ABSTRACT Northern Borneo provides a key archive of how convergent‑margin processes and drainage reorganization shaped the southern South China Sea margin from the Paleogene to the Neogene. This study integrates whole‑rock major–trace element data from Rajang–Crocker and Neogene successions in Sabah with detrital zircon U–Pb age spectra to reconstruct source‑to‑sink evolution and to evaluate the relative contribution of first‑cycle and recycled sediment sources. Paleogene to Lower Miocene formations are dominated by sand and mud‐rich submarine‑fan and slope deposits associated with the sedimentation along the evolving Proto‐South China Sea (PSCS) margin and subsequently incorporated into the northern Borneo accretionary–orogenic system, whereas overlying Neogene units preserve tide‑ and storm‑influenced fluvio‑deltaic and shallow‑marine systems within successor basins. Whole‐rock geochemistry indicates predominantly evolved upper‐crustal and recycled sedimentary components, with CIA values recording variable degrees of chemical alteration and compositional maturity among formations. Zr/Sc–Th/Sc relationships reveal variable source composition and sediment maturity, reflecting differences in zircon enrichment, recycling intensity, and sediment sorting. Detrital zircon age distributions contain recurring Early Cretaceous and Permian–Triassic populations together with variable Palaeozoic and Precambrian components, indicating persistent regional source contributions and changing proportions of inherited and recycled sediment components through time. These integrated proxies support a long‐lived mixed provenance system involving Sundaland and adjacent continental terranes, Cretaceous magmatic provinces in Borneo, recycling of older Rajang–Crocker successions, and subordinate local inputs. These results demonstrate that Paleogene–Neogene basin evolution was controlled by progressive reorganization of sediment‐routing pathways, uplift, recycling, and basin development during regional tectonic change, providing new constraints on the source‐to‐sink evolution of northern Borneo and its relationship with the southern South China Sea margin.
ABSTRACT Although detrital zircon geochronology is widely used to link sediment sources with sedimentary deposits, this method is not always effective in reconstructing specific sediment transport pathways and differentiating sedimentary recycling from first‐cycle deposition. The morphology of detrital zircon grains, including roundness, can change during transport in sedimentary systems as a result of mechanical abrasion, potentially enabling additional constraints in reconstructing ancient patterns of sediment routing. Integration of detrital zircon morphology with U–Pb geochronology suggests the Paleogene Raoyang Sag, Bohai Bay Basin, primarily received sediments from four sources: the northern margin of the North China Craton (NCC), Fuping Region, Taihang Mountain and Wutai Mountain. Kernel density estimation reveals potential bimodal roundness distributions within the 100–200 Ma, 200–500 Ma and 1700–2000 Ma age fractions, indicating multiple sources with distinct sediment transport histories. Relatively less rounded detrital zircons in these three U–Pb age fractions were interpreted to have been transported directly (first cycle) from respective crystalline sources to the Raoyang Sag. In contrast, anomalously rounded detrital zircons in these three age fractions are interpreted to have been originally sourced from more distant Mesozoic intrusive rocks, Palaeozoic igneous rocks and Paleoproterozoic metamorphic rocks that crop out in the northern margin of the NCC. Sediments from these more distant sources were eroded during the collision of the NCC and Siberia Plate, transported via aeolian and/or fluvial processes, and deposited in the Taihang Mountain area before being re‐exhumed during the Paleogene uplift of Taihang Mountain. This sedimentary recycling of older aeolian/fluvial sediment contributed to a higher degree of roundness relative to first‐cycled sediment sources. This study suggests that morphological analysis of detrital zircon grains, including roundness, sphericity, aspect ratio and equivalent spherical diameter, when integrated with U–Pb geochronology, can provide additional constraints in reconstructing ancient sediment routing systems.
ABSTRACT We use offshore seismic reflection data combined with published geologic and geodetic studies to examine the timings and styles of deformation around the South Caspian Basin, an enigmatic aseismic ‘block’ within the Arabia‐Eurasia collision that moves relative to its surroundings. We show that the presently active tectonics of the South Caspian began relatively recently, likely in the range 1.8–2.4 Myr, with components of both shortening and lateral‐slip along its northern and western edges. Along the northern margin (the Absheron Ridge), structures related to the active tectonics are superposed on an older tectonic configuration related to north–south shortening and subduction of the South Caspian, ending in the Miocene at ~6 Ma. In the west (Kura margin), the present‐day oblique right‐lateral transpression began at 1.8–2.4 Myr, replacing an earlier phase of shortening. The tectonic history is hence one of initial Miocene shortening and northward‐directed subduction of SCB basement, followed by a hiatus in deformation along the Absheron ridge, which we infer to result from a switch to oroclinal bending in the ranges surrounding the basin until 1.8–2.4 Myr. At that time the active tectonic configuration was established, and the basin began to be expulsed to the northwest. This change led to the development of major transpressional fault systems along its north, east, and southern margins, the likely resumption of underthrusting of SCB basement northward beneath the Absheron ridge, and the start of underthrusting and incipient subduction beneath the Kura basin along its western margin. The various short‐lived stages in the destruction of the South Caspian have potential for insight into the late stages of basin closure and the transition to mature continental collision.
ABSTRACT This study investigates the footwall crest and fault scarp geomorphology of crustal‐scale fault blocks developed during Late Jurassic rifting on the Greater Tampen Spur, northern North Sea, using 3D seismic data and 84 exploration wells. The Snorre and Visund footwalls represent contrasting geomorphic end members. Snorre is characterised by a broad, plateau‐like erosion surface that truncates tilted Triassic strata and its fault scarp comprises degraded slopes, centrally developed U‐shaped gullies and canyons and hanging‐wall rider blocks developed in an area of overlapping fault segments. The Visund footwall, in contrast, is convex‐up and asymmetric, locally preserves Late Jurassic strata at its crest and is associated with a steep fault scarp containing structurally guided V‐shaped gullies and canyons, larger U‐shaped canyons and a large submarine landslide. These contrasting morphologies reflect different balances between fault‐related uplift, regional subsidence and the timing and duration of drowning. At Snorre, large displacement on the Snorre–Zeta Fault, combined with additional uplift from west‐dipping faults bounding the Marulk Basin, kept the footwall at shallow levels long enough for prolonged wave ravinement. At Visund, local footwall uplift was offset by hanging‐wall subsidence related to the Snorre–Zeta Fault system and by greater regional tectonic subsidence toward the North Viking Graben. This lower structural position led to earlier drowning, favouring submarine diffusive hillslope retreat, repeated mass wasting and preservation of fault‐scarp incisions. Together, these results show that displacement history, structural position within a fault network, drowning history, bedrock lithology, secondary faulting and geomorphic preservation collectively govern footwall and fault‐scarp morphology in marine rift basins. Recognising these controls improves reconstruction of sediment source areas and routing pathways and provides a more robust basis for predicting syn‐rift depositional architecture in adjacent hanging‐wall basins.
Pockmarks are geomorphological depressions observed in diverse marine environments, typically associated with fluid release from subsurface reservoirs. In addition to seafloor features, buried paleo-pockmarks offer valuable records of past fluid escape events. However, the processes, fluid types and conditions controlling their formation and recurrence remain poorly constrained. This study examines potential subsurface fluid sources and pathways that contribute to the cyclic formation of a prominent pockmark field located on the southwestern Chatham Rise, offshore New Zealand. Previous geochemical analyses have revealed no evidence for biogenic or thermogenic methane in the shallow subsurface, necessitating alternative interpretations of the fluid source(s). Here, we use quasi-3D multichannel seismic reflection data to examine the relationship between subsurface fluid flow pathways and spatio-temporal pockmark distribution. A polygonal fault system (PFS), characterized by low fault network connectivity and preferential fault orientations, indicates the influence of the regional stress field. Additionally, a distinct, discordant reflection with relatively high-amplitude, interpreted as a diagenetic front, is hosted within the PFS. Vertically extensive faults extend above the PFS and align spatially with basement faults, forming West-East trending half-grabens that may provide pathways for buoyancy-driven fluid migration. However, spatial pattern analysis reveals no statistically significant spatial association between pockmarks and faults, indicating primarily diffuse fluid flow in the upper subsurface. Generally, the upslope extent of pockmarks on the Chatham Rise appears to be lithologically controlled and coincides with the limit of the PFS in underlying strata. Recurring pockmark formation is interpreted to reflect a combination of compaction-related dewatering during polygonal faulting and silica diagenesis, coupled with deeply sourced, possibly CO2-rich fluids from subducted limestones migrating along basement structures. These findings are combined into a conceptual model of the subsurface fluid flow system, offering new insights into the controls on recurring pockmark formation in non-hydrocarbon settings.
