1,720,971 research outputs found
Seismic sequence stratigraphy of the Paleozoic of Central Arabia, Hawtah area (Saudi Arabia)
No full textNine second-order sequences in Central Arabia are in part correlatable with worldwide seismic sequences. Differential uplift and subsidence occurred throughout the Paleozoic and was interrupted by a late Ordovician-early Silurian and an Upper Carboniferous to lower Permian glaciation.
The wedge-like sequences A and B represent an incomplete Cambro-Ordovician encroachment cycle. The uppermost Ordovician-lowermost Silurian sequence C represents a thin sequence of glaciogenic clastics. The wedge like sequences D, E and F represent the resumption of passive margin subsidence around the margin of the Central Arabian arch. Sequence G is underlain by a major unconformity (SB 7) which terminates much of the formation of the Central Arabian arch. Sequence H, the upper Permian Khuff carbonates mark the beginning of the wide Mesozoic passive margin of the Tethys
A stratigraphic analysis of Paleogene deposition in northwest Europe and the role of graphic correlation in sequence stratigraphy
No full textA sequence stratigraphic analysis of Paleogene deposits, using subsurface data (well logs, seismic data, and biostratigraphy) from the Central North Sea and published outcrop information from northwest Europe, has documented a framework of 30 "third order" depositional sequences nested within 5 "second order" major regression/transgression cycles. The order of a cycle is based on observations concerning its constituents and its impact on the depositional systems of the basin, not strictly on its duration.
Integration of composite standard biostratigraphy with sequence stratigraphy builds a consistent chronostratigraphic depositional framework. The framework is based on the identification of hiatal intervals in wells, boreholes, and outcrop using graphic correlation. Hiatal interval is a generic term that differs from condensed section. Discontinuous sedimentation is assumed of across some units traditionally called "condensed sections". This assumption is based on evidence from regional correlation of graphic correlation terraces. An ideal relationship of graphic correlation terraces within a sequence stratigraphic model is presented, providing the theoretical basis for regional correlations. Weaknesses in graphic correlation (underuse and static application) are countered with strengths in sequence stratigraphy (widespread use and dynamic application). Conversely, weaknesses in sequence stratigraphy (documentation and consistency) are the strengths of graphic correlation. This study emphasizes the interdependence of the two methodologies.
A depositional model is also proposed as a variant of the classic Vail model. This model considers the effect of depositional profile and sediment supply in the preservation and distribution of systems tracts. Recent revisions in Central North Sea lithostratigraphy and sequence stratigraphy provide an opportunity for comparison between different methods and data resolutions. The stratigraphic framework built from subsurface data is compared with age-equivalent deposits outcropping in Northwest Europe. This correlation reveals that sedimentation in the deep basin occurs as depositional pulses, separated by time-correlative graphic correlation terraces (hiatal intervals). Data terraces expand into thick deposits in Northwest Europe. Not all sequence boundaries are resolvable by graphic correlation, but the method brackets packages defined by seismic, log interpretation and biostratigraphy. By correlating outcrops and subsurface data, it is possible to construct a relative sea level signal for the entire basin
Seismic sequence stratigraphy of the Lower Congo, Kwanza, and Benguela Basins, offshore Angola, Africa
No full textSequences are recognized throughout the geologic record. The Angolan margin provides an excellent opportunity to examine the factors that control the deposition and preservation of sediments in sequences, as well as the factors that create the erosion or non-deposition along sequence boundaries. The Angolan sequences can be compared to global sequence charts and used to investigate the effects of local events versus global events on the area's sequences.
Using seismic sequence stratigraphic principles, a 2D regional seismic data set covering three basins offshore Angola, the Lower Congo, Kwanza, and Benguela Basins, was interpreted. Sequences and their unconformities were correlated within each basin as well as between basins. Major sequences could be interpreted throughout and between the three basins with a high degree of confidence. Additional sequences within these major sequences were interpreted within a basin, but could not be correlated to the adjacent basin with a high degree of confidence. Detailed interpretation of the sequence stratigraphic significance of each reflector was performed on three profiles, one for each basin. Chronostratigraphic charts were constructed using the detailed interpretation of the profiles. Within the interpreted sequence stratigraphic framework, the timing and mechanics of the formation of salt structures was examined. The Angolan basins contain a variety of salt tectonic features. The reflectors of strata adjacent to the salt features were used to determine the timing and mechanics of the salt structure formation.
This study accomplished several objectives. The tectonic evolution of the Angolan margin was reviewed. This study established a sequence stratigraphic framework for Angola. The process of deposition and preservation of sediments as depositional sequences was examined. The sequences were compared with the global sequence charts as well as with eustatic, tectonic, and oceanic circulation events. The formation of the sequence bounding unconformities was examined. Within the sequences, the interaction of sedimentation and salt movement was described
Stratigraphic and structural evolution of the western Malvinas and southeastern Magallanes basins, Argentina
No full textThe area evolved from a Jurassic rifting stage to a Cretaceous sag and a Tertiary foredeep stage.
The sedimentary record is subdivided into four tectonostratigraphic units: Jurassic rift deposits, late-Jurassic-Cretaceous sag deposits, latest Cretaceous-Eocene foredeep-transition deposits, and late Eocene-Pliocene foredeep deposits. The rifts are filled with continental volcanics and pyroclastics. The sag deposits form a backstepping marine wedge, which contains the Springhill Formation (main reservoir) and is covered by a muddy and marly aggradational interval deposited in neritic waters of an epeiric sea (main petroleum source and seal). The latest Cretaceous to Eocene is a forestepping-backstepping wedge of glauconitic sandstones and claystones and carbonate buildups of shallow marine origin. The foredeep deepens during the late-Eocene to Oligocene. It is infilled during the Oligocene-late Miocene by a forestepping wedge that prograded from the west and southwest.
The age of the foredeep suggests that the southern Andean Orocline formed during the Paleocene-late Eocene interval
A sequence stratigraphic analysis of Campanian to middle Miocene sediments of the Sable Island area: Offshore Nova Scotia, eastern Canada
No full textThe continental shelf offshore Nova Scotia is within a passive margin setting and is an excellent area to study the sequence stratigraphy of late Cretaceous and Tertiary sediments. Hydrocarbon exploration offshore Nova Scotia over the past twenty years has produced a substantial amount of well log data. This study integrates the well log data with seismic and biostratigraphic data to create a sequence stratigraphic framework of late Cretaceouse to middle Miocene strata. Sigma Exploration of Calgary has donated access to a large grid of 2D seismic data, covering the outer modern shelf. To help constrain the ages of the sequences, a biostratigraphic analysis of the well Marmora C-34 was performed.
Twelve sequences from Campanian to middle Miocene are resolved by integrating the data. Global correlation of results suggest that eustasy is the primary factor in the formation of sequences within the Scotian Basin between lower Eocene and middle Miocene sediments
Pliocene-Pleistocene depositional sequences of the northern Gulf of Mexico, offshore Texas and Louisiana
No full textThis work tests the consistency of sequence stratigraphic methods by comparing the model documented in this study with previous models for growth faulted, siliciclastic environments. Interpretations derive from sequence stratigraphic analysis of high quality seismic integrated with well control and detailed biostratigraphy.
Hierarchic cyclicity determines sequence type and facies distribution. Sequences with durations of approximately 5 My. include four components that fill and determine basin physiography. Sequences with 1-2 My. durations result in landward-seaward stepping trends of depositional sequences. Depositional sequences comprise two, three, or four components and range in duration from 100,000-400,000 years.
A relative sea-level curve deduced from the chronostratigraphy of depositional sequences is compared to a filtered oxygen isotope record. Comparison shows frequencies and trends correlate very well; but magnitudes do not. This correlation implies that glacio-eustasy and depositional sequences are intimately related, and sequence stratigraphic methods are consistent
Separating tectonic, eustatic, and episodic depositional processes in the stratigraphic record of the basins of southeastern and northwestern Australia (Cretaceous Period)
No full textFour dynamic processes interact to create the stratigraphic record in a basin: climate, sediment supply, eustasy, and subsidence. To identify the contribution of each of these processes, techniques that can uniquely separate the effect of each component process on the stratigraphic record must be applied to produce a thorough understanding of the process, how it evolves through time and interacts with other processes. Recently published techniques (sequence stratigraphy, one- and three-dimensional backstripping), as well as techniques developed herein (Relational Tectonic Analysis), provide high resolution basin eustatic and tectonic histories. Integrating these new techniques with standard stratigraphic methods illuminates aspects of basin evolution heretofore hypothesized but unrecognized.
Application of integrated analysis techniques indicates that plate tectonic reorganization events occurring during the Cretaceous Period had profound effects on the recognition of important sequence stratigraphic surfaces in southeastern and northwestern Australia. Seven reorganization events are recognized to have influenced the Cretaceous motion history of Australia. Eleven third-order eustatic cycles are recognized to have occurred during deposition of the Neocomian sediments of the Exmouth Plateau/North West Shelf. Sixteen third-order eustatic cycles are defined in Late Cretaceous sediments of the Otway Basin. The numeric ages determined from these twenty-seven biochronostratigraphically dated eustatic cycles are used to produce one- and three-dimensional subsidence histories. Each tectonic event creates a paired increased subsidence-decreased subsidence cycle. Each change in subsidence induces changes in the space available for sediment deposition. Changes in subsidence that create more space for sediments causes depositional systems to retrograde and transgressing the continent. Transgressive aspects of sediments deposited during each sea level rise associated with third-order eustatic cycle are amplified and therefore easier to recognize. Concurrently, the ability to recognize the regressive aspects of each eustatic cycle is diminished. If subsidence change reduces space available for sediments, the opposite effect occurs: depositional systems prograde, and regressive aspects of the third-order cycles are enhanced. Not all subsidence rate changes are due to tectonic reorganizations. Change in flexural subsidence induced by sudden large localized sediment influxes also cause enhancement of aspects of third-order eustatic depositional patterns
A sequence stratigraphic analysis of an Oligocene to Miocene carbonate platform: Beagle and northern Dampier subbasins, Australia
No full textThis sequence stratigraphic analysis examines an Oligocene to Miocene carbonate platform from the Northwest Shelf of Australia. Five Oligocene sequences, eleven Miocene sequences and one Pliocene sequence are identified with the aid of seismic, well logs, and biostratigraphy. To test the global nature of these sequences, their ages are compared to Europe, New Jersey, and the Bahamas. Most sequences correspond well, within a few hundred thousand years, with the exception of five sequences 32.0 Ma, 29.4 Ma, 20.5 Ma, 19.5 Ma, and 17.3 Ma (listed with European ages) that are not found in Australia.
The global correlations and oxygen isotopes from an industry well suggest that eustasy is the primary control on the genesis of Oligocene to mid-Miocene sequences. Sequence boundaries correlate to heavy delta18O peaks while maximum flooding surfaces coincide with light delta18 O peaks
Eastern Venezuela Basin: Sequence stratigraphy and structural evolution
No full textA regional study has been carried out within the Eastern Venezuela Basin and its offshore continuation to the Orinoco Delta and the Barbados Accretionary Complex. The Eastern Venezuela Basin and its offshore continuation is a Neogene foredeep superimposed on a Mesozoic passive margin.
The Cretaceous to Paleocene of Eastern Venezuela is best subdivided into five second order transgressive-regressive cycles bounded by a 131 Ma (basal Cretaceous) sequence boundary, four maximum flooding surfaces with the inferred age of lower Aptian (111 Ma), upper Albian (98 Ma), middle Cenomanian (95 Ma), middle Turonian (91.5 Ma) and an upper Paleocene sequence boundary (58.5 Ma).
An upper Paleocene to Eocene second-order cycle (58.5 Ma-36 Ma) is followed by the Oligocene which is subdivided into two third-order cycles bounded respectively by 36 Ma, 30 Ma and 25.5 Ma sequence boundaries.
An uppermost Oligocene to lower Miocene (25.5 Ma) basal foredeep unconformity is associated with the sudden deepening of the passive margin in response to the emplacement of the Serrania del Interior.
The Neogene of the Eastern Venezuela foredeep consists of three second-order sequences defined by 25.5 Ma, 16.5 Ma and 10.5 Ma boundaries. In the offshore an upper Miocene (5.5 Ma) unconformity is associated with deeply incised submarine canyons. Sixteen third-order sequence boundaries are recognized and correlated over the region
A sequence stratigraphic analysis of the late Jurassic-Turonian in the context of the evolution of the West Siberian basin
No full textDuring the Triassic, Siberia was a basin approximately 1800 kilometers wide filled by red beds and the widespread Tunguska basalts. Rifting occurred in the northern part of the basin. The western part of the Siberian basin became the West Siberian basin, which was bounded by rising uplifts both to the east and to the west.
The differentiation between the effects of tectonics and eustasy in cratonic basins is simple in that the global eustatic signal is basin-wide and enhanced by regional and local tectonics. Thus the first, second and third order cycles of the Upper Jurassic - Turonian in the West Siberian Basin were primarily influenced by eustasy. The Upper Jurassic - Turonian was deposited during an overall transgression and is subdivided into two second-order and sixteen third-order transgressive-regressive cycles. Fourth-order cycles appear to be controlled by delta shifting. A relative sea-level curve for the Upper Jurassic - Turonian resembles the "global" sea-level chart of Hardenbol, et al. (1998)
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