2)  Why does sedimentary petrography focus on sand-grain-sized sedimentary rocks?

3)  What components in sandstones serve as the basis for classifying sandstones?

4)  What is the difference between a rock fragment and a lithic fragment?   Can feldspar or quartz be lithic fragments?

5)  List some methods for distinguishing feldspar from quartz in thin section.  What would you look for?

6)  If you had to plot the composition of sandstone grains on a ternary diagram, how would you plot chert?  Polycrystalline quartz?  Limestone?

7)  What is the difference between matrix and cement?  How would one distinguish between them in thin section?  In a hand sample?

8)  What is the relationship between % matrix and sediment accumulation rate in sandstones?  What types of depositional processes produce sandstones rich in matrix?  Can you relate % matrix to the continuity equation?

9)  How does "maturity" apply to framework grains?   How does age of a detrital sedimentary rock differ from its maturity?   Can you describe a scenario that produces a young rock (absolute age) that is compositionally mature?

10)  What might a very high quartz content in a sandstone indicate about the sediment source?

11)  What is meant by sediment recycling?    What types of framework grains would you expect to see in thin section if sediment is recycled?  If you were asked to draw an arrow representing sandstone composition through time on a sandstone-classification diagram, how would the arrow appear if sediment is recycled repeatedly?

12)  What is the difference between euhedral grains versus angular grains?  How would your interpretation of the sediment source(s) change for euhedral grains versus angular grains?

13)  If a sandstone records first-cycle volcanic detritus dispersed from an eruption, what characteristics would you predict to observe in the framework grains?

14)  If a sandstone records first-cycle metamorphic detritus dispersed from a low-grade fold-and-thrust belt, what characteristics would you predict to observe in the framework grains?

15)  If a sandstone records first-cycle metamorphic detritus dispersed from a granulite-facies belt, what characteristics would you predict to observe in the framework grains?

16)  How would your interpretation differ if you found Boehm lamellae in isolated sedimentary grains versus finding Boehm lamellae crossing grain boundaries in a sandstone?

17)  Describe what happens to volcanic glass over time.  What does it ultimately become and how would you recognize it in thin section?

18)  What are accessory minerals in sandstone?   List some metamorphic minerals that withstand transport.   What kinds of questions can one answer through the study of accessory minerals?

19)  Why is zircon such a useful accessory mineral in sedimentary and metamorphic rocks?

20) What is sediment provenance?  What questions can one address through a study of sediment provenance?  Why study sediment provenance?

21)  What information can be derived from dating individual accessory minerals in a detrital sedimentary rock versus dating the sedimentary rock?

22)  What is the oldest dated material on Earth?  What role did sandstone petrography play in interpreting the geologic history of the dated material?

23)  What is the relationship between sandstone composition and soil-forming processes?  What role does climate play?


SILICICLASTIC  DIAGENESIS

1a)  How does diagenesis differ from authigenesis?

2a)  What is the difference between primary porosity versus secondary porosity?  What are typical ranges of primary porosity in modern unconsolidated sands?  How does depositional process affect the primary porosity of sand?

3a)  If sediment consists of highly spherical grains of uniform grain size, why doesn’t increase or decreasing the grain size affect the percent primary porosity?  What aspects of the grain-size distribution do affect the porosity?

4a)  What is illuviation?  Draw a sketch of it.  In what kind of environment(s) does it occur?  How does illuviation alter porosity?  How does it affect permeability?

5a)  What is the difference between mechanical compaction and pressure solution?   Do compaction and pressure solution affect porosity in similar ways?  How would one recognize mechanical compaction versus pressure solution in thin section?

6a)  How is overpressuring related to rate of deposition of the overpressured bed? How is it related to the rate of deposition of the overlying beds? How is it related to permeability?  What happens to mechanical-compaction and/or pressure-solution rates under overpressured conditions?  Can authigenic overgrowths grow under overpressured conditions?  How can overpressured conditions be destroyed?

7a)  How might pressure solution be expressed in a hand sample (as opposed to a thin section)?  How do rates of pressure solution compare to rates of mechanical compaction?  Do they occur under similar conditions?

8a)  What minerals commonly form overgrowths? What conditions have to be met for an overgrowth to grow?  How are those overgrowths similar to the framework grain or how do they differ?

9a)  What is a typical geothermal gradient in a sedimentary basin?

10a)  Petroleum companies are particularly interested in the thermal history experienced by sedimentary rocks as temperature controls the maturation of organic material to produce petroleum, yet most of the inorganic diagenetic reactions in sands are not temperature dependent.  How could one use the diagenetic history of sandstone to infer its thermal history?

11a)  Pressure solution often occurs as a response to load stress.  How are such loads generated?  What other processes might generate loads sufficient to cause pressure solution?

12a)  If pressure solution involves the dissolution of solid rock material, can it generate secondary porosity?

13a)  How does the first clay dewatering differ from the second clay dewatering?  Where does the water go once it is released from the clays?  What is the composition of the water that is released?

14a)  If one is examining pore spaces in a sandstone in thin section, how might one distinguish between secondary versus primary pore?

15a)  What are dust rims and how are they useful petrographically?  Where might the “dust” come from, i.e. its source?

16a)  What conditions have to be met to generate a fracture porosity?  What types of rock materials would not allow a fracture porosity to develop?  Would you expect fracture porosity and pressure solution to occur in the same thin section of a sandstone?  Why or why not?

17a)  What observations could you make in thin section to interpret the depositional environment and initial diagenetic setting of sand?  How would those observations differ from those used to determine sediment provenance?

18a)  What is the relationship between clay pore linings and climate?  If sand were initially deposited in sea water rather than meteoric water, how would the production of diagenetic clay pore linings be different?

19a)  Many reactions produce products that decrease porosity, whereas others increase secondary porosity?  Can they occur simultaneously in the same rock material?  Why or why not?

20a)  If one samples a vertical core drilled in a sedimentary basin, how would one expect porosity to change with depth?  What processes can lead to exceptions to this predicted trend with depth?

21a)  What observations in thin section would be critical to distinguish between clay pore linings versus clay matrix?

22a)  How does mixed-layer illite/smectite differ from illite?  How is mixed-layer illite/smectite related to sediment provenance?  How is it related to sandstone maturity?

23a)  If a volcanic glass is altered to the Na smectite, Na(Al ₅Mg)Si₁₂O₃₀(OH)₆ , what mineral components were likely in the original glass?

24a) In what way do bio-mediated reactions mimic inorganic silicate diagenetic reactions?   How do the inorganic reaction rates compare to the bio-mediated rates for equivalent diagenetic reactions?

CARBONATE CHEMISTRY AND PETROLOGY

1b)  What is the primary method of producing carbonate rock? How does it differ from the production of detrital siliciclastic rocks?
 Can carbonate grains act as detritus?  How is it produced?

2b)  How does aragonite differ from calcite?  How are they similar?  What are some ions that can substitute for Ca in calcite and/or aragonite?  How do those substitutions lead to other carbonate minerals?  Why do different ions substitute in aragonite verses calcite?

3b) Is meteoric water an acid, basic, or neutral, and how does it compare to the pH of 'normal' sea water?  How is brackish water different from a brine?

4b)  Of the carbonate equilibrium reactions, which one dominates the marine system?  What controls the solubility of carbonate ultimately?

5b)  What is the relationship between pH, [CO₂] and the carbonate equilibrium reactions?  What conditions result in the precipitation of carbonate?  Why is it so difficult to change the pH of the oceans?

6b) What is the relationship between the burning of fossil fuels and global carbonate production?

7b)  How does burial of CaCO₃ in sedimentary basins or down subduction zones affect the global carbon cycle?  Can you speculate on the relationship between climate and global carbonate production?

8b) What is K_sp?  Upon what does it depend?  How does freshwater affect the K_sp of CaCO₃ ? 

9b) Why is carbonate production highest at low latitudes?  At shallow water depths?  

10b)  What does the saturation ratio suggest about calcite in sea water? What interferes with spontaneous precipitation of calcite in sea water?  Even though aragonite whitings are not well understood, what do you think could happen to the carbonate system to allow spontaneous inorganic precipitation of aragonite?

11b)  What controls the precipitation of biogenic carbonate?  How might the precipitation of biogenic carbonate have changed through geologic time?  Would you anticipate biogenic precipitation of carbonate to have occurred in Early Precambrian time?  Which organisms might have been functioning in that way?

12b) Where do foraminifera live?  In what depositional environment(s) are they concentrated enough to form a sedimentary rock composed almost entirely of their skeletons?  Name that rock type.  If you were to walk through a calcareous ooze, what do you think it would feel like?
  
13b) What are the sources of carbonate mud (at least 5)?  What is the difference between carbonate mud, a calcareous ooze and micrite?

14b) What are potential sources for sand-sized carbonate grains?  How might cobbles of carbonate be produced?

15b) How do pelloids differ from ooids?  How are they similar?  What kind of depositional setting do ooids suggest? What conditions might allow them to form in non-marine settings?  Would they have the same composition as ooids formed in sea water?

16b) What are the primary observations necessary to classify carbonates using the Folk classification?  What components in carbonates  serve as the basis for classifying carbonates?  How would your ability to classify a carbonate rock differ if you were looking down a microscope versus making the interpretation in the field?



CARBONATE DIAGENESIS

1c)  As you think back to our discussions of siliciclastic sandstone petrology, which silicic diagenetic processes would you predict to occur in the vadose zone?  How do those processes differ from vadose zone diagenesis of carbonates?

2c)  Is sediment sitting on the sediment–water interface on the ocean floor in the vadose zone or the phreatic zone?  Is sediment sitting on the sediment–water interface on a lake bottom in the vadose zone or the phreatic zone? Is sediment sitting in a soil profile in the vadose zone or the phreatic zone?  Is sediment sitting on a marine beach in the intertidal zone in the vadose zone or the phreatic zone?

3c)  Does the position and/or geometry of the boundary between the meteoric vadose zone and the meteoric phreatic zone change through time?  Why or why not?

4c)  Why are meniscus cement and pendulous cements restricted to the vadose zone?  How do they form?  Can you sketch them?  How long do you think it takes to grow meniscus or pendulous cements?  Given the carbonate equilibrium reactions, what do you think controls their growth rate?

5c)  Given the carbonate equilibrium reactions, why do the CCD and the ACD exist?  Do you think the CCD is a planar surface?  How might the CCD and the ACD have changed through geologic time?  

6c)  What observations could one make to determine if an aragonite grain had passed through the ACD?  If that grain had passed through the ACD, why would that grain still exist?

7c)  Could you draw a cross-section of the CCD and/or ACD in the world oceans?

8c) What would happen to a foraminifera skeleton if the organism died at low latitudes on the continental shelf?  What would happen to a foraminifera skeleton if the organism died at high latitudes on the continental shelf? What would happen to a foraminifera skeleton if the organism died at low latitudes but above an abyssal plain?

9c)  What types of diagenetic processes help to decrease primary porosity in carbonates?  How and where do they occur?  What types of diagenetic processes generate secondary porosity in carbonates?  How and where do they occur?  Can you list and explain the processes?

10c)  Could you construct a table with pore-water chemistry on one axis and degree of saturation of the pore spaces on the other axis, and then fill in the diagenetic processes, with respect to both resultant mineralogy and porosity, for each of the settings?

11c) What are key signs in thin section that a marine-invertebrate skeleton composed of Mg-calcite has been subjected to meteoric pore waters during a relative sea-level fall?  How would it appear if the marine invertebrate had precipitated an aragonite skeleton and then sea level fell?  How would it appear if the marine-invertebrate skeleton was composed initially of low-Mg calcite?

12c) How does one recognize pore-lining cement and what type(s) of diagenetic settings would produce such pore linings?

13c)  If you were to examine a hardground in thin section, what features would you expect to observe?  If you were to examine a hardground in outcrop, what features would allow its recognition?  Where and why do they develop?  How might the presence of a hardground influence pore-fluid flow and subsequent diagenesis?

14c)  What features and observations would one use to recognize carbonate rock that has been buried to >3 km depth and then uplifted into the meteoric phreatic realm?

15c)  If a carbonate rock contains a coarse crystalline cement of calcite spar, where might diagenesis and cementation occurred?

16c)  Why are aragonite and Mg-calcite stable in sea water, but dissolve in meteoric water?

17c)  If a brachiopod shell is deposited on the sea floor and remains in the marine phreatic realm, will the shell dissolve?  If calcite precipitates on the shell, what will be its composition?

18c) What sequence of carbonate cements would you predict to fill pores if sediment was deposited initially on the nearshore part of the continental shelf, and sea-level fell to the shelf edges but was then followed by a sea-level rise?  How would the rates of sea-level fall and sea-level rise affect your answer? 

19c) What sequence of carbonate cements would you predict to fill pores if sediment was deposited initially on land in a non-marine setting (such as on a river floodplain) only to be submerged as sea level rose?

20c) Signs of mechanical compaction are rarer in carbonate rocks compared to siliciclastic rocks. Why?

21c) If you were a hydrologist or a petroleum geologist, and you were assigned the task of targeting carbonate strata as an aquifer or as reservoir rocks, which diagenetic histories would favor strata with high porosity?

22c)  What is meant by a 'brine' that results from evaporation of marine water at the Earth's surface?  What is meant by a 'brine' that forms at 3-5 km burial depth?  Are the two brines of similar composition?  Why or why not?

23c) Why is the precipitation of gypsum in an evaporitic hypersaline environment important to the formation of dolomite?

24c) What happens to porosity when low-Mg-calcite is deeply buried?  Explain.

25c) How old is the oldest aragonitic sedimentary rock?  Why not older?  If you were setting out to map an area containing Archean carbonate sedimentary rocks, what mineral composition(s) would you anticipate in those rocks?  

26c) How does dolomite that is produced in an evaporitic setting or in mixed ground water differ chemically and physically from dolomite that grows during deep burial? Why?

27c) In what way do bio-mediated reactions mimic inorganic carbonate diagenetic reactions?   How do the inorganic reaction rates compare to the biomediated rates for equivalent diagenetic reactions?  What are bio-mediated carbonate reactions for which there are no known inorganic equivalent reactions?

28c)  If you were shown a diagram of the different diagenetic environments (meteoric vadose, marine phreatic, marine sediment-water interface, deep-burial phreatic zone, etc.), could you plot the silicate diagenetic processes associated with each environment?

Introduction to Sedimentary Facies

1d)  What are potential purposes of studying the lithofacies within a sedimentary basin, i.e. which questions might be answered through a study of lithofacies?

2d) For what reasons might the principle, "the present is the key to the past", break down and not be applicable in a sedimentary basin?

3d)  How is Walter's Law related to subsidence in a sedimentary basin?

4d)  What kinds of field or core observations are typically reported on a measured stratigraphic profile?  How are those data represented?

5d)  How are data from a map view of a basin merged with data from vertical profiles to provide a 3-D view of the evolution of a sedimentary basin?

Carbonate Depositional Environments

1e)  Why does carbonate production dominantly occur shallow, low-latitude marine settings?

2e)  If one wants to observe Paleozoic deep-marine carbonate, where would one look?  Why?

3e)  What similarities and/or differences would you anticipate between large dunes composed of carbonate detritus migrating on a carbonate platform versus large dunes composed of siliciclastic detritus migrating on a shallow continental shelf?

4e)  In what ways do organisms influence sedimentary lithofacies on carbonate platforms?

5e)  In which lithofacies produced on a carbonate platform would you predict the highest primary porosity?

6e)  If migrating dunes composed of ooids are present on a carbonate platform, what do they imply about the water chemistry?

7e)  What is a typical lateral arrangement of lithofacies on a modern carbonate platform?  How might that arrangement change if the platform were wider?  If relative sea-level fell?  If relative sea-level rose?  If that platform experienced hurricanes each year?  If the tidal range decreased?

8e)  Where are the lowest-energy lithofacies produced on a carbonate platform and what rock types would that lithofacies contain?

9e)  If dunes on a carbonate platform become stabilized, what would you predict would be the first cement to form diagenetically?  What would you predict would be the first cement to form diagenetically in a reef-crest facies?  Where might dolomite form as a cement?



Arid & Aeolian Environments/Evaporites

1f)  If freshwater evaporates, which mineral phases are likely to precipitate?   What mineral assemblages result from the evaporation of marine waters?  How do these mineral phases differ in their chemistry and density?

2f)  What is the relation between gypsum and anhydrite, and where does each form?

3f)  What are signs in the geologic record that gypsum has altered to anhydrite?  How does one recognize the alteration of anhydrite to form gypsum?  Where would such diagenetic changes take place?  Why would it take place?  What % volume change results and why is it so large?

4f)  What diagenetic effects might results from the storage of nuclear waste in abandoned underground gypsum mines?  Why?

5f)  We talked about how anhydrite can hydrate or rehydrate in the presence of water, but what will likely happen if gypsum beds are flushed with fresh pore waters?

6f)  Where does the water come from to fill a lake that is usually dry?  Where does the water come from to inundate a coastal area that is usually above marine influence?

7f)  If you were traveling in a new region, how would you recognize a sabkha if you arrived at one?   

8f)  Why are sabkhas relatively rare on the modern Earth?  Where would you look for an example closest to Minnesota? Where might you find a hypersaline marine setting in the modern world?

9f)  Sketch the pattern of evaporite facies during initial deposition within a playa lake and within a marine coastal sabkha. Explain how the remaining water in the lake or marine setting changes (chemically and physically) if evaporation continues, or if the remaining water becomes more dilute?  Why doesn't halite always precipitate?

10f)   If you were assigned a project to interpret Upper Miocene deposits in the Mediterranean region, what criteria would you use to distinguish evaporite deposits that were generated during a coastal-sabkha phase (desiccation of the basin) versus those generated during a phase in which the deep marine basin was filled with deep water?

11f)  What role does the water table play in governing the distribution of evaporite facies versus aeolian facies in a desert setting?  How would one recognize a change to a wetter climate?

12f)  Using Walther's Law, which facies would you anticipate occurring laterally to evaporite facies?  How might a change in climate affect your answer?

13f) What features characterize aeolian deposits at the scale of 1-10's of cm's?  How would one recognize an aeolian origin if making observations at that scale?  Would the interpretation differ if one had only core to work with rather than outcrops?  How would distinguish aeolian versus subaqueous deposits if one were restricted to making observations from a helicopter?

14f)  If one were working in a non-marine Archean basin, would you predict that you might encounter evaporite facies?  Aeolian facies?  Why or why not?

15f)  What features would record strong control by groundwater flux in an evaporitic setting?  

16f)  What processes control the sediment supply in an arid setting?

17f)  If clay-sized particles are put into suspension by the wind, how far can they be transported as suspended load?

18f)  Why are aeolian dunes able to achieve such large sizes compared to dunes in subaqueous settings if the ocean is several kilometers deep?



Fluvial Systems and Alluvial Fans

1g)  What is the  difference in meaning between "alluvial" versus  "fluvial"?  Give examples.

2g) What factors control whether a fluvial system assumes braided versus meandering channels?  Some fluvial systems display a braided channel pattern in some reaches but may change to a meandering habit upstream or downstream.  What factors could change within a single drainage system to force the change in channel habit?  What kinds of environments are typified by braided fluvial systems?  What are the characteristics of environments in which meandering channel dominate?

3g)  How is fluvial discharge defined and how is it measured?  What parameters change to force sediment accumulation on the levee and flood plain during a river flood?

4g) Describe and explain 4 ways in which rivers can change course.  Which processes occur in meandering systems?  In braided systems? Which processes operate on a daily basis versus which processes are more associated with flood events?  How fast do these 4 processes operate?

5g)  How is the "100-year flood" defined for a fluvial system?  The 500-year flood?  What controls the width of a floodplain?  What controls the height and width of levees along a river channel?

6g)  Explain how a mid-channel bar might form.  Which direction does it migrate?  Why?

7g)  Describe a typical sedimentary sequence resulting from a lateral migration of a curved segment of a river channel?  What are its overall trends?  What controls the sequence's total thickness?  What sedimentary structures would you predict internally in the sequence?

8g)  How would sedimentary structures/deposits resulting from a meander cut-off differ from those resulting from a lateral migration of a curved segment of a river channel?  Could you draw a picture of both types of sequences?

9g)  What is a crevasse splay?  How are crevasse splays related to avulsion?  How do the deposits of a crevasse splay differ from those of a fluvial levee?

10g)  What is avulsion and what processes make it occur?  How is it similar to a meander cutoff?  How does it differ?  How would avulsion relate to climate change?

11g) Draw a cross-sectional sketch in 3D of the preservation of meandering fluvial-channel bodies in a subsiding basin? What controls the spacing and shape of the channel bodies?  What spacing would you predict if one side of the basin were subsiding more rapidly than the other side?

12g) What 4 variables control the geometry (3D shapes) of fluvial deposits as they are preserved in the geologic record?

13g) What is the difference among alluvial fans, fan deltas and deltas?  What are the key observations that would allow one to distinguish among these depositional processes in the geologic record?

14g)  Why do debris flows dominate the apex of an alluvial fan whereas stream flow in braided channels dominates downstream?  Do all alluvial fans display debris flow deposits in the region of the fan apex?   Do all alluvial fans display braided stream-flow deposits in the more distal parts of the fan?

15g) If given a diagram of an alluvial fan, could you describe and label the grain size and shape, bedforms, and channel characteristics of the fan at its apex, the mid-fan region, and distal part of the fan?  Could you summarize the downstream trends moving in a distal direction?

16g) Explain the conical shape of an alluvial fan. How is the fan shape related to avulsion history?  What controls the rate of avulsion?  In a cross-section parallel to the fluvial channels do you think the cone is convex upward or concave upward?  Why?  How is the fan's shape related to climate?

17g)  If an alluvial fan were to continue to grow and prograde, predict the resultant vertical sequence that one would encounter if one extracted a core at a site that was initially in the outer-fan (distal) region.  What vertical sequence would result in the mid-fan region if the discharge decreased and the fan were to shrink?