the early Cenomanian along the Guinea Marginal Ridge, a potential structural barrier that restricted marine connection across the EAG. Bulk geochemical data from the shallow Guinea Plateau indicate that enhanced carbon burial in this setting was primarily driven by the deposition of reworked, oxidised organic matter during OAE, independent of gateway opening.
... Hydrocarbon fluids from the deeper sequences are likely to migrate upward through present fault systems (Xia et al., 2022), gas chimneys (McNeil et al., 2011), mud diapirs, mud volcanoes (Zhang et al., 2021), and unconformities (Levell et al., 2010). However, gas chimneys and unconformities, mud diapirs, and mud volcanoes have not yet been reported near the onshore subpermafrost GH reservoirs in the MD. ...
The Canadian Mackenzie Delta exhibits a high volume of proven sub-permafrost gas hydrates that naturally trap a significant amount of deep-sourced thermogenic methane (CH4) at the Mallik site. The present study aims to validate the proposed Arctic sub-permafrost gas hydrate formation mechanism, implying that CH4-rich fluids were vertically transported from deep overpressurized zones via geologic fault systems and formed the present-day observed GH deposit since the Late Pleistocene. Given this hypothesis, the coastal permafrost began to form since the early Pleistocene sea-level retreat, steadily increasing in thickness until 1 Million years (Ma) ago. Data from well logs and 2D seismic profiles were digitized to establish the first field-scale static geologic 3D model of the Mallik site, and to comprehensively study the genesis of the permafrost and its associated GH system. The implemented 3D model considers the spatially heterogeneously distributed hydraulic properties of the individual lithologies at the Mallik site. Simulations using a proven thermo-hydro-chemical numerical framework were employed to gain insights into the hydrogeologic role of the regional fault systems in view of the CH4-rich fluid migration and the geologic controls on the spatial extent of the sub-permafrost GH accumulations during the past 1 Ma. For > 87% of the Mallik well sections, the predicted permafrost thickness deviates from the observations by less than 0.8%, which validates the general model implementation. The simulated ice-bearing permafrost and GH interval thicknesses as well as sub-permafrost temperature profiles are consistent with the respective field observations, confirming our introduced hypothesis. The spatial distribution of GHs is a result of the comprehensive interaction between various processes, including the source-gas generation rate, subsurface temperature, and the hydraulic properties of the structural geologic features. Overall, the good agreement between simulations and observations demonstrates that the present study provides a valid representation of the geologic controls driving the complex permafrost-GH system. The model’s applicability for the prediction of GH deposits in permafrost settings in terms of their thicknesses and saturations can provide relevant contributions to future GH exploration and exploitation.
... Evidence about geological controls on gas hydrate accumulation was summarized through a combination of the fluid migration pathways from coherence slice, the reservoir from RMS amplitude attributes, and pressure-temperature. Figure 11 is a 3D display showing the occurrence of gas hydrate, the faults identified from T2 and T5 horizons, and the basement structural form interpreted from 3D seismic data. Previous studies have shown that the polygonal faults, normal faults, and volcanic activity contribute to the formation of gas hydrate, which provides the fluid migration pathways (Xia et al., 2022). Our study supports this founding about fluid migration. ...
The amplitude and coherence attributes of three-dimensional (3D) seismic data are used to confirm gas hydrate occurrence and to delineate its distribution in the Zhongjiannan basin, South China Sea. High amplitude anomalies (HAAs) are distributed above or below the regional base of gas hydrate stability zone (BGHSZ), which intersect with the bottom simulating reflectors (BSRs) or are interrupted by different types of pockmarks. The maximum amplitude attribute extracted along T1 (5.5 Ma) horizon is controlled by the widely distributed faults. The layer-bound polygonal faults (PFs) show networks of small normal faults, and the dominant orientations of PFs are similar or orthogonal to the regional tectonic faults, which provide the fluid migration pathways for gas and fluids to form HAAs. BSR shows the strong amplitude and continuous reflection where the faults or PFs can reach the BGHSZ without the influence of the pockmarks. Most of the pockmarks are related to the reactivation of faults and magmation, and some pockmarks are caused by the dissociation of gas hydrate. Around the matured pockmark, the BSR is discontinuous, and HAAs locally appear within the pockmarks. The inverted acoustic impedance profile shows obviously high values of HAAs except in pockmark zones. Partial HAAs occur above BGHSZ, and the continuity is interrupted by the pockmarks with only high values around the pockmarks. We propose that BSR, HAAs, pockmarks, and different types of faults are closely related to the occurrence and distribution of gas hydrates in the study area. This work allows us to understand the relationship between gas hydrate occurrence and accumulation with pockmarks, faults, and magmatic activities.
... Thus, these polygonal faults are ~650 m deeper than the paleo-pockmark interval (U6) (Figs. 5 and 9). Seismically resoluble polygonal faults can be initiated as shallow as 78 m blow seafloor, and most of them around the world developed in layers buried less than <700 m (Gay et al., 2004;Xia et al., 2022). This suggests that the polygonal faults in the study area could be active during and contributed to the formation of paleo-pockmarks. ...
Pockmarks are morphological expressions of fluid escape along continental margins. Identifying the underlying controls on their formation and spatial distribution is crucial for understanding the substrate fluid plumbing systems and has important implications for hydrocarbon exploration, seafloor stability and global warming. Here, we use 3D seismic reflection dataset and a machine learning approach to present the first evidence for paleo-pockmarks in the Bass Strait, southeast Australia. The paleo-pockmarks are identified in the Pelican Trough of the Bass Basin, within an interval between 130 and 300 m below present-day seafloor, corresponding to the Miocene carbonate-dominated Torquay Group. The paleo-pockmarks have depths ranging from 15 to 74 m and areas between 0.006 to 0.8 km 2 , with diameters varying between 0.1 and 1.1 km. The absence of an underlying seal-bypass system such as pipes and faults associated with these paleo-pockmarks discounts a deeper thermogenic source or a potential magmatic-driven fluid system. Rather a biogenic fluid system derived from the degradation of organic-rich layers is hypothesised to drive the paleo-pockmark formation. The seismic interval comprising the paleo-pockmarks demonstrates a distinctive seaward progradation and stepping-down configuration, indicating a forced regression. We propose this resulted in destabilisation of hydrostatic pressure triggering the creation of the paleo-pockmarks. The findings from this study shed light on pockmark formation mechanisms in shallow water sedimentary systems.
... Thus, these polygonal faults are ~650 m deeper than the paleo-pockmark interval (U6) (Figs. 5 and 9). Seismically resoluble polygonal faults can be initiated as shallow as 78 m blow seafloor, and most of them around the world developed in layers buried less than <700 m (Gay et al., 2004;Xia et al., 2022). This suggests that the polygonal faults in the study area could be active during and contributed to the formation of paleo-pockmarks. ...
The occurrence of natural hydrogen and its sources have been reviewed extensively in the literature over the last few years, with current research across both academia and industry focused on assessing the feasibility of utilizing natural hydrogen as an energy resource. However, gaps remain in our understanding of the mechanisms responsible for the large‐scale transport of hydrogen and migration through the deep and shallow Earth and within geological basins. Due to the unique chemical and physical properties of hydrogen, the timescales of migration within different areas of Earth vary from billions to thousands of years. Within the shallow Earth, diffusive and advective transport mechanisms are dependent on a wide range of parameters including geological structure, microbial activity, and subsurface environmental factors. Hydrogen migration through different media may occur from geological timescales to days and hours. We review the nature and timescale of hydrogen migration from the planetary to basin‐scale, and within both the deep and shallow Earth. We explore the role of planetary accretion in setting the hydrogen budget of the lower mantle, discuss conceptual frameworks for primordial or deep mantle hydrogen migration to the Earth's surface and evaluate the literature on the lower mantle's potential role in setting the hydrogen budget of rocks delivered from the deep Earth. We also review the mechanisms and timescales of hydrogen within diffusive and advective, fossil versus generative and within biologically moderated systems within the shallow Earth. Finally, we summarize timescales of hydrogen migration through different regions within sedimentary basins.
The occurrence of natural hydrogen and its sources have been reviewed extensively in the literature over the last few years, with current research across both academia and industry focused on assessing the feasibility of utilising natural hydrogen as an energy resource. However, gaps remain in our understanding of the mechanisms responsible for the large-scale transport of hydrogen and migration through the deep and shallow Earth and within geological basins. Due to the unique chemical and physical properties of hydrogen, the timescales of migration within different areas of Earth vary from billions to thousands of years. Within the shallow Earth, diffusive and advective transport mechanisms are dependent on a wide range of parameters including geological structure, microbial activity, and subsurface environmental factors. Hydrogen migration through different media may occur from geological timescales to days and hours. We review the nature and timescale of hydrogen migration from the planetary to basin-scale, and within both the deep and shallow Earth. We explore the role of planetary accretion in setting the hydrogen budget of the lower mantle, discuss conceptual frameworks for primordial or deep mantle hydrogen migration to the Earth's surface and evaluate the literature on the lower mantle's potential role in setting the hydrogen budget of rocks delivered from the deep Earth. We also review the mechanisms and timescales of hydrogen within diffusive and advective, fossil versus generative and within biologically moderated systems within the shallow Earth. Finally, we summarise timescales of hydrogen migration through different regions within sedimentary basins.
Along continental margins with rapid sedimentation, overpressure may build up in porous and compressible sediments. Large-scale release of such overpressure has major implications on fluid migration and slope stability. Here, we study if the widespread crater-mound-shaped structures in the subsurface along the mid-Norwegian continental margin are caused by overpressure which accumulated within high-compressibility oozes sealed by low-permeability glacial muds. We interpret 56,000 km ² of 3D and 150,000 km ² of 2D-cubed seismic data in the Norwegian Sea, combining horizon picking, well ties, and seismic geomorphological analyses of the crater-mound landforms. Along the mid-Norwegian margin, the base of the glacially-influenced sediments abruptly deepens to form 28 craters with typical depths of ∼100 m, areal extents of up to 5130 km ² , and volumes of up to 820 km ³ . Mounds are observed in the vicinity of the craters at several stratigraphic levels above the craters. We present a new model for the formation of the craters and mounds where the mounds consist of remobilized oozes evacuated from the craters. In our model, repeated and overpressure-driven sediment failure is interpreted to cause the crater-mound structures, as opposed to erosive megaslides. Seismic geomorphological analyses suggest that ooze remobilization occurred as an abrupt energetic and extrusive process. The results also suggest rapidly-deposited, low-permeability and low-porosity glacial sediments seal overpressure which originated from fluids being expelled from the underlying, high-permeability and high-compressibility biosilicious oozes.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.6710712
