Transitional environments Flashcards
Where is the transitional environment?
At the interface between land and sea
What type of coast is where deltas, estuaries, or lagoons form?
Delta = on a prograding coast
Estuary or lagoon = transgessive coast
Transgression/regression?
Transgression (retrogradation) = vand ind mod land
Regression (progradation) = vand væk fra land
What are the 3 main controls of a marine delta?
Climate
Tectonics
Eustatic sea level changes
(Other than that: waves, tides)
What are the characteristics of deltaic deposits?
Lithologies: conglomerate, sandstone and mudstone.
Mineralogy: variable, delta-front facies may be compositionally mature.
Texture: moderately mature in delta-top sands and gravels, mature in wave-reworked delta-front deposits.
Bed geometry: lens-shaped delta channels, mouth- bar lenses variably elongate, prodelta deposits thin bedded.
Sedimentary structures: cross-bedding and lamination in delta-top and mouth-bar facies.
Palaeocurrents: topset facies indicate direction of progradation, wave and tidal reworking variable on delta front.
Fossils: association of terrestrial plants and animals of the delta top with marine fauna of the delta front .
Colour: not diagnostic, delta-top deposits may be oxidised.
Facies associations: typically occur overlying shallow-marine facies and overlain by fluvial facies in an overall progradational pattern.
What is an estuarine?
Flodmunding
When the sea transgresses in the river plain
Two energies (both high) meet and annihilate in the middle (low energy)
What is the geological definition of - and difference between - an estuary and a lagoon?
Estuary
- receives sediment from fluvial + marine sources
- facies influenced by tides, waves, and fluvial processes
- sea portion of a drowned valley system
Lagoon
- shallow body of water partly/completely separated from a larger body of water by a barrier
– barrier = reef, beach…
What are the two types of estuaries?
Tide-dominated
Wave-dominated
What are the characteristics of estuarine deposits?
Lithologies: mud, sand and less commonly conglomerate.
Mineralogy: variable.
Texture: may be well sorted in high energy settings.
Bed geometry: lenses with erosional bases, or tabular muds with thin sheets and lenses of sand.
Sedimentary structures: cross-bedding and cross-lamination and inclined heterolithic stratification, ripple cross-lamination and flaser/lenticular bedding.
Palaeocurrents: bimodal.
Fossils: shallow marine fauna and salt marsh vegetation.
Colour: usually not diagnostic, but often dark due to anaerobic conditions in mudflats.
Facies associations: may be overlain by fluvial, shallow marine, continental or delta facies.
What are the two main clastic coasts?
Dissipative coast
- flat beach
- depositional
- less energy when it reaches the coast
Reflective coast
- steep beach
- erosional
What is a berm?
Marks the division between the foreshore and back- shore area
Aka. a ridge of sand between the actual beach and the sea
Behind it is the backshore (oftentimes wet)
How can dunes show that a coast is prograding (regression)?
Multiple dunes behind each other away from the beach = once the water went up to the first dunes.
SO if you see a dune behind, the coast is prograding (moving away).
What are the characteristics of littoral deposits?
Lithologies: sand and conglomerate.
Mineralogy: mature quartz sands and shelly sands.
Texture: well sorted, well rounded clasts.
Bed geometry: elongate lenses.
Sedimentary structures: low-angle stratification and wave reworking.
Palaeocurrents: mainly wave-formed structures.
Fossils: robust shelly debris.
Colour: not diagnostic.
Facies associations: may be associated with coastal plain, lagoonal or shallow-marine facies.
