416M_strat-concepts_various kinds of stratigraphy

416M_strat-concepts_various kinds of stratigraphy -...

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1 STRATIGRAPHY FUNDAMENTAL CONCEPTS
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2 Stratigraphy = Study of rock strata These strata preserve an integrated response of depositional systems to tectonics, sediment flux, sea level, subsidence, climate, and other environmental forcings. Strata are classified with respect to any one of many characteristics. For example: classification based on : Lithology “lithostratigraphy” Fossil content “biostratigraphy” Age “chronostratigraphy” Chemical composition “chemostratigraphy” Magnetic properties “magnetostratigraphy” Sonic reflection features seismic stratigraphy Stratal geometries “sequence stratigraphy” Formation = Lithologically distinctive, relatively homogeneous succession of strata that is mappable at 1:25,000 scale “Homogeneous” means relatively constant facies.
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3 THE HISTORICAL CONTEXT 300 years ago: Nicholas Steno and superposition, original horizontality, and original lateral continuity 200 years ago: James Hutton and Charles Lyell – uniformitarism present Key to past; physical and chemical laws invariant with time; probably the grandest of all geological concepts, maybe all scientific concepts 200 years ago: William (Strata) Smith: Map that shaped the world (Simon Winchester) – biostratigraphy and correlation
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4 THE HISTORICAL CONTEXT 160 years ago: Amanz Gressly – concept of facies; Henry Sorby- petrographic microscope; Alcide d’Orbigny, global fossil zones 100 years ago: Johannes Walther (Walther’s law) forerunner of modern depositional systems and sequence stratigraphy “facies that overlie each other in a conformable vertical sequence must have been laterally adjacent to one another at the time of deposition;” rediscovered 70 years after publication; one of the most fundamental papers
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5 History of Stratigraphic Concepts Superposition : Steno, 1669 Law of superposition: In any succession of strata, not subsequently disturbed or overturned since deposition, younger rocks lie above older rocks. Unconformities : Hutton, 1788 Surfaces separating strata that are not in immediate order of age (i.e. represent missing time). Faunal Succession : Smith, 1800 Law of faunal succession: Rocks formed during a particular interval of geologic time can be recognized and distinguished by their fossil content from rocks formed during other time intervals.
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