沉积旋回与相——2课件

Teaching MaterialTeaching MaterialChapter 2 Introduction of Sedimentary CyclesSedimentary Cycles and Facies AnalysisSedimentary Cycles and Facies AnalysisContentsConceptClassification of Sedimentary CyclesDescriptive classificationGenetic ClassificationRecurrence Time of Cyclic and Discyclic BeddingFour Basic Types of Sedimentary CyclesConceptSedimentary cyclesa group of rock units that occur in a certain order,with one unit being repeated frequently throughout the succession(Duff and Walton,1962).可重复重现的一组岩相或岩相组合可重复重现的一组岩相或岩相组合Represented by a series of events that are normally recurrent and repeated in a same orderACBBACCABConceptRhythmic Bedding and Sedimentary Cycles of Different ScalesVarious sedimentary successionRhythmic succession:two alternating bed types(succession AB,AB)AAABBConceptRhythmic Bedding and Sedimentary Cycles of Different ScalesVarious sedimentary successionCyclic succession:several different sediment types,at least three,forming a succession(e.g.,ABC,ABC,etc.)Classification of Sedimentary CyclesDescriptive classificationGenetic ClassificationRecurrence Time of Cyclic and Discyclic BeddingFour Basic Types of Sedimentary CyclesDescriptive classification Repetition of rhythmic and cyclic beddingSlow gradual Slow gradual changes:changes:cyclic bedding,or periodic bedding with strictly period allocyclic,e.g.,orbital climatic phenomenaExample:chalk-marl cyclesDescriptive classification Repetition of rhythmic and cyclic beddingSlow gradual Slow gradual changes:changes:Descriptive classification Repetition of rhythmic and cyclic beddingAbrupt changesAbrupt changes of bedding variations depositional events or episodes at random to quasi-periodic time intervals(stochastic,episodic,and discyclic bedding)Examples:tempestites,turbiditesChannel FillingTurbiditeDescriptive classification Repetition of rhythmic and cyclic beddingAbrupt changesAbrupt changes of bedding variationsDescriptive classification Scale of rhythmic and cyclic sedimentsVarve-scale laminationsVarve-scale laminationsBed-scale rhythms and cyclesBed-scale rhythms and cyclesField-scale sedimentary cyclesField-scale sedimentary cycles100 kyr-several m.y.,20-100 kyr MacroscaleMacroscale cyclic sequences cyclic sequences100 m-several km,10 m.y.-100 m.y.-Einsele,1991Descriptive classificationGenetic Classification Controlling factorsAutocyclic successionCyclothemic deposition that requires no change in the total energy and material input into a sedimentary system but involves simply the redistribution of these elements within the system.It involves such mechanisms of deposition as channel migration,channel diversion,and bar migration.Genetic Classification Controlling factorsAllocyclic successionCyclothemic deposition that results from changes in the supply of energy or material input into a sedimentary system.It involves such mechanisms as uplift,subsidence,climatic variation,eustatic change in sea level,and other changes external to the sedimentary unit.Genetic Classification Time periods of sedimentary cycles(Vail et al.,1987;Haq et al.,1987)First-and second-order cycles:First-and second-order cycles:Third-order sequences:Third-order sequences:0.5 to 5 m.y.Fourth-order Fourth-order cycle:cycle:0.1 to 0.5 m.y.eustatic variationsFifth-order Fifth-order cycle:cycle:0.01 to 0.1 m.y.Milankovitch frequency bandSixth-order Sixth-order cycle:cycle:shorter 10 kyr Milankovitch variationsRecurrence Time of Cyclic and Discyclic Bedding Strictly periodic cycleExample:11-year sun spot cycles,Milankovitch cyclesquasi-periodic cycleExample:tidal,rotational,and orbital parametersRecurrence Time of Cyclic and Discyclic Bedding CharacteristicsLonger-term,third-order sea level varying time periods within a certain order of magnitude superposition of several mechanism of differing time periods difficult to find out from the response of sediments whether there is a true periodic process in operation above the depositional background noiseRecurrence Time of Cyclic and Discyclic Bedding nonperiodic cycle(episodic event)Example:Example:turbidite or tempestit,epibenthic shell bedsEpibenthic shell beds occur throughout the Phanerozoic.If the coarse particles are produced in place by biological processes,boundary shell beds can be placed into the ongoing transgression-peak.Truth:Truth:The background sediment is discontinuously interrupted by laterally transported,allochthonous turbidite sediment.Four Basic Types of Sedimentary Cycle Origin:An empirical classification of sedimentary sequences using rank-order designations,based on their duration.-Vail et al.,1977Counterview:although a hierarchy of sequences exists in the stratigraphic record,their distinctiveness in terms of duration or recurrence interval is only approximate.-Carter et al.,1991 2.4 Four Basic Types of Sedimentary Cycle Counterview:quantitative study of the duration and thickness of stratigraphic sequences-Drummond&Wilkinson,1996 discrimination of stratigraphic hierarchies and their designation as nth-order cycles may constitute little more than the arbitrary subdivision of an uninterrupted stratigraphic continuumStratigraphic cycles and their originsThe Supercontinent CycleCharacters:Four cycles,spanning 200-500 m.y.=first-order cycles-Vail et al.,1977Late Cambrian to MississipianMaximum transgressionCretaceousMaximum transgressionPennsylvanian to JurassicMaximum regressionOrigin:assembly of supercontinents by seafloor spreading,rifting and dispersal Major cycles of sea-level rise and fall during the PhanerozoicSupercontinent CycleSupercontinent CycleSupercontinent Cycle87Sr/86Sr Basalt:0.704Weathering:0.7050.735Sea Level and ClimateFIVE ORDERS OF CYCLESCycles with Episodicities of Tens of Millions of YearsCharacters:Six cycles in Phanerozoic-Sloss,1963detailed isopach and lithofacies maps of the Western Canada Sedimentary Basin and the Russian Platform.The data from two areas show remarkable similarities,and confirms that Slosss six sequences can be recognized in two separated continents.Origin:global,eustatic changes in response to volume changes in oceanic spreadingSix sequences of Sloss(1963)FIVE ORDERS OF CYCLESCycles with Million-Year EpisodicitiesCharacters:1-10 m.y.=third-order cycles=sequence stratigraphy models-Vail et al.,1977Techniques:seismic techniquesoutcrop-area plotsdetailed stratigraphic reconstructionsemphasizing lithofacies or biofacies dataCycles with Million-Year EpisodicitiesExample:Eocene marine section of the Hampshire Basin,EnglandControversy regarding:origins of these cycles,whether they are regional or global in scopeCycles with Episodicities of Less Than One Million Years Characters:Fourth-order rank(0.2-0.5 m.y.)Fifth-order rank(0.01-0.2 m.y.)Origin:Climatic origin GlacioeustasyTectonicOrbital ForcingMilankovitch cyclesMajor recurrence time of quasi-and nonperiodic process