GY 402: Sedimentary PetrologyGY 402: Sedimentary PetrologyLecture 8: Sedimentary FaciesLecture 8: Sedimentary FaciesUNIVERSITY OF SOUTH ALABAMAUNIVERSITY OF SOUTH ALABAMATodayToday’’s Agendas AgendaSedimentary FaciesSedimentary Facies1.1.What are facies What are facies 2.2.Defining characteristics of faciesDefining characteristics of facies3.3.Facies and depositional environmentsFacies and depositional environmentsSedimentary FaciesSedimentary FaciesWhy do Why do sedimentologistssedimentologistscollect all this data in the first place?collect all this data in the first place?..Sedimentary FaciesSedimentary FaciesWhy do Why do sedimentologistssedimentologistscollect all this data in the first place?collect all this data in the first place?Ultimately, it is in order to interpret the Ultimately, it is in order to interpret the environment of depositionenvironment of depositionof the sediment/sedimentary rocks.of the sediment/sedimentary rocks.http://http://earthsci.org/mineral/rockmin/sed/clastics.gifearthsci.org/mineral/rockmin/sed/clastics.gifSedimentary FaciesSedimentary FaciesThere are literally dozens of different depositional environmentThere are literally dozens of different depositional environments s that cover every imaginable marine and nonthat cover every imaginable marine and non--marine situation. And marine situation. And in most cases, there are multiple varieties of each basic in most cases, there are multiple varieties of each basic environment of deposition. environment of deposition.Sedimentary FaciesSedimentary FaciesFor example, rivers come For example, rivers come in at least 3 in at least 3 ““flavorsflavors””::1) Meandering1) Meandering2) 2) BraidedBraided3) 3) AnastimosingAnastimosingThere are literally dozens of different depositional environmentThere are literally dozens of different depositional environments s that cover every imaginable marine and nonthat cover every imaginable marine and non--marine situation. And marine situation. And in most cases, there are multiple varieties of each basic in most cases, there are multiple varieties of each basic environment of deposition. environment of deposition.Sedimentary FaciesSedimentary FaciesSedimentologists also need to consider the full range of variabiSedimentologists also need to consider the full range of variability lity within each depositional environment.within each depositional environment.Sedimentary FaciesSedimentary FaciesSedimentologists also need to consider the full range of variabiSedimentologists also need to consider the full range of variability lity within each depositional environment. For example, a braided within each depositional environment. For example, a braided river channel has deep areas, flats and bars (longitudinal and river channel has deep areas, flats and bars (longitudinal and transverse).transverse).Sedimentary FaciesSedimentary FaciesWhen you look closely at braided river depositional systems, it When you look closely at braided river depositional systems, it is is clear that they consist of a lot of subcomponents. Not just a clear that they consist of a lot of subcomponents. Not just a channel and a floodplain. So we lied (again!) in GY 111.channel and a floodplain. So we lied (again!) in GY 111.Sedimentary FaciesSedimentary FaciesUltimately, depositional Ultimately, depositional environments are the sum of environments are the sum of their various components and their various components and each of those components are each of those components are distinguished from one another distinguished from one another of the basis of geological of the basis of geological characteristics.characteristics.The components that The components that collectively define depositional collectively define depositional environments are called environments are called sedimentary facies (or just sedimentary facies (or just facies).facies).http://www.kgs.ku.edu/PRS/publication/ofr2003http://www.kgs.ku.edu/PRS/publication/ofr2003--82/gif/figure1_06.gif82/gif/figure1_06.gifSedimentary FaciesSedimentary FaciesDefining characteristics for facies include:Defining characteristics for facies include:Obvious sedimentary trends Obvious sedimentary trends Bedding (Bed thickness) Bedding (Bed thickness) LaminationLaminationBedding contactsBedding contactsLateral variations Lateral variations Anything else that you can think of Anything else that you can think of Grain size Grain size LithologyLithologyMineralogyMineralogyPaleontology Paleontology Sedimentary and biogenic structuresSedimentary and biogenic structuresPalaeocurrentPalaeocurrentorientations orientationsSedimentary FaciesSedimentary FaciesFacies can, and will, repeat Facies can, and will, repeat vertically through a vertically through a sedimentary sequence, but sedimentary sequence, but may vary in character as a may vary in character as a result of environmental result of environmental and/or evolutionary change and/or evolutionary change through time. through time.Sedimentary FaciesSedimentary FaciesFacies can, and will, repeat Facies can, and will, repeat vertically through a vertically through a sedimentary sequence, but sedimentary sequence, but may vary in character as a may vary in character as a result of environmental result of environmental and/or evolutionary change and/or evolutionary change through time through time e.g., fossil content. e.g., fossil content. offshore (10m)offshore (10m)shoreface (5m)shoreface (5m)shoreface (5m)shoreface (5m)swash zoneswash zone(0m)(0m)Sedimentary FaciesSedimentary FaciesFacies may also change laterally through a deposit as a result Facies may also change laterally through a deposit as a result of changing environments with distance at the same time. of changing environments with distance at the same time.http://geology.isu.edu/Digital_Geology_Idaho/Module2/Belt_SedStrhttp://geology.isu.edu/Digital_Geology_Idaho/Module2/Belt_SedStruct_sml.jpguct_sml.jpgSedimentologists Sedimentologists distinguish distinguish component facies in component facies in the outcrops that the outcrops that they are examining.they are examining.Sometimes they go Sometimes they go overboard.overboard.Then they Then they determine which determine which depositional depositional environment best environment best fits this variety of fits this variety of facies.facies.This is called:This is called:Facies ModelingFacies