Interpretation Of Seismic Lines Research Articles

Structural evolution of the Rides Prerifaines (Morocco): structural and seismic interpretation and analogue modelling experiments

The Rides Prerifaines (RP) of Morocco constitute the leading edge of the Rif chain. They involve a Triassic–Palaeocene succession deposited on a peneplained Palaeozoic fold belt and accumulated in basins delimited by NE–SW-trending normal fault systems. A significant hiatus separates an overlying Middle Miocene–Upper Miocene foredeep sequence. The reconstruction of the complex structural evolution of the RP during the later compressive phases that affected the Rif chain since Middle Miocene time has been the aim of this paper. We integrated field structural analyses, seismic line interpretation, and analogue modelling in order to evaluate the control exerted by the Late Triassic–Jurassic normal fault systems onto the later compressive tectonics. The maximum compression direction associated with the first compressive phase is roughly NE–SW to ENE–WSW oriented. During this phase the Mesozoic basin fill was scooped-out from the graben and the main decollement level were the Triassic evaporites. Since Pliocene times the maximum compression direction was oriented roughly N–S. During this phase the RP assumed their present structural setting. The earlier normal faults delimiting the Mesozoic graben were reactivated in a strike–slip mode also involving the Palaeozoic basement. The analogue modelling experiments demonstrated that the basement reactivation promoted salt tectonics and favoured fluid circulation.

Post-Eocene extensional tectonics in Southern New Caledonia (SW Pacific): Insights from onshore fault analysis and offshore seismic data

Ductile to brittle extensional deformation following thrusting of the peridotites nappe during the Upper Eocene has been shown to play a major role in the Tertiary tectonic evolution of the northern part of the main island of New Caledonia and its eastern and western margins. In this study, we provide new tectonic data from southern New Caledonia that allow to better constrain the tectonic evolution of the southern part of the main island. We present a kinematic analysis of faults and striations obtained mainly from exposures of sedimentary rocks in the region of Nouméa with complements from measurements made farther north at Népoui within post-obduction Middle-Miocene deposits. We also present additional results of an interpretation of seismic lines from the lagoon south of the Nouméa Peninsula which provide constraints on the current tectonic regime of southern New Caledonia. Extensional faults in the Nouméa region have been studied within terranes of various ages including pre- and syn-obduction deposits and ophiolites. Hence, we demonstrate that important extensional events have affected the southern part of the New Caledonia block after the obduction of the peridotite nappe. The direction of maximum extension is variable at the scale of the region. Both high angle and low angle normal faults are present and block rotation is observed at some localities. This suggests that detachments accommodating significant displacements are cutting through the sedimentary pile. The average final strain pattern of the region can be regarded as the results of a multidirectional flattening, a hypothesis consistent with vertical uplift associated with regional extension. These results are in good agreement with conclusions of earlier workers showing late extensional evolution of the ophiolites along the chain and generalized extension in northern New Caledonia. The extensional faulting event in southern New Caledonia started after the obduction of the ophiolite, probably during the Oligocene. Extension was still active after the Middle Miocene, as shown by normal faulting in the Népoui conglomerates. Quaternary neotectonic features are observed in the lagoon and correspond to groups of short segments of vertical faults having orientation of N90, N40–50, N0–10 and minor N140, delineating subsiding areas. These faults are reactivated features with orientations corresponding to trends of coastlines and other main morphological features of the island. This study enhances the strong influence of normal-faulting neotectonics and recent tectonics on the current landscape evolution of southern New Caledonia. We infer that these tectonic processes played an important role during the weathering of the peridotites and subsequent development of the lateritic Ni-bearing layers as they increase the penetration of ground waters within the actively expending peridotite basement.

Evidence of flexural extension of the Rif foreland: The Rharb-Mamora basin (northern Morocco)

Abstract The Rharb-Mamora basin is the foreland of the Rif Cordillera (orogenic belt). The Mamora area (northern Morocco) is located at the southern border of the Rharb basin and intercalated between the Alpine Rif Mountains to the north and the Hercynian Moroccan Meseta domain to the south. Analysis and interpretation of seismic lines, hydrogeological and oil wells, have allowed to precise the major structural elements of the Mamora area, which is covered by late Neogene sediments. The structure of the area is controlled by faults that also affect the Paleozoic basement. The NE-SW and NW-SE trending faults induce the palaeogeographical evolution and control, the facies distribution and the thickness variations. The most important or relevant structural feature of the Mamora area is the Kenitra-Sidi-Slimane fault (K2SF) [Zouhri et al., 2001]. This fault N110oE trending is south of the Rif Alpine thrust front and is marked by a progressive deepening of its northern compartment, at least since Cretaceous time. Thus the Mamora appears as a hinge between the Rharb Basin and the Moroccan Meseta from Cretaceous to Neogene time.

The Neogene–Quaternary evolution of the Guercif Basin (Morocco) reconstructed from seismic line interpretation

The Neogene Guercif Basin of northeastern Morocco is the eastern continuation of the Rifean foredeep, from which it has been separated by the late Neogene uplift of the Tazzeka spur of the Middle Atlas. A dense grid (more than 1200 km) of seismic reflection profiles across the basin acquired during various surveys (1977, 1982, 1984–1985), the drilling of several wells, used to calibrate the seismic profiles, in particular those affecting the Neogene–Quaternary sequence, as well as the available superficial geological data, allow us to describe the late Tertiary–Quaternary evolution of this basin. The Guercif Basin is superimposed on late Cretaceous–Eocene inversion structures involving Jurassic half-grabens which are the downplunge northeastern continuation of the Middle Atlas. Extensive pre-Tortonian erosion, mainly due to tectonic uplift, occurred prior to the main Neogene subsidence event, which was due to the emplacement of the Rifean nappes. Minor early Tortonian extension is observed, but by the end of the Tortonian an overall compressional regime began which continued into the Plio-Quaternary and involves minor reactivation of the pre-existing inversion structures as well as the formation of narrow salt-cored anticlines. The same compressional regime is also responsible for the renewed uplift of the Middle Atlas and the Masgout uplift to the north of the basin.

Stratigraphic and structural analysis of the Late Palaeozoic–Mesozoic of NE Wales and Liverpool Bay: implications for hydrocarbon prospectivity

Interpretation of seismic lines from the offshore NE Wales area has provided information on the structural and stratigraphic evolution of the southern part of Morecambe/Liverpool Bay. Basin-wide megasequence boundaries are present between the Dinantian and overlying sequences and between the Upper Carboniferous and Permo-Triassic megasequences. Geological information obtained from seismic lines has been used to construct an E–W geological cross section and a basin analysis summary chart for the NE Wales–Cheshire onshore area. Stratigraphic interpretations have been considered in an assessment of the petroleum potential of the region. The distribution of Carboniferous oil and gas prone source rocks is a key element in predicting hydrocarbon accumulations. Source rock maturity may have been reached in the offshore area prior to a phase of inversion and uplift during Tertiary times. Fault-controlled hydrocarbon traps generated during Triassic-Jurassic rifting were modified during Tertiary inversion and new structures were generated.

The Geoseismic Character of the Rift and Fault-Subsident Continental Basins of Eastern Mongolia

The geoseismic interpretation of seismic lines from the East Govi, Tamtsag, and Choibalsan basins of eastern Mongolia illustrates basin development from typical rift geometry through fault subsidence, to a phase of wrench structuration and fault-block inversion. These eastern Mongolian basins are located in an accretion zone to the south of the Siberian craton. They are close to a number of similar Chinese intraplate basins. In particular, the geology of the Songliao basin is well documented and the Mongolian basins appear to have a similar geological history. The good-quality seismic response allows identification of the following features characteristic of different phases of the evolution of the basins: (1) rift fill sequences with typical chaotic to divergent seismic configuration on the edges of V-shaped grabens, (2) the oblique and sigmoidal internal seismic configuration of a prograding delta system, (3) parallel seismic reflectors in the center of the subsiding basins (By analogy with the adjacent Chinese basins these sediments are thought to consist of low-energy lacustrine sediments. In the Songliao basin these deposits are important source beds and it is likely that they represent the source of oils known in the East Govi basin), (4) deep fossil river erosion and subsequent infill, (5)more » wrench-type fault patterns, associated intrusions, and inversion of fault blocks, and (6) limited Neogene subsidence as a result of uplift due to interplate collision.« less

A Model for the Evolution of Salt Dome Overhang, East Texas Basin

Interpreting the geometry and attitude of the salt stock and beds beneath a salt overhang is difficult. Often the geophysical data sets are ambiguous or incomplete and interpretative thinking has to be guided by geologic models. However, some geologic models are based on an apparent geometry of the salt on seismic lines and result in a volume problem between the salt and sediment. The model shown here preserves bed lengths and sediment volumes in cross sectional drawings and block diagrams during the pillow, diapiric, and postdiapiric stages of growth. The volume of the diapir is accommodated by bed thinning and drawbridge movement instead of by sediment removal by erosion. The growth of the overhang is interpreted as a second episode of salt movement after the diapir stage has concluded. Competent beds above the diapir form a barrier to the renewed growth of the stock. The upward force of the salt lifts the overlying beds instead of breaching them. The salt then spreads laterally, splaying the beds apart and swelling the overhang salt mass in a balloon-like fashion. The overhang growth continues until the basal salt chamber is evacuated. As the basal salt is taken into the overhang, the flank sedimentsmore » surrounding the stock may cave in, squeezing off the salt stock and filling the void created by the evacuated salt. The application of the model to seismic line interpretation results in a unique geometry with a small salt stock, a vent closing fault, and an umbrella-like overhang.« less

TECTONIC CONTROL OF WORLD OIL RESERVES: AUSTRALIA'S POSITION

Although simple extensional clay models may be representative of grabens tens of kilometres in length, rotational divergence of continents on a sphere produces very different structures. Repeated periods of compression during separation result in wrench faults and compressional anticlines developing along major crustal fractures as a consequence of changes in momentum between a continent and adjacent smaller continental blocks along its rifted margin.The global distribution of rotationally divergent continental margins can be accounted for by asymmetric expansion of the earth. The southern bulge caused by expansion has emphasised non-marine deposition on southern continents with marine deposition more common in the northern hemisphere.Phanerozoic source rocks of the northern hemisphere account for 97 per cent of the world's produced and current reserves of oil. Australia's share of this extreme distribution asymmetry is less than one half of one per cent, yet the country covers five per cent of the Earth's continental crust.The proportion of undiscovered oil reserves outside OPEC and the former USSR is approximately 30 per cent, or some 12 per cent of the world's estimated ultimately recoverable reserve of 2 trillion (Tera) barrels. The majority of Australia's undiscovered reserves lie on the North West Shelf where about 12 per cent of the country's estimated ultimately recoverable reserve could be found.Although Australia is politically stable, lower petroleum taxes would attract exploration for smaller, structurally complex oil fields. While such taxes may be considered politically difficult at present, a by-product of concerted oil exploration would be an enormous increase in Australia's gas reserves to feed the national pipeline grid for the 21st century. Industry can assist increased success rates by greater attention to current technical deficiencies, such as the structural interpretation of seismic lines.

Pre-Late Weichselian submerged rock platforms off Stonehaven

The existence of rock platforms around Scotland which pre-date the Late Weichselian (equivalent to the Late Devensian) glaciation is becoming increasingly apparent ([Sissons 1981][1]; [Browne and McMillan 1984][2]). This note describes the occurrence of three such platforms in the offshore area around Stonehaven, on the east coast of Scotland. The evidence for the platforms is based on the interpretation of seismic lines as shown in Plate 1. The platforms have been numbered 1 to 3 for reference, and their areal extent is indicated in Figure 1. These features appear to be unique to this area; however, work is in progress to find equivalent features elsewhere. The platforms have a step-like appearance and can be considered to be horizontal in profile as they slope gently away from the coast with apparent gradients of 0.5 to 2 m per kilometre. Platforms 1 and 2 appear to trend sub-parallel to the present shoreline; the trend of platform 3 is uncertain. Platform 1 occurs at a depth of 30 m below sea level and is over 1 km in width. The nature and location of the shoreward termination of this platform is uncertain because the seismic data do not extend inshore. Platform 2 occurs at a depth of 45 to 50 m and is about 4.5 km wide. Both platforms are cut into Devonian strata and are overlain by a discontinuous veneer of till and lithic-dominated littoral sands and gravels derived from the till. Platform 3 is the broadest platform extending to 7.5 km, . . . [1]: #ref-2 [2]: #ref-1