Lecture 5 - Sedimentary Rocks and Facies Flashcards
What do vertical changes in strata reflect?
The passage of time.
How do horizontal strata change?
They change over distance but the changes occur within the same stratum.
What is a change of facies?
A lateral change from one depositional environment to another.
What is a facies?
A body of rock that has defined characteristics.
This could be bedding, composition, texture, structure and fossils.
What is Walther’s Law of Facies?
Facies that occur in conformable vertical succession of strata also occur in laterally adjacent environments.
What is eustatic sea level rise?
Actual and global sea level rise caused by an increase in the volume of water.
What is tectonic sea level rise?
A relative and local sea level rise caused by a change in the altitude of the land.
What does an increase in sea level result in in terms of facies?
Facies prograde into the basin.
What are alluvial fans?
An accumulation of sediments that fans outwards from a concentrated source of sediments.
Where is the proximal fan?
The narrow section close to a sediment source.
Where is the distal fan?
The wide section far from the sediment source.
What factors favour the formation of braided rivers?
Steeper slopes with high quantities of coarser sediments.
What factors favour the formation of meandering river facies?
Shallower slopes with a lower flow velocity and finer sediments.
What is a cyclothem?
Alternating stratigraphic sequences of marine and non-marine sediments, sometimes interbedded with coal seams.
What do swamp facies represent?
Interactions between life, climate and geology.
