Lecture 10: Shallow water carbonates Part 1 Flashcards
Why study shallow water carbonates?
1) in the geological record most CaCo3 seds are formed here
2) Half the worlds petroluem reserves are in carbonates
3) evolution of life through fossils
4) Eaths histroy, evolution and climate
What are limestomes made of?
either 1) non skeletal grains (inorganic) 2) skeletal grains (biogenic) 3) matrix and cements
What are the three types of non skeletal grains
They are ooids, peloids or aggregates
Ooids in depth..
Subherical/subspherical grains, consisting of one or more regular concentric lamellae around a nucles. Form in warm shallo agiated waters
Peloids in depth..
Spherical or angular, mostly faecal pellets
Aggregates in depth..
Serveal carbonates particles cemented together
What are skeletal grains
Grains released by Bivalves, Gastropods, Cephalopods, Corals etc
What is the matrix and cement
The grains in a many limestones sit within a matrix of calcerous mud
Why is cemenation key
its a major process which produces hard limestone from loose sediment. Supersaaturared fluids lead to mineral precipating between grains
What are carbonates different to silliciclastic sediments?
Silliciclastics are formed from pre exsisting grains, roundess and sorted where as carbonates grains are usual loccaly produced, inorganic or orgnic
Where are the produced the three envrioments
Lagoonal limestones
Indertial/super tidal carbonates
Intertida/subtidal carbonates
Lagoon limestone properties
Protected by barriers (reefs)
Low energy enviroment
Carbonate sands and muds
inter/super titdal properties
regulary to rarely covered by water
tidal flats
calcerois muds
stromatalites
inter/sub
High wave activity
barries and becahes
Similar to siliciclastic shorielines
carbonate sands
But which are which, what is the classification scheme
Durgam classification scheme
