sedimentary rocks

Question 1

Which of the three (component, matrix, cement) is always present in sedimentary rocks?

Answer 1

Cement is always present in sedimentary rocks.

Sedimentary rock = ±component±matrix+cement. The cement is what makes it a rock.

Question 2

How are terrigenous rocks classified?

Answer 2

Terrigenous rocks are classified according to grain size.

They are derived from the erosion of rocks on land and have grain mineralogy including Quartz (SiO2), Feldspar, and Lithic fragments.

Question 3

What is an allochem?

Answer 3

Allochems are components in carbonate rock.

Examples include Bioclast (skeletal material), ooids, peloids, and intraclast.

Question 4

What is the difference between an ooid and a peloid?

Answer 4

Ooids are small spheroidal grains formed in shallow marine environments, while peloids are fecal pellets produced by organisms.

Ooids form around a small shell or piece of sand; peloids are made from compacted mud or sediment.

Question 5

What are the characteristics of mudstone, wackestone, packstone, floatstone, and grainstone?

Answer 5

Mudstone: mud supported, <10% grains.
Wackestone: mud supported, >10% grains.
Packstone: grain supported, components touching with mud.
Floatstone: grain supported, big components ‘float’ in the matrix with mud.
Grainstone: no mud, grain supported.

Question 6

What is hardground?

Answer 6

Hardground is a marine surface that has been lithified

Question 7

What are biogenic silica deposits made of?

Answer 7

Diatoms, radiolarians, silicoflagellates, siliceous sponges, and other marine silicifiers

Question 8

What is a rock made from microorganisms called?

Answer 8

microbialite

examples: stromatolites, thrombolites and oncoids