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File: Stratigraphy Pdf 200854 | Stratconcepts
stratigraphy concepts in stratigraphy basic concepts lithostratigraphy sequence stratigraphy sea level and sediment supply consequences of changes in sea level types of sequences biostratigraphy other types of stratigraphy younger basic ...

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                                                                                                                    Stratigraphy
                              Concepts in Stratigraphy                                                          „ Basic Concepts
                                                                                                                „ Lithostratigraphy
                                                                                                                „ Sequence Stratigraphy
                                                                                                                   „ Sea level and sediment supply
                                                                                                                   „ Consequences of changes in sea level
                                                                                                                   „ Types of sequences
                                                                                                                „ Biostratigraphy
                                                                                                                „ Other Types of Stratigraphy
                                                                                                                                    Younger
                                Basic Principles
                           „ Steno (1669)
                           „ Principal of original horizontality                                                                      Older
                               „ Sediments deposited as essentially                                                                    Younger
                                 horizontal beds
                           „ Principal of superposition
                               „ Each layer of sedimentary rock 
                                 (sediment) in a tectonically undisturbed                                                                 Older
                                 sequence is younger than the one 
                                 beneath it and older than the one above 
                                 it
                                Basic Principles                                                                    Basic Principles
                           „ Hutton (1700s)                                                                     „ Walther (1884)
                               „ Principle of Uniformitarianism: The                                               „ Walther’s Law: Only those facies and 
                                 processes that shaped Earth throughout                                              facies-areas can be superimposed 
                                 geologic time were the same as those                                                primarily which can be observed beside 
                                 observable today                                                                    each other at the present time
                               „ “The present is the key to the past”                                                  „ Only applies to conformable successions –
                               „ Sometimes there are                                                                     i.e., no major breaks in sedimentation
                                 environments/conditions that do not                                                   „ Vertical successions do not always reproduce 
                                 have good modern analogues                                                              horizontal sequence of environments
                                                                                                                                                                                              1
                                                                                                                   SSeevveerraall km km,, 10s of 10s of  kmkm
                                                                                                       FFFooorrreshoreshoreshore sandse sandse sandstttoneoneonesss
                                                                                                   SSShhhooorrreeefffaaace sce sce saaandstndstndstonesonesones
                                                                                                 0s of m0s of mIIInnnttteeerrrbbbeeedded sandstdded sandstdded sandstonesonesones///shashashallleseses
                                                                                                 11
                                                                                                            “““DDDiiissstttaaalll””” shal shal shaleseses
                        „ “Shalier (fining) upward” succession
                            Lithostratigraphy                                                         Lithostratigraphy
                       „ Formation                                                               „ Formation
                          „ Fundamental unit of lithostratigraphic                                  „ Generally considered to be tabular in 
                            classification                                                            geometry
                          „ A body of rock identified by lithic                                     „ Large enough to be mappable at the 
                                                                                                      Earth’s surface or traceable in the 
                            characteristics (composition, colour,                                     subsurface
                            sedimentary structures, fossils, etc) and                               „ Existing formations range from a few m 
                            stratigraphic position                                                    to several 1000s of m thick
                                                                                                    „ Traceable for a few km or several 1000 
                                                                                                      km
                            Lithostratigraphy
                       „ Formation                                                                          Todilto
                          „ Names (unfortunately...) may change at                                          Entrada
                            political boundaries or from one region 
                            to another
                          „ Names generally based on geographic                                                  Chinle
                            locations
                          „ Contacts between formations 
                            established at obvious lithologic
                            changes (sharp or gradational; lateral or 
                            vertical)
                                                                                                                                                                      2
                             rd                                                                    Lithostratigraphy
                             a
                             w ardard                                                          „ Members
                             upw                                                                  „ Subdivisions of formations
                             ning-png-upw                                                         „ Possess characteristics that distinguish it 
                             e er-u                                                                 from other parts of the formation
                             s
                             CoarSandiShoali                                                      „ Not all formations are subdivided into 
                                                                                                    members
                                                                                               „ Beds
                                                                                                  „ Smallest formal lithostratigraphic unit
                                                                                                  „ Used only if official designation is useful
                           Lithostratigraphy                                                       Lithostratigraphy
                       „ Groups                                                                „ Units described at “type sections”
                          „ Two or more formations related                                        „ Outcrops, well logs
                            lithologically                                                     „ Independent from inferred geologic history
                          „ Component formations may change                                       „ Based on objective, identifiable characteristics
                            laterally (e.g., due to facies changes)                               „ Interpretations of geologic history may change 
                       „ Supergroups                                                                with time
                          „ Assemblage of related or superimposed                              „ Diachronous to some extent
                            groups                                                                „ Produced by shifting depositional environments
                          „ Sometimes useful for regional syntheses
                                        SSeevveerraall km km,, 10s of 10s of  kmkm
                            FFFooorrreshoreshoreshore sandse sandse sandstttoneoneonesss
                        SSShhhooorrreeefffaaace sce sce saaandstndstndstonesonesones
                      0s of m0s of mIIInnnttteeerrrbbbeeedded sandstdded sandstdded sandstonesonesones///shashashallleseses
                      11                                                                       Sand
                                “““DDDiiissstttaaalll””” shal shal shaleseses                                                      T1
                                                                                               Shale
                                                                                                                                                                  3
                     Sand                              T2                              Sand                               T3
                     Shale                                                             Shale
                                                                                           Problems with 
                                                                                           Lithostratigraphy
                                                                                       „ Different facies represent different 
                                                                                         depositional environments
                                                                                       „ As laterally contiguous environments 
                       Formation “A”                      T4                             shift with time, facies boundaries shift 
                            Formation “B”                                                so that the facies of one environment 
                                                                                         lie above those of another 
                                                                                         environment
                                                                                          „  Walther’s Law
                         Problems with                                                     Problems with 
                         Lithostratigraphy                                                 Lithostratigraphy
                     „ Timelines cross lithologic boundaries                           „ Quest: Find/define “timelines” that will 
                     „ Obscures genetic relationships when                               permit depositional histories to be defined 
                       we are reconstructing geologic history                            with precision
                                                                                       „ Timelines: stratigraphic surfaces generated 
                                                                                         by the interplay of tectonics, eustacy
                                                                                         (global sea level) and sediment supply
                                                                                       „ Use links between sea level, sediment 
                                                                                         supply and other factors to develop 
                                                                                         predictive models
                                                                                                                                                    4
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...Stratigraphy concepts in basic lithostratigraphy sequence sea level and sediment supply consequences of changes types sequences biostratigraphy other younger principles steno principal original horizontality older sediments deposited as essentially horizontal beds superposition each layer sedimentary rock a tectonically undisturbed is than the one beneath it above hutton s walther principle uniformitarianism law only those facies processes that shaped earth throughout areas can be superimposed geologic time were same primarily which observed beside observable today at present key to past applies conformable successions sometimes there are i e no major breaks sedimentation environments conditions do not vertical always reproduce have good modern analogues sseevveerraall km kmkm fffooorrreshoreshoreshore sandse sandstttoneoneonesss ssshhhooorrreeefffaaace sce saaandstndstndstonesonesones ms miiinnnttteeerrrbbbeeedded sandstdded sandstonesonesones shashashallleseses dddiiissstttaaalll sha...

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