Sedimentary structures- Clastic and Lacustrine facies Flashcards
List 11 Primary Sedimentary Structures
- Planar bedding, laminations, varves
- Ripple Marks
- Cross-Bedding
- Graded Bedding
- Incised channels
- Flute channels
- Rills and Gullies
- Mud Cracks
- Raindrops
- Mud Volcanoes
- Trace Fossils
Planar bedding is separated by variations in?
color, composition, grain size with bedding surfaces parallel to bedding.
What is the depositional environment of a Planar Bed?
- Deposition from high flow velocity
- settling from standing body of water with very low flow velocity (e.g.. lakes, varves)
What is hummocky cross bedding?
Is a distinctive sign of storms like hurricanes. Formed when piles of sand at least 1m high (called hummocks), are built up at the bottom of the sea floor. This results in a permanent new coat of sand covering the whole seafloor.
What are glacial varves?
Annual glacier laminations consisting of 1 dark layer (winter) and 1 light layer (summer)
How are asymmetrical ripple marks formed?
By unidirectional currents (asymmetrical)
How are symmetrical Ripple marks formed?
generated by multidirectional flows (currents, waves)
What is imbrication?
a stacking pattern of sediment particles that point to ancient currents.
How is imbrication formed?
by transporting (rolling) of disk shaped gravel class.
Cross bedding results from?
a change in current direction
Cross bedding is common in what depositional environments?
eolian, fluvial and marine sand bar deposits.
What is graded bedding?
fining upward sequence
graded bedding is a primary clue in the identification of?
deep water turbidites
Coarsening upwards sequence is indicative of what depositional environment?
Deltas
What are the 5 principles of stratigraphy?
- Principle of Uniformatarianism
- Principal of Original Horizontality
- Walter’s Law
- Law of superposition
- Law of faunal succession
What is a barchan dune?
an arc-shaped sand ridge, comprising of well sorted sand
What are secondary bedding plane marking are signs of what?
vigorous activity in sediments before they turned to rock
How are secondary bedding plane marking caused?
due to the alteration of primary depositional structures such as trace fossils, diagenetic, nodules, concretions and other features.
What are primary bedding plane markings related to and what are 4 examples?
to erosion and deposition of sediments.
- Incised channels
- Sole markings (flute casts)
- Mud cracks
- Rain drops
What are secondary primary bedding plane markings related to and what are 3 examples?
related to alteration of depositional fabric
- Mud volcanoes and load casts
- Trace fossils
- Diagenetic- nodules, concretions, stylolites
Name 5 load casts
sole marks flute structures flame structures ball and pillow structures mud cracks rills and gullies
When is a ball and pillow structure formed?
is formed when a sudden load of sand deposits is laid down on a soft mud bed.
When is a pillar structure formed?
as fluid escapes from under-pressure sediments
What is a rill?
a narrow and shallow incision into the underlying structure
How are gullies formed?
gullies are small valleys formed by the development of rills
What are mud cracks a product of?
dessication and contraction of deposited muddy sediments
What is a trace fossil or ichnofossil?
a biogenic sedimentary structure, where preserved intact, are closely related tp the depositional setting
What are stromatolites?
layered bio-chemical accretionary structures formed in shallow water by trapping, binding and cementation of sedimentary grains by biofilms of microorganisms (especially blue-green algae)
Define walter’s law
whatever happens vertically, happens laterally!!!!!!!!!!!!
What is lithostratigraphy?
Correlation of sedimentary rocks based upon lithology
What are the units of lithostratigraphy?
supergroup group formation member bed
What is chronostratigraphy?
Correlation of sediments based upon relative or absolute age
What are the units of chronostratigraphy?
Eon Era Period Epoch Age
What is biostratigraphy?
Correlation of sedimentary rocks based upon fossil content
What are the units of biostratigraphy?
system
series
stage
zone
Name 5 terrestrial systems and facies
- rivers
- deserts
- lakes
- downslope basins in mountains
- ice sheets/glaciers
What are the 3 main terrestrial systems that we are focusing on in this class?
- fluvial
- eolian
- lacustrine
What is the basic 3 fold sub division of terrestrial basins?
- Basins with thorough drainage are dominated by well established river systems.
- Basins with internal drainage (shallow, short lived, sabkhas, deserts)
- Basins with well developed lake environments.
What are the 3 principal river types?
- Meandering river model
- Sandy braided stream model
- Anastomosing rivers
In a meandering river system, sand deposition is normally restricted where?
to the main channel
Does the channel floor in a meandering river have a coarse or fine layer?
Coarse…only moved at high velocities
During normal discharge, how is sand moved through the system?
- dunes on the channel floor
2. ripples higher on the point bar
Do meandering river fine upwards or coarse upwards?
fine upwards
What are sandy braided rivers dominated by?
bars, channels, and sinuous crested dunes
When does an anastomosing river occur?
when a river has multiple number of relatively stable channels.
How are anastomosing rivers formed?
formed by high rates of vertical sediment accumulation/aggradation
The occurrence of eolian deposits in the stratigraphic record is an indicator of what?
ancient climatic zones
Eolian sequences are dominated by what kind of deposition?
dominated by cross-stratified sandstones reflecting migrating eolian bedforms developing during the lateral movement of sand dunes
Are sediments commonly well sorted in a lacustrine sedimentary facies?
YES
Do facies fine inward or outward in a lake?
fine inward toward the basin center
lake sediments are predominantly fine or coarse sediments?
FINE
What is a typical sequence that may be produced when a lake dries up?
coarsening upward sequence from laminated shales, marles and limestones to rippled and cross bedded sandstone and possibly conglomerates.
What sedimentary facies typically shows varves?
LAKES
How are varves produced?
by seasonal variation in sediment supply
Lakes are typically ephemeral features, what does this mean?
only the largest lakes are likely to leave a significant sedimentary record.
What 2 headings are lakes classified under?
- Hydrologically open lakes (outlet streams eg. glacial lakes)
- hydrologically closed lakes(inland drainage) (characterized by evaporate deposits eg. playa lakes)
In a lake, where are the coarser clastics deposited?
close to shore and may display ripple marks and cross-bedding.
What is generally found in the offshore region of a lake where clastics accumulation is reduced?
thin limestone and marls
In a deeper part of a lake, what accumulates and why?
clays and silts accumulate from suspension at very slow rates
In rare cases, tubidity currents may deposit what in the deeper part of a lake?
fining upwards sediment
Are lakes a good place to find hydrocarbon?
not great, only found sometimes.
Lake basins have many diverse origins created by the action of what 6 things?
- Glaciers
- Rivers
- Wind deflation
- Tectonics
- Volcanoes
- Meteor Impact
What is a Tarn?
a small mountain lake, especially one that occupies an ice-gouged basin on the floor of a cirque.
What are the margins of the sedimentation of a lake marked by?
alluvial fans and fluvial desiment
What is the sedimentation in the center of a lake from?
Finer sediments and turbidite cycles cycles in order from: -Clastics and organics -Limestones and Organics -Evaporties and organics
What sedimentary signature is a lake similar to?
A foreshortened marine setting
A lake has what kind of shoreline?
narrow shores with beaches and deltas
What does micritic mean?
oil
Common ways lakes are formed?
glacial, flash flooding, wind deflation and mass wasting/man-made.
less common: Tectonics (e.g. fault-bounded lakes; cratonic sags) Volcanoes (crater lakes) Meteor Impact (crater lakes) Karsting (carbonate solution sinks)
Great Lakes
Bodies of fresh water trapped on glacially scoured depressions on craton behind glacial moraines
Act as traps to clastic sediments
Climatic change is recorded in record of sediment fill
Water draw down encourages precipitates
Caspian and the Aral Sea
Bodies of fresh to saline water trapped on craton behind major mountain chains
Tend to act as traps to clastics, carbonates and evaporitic sediments
Climatic change is recorded in the record of the sediment fill
Water draw down encourages evaporites
Lake sedimentary facies
Sedimentary signature like that of a foreshortened marine setting
Narrow shores with beaches and deltas
Finer sediments and turbidites fill the lake center
What kind of reservoir is the Daqing Oilfield?
Lower Cretaceous lacustrine-deltaic and fluvial sandstone
what kind of source rock is in the Daqing oilfield
deep-water lacustrine shale and mudstone of early Cretaceous age
Daqing Oilfield size?
It is 138 km long in north - south and 73 km wide in east - west, covering an exploration area of 72X104 km2 with 4103.37 km2 of oil-bearing area proven.
