Sedimentary Rocks and Processes (A2) Flashcards
Define Weathering
The in situ breakdown or decomposition of rocks and minerals through chemical, biological and physical processes
Define Erosion
The weathering down of rocks by the mechanical action of transported debris
What are two types of physical weathering?
Freeze-thaw, Insolation
What are five types of chemical weathering?
Carbonation, Oxidation, Hydration, Hydrolysis, Solution
What is a type of biological weathering?
Root growth
Define Arenite
A sandstone with less than 15% matric
Define Wacke
A sandstone with between 15 and 75% matrix
Define Lithic Fragment
A rock fragment
Define Facies
An area with a distinctive sediment type
What are the four facies in a desert environment?
Scree, Alluvial fan, Aeolian sandstone, Playa lake
Define Mesa
A portion of a plateau separated from the main plateau
Define Butte
An isolated tower, remnant of a plateau
Define Wadi
Dry riverbed eroded by flash flooding
Define Sabkha
Evaporate deposits left behind after floodwater in coastal areas/lagoons is evaporated
What is the trend in grain size in an alluvial fan?
Courser closer to the source and finer further away
What are two factors controlling grain size in an alluvial fan?
The amount of water and The velocity of the water
What is the mode of transportation of the grains in an alluvial fan?
Carried as a bed load in water
What is the reason for deposition of the grains in an alluvial fan?
Grains are deposited when the water loses velocity
What is the mode of transportation of the grains in sand dunes?
Wind
What is a sedimentary feature commonly found in sand dunes?
Large scale cross bedding
What is the texture of the grains in a sand dune?
Sand sized particles, Well rounded, Well sorted
What is a playa lake?
Site of a former or occasional lake
What are the four main deposits found in a playa lake?
Calcite, Gypsum, Halite, Magnesium
What is the reason for the order of the deposits of a playa lake?
Differing evaporation rates of the deposits mean some come out of solution before others e.g. Magnesium is most soluble so is deposited last
How are ripples formed?
High velocity water picks up sand grains on the stoss side of the ripple and a drop in velocity on the lee side causes the grain to be deposited
What are two fossils found in a fluvial environment?
Roots from plants will be preserved on the flood plain, Fish in rivers
What are three bedforms in a fluvial environment?
Floodplain, Point bar, Channel
Define Delta
Formed when a current of water carries sediment into deeper, relatively still water, causing sediment to be deposited
What are five features of a delta top?
Channels, Point bar sands, Levees, Distributaries, Fan shaped lobes
Define Flocculation
Saltwater is an ionic solution which causes clumping and cohesion of clay particles, increasing size and mass allowing it to settle
What is Walther’s Law?
Facies that occur next to each other are recorded vertically in sequence
Define Prograding Delta
Building out into the sea because sediment brought in is greater than subsidence on the delta
What is recorded in the deposits in a prograding delta?
Marine transgression
Define Retrograding Delta
Reducing in size because sediment brought in is less than subsidence on the delta
What is recorded in the deposits in a retrograding delta?
Marine Transgression
Define Isostatic
Local change in sea level related to the loading of the lithosphere by sediment deposited on the delta
Define Eustatic
Global changes in sea level linked to periods of glacial/interglacial as well as an increase in mid-ocean ridge activity
Define Turbidite
A deposit from the turbidity current
Define Turbidity Current
An underwater avalanche
Define Bouma Sequence
Idealised sequence of one turbidity event
What are two reasons a bouma sequence might be incomplete?
Distance from source, Top layers could be eroded
What are five conditions required for limestone formation?
Marine water, Shallow water depth, Warm water temperature, Clear water, Well oxygenated and nutrient rich
Define Fringing Reef
Formed around the edge of a small landmass/volcanic island, attached to the land
Define Barrier Reef
Reef grows at the same rate as the sea levels rise
Define Atoll
Eventually, the island is covered by water, creating an atoll and lagoon
Where does chalk form?
In shallow water in the photic zone
What are the three steps in chalk formation?
(1) Coccolithophore dies (2) Coccolithophore falls apart, taking a long time to settle to the ocean floor (3) Form usually on continental shelf due to Carbonate Compensation Depth (CCD)
Define Carbonate Compensation Depth (CCD)
The depth of water carbonate shells will dissolve back into the water
What are the two stages of diagenesis?
Compaction and cementation
