Sedimentary Rocks Fossils

Transcription

1 Sedimentary Rocks Fossils Sedimentary rocks Two main types Rocks formed by deposition of sediment Clastic Rocks formed by precipitation from water Chemical (includes rocks formed by organisms) Clastic Sediment Grains Lithification Particle loosened from pre existing rock Transported to place of deposition Shape, size, and sorting of grains can tell about the environment of deposition Process of becoming stone Burial and compaction Precipitation of cement Each reduces pore space Cement Bedding and bedding planes Brought in by water Mineral material between grains Fills in pore spaces Commonly calcite, silica, and sometimes iron oxide STRATA 1

2 Types of Clastic Rocks Fossils Shale (most abundant) Sandstone Conglomerate Traces or remains of prehistoric life Are the most important inclusions Help determine past environments Used as time indicators Used for matching rocks from different places Shale with plant fossils Shale Composed of very fine grained sediment Shows obvious tendency to split along planes (fissile) Usually gray Most common type of sedimentary outcrop Sandstone Sandstone Composed of sand size particles Between 1/16 mm and 2 mm diameter Particles may be individual mineral grains or rock fragments Quartz most common type of grain Environments include Beach, river, shallow sea, sand dunes 2

3 Conglomerate Conglomerate Composed of particles larger than 2 mm Usually particles are rock fragments Clastic rocks Shaleis the most common one Made from solid particles Classified by particle size Chemical rocks Material was once in solution and precipitates to form sediment Directly precipitated as the result of physical processes, or Through life processes (biochemical origin) Chemical rocks Limestone Composed of the mineral calcite (calcium carbonate) Much of this calcite was precipitated by organisms Considered an organic chemical sediment if from organisms Most common type of chemical rock second most common type of sedimentary rock Chalk 3

4 Fossiliferous limestone Coquina Close up of coquina Chemical rocks Direct mineral precipitation from water Evaporites such as rock salt or gypsum Microcrystalline quartz (precipitated quartz) known as chert, flint, jasper, opal or agate Travertine (calcite) and sinter (silica) from hotspring deposits Evaporites Travertine rals/2sedimentarymineralz/gypsum.html ~whtsai/world%20highlight s/new%20side%20show%2 0Webpages/imagepages/Tur key% Travertine%20stones%20an d%20water%20in%20pamu kale.html karlsruhe.de/925.php

5 Rock salt Chert Classification of sedimentary rocks Features of sedimentary rocks Porosity Permeability Sedimentary rocks Economic importance Coal Petroleum and natural gas Precipitation of iron and aluminum Deposition of gold and tin Sand, gravel, clay Fossils: evidence of past life Remains or traces of prehistoric life 5

6 Petrified Petrified Cavities and pores are filled with precipitated mineral matter Formed by replacement Cell material is removed and replaced with mineral matter Mold Shell or other structure is buried and then dissolved by underground water Cast Hollow space of a mold is filled with mineral matter Shape is preserved in the surrounding sediment Carbonization Impression Organic matter becomes a thin residue of carbon. This is a compression of the original organism Replica of the fossil's surface preserved in fine grained sediment 6

7 Preservation in amber Hardened resin of ancient trees surrounds an organism Indirect Evidence Includes Tracks Burrows Coprolites fossil dung and stomach contents Gastroliths stomach stones used to grind food by some extinct reptiles Tracks Types of fossils Dinosaur footprint in fine grained limestone near Tuba City, Arizona. Petrified Formed by replacement Mold Cast Carbonization Impression Preservation in amber Indirect evidence Conditions favoring preservation Rapid burial Possession of hard parts Fossils and correlation Principle of faunal succession Index fossils 7

8 Principle of faunal succession Geologic Time Scale Proposed by William Smith late 1700s Fossil organisms succeed one another in a definite and d bl order, d therefore h f determinable any geologic time interval can be recognized by its fossil content Archean through Devonian Cambrian Marine Life Carboniferous through Quaternary Trilobite 8

9 Crinoid 380 ma Ordovician Invertebrates Ordovician sea floor Silurian reef Silurian Reef Silurian Landscape Devonian Sea 9

10 Mid Paleozoic Carboniferous Fern Forests Permian Reptiles Late Paleozoic Permian Sea Permian Extinction Link to hypotheses of the Permian Extinction 80 95% of marine species died out 70%+ of terrestrial vertebrates Largest extinction episode in geologic record 10

11 Geologic Time Scale Mesozoic Mesozoic Mesozoic Mesozoic Archeopteryx 11

12 Mesozoic Mammal Mesozoic Mammal Eomaia Repenomamus Jurassic Mesozoic Sea Cretaceous Mesozoic sea 12

13 Cretaceous Extinction Cenozoic mammals Perhaps 60% of species died Result of radical change in environment Perhaps Earth encountered a large meteorite 10 km in diameter 90,000 km/hr Equivalent to 100 megatons of TNT exploding Cenozoic Cenozoic Cenozoic Geologic Time Scale 13