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