Reefs - Lecture 7 Flashcards
What are organic reefs?
Calcareous deposits with a topographic relief created by sessile organisms. High fossilisation potential
How are organic reefs formed?
Formed from growth of corals and other organisms (e.g. algae, sponges) creating a framework for sediment to be trapped
What are the three main components of reef rocks?
Cement, Matrix and Skeletons
Name three types of reef.
Cement-supported reefs (early seafloor cementation between skeletons), Matrix-supported reefs (e.g. Cluster and Segement reefs) and skeleton-supported reefs (e.g. frame reefs)
What is special about an ahermatypic coral?
They lack photosymbiontic algae
Hermatypic corals have symbiotic algae, what is the algae called?
Dinoflagellates
What traits are characteristic of a basic coral body plan?
Skeletons always made of calcium carbonate and environmental conditions strongly influence morphology (ecophenotypy)
What are common features of corals living in both high energy environments and low energy environments?
High energy: large surface area, high polyp density and rapid regrowth following damage. Low energy would have small surface area with low polyp density due to limitations of light and nutrients
What were the key Palaeozoic reef formers?
Sponges, Bryozoans and ahermatypic corals
How do Modern and Palaeozoic reefs compare?
They contained different groups of corals and organisms, less bioerosion from fish in palaeozoic coral reefs, palaeozoic corals could not attach to hard substrate and lacked symbiotic algae
What are the two major polymorphs of calcium carbonate?
Calcite and Aragonite
Mg/Ca in the oceans is closely linked to ocean spreading rates. What is the Mg/Ca concentration at high and low spreading rates?
High spreading rates: lower Mg/Ca Lower spreading rates: Higher Mg/Ca
