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Sept 14.doc

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University of Toronto Mississauga
Jessica Hawthorn

BIO211 th Sept 14 The Rock Cycle and Principles of Stratigraphy Foundations of Geology Principle of Uniformitarianism - there are inviolable laws of nature that have no changed in the course of time - first founding principle of geology - the present is the key to the past Actualism - application of modern processes to ancient system Catastrophism – an Opposing View - popular until 1800s - all rocks were laid down in catastrophic events Actualism - sedimentary structures show that different processes have been at work o ex. ripple marks in sand  rocks (waves) Materials and Processes - mineral o naturally occurring inorganic solid element or compound o particular chemical composition/range of compositions and characteristic internal structure - rock o interlocking of bonded grains or minerals - outcrop/exposure o exposed rock surfaces Rock Units - group: named groups of formations - formation: named unit of rock with specific lithology formed in a particular way - member: smaller named rock unit; part of formation - bed: distinctive layer in a formation or member o don’t have to have a member to have a bed… - group  formation  member Rock Cycle - surface and subsurface processes link materials to form three rock types o igneous o sedimentary o metamorphic Igneous Rocks - means born of fire - formed by cooling and hardening of molten material o composed of interlocking grains, each consisting of a particular mineral - magma: molten rock below surface o  cools slowly  intrusive igneous rock (because it cools below the surface, cools more slowly – bigger crystals) - lava: molten rock at surface o  cools quickly  extrusive igneous rock (smaller crystals) o extrudes from vents o lava flows vary in viscosity  flood basalts: extensive surface area where lava cooled (runny)  pahoehoe: low viscosity basaltic lava flow  pillow basalts: formed by lava cooling rapidly underwater - tuff: rock from consolidation of loose volcanic debris Sedimentary Rocks - sediments: material deposited on Earth’s surface by water, ice, air, chemical, or organic means - sediments are produced by: o weathering and erosion of other rocks  form siliciclastic sedimentary rocks o organismal skeletal debris  form carbonate sedimentary rocks o chemical precipitates  form chemical sedimentary rocks - deposited as strata - stratum: tabular layer of sediment accumulated in a discrete episode Siliciclastic Sedimentary Rocks - weathering: chemical and physical processes that break down rocks at earth’s surface o water o plant action o freeze-thaw cycles o chemical reactions o animal activity - erosion: processes that loosen sediments and move them downhill - made up of clasts (grains) that contain mostly silicate minerals - lithification: o primary process of formation if compaction o cementation: chemical process; minerals crystallize from solution that percolates between grains of sediment  chemicals from ground water - classification based on grain size, shape, and sorting - sorting: o grains settle out of suspension (when being transported by water and such) o coarse, dense material settles first - measure of similarity in grain size o poorly sorted  mixed sizes o well sorted  similar sizes Carbonate Sedimentary Rocks - carbonate sediments o often skeletal particles (algae, other micro-organisms) o usually made of calcium carbonate - limestones, dolomites, oolites Chemical Sedimentary Rocks - evaporites: form from precipitation of crystals during evaporation of water o ex. anhydrite, gypsum, halite (salt) o associated with drying - other chemical sedimentary rocks include chert, flint: o extremely small quartz crystals
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