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
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                                                                                                                   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
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