Introduction
Transgressive system tracts [TST]
It is formed by the rise in sea level over the shelf edge and the general conditions of the transgressions. Sediment deposited on the shelf and slope sedimentation moves toward the continent as a transgressive series. TST presented retrogradatsionnym package parasikvensov characterizing transgression as the shelf and in the coastal lowlands.
In zashelfovoy area due to lack of precipitation formed clay-fused incision [condensed-section deposits]. The foot of the front surface is called transgressive [transrgessive surface]. It represents the maximum flooding surface, which marks the beginning of transgression, reflected in a shift of the coastline in the land.
TST deposits are characterized by plantar overlap the boundary sequence in the direction of land and form fit to the plantar surface of the transgressive toward the pool.
With continuous reaching sea level highstand systems tracts a state of high standing [HST]. Sea shelf stable floods that overlap sedimentary material. Most of the debris covers offshore and transported to the edge of the shelf and continental slope, where a system of shallow shelf clinoforms progradation complex towards the continental slope.
Lowstand System Tract
Lowstand System Tract is formed in the fall of the sea level to the lowest state and draining shelf. The main sedimentation occurs due to rapid transport of clastic material in the foot of the continental slope (the state of systems tracts of low early state EPLST). In this deposition is carried out in the deep parts of the basin, where a bottom apron. Its accumulation due to the action of erosion channels on the slope and incised valleys on the shelf. Sloping apron [slope fan] presented grain flows formed in the middle of or close to the base of the slope. After the maximum drop in sea level, in a much dried shelf large transport debris from the land leads to zacypaniyu area of the continental slope in the form of progradation (forward) clinoform complex mainly in the area of the continental slope and the foot (the state of systems tracts late low standing LPLST).
Highstand system tract [HST]
It is the top element of the sedimentary sequence data, which lies on its underlying sediments transgressive tract, or (in the coastal parts of the sequencing) sequencing directly on the border. In this sea shelf stable floods that overlap sedimentary material, and the majority of its transported to the upper continental slope. Here begins the formation progradatsionnyh systems aimed at pool side. HST is formed at slower speeds increase relative sea level due to the fact that the supply of sediment from the land greatly exceeds the rate of increment of the area of deposition. HST is responsible highstand sea level and is characterized by a set of regressive facies (based on the book "Sekventnaya stratigraphy" RR Gabdullin and others, 2008).
Parasikvens [parasequence] - is a shoaling upward sequence of layers bounded by the surfaces of sea flooding [marine fl ooding surface / MFS]. Parasikvens a regressive cycle.
How the grain size would differ both vertically and laterally.
Full sequencing sediment consists of three parts, called tracts of sedimentary systems [system tracts]. Tracts are lateral facies series [depositional system], formed in different conditions of sedimentation. It is particularly important is the variation in relative sea level and its position relative to the shelf edge [shelf break]. Each system tract presents a collection of rainfall associated with sedimentary processes that were active in different phases of the sea level fluctuations. Precipitation of these systems can be considered as sedimentary units that were deposited simultaneously and that may be depicted concluded between continuous surfaces, spread from sub-aeralnyh [sub-aerial] to sub-aquatic [sub-aqueous] conditions (based on the website http:/ / sepmstrata.org).
The early phase of low tract of standing EPLST:
Drop in relative sea level due to rapid eustatic lowering and / or tectonic uplift, outstripping repositioning sea level. River incision cuts to form a dissenting border or boundary cycle, and most of the precipitation are focused on the waterfront.
Forced regression [Forced regressions], induced by the lack of accommodative space, producing consistent laying down the section of the particles to form progradatsionnyh clinoforms of condensed surface formed during the previous transgressive tract and highstand tract. Unstable slopes, formed rapid sedimentation of fluvial systems [fluvial system].
Hairdryers [Basin floor fans] are formed from sediments transported from the border of the shelf, while rapid accumulation associated with forced regression. The boundary of the shelf and slope hairdryer [slope fan] are formed when the rate of sedimentation and slope instability and slow down accordingly, so precipitation is not moved far down the slope.
The occurrence of precipitation over progradirovannymi clinoforms before the end of the shelf The lower bounding surface early phase tract low state is disagreement and the upper part of the underlying condensed part of the section. These surfaces are formed by different mechanisms and at different times.
The upper part of the condensed nizhezalegayuschey surface lies directly under progradirovannymi clinoforms forced regression. The upper part of the early phase of the path of low standing in the theory says the initial occurrence of rocks eroded surface progradirovannyh clinoforms forced regression.
The late phase of low standing LPLST:
- Slow rise of relative sea level.
- Precipitation is now lagging behind the increase in the accommodative space, in connection with which they are located at the edge of the pool.
- Profile of the river stabilizes.
- Valley fill.
Transgressive tract TST:
The rapid rise in sea level caused by outrunning eustatic sea-level rise over the tectonic uplift. Condensed sequencing often consist of layers of rich fauna, low sedimentation rate, a large part of the sea floor is exposed to sedimentation. Maximum flooding surface is formed when the accumulated fine-grained transgressive deposits.
Highstand tract HST:
Slow growth in sea level accompanied by a slow subsidence.
Sediments accumulate faster growth accommodative space.
Stabilize river profiles.
River valleys spread horizontally in the direction from the edge of the shelf in the land.
Progradirovannye highstand clinoforms developed with agradirovannymi nodes that are thinning up the section.
Stacking Velocity
In seismic exploration in the velocity spectrum usually refers to and multiple stacking velocity spectra covering technology. Called stacking velocity based on common reflection point from the curve obtained speed. Superimposed after NMO correction, NMO correction speed appropriate, superimposed upon the most significant wave energy when the speed is known as the best stacking velocity. Instead, the moving speed of correction is inappropriate, superimposed upon the effective wave energy is necessary to weaken. Superimposed records the amplitude change with the stacking velocity, this stacking velocity spectrum. Conventional stacking velocity analysis method has matured, the conventional movable correcting equation, however, is based disorderly in the assumption of the same horizontal reference plane, the undulating regions on the surface, even with the method of the floating datum, and its speed of analysis error cannot be ignored.
The interpretation of seismic data we do is primarily to understand the regional geology of the continental territories of Canada and the Arctic. The scope of seismic sedimentary basin in Western Canada and the deformed belt is smaller due to the small amount of data involved. These studies contribute to a greater understanding of a wide range of geological problems, the party is directly beneath the surface to the base of the continental crust. It is therefore a fundamental component of integrated multidisciplinary studies conducted in the GSC in Calgary and on the vast landmass of Canada.
Sequence Stratigraphy: "Sequence stratigraphy is the study of relationships within a chronostratigraphic rocks, consisting of genetically related strata repetitive, limited by surfaces of erosion or non-deposition or by their continuity concordance" (Posamentier and al, 1988).
• Sequence Deposit: The deposit sequence defined by Mitchum et al. (1971) is a stratigraphic unit composed of a relatively conformable succession of genetically related layers, limited to roof and wall by discontinuities or continuity in accordance parasequence: A parasequence is a unit of successive benches consistent with each other, from the same dynamic installation in limited roof by a minor flooding surface.
• The types of discontinuities:
- Discontinuities regression or transgression are surfaces along which it there's a demonstration of erosion air (and diving in some areas) or subaerial exposure with a marked gap in sedimentation (Posamentier et al, 1988). During marine transgressions, manifestations of exposure are reworked by wave erosion on the coast, there follows a transgressive surface of erosion or ravinement surface. During phases of sea level fall, erosion surfaces are developed in the open air behind the coast and in the water in front of the coast due to wave action ensues regressive surface of erosion (Walker, 1984).
- Marine flooding surfaces: These surfaces reflect an abrupt change in the depth of hand and on the other they separate layers. These surfaces are moths natural parasequences.
- Surfaces of maximum transgression: When sea level rise, the terrigenous sedimentation bends as much coarse sediment is confined to the alluvial plain. A stabilization of the sea level, sediment can again advance towards the sea downlap on the deposition surface corresponding to the slow sedimentation that was previously established. This surface is called surface transgression maximum or maximum flooding surface (MFS), it separates the sediments were deposited during the transgression phase from those of the next step which marks a regression. This surface corresponds to a horizon of accumulation of condensed fauna and often emphasized by levels of phosphate and glauconite or detectable on the curve of Gamma-ray by a sharp deflection resulting enrichment of clay. It can also be detected by a change in the size of the animals.
• Problems of sequence boundaries: There is controversy about the limits to be adopted for sequences that resulted in two designs:
- Vail et al. retained the discrepancies related to sea level fall (discontinuities regressive) to define depositional sequences between two discontinuities arguing there is essentially continuous sedimentation and that it represents the major cuts.
- Galloway in 1989, introduced the concept of genetic stratigraphic sequence based on the surfaces of maximum transgression. These sequences are formed by deposition units identical to parasequences as defined by the Exxon group, but they are limited by maximum flooding surfaces (MFS). The findings identified in this design are:
- In many basins, the sedimentary fill is relatively rapid during periods of high and low sea level, while sedimentation is slow or tends to cancel during the transgressive phases. It follows that the major units of depot that correspond to a continuous sedimentation in marine conditions are separated by homogeneous surfaces downlap surfaces and not by discontinuities as defined by the Exxon group.
- Sequential limits allowed by the Exxon group correspond to sedimentary surfaces whose expression is chosen because the subaerial erosion affects only limited areas. In a large part of the basin these surfaces can be difficult to recognize. Instead limits in relation to the MFS on the seismic profiles are the most obvious.
- The erosion surfaces are diachronous while transgressive surfaces approximate maximum time lines.
In this study, the MFS is used as a means of correlation between surveys because they are extensive and synchronous as discrepancies.
• The cyclical in stratigraphy: cyclical phenomena on different fields such as stratigraphy and tectonic evolution orogenic volcanism and magmatism, climate changes, biological and geochemical tectonic events etc..
Einsele in 1992 summarized the main phenomena involved in cyclic sedimentation. He distinguishes:
- Cycles of the first order: they are long-term megacycles related to plate tectonics a period greater than 50 Ma
- Cycles of second order: megacycles are medium term duration is between 50 Ma and
- 3rd order cycles: cycles are short-term duration between 0.5 and 5 Ma, but most often not exceeding 3 Ma
- 4th order cycles: their duration is between 0.1 and 0.5 Ma and are interpreted as parasequences (Posamentier et al., 1988).
- 5th order cycles: their duration is between 0.05 and 0.1 Ma
Brief introduction to sequence stratigraphy.
Sequence Stratigraphy. - Son rocks relations in context genetically related strata chronostratigraphic repetitive and limited by surface erosion (mismatches), or reservoir (hiatus) or their Correlate matches. (Van Wagoner et al., 1990). Posamentier and Allen (1999), defined as a pattern analysis cyclic sedimentation present in stratigraphic successions, developed in response to variations in sediment supply and space available for accumulation.
Depositional sequence. - Stratigraphic unit composed of a succession genetically related strata continuous and limited in its top and base by unconformities or their relative concordance (Mitchum et al., 1977). Geometries and seismic reflectors ENDINGS The geometries and finishes sismoestratigrafía establish a framework and sequence stratigraphy, defined based on the parallelism of layers and surfaces that limit or against ending, taking five types:
a) Top Top lap. - Reflectors or strata are inclined to end against a surface overlying lower angle. Erosional truncation. - Termination of strata or lateral seismic reflectors against overlying erosion surfaces.
Structural truncation. - Termination or side of a reflector layer structures (e.g. faults, gravity sliding, or hialoquinesis igneous intrusions). Concordance. - Strata or limited parallel reflectors in the bottom and above.
b) Bottom Onlap. - Terminations strata or low-angle seismic reflectors or horizontal surface against a greater angle.
Baselap. - When a onlap can not be distinguished because downlap deformation.
Downlap. - Strata or reflectors initially inclined towards ending the basin against an incline or horizontal.
Seismic facies. - Dimensional seismic mappable units, composed reflectors groups whose characteristics are different from those of facies adjacent seismic.
Systems tracts. - Sedimentary packages are representing a group of contemporary depot systems (Brown and Fisher, 1977). Comprises a sequence of tracts of systems defined by: -Limiting surfaces -Geometry of seismic reflectors strata or -Position in the sequence -Stacking patterns of parasequences and parasequences games.
Parasequences. - Relatively conformable succession of layers or games genetically related layers bounded by marine flooding surfaces or its correlative surfaces (Van Wagoner, 1990).
Marine flooding surface. - Separate old younger strata with Evidence of abrupt change in bathymetry, identified in environments coastal plain, deltaic, tidal marshes and platform (Van Wagoner, 1990).
Parasequences game. - Succession genetically parasequences Related forming a distinctive pattern and limited by stacking flood over marine surfaces or surfaces correlated (Van Wagoner, 1990).
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