Sedimentary Rock
deposition within different sedimentary environments can produce a range of structures such as:
- bedding (stratification) - cross-bedding - graded bedding - ripples - bioturbation - bedding sequences
carbonate sediment slide too lazy to ask questions
- calcium carbonate CaCO3 formed by direct or indirect precipitation by organisms - calcite is the most abundant carbonate material - aragonite is a less stable polymorph
three classes of chemical and biological sedimentary environments
- carbonate environments - siliceous environments - evaporate environments
describe clastic sedimentary environments:
- characterized by terrigenous sediments (from land) - include continental and shoreline environment - may include marine environments
> ________ % of the land surface is sedimentary rock
75 %
more than ____% of all sedimentary rocks are ______ how are they are characterized?
85% are clastic they are characterized by grain size
mud, mudstone shale .. majority of particles how big
< 0.0062mm varying proportions of clay and silt sized particles fined grained are mudstone and shale (lithified)
limestone forms by accumulation and lithification of ?
CaCO3
clastic sed rock are distinguished by ?
grainsize and shape, grain type (mineralogy), texture of the grain, matrix and cements
what is the coarsest clastic sediment ?
gravel > 2 cm includes boulders, cobbles and pebbles
sea water contains dissolved minerals which are concentrated during evap to form ?
halite - nacl gympsum - caso4
what characterized the alberta floods in mountain region?
high velocity - turbulent flow - high suspended load - high bed load
does natural gas form at higher or lower concentrations than gas
higher
most bedding is nearly _____ at the time of deposition with some exceptions
horizontal
physical weathering
increase surface area
iron oxide sediments
indirectly precipitated by micro-organisms lithified after oxygen increased in oceans
diagenesis
is the change of sediments or existing sedimentary rocks into a different sedimentary rock during and after rock formation (lithification), at temperatures and pressures less than that required for the formation of metamorphic rocks. It does not include changes from weathering.
tyndall stone
limestone with extensive bioturbation structures pressured in dolomite burrows originally created in soft sediments on ancient sea flow differences in chemistry or porosity caused formation of dolomite in burrows in calcite-dominated rocks
comglomerate is _____ equivalent of _____
lithified, gravel
sedimentary basins are regions of:
long-term subsidence that create space to accommodate infilling sediments - depressions are formed when are of crust subsides (sinks) relative to surrounding crust
what characterized the alberta floods in calgary region? or perhaps later on in the flood? no clue
lower velocity - high suspended load - deposition of silt / clay
sand particles are transported by ___ currents, such as:
moderate such as: rivers, waves, shorelines, wind
there are few sedimentary environments where current is strong enough to transport gravel what are they ?
mountain streams rocky beaches with high waves and glacial meltwater
sed rocks contain direct and indirect evidence of what ?
of life and its evolution
saltation
particles is lifted from the bottom and transported a little bit than deposited, process happens over and over when the fluid moves over top of it
erosion
processes that dislodge rock particles produced by weathering and move them away from source area - energy from moving water, ice and air
sedimentary rocks are important sources of ?
resources: metal, building materials and energy
what is bigger: sand or silt and clay?
sand
mud > shale sand > gravel >
sand > sandstone gravel > conglomerate
gravel > conglomerate sand > silt > clay and silt >
sandstone siltstone shale
types of sediment is determined by ?
sediment's history: transport energy and distance, weathering intensity, and composition of source rock
siliceous environments
silica (SiO2) - forms in marine sedimentary environments by: - chemical precipitation - water reaches saturation with Si / O2 - bio mineralization - diatoms precipitate amorphous silica
shales are composed of ? bedding planes?
silt and significant clay - break along distinct bedding planes
what makes up most clastic ? what makes up mall portion of clastic ?
siltstone, mudstone and shale less - sandstone, conglomerate
_______ dictates the size of clastic particles that are transported or deposited at a given location
size
ripples
small ridges often observed in modern sands and ancient sandstones. generated by flowing water or wind - sand bars in streams - sand beaches - sand dunes
sedimentary rocks reflect physical and chemical characteristic of their ______ ________ and _________ processes
source environments and depositional processes
fast, moderate, and weak currents talk about speed and the size of things they carry
strong - >50cm/s - carry gravel and large solid load moderate - 20-50cm/s - carry and deposit sand weak > 20cm/s - carry fine clastic sediments - silt and clay
eddy
swirling of fluid and reverse current when it encounters an obstacle
symmetrical ripples create ? asymmetrical ripples create ?
sym - beach, looks like waves going either way asymm - dune, steeper slope on other side of direction of wind/ water - (cross beds?)
foreland (flexural) basins - form on ______ side of mountain belt due to ____ deformation at ______ plate boundaries
these form at continental side of the mountain belt due to crustal deformation at convergent plate boundaries
how are oil and gas generated ?
they are generated during diagenesis of sediments that contain organic matter - diatoms - subsidence and burial over time increases temperature - oil forms between 60-150
true or false: sediment is scarce on earths surface?
this is false, most of earths surface is covered with layers of loose sediment
what dictates mineralogy of sediments
weathering intensity
how is sedimentary rock formed?
weathering, transportation, deposition, lithification
dissolved ions accumulate in water due to chemical weathering, why is this significant for this unit
- chemical and biological reactions precipitate minerals from these dissolved ions biogenic sediments - produced by bio precip chemical sediments - produced by inorganic precip reactions
western Canadian sedimentary basin - _____ and crustal ____ during mountain building - tectonically-induced ____ produced broad _______ basin
- deformation and crustal-thickening during mountain building - tectonically-induced subsidence (sinking) produced broad foreland basin
why do foreland (flexural) basins form? how? example?
- immense mass associated with crustal thickening causes lithospheric flexure - wedge-shaped depression oriented adjacent and parallel to mountain belt - fills with sediment eroded from mountain range Persian gulf
cross bedding
- near horizontal sedimentary units that are internally composed of inclined beds - can be inclined as much as 35 degrees from the horizontal - I guess formed by wind or water currents
sedimentary structures are important in geological structures for examining:
- original position of the lithostratigraphic sequences in geologically complex terrains - processes occurring in paleodepositional environments
which particles undergo extensive abrasion during stream transport? what happens to these particles as a result of abrasion ?
- particles transported with bedload (sand/gravel) - particle size: diameter decreases as material removed - particle shape - edges become more rounded so as these particles get further away from the surface they go from angular to rounded
sedimentary basins
- receive dissolved ions and clastic particles produced by weathering - beaches - sand/gravel - stream - clay/silt - lake bed - rock/mineral fragments
bioturbation structures
- remnants of burrows and tunnels excavated by marine organisms in muds and sands examples: clams, worms, shrimp - commonly occur as cylindrical tubes that may extend across bedding planes - infilled and preserved sedimentary rock - characterized by different mineralogy
rift and passive margin basin examples
- rift valley - new ocean basin - (red sea) - mature ocean - (Atlantic)
diagenesis
- sediment or sedimentary rock changed to different sedimentary rock - occurs at temperatures and pressures lower than those required to produce metamorphic rock
lithification
- sedimentary rock formation - squeeze water out of pores - cementation: ions precipitating between grains , kinda form bridges between the existing grains
area of sediment deposition characterized by:
- specific climatic conditions; and physical, chemical and biological processes
what is a passive margin ?
- trans between oceanic and continental crust which is not an active plate margin - it is constructed by sedimentation above an ancient rift - can be volcanic or non
key characteristics of depositional environments include:
- type and amount of water - transport type and strength - topography - biological activity - tectonic setting - climate
describe the surface processes that produce sedimentary rocks
- weathering breaks down rocks physically and chemically - erosion carries away particles produced by weathering - transportation via streams, glaciers and wind moves particles downhill - deposition ( or sedimentation ) occurs when particles settle out or dissolved minerals precipitate - burial occurs as layers of sediment accumulate and compact previous layers - diagenesis lithifies the sediment to make sed rocks
sand includes particles ranging from ___ to ___
0.062mm to 2mm in diameter
clastic rock
Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. Geologists use the term clastic with reference to sedimentary rocks as well as to particles in sediment transport whether in suspension or as bed load, and in sediment deposits.
graded bedding
a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Associated with turbidity current. Usually a graded bed has the finer stuff at the top
moving water - a major driver of erosion - involves several processes: (3)
abrasion - scouring of stream bed by transported particles scouring and lifting - flowing water dislodges and loosens rocks dissolution - stream flows over soluble bedrock
sedimentary environments are classified?
also classified according to sediment type and sediment-forming processes
sediment transport - clastic particles and ___ ions are transported downhill to _____ ______
and dissolved ions are transported downhill with gravity to sedimentary basins
sediments and sedimentary rocks are generally characterized by _______ or ________
bedding or stratification
mudstones are ___ and show poor ____
blocky, poor bedding - initial sediment bedding lost to bioturbation
clastic sediments
broken and eroded pieces of rocks and minerals - produced by chemical and physical weathering of common silicate-bearing rocks - range in size from boulders to sand, silt and clay
how are sedimentary rocks differentiated ?
by rock or mineral type and particle size
phosphorite sediments lithify to form ?
calcium phosphate
carbonate environments
chemical precipitation or bio mineralization
dolomite forms when
chemical reaction between CaCO3 and dissolved magnesium
evaporites
chemically precipitated from evaporating sea water and sometimes lake water
Siliceous sediments lithify to form ?
cherts - flint
diatoms > oil and gas plant material >
coal
important clastic sedimentary rocks
conglomerate breccia quarz sandstone arkose lithic sandstone siltstone claystone shale
________ grain size with increased transport distance and _______ energy level
decreased, decreased
how are different types of sedimentary basins defined ?
defined in the context of plate tectonics - rift basins - passive-margin basins - foreland (flexural) basins (convergent)
what increases with transport distance?
degree of sorting increases with transport distance
direct and indirect mechanism of biomin
direct - organisms utilize dissolved ions or molecules to produce shells or skeletons indirect - minerals precipitate due to environmental conditions created by organism
reefs
direct precipitation of carbonate sediments - bahamas example - built in warm shallow seas by organisms that precipitate calcium carbonate
define weathering
disintegration of rock into separate grains by chemical and physical weathering
chemical weathering
dissolves and weakens rock
whens is stream erosion most efficient ?
during floods - large volumes of fast-moving turbulent water
what is the processes that allows chemical sediments to form
evaporation - mineral precipitation due to seawater evaporation from chemical sediments
true or false: when a sediment is weathered and than is transported to its depositional environment It remains the same?
false, they change as they are transported across earths surface
organic sediments
formed from accumulation of wetland vegetation burial and diagenesis converts peat to coal
sedimentary rocks can be interpreted to understand what?
geological history
variations sort particles according to _____-size and density
grain size