GEOL-1021EL Lecture Notes - Lecture 6: Depositional Environment, Weathering, Sedimentary Structures
16 Jun 2018
School
Department
Course
Professor
GEOL-1021
October 26th, 2017
Sedimentary Rocks
•produced on the Earth’s surface by specific processes:
•Weathering
•both physical and chemical
•Chemical is due to the minerals reacting with oxygen or water
•water (hydrolysis)
•carbon dioxide (carbonic acid)
•Moist soils
•Produces all soils, clays, etc
•Factors that affect are climate, time and other soils
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•erosion
•Removal of sediments by natural processes such as wind and rivers
•transportation
•deposition (sedimentation)
•burial and compaction
•Preservation of sediments within a sedimentary basin
•diagenesis
•Physical and chemical age that converts sediments to sedimentary rocks.
•Lithification includes compaction and cementation
•transported and become sedimentary rocks after they come to rest
•gives evidence to ancient sedimentary environments and where they came from
•Produced by surface processes
•Ex of sedimentary environments!
glaciers!
river!
delta!
desert!
Lakes and playas (vamos a la playa)!
marine shelf
•Controls on Weathering
•Properties of the parental rock
•different materials decompose (chemical weathering) at different rates
•The rock’s internal structure affects it’s susceptibility to cracking and fragmentation
(physical weathering)
•Chemical Weathering
•chemical stability dictates the rate of chemical weathering
•stability depends on:
•Solubility (linked to bond type)
•Reactivity to water (which is influenced by the acidity of water)
•Example: clays
•Chemical weathering of silicates results in loss (into solution off cations such as Ca,
Na, K, Mg, etc)
•intense weathering results in feldspars (NaAlSi3O8, KAlSi3O8, CaAl2Si2O8) into
Kaolinite (Al2Si2O5(OH)4), which is used in pottery
•notice how the main chain is the loss of K, Ca, Na and addition of OH!
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•Physical Weathering
•What determines how a rock breaks?
•natural zones of weakness
•activity of organisms
•Frost wedging
•Exfoliation
•Classifications of sediments
•Siliciclastic sediments (from the residual material of weathering ex) sand, but also larger
pieces of rocks)
•Four main groups- Arkose, ethic, Quartz arenite, graywacke
•Environments:
•continental (alluvial, desert, glacial, lake)
•shoreline (clats, beaches, tidal flats)
•marine (shelf, margin, slope, deep sea)
•current strength and distance of transport affect
•Size of clastic particles
