origin of sediments Flashcards
(7 cards)
What is the difference between weathering and physical erosion?
Weathering is the chemical process of breaking down the rock, changing its chemistry and making it weaker. Physical erosion involves physical forces like water, ice, wind, or temperature changes that break the rock into smaller pieces.
If a rock is weathered, it is more likely to get eroded, and a freshly eroded surface is more likely to be weathered.
What is the Goldich series?
The Goldich series indicates how vulnerable a mineral is to weathering, describing its ‘weatherability’.
Minerals like olivine and Ca-feldspar that precipitates under highest P & T have the highest weatherability, whereas K-feldspar, muscovite and quartz have an increased stability - they are less likely to get weathered, because they are stable at lower P & T
What is the link between clay minerals formation and climate?
Climate influences which clay minerals are produced.
Different clay minerals are formed under specific climatic and weathering regimes:
Kaolinit: Tropical and savannah. Warm and humid, acid weathering conditions for the alteration of feldspar-rich rock.
smectites: Mediterranian and savannah. drier climate, weathering of igneous rocks under alkaline conditions.
Illite: weathering of feldspars and micas under alkaline weathering conditions where significant leaching of mobile cations such as potassium does not occur.
Can you explain the chemistry of seawater carbonates (in a nutshell)?
CO2 is absorbed in the ocean to form H2CO3, CO3- and CO3 2-, allowing shelly fauna to create shells from CaCO3.
The concentration of CO2, HCO3- and CO3 2- is a function of the seawater PH. Normally the PH is around 8, which is around:
CO2: 0.5%
HCO3-: 89%
CO3 2-: 10.5%
Photosynthesis can remove CO2 from water, making it more basic, which promotes the precipitation of CaCO3. The temperature also affects how much CO2 can be absorbed in the water, as well as the atmospheric levels of CO2.
What are the main evaporitic minerals and in which order do they precipitate?
The main evaporitic minerals are calcium carbonate (CaCO3), gypsum (CaSO4*2H2O), halite (NaCl), and sylvite (KCl).
What is bulls-eye evaporation?
->sea level fall = calcium carbonate precipitates
-> sea level fall = gypsum precipitates
-> sea level fall = halite precipitates
this happens from the outside with CaCO3 as the outer ring and halite will precipitate in the middle to form the bulls-eye.
Bulls-eye happens when evaporation of a whole isolated waterbody occurs.
Evaporite sedimentation occurs only in situations where a body of water becomes partly isolated from the ocean realm and salinity increases to supersaturation point and there is chemical precipitation of minerals
What is teardrop evaporation?
In a lagoon with a very small connection to the water, the salinity gradient will rise the further in you go. Calcite will be closest to the water, gypsum and then halite where the salinity is highest furthest away from the ocean.
Evaporation increases across a semi-isolated bassin
Evaporite sedimentation occurs only in situations where a body of water becomes partly isolated from the ocean realm and salinity increases to supersaturation point and there is chemical precipitation of minerals
