Seismostratigraphy of the inner shelf adjacent to Suape Bay, Northeastern Brazil

Mechanisms of sediment transport and deposition: Sediment sequences and accumulation during the Holocene on the Thermaikos plateau, the continental slope, and basin (Sporadhes basin), northwestern Aegean Sea, Greece

The Ontong Java Plateau (OJP) is the largest and thickest oceanic plateau on Earth and one of the few oceanic plateaus actively converging on an island arc. We present velocity determinations and geologic interpretation of 2000 km of two‐dimensional, multi‐channel seismic data from the southwestern Ontong Java Plateau, North Solomon Trench, and northern Solomon Islands. We recognize three megasequences, ranging in age from early Cretaceous to Quaternary, on the basis of distinct interval velocities and seismic stratigraphic facies. Megasequence OJ1 is early Cretaceous, upper igneous crust of the OJP and correlates with basalt outcrops dated at 122–125 Ma on the island of Malaita. The top of the overlying megasequence OJ2, a late Cretaceous mudstone unit, had been identified by previous workers as the top of igneous basement. Seismic facies and correlation to distant Deep Sea Drilling Project/Ocean Drilling Program sites indicate that OJ2 was deposited in a moderately low‐energy, marine environment near a fluctuating carbonate compensation depth that resulted in multiple periods of dissolution. OJ2 thins south of the Stewart Arch onto the Solomon Islands where it is correlated with the Kwaraae Mudstone Formation. Megasequence OJ3 is late Cretaceous through Quaternary pelagic cover which caps the Ontong Java Plateau; it thickens into the North Solomon Trench, and seismic facies suggest that OJ3 was deposited in a low‐energy marine environment. We use seismic facies analysis, sediment thickness, structural observations, and quantitative plate reconstructions of the position of the OJP and Solomon Islands to propose a tectonic, magmatic, and sedimentary history of the southwestern Ontong Java Plateau. Prior to 125 Ma late Jurassic and early Cretaceous oceanic crust formed. From 125 to 122 Ma, the first mantle plume formed igneous crust (OJ1). Between 122 and 92 Ma, marine mudstone (OJ2 and Kwaraae mudstone of Malaita, Solomon Islands) was deposited on Ontong Java Plateau. At 92 Ma a second mantle plume caused widespread volcanism on the plateau. From 92 to 15 Ma, pelagic carbonate sediment (OJ3) was deposited. At ∼15 Ma the southern Ontong Java Plateau was deformed by normal faults during its approach toward the North Solomon Trench. Finally, from 4 to 0 Ma, the Malaita Accretionary Prism formed during collision between a substantially thicker portion of the Ontong Java Plateau and the Solomon Islands arc. Flexure of the Ontong Java Plateau near the trench caused coeval normal faulting.

The South Yellow Sea (SYS) is a semi‐closed epicontinental sea, where voluminous material input and regional tectonic subsidence facilitate preservation of depositional strata, making it an ideal place for studying the regional responses to global sea‐level changes during the Quaternary. Based on high‐resolution single‐channel seismic data, we conducted a detailed study of the SYS shelf in terms of its stratigraphic architecture and seismic facies. In combination with borehole data, we analysed the depositional processes of the SYS shelf since the Quaternary. A minimum of 14 seismic sequences were identified on the seismic profiles, which primarily show four typical seismic reflection facies: progradational reflection facies, parallel reflection facies, chaotic reflection facies and incised valley facies, with the former two seismic facies usually alternating with the latter two vertically. Borehole and seismic data revealed that the SYS shelf has been basically controlled by global sea‐level changes since the Quaternary, and three significant transgression events had occurred over the SYS shelf since the Middle Pleistocene (ca. 730 ka BP–Present), taking place in the early Middle Pleistocene, the early Late Pleistocene and at the end of the Late Pleistocene–Holocene, respectively, with their products corresponding to seismic sequences U90, U50 and U10, respectively. Seismic data showed that, in a previous division of the main boundaries for holes EY02‐2, NHH01 and QC2, the Holocene and the Upper Pleistocene bottom boundaries are concordant, while the Middle Pleistocene bottom boundary is discordant, and our study indicated that the division scheme for the Middle Pleistocene bottom boundary related to holes EY02‐2 and NHH01 is more reasonable. The turning point of variation in the depositional environment of the SYS is at the end of the Middle Pleistocene, before which global sea‐level change and tectonic subsidence controlled the shelf deposition. The shelf was inclined westwards and the tectonic topography of the southern margin of the shelf‐forced seawater to invade via passages during sea‐level rise. This resulted in a limited stratigraphic distribution formed by short‐duration transgression events with low‐amplitude sea‐level rise; thereafter, the shelf deposition was predominated by global sea‐level and rivers, and the shelf sediments were mainly derived from mainland China on the west of the shelf and were primarily accumulated on the middle and western parts of the shelf. Copyright © 2016 John Wiley & Sons, Ltd.

Limitations in sonic and density logs and marine COP data produce ambiguities in analysis and interpretation of this information for exploration prospect evaluation and production reservoir delineation. Marine vertical seismic profiling (VSP) provides an added tool to help unravel many of these ambiguities by measuring seismic wave reflections and propagation parameters (e.g., travel time, velocity, and attenuation) in the vicinity of the borehole at seismic frequencies. In the marine environment, special restrictions are imposed on VSP acquisition by the drill rig, deviated boreholes, and high offshore operating expenses. Moreover, marine VSP signal processing must contend with the effects of these problems, such as source reverberation and limited frequency bandwidth. These processed VSP resu1ts are used to correlate seismic data to the borehole for seismic interpretation. The basic applications for a marine VSP are:Accurate time-to-depth relationshipInterval velocities at seismic frequenciesCorrelation of the seismic data near and below the boreholeCorrelation of the seismic data to both logs and drilling information measured in depth.Seismic wave attenuation estimatesImproving modeling of synthetic seismogramsImproving processing of surface COP data andImproving structural and stratigraphic interpretation of surface COP data. INTRODUCTION This overview of marine Vertical seismic profiling (VSP) consists of discussions on:acquisition and processing of VSP data,VSP deconvolution,VSP interpretation and integration (with logs and surface COP data),VSP in deviated boreholes, andVSP applications. Emphasis is placed on those unique applications and problems of VSP for the offshore environment.Special consideration is given to VSP applications that assist in the exploitation of seismic data for offshore exp1oration and production reservoir delineation. Major limitations arise in the analysis and application of surface seismic data and borehole logs in exploration and production. For surface seismic data, the seismic profiles provide a continuous view of the reflecting horizons in the subsurface and are interpreted in terms of their geological significance. The interpretation of these data is limited by the resolution (25 to 100 ft) and the discrete subsurface sampling along survey lines. The data are recorded in time and must be converted to depth and mi grated to the proper spatial position. On the other hand, typical logs have excellent vertical resolution in depth and provide the needed detailed information about the reservoir and its geology. However, the log investigates only the subsurface penetrated by the bit and looks only at a few feet of the formation surrounding the borehole. The correlation and mapping of this log information between wells is especially difficult in complex geology (e.g., faulting). The trend in interpretation is to integrate as much log and drilling information as available with the surface seismic data to fill the information gap between these data sets. VSP, as a seismic log, can aid in the integration while providing critical additional information.

The Congo Basin: Subsurface structure interpreted using potential field data and constrained by seismic data

Carried out in 2021, the wide-angle reflection-refraction (WARR) SHIELD’21 profile crosses, from SW to NE, the main tectonic structures of Ukraine. It has targeted the crustal and uppermost mantle structure underlying the Archaean and Paleoproterozoic crystalline complexes of the Ukrainian Shield and the adjacent platformal areas. To the SW of the Ukrainian Shield, the crystalline basement is overlain by Vendian through Paleozoic strata of the Volhyno-Podolian Homocline, plunging at its SW end below the Carpathian belt and its Neogene foredeep. To the NE, the crystalline cratonic basement is covered by Devonian and Carboniferous successions of the Dnieper-Donets rift basin. The ~650 km long SHIELD’21 profile is a northeasterly extension of the RomUkrSeis profile carried out in 2014 and running from Romania to the southwestern part of the Ukrainian Shield (Starostenko et al., 2020). The WARR study along the SHIELD’21 profile provided high-quality seismic records. The main recorded seismic waves are refractions of P- and S-waves in the sedimentary layer, crystalline basement, middle and lower crust and uppermost mantle, as well as reflections from crustal boundaries, the Moho interface and boundaries in the uppermost mantle. The correlation picking of their arrival times allowed us to build a velocity model not only for the P-, but also for S-waves and Vp/Vs ratio. The model reveals that over the entire thickness of the crust, the Vp in the crystalline basement nowhere exceeds 6.85 km/s, which – particularly in the context of the lower crust – represent low values, but similar to those known from the other nearby deep seismic profiles (e.g. TTZ-South, and DOBRE-4). Patterns of crustal boundaries combined with velocity differences across them, permit hypothesizing on Proterozoic large-scale subhorizontal extensional faulting in the crystalline upper crust. A prominent dome-like structure in the lower crust may represent a longitudinal section of a major duplex resulting from Paleoproterozoic overthrusting to the NW, comparable to those interpreted on the TTZ-South profile (Janik et al., 2022). The Moho shows strong variability of a depth (~32-50 km), and is underplated by lenticular horizontal ca. 10 km thick high velocity mantle bodies with Vp>8.36 to 8.40 km/s, also present deeper in the upper mantle of Vp between 8.15 and 8.25 km/s. The Moho is prominent and marked by the Vp velocity contrast of c. 1.4 to 1.8 km/s between the upper mantle and lower crust. It is characteristically undulated with successive downward and upward bends, with the amplitude locally exceeding 15 km and wavelength of the order of 150 to 250 km. A similar Moho undulation form was described along the DOBRE-4 profile and was interpreted as Mesozoic(?) buckle mega-folds (Starostenko et al, 2013). Janik, T. et al. (2022). TTZ-South, Minerals, 12, 112, doi.org/10.3390/min12020112 Starostenko, V. et al. (2013). DOBRE-4, Geophys. J. Int. 195, 740–766, doi.10.1093/gji/ggt292 Starostenko, V. et al. (2020). RomUkrSeis, Tectonophysics, 794, 228620, doi.org/10.1016/j.tec to.2020.228620

Comparison between high-resolution seismic and sequence stratigraphic approaches applied to the upper Jurassic deposits of the Dover Strait area (Northern France)

High-resolution 3D seismic reflection and coring techniques applied to late Quaternary deposits on the New Jersey shelf

<p>The Northern Alpine Foreland Basin developed in response to the collision between the European and Adriatic plates. During the Oligocene-Early Miocene coeval along-strike deposition of terrestrial and deep marine conditions are recorded in the western and eastern parts of the basin respectively. However, the mechanisms driving the observed variability in along-strike development of the basin are still poorly understood.</p><p>To study the causes of the observed along-strike variability we review published geological data and (re)interpret available 2D and 3D seismic data, constrained by well data. We interpret (1) seismic facies, (2) stratigraphic surfaces and (3) tectonic structures. Our current focus area covers the transitional zone between the western and eastern parts of the basin.</p><p>In our study we distinguish 6 stratigraphic surfaces from the Base Tertiary to the Top Aquitanian. From Upper Swabia to the German-Austrian border (along the basin strike) we observe that the top of the crystalline basement is tilted towards the east with an angle of 2-3°. Furthermore, the base of the Tertiary deposits is also tilted towards the east with an angle of 0.3°. The main structural features are E-W and NW-SE striking normal faults. In the western part of our study area the normal faults cut the crystalline basement, Mesozoic and Oligocene deposits. The faults are sealed by Rupelian deposits. Thickness changes (~20 m) occur in Rupelian and overlying Chattian deposits. Maximum offsets of up to 60 m are observed for Mesozoic reflectors. In the eastern part of our study area the normal faults cut the crystalline basement, Mesozoic, Oligocene and Early Miocene deposits. Thickness changes across these faults indicate fault activity during the Rupelian, Chattian and Aquitanian. Maximum offsets (>150 m) are observed for Chattian reflectors. Upper Aquitanian deposits seal these faults, which is younger than observed in the western part of the study area. The NW-SE striking faults confine Paleozoic grabens within the crystalline basement.</p><p>We relate the observed normal faulting of the Oligocene and Early Miocene deposits to flexural downbending of the European plate, assumed to have been caused by tectonic loading of the Alps and/or European slab pull. Furthermore, we suggest that the observed temporal variation in termination of fault activity is related to temporal and spatial variations in tectonic loading of the Alps and/or European slab pull. Finally, based on the observed eastward tilt of the top crystalline basement and Base Tertiary along the basin strike, variations in pre-existing crustal architecture must be considered.</p>

High flow rate injection and related hydromechanical interaction are the most important factors in reservoir development of Enhanced Geothermal Systems (EGS). GeoLaB, a new generic geothermal underground research laboratory (URL), is proposed for controlled high flow rate experiments (CHFE) to address limited comprehension of coupled processes connected to EGS reservoir flow conditions. As analogue for typical EGS development, CHFE require specific hydromechanical conditions including a connected fracture network in crystalline basement rock, sufficient hydraulic fracture transmissivities, a strike-slip to normal faulting tectonic regime, controllable hydraulic boundary conditions, and hydrothermal alteration fracture fillings that improve conditions for hydromechanical interaction. With the aim to identify most appropriate areas for future site selection, four criteria have been established based on the EGS reference site of Soultz. Two URLs in crystalline basement worldwide approximate the requirements of a new generic GeoLaB and may be used for accompanying experimentation. Besides favourable geological, hydraulic, and stress conditions, the vicinity to long-term EGS production favours the southern Black Forest as potential region for GeoLaB. Therefore, an exemplary site assessment has been carried out at “Wilhelminenstollen” in the southern Black Forest (Germany). New remote sensing, hydrochemical, and geophysical analyses as well as reactivation potential, and stress modelling were added to complement existing geological and hydrogeological information. At this site, reactivation potential analysis reveals two local maxima prone for shear reactivation as strike-slip faults. The highest lineament density is observed for the N110°E strike direction that is associated with both slip and dilation tendency maxima. Clay minerals occur in fractures and the matrix. Local, partly water-bearing fractures, when partly filled with ore minerals, were connected to veins in the tunnel using shallow geophysical methods. Hydrochemical data reveal infiltration of the tunnel water from at least 500 m above the tunnel. The results suggest a crystalline basement with a fracture network that is regionally connected and water-conducting. Hydraulic conductivity in the southern Black Forest granite is estimated to amount to about 4.5·10−8 m s−1 at 500 m depth. The hydraulic boundary conditions exclude unknown drainage. Analyses of the influence of topography on orientation and magnitude of the maximum stress indicate a minimum overburden of about 500 m for regional reactivation to be valid. In conclusion, the southern Black Forest and in particular “Wilhelminenstollen” offers favourable condition for CHFE. Final decision on the GeoLaB site is to be drawn from forthcoming exploration wells.

Seismic facies analysis is important for oil and gas exploration. The conventional seismic facies recognition methods are implemented manually with high workload and low accuracy. Therefore, how to obtain seismic facies characteristics quickly, efficiently, and accurately is an urgent requirement in seismic facies research. To alleviate this issue, we propose a novel seismic facies recognition method based on the region growing algorithm with expert knowledge constraint. The processes of this algorithm are as follows: firstly, we select high-density 3D seismic data in the target area for seismic facies identification. Then, we utilize expert knowledge to define the priori geological constraint for regional growing algorithm. Finally, the region growing algorithm is used to pick up and divide different 3D seismic facies boundaries in the study area. The verification of known geological knowledge proves that the results are reasonable and reliable. The accuracy and efficiency of the proposed seismic facies identification method based on region growing are significantly improved.

Integrated geophysical methods of Electrical resistivity tomography (ERT), Induced Polarization (IP), and Well Logging were employed in this study to delineate the lateral and depth extent of saline water intrusion in Oniru area of Lagos State, South-western Nigeria due to reported saltwater contamination of some wells at relatively shallow depths. Ergo, improving the scientific understanding of fresh and saline waters occurrence in the coastal areas of Lagos State.Five traverses, each of variant lengths (100 to 200 m) were established for both ERT and IP as space permitted. For each profile level, Wenner electrode configuration was adopted with a minimum electrode spacing of 3 m and maximum electrode spacing of 50 m. Ten levels were achieved for profiles 1, 2, 4, and 5 while eight levels were accomplished for profile 3. The ERT and IP data were processed using RES2DINV 2-D resistivity data processing software. The well log data utilized were acquired from two existing lithological logs within the study area to validate the results of the ERT and IP.The unconsolidated sandy formation was characterized by high resistivity with corresponding low to medium chargeability while the clay units were characterized by low resistivity with equivalent high chargeability. The sandy formation saturated by saltwater was characterized by very low resistivity with corresponding low chargeability while that of freshwater was characterized by medium to high resistivity with corresponding low chargeability. The integrated geophysical methods of ERT, IP and borehole logging in the study area identified three lithological sequences. The first layer corresponded to high resistivity values of unconsolidated sandy topsoil, mostly less than 5 m. However, in profiles 3 and 4, it occurred as saturated marshy topsoil. The top layer was underlain by sand/clayey sand formation, which was observed to have pockets of saline water intrusion as evinced from the results of the ERT and IP data. The saline water-bearing zones were observed to intermingle with the freshwater-bearing sand units. The freshwater-saline water transition tends to be conspicuous especially in profiles 3 and 5. The base of profiles 1 and 2 was occupied by clay units which were evident from the results of the borehole log, the ERT, and the IP sections.The integrated geophysical method was able to successfully delineate the fresh and saline water interface and extent of saltwater intrusion within the study area and thus would provide a reliable database for future groundwater development and management within the study area.

The seismic reflection method is well established in the exploration end of the petroleum industry but little used in reservoir analysis by petroleum engineers. As the major structures have been discovered in many areas, seismic profiling has been turned more and more toward smaller structures and toward exploration for stratigraphic traps which require a far greater precision and fineness of detail to locate. This redirection has precision and fineness of detail to locate. This redirection has resulted in improved seismic equipment design, field recording techniques and seismic data processing procedures. This means that the petroleum engineer, for the first time, may be able to utilize this technique to assist in delineation of the fine subsurface stratigraphy within individual reservoirs. The technique used for high resolution reservoir profiling is a greatly scaled-down version of that employed in most exploration operations. Every 5 to 20 meters (16 1/2 to 65 feet), a detector produces a new seismic "pseudo" log trace which will subsequently produces a new seismic "pseudo" log trace which will subsequently be correlated with borehole logs and other seismic log traces. Structural information derivable from the log trace displays includes location of very small faults, sand channels and shale-outs. Shape variations in the log traces can provide the petroleum engineer with valuable reservoir information regarding localized depositional environments, pore fluid characteristics, and even porosity and permeability variations across a given reservoir bed, porosity and permeability variations across a given reservoir bed, once a local reference has been established. Acoustical amplitude analysis of injected, produced or in situ reservoir gases should be a valuable method of monitoring a variety of enhanced oil recovery techniques. Carbon dioxide or other gas injection projects are ideal for seismic pseudo log monitoring. Combustion products from fire floods or injected steam should also be easily seen with high resolution seismic techniques. High frequency surface to surface seismic profiling offers great potential as a reservoir analysis tool. This potential will be developed by the petroleum engineer working with seismic log displays and field well logs rather than exploration geophysicists using smoothed structural displays. Introduction Porosity, fluid saturation, rock compressibility, permeability and capillary pressure are all terms familiar to the permeability and capillary pressure are all terms familiar to the reservoir engineer but seldom used by the geophysicist. On the other hand root mean square velocity, predominant reflection frequency, normal moveout, wavelet amplitude, deconvolution and other terms in the geophysicists vocabulary are almost never involved in reservoir analysis. Until recently, this language problem created no particular difficulty since the geophysicists were almost exclusively involved in exploration activities where the targets were big structures and the geological "details", involving potential reservoir rock type, matrix porosity and permeability as well as pore fluid identification, were considered inconsequential as they routinely fell beyond the resolving power of the seismic reflection method. This has now changed. As the larger structures have been discovered, exploration activities are being redirected to smaller features and especially to stratigraphic traps which require much greater geophysical precision to locate. Demand for increased fineness of detail is resulting in improved geophysical equipment, field recording techniques and computer processing procedures. These improvements allow one for the first time to look at the individual producing formations of immediate interest to the petroleum engineer. petroleum engineer. The change started a few years ago when seismic "Bright Spots" were heralded as a direct hydrocarbon indicator. The "Bright Spot" is caused by the increased seismic reflection amplitude caused by the relatively lower density and velocity of gas filled reservoirs compared to those filled with water. As many operators discovered somewhat later, coal also has low density and velocity and produced bright spots which were easily mistaken for gas. Also depending on the reservoir material, the "Bright Spot" may in fact be a "Dim Spot" or may have no measurable amplitude effect at all.

We present a high-resolution, three-dimensional P-wave seismic veloc- ity model of the sedimentary basin in the Salton Trough, southern California, and use the model for spectral-element method (SEM) wave propagation and ground- motion simulations to quantitatively assess seismic hazard in the region. The basin geometry is defined by a surface representing the top of crystalline basement, which was constrained by seismic refraction profiles and free-air gravity data. Sonic logs from petroleum wells in the Imperial Valley and isovelocity surfaces defined by seismic refraction studies were used to define P-wave velocity within the sedimentary basin as a function of two variables:(1) absolute depth and (2) depth of the underlying crystalline basement surface (CBS). This velocity function was used to populate cells of a three-dimensional spatial array (voxet) defining the P-wave velocity structure in the basin. The new model was then resampled in a computational mesh used for earthquake wave propagation and strong ground motion simulations based upon the SEM (Komatitsch et al., 2004). Simulation of the 3 November 2002 Mw 4.2 Yorba Linda earthquake demonstrates that the new model provides accurate simulation of strong ground motion amplification effects in the Salton Trough sedimentary basin, offering substantial improvements over previous models. A hypothetical Mw 7.9 earthquake on the southern San Andreas fault was then simulated in an effort to better understand the seismic hazard associated with the basin structure. These sim- ulations indicate that great amplification will occur during large earthquakes in the region due to the low seismic velocity of the sediments and the basin shape and depth.

Most geophysical applications in North American coal exploration have centered around the conventional surface seismic reflection method to provide continuous subsurface coverage for evaluating both good and anomalous coal reserve areas (Ruskey, 1981; Dobecki and Bartel, 1982; Greaves, 1984; Lawton, 1985; Lyatsky and Lawton, 1988; Gochioco and Cotten, 1989; Lawton and Lyatsky, 1989; Gochioco and Kelly, 1990; Gochioco, 1991; Henson and Sexton, 1991). The surface seismic reflection method, however, has inherent resolution limitations because the seismic wavelet must propagate substantial distances through the weathered layer, resulting in rapid attenuation of the desired higher frequencies. Since the depths and thicknesses of coal seams are usually known beforehand, it is imperative that the seismic reflection associated with the target coal seam is absolutely identified in the seismic section to avoid misinterpretations. However, it is common that checkshot data and sonic and density logs are not available to generate synthetic seismograms to assist in the interpretation of coal seismic data. To overcome some of these limitations, the vertical seismic profiling (VSP) technique was tested in a coal exploration program to provide additional information for correlation with surface seismic reflection [or common-depthpoint (CDP)] data and a synthetic seismogram generated from density and sonic logs. VSP has an advantage over the surface seismic reflection method in that the receiver is placed in the borehole beneath the weathered layer, which is responsible for severely attenuating higher signal frequencies. As a result, VSP data tend to have a broader frequency spectrum. The recorded VSP field data also provide better insight into the fundamental properties of reflection and transmission of seismic wavelets in the subsurface near the borehole location because the receiver records both upgoing and downgoing seismic events. In this study, the VSP data are correlated to the CDP seismic data as well as to a synthetic seismogram for comparative analysis of its accuracy