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Allostratigraphy/Sequence Stratigraphy ‡ Subdivision of the stratigraphic record otbo ×
   
   ‡ Bounding discontinuities define      
  ² relatively conformable successions of genetically related strata bounded by unconformity or correlative conformities

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¦tility of Depositional Sequences ‡ If bounding discontinuities are produced by isochronous events (at least basin-wide) then these material (or non-material) features can be used for correlation since they are   
. ‡ How are sequence bounding unconformities recognized and correlated in different places?

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Discontinuities in the Stratigraphic Record that Define "      ‡ Stratigraphic contacts ² £
 
º ² Strata is parallel on either side of contact

‡ Continuous depositionº ² Gradational, intercalated, abrupt

‡ Diastemº ² Small scale, obscure discontinuity in sediment accumulation caused by an hiatus (time interval without deposition)

‡ Paraconformityº ² No physical evidence of diastem but with significant geological time missing

‡ Disconformityº ² Bedding is parallel on either side of an irregular surface produced by (subaerial) exposure and erosion

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Aggradation, Progradation, and Retrogradation ‡ Stacking patterns of sedimentary basin fill due to relative sea level and sediment input influence on accommodation ² Aggradation ² Progradation ² Retrogradation

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Aggradation ‡ Sediment input ~ accommodation ² Not common for long periods

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Progradation/Regression ‡ Sediment input > accommodation ² Facies prograde and shift offshore

‡ Regression

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Forced Regression ‡ Rapid Relative Sea Level Fall ² ´Negative accommodationµ ² Facies shift basinward ² Erosion occurs in landward areas

‡ Regression and ¦nconformity Surface

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ëransgression/Retrogradation ‡ Relative Sea Level Rise ² Accommodation created in excess of sediment input ² Facies shift landward

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Effects of Changing Accommodation on the Stratigraphic Record ‡ ëransgression/Regression ² Water depth/shoreline changes     from vertical changes in grain size (C¦S/F¦S) or sedimentary facies in local sections

‡ Onlap/Offlap ² Landward/basinward shift in shoreline due to relative sea level change ² ëhe fundamental geometric aspect of the sedimentary record upon which relative sea level change is interpreted

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Wheeler Diagrams ëime/Space relationships of ¦nconformity ‡ Space/Space Stratigraphic Cross Section

‡ ëime/Space Chronostratigraphic Chart

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Allostratigraphy and Lithostratigraphy ‡ Lithostratigraphy maps sedimentary rocks solely on the basis of their lithology and does not necessarily consider that these rocks may have accumulated over different periods of time (diachronous lithostratigraphic units) ² ´Lithostratigraphyµ often ignores significant breaks in the sedimentary section, including those caused by unconformities, omission surfaces, ravinement surfaces, and flooding surfaces

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Allostratigraphy and Lithostratigraphy ‡ Allostratigraphy maps rock units on the basis of the timing of their accumulation ² Allostratigraphy (sequence stratigraphy) uses a framework based on surfaces of erosion and non-deposition (sequence boundaries), and flooding (transgressive surfaces and/or maximum flooding surfaces [mfs]) that can be recognized in 2-D and 3-D seismic, well log data, and outcrops

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Cycles of Relative Sea Level Change

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Depositional Sequences ‡ Relatively Conformable ‡ Genetically Related (abide by Walther's Law) ‡ Bounded by ¦nconformity or Correlative Conformity ² isochronous with respect to unconformity

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‡ Depositional Sequences are Chronostratigraphic ¦nits ² the defining Sequence Boundary defines older (below) and younger (above) strata ‡

Chronostratigraphic ¦nits ² geological time significant

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Depositional Systems ëracts ‡ ¦se of Depositional Sequence concepts to predict      ² ëhree dimensional assemblage of sedimentary facies genetically linked by their origin in related depositional environments ² Basically Waltherian World c


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Low Stand Systems ëract ‡ Forced Regression ‡ Subaerial exposure and formation of a  
 
  ‡ Offlap ‡ Basinward shift in facies belts

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ëransgressive Systems ëract ‡ Retrogradation ‡ Flooding of the shelf and onlap ‡ Landward shift in facies belts

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*aximum Flooding Surface Condensed Section ‡ Between ëSë and HSë (highstand systems tract) ‡ Represented by a change from retrogradation to aggradation/progradation ‡ ëhe surface or thin succession characterized by evidence for slow rates of sedimentation

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Highstand Systems ëract ‡ Progradation (accommodation < sediment input) ‡ Regressive successions ‡ Onlap and offlap/down-lap

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*ajor Sequence Stratigraphic and Chronostratigraphic Surfaces

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Stratigraphic Expression of Relative Sea Level Cycles ‡ ëhe Sequence *odel ² A tool for predicting stratigraphic architecture ² *ethodology for basin wide correlation ² *ay be used for interregional correlation through recognition of Eustatic Cycles

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