Stratigraphic Correlation Research Articles

Identification of Astronomical Cycles in Fine‐Grained Rocks and Their Application in High‐Resolution Stratigraphic Correlation: A Case Study of the Fourth Member of the Shahejie Formation in the Leijia Area, Western Sag of the Liaohe Depression, China

ABSTRACTIn the Western Sag of the Liaohe Depression within the Bohai Bay Basin, the fourth member of the Shahejie Formation (E2s4) in the Leijia area is characterised by lacustrine fine‐grained sedimentary rocks, primarily composed of clay, felsic minerals, carbonates and analcime. These rocks serve as the key hydrocarbon reservoirs in the region. However, their complex lithology and rapid lateral variations lead to significant reservoir heterogeneity, posing challenges for the identification of favourable reservoirs. This study addresses these challenges through cyclostratigraphic analysis to enhance stratigraphic resolution and improve reservoir prediction. We employed time‐series analysis, high‐precision U–Pb carbonate dating and gamma ray (GR) logging data to identify astronomical cycles within the E2s4 fine‐grained mixed rocks. Spectral analysis of GR data from wells lei93, lei37, lei53 and lei14 revealed signals consistent with standard eccentricity, obliquity and precession cycles. Using the 405 kyr long eccentricity cycle for astronomical tuning, we established a detailed chronostratigraphic framework for the E2s4, constrained by U–Pb dating results from several wells. In total, we identified six long eccentricity cycles (405 kyr) and approximately 19 short eccentricity cycles (~129 kyr). The correlation between Earth's orbital cycles and high‐frequency sequences allowed us to construct a refined stratigraphic division and correlation framework at an eccentricity timescale. This refined framework offers a clearer understanding of reservoir distribution, greatly enhancing hydrocarbon exploration accuracy in the Leijia area. Moreover, our findings highlight the significant role of cyclostratigraphy in guiding future oil and gas exploration efforts in the Bohai Bay Basin, showcasing its potential application in broader geological contexts.

Discovery of Hemeroscopus baissicus (Odonata, Anisoptera, Hemeroscopidae) from the Lower Cretaceous Naijiahe Formation (Ningxia, NW China) and its stratigraphic significance

Several newly collected dragonfly wings from the Lower Cretaceous Naijiahe Formation (Kangjiawan locality, Tongxin County, Ningxia Hui Autonomous Region, NW China) have been identified as belonging to the widely distributed species Hemeroscopus baissicus, found in North China and South Korea at similar palaeolatitudes. This species shows potential for stratigraphic correlation. The findings suggest that the Shahai-Fuxin Formation (western Liaoning), Lushangfen-Xiazhuang Formation (western Beijing), Madongshan-Naijiahe Formation (Ningxia), and Zhonggou Formation (Jiuquan Basin) are likely of comparable ages.

Reconstruction of high-resolution paleomagnetic variations in the middle Gauss chronozone, including the upper and lower boundaries of the Mammoth reversed subchronozone

AbstractIn this study, we provide paleomagnetic records, including the upper and lower boundaries of the Mammoth reversed subchronozone, reconstructed from a continuous outcrop of the upper marine Pliocene in the southernmost part of the Boso Peninsula, which is more than 200 m thick. In this interval, the Mammoth reversed subchronozone was recognized in an interval of approximately 50 m thickness, including a polarity transition zone at its lower boundary of approximately 10 m thickness. Simultaneously, the upper boundary showed no polarity transition zone and a rapid polarity reversal, suggesting a probable lack of strata. Several significant variations were recognized in the paleomagnetic directions in the middle Gauss chronozone, some of which may qualify as new geomagnetic excursions. The relative paleointensities (RPIs) obtained in this study are consistent in their character of change with those reported from deep-sea cores in the distant Caribbean Sea and the equatorial Pacific, indicating the potential of stratigraphic correlation using RPI. The RPI around the lower Mammoth boundary was significantly attenuated compared to the average of the entire section. On the other hand, the virtual geomagnetic pole (VGP) path of the lower Mammoth boundary shows a rapid shift from the southern hemisphere to the northern hemisphere during transition. This movement passes through regions affected by non-axial dipole fields. Following this, the RPI shows a recovery trend, and the VGP stabilizes in the southern hemisphere, forming clusters that align with records from Italy and Hawaii. This sequence offers significant insights into changes in the axial dipole field during geomagnetic polarity reversals. Graphical Abstract

Correlation of the Upper Pliocene sediments of the Dnipro-Donetsk Depression based on palynological data

The problems of intra- and inter-regional correlations have always been the most difficult in stratigraphic studies. Particular difficulties arise when comparing same-age subaerial continental sediments that are depleted in palaeontological remains. The spore-pollen analysis, which is a component of the palynological method, is most effective in stratigraphic dissection and correlation of subaerial sediments, since pollen and spores, with few exceptions, are almost the only paleontological remains contained in fossil soils and intersoil clays and loess. The author has developed the methodological approaches to stratification and correlation of continental Pliocene and Pleistocene sediments of the Ukraine based on palynological data (Sirenko, 2017). These methods are applied in the presented work. Due to the changes in the International Stratigraphic Scale, including a change in the position of the lower boundary of the Quaternary period, it became necessary to modify the existing stratigraphic schemes of Cenozoic sediments. Therefore, there is a need to obtain new representative materials on sediment characteristics, as well as to solve the problems of intra- and interregional correlations. At the present stage of research on the Upper Cenozoic continental sediments of Ukraine, the least studied by the palynological and palaeopedological methods are Pliocene fossil soils and intersoil clays of the central and southeastern parts of the Dnipro-Donetsk depression. The presented paper is devoted to solving the issues of correlation of Upper Pliocene sediments of the Central Graben of the Dnipro-Donetsk Depression and its junction with the North-Western part of the Donetsk folded structure. Two sections (well 11 and the outcrop near Kamianka village) are located within these areas. The analysis of materials on the palynological characterization of the Kyzylyr and Bogdanivka climatoliths of these sections allowed us to identify the general patterns of the spore-pollen complexes that characterize them. The identified common patterns of the complexes from the Kyzylyr and Bogdanivka climatoliths can serve as a basis for comparing sediments of the same age located in different parts of the study area and for interregional correlations. The individual features of the described spore-pollen complexes are associated with different geomorphological and geographical locations of the compared sections. It is concluded that it is necessary to take into account the geographical and geomorphological location of the sections when performing stratigraphic and correlation constructions based on the palynological data. The efficiency of the palynological method for stratigraphic and correlation constructions is proved by comparing the sediments of two sections. The obtained conclusions on the correlation of the sediments of these sections are confirmed by the materials of palaeopedological studies. Key words: Upper Pliocene; fossil soils; stratigraphy; palynological method; spore-pollen complex; Ukraine.

High-precision age constraint for the Xiyingzi Bed of the Jiufotang Formation in western Liaoning, Northeast China

The Jehol Biota includes exceptionally well-preserved fossils that are major components of Early Cretaceous land ecosystems. The youngest example of the Jehol Biota occurs in the Jiufotang Formation, which potentially records palaeoenvironmental factors triggering evolutionary turnover. However, the lack of stratigraphic correlations and uncertain age horizons for many fossil taxa lead to conflicting interpretations of events. This study describes a new significant fossiliferous bed (Xiyingzi Bed) from the upper Jiufotang Formation of the Baomayingzi-Yuanjiawa outcrop in western Liaoning, Northeast China. High-precision CA-ID-TIMS U-Pb analysis of a tuff sample from the Xiyingzi Bed provides an age of 121.272 ± 0.040/0.068/0.15 Ma, representing the first reliable age for the upper Jiufotang Formation in western Liaoning.Vertebrate fossils preliminarily reported from this bed include the confuciusornithid and enantiornithine birds, the istiodactylid pterosaur, the non-hadrosaurid iguanodontian dinosaur, the long-necked choristoderan reptiles, the sinemydid turtles, and the polyodontid and sinamiid fish. These fossils were previously reported from the lower horizons, indicating stable development of the late Jehol Biota. New results from the Xiyingzi Bed provides a glimpse of the late Jehol biota before transforming into a typical mid-Cretaceous biota in western Liaoning. Systematic biostratigraphic and chronostratigraphic analysis of the Xiyingzi Bed helps the evolutionary interpretations of the late Jehol Biota and the correlation of the Jiufotang Formation within different basins of western Liaoning.

Palaeoenvironmental interpretation and isotope stratigraphy of the Campanian–Danian successions in the Zagros Foreland Basin (Kabir Kuh, Lurestan, Iran)

The successions of the Gurpi Formation and the lower Pabdeh Formation were examined through analyses of lithology, sequence stratigraphy, stable isotope stratigraphy, and ichnofossils in the Jahangir Abad and Abhar sections of the Kabir Kuh anticline within the Lurestan Zone. Stratigraphic correlation with the well-dated Gandab section, located within the same anticline, indicates a late Campanian to early Danian age for these successions. This correlation further confirms the presence of notable carbon isotope excursions associated with the Campanian-Maastrichtian Boundary Event (CMBE) and Mid-Maastrichtian Event (MME). Field observations, along with sedimentological and paleontological analyses, suggest that the Kabir Kuh area was situated within the fore-bulge of the Zagros foreland basin during the Late Cretaceous. Changes in lithology, fossil content, and ichnofacies indicate a significant decrease in water depth at the end of the Campanian and the beginning of the Maastrichtian. This interval contains shallow marine macrofossils, including oysters (mainly Lopha), benthic foraminifers, and fossil debris traces, indicative of a high-energy environment. In contrast, shallow-water facies are not recorded within the middle and late Maastrichtian sequences. These sequences are composed of pelagic mud-dominated facies containing deep-sea ichnofossils, indicating a rapid increase in water-depth during the middle–late Maastrichtian. The observed late Campanian to early Maastrichtian shallowing is associated with the development of the Zagros fore-bulge, while the subsequent deepening and significant sediment deposition during the mid to late Maastrichtian are attributed to the subsidence of the basin. This research re-evaluates and refines the existing sequence stratigraphic and sedimentary models of the Zagros foreland basin, offering new perspectives on its geological evolution.

A Quaternary aminostratigraphy for the Pannonian Basin: The competing influences of time, burial depth and temperature in deep-core material

Long-term terrestrial archives of Quaternary climate change illustrate how global changes affect regional climates, but correlation of terrestrial deposits to global records can be challenging due to a lack of material for radiometric dating. The Pannonian Basin (Hungary) contains large river basins, with near-continuous Quaternary deposits ∼600 m in depth. This study tested the IcPD (intra-crystalline protein degradation) approach to amino acid geochronology using bithyniid snail opercula to date deep-core material in geothermally warm regions. Material from seven fully-cored boreholes was collected from four sub-regions: the Körös and Jászság basins, Makó Trough and Békés Basin. IcPD increased with age until approximately 2.3 million years ago, generally supporting stratigraphic correlations previously made between the boreholes. IcPD was consistent between different boreholes within the same sub-region. However due to the steep geothermal gradient in this region, IcPD was systematically different between sub-regions that had different sedimentation rates. Equivalently aged samples buried more deeply had higher IcPD levels, indicating a greater geothermic effect. This provides an insight into how variations in burial temperature can affect protein decomposition within a deeply-buried (>80 m) fossil over geological time, and demonstrates the importance of understanding the geothermal setting for amino acid geochronology. This study shows the utility of IcPD to correlate terrestrial deep-core sediments over the Pleistocene.

The Scriniodinium crystallinum dinoflagellate cyst zone in the Middle–Upper Oxfordian, Upper Jurassic, Ilimananngip Nunaa (Milne Land), East Greenland

The biostratigraphy of the Jurassic in East Greenland is historically based on macroscopic fossils. Stratigraphy based on palynomorphs (spores, pollen and dinoflagellate cysts) has progressed more slowly and sporadically. The Scriniodinium crystallinum dinoflagellate cyst Zone is identified in middle – upper Oxfordian strata of Ilimananngip Nunaa (Milne Land), central East Greenland. The lower boundary is defined by the last occurrence of Trichodinium scarburghense in the Cardioceras tenuiserratum ammonite Zone. The upper boundary is defined by the last occurrence of S. crystallinum in the uppermost Amoeboceras rosenkrantzi ammonite Zone. However, the subzonal division of the S. crystallinum Zone recorded in North-West Europe is not identified in Greenland. Eighteen characteristic dinoflagellate cyst events are considered stratigraphically significant and useful in East Greenland. Fifteen of these events provide an informal, detailed stratigraphical subdivision of the S. crystallinum Zone into 10 subunits. Identification of the zone is an addition to the previously defined upper Bathonian – middle Oxfordian zonation, where the uppermost palynostratigraphical event was recorded to be the last occurrence of T. scarburghense. With this study, the correlation of dinoflagellate cyst and ammonite stratigraphy in the lower and middle Oxfordian is slightly modified. The S. crystallinum Zone documented here, in combination with the zonation used for the stratigraphy of the Blokelv-1, Rødryggen-1 and Brorson Halvø-1 cores of the Upper Jurassic to Lower Cretaceous, completes the dinoflagellate cyst stratigraphy of the marine Jurassic in East Greenland. Together with previous studies of spores and pollen in less marine units, the first complete palynological Jurassic stratigraphy is thus established for the Jurassic succession in East Greenland.

Occurrence of Mafic Rocks within Ediacaran Strata in the Aksu Region, NW Tarim Craton, and its Geological Implications

AbstractThe Tarim Craton is an ancient Precambrian continental block, and detailed knowledge of its thermo‐tectonic history is crucial for understanding the early history of continental evolution. Abundant layered mafic rocks, which have commonly been regarded as basalts, occur within the Ediacaran Sugetbrak Formation (Fm.) in the Aksu region of the northwestern Tarim Craton. Clear intrusive features have now been discovered, including mafic rocks truncating Ediacaran sedimentary layers, exhibiting an intrusion‐baked margin where they interact with both the overlying and bottom wall rocks, and displaying a fine‐grained transition zone from their interior to their margins. The new findings demonstrate that these mafic rocks within the Aksu Ediacaran strata were not erupted basalts but instead are intrusive diabase dykes. Therefore, these mafic rocks cannot be used to constrain the timing of the Sugetbrak Fm. in the Aksu area, nor as marker layers for regional stratigraphic correlation. Furthermore, the Ediacaran thermo‐tectonic evolution in this region, deduced from the assumption that the mafic rocks are lavas, needs to be revised.

The Paleogene Forebulge Carbonate Banks, Zagros Foreland Basin, Northern Iraq: their Paleogeography, Basin Evolution, and Economic Implications

The Paleogene sequence of Zagros foreland basin NE Iraq during the Late Paleocene- Middle Eocene is punctuated by linear and disconnected chains of carbonate bank-ramp associations. These carbonate units had developed over the NW-SE trending Paleogene basin forebuldge. Discussion of origin, facies type, and stratigraphic architecture of these banks and associated facies was fully covered by the first part of this research project. In this part the chronostratigraphic synthases of the sequence, the paleogeography, and basin evolution is examined as an integral part of the investigation of the evolution of the Paleogene Zagros foreland basin. Research methods include regional stratigraphic correlation, and biostratigraphic data compilation to infer the chronostratigraphic sequence of the events. The paleogeographic facies mapping and basin history are reviewed accordingly. Research data are collected from 15 master surface sections. In addition to the re-examination and re-interpretation of 40 previously studied surface and subsurface well logs, which are compiled for basin-wide study and regional paleogeographic mapping. The analysis of the compiled biostratigraphic data shows that the inferred age of the associated stratigraphic units is as follows: Sinjar Formation. (E. Thanetian – L. Ypresian), Khurmala Formation (Ypresian - E. Lutetian), Kolosh Formation (Daian -Thanetian), and Aaliji Formation (Danian - Ypresian). Based on this chronostratigraphic synthesis, the basin forebulge history during the Paleogene period is divided into 5 stages: the Pre-bank, Early Bank Development, Bank-ramp Development, Back-bank Lagoon, and Lagoonal dolomitization stage. The paleogeography and paleofacies maps of each stage is discussed in terms of the basin forebulge evolution. An alternative hydrocarbon play of the forebulge-controlled Paleogene sequence is discussed, with a case study from the Sufaiyah oil field of northwest Iraq.

Pleistocene glacial advances and exposure age scatter in the Olympus Range, Antarctica: A study of cosmogenic 36Cl/3He in dolerites and 10Be in sandstones

In three cirques in the western Olympus Range of the McMurdo Dry Valleys, Antarctica, previous advances of cirque glaciers are recorded by a sequence of three drifts in each of the cirques. We dated drift limits and the deposits on modern glaciers in two of these cirques, Dean and Dipboye, via cosmogenic 3He in pyroxene from 41 dolerite boulders, 36Cl in pyroxene from 12 of those dolerites, and 10Be in quartz from 11 sandstone boulders. Exposure age scatter is high on all deposits. The 3He exposure ages across all deposits range from ∼35 to ∼2300 ka and 10Be exposure ages range from ∼7 to ∼435 ka. Coupled 36Cl/3He from dolerites support constant exposure with erosion for nine of the 12 samples, while the other three might have experienced complex exposure-burial histories. Due to the mesa-butte topography and slow bedrock erosion rates, nuclide inheritance is the primary cause of age scatter in dolerites, accounting for >1 Myr of exposure age error. Mean exposure ages from sandstones are 2–7 times younger than those from dolerites for the same deposits, indicating that inheritance is less common in sandstones in this region. Weathering analyses of sandstone boulders show an increase in average siliceous crust thickness and rock strength with deposit age, an example of case hardening. Based on both relative and exposure age dating, drift age increases with distance from the modern glaciers in both Dean and Dipboye cirques, with three advances during the past <700 ka. However, due to high exposure age scatter, it cannot be determined if the three drifts are temporally correlated across the two cirques and therefore the drifts might record different glacial advances in Dean Cirque vs. Dipboye Cirque despite the apparent stratigraphic correlation of the drifts. This study has implications for drift depositional processes of cold-based glaciers and the importance of source-bedrock lithology and geomorphology on nuclide inheritance in Antarctica.

New zircon U-Pb age of the top Duoni Formation, Basu County: constraits on the collision between Qiangtang and Lhasa blocks in Eastern Tibet

The Duoni Formation is widely distributed along the Bangong-Nujiang suture belt and surrounding blocks in Tibet, serving as a key sedimentary record of the collision between the Qiangtang and Lhasa blocks. The upper sections of the formation typically contain andesite, volcanic rocks and tuff offering potential for precise stratigraphic correlations across the suture belt. The Duoni Formation in the central and western belt has been well-constrained geochronologically through zircon U-Pb dating; however, the insufficient age constraints on Duoni Formation in eastern Tibet hinder effective stratigraphic correlation and limit the understanding of the timing of this collision. Building on prior stratigraphic and paleontological studies, we collected three tuff samples from the upper Duoni Formation at the Wada coal mine section in Basu County, eastern Tibet. Zircon U-Pb dating was used to determine the age of the Duoni Formation, yielding results of 112.8 ± 1.0 Ma for sample XZ01, 111.48 ± 0.37 Ma for sample XZ03, and 110.95 ± 0.41 Ma for sample XZ05. These absolute ages correspond with early Albian and are generally consistent with those absolute ages from the central and western suture belt. Our study therefore suggests the similar timing for the Qiangtang-Lhasa collision across the whole Bangong-Nujiang belt.

FACIES PARTITIONING AT REGIONAL AND FIELD SCALES IN THE BARREMIAN KHARAIB‐2 CARBONATES, UAE

Carbonates in the Lower Cretaceous (Barremian to early Aptian) Kharaib Formation are reservoir rocks at giant oil fields in the UAE and Qatar. The Barremian Kharaib‐2 member (K60), the focus of this study, is in general composed of a regionally continuous succession of high‐energy, shallow‐water limestones bounded above and below by “dense” low‐energy mud‐rich strata. Despite several decades of research, conventional carbonate facies classification schemes and resulting facies groupings for the Kharaib‐2 member have failed to show a statistically acceptable correlation with core‐ and log‐derived petrophysical data. Moreover, sedimentary bodies potentially responsible for dynamic reservoir heterogeneities have not clearly been identified. This paper proposes a standardized facies classification scheme for the Kharaib‐2 carbonates based on vertical facies proportion curves (VPCs) and variogram analyses of core data to construct stratigraphic correlations at both field and regional scales. Data came from 295 cored wells penetrating the Kharaib‐2 member at ten fields in the on‐ and offshore UAE. Thin, dense intervals separating reservoir units were adopted as fourth‐order transgressive units and were used for stratigraphic correlation. Field‐scale probability maps were used to identify sedimentary bodies such as shallow‐water rudistid shoals.Regional stratigraphic correlations of the Kharaib‐2 member carbonates based on the VPCs identified variations in depositional environments, especially for the lower part of the reservoir unit; depositional facies at fields in the SE of the UAE were interpreted to be more distal compared to those at offshore fields to the NW. At a field scale, the VPCs failed to identify significant lateral variations in the carbonates. However, variogram analyses of cored wells showed spatial concentrations of specific facies in the inner ramp domain which could be correlated with high‐energy depositional bodies such as shoals dominated by rudist debris. The bodies were sinusoidal in plan view with lengths of up to 8 km and widths of ca. 1 km. Although similar‐shaped bodies with these dimensions have been reported from other carbonate depositional systems, they have not previously been reported in the Kharaib Formation. At a regional (inter‐field) scale, the stratigraphic correlation of standardized sedimentary facies remains problematic; however, mapping of facies associations and their relative proportions relative to their environments of deposition demonstrated new patterns for the stratigraphic architecture of the Kharaib‐2 member in the UAE.

A new Re-Os age constraint informs the dynamics of the Great Oxidation Event

Abstract The early Paleoproterozoic (ca. 2.5–2.2 Ga) represents a critical juncture in Earth history, marking the inception of an oxygenated atmosphere while bearing witness to potentially multiple widespread and severe glaciations. Deciphering the nature of this glacial epoch and its connection with atmospheric oxygenation has, however, proven difficult, hindered by a reliance on disputed stratigraphic correlations given the paucity of direct radiometric age constraints. Nowhere is this more acute than within the South African Transvaal Supergroup: Here, while the loss of oxygen-sensitive mass-independent sulfur isotope fractionation (S-MIF) has been reported from both the Duitschland and Rooihoogte formations, divided opinion surrounding the time-equivalence of these units has prompted authors to argue for vastly different oxygenation trajectories. Addressing this debate, we present a depositional Re-Os age (2443 ± 33 Ma) from diamictite samples preserved in drillcore of the upper Duitschland Formation. The 100-million-year separation between the Duitschland Formation and its previously presumed equivalent reveals at least two isolated disappearances of S-MIF, requiring that the Great Oxidation Event was dynamic and proceeded via discrete oxygenation episodes whose structure remains incompletely understood. Importantly, our revised framework aligns the lower Duitschland diamictite with the low-latitude glacigenic Makganyene Formation, supporting hypotheses of widespread regional, and potentially global, early Paleoproterozoic glaciation.

Late Ediacaran to Early Cambrian stratigraphic correlation and its geological implications in the northwestern Sichuan Basin: insights from phosphorus, isotopes, and small shelly fossils

The characteristics of elements, isotopes, and small shelly fossils were investigated for Late Ediacaran to Early Cambrian stratigraphy division and to discuss their geological implications in the northwestern Sichuan Basin. The results reveal that small shelly fossils can be detected in the high-phosphorous section, with the concentration of phosphorus mainly ranging from 2% to 8%, suggesting that this interval belongs to the Early Cambrian, which is also consistent with the carbon isotopic composition results. In addition, the Early Cambrian is denudated in the Sichuan Basin due to tectonic movement, and the characteristics of some isotopes and small shell fossils are different from those in other basins. It can be proposed that P content can support the recognition of lithological boundaries, and the high phosphorus content can be used as a reference to identify the top and bottom boundaries of the Maidiping Formation in the study area. According to the elemental compositions in the Ediacaran Dengying Formation, the variations in Si, Al, Fe, and K contents are similar in the platform area and rift area, suggesting that the third and fourth member of the Dengying Formation are also developed in the Deyang–Anyue Rift. The results suggest that both the Deng-4 member and Maidiping Formation feature contemporaneous deposition of different facies in the northwestern Sichuan Basin. The strata consist of shale intercalated with thin carbonate rock deposits in the Deyang–Anyue Rift, while carbonate rock deposits in the platform. The Deyang–Anyue Rift expanded gradually in the Late Ediacaran and eventually filled in the Early Cambrian. The data in this study illustrate that elemental compositions, isotopes, and small shelly fossils can be combined to correlate the Late Ediacaran to Early Cambrian strata and provide new evidence for Deyang–Anyue Rift evolution. The results offer some new insights for deep oil and gas exploration in the Sichuan Basin and for the tectonic–depositional–environmental–biological synergistic evolution in the Late Ediacaran to Early Cambrian transition.

Tectonic setting and Pan-African structural evolution of the western Saldania Belt, South Africa

Abstract The western Saldania Belt records the closure of the Adamastor Ocean and amalgamation of southwest Gondwana in the latest Neoproterozoic and early Phanerozoic, but the geodynamic setting and evolution of the belt remains controversial. Regional mapping and the integration of structural data presented in this paper document the juxtaposition of domains with distinct fabric development and kinematics. Structures record Pan-African strains and a strike-slip dominated sinistral transpression during southeast-directed subduction and convergence at low angles to the continental margin. Two main, structurally overlying domains – an upper and a lower domain – can be distinguished. Rocks of the upper domain record the partitioning of the transpressional strain into (1) broad regions of more or less upright, north to northwesterly-trending folds (F2) that record horizontal, mainly coaxial, east-northeast to west-southwest directed shortening at high angles to the continental margin, and (2) the northwesterly-trending, sinistral strike-slip Colenso Fault Zone that accommodates the margin-parallel, non-coaxial component of deformation between ca. 555 and 520 Ma. The strike-slip partitioning was promoted by strain localisation into synkinematic plutons of the Cape Granite Suite. In contrast, rocks in the pervasively transposed, mélange-like lower domain in the central Swartland region record episodes of vertical, coaxial shortening alternating with non-coaxial top-to-the-west and -northwest thrusting. The coaxial shortening strains relate to the thickening and gravitational loading of the succession in response to thrusting and tectonic underplating. Non-coaxial strains denote episodes of seismic slip during underthrusting. The different fabric domains are interpreted to represent a section through a fore-arc region, from the deeper level accretionary prism (lower domain) to the overlying, folded fore-arc basin succession (upper domain). Regional-scale klippen structures indicate the transfer of lower-domain phyllites into the overlying fore-arc sequence. The proposed fore-arc setting of the Saldania Belt suggests the subduction of the Adamastor Ocean below the leading edge of the Kalahari Craton. This challenges stratigraphic and structural correlations between the Saldania Belt and the Gariep Belt to the immediate north.

Regional variance in alluvial sedimentation and revised stratigraphy of the Klipheuwel Group and Franschhoek Formation

Abstract The siliciclastic sediments of the Klipheuwel Group mark the transition from Pan-African tectonism and amalgamation of Southwest Gondwana to the shallow marine deposits of the Cape Supergroup in the Western Cape. The rocks are preserved in a number of seemingly isolated depositories and previous studies have mainly focused on selected occurrences. The lack of any integration of regional sedimentological or structural characteristics has, to date, resulted in only tentative stratigraphic correlations and subdivisions of the Klipheuwel Group. Lithological and structural data from the Klipheuwel Group indicate at least two separate depocentres that accommodated the post Pan-African peneplanation of the Saldania Belt and clastic detritus in distinctly different palaeoenvironments. A northern depocentre can be distinguished from a southern depocentre, each characterised by distinct architectural elements and facies associations that reflect topographic and structural controls. The northern depocentre, including Klipheuwel Group occurrences at Eendekuil, Redelinghuys and Elands Bay, show laterally persistent braided fluvial facies associations that developed multi-storey superimposed ‘braided sheet’ deposits. Here, the rocks show gentle dips and thicknesses range from 300 to 450 m. The southern depocentre, including the Klipheuwel and Klapmutskop localities, are characterised by much larger thicknesses (up to &amp;gt;2 000 m), steep dips of the rocks and laterally discontinuous braided fluvial facies associations that developed staggered channelised braided deposits. The lateral continuity of fluvial facies in the northern depocentre reflect sedimentation on a peneplained basement. The larger thickness, steep dips and strongly channelised deposits in the southern facies, in contrast, indicate deposition in actively subsiding half-graben structures that reactivated basement faults. The spatially closely associated Franschhoek Formation shares numerous characteristics with the Klipheuwel Group but preserves Pan-African strains similar to that of the underlying Malmesbury Group, that may indicate its formation as compressional piggyback basins with synorogenic sedimentation.

Sparse-spike seismic inversion with semismooth newton algorithm solver

Seismic prospecting has been widely used in the exploration and development of underground geological resources, such as mineral products (e.x., coal, uranium deposit), oil and gas, groundwater, and so forth. Seismic impedance is a physical characteristic parameter of underground formation, which can be used in lithologic classification, rock characterization, stratigraphic correlation, and further mineral reservoir prediction, reserve estimation, and so forth. To estimate impedance from seismic data, one must perform reflectivity series inversion first. Under a simple exponential integration transformation, the reflectivity series can give the final estimated impedance. Sparse-spike seismic inversion is the most common method to obtain reflectivity series with high resolution. It adopts a sparse regularization to impose sparsity on reflectivity series. From sparse reflectivity series, the final estimated impedance has blocky features to make formation interfaces and geological edges precise, which is very important to accurately delineate the distribution range of mineral resources. The development of sparse-spike seismic inversion is still facing major challenges of fast optimization algorithms in real-life application, especially for massive seismic data in 3D case. Semismooth Newton algorithm (SNA), which is a second order mehtod and has super-linear, even quadratic convergence rate, is used to solve sparse-spike seismic inversion. The proposed algorithm has been compared with common used algorithms through a synthetic seismic trace and a 3D real seismic data volume. The results show that the proposed algorithm has faster convergence rate and fewer computation time. It provides a new effective algorithm to solve sparse-spike seismic inversion.

A Carboniferous to Permian tectono-paleogeographic reconstruction for the southernmost Central Asian Orogenic Belt

The Central Asian Orogenic Belt was formed by the subduction to closure of the Paleo-Asian Ocean (PAO). However, it is highly controversial about the closing time of the PAO, especially its middle segment in the northern Alxa orogenic belt (NAOB). In this study, the new and published zircon U–Pb and Hf data for the Carboniferous to Permian sediments across the NAOB have been integrated to reply the above problem. The depositional ages have been constrained as the Carboniferous to Permian by the detrital zircon ages, fossil assemblages and stratigraphic correlation. The Carboniferous sandstones are dominated by the Paleozoic zircons (mainly around 380–510 Ma) with a few Precambrian zircons. The late Cambrian to early Carboniferous zircons with positive to slightly negative εHf(t) values were probably sourced from the orogen itself. The early Paleozoic zircons with slightly to extremely negative εHf(t) values and the late Archean to Paleoproterozoic zircons were likely derived from the surrounding cratonic blocks in the south. For the Permian samples, the Carboniferous to Permian age signal is enhanced. The Permian zircons yield similar age peaks around 278–279 Ma and similar εHf(t) values, and thus shared a similar source. Thus, the Carboniferous to Permian sediments received detritus across the PAO, indicating the closure of the PAO. Subsequently, the NAOB entered into an extensional setting based on the detrital zircon age patterns, rift-related volcanic rocks and basin analysis. Finally, a tectono-paleogeographic reconstruction from the Carboniferous relic sea and marine transgression to Permian marine regression-transgression-regression with crustal extension was proposed.

Japan Trench event stratigraphy: First results from IODP giant piston coring in a deep-sea trench to advance subduction zone paleoseismology

The International Ocean Discovery Program (IODP) Expedition 386, Japan Trench Paleoseismology, represents the first utilization of giant piston coring (GPC) within scientific ocean research drilling. This allowed for a Mission Specific Platform (MSP) multi-site, multi-hole, shallow subsurface coring in an ultra-deep water subduction zone trench. The primary objective of the expedition was to investigate the concept of submarine paleoseismology in the Japan Trench, which involves studying long-term records of deposits in the deep sea that can provide insights into past earthquake events. In this paper, we compile and interpret initial shipboard data and results to (1) establish first-order event stratigraphic correlation of thick event beds (> 50 cm in thickness) between sites, (2) test previously published event-stratigraphic predictions of earthquake-related event deposits as proposed based on high-resolution hydro-acoustic subbottom profiler (SBP) data, and (3) derive SBP-scale event deposits age estimates to (4) discuss the advantages and limitations of giant piston coring for scientific drilling operations and the potential of new event stratigraphy results for advancing submarine paleoseismology.The findings of the study identified a total of 77 SBP-scale event beds across 15 sites along a trench-parallel transect spanning over 600 km. These event beds exhibit clear expressions in SBP data, with approximately 49 % matching precisely with SBP units previously identified by Kioka et al. (2019a). For the remaining 51 % of SBP-scale event beds, thin, acoustically-transparent bodies were observed between high-amplitude horizons, for which SBP-based seismic interpretation alone would not be definitive. Consequently, the study concluded that the SBP-scale event-stratigraphy observed in IODP 386 cores validates the event-bed mapping conducted by Kioka et al. (2019a) and improves SBP interpretation for event beds in the 0.5 to 1 m thickness range.The initial age constraints obtained from shipboard radiolarian biostratigraphy enable us to provide rough estimates of event ages by linearly interpolating between previously dated events occurring less than 2000 years ago and a datum around 11,000 years ago reported in four boreholes from trench basins in the Southern, Central, and Northern Japan Trench. Inter-site stratigraphic correlation reveals distinct SBP-scale event stratigraphies for the trench segments located to the north and south of the structurally complex “boundary area” at approximately 39.3–39.4°N, which is hypothesized to potentially act as a persistent rupture barrier for megathrust earthquakes. We observe more frequent but thinner event deposits in the Southern and Central Japan Trench, and fewer but thicker event beds in the Northern Japan Trench. This spatial variation may be related to the different seismogenic behavior of the various asperities along the Japan Trench megathrust and/or to differences in the response of slope sediments to earthquake shaking. However, here-presented investigations at the SBP-scale level are deemed too simplistic for robust application of the “submarine paleoseismology” approach. The extensive and high-quality dataset from IODP GPC, coupled with the encouraging initial correlation results presented here, leads us to hypothesize that further detailed studies can identify and characterize event deposition dynamics at the micro-facies level, refine sediment provenance, and constrain precise event ages necessary for evaluating synchronicity in paleoseismological interpretation. These studies will also enable robust exploration of along-strike correlations or variations, facilitating the extraction of paleo-earthquake signals from Japan Trench event stratigraphies.