Sedimentary Structures Flashcards
What different types are there?
Induced by physical processes
- Erosional (before deposition)
- Depositional (during deposition)
- Deformational (after deposition)
Biologically induced
- Bioturbation
- Binding
Chemically induced
What are “sole marks”?
Erosional structure.
When a stone bounces/skips/etc. on a bottom of cohesive, fine-grain sediment (usually mud) and then leaves marks after that.
Two main types: Scour & Tool marks
Hvordan ser scour marks ud?
L__—
Dvs. der er en hård kant ned i sedimentet, der flader ud på den anden side, så det igen flugter med sedimentets overflade.
Når sand aflejres ovenpå, vil det derfor give små “buler”. Vandets retning kan aflæses som at den hårde kant bliver ramt først, og så flader det ud bagved = vandet rammer først kanten.
What makes laminations/bedding visible?
Differences in grain type, size and/or sorting
What are the two types of cross-bedding?
Planar (2D) and trough (3D)
Planar = skrå streger i rækker m. fladt lag mellem rækker, der står på hinanden
Trough = halvcirkler i halvcirkler ved siden af halvcirkler m. flade rækker oven på. Her vil vandretningen altid være, så strømmen rammer den mest buede del.
The curvature will always go ‘out’ towards the sides, and so we know the direction of the water
What are vortex ripples?
High energy, creates eddies
What does a fork in an area with ripples indicate?
Changes in the wave length of the flow
What is a linguoid ripple?
Looks like tongues
Linguoid —> language —> tongue (roman word)
Where are ladder ripples formed?
Deposited in very shallow marine environment; wind moves sediments across existing ripples.
The long ripples will be linear
What is true about the angle of climbing ripples?
Increase in angle of climb from sub- to supercritical
Where is the stoss side on a ripple?
The long stretch on the dune-ish looking ripple
What is HCS?
Hummocky cross-stratification
Hummocky is when it goes down (happy smile - think of a hammock)
What is SCS?
Swaley cross-stratification
Swaley is when it goes up (sad smile)
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 is the lower flow regime?
A tranquil flow
Ripples and dunes
What is the upper flow regime?
A rapid flow
Plane bed and antidunes migrating upstreams
What is an antidune?
Moves upward against the stream; need high velocity and high amount of sediments.
Look like dunes but aren’t; smooths surfaces.
Accumulates sediments opposite of the stream.
Rarely preserved in the rock record.
Most examples are from volcanoclastic setting (very high velocity and large sediment load during pyroclastic surges).
What does herring-bone cross-bedding look like?
Like a herring-bone…
What types of laminations are associated with tidally-influenced environments?
Flaser, wavy and lenticular lamination
What does flaser lamination look like?
Like someone has dug their nails (of various sizes of course) into the bedding
What does imbricated pebbles indicate?
The flow direction.
Imbricated pebbles = the pebbles have aligned each other around each other so that the water can move the fastest above them
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
