Carbonates and Evaporates Flashcards
carbonate rocks consist primarily of what two carbonate minerals
Limestone - predominately calcite (Calcium carbonate, CaCO3)
Dolomite - Predominately Dolostone (Calcium Magnesium Carbonate, CaMg(CO3)2
how are carbonate rocks formed?
through biological and biochemical processes and through inorganic precipitation from seawater
what period did the spreading of carbonate rocks start with?
the Cambrian period
What percentage of all sedimentary rocks are made of carbonates? And what fraction do these carbonate rocks make up for the worlds petroleum reserves?
20-25%
and
1/3
Most carbonates form in what temperature of water?
Warm
most carbonate sediments are generated in which zone?
Photic zone
True or fales.
Unlike sandstones, most carbonate grains are formed in the environment in which they are deposited?
True
Carbonates are not usually found / occur after approx. what depth? And why is that? And what is the name of that depth range?
3500-4000m and this is because the carbonate sediments dissolve here. This depth is called the Carbonate compensation Depth CCD
List 4 chemical carbonate rocks
Limestone
Dolostone
Rock Gypsum
Rock Salt
List 3 BIOchemical carbonate rocks
Limestones (chalk and coquina)
Chert
Coal
Is Coquina a Clastic or Carbonate?
This was a trick question,
Coquina is a clastic carbonate.
What is the major rock forming mineral found in mt.rundle?
Calcite (CaCO3)
Carbonate reservoirs are predominately composed of what?
chemical precipitates
What is a chemical precipitate?
they consist of mineral matters that was precipitated at the place here the rocks first formed and not transported as clastic grains
What is the most dominate chemical reservoir rock?
Limestone
What is the secretion process? and what are formed by this process?
Rocks of biochemical origin are formed by this process in which animals and plants extract mineral material from solution and transform in into skeletal forms
what is the carbonate secreted by living organisms? and how is it formed?
CaCO3 in the form of either aragonite or calcite
What are the main biochemical agents in forming limestones?
Algae, bacertia, corals, foraminifera, bryozoa, brachiopods
What is the most important rock builder of lime secretions and deposition?
Algae
what is the general way dolomite is formed?
formed from limestone as the calcium in calcite is partially replaced by magnesium. Usually as water solutions move through the limestone
explain the process of dolomite recrystallization and it’s importance
Magnesium ion migration through layers of limestome form the dolomite and this replacement process causes the recrystallization of the pre-exisiting limestone which enhances the porosity of the carbonate rocks
What are the two principal classifications for carbonates?
Folk’s classification: named after Robert Folk
Dunham’s classification: named after Robert Dunham
How does Folk’s classification system work?
Based on the presence / absense of Allochem (carbonate particles or grains), matrix and type of cement
How does Dunham’s classification system work?
It is based on texture of the rock.
Limestones are formed in what environments (4)?
Shallow marine
deep marine
karsts
Lakes
High temperature and low pressure and breaking waves favor what?
carbonate precipitation
CaCO3 precipitates in warm or cool water?
Warm shallow water
What are the four controls on carbonate accumulation?
Temperature
Light
Agitation of waves
Organic activity
Are carbonate sediments born or made?
Born
What are the four carbonate platforms?
Ramp
Rimmed Shelf
Epieric platform
Isolated platform
What is the Carbonate mineralogy consist of?
Aragonite - high temp CaCO3 mineral
Calcite - Stable in sea water and near surface crust
Dolomite - stable in sea water and near surface
Lime muds and skeletal material are lithified into what?
Limestone
What are the four keys for the interpretation of a depositional setting of a carbonate?
Grain types
Grain packing or fabric
Sedimentary structures
Early diagenetic changes
What is an Ooid?
spherical grains formed by calcite precipitation around the nucleus. Such as shell fragment
They are less than 2mm in diameter
Where are Ooids found/formed?
Typically form in shallow warm , agitated and carbonate - saturated waters such as those near the bahamas.
What kind of sedimentary structures are present in carbonate rocks?
Cross bedding
Laminated bedding
Mud cracks
Trace fossils
What are two carbonate marine depositional systems?
Carbonate reefs
Carbonate shelves and platforms
What are four examples of Carbonate tectonic extension settings?
Great barrier reef of Australia
Bahamas
East Africa
Red Sea
What are three examples of Carbonate tectonic Compression settings?
Persian Gulf
Appalachians
Australia
What is a Karst?
a landscape formed by the dissolution of soluble rocks including limestone, dolomite and gypsum
What is a Karst modified reservoir?
Carbonate reservoir
Examples of Karst features that can affect reservoir performance
Collapse feature
Residual Paleo-Highs
Solution - enlarged fractures
What are Two factors that shape coral reefs?
The foundation on which they grow
sear level history
What are the three major reef types?
Atoll
Fringing
Pinnacle / Barrier
What is an Atoll reef?
circular reef enclosing lagoons
What is a Pinnacle reef?
shaped like a tower and rises from the sear floor to form mounds
What is a fringing reef?
they grow attached to the shoreline or island
Name four carbonate depositional environments
Shelf (reef) margin crest
Shelf Platform
Basin
Shelf base
What is a reef margin
forms linear bodies parallel to the basin
Why are shelf platform carbonate depositional environments important?
they form major caps to oil fields.
What is important to know about the shelf margin slope system?
Gravity dominant sedimentary driver
What is important to know about the basin systems?
they are set in the deeper water down slope
they tend to exhibit thin beds of alternating carbonates, silts and shales
