Chapter 5
Description: Sediments and Sedimentary Rocks
Complete list of Terms and Definitions for Chapter 5
| Terms | Definitions |
|---|---|
| Sed rocks were once sediments, thus.... | Thus are records of conditions at Earth's surface when seds were deposited |
| Sed rocks can be used to deduce what? | presence / properties of ancient water bodies, mountains, deserts, etc. |
| Why is the study of sediments / see rocks of practical value? | oil, gas, coal, uranium, iron ore |
| What are the 6 key processes that make up sed stages of the rock cycle? | 1. Weathering 2. Erosion 3. Transportation 4. Deposition / Sedimentation 5. Burial 6. Diagenesis |
| Clastic Particles | Physically transported solid fragments produced by weathering of preexisting rocks |
| Clastic Sediments | Accumulation of clastic particles "siliciclastic" |
| Mixture of minerals in clastic seds varies | Where weathering intense; only stable & hard minerals (& clay minerals) |
| How can dissolved substances be precipitated from water? | By chemical / biochemical reactions |
| Chemical Seds | Formed at or near place of deposition, inorganically |
| Biochemical Seds | Minerals precipitated through biological processes; bioclastic particles |
| What drives transportation? | Gravity |
| Materials can be moved & sorted by what? | Fluids such as both liquid & solid water, & air |
| As a given current of water slows, then... | It can no longer keep largest particles suspended, so they settle |
| What do strong currents do? |
Carry gravels
Sentence: (>50 cm/s)
|
| What do moderately strong currents do? |
Deposit sand beds
Sentence: (20-50 cm/s)
|
| What do weak currents do? |
Carry muds
Sentence: (<20 cm/s)
|
| What sediment is homogenous? | A well-sorted sediment |
| What sediment contains particles of many sizes? | A poorly-sorted sediment |
| What generally reduces size and rounds angles? | Physical Weathering |
| What reduces size but often does not round? | Glacial transport |
| Dissolved Materials | A part of the water solution itself, does not settle out unless it becomes concentrated; they accumulate in lakes and oceans |
| The geographic location of the sedimentary environment is characterized by what? | The particular combination of processes and conditions |
| Sediment environments are related to what settings? |
Plate-tectonic settings
Sentence: (e.g. deep ocean trench at subsections zone; thick alluvial deposits at mountains)
|
| What can influence the sedimentary environments? | Climate |
| What are the 3 continental environments? | Alluvial, desert, glacial |
| Alluvial environments | River channel, channel banks, adjacent flood plain |
| Desert environments | Conditions inhibit organic activity; wind action & river flow |
| Glacial environments | Cold climate; vegetation minor; moving masses of ice; meltwater streams |
| Shoreline environments | Dominated by waves, tides, currents on sandy shores |
| Deltaic environments | Where rivers enters lakes or oceans |
| Tidal flat environments | Where areas exposed at low tide are dominated by tidal currents |
| Beach environments | Strong waves; long strips of sediments |
| What are the 3 Shoreline Environments? | Deltaic, tidal flat, and beach |
| Marine environments | Wide range of sub-environments |
| Continental-shelf environment | Deeper waters at edges of continents; turbidity currents & turbidite deposits |
| Organic Reefs | Carbonate structures formed by organisms; on continental shelves or oceanic volcanic islands |
| Deep-sea environments | Continental slope to floors of deep ocean; mainly quiet waters |
| What are the 3 Marine Environments? | Continental-shelf, organic reefs, deep-sea environments |
| What do clastic environments include? | Include 1. alluvial, desert, lake, and glacial environments 2. Deltas, beaches, tidal flats 3. Continental-shelf, continental margin, deep-ocean floor |
| What are 3 chemical / biochemical environments? | Carbonate environments, siliceous environments, evaporite environments |
| Chemical / biochemical environments | Dominated by chemical / biochemical precipitation |
| Carbonate environments | Marine settings where calcium carbonate is main sediment; mainly warm tropical / subtropical regions of oceans |
| Siliceous environments | Deep-sea accumulations of silica shells |
| Evaporite environments |
Seawater in arm of sea evaporates more rapidly than can mix with connected seawater
Sentence: e.g. deps of halite, gypsum (also at lakes)
|
| Sedimentary structures | bedding and other surfaces formed at time of deposition |
| Bedding / stratification | Layers in sediment accumulations and sed rocks |
| Cross-bedding | Bedded material deposited by wind / water and inclined from horizontal; form on lee slopes of sand dunes on land or sandbars in rivers and under sea |
| Ripples | Very small dunes of sand or silt; low ridges (up to 1-2 cm) separated by wider troughs; symmetric and asymmetric |
| Graded bedding |
Beds progress from coarse grains at base to fine grains at top; waining current
Sentence: (e.g. turbidity current - "turbidite" deposit)
|
| Bioturbation structures | Remnants of burrows and tunnels excavated by marine organisms |
| Bedding sequences | Patterns of layers related to environments of deposition |
| How do most clastic particles produced by weathering & erosion of land end up on the bottom of the ocean? | Rivers, wind, and glaciers |
| What sediments are mostly deposited on the floor of the ocean? |
Chem / biochem seds
Sentence: (Others end up in lakes / swamps)
|
| Erosion on the ocean floor is much less than the erosion on....... |
Land
Sentence: Ocean floor seds are better preserved / represented in rock record
|
| Subsidence | Movement by which broad area of crust sinks relative to crust of surrounding areas |
| Sedimentary basins | Large regions where depositions and subsidence have formed thick acc's of seds and sed rock |
| Diagenesis |
Physical and chemical changes at - low T & P after deposition / burial
Sentence: (Prior to weathering or metamorphism)
|
| In diagenesis, when temperature increases with depth (30 degrees celsius / km) what happens? | It allows / accelerates chemical reactions between minerals / pore waters |
| When P increases with depth (1atm / 4.4 m) what happens? | It compacts sediments |
| Cementation | Minerals precipitated in pores of seds, forming cements that bind clastic sediments and rocks |
| Cements include what? | e.g. calcite and quartz |
| Cementation reduces what? | Porosity |
| Porosity | Percent of rock volume of open pores between grains |
| What does cementation result in? | Lithification |
| Lithification | Hardening of soft sediment into rock |
| Compaction |
Decrease in volume and porosity of sediment caused by overlying material
Sentence: Physical Alteration
|
| In Physical Alteration, muds can lose how much water? | 1/2 water |
| 3 particle sizes | 1. Coarse (gravels / conglomerates) 2. Medium (sand & sandstone) 3. Fine (silt & siltstone; mud, mudstone, shale; clay & claystone) |
| What does classifying by particle size do? | It distinguishes materials by current strength |
| What does further subdivision by mineralogy identify? |
Parent rocks
Sentence: (e.g. quartz-rich sandstone)
|
| Coarse-grained Clastics |
Gravel and conglomerates
Sentence: Classifications of Siliciclastic sediments and sedimentary rocks
|
| Medium-grained Clastics |
Sand and Sandstone
Sentence: Classifications of Siliciclastic sediments and sedimentary rocks
|
| Fine-grained Clastics | Silt / siltstone; Mud, mudstone, shale |
| The coarsest clastic sediment |
Gravel
Sentence: (>2 mm)
|
| What is lithified gravel? | Conglomerates |
| Gravel and conglomerates are mainly restricted to what? | e.g. mountain streams, high energy beaches, glacier meltwaters |
| What is 0.062 - 2 mm in diameter? | Sand |
| What is the lithified equivalent of sand? | Sandstone |
| What are sand & sandstone sizes? |
Fine, medium, and coarse
Sentence: (Medium-grained clastics)
|
| What are the shapes of sands and sandstones? |
Angular & rounded
Sentence: (Medium-grained clastics)
|
| What can sometimes deduce nature of source areas? | Mineralogy |
| Quartz arenites |
Entirely made up of quartz grains; usually well sorted and rounded; extensively weathered
Sentence: (Medium-grained clastics)
|
| Arkoses |
>25% feldspar; usually poorly rounded & less well sorted than quartz arenites
Sentence: (Medium-grained clastics)
|
| Lithic sandstones |
Contain many fragments of fine-grained rocks
Sentence: (Medium-grained clastics)
|
| Graywacke |
heterogenous mix of rock fragments & angular quartz & feldspar grains; sand surrounded by fine-grained clay matrix
Sentence: (Medium-grained clastics)
|
| What particles are deposited by the gentlest currents? |
All <0.062 mm in diameter
Sentence: (Fine-grained clastics)
|
| A clastic sediment in which most grains are 0.0039-0.062 mm |
Silt / Siltstone
Sentence: (Fine-grained clastics)
|
| A clastic sediment with grains <0.062 mm |
Mud
Sentence: (Fine-grained clastics)
|
| What is deposited by rivers and tides? |
Muds
Sentence: (Fine-grained clastics)
|
| Much of the deep ocean floor is covered by what? |
Mud
Sentence: (Fine-grained clastics)
|
| A sediment with grains <0.0039 mm |
Clay-sized material
Sentence: (Fine-grained clastics)
|
| Where does most chemical / biochemical sedimentation take place? | In oceans (but also in lakes and streams, etc.) |
| In order to differentiate the importance of organisms in formation what must you do? |
Divide nonclastic seds into chemical and biochemical seds
Sentence: Recall:
|
| What forms the most carbonate sediment of the planet? | (Biochemically precipitated) shells of organisms |
| What is by far the most abundant nonclastic sediment? | Ca-carbonate |
| Chemical sediments are precipitated by what? |
Inorganic processes alone
Sentence: (Far less abundant)
|
| Formed from accumulation of carbonate minerals precipitated organically or inorganically | Carbonate seds and sedimentary rocks |
| Why are carbonate rocks abundant? | Because of large amounts of calcium & carbonate in seawater |
| Most carbonate seds of shallow marine environments are what? |
Bioclastic
Sentence: (Originally secreted biochemically as shells, then broken and transported by currents)
|
| Most carbonate seds of ocean derived from what? | Calcite shells / skeletons of foraminifera & other organisms that secrete calcium carbonate extracted from seawater. |
| Reefs | Mounds / ridge-shaped organic structures made of carbonate skeletons of countless organisms |
| Most reefs built by coral are found where? | In modern warm seas |
| What produces rigid, wave-resistant structure built up to and slightly beyond sea level? | Most reefs built by coral |
| Reef environments contain many species of what organisms? |
Other carbonate-precipitating organisms
Sentence: (e.g. clams & mussels) - Single-celled marine algae also precipitate carbonate
|
| Limestone |
Main biochemical sed rock lithified from carbonate seds (sands & muds)
Sentence: Composed mainly of CaCO3 in form of calcite
|
| Dolostone | Abundant carbonate rock composed of dolomite: CaMg(CO3)2 |
| Dolomite is produced through what? | Diagenesis of original calcite / aragonite by addition of Mg from seawater |
| Chert | Chemically / biochemically precip silica (SiO2) |
| Chert = flint | Can use for arrowheads and tools since it is hard and has sharp edges |
| Much silica sed is precipitated how? |
Biochemically
Sentence: (Secreted as shells by ocean-dwelling organisms; when organisms die, sink to deep-ocean floor where shells accumulate; once buried, diagenetically cemented into chert)
|
| Evaporite seds and sed rocks | Precipitated inorganically from evaporating seawater and from water in arid region lakes that have no river outlets |
| How do marine evaporates form? | By evaporation of seawater: Halite, gypsum, anhydrite |
| Sequences of marine evaporates can be very, thick or thin? |
Thick, suggesting formation in constricted bays or large arms of sea
Sentence: (e.g. 100's of m's)
|
| Siliceous sediment is also known as what? | Chert |
| Iron oxide sediment is also known as what? | Iron Fm |
| What are iron formations? | Sed rock with >15% iron in form of iron oxides & some iron silicates / iron carbonates |
| Coal | Biochemically produced sed rock; organic C; formed from swamp vegetation |
| Oil & gas | Not sed rocks, but organic seds; formed by diagenesis of organic material in pores of sed rocks; can move within porous units until trapped by impermeable layers |
| Direct relation between plate tectonics and what three things | 1. Sed environments 2. Composition / texture of seds 3. Geometry of sed basins |
| Have thick alluvial deposits at mountains | Plate tectonics and sed basins |
| Have thick delta and sea fan deposits at continental margins | Plate tectonics and sed basins |
| Seds accumulate in what that are formed by what? | Accumulate in depressions formed by subsidence of Earth's crust |
| Large regions (>10,000 km^2) where dep and subsidence have formed thick acc's of sed and sed rx --(rocks??) | Sed basins |
| Deep, narrow, elongate basins with thick accumulations of sed rocks and intrusive / extrusive igneous rocks |
Rift basin
Sentence: (e.g. East Africa)
|
| Formed by cooling and increase in density of lithosphere; seds supplied by erosion of adjacent land to form continental shelf deps |
Thermal sag basin
Sentence: (e.g. Atlantic coasts)
|
| Form at zones of tectonic convergence; weight of overriding plate causes overridden plate to flex down | Flexural basins |