Sedimentation and Sedimentary Rocks

Question 1

It is commonly defined as the ability of a medium to transmit a fluid. Rock permeability can be thought of more simply as the property of a rock that permits the passage of a fluid through the interconnected pores of the rock.

Answer 1

Permeability

Question 2

Refers to the annually laminated sediment deposited at the base of some lakes, or marine settings.

Answer 2

Varves

Question 3

Woody residue of plant tissues, most constituents of coal.

Answer 3

Humic

Question 4

Commonly occurring on when mud is overlain by sandstone, and heavier sediments, where the mud sediments are reaching upwards owing to the weight of the heavier overlying sediments.

Answer 4

Flame Structures (Also Commonly, co-occurring with Ball and
Pillow structures)

Question 5

Solid, asphaltic residue form from petroleum through the loss of volatiles, oxidation and polymerization.

Answer 5

Bitumens

Question 6

Organosedimentary structures formed largely by the trapping and binding activites of cyanobacteria.

Answer 6

Biogenic Structures

Question 7

Give the other latin terms for sandstones, mudrocks, and clastics.

Answer 7

Sandstones (Arenites), Mudrocks (Lutite), Clastics (Rudite)

Question 8

The term used to describe a mature sandstone.

Answer 8

Quartz Arenite

Question 9

Quartz – makes up approximately ___ of average sandstone, ___ of average shale; ___ of average carbonate rock.

Answer 9

65% of average sandstone
30% of average shale
5% of average carbonate rock.

Question 10

This term is specifically applied to shallow marine sediment that contains noticeable quantities of rounded greenish grains. These grains are called glauconies and consist of a mixture of mixed-layer clay minerals, such as smectite and glauconite.

Answer 10

Greensands

Question 11

This is a sandstone composed of calcite grains.

Answer 11

Sparite

Question 12

Lime mud mixed with silicate sand/silt.

Answer 12

Marl

Question 13

Differentiate aulacogens, impactogens, and successor basin.

Answer 13

o Aulacogens – Former failed rifts at high angles, which have been reactivated during convergent tectonics.
o Impactogens – rifts formed at high angles to continental marins without preorogenic history.
o Successor Basin – Basins formed in intermontane settings following the cessation of local orogenic or taphrogenic activity.

Question 14

Is roundness and sphericity the same? Why or why not?

Answer 14

No. • Roundness refers to the absence of sharp edges of the individual grains • Spherecity refers to the overall shape of the particles approaching the shape of a sphere

Question 15

Differentiate porosity and effective porosity.

Answer 15

Porosity is defined as the ratio of the pore spaces versus the total volume of the sedimentary rocks. Effective porosity is more important to assessing resources such groundwater and petroleum. It is the pore spaces that are interconnected.

Question 16

What are the two types of porosity? Describe each.

Answer 16

• Primary (Depositional) – Pore spaces formed during lithification o Intergranular/Interparticle o Intragranular/Intraparticle – pore spaces between the grains o Intercrystalline – chemical sedimentary rocks; crystal to crystal • (P Secondaryost-Depositional) – Pore spaces formed after deposition o Solution porosity – cementing minerals are eroded o Intercrystalline – authigenic o Fracture – in between the spaces of fractured rocks

Question 17

What is the difference between beds and laminae?

Answer 17

Laminae are normally smaller and less pronounced than bedding. Lamination is often regarded as planar structures one centimetre or less in thickness, whereas bedding layers are greater than one centimetre.

Question 18

Enumerate the different types of bedding.

Answer 18

• Graded bedding (normal bedding - finering upwards and indicates a sequence of “sinking” basin; reverse grading - coarsening upwards). • Massive beddings (No internal structures; Quite rare with coarser sediments; For finer sediments, sandstorm deposits - “Loess”). • Cross-bedding (Tabular cross bedding; Trough cross bedding) • Flaser and Lenticular Bedding (Flaser cross bedding and Lenticular bedding). • Cross-bedding (Hummocky cross stratification - Commonly around 15-20 cm thick; Some with sole marks; Indicates continental shelf, and shoreface environments; Continuous).

Question 19

Enumerate the different chemical cements and give examples for each categories of minerals.

Answer 19

 Silicate minerals – predominantly quar t z, others may include chalcedony, opal, feldspars, and zoolites.  Carbonate minerals principally calcite; less commonly aragonite, dolomite, siderite.  Iron oxide minerals – hematite, limonite, goethite.  Sulfate minerals – anhydrite, gypsum, barite.

Question 20

Enumerate the evaporation sequence of seawater in increasing evaporation rates.

Answer 20

1. Calcite (CaCO3) and Dolomite (CaMg(CO3)2 2. Gypsum: Gypsum Precipitates (Gypsum: <42degC) or (Anhydrite: >42degC). 3. Halite: Precipitates if 86-94% of original seawater has been removed; Brine (solution) is very dense. 4. Potassic Salts: Precipitate if >94% of original seawater has been removed; So: ionic strength (potential) of evaporating seawater has a strong control over minerals that form.

Question 21

Enumerate the evaporation sequence of lakes in increasing evaporation rates.

Answer 21

1. Calcite CaCO3 and Magnesite (MgCO3) 2. CaSO4 precipiates next. 3. NaSO4 (in form of Hanksite) precipitates next leaving mostly the chloride compounds. 4. NaCO3 (in form of Trona and Natron) next in order precipitates if any CO3 left 5. MgSO4 (in form of Epson Salts) precipitates out all that is left is NaCl 6. NaCl saltern is left.These are fairly common (Great Salt Lake) - rich in sodium chloride; sodium sulfate (Na2SO4); and sodium carbonate (Na2CO3) 7. MgCl2 and CaCl2 lakes are rare (called Bitterns Dead Sea) 8. If all water evaporates - bed of salts (NaCl) usually results.

Question 22

Enumerate and describe the different Deposition Models in Evaporites.

Answer 22

 Subaerial Evaporites – Sabkhas and Playas, salt flats, both marginal and continental settings.  Shallow subaqueous evaporites – Salinas, marginal marine environment/coastal, carbonate basal member overlain by gypsum then salt.  Deep-water evaporites – thin bedding and lamination.

Question 23

What do you mean by Mosaic and Chicken-wire patterns in nodular anhydrites.

Answer 23

 Nodular – irregularly shaped lumps of anhydrite that are partly or completely separated from each other. o Mosaic – more or less equidimensional lumps, separated by dark carbonates/mud/clay o Chicken-wire – slightly elongated separated by thin dark stringers

Question 24

Enumerate the three associated facies in sedimentary iron deposits.

Answer 24

 Algoma Type – thinly bedded, volcanic related, lack oolitic and granular.  Superior Type – no volcanic associations, occurs with quartzite, black carbonaceous shales, conglomerate, dolomite, cherts, breccia, and argillites.  Raritan Type – in relation with glacial deposits.

Question 25

Where can you find Bog-iron deposits? Describe them.

Answer 25

o Small Freshwater lakes of high altitude o Hard, oolitic, pisolitic, and concretionary forms to soft earthy types

Question 26

Explain the mechanism of a Dish and Pillar Stucture.

Answer 26

• Commonly are water escape structures o Dish – laterally extensive, some are impermeable, around 1 to 50 cm o Pillar – vertical to near vertical cross cutting columns, saturated with water

Question 27

Enumerate and describe the principal kinds of cherts.

Answer 27

 Flint – Nodular chert  Jasper – red colored chert, trace amounts of hematite  Jaspilite – interbedded chert and hematite, BIF • Novaculite – dense, fine grained  Porcellanite – resembles unglazed/unpolished porcelain  Siliceous Sinter – low density, light colored, associated with hot springs, exploration marker

Question 28

In this situation you encounter in your matrix supported breccia samples: Clasts are composed of Olivine, Mica, Limestone Pieces, Sandstone, Basalt Pieces, the matrix is composed of coralline limestone. What is the provenance of your sample and how did it occur? Where will most likely be the area of lithification/deposition?

Answer 28

The provenance of the sample is from an obducted ophiolite. It occured through coastal landslide and the area of lithification/deposition will most likely be in tidal flats.

Question 29

Enumerate the principal varieties of phospherites.

Answer 29

o Flourapatite Ca5(PO4)3F o Chlorapatite Ca5(PO4)3Cl o Hydroxyapatite Ca5(PO4)3OH o Francolite Ca10(PO4,CO3)6F2-3

Question 30

Enumerate and describe the principal kinds of phospherites.

Answer 30

 Bedded – interbedded/interfingering with carbonaceous mudrocks, cherts, carbonate rocks. Peloids, ooids, phosphatized fossils and skeletal fragments, and cements.  Bioclastic – mostly from vertebrate remains: fish bones, teeth, scales, coprolites.  Nodular – brownish to black, spherical to irregular-shaped nodules ranging in size from a few cms to meters or more, grains, pellets, shark teeth, other fossils.  Pebble-bed – phosphatic nodules, phosphatized limestone fragments, fossils, might be diagenetic origin.  Guano – excrements of birds and bats leached to form an insoluble residue of calcium phosphate.

Question 31

What is the difference between Sabkha, Playa, and Salinas?

Answer 31

Sabkha - coastal, supratidal mudflat or sandflat in which evaporite-saline minerals accumulate as a result of semi-arid to arid climate. Playa - an area of flat, dried-up land, especially a desert basin from which water evaporates quickly. Salinas - shallow water evaporites

Question 32

Explain how grain/clast supported rudites differ from matrix supported ones.

Answer 32

Grain/Clast Supported (>50% clast composition) - Orthoconglomerate (>85% clast composition) Matrix Supported (<50% clast composition) - Paraconglomerate/Diamictite [30% (or 25% on some authors) to 5% clasts, however some might consider this as not under the rudite group] since rudites are of 30% clast composition.