Facies Flashcards
facies
Includes all the characteristics of a sedimentary rock that are produced by its environment of deposition and allow it to be distinguished from rock deposited in an adjacent environment.
lithofacies
include all the physical and chemical characteristics of a rock
biofacies
include the palaeontological characteristics of a rock
facies association
describes a group of sedimentary facies that occur together and typically represent one depositional environment
what characteristics are used to distinguish rocks from each other? x5
mineral content, grain size, sorting, structures, fossil content etc.
how can ancient glacial deposits be recognised? x4
striations, tillites, varves, fluvio-glacial sand and gravels
littoral zone
the area between the extreme low and extreme high water of the spring tides
polymictic conglomerate
a coarse grained sedimentary rock containing clasts of many different rock types
oligomictic conglomerate
a coarse grained sedimentary rock containing clasts of few different rock types
monomictic conglomerate
a coarse grained sedimentary rocks containing clasts from a single rock type
what is the most important process in fluvial transport?
Sorting by size. Coarser grains are deposited near river source, sand size grains- middle course, finer grained- near mouth.
what is the maturity of river transported sediments?
sub-mature
where do deposits in shallow marine environments occur?
littoral zone and continental shelf
how are littoral deposits sorted?
opposite to rivers. coarser grains are transported greater distances
How is weathering important to shallow marine transport?
grains must be able to withstand high-energy waves
till fabric analysis
a method of tracing the former movement direction of ice by taking compass bearings on the long axes of large clasts in till deposits
fluvial -glacial deposit
sediments produced by meltwater streams flowing from a glacier
Describe the properties of sedimentary rocks transported by glaciers
very poorly sorted
fine matrix of non-resistant roc
coarser pebble and cobble are more resistant
what is the name for sediments transported by glaciers?
till
lithified= tillites
what does till fabric analysis show?
boulders within till tend to lie with their long axes parallel to the direction of movement of the ice.
what is the most common mineral transported by wind|?
quartz
why are sediments transported by wind texturally and mineralogically mature?
limited size range and grains resistant to mechanical weathering
Banded Iron Formations (BIFs)
Units of sedimentary rock of Precambrian age consisting of alternating layers of iron oxide and chert
why do streams migrate across flood plains?
Bank undercutting on one side of meander and deposition of point bar deposits on the other side. in-between are channel deposits
What happens to shallow siliciclastic seas and beaches during marine transgression ad regression?
they migrate laterally along the coast
Walter’s law
to be conformable, vertically adjacent facies must reflect those environments which occur side by side.
How do BIFs form?
photosynthetic bacteria oxidise ferrous iron into ferric iron using sunlight. Chert bands deposited by silica-forming organisms. rhythmic nature of deposition suggest cyclic variation in conditions.
