Sedimentary Rocks

Question 1

Sedimentary rocks

Answer 1

Formed by the accumulation of material derived from the physical disintegration (physical weathering) and chemical decomposition (chemical weathering) of older rocks.

Question 2

Four processes involved in their production

Answer 2

1. Weathering- Breaking up of pre-existing rocks
2. Erosion- Transportation of the particles either as solid particles or in solution
3. Deposition and accumulation of the particles either as solid particles (or chemical precipitation)
4. Lithification- cementation of a sediment so that it becomes a rock

Question 3

What is layering (or bedding)?

Answer 3

Layering or bedding is a characteristic feature of all sedimentary rocks reflecting the episodic nature of sediment accumulation.

Question 4

Sedimentary Bedforms

Answer 4

• Indicative of grain size & flow regime
• Bedding - layering >1cm
• Lamination - mm thick

Question 5

Sediment Layering

Answer 5

Ripple marks
*Asymmetric ripples indicate flow direction, with the steep slope on the
down-current direction
*Symmetric ripples form as a result of constant wave energy oscillating
back and forth.

Question 6

Sedimentary Bedforms (characteristics of depositional environment)

Answer 6

• Fluvial
• unidirectional
• ripples, dunes
• sorting
• Glacial
• not sorted
• massive

Question 7

Sediment Layering

Answer 7

Crossing bedding:

• Sets of beds that are inclined relative to one another
• Beds are inclined in the direction that wind or water was moving at time of deposition
• Boundaries between sets of cross beds usually represent on erosional surface
• Very common in beach deposits, sand dunes, and river deposited sediment.

Graded Bedding:
-As current velocity decreases, first the larger or more dense particles are deposited
followed by smaller particles
-Multiple graded-bed sequences called turbidites