Marine environments Flashcards
How is the marine realm divided?
Neritic zone = sea level to shelf edge break
Bathyal zone = shelf edge break to ∼4000 m
Abyssal zone = ∼4000 m to ∼5000 m
Nadal zone = below ∼5000 m
How is the neritic zone divided?
Backshore = left side of foreshore
Nearshore = foreshore + shoreface
Foreshore = lower part of beach = sea level (mean high water) to mean low water
Shoreface = mean low water to fair weather wave base
Offshore-transition = upper offshore, moves only in storms = fair weather wave base to storm wave base
Offshore = lower offshore, moves only in really big storms = beneath storm wave base
Where is the water in the neritic zone moving?
Water always moving nearshore (foreshore and shoreface) down to the fwwb
Water not moving offshore
What applies to the Foreshore – Shoreface?
Any sediment will be extensively reworked by wave processes
Wave-ripple cross-lamination and horizontal stratification
Wave ripples are less common as the fair-weather wave base is approached in the lower part of the shoreface
What applies to the Offshore transition?
Between the fair-weather and storm wave bases
Sands are deposited and reworked by storms
Periods between storm events = deposition of mud from suspension
Storm deposits are therefore separated by layers of mud
What are tempestites?
Individual storm deposits
Thickness = a few tens of centimetres to millimetre-thick beds in the outer parts of the offshore transition zone
How does an idealised tempestite bed look?
Sharp, possibly erosive base, overlain by structureless coarse sediment
As the storm wanes, hummocky–swaley cross-stratification forms in finer sands –> overlain by fine sand and silt that shows horizontal and wave-ripple lamination
At the top of the bed the sediment grades into mud.
What is HCS and SCS?
Product of strong and complex wave activity, mainly in areas below fair-weather wave base.
Typically interpreted as produced by !storm activity!
Typically found in silt or fine sandstones
What applies to the Offshore?
Region of mud deposition
Exceptional storms = represented by thin, fine sand deposits interbedded with the mudstone
Relatively poorly oxygenated = commonly grey sediments
Hvordan ville man tegne en weathering profile over en tegning med mange “takker” af et materiale ind i et andet materiale? (som set ved tegning af overgang fra coastal til transition til shelf mud facies)
Som lag af materiale A i materiale B, hvor tykkelsen af A varierer efter tykkelsen af takken, og hvor afstanden mellem venstresiden og den rette højreside af profilen bliver “mindre”
What are large sand ridges?
Found on modern shelves
Sands are moderately well sorted, medium grained - may include mud
What are the characteristics of deltaic deposits?
Lithologies: mainly sand and mud, with some gravel.
Mineralogy: mature quartz sands, shelly sands.
Texture: generally moderately to well sorted.
Bed geometry: sheets of variable thickness, large lenses formed by ridges and bars.
Sedimentary structures: cross-bedding, cross- and horizontal lamination, hummocky and swaley cross- stratification.
Palaeocurrents: flow directions very variable, reflecting tidal currents, longshore drift, etc.
Fossils: often diverse and abundant, benthic forms are characteristic.
Colour: often pale yellow-brown sands or grey sands and muds.
Facies associations: may be overlain or underlain by coastal, deltaic, estuarine or deeper marine facies.
What is the Bouma sequence?
Describes a classic set of sedimentary structures in turbidite beds deposited by turbidity currents at the bottoms of lakes, oceans and rivers.
Ie. the ideal vertical succession of structures deposited by low-density
Divided into 5 distinct layers labelled A through E, with A being at the bottom and E being at the top - with the layers overall getting finer-grained from bottom to top.
A: Erosive base at the bottom
B + D: horisontal lamination (horisontal lines)
C: current ripples
The higher up in the alphabeth, the finer the grains
What are turbidites?
Turbidites = avalanches
Erode in the beginning because of the speed; when it slows, deposition will start (therefore you don’t have all of the layers everywhere)
A – will be deposited early when the speed slows, but the finer sediments won’t be deposited before the speed is much slower (A and the other coarser sediments will be gone (already deposited))
What are the characteristics of deep-clastic deposits?
Lithologies: mud, sand and gravel.
Mineralogy: arenites may be lithic or arkosic.
Texture: variable, some turbidites poorly sorted.
Bed geometry: mainly thin sheet beds, except in submarine fan channels.
Sedimentary structures: graded turbidite beds with some horizontal and ripple lamination.
Palaeocurrents: bottom structures and ripple lamination in turbidites show flow direction.
Fossils: pelagic, free swimming and floating organisms.
Colour: Typically dark mud, and yellow or red coarse grained beds.
Facies associations: may be overlain or underlain by shelf facies.
