Chapter 7 - Sediment and Sedimentary Rocks Flashcards
Name the types of Physical erosion accompanying or following weathering, and what they create
Rill erosion - shallow rivulets
Incision - ravines, gullies
Washout - spires, pillars, arches, hoodoos
Mass Wasting - slumps, falls, slides
What is rill erosion, and what does it create?
Type of physical erosion.
- erosion by a heavy rainfall, and then water draining off. Creating a narrow rivulet (narrow little stream)
- creates shallow rivulets
What is an incision and what does it create?
Type of physical erosion
- a cut into a surface
- creates ravines, gullies
Incisions + washouts create canyons
What is a washout and what does it create?
Type of physical erosion
- creates spires (individual column of rocks that are separated from other rocks)
- rainfall that is more or less vertical washes it out, and then the big boulders act as roofs and prevent further erosion, leaving only a column there
- east of drumhellar and yoho national park you find these
- washouts also create hoodoos pillars and arches
Difference beteen hoodoos and spires?
Spires are a column of rock with constant thickness separated from other rock due to washout, and hoodies are the same but have variable thickness
What happens when incisions combine with washouts?
- you get canyons
- ex) grand canyon
1) What is shear strength:
With respect to rocks;
2) What does shear strength depend on?
1) You must overcome shear strength cause slope failure
2) Shear strength depends on
- slope
- friction/cohesion
- external support
With respect to rocks;
What are the most common causes of slope failure in
a) poorly consilidated material
b)hard bedrock
Most common causes of slope failure are:
- in poorply consolidated material: rain
- in hard rock: bedding relative to slope, fractures (more parallel bedding to slope = more chance of slope failure)
- insufficient external support
Explain the slumping in the Pacific Palisades in southern california
-Undercutting of steep sea cliffs by wave action resulted in massive slumping in the pacific palisades area of souther california
What is the most common cause of slope failure in unconsolidated material?
Most common causes of slope failure is rainfall on a poorly consolidated material (not hard rock)
- rain comes in and lubricates the grains between them
- common when slope of underlying material is parallel to the entire landscape
- so if bedding is not parallel to slope, its harder to cause this kind of slope failure
4 types of soil creep are:
- Land slides (mudslide / earthflow)
- Slump
- Rock slides
- Steep cliff
Describe land slides
MASS WASTING
land slides / mud slide / earth flow
-after heavy rain, a chunk of soil just moves uniformly and slides down the slope
Describe slumping
MASS WASTING
In a slump, material moves downward along the cuved surface of a rupture(concave), causing the slump block to rotate backward.
-Most slumps involve unconsolidated or weakly consolidated material and are typically caused by erosion along the slope’s base
-When there is a pre-existing slope that is very steep, a homogeneous material detachees along one or more CONCAVE
-figure 11.9 is very helpful
Describe rock slides, and explain the difference between rock slide and a land slide
MASS WASTING
- rock slide: large rocks are parallel to bedding planes, and an entire chunk/slab just slides down parallel to slope
- land slide occurs after a heavy rain, and a chunk of soil just moves uniformly down the slope
Describe a Rock-fall.
MASS WASTING
Rockfalls result from failure along cracks, fractures, or bedding planes in the bedrock and are common features in the areas of steep cliffs
-occured in frank slide
-rock fall and roll, big boulders kinda just rolled off the hill
What is the rock fall and roll
-rock fall and roll, big boulders kinda just rolled off the hill
Explain the Boscobel Landslip, where, when, how?
Is it likely to occur again? why or why not
- happened 1901, largest historic landslide in barbados
- carribean is a very active subductive plate zone
- barbados is sitting right on where there are subductive compression
- trails of bolder marked by cacti (cactus grow where limestone is)
- couple of hurricanes came through, torrential rains + earthquakes, the landslide happened when the hurricane came through
- note that there is a slight depression in the side of the island, so its just a matter of time before another landslide happens in that area
How much % of earths surface do sedimentary rocks take up?
75%
What is the aim of sedimentologicl studies?
Reconstruct DEPOSITIONAL ENVIRONMENTS
What is a depositional environment? Why are they important?
Geographic area where sediment is deposited
-almost all depositional environments are important for petroleum geology. Source, reservoir, and cap rocks
Define cap rock
layer of hard, impervious rock overlying and often sealing in a deposit of oil, gas, or coal
Regarding Deposition and Transport, what are transport agents?
Ice, water, wind
Regarding Deposition and transport, what can you say about the grain size of the deposition?
Function of energy
- water/wind high energy, so large grain sizes
- water/wind low energy: small grain size
- ice: anything
- also, grains get sorted and rounded through the distance and turbulence (further away, more round)
define lithification; what is it facilitated by?
Process of pores being destroyed through (facilitated by) compaction and cementation
-so like bunch of random minerals and grains, then they get compacted, and make a sedimentary rock
define diagenesis; what is it facilitated by?
Diagenesis is the physical and chemical changes occuring during the conversion of sediment to sedimentary rock
-facilitated by compaction, cementation, and recrystallization
(lithification is physical, diagenesis is chemical)
What happends to a sandy, clastic sediment after it is compacted and cemented?
Makes sandstone
Compare dissolution and cementation
Cementation puts pressure on rocks, and they lose their pores.
-dissolution is the dissolving of rocks (probably by acid), so that makes more pore space
so cementation reduces pore space
dissolution creates pore space
Difference between slump and landslide?
Slump are very slow, move as a unit, wont even be able to tell if you were on it
Land slide very fast, more dangerous, u can tell by looking that a land slide occured
What is mass wasting?
Type of physical erosion
-soil/sand/regolith/rock move downslope as a mass, mainly by gravity, sometimes by water and water content (mudslides)
Types of mass wastings?
rock slide
land slide
Whats the landslide in barbados called?
Boscobel landslip
