Popular in Evolution of the Earth
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This 4 page Class Notes was uploaded by Ryan Neubauer on Friday October 9, 2015. The Class Notes belongs to Geography 202 at Illinois State University taught by James Day in Fall 2015. Since its upload, it has received 17 views. For similar materials see Evolution of the Earth in Geography at Illinois State University.
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Date Created: 10/09/15
l Week 8 A Lithostratigraphic Units 1 Classi cation and correlation of bodies of strata stratigraphic units based entirely on their lithologic or physical properties 2 Lithology a Composition and texture of sedimentary rock comprising a stratum or group of strata i Limestone Dolomite Shale Sandstone Siltstone B Formation 1 Fundamental unit or division of local strati cation where a formation is de ned entirely on lithologic characteristics 2 These are mappable units that can be traced or correlated between surface exposures or in the subsurface 3 FORMATIONS ARE NAMED AFTER a Speci c geographic features landmarks distinctive lithology or the region where they are well exposed or well studied in the subsurface 4 Navajo Sandstone a Well sorted sand particles sandy texture b Crossbedding c Red Color C Lithostratigraphic Correlation 1 Correlation of Lithostratigraphic units such as formations a Tracing of rocks ll Week 82 B Units of Stratigraphic Classi cation 1 Biostratigraphic Units a Bodies of rock distinguished from each other and correlated on the basis of their distinctive fossil content 2 The basis fro Biostratigraphic subdivision of sedimentary rock successions is fossil succession 3 The basic nit of Biostratigraphic classi cation is the biozone a Body of rock de ned on the basis of the rst and last occurrences of fossil species B Fossil Succession 1 Principle simultaneously formulated by Cuvier French naturalist and William Smith Scottish engineer a Fossil assemblages succeed one another through time in a regular determinable order b Fossils have formed continuously as new species evolve and appear in record become extinct and disappear from record c Distinctive assemblages in rocks in different areas are of same relative age C lndex Fossils U39lbUUNH Useful for fossil or Biostratigraphic correlation Geographically widespread Easily recognized Short Geological stratigraphic range The most useful groups used for Biostratigraphic zonation and correlation are those that tend to be widespread Pelagic groups are most useful species of benthic groups tend to be endemic or restricted to certain faciesOfacies fossils D Biostratigraphic Zones 1 Stratigraphic intervals characterized and names on the basis of the ranges of zonal index fossils E Stratigraphic Classi cationUnits 1 TimeRock Units a Bodies of rock that were deposited or formed during a particular Geologic Time Unit Recognized on the basis of their fossil content or absolute ages By identifying and correlation using biostratigraphy or absolute age dates all rocks that accumulated during a particular geologic time interval geologists can map distributions of ancient sedimentary facies and reconstruct the regional and global geography Paleogeography We can also identify facies patterns that record global environments changes in uenced directly by sea level climate or tectonic events F Stratigraphic Classi cation 1 Magnetostratigraphic Units a Bodies of rock of a given age that can be distinguished on the basis of their magnetic properties 2 Rocks acquire magnetic properties as they form the most important property is ancient magnetization patterns of the Earth s magnetic eld that rocks record when a body of rock formed at in the part lronO rich minerals in igneous and sedimentary rocks record these properties because they behave like compass needles Week 83 A Chrons 1 Magnetic polarity timerock Units 2 Rocks acquire magnetic properties as they form 3 The pattern of magnetization changes abruptly on a global scale sea oor and volcanic rocks record these changes that rare dated by radiometric means B Absolute Geologic Time 1 Refers to a Actual age of geological material or bed ash beds lava ow etc b Time in the past when an event occurred c Duration of geological time interval 2 Absolute Ages of earth materials are based on numerical age dating of events amp materials usually expressed in years before presentBP 3 Basis a All are based on observation and measurement of materials that accumulate or change in earth materials as a consequence of timedependent processes of change b The most common process of timedependent change in earth materials used in their dating is radioactive decay of unstable isotopes of certain chemical elements C Attempts to Date the Earth 1 Biblical Age from scriptures a 6000 BP 2 Buffon 1760 a 75000 BP 3 Hutton Lyell and others a Ancient far older than 75000 BP 5 Kelvin s a Re ned Buffon s calculations in 1862 b He derived the time for a molten Earth to cool of 98 Million years which he revised downward to 20 40 million years in 1897 c Both are gross underestimates because they do not take into account natural radioactivity in rocks which Kelvin did not know about that makes the earth warmer that it would be in the absence of any other sources of heat D Numerical Estimates of the Age of Earth Materials 1 Methods by which crustal materials and depostits can be dated in calendar years before present or time duration that it took for a material deposit E Biochronometric Age Dating 1 Assessment and comparison of time dependent tissue growth features of organisms to determine a Age of tissue in calendar years before present b Age of organism at time of death F Dendrochronology 1 Tree Ring Dating a Age in years before present 8000 yrs BP