Flashcards
Sedimentary Structures
Cards in this deck (20)
- 1What are strata?Distinct layers of sediments
- 2What is the difference between beds & laminations?Beds = strata > 1 cm thick
Laminations = strata < 1 cm thick - 3What are sedimentary structures?Physical, biological, and chemical features of sedimentary rocks that give info about original depositional environment.
- 4What is horizontal bedding?Basic cross bedding (#1 common)
=======
=========
=========
======== - 5What is cross bedding?Tilted layers between horizontal layers.
Formed by 1-directonal currents
=======
\\\\\\\\\
========
current ----> - 6What is graded bedding?Changes in grain size within a bed.
- 7What causes graded bedding?A storm or flood or shaking events such as a landslide.
- 8What is normal graded bedding?Large grains below smaller grains.
Most common. - 9What is reverse graded bedding?Larger grains above smaller grains.
More scarce.
shaking events - 10What are the two major types of ripple marks?Asymmetrical: formed by 1-directional current. Toward the short side.
Symmetrical = Formed by 2-directional current. Wave action in shallow water. - 11What are mudcracks?Cracks in mud formed by alternating wet and dry conditions (land)
- 12What are raindrop impressions?Small pits or craters on top of a bedding plain.
- 13How do raindrop impressions form?They form by light sprinkle on mud or sand.
- 14What are flute casts?Scoop-shaped structures on the bottoms of beds.
- 15How & where do flute casts form?Formed by 1-directional evosional scour.
They form underwater in sediment slides. - 16What are trace fossils? (What is bioturbation?)Indirect evidence of ancient life.
- 17Examples of trace fossils?Burrows, tracks, trails
- 18What are stromatolites?Large layered structures built up by mats of bacteria.
Fossils and sedimentary structures
(Shark bay, Australia) - 19How do stromatolites form?Bacteria keeps growing to the top of sediments, and sediments keep covering the bacteria.
- 20What do stromatolites look like?Domes, clubs, columnar, subspherical.
(head of cabbage looking)