Sedimentary Basins, Environments, Structures

Question 1

Rift basins - location

Answer 1

Formed at divergent plate boundaries

Question 2

Rift basins - cause

Answer 2

Downward slip on faults produces narrow troughs

Question 3

Passive margins - location

Answer 3

Edges of continents that are not tectonic plate boundaries

Question 4

Passive margins - cause

Answer 4

Subsidence occurs over thinned crust at the edge of an ocean basin

Question 5

Intracontinental basins - location

Answer 5

Far from continental margins or tectonic-plate boundaries

Question 6

Intracontinental basins - cause

Answer 6

Basin forms in the interior of a continent, perhaps over an old rift

Question 7

Foreland basins - location

Answer 7

Next to collisional mountain belts

Question 8

Foreland basins - cause

Answer 8

Weight of the mountain belt pushes down the crust’s surface

Question 9

Siliciclastic sediments - continental environments (4)

Answer 9

Alluvial, desert, lake, glacial

Question 10

Siliciclastic sediments - shoreline environments (3)

Answer 10

Deltas, beaches, tidal flats

Question 11

Siliciclastic sediments - marine environments

Answer 11

Shelf, margin, slope, deep sea

Question 12

Chemical/biological sediments - carbonate deposit environments

Answer 12

Beaches, reefs, shelves, deep sea

Question 13

Chemical/biological sediments - siliceous environments

Answer 13

Deep sea

Question 14

Chemical/biological sediments - evaporitic environments

Answer 14

Lakes

Question 15

River environments - characteristics

Answer 15

Evidence of channelized sediment transport.
Sand/gravel fill concave-up channels that often scour into previously deposited floodplain fines.
Fine sand, silt, and clay are deposited on nearby floodplains.

Question 16

Lake environments - characteristics

Answer 16

Gravels and sands are trapped near shore.
Well-sorted muds in deeper water.
Deep muds may show “varves” (thin stripes of finer/coarser sediment reflecting seasonal changes in sedimentation).

Question 17

Shallow-water carbonate environments - characteristics

Answer 17

Develop in tropical, warm, clear, shallow, normal salinity, marine water.
Protected lagoons accumulate mud.
Wave-tossed reefs made of coral/reef debris.

Question 18

Deep-Marine Environments - characteristics

Answer 18

Skeletons of planktonic organisms make chalk/chert.
Fine silts/clays lithify into shale.

Question 19

Why doesn’t the sea get saturated with NaCl over time?

Answer 19

Evaporite formations

Question 20

Cross-bedding structures

Answer 20

Sedimentary structure. Consist of beds deposited by wind/water at angles as much as 35 deg from horizontal, as particles are deposited on the downcurrent slopes of sand dunes/sandbars.
Changing wind can create crazy patterns!
Common in sandstones.
Looks like a child’s drawing of waves from the side.

Question 21

Graded bedding structures

Answer 21

Progresses from large particles at the bottom to small particles at the top, due to current getting slower and slower as it weakens. Can also be called a turbidite.

Question 22

Ripple structures

Answer 22

Very small ridges of sand/silt at right angles to current, present both in sediments and the rocks they turn into.
Difference between symmetrical ripples (waves moving back and forth on a beach) and asymmetrical ripples (currents/wind moving in a single direction).

Question 23

Bioturbation structures

Answer 23

A whole bunch of tubes a few centimeters in diameter, left by burrowing animals.
Looks like hashbrowns, which I find creepy.

Question 24

Bedding sequences

Answer 24

A structure comprised of a series of sedimentary beds, which together tell the story of a region.