Lecture 11 Shallow water carbonates Part 2 Flashcards
Fossils are abundent inlimestone, what are the three key points about them
Diversity, Morpology and evolution
What do high diversity fossil content indicate?
Stable conditions
What does low diversity fossil content indicate
Intial colonization or
Unpredictable stressful environment (temp, salinity, light levels)
What does fosil morpohogy show?
it gives an idication of where the fossil lived (ed marine and non marine sepcies, this shell of deep water vs thick shell of tidal) Trace burrows, body size (related to temp - climate indicator) Coral morpoholgy - where did they form on the reef
why is coral morphology useful
Use for reconstructing the reef type and hence overall morpoholgy for a trap for oil
what are framwork builders?
THese construct the structures of framework reefs, in the past these inlcudded stromatolites and cyanobactieral.
Case study in the UK
Carboniferious Limestone in UK
What is this case study
A wallconstructed of reef buildnig organisms, including a fore-reef, back reef, and a wall. Structure is similar to modern day examples but the bioenigeneers were not
How were these reefs built?
Largely built by algea, with some coral
Little detrail sediment
Diverse fossil assembalages
What are the properties of a palaeoenviroment
Shallow water
Clear well lit water
Warm stable climate with nutrient supply
What are the major two minerals of calcium carbonate
Aragonite (more compact dense)
Calcite (more open, less soluble in water)
relationship between the two
fossils or orgaisms that were orginally aragonite are often preserved as calcite
What are the two chemical controls
Carbon doixide levels
Seawater Mg/Ca ratio (most important)
What do calcite seas show
High seafllor spreading rates high pCO2 High sea level warm low sewater mg/ca ration GREENHOUSE
What do aragnoite seas show
Slow seafloor spreading low pCO2 Low sea levels Cold High seawater mg/ca ratio ICEHOUSE
