An introduction to the volume, and definition and use of the term ‘tectono-sedimentary element’

Modelling of potential fields can significantly contribute to the understanding of the subsurface geology, particularly if constrained by field geology, well-data and seismic profiles. This approach becomes crucial to define the subsurface setting when some of such constraints are sparse like in underexplored marine settings. The East Shetland Platform and surrounding basins (i.e. the Dutch Bank Basin, DBB; the East Orkney basin, EOB) are examples of poorly explored areas in the UK Continental Shelf in the northern North Sea. In this area, a laterally discontinuous but locally thick Devonian-to-Tertiary sedimentary succession (up to 7-8 km in thickness) mainly consisting of sandstones, claystones and limestones with locally dolomites and anhydrites, unconformably overlies the Caledonian crystalline basement.Starting from interpreted seismic profiles, we provide a first-order geophysical characterization through the combined forward modelling of the observed Bouguer gravity and reduced to the pole magnetic anomalies along five regional geological cross-sections. Furthermore, we return an overall tectono-stratigraphic framework of the Devonian-to-Recent sequences and tentatively define the crustal sources for the observed anomalies.The modelling of the sedimentary sequence was supported by the available few exploration wells data and wireline logging (i.e. lithology, seismic velocity, bulk density) and their geometries were constrained by the time-to-depth conversion of five regional seismic reflection profiles recently acquired and processed.The first-order contributors to the observed Bouguer gravity anomalies are related to the scattered distribution of the Mesozoic sedimentary sequences. In particular, two gravity lows result from the main Triassic-Jurassic sedimentary successions within the area (i.e. DBB, EOB). On the contrary, the gravity highs are mainly controlled by shallow exposures or structural highs of basement (i.e. Caithness Ridge, Fair Isle Platform) underneath the tertiary cover.The Caledonian basement and high-susceptibility (up to 0.05 SI units) intrusive bodies are interpreted as the main sources of magnetic anomalies. Such intrusive bodies are modelled both inside the basement and the lower crust. These deeper sources are related with areas of high reflectivity observed in the seismic profiles and could be related to structural paleo-domains connected to the pre-Devonian evolutionary phases of the study area. If confirmed, this interpretation will provide important constraints to the reconstruction of the geodynamic evolution of the area, defining the off-shore extension of the first-order Caledonian and post-Caledonian tectonic lineaments exposed in the Scotland peninsula and surrounding islands.This integrated forward modelling has proved valuable for the validation of the geometries retrieved after seismic profiles interpretation against the observed gravity and magnetic fields. Furthermore, we provide a more detailed and geologically-consistent reconstruction of the supra-basement sedimentary basins and retrieve location and geometries of the deeper intrusive bodies addressing their nature in the complex geodynamic evolution of the area. Some of such newly defined basins (i.e. the DBB and EOB) could be of interest in the topics of the energy transition and their need further detailed investigations.

Summary. Correlation of gravity and magnetic anomalies combined with other geological and geophysical data is useful for enhancing the quality of geological interpretation of potential anomaly fields. Maps produced by equivalent point source inversion are used to investigate visual-spatial correlations of surface free-air gravity and POGO satellite magnetic anomalies and regional heat flow and tectonic data for North America and adjacent marine areas. A quantitative analysis of regional potential field anomaly correlations at satellite elevations is also considered utilizing Poisson’s theorem in a moving-window linear regression between derivatives of the anomalous gravity and magnetic fields. An inverse relationship is observed between long-wavelength gravity and magnetic anomalies over continental terrain. Negative gravity and positive magnetic anomalies are areas characterized by relatively thick crust and high magnetization. An example is a prominent magnetic high which corresponds to a trend of gravity minima extending from the Anadarko Basin to the Cincinnati Arch. Negative magnetic and positive gravity anomalies characterize thinner crust and regions of higher heat flow such as the Cordillera of North and Central America and specifically the Yellowstone geothermal region. Although gravity and magnetic anomalies over oceanic areas show poor correlation, the sign of the statistical correlation generally is positive. 1 Crustal correlation considerations The utility of long-wavelength gravity anomalies, covering several degrees of surface area, for geological analysis is well recognized. Magnetic anomalies which have significant energy in wavelengths of several hundred kilometres also have been identified as originating from within the Earth’s crust and perhaps the uppermost mantle. The geological interpretation of these regional anomalies is hindered by the effect of anomaly superposition and source ambiguity which is inherent to the analysis of potential fields. An approach to minimizing these limitations, especially in continental terrains, is to evaluate the correlation between anomalous gravity and magnetic fields. The basis of correlation analysis is the hypothesis, commonly validated in continental areas, that variations in lithology and physical properties of the crystalline crust are reflected

The basic theoretical foundations of the spectral analysis of gravity and magnetic data based on the approximation approach have been considered and corresponding expressions implementing various statements of the F-approximation method have been derived [Strakhov and Kerimov, 1999; 2000; 2001]. The author considered the algorithms and computer implementation of the F-approximation of anomalous gravity and magnetic fields presented in the results of testing with the use of a number of model examples and data on the accuracy of the model field approximation earlier on in [Kerimov, 2003]. In this paper, I consider methodological features of constructing the F-approximation from the detailed gravity and magnetic surveys, anomalous gravity and magnetic fields reconstructed with the use of the F -approximation, and examples of the field transforms obtained with the use of this approach.

Stratigraphic evolution of deep-water Dangerous Grounds in the South China Sea, NW Sabah Platform Region, Malaysia

Sedimentological response to neotectonics and sea-level change in a delta-fed, complex graben: Gulf of Amvrakikos, western Greece

The paper reports on the deep geophysical studies performed by the Geological Survey of Russia (VSEGEI) under the international project – Deep Processes and Metallogeny of Northern, Central and Eastern Asia. A model of the deep crustal structure is represented by a set of crustal thickness maps and a 5400-km long geotransect across the major tectonic areas of Northeastern Eurasia. An area of 50000000 km2 is digitally mapped in the uniform projection. The maps show the Moho depths, thicknesses of the main crustal units (i.e. the sedimentary cover and the consolidated crust), anomalous gravity and magnetic fields (in a schematic zoning map of the study area), and types of the crust. The geotransect gives the vertical section of the crust and upper mantle at the passive margin of the Eurasian continent (including submarine uplifts and shelf areas of the Arctic Ocean) and the active eastern continental margin, as well as an area of the Pacific plate.

The western South Korea Plateau in the East Sea (Sea of Japan) is occupied by rifted continental fragments formed in association with the early phase of back-arc opening. The present study focuses on the seismic stratigraphy of the sedimentary succession and the underlying acoustic basement in this region, based on closely spaced multichannel seismic reflection profiles. The sedimentary succession occurs mainly within a series of subparallel basement troughs (grabens or half grabens) bounded by faulted continental blocks (horsts) or volcanic ridges, and commonly floored by extrusive volcanic rocks showing hyperbolic reflectors. These features are strongly suggestive of continental rifting accompanied by normal faulting, volcanic activity and high rates of basin subsidence. The sedimentary succession can be subdivided into four seismic units. Unit 1 is characterized by short and irregular high-amplitude reflectors and interpreted as a syn-rift deposit consisting of a non-marine volcanics/sediment complex in topographic lows. Units 2 and 3 formed in an open marine environment during the Middle Miocene to Early Pliocene, characterized by an onlap-fill and later draping marine sedimentary succession dominantly composed of hemipelagic sediments and turbidites with frequent intercalation of mass-flow deposits. Along the western margin of the plateau, these units were deformed under a compressional regime in the Early Pliocene, associated with the back-arc closing phase. Unit 4 (deposited since the Early Pliocene) comprises hemipelagic sediments and turbidites with evidence of sporadic slides/slumps.

Aminostratigraphy and taphonomy of ostrich eggshell in the sedimentary infill of Apollo 11 Rockshelter, Namibia

The sedimentary succession of the last ~ 3.50 Myr in the western South Yellow Sea: Paleoenvironmental and tectonic implications

The COSC (Collisional Orogeny in the Scandinavian Caledonides) project is an integral of the International Continental Scientific Drilling Program (ICDP), performed by a multidisciplinary and international team of geoscientists. It focuses on processes related to the Early Palaeozoic continent-continent collision between Baltica and Laurentia. The collision resulted in the final closure of the Iapetus Ocean in the Middle-Late Silurian when the Baltoscandian margin was partially subducted beneath Laurentia, forming a Himalayan-type orogen. In west-central Sweden this collisional mountain belt is deeply eroded and COSC-2 successfully recovered a continuously cored succession to a depth of 2276 m..Based on seismic profiling, geophysical models and the resulting interpretations, COSC-2 predicted a continuous Lower Palaeozoic allochthonous sedimentary succession, the main Caledonian décollement in the Cambrian Alum Shale Formation, and a Fennoscandian basement. The unexpected core record therefore perfectly underlines the importance of deep continental drilling. Logging and early studies show that the succession intruded by dolerite dykes involves a thick porphyry sequence instead of Paleoproterozoic granitic basement. Drilling shows that an imbricate zone with Proterozoic and Cambrian sandstones, formed in different settings, covers the basement. The basal sandstones are overlain by deformed Alum Shale comprising the main décollement and by Lower Palaeozoic siliciclastics formed in more outboard and deeper environments. This differs significantly from interpretations based on the preliminary site investigations, which also suggested a main detachment hosted in Alum Shale, but close to the top of the basement, overlain by a zone of imbricates.New detailed core descriptions show that there is a continuous sedimentary succession on top of a weathered basement (saprock and saprolith) covered by regolith (level of the Sub-Cambrian Peneplain?) which is overlain by basal conglomerates and a few meters of heterogeneous sediments (Lower Cambrian?), displaying the unusual development of a basin filled initially by mostly coarse-grained sediment gravity flows grading into finer-grained turbidites. This sedimentation was interrupted by a longer period of Alum Shale deposition (Middle Cambrian through Tremadocian), which transitioned into turbidite sedimentation again. This higher turbidite sequence (Tremadocian and younger) shows fining upward indicating a general deepening and was previously regarded as a much younger foreland basin fill (Föllinge greywackes). However, local sources of the turbiditic sediments below the Alum Shale and the extended time of deposition may rather point to a continuous sedimentation in a long-lived pull-apart basin preserved in a window beneath the Caledonian thrust sheet.After many delays caused by Covid pandemic restrictions, the core was logged in fall 2021 and afterwards by the sampling party at the BGR Core Repository in Berlin/Spandau (summer 2022). Dating of the sedimentary units is the base of a stratigraphic framework for further correlations of geotectonic events, sea-level fluctuations, evolutionary pulses, climate changes, and the re-interpretation of seismic models. The continuous COSC-2 sequence provides various possibilities for interdisciplinary collaborations and studies performed by the COSC science team. The first scientific results are presented in session TS6.4 "The Caledonian Orogen of the North Atlantic region: insights from geological and geophysical studies".

The evolution of the southern part of the Ulleung Basin, East Sea (Sea of Japan) is analysed using a two-dimensional computer-based graphical simulation (SEDPAK) on a multichannel seismic profile. Iterative editing of the input data file includes various factors: initial basin configuration, local tectonic behavior, eustatic sea level, and the amounts and direction of clastic sedimentation. The sedimentary succession on the seismic profile can be divided into seven sequences bounded by sequence boundaries. The simulation relatively well reproduces evolving geometry shown on the interpreted seismic profile and burial history of sediments through time. The over 3000-m-thick sedimentary body is composed of sandstone and shale which have been accumulated in deltaic setting and as slumping or turbidites in a shelf-slope setting since the middle Miocene (16.5 Ma). The SEDPAK simulation shows all sequences except for the upper part of Sequence 5 which displays progradational clinoforms and onlapping transgressive units. It well reflects that the simulated sequences were formed during the mature stage of the back-arc basin development since the early Miocene. Scouring by incised valleys occurred extensively after the deposition of Sequence 5 on the margin, most obviously during the lowstand of sea level. Scouring may be related to the late Miocene thrusting and wrenching caused probably by collision of the Bonin Arc with the Amurian Plate. Simulation also shows the evolutionary development of the sedimentary sequences, which can track the burial history of individual layers throughout the run. When the 16.5 Ma surface is assumed to be the initial basin surface (the top of the pre-16.5 Ma sequence), the burial path of the 17.5 Ma to 16.5 Ma sequence reveals that it was at a depth of 3000 m at 12.5 Ma; 3200 to 3900 m at 6.3 Ma; at 3500 to 4200 m at 3.8 Ma; and at 4000 to 4700 m today. In addition, one can follow the burial history at a particular location using the time-depth-elevation plot for a specific column of the output within the simulated section. These features aid in the prediction of sedimentary facies distribution and geothermal history of the sequences.

The modern stratigraphy of clastic continental margins is the result of the interaction between several geological processes acting on different time scales, among which sea level oscillations, sediment supply fluctuations and local tectonics are the main mechanisms. During the past three years my PhD was focused on understanding the impact of each of these process in the deposition of the central and northern Adriatic sedimentary successions, with the aim of reconstructing and quantifying the Late Quaternary eustatic fluctuations. In the last few decades, several Authors tried to quantify past eustatic fluctuations through the analysis of direct sea level indicators, among which drowned barrier-island deposits or coral reefs, or indirect methods, such as Oxygen isotope ratios (δ18O) or modeling simulations. Sea level curves, obtained from direct sea level indicators, record a composite signal, formed by the contribution of the global eustatic change and regional factors, as tectonic processes or glacial-isostatic rebound effects: the eustatic signal has to be obtained by removing the contribution of these other mechanisms. To obtain the most realistic sea level reconstructions it is important to quantify the tectonic regime of the central Adriatic margin. This result has been achieved integrating a numerical approach with the analysis of high-resolution seismic profiles. In detail, the subsidence trend obtained from the geohistory analysis and the backstripping of the borehole PRAD1.2 (the borehole PRAD1.2 is a 71 m continuous borehole drilled in -185 m of water depth, south of the Mid Adriatic Deep - MAD - during the European Project PROMESS 1, Profile Across Mediterranean Sedimentary Systems, Part 1), has been confirmed by the analysis of lowstand paleoshorelines and by benthic foraminifera associations investigated through the borehole. This work showed an evolution from inner-shelf environment, during Marine Isotopic Stage (MIS) 10, to upper-slope conditions, during MIS 2. Once the tectonic regime of the central Adriatic margin has been constrained, it is possible to investigate the impact of sea level and sediment supply fluctuations on the deposition of the Late Pleistocene-Holocene transgressive deposits. The Adriatic transgressive record (TST - Transgressive Systems Tract) is formed by three correlative sedimentary bodies, deposited in less then 14 kyr since the Last Glacial Maximum (LGM); in particular: along the central Adriatic shelf and in the adjacent slope basin the TST is formed by marine units, while along the northern Adriatic shelf the TST is represented by costal deposits in a backstepping configuration. The central Adriatic margin, characterized by a thick transgressive sedimentary succession, is the ideal site to investigate the impact of late Pleistocene climatic and eustatic fluctuations, among which Meltwater Pulses 1A and 1B and the Younger Dryas cold event. The central Adriatic TST is formed by a tripartite deposit bounded by two regional unconformities. In particular, the middle TST unit includes two prograding wedges, deposited in the interval between the two Meltwater Pulse events, as highlighted by several 14C age estimates, and likely recorded the Younger Dryas cold interval. Modeling simulations, obtained with the two coupled models HydroTrend 3.0 and 2D-Sedflux 1.0C (developed by the Community Surface Dynamics Modeling System - CSDMS), integrated by the analysis of high resolution seismic profiles and core samples, indicate that: 1 - the prograding middle TST unit, deposited during the Younger Dryas, was formed as a consequence of an increase in sediment flux, likely connected to a decline in vegetation cover in the catchment area due to the establishment of sub glacial arid conditions; 2 - the two-stage prograding geometry was the consequence of a sea level still-stand (or possibly a fall) during the Younger Dryas event. The northern Adriatic margin, characterized by a broad and gentle shelf (350 km wide with a low angle plunge of 0.02° to the SE), is the ideal site to quantify the timing of each steps of the post LGM sea level rise. The modern shelf is characterized by sandy deposits of barrier-island systems in a backstepping configuration, showing younger ages at progressively shallower depths, which recorded the step-wise nature of the last sea level rise. The age-depth model, obtained by dated samples of basal peat layers, is in good agreement with previous published sea level curves, and highlights the post-glacial eustatic trend. The interval corresponding to the Younger Dyas cold reversal, instead, is more complex: two coeval coastal deposits characterize the northern Adriatic shelf at very different water depths. Several explanations and different models can be attempted to explain this conundrum, but the problem remains still unsolved.

The Late Quaternary sedimentary succession and sea-level changes in the Gulf of Kuşadası, located in the Aegean Sea, have been comprehensively examined using high-resolution seismic reflection profiles and sediment cores collected by R/V TUBITAK Marmara in 2022. The seismic stratigraphy reveals four main depositional units, each bounded by distinct reflection surfaces that reflect significant sea-level fluctuations since the Last Glacial Maximum (LGM). Correlation of the seismic profiles with the 14C-dated sediment cores provides the robust chronology of seismic stratigraphic units, seismic boundaries, paleo wave-abraded platforms, and marine terraces. The depths of the paleoshorelines observed in the seismic profiles were compared with the global sea-level curve to more accurately determine the timing of sea-level changes in the gulf. The deepest wave-abraded platform observed in the seismic profiles is at a depth of -172 m. According to chronology of the depositional units in the seismics adjusted with 14C-datings from the cores, the deepest wave-abraded platform at -172 m in the seismic profile conforms with the sea-level lowstand (-135 m) at ca. 21.5 cal ka BP during the LGM based on the global sea-level curve. Such comparison reveals the subsidence of the submerged seafloor due to vertical displacement along active normal faults in the Gulf of Kuşadası since the LGM. Subsequent sea-level rise triggered by post-glacial warming led to the deposition of transgressive units characterized by coastal onlaps and localized channel fills. Brief sea-level stillstands disrupted this transgressive phase at approximately 17 cal ka BP and 14.6 cal ka BP, forming younger wave-abraded platforms at -135 m and -112.5 m, respectively. The depths of these platforms, compared with the global sea-level curve, suggest ongoing subsidence at a slower rate, indicating a complex interplay between sea-level changes and tectonic activity in the Gulf. The subsidence is likely attributed to tectonic movements along the seafloor rather than hydrostatic loading.The acoustic reflection characteristics, together with the geometry and spatial extents of the seismic stratigraphic units, also provide important insights into the depositional processes during the changing sea-level. The most prominent depositional facies can be presented in the seismic profiles as two amalgamated deltaic sequences of the paleo-Küçük Menderes River. Their depositional periods can be confidently deduced from the correlation of the seismic stratigraphic units with the chronostratigraphic units in the cores. The topset/foreset transitions of these deltaic sequences, located at depths of -37.5 m and -112.5 m in the seismic profiles, correspond to estimated ages of 9.3 cal ka BP and 14.6 cal ka BP, respectively.

This volume contains an unparalleled summary of the geology and hydrocarbon potential of all Arctic sedimentary successions. The successions are organised into 67 ‘tectono-sedimentary elements’ according to deformational and lithostratigraphic characteristics, and described in an easy-to-navigate standardized framework. Includes over 800 illustrations and 6 foldout Circum-Arctic maps.

Structural imaging of Mesozoic sediments of Kachchh, India, and their hydrocarbon prospects