Regional Seismic Profiles Research Articles

Structural features and evolution of the Dniepr-Donets Basin, Ukraine, from regional seismic reflection profiles

A set of regional multichannel seismic reflection profiles crossing the Dniepr-Donets (DD) Basin in Ukraine, 100–200 km long and with a spacing of 10–15 km along strike illuminates the structure of the whole sedimentary cover. The rift, filled with pre- and syn-rift Devonian sequences and overlain with post-rift Carboniferous, Permian, Mesozoic and Palaeogene fill, is clearly seen on all sections. A ‘basement’ layer, previously identified as a Riphean rift succession by refraction seismic studies constitutes, in the main, strata of the Devonian and Early Carboniferous successions. The structure of the rift is characterised by large-scale rotational fault blocks and half-grabens, carried by basin-parallel to normal marginal faults or by major horst blocks. The total thickness of the Devonian and younger succession is up to 19 km in the study area. Post-rift Carboniferous and Mesozoic sediments cover the rift flanks and increase in thickness towards the rift axis and to the southeast. The cumulative thickness of the Carboniferous succession alone reaches 11 km, with the maximum depth of their base at about 15 km. Major post-rift tectonic events took place at the end of early Visean, in the middle of Serpukhovian, in Permian times, and between the Mesozoic and Cenozoic. Tectonic reactivations during Carboniferous and Early Permian times were most pronounced in the southeastern part of the DD Basin, while they were least pronounced in the northwestern part of the basin merging with the Pripyat Trough where they are barely observed. The most active development of salt structures and stocks corresponds with the periods of tectonic reactivation.

Late Cenozoic evolution of the western Barents Sea-Svalbard continental margin

Seven regionally correlatable reflectors, named R7 (oldest) to R1, have been identified in the Upper Cenozoic sedimentary succession along the western continental margin of Svalbard and the Barents Sea. Regional seismic profiles have been used to correlate between submarine fans that comprise major depocentres in this region. Glacial sediment thicknesses reach up to 3 seconds two-way time, corresponding to 3.5–4 km. Despite limited chronostratigraphic control, ages have been assigned to the major sequence boundaries based on ties both to exploration wells and to shallow boreholes, and by paleoenvironmental interpretations and correlations with other regions. Lateral and vertical variations in seismic facies, between stratified and chaotic with slump structures, have major implications for the interpretation of the depositional regime along the margin. The main phases of erosion and deposition at different segments of the margin are discussed in the paper, which also provides a regional seismic stratigraphic framework for two complementary papers in the present volume. Reflector R7 marks the onset of extensive continental shelf glaciations, but whereas the outer Svalbard shelf has been heavily and frequently glaciated since R7 time, this did not occur, or occurred to a much less extent, until R5 time in the southern Barents Sea. The present study provides the background for a quantification of the late Cenozoic glacial erosion of Svalbard and the Barents Sea. The rates of erosion and deposition exhibit large temporal and spatial variations reflecting the importance of glacial processes in the Late Cenozoic development of this nearly 1000 km long margin.

Tectonic Inheritance, Crustal Architecture and Contrasting Structural Styles along the Northern and Southern Andean Flanks, Venezuela: ABSTRACT

Regional seismic profiles, exploration wells, geological maps and field studies image contrasting structural styles of the northern and southern flank of the Venezuelan Andes. In the north, a flexural basin developed in Neogene times between the Andes and the Maracaibo Lake. North verging thrusts are mainly detached in the pre-Cretaceous substratum and form a deeply buried antiformal stack, whereas secondary decollement levels occur either in the Lower Cretaceous or in the Tertiary, accounting for the passive roof thrusting of the frontal triangle zone. In the south, the Barinas Basin can hardly be compared with a flexural basin. It is largely dominated by basement involved structures, either north or south verging. Tectonic inheritance is obvious, as Paleogene normal faults have been locally inverted, and early Caribbean nappes (Paleogene structures) are frequently reactivated or refolded by younger oblique Andean (Neogene) structures. All these data have been integrated to compile two crustal scale balanced sections which have been constrained by an inversion of the gravimetric data. The Present relief of sections is directly inherited from the Jurassic (Tethyan) rifting event. The southern low land results from the structural inversion of Jurassic extensional structures (thin initial crust), whereas the northern culmination relates to newlymore » created Andean structures (thick Jurassic crust). Whether the Hercynian structures have been or not reactivated during the Tethyan rifting or the Andean deformation, remains an open question. The Hercynian thrusts trend more or less parallels to the younger structures, especially Mesozoic extensional ones which could thus partially result from the negative inversion (collapse) of the Paleozoic edifice.« less

Advances of geophysical prospecting for petroleum in marine carbonate areas of the upper Yangtze region, southern China

In the marine carbonate area of the upper Yangtze region, southern China, including parts of Guizhou and Sichuan Provinces, complex subsurface structures and undulating surface terrain exist because of multiple tectonic events. Various geophysical prospecting methods have been conducted in local areas in an attempt to map these structures. In the Guizhou Plateau, a carbonate‐exposed area, crooked seismic lines were acquired using vibrators as the main source, supplemented with dynamite. In Sichuan Province, a mountainous area, regional seismic profiles, wide‐line profiling, and 3-D seismic surveys were conducted. These were accomplished with portable air drills and human transport. Data processing techniques were designed to improve data quality in the presence of noise and to image complex structures. In central Sichuan Province, high‐resolution and converted‐wave seismic surveys were carried out for imaging complex structures and for collecting lithologic parameters. These methods have enabled us to get effective information from complex structural, mountainous, and carbonate‐exposed hilly areas in the upper Yangtze region of southern China. These collective efforts have produced a database appropriate for sedimentology, tectonic, and prospective area evaluation studies.

Stacking of wide-angle data from the BABEL project

Here I apply the extended correlation technique to a 156-km long regional seismic profile, PL1-5100, from the PolandSPAN™ survey located in SE Poland. This method allows the extension of the nominal record length of the survey (12 s in this case) to much longer times (22 s tested here), given that in the field the raw uncorrelated data were stored and a broadband sweep was used. Processing of the ground force correlated data compared to pilot sweep correlated one produced qualitatively similar results. Based on the consistency of the ground force measured along the profile, data were correlated with the mean of the ground force estimates. Results of the processing were validated against the coincident wide-angle reflection/refraction (WARR) profile (CELEBRATION 2000 CEL05 profile) and a deep reflection profile located further to the SE (POLCRUST-01 profile). I found a good correspondence between the wide-angle Moho signature and the near-vertical incidence (NVI) Moho reflectivity, both in terms of the depth and the reflection strength, with the exception of the area of the crustal keel (Moho > 50 km) interpreted from the WARR data, where the NVI reflectivity is observed at depth ca. 47 km. Similarly to POLCRUST-01, line PL1-5100 is portraying the attenuated crust of the East European Platform margin with the dipping crystalline basement down to ca. 20 km depth and the reflective lower crust. Two important fault zones: Izbica-Zamość Fault and Wilczopole Fault Zone are interpreted as the deeply-rooted crustal features, but there is no evidence for the Teisseyre–Tornquist Zone itself.

New evidence on the structure of the Labrador Sea/Greenland continental margin

A 275 km section of a regional seismic reflection profile from the Greenland side of the Labrador Sea has been reprocessed and interpreted. Three zones of different structural style have been identified, the innermost of which is block-faulted. Magnetic modelling based on the seismic line shows that sea-floor spreading anomalies are confined to the outermost zone and the oldest identified anomaly is 27N. All attempts to model the area landward of anomaly 27N as a series of remanent magnetizations of alternating polarity failed. However a model in which the innermost zone is interpreted as extended and block-faulted continental crust and the intermediate zone as continental crust intruded and overlain by reversely magnetized igneous material fits the magnetic and seismic data. It is concluded that, at least in the northern Labrador Sea, sea-floor spreading started in Palaeocene times (chron 27), and large areas formerly thought to be underlain by oceanic crust should now be considered to be continental. One plate kinematic consequence may be a reduced need to postulate large strike-slip movements along Nares Strait.

Regional seismic reflection profiling in the caledonides: Data acquisition and preliminary results

Regional seismic reflection profiling in the caledonides: Data acquisition and preliminary results

Evidence and implications of an extensive early Mesozoic rift basin and basalt/diabase sequence beneath the southeast Coastal Plain

Regional seismic reflection profiles across the Georgia and South Carolina Coastal Plain provide a detailed view into the internal structure and stratigraphy of the buried Triassic-Jurassic South Georgia basin. Reflection data indicate that the basin is a complex composite of smaller, individual basins which vary drastically along strike. These basins are relatively wide along north-south profile (maximum >100 km) but appear to be more restricted along strike. In cross section, the basins are asymmetric, being typically bounded on their south sides by an interpreted north-dipping master normal falult. The thickness of interpreted basin fill below the Cretaceous-Tertiary overlap also varies drastically, locally reaching 6 km. Analysis and correlation of the reflection profiles, when integrated with drill-hole and offshore reflection data, suggest the presence of an areally extensive basalt flow and/or diabase sill sequence of probable Early-Middle Jurassic age, covering a large part of the Triassic-Jurassic South Georgia basin. The sequence is traceable on seismic reflection profiles across much of the South Georgia basin and may extend as far as from western Georgia to offshore South Carolina. The implied areal extent of this sequence would be more than 100,000 km 2 , ranking it among the great basalt flows and/or sills of the world. On seismic reflection profiles over the South Georgia basin, the basalt/diabase sequence is also important in marking a post-rift unconformity which separates tilted and apparently faulted lower Mesozoic rift-related strata below from a thinner, more widespread, and generally unfaulted sequence above. This configuration is interpreted to mean that basalt extrusion and/or hypabyssal intrusion occurred after the main episode of Late Triassic-Early(?) Jurassic normal faulting and associated localized subsidence (syn-rift phase) and prior to a later, Jurassic episode of more widespread uniform subsidence (post-rift phase) accompanied by relatively minor normal faulting. This two-stage evolutionary sequence is analogous to that of many rift basins throughout the world and suggests a hypothesis that the South Georgia basin was an area of incipient crustal spreading associated with the early formation of the central Atlantic Ocean.

Application of Sequence Stratigraphy to Oil and Gas Exploration in Bredasdorp Basin, Offshore South Africa: ABSTRACT

For more than two decades, oil and gas exploration in offshore South African rift basins within structural synrift plays yielded limited success. After the first oil discovery in postrift sediments in the Bredasdorp basin in 1987, sequence-stratigraphic concepts were applied to the Lower Cretaceous postrift sequences to permit correlation of depositional systems tracts and related facies throughout the basin. Extensive high-resolution seismic coverage and borehole control supported the study. The interplay of diminishing rift tectonics, thermal cooling, and inferred eustatic variations in global sea level produced a distinctive series of repetitive cycle depositional sequences. As many as 10 cyclic sequences and megasequences, deposited between the mid-Valanginian and lower Santonian, can be recognized within resolution limits of regional seismic profiles. Various elements of lowstand systems tracts within these sequences appear to contain potential reservoirs. Highly erosional (type 1) unconformities, commonly exhibiting incised valleys and canyons, provide surfaces on which (1) mounded and sheetlike submarine/basin-floor fans, (2) submarine channel fill and associated mounds and fans, and (3) prograding deltaic/coastal lowstand wedges were deposited. These fans, channel fills, and wedges are top sealed and sourced by transgressive shales and marine condensed sections, deposited at a time of regional transgression of the shoreline. Onemore » discovery well and various reservoir-quality sandstones occurring at predicted stratigraphic levels in other wells support the application of the sequence-stratigraphic concepts to hydrocarbon exploration.« less

A deep seismic profile of 800 km length recorded in southern Queensland, Australia

Summary. In 1984, the Australian Bureau of Mineral Resources and the Geological Survey of Queensland recorded a regional seismic reflection profile of over 800 km length from the eastern part of the Eromanga Basin to the Beenleigh Block east of the Clarence Moreton Basin. A relatively transparent upper crustal basement with an underlying, more reflective lower crust is characteristic of much of the region. Prominent westerly dipping reflectors occur well below the sediments of the eastern margin of the Clarence Moreton Basin and the adjacent Beenleigh Block, and provide some of the most interesting features of the entire survey. A wide angle reflection/refraction survey of 192 km length and an expanding reflection spread of 25 km length were recorded across the Nebine Ridge. The only clear deep reflectors are interpreted as P-to-SV or SV-to-P converted reflections from a mid-crustal boundary at a depth of about 17 km. The combined Nebine Ridge data provide well-constrained P and S wave velocity models of the upper crust, and suggest a crustal structure quite different from that beneath the adjacent Mesozoic basins.

Some Preliminary Results from Regional Seismic Profiling in Central Australia

In 1985, the Bureau of Mineral Resources (BMR) recorded a regional deep seismic reflection profile of 420 km length from the Northern Arunta Province to the southern part of the Amadeus Basin (Fig. 1); record lengths were 24 s. An additional 90 km of reflection recording were obtained in the form of cross lines or parallel lines. Experimental reflection recording to moderately large offsets was undertaken to study specific geological or structural problems. An east-west seismic refraction profile of 400 km length was also recorded within the Arunta Complex to determine crustal thickness and seismic velocity variations throughout the crust. Gravity was measured at 333 m intervals along all reflection traverses, and airborne magnetics were recorded along line 1 (Fig. 1).

Deep Seismic Profiling Across the Nebine Ridge, Surat Basin, Kumbarilla Ridge and Clarence Moreton Basin in Southern Queensland

In 1984, the Bureau of Mineral Resources (BMR) and the Geological Survey of Queensland recorded regional seismic reflection profiles of more than 800 km length from the eastern part of the Eromanga Basin to the Beenleigh Block east of the Clarence Moreton Basin (Johnstone et al. 1985; Wake-Dyster et al. 1985). Gravity measurements at 500 m intervals and an aeromagnetic survey at an altitude of 150 m were also undertaken. The main objectives of the work were as follows: to obtain seismological data that would assist in (i) understanding the evolution of the Surat and Clarence Moreton Basins, (ii) defining the role of the Tasman Orogenic Zone in the development of eastern Australia and (iii) providing regional ties between petroleum exploration leases. This paper provides a brief summary of the geological problems that have motivated the present work and emphasises results for the Nebine Ridge and Clarence Moreton Basin areas.

Contourite Anticlines as Exploration Objectives: ABSTRACT

Regional seismic profiles off the east coast of the United States gathered by the University of Texas Marine Science Institute and Woods Hole Oceanographic Institute have crossed three types of They are symmetric, asymmetric, and half-anticlinal forms and have up to 3,000 ft (1,000 m) of relief. Off the east coast, anticlines have been found in sections of Paleocene to recent age. They are the result of erosion, transport, and deposition by bottom currents that flow along the break between the continental slope and the continental rise. Because of the relation to deep-water currents flowing along this break in slope, the resulting deposits have been named contourite anticlines. Explorationists should be alert to the presence of contouri e anticlines and realize the limited exploration potential of this type of anticline. Recognition of their true nature early in exploration programs may save millions of dollars. Seismic reflections from Wilcox (lower Eocene) deep-water sediments of south Texas show that large--more than 10 × 5 mi (16 × 8 km), 2,000± ft (600± m) closure--anticlinal features were developed by deposition basinward from submarine fans. Texaco 1 Rodriguez was drilled in 1968 to 17,752 ft (5,326 m) on one of these The section within closure (below a drill depth of 8,700 ft; 2,610 m) penetrated by this test was entirely shale. Available data on present-day anticlines indicate that the currents that form them are capable of moving only clay-size material. Until stronger currents are documented, sandstones or any other type of reservoir, with the possible exception of fractured chalk, would not be expected in these features. Drape crestal grabens are present over some of the Wilcox anticlines of south Texas. Production has been obtained from the median-depth (9,000 ± 1,000 ft; 2,700 ± 300 m) upthrown fault traps associated with these grabens. End_of_Article - Last_Page 495------------