IPT-SIG4024-M Seis. Stratigraphy v1-4.ppt

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HomeUnconformitiesSeismic SequencesDepositional Sequences Parallel ReflectionPrograding clinoform reflectionMound Fill Bank and LensVolcanic- and Contourite mounds and Migrated wave

AuthorsReferencesSummaryGeneral infoIntroEgil Tjland Camilla Hagelund

Introduction

Title of learning contentIntroduction to Seismic StratigraphyName of authorEgil TjlandName of producerCamilla HagelundContent abstractRecognition, mapping and interpretation of unconformities, seismic sequences and depositional sequences. 4 keywordsSeismic sequences, depositional sequence, unconformities, seismic faciesLearning goalsTo recognize seismic sequences and unconformities and to identify important reflectors representing either a depositional feature or a tectonic event. Learning activities



General Information

Size in megabytes (included sound, video, animation files)5.3Software requiredMS PowerPoint XPEstimated time to complete (minutes)60Topic disciplineGeophysicsPrerequisitesGeneral knowledge of GeologyLevel (0 is very easy 4 is most difficult)2MethodIndividual learning, a referencewhen interpreting seismic data.Version number (start with 1.0)1.0



HomeSeismic SequencesIt is necessary to detect reflection terminations in order to predict seismic sequences. These sequences will then provide the basis for interpretation of depositional environment and estimation of lithofacies.Unconformities Recognition and mapping of unconformities are the first steps in understanding the geologic history of a basin or a geologic province.Depositional SequenceAnalysis of configuration, continuity, amplitude, and frequency is most meaningful when done within the stratigraphic framework of the depositional sequence.General prosedureSeismic SequencesUnconformitiesDepositional Sequences



Seismic Stratigraphy Interpretation ProcedureSeismic sequence analysisUnconformitiesSeismic SequencesDepositional SequenceWell-log sequence analysisFuture topic in a module, one example givenSynthetic, well-to-seismic tiesFuture topic in a moduleSeismic facies analysisFuture topic in a moduleInterpretation of a depositional environment and lithofaciesFuture topic in a moduleForward seismic modellingFuture topic in a module Final interpretationInterpretation practice is given in Seismic Key Examples and Seismic interpretation reservoir

This module mainly focus on step 1. Example of a Well LogCorrelation



Well log correlationABCNote the termination of reflections and the thinning of the interval between wells A and BThe unconformity surface changes from an angular unconformity in the uplifted part to a disconformity off the structure



Unconformities of the Grand CanyonDiagrammatic representation of the north side of the Grand Canyon, summarizing the character and relationship of the different rocks.D DisconformityAU - Angular UnconformityNC NonconformityLU - Local UnconformityDefinition of Unconformity



A surface of erosion or nondeposition that separates younger strata from older rocks and represents a significant hiatus.

Classified on the basis of the structural relations between the sequences. The unconformities record periods of time that are not represented in the stratigraphic column.

Records a fundamental change in the environment from deposition to nondeposition and/or erosion. This change may indicate an important tectonic event. Definition of Unconformity



Angular UnconformityThe older strata have a different angle than the younger strata. It is an obvious mark of a hiatus since it implies that the older beds were deformed and then truncated by erosion before the younger ones were laid down.



DisconformityThe beds above and below are parallel and the unconformity is of regional extent but are separated in time by a hiatus



Local UnconformityThe beds on either sides are parallel to one another, but the unconformity appears to be only of local extent or significance.



NonconformityStratified rocks rest upon granitic or metamorphic rocks.



Seismic SequencesClick on an element to look at it more closely.



Interpretation using Seismic Stratigraphy Diagram showing reflection terminations patterns and discontinuities. Discontinuities are underlinedCLIMATEDiagram of seismic reflections, lithofacies, and major variables affecting stratigraphy



Baselap: OnlapIf onlap cannot be distinguished from downlap because of a subsequent deformation, the more inclusive term baselap may be necessary.



Baselap: DownlapDownlap is a relation in which seismic reflections of inclined strata terminate downdip against an inclined or horizontal surface

Note: downdip is a stratal term, not solely restricted to seismic reflection patterns



OnlapOnlap is a base-discordant relation in which initially horizontal strata terminate progressively against an initially inclined surface or in which initially inclined strata terminate progressively updip against a surface of greater initial inclination



Erosional TruncationErosional truncation implies the deposition of strata and their subsequent tilting and removal along the unconformity surface It is the most reliable top-discordant criterion of a sequence boundary



Down Cutting Erosional TruncationDown-cutting erosional truncation is where horizontal strata terminate against an erosional surface, in this example a channel or gorge



ToplapToplap is the termination of reflections interpreted as strata against an overlying surface as a result of nondeposition (sedimentary bypassing) and only minor erosion.



Depositional Sequences Reflection configuration patterns within the depositional sequenceExternal configuration forms within the depositional sequenceVolcanic- and Contourite mounds and Migrated waveBank and LensFillMoundParallel ReflectionPrograding clinoform reflectionClick the blue Icons



Parallel Reflection ConfigurationsParallel reflection configurations suggest uniform rates of depositions on a uniformly subsiding shelf or basin.

Subdivisions of this pattern are based on variations in AmplitudeContinuityFrequency

Example 1Example 2



Parallel Reflection: Example 1Continues

Reflection as in figure 2

Reflection as in figure 1 Click the rectangles to learn more about the reflections shown



Parallel Reflection: Example 2ContinuesClick the rectangles to learn more about the reflections shown



Parallel Reflection: Figure 1 Figure 1The profile shows continous events of varying amplitude.This pattern represents an alternation of shelf carbonates and mudstones which produced paired reflections



Parallel Reflection: Figure 2Figure 2: Good continuity, showing high amplitudes, broken by areas of discontinuous lower amplitudes indicating intervals of sand and shale. Typical feature of a deltaic plain.



Parallel Reflection: Figur 3Figure 3Thick interval of distinct low amplitudes or quiet reflections with occasional high amplitudes indicating a thick section of marine shales with thin sand and siltstone beds



Prograding Clinoform Reflection ConfigurationsPrograding reflection configurations interpreted as strata in which depositions are due to lateral outbuilding

Three classes: Sigmoid Oblique Complex Sigmoid-Oblique

SigmoidObliqueComplex Sigmoid-Oblique



SigmoidTypical features of Sigmoid pattern:S-shapedGently dipping strata in the higher and lower segmentsMore steeply dipping middle segment

Depositional conditions: Low sediment supply with rapid basin subsidence and/or rapid rise in sea level to allow deposition and preservation of the topset beds



ObliqueTypical features of the Oblique pattern

Depositional ConditionsCombination of relatively high sediment supplySlow to no basin subsidenceStillstand of sea level, to allow rapid basin infill and sedimentary bypass with some erosion of the upper depositional surface.



Prograding clinoform pattern of alternating sigmoid and oblique within a single seismic facies unit.

The upper segment is characterized by a complex alternation of horizontal sigmoid topset reflections and segments of oblique configuration with toplap terminations.

Complex Sigmoid-Oblique



Mound ConfigurationsMounds are reflection configurations interpreted as strata-forming elevations or prominences, rising above the general level of the surrounding strata.

Most mounds are topographic buildups resulting from either clastic or depositional processes or organic growth.

Mounds have diverse origin and shapes and internal stratal configurationDelta LobeDeep Sea Fan



Delta LobeThe Delta Lobe here is a broad, low-relief mound seismic facies.

The external form has reflections concordant at the top and downlapping in the opposite direction at the base.

It is interpreted as a delta lobe on a subsiding shelf.



Deep Sea FanA very broad symmetrical low-relief mound seismic facies. This figure illustrates a cross section view of a large deep sea fan near mid-to-outer fan position. It is characterized by parallel, hummocky, wavy and chaotic reflection configuration patterns typical of a channel lobe complex.



Fill configuration patterns are interpreted as strata filling negative-relief features in the underlaying strata. The underlying reflectors generally show erosional truncation along the basal surface

Fill forms are classified by external forms:Channel FillTrough FillBasin/Slope-front Fill

Fill Configurations

Channel FillTrough FillSlope FrontFill



Channel/Through FillThis figure displays two contrasting canyon fills.

The canyon on the right appears to have filled symmetrically with a coarse lag at the base (high amplitude reflection) and fine clasts in the upper parts (low amplitude).

The canyon on the left appears to have filled symmetrically with an alternation of coarse and fine sediments from bottom to top.



Slope Front FillThis Fill reflection pattern is interpreted to be a distributary channel complex incised into delta fringe silts and clays. The depositional cycle occuring within this distributary channel is an active channel fill at the top



A Bank seismic facies is a unit with a bank-like external form with a clinoform or bank-front leading edge that commonly marks a shelf-slope break. Bank and Lens ConfigurationsA Lens seismic facies unit form is bounded by converging surfacesBankLens



Bank Seismic Facies UnitThis seismic section illustrates a Bank external form well-defined clinoform marking the shelf-slope from the onlapping basin fill.



Lens Seismic Facies UnitThis seismic section illustrates a large salt lens based on well data, which is clearly defined by a high amplitude reflection.



Progressively offset wave-shaped reflections, showing a series of sediment waves migrating over a horizontal surface.Form in the deep sea from volcanic processes that significantly postdate emplacement of adjacent oceanic crust.

Depositional features caused by bottom current activity. These currents are capable of submarine erosion.

Volcanic- and Contourite Mounds and Migrated Wave Volcanic MoundContourite MoundMigrated Wave



Volcanic MoundsBuried volcanic mounds in the vicinity of New England (USA).

Note the younger sediments onlapping and draping the volcanics.



Contourite MoundContourite Mounds are commonly elongate dune-like features with asymmetric mounded internal patterns.

Here you can see contourite buildups from Western Atlanta (USA)



Migrating WaveThis seismic section is an example from the lower continental rise and abyssal plain of the Western Atlantic (USA).Note the undulating expression of the sea floor and shallow sub-bottom section.Also note the diffraction patterns from oceanic basement



AuthorsAuthor: Egil TjlandAssociate ProfessorDepartment of Petroleum engineering and applied Geophysics, Faculty of applied earth sciences Norwegian University of Science and Technology (NTNU)

Producer:Camilla Hagelund5th year student, Department of Petroleum engineering and applied Geophysics, Faculty of applied earth sciences Norwegian University of Science and Technology (NTNU)



ReferencesA.W. Bally, Atlas of Seismic StratigraphyAAPG Studies in Geology # 27, vol. 1, 1987



SummaryThis e-learning course is an introduction to seismic interpretation methodology. The course provides the user training in recognizing seismic sequences and unconformities, in addition to identification of important reflectors representing either depositional features or tectonic events. The End

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IPT-SIG4024-M Seis. Stratigraphy v1-4.ppt