Sedimentary practical's (pre-reading) Flashcards
What are poorly sorted sediments?
when the grains are of varying sizes
What are well sorted sediments?
when the grains are all about the same size
How does rounding occur?
when the sharp edges of rock is worn down by abrasion when transported
What does the speed of sediment rounding depend upon?
hardness and composition
What are ripples and what do they reflect?
Type of bedform
Reflect flow (direction and energy)
What 2 types of sediment ripple are there?
Symmetrical
Asymmetrical
How do symmetrical ripples form?
oscillatory flow (on a beach)
Forward and back current flow
Where do asymmetrical ripples form?
areas with unidirectional flow (rivers or beach’s with dominant current direction)
What is a facie?
distinctive sedimentary rock packet with distinctive sedimentary features
What are lithofacies?
facies based on sediment characteristics such as grain size and minerology
What are biofacies?
facies based on fossil content
What can form when facies interact?
facie association or succeed one another to form facie sequence
What is Walthers law?
states vertical succession of facies reflects lateral environment change
What are good examples of vertical stratigraphic succession?
Marine transgressions (sea level rise)
and
Marine regression (sea level fall)
What is another name for ‘rock layers’?
strata
What are Nicolaus Stenos 4 principles of stratigraphy?
Principle of superposition
Principle of original horizontal
Event that cuts across exiting strata is younger
Strata presumed to continue laterally from present end point
What is subsidence?
local and regional scale change in earths crust in the form of a downward shift
When do rift basins form?
When the continental crust is stretched
During early rifting earth surface subsides as its stretched and thinned
What is a good example of a rift basin?
the east African rift system
What sort of area will intracratonic basins form?
Interior of continents away from plate margins and mountain belts
What are intracratonic basins usually like?
round or oval in shape
Long geological history of low subsidence
What is one formation theory for intracratonic basins from rifting?
Form over areas of previous rifting
Rifting stops and hot stretched crust cools it contracts and shrinks (thermal sag)
What 2 things can intracratonic basins be filled with?
Continental sediment
Flooding from adjacent ocean
What can the flooding of a intracratonic basin form?
Epicontinental seas