Study Guide for Final Exam - Geo 4602 - Kleinspehn

Deltaic systems

1)  What conditions must be met in order for a delta to accumulate and be visible from the air?  What happens to a deltaic system if sea level or lake level rises?  Or falls?

2)  Why does a fluvial flow deposit its sediment load at its channel mouth?  Is all of the sediment load deposited? In a deltaic deposit, where do you expect to find the coarsest grains?  Why?

3)  Several processes associated with a delta generate coarsening-upward sequences in cross-section. What are their differences in terms of scale and internal sedimentary structures?

4)  How does a mouth bar differ from a levee?  What does the height of a mouth bar indicate?  Does it coarsen or fine upwards?  Why?

5) What are key observations that could be used to recognize levee deposits in the geological record (in terms of grain size, sedimentary structures, bed thickness, shape of beds, etc) ?

6) How would a deltaic crevasse splay differ from a crevasse splay upstream in the same fluvial system?  How does the deposition of a crevasse splay affect delta deposition and growth?

7)  If a crevasse splay is generated during a flood, what controls whether the river system will continue to flow or stop flowing through the breach in the  levee once the flood waters recede?

8) Why are deltaic lobes abandoned and what happens subsequently to the abandoned lobes?  How would you recognize lobe abandonment in the geologic record?

9) How does the chemistry of the pore fluids evolve once a marine deltaic lobe is abandoned?

10)  Does subsidence of a deltaic lobe occur during the period when the lobe is active?  What drives subsidence of deltaic deposits?  Is subsidence a process that can be stopped by engineering practices?


Paleocurrent Analysis

Omitted from this year's syllabus; you will not be tested on this lecture


Wave-dominated Beach and Barrier Island Systems

1b)  Why is the long-term prognosis for a shoreline that it will straighten with time?

2b) What defines the outer limit of the nearshore zone that is affected by longshore currents?  What water depth does this limit correspond to and why?  What happens at the sea or lake bottom at water depths greater than that limit?

3b) What controls the speed and direction (velocity) of the longshore current?  In which would one expect faster longshore currents, lakes or a marine setting?  Why?

4b) Within the zone affected by waves and longshore currents, what sedimentary bedforms would you predict to form on the bed?  Could you plot those bedforms on a diagram of current and wave-orbital velocities?

5b) Can you think of a standing body of water in which longshore currents would not occur?

6b) What hazards for people or coastal structures might be associated with longshore currents?

7b) Why does the season characterized by the largest waves result in a net loss of beach sand, but the construction of a bar offshore?  Would such a seasonal change in the beach occur if the beach were composed of gravel?

8b) What is the relationship between the growth of spits and longshore currents?

9b) Which features/observations in sedimentary deposits are key to recognize ancient beach deposits?  Are they different for sand beaches versus gravel beaches?  How would one recognize beach deposits in a Precambrian sequence? 

10b) Will a barrier island migrate if sea level or lake level remains unchanged?  What process drives barrier island migration?  Will barriers composed of gravel migrate or is the process reserved for barriers composed of sand?

11b) What role(s) does vegetation play in barrier stability and/or migration?  How would have barrier processes differed prior to the advent of land vegetation in Silurian time?

12b) What controls whether a washover event is net erosional or depositional?  What geomorphic feature results if it is net erosional?

13b) What controls the rate at which a tidal inlet migrates through a barrier island?  Do inlets migrate through barrier islands in lakes?  To what depth do inlet channels erode?

14b) What observations are key to recognize the deposits generated by inlet migration?  What is a washover fan?  How would washover-fan deposits differ from inlet deposits, and could you sketch them?

15b) In what ways do washover events or inlet-migration pose hazards to people or coastal structures?

16b) How would washover events or inlet-migration rates be affected by climate change?  How would washover events or inlet-migration rates be affected by increasing lake level or sea level? 

17b) If sea level rises, what is the predicted 3D geometry of the resultant barrier-island sand deposits?  Why is the question important for aquifers or reservoir bodies?

18b) If sea level or lake level were rising at the same time an inlet was migrating through a barrier island, what would the migration trajectory be of the inlet in map view?

19b) What happens when wave processes dominate a delta?


Estuaries and Tidal Systems

1c) Is the existence of estuaries favored by a sea-level fall or a sea-level rise?  Why?  What is an estuary?  Are all tidal deposits generated in estuaries?

2c)  How is the tidal range defined along a shoreline?  What is the distinction among micro-tidal, meso-tidal and macro-tidal ranges?

3c) Explain why you might not find bidirectional cross-stratification preserved in the geological record despite the bedforms having migrated on the bottom of a macrotidal estuary?

4c) Draw a map-view distribution of grain sizes in a generalized estuary.  Why do the different grain sizes get deposited in their respective locations?

5c)  If sea level remains unchanged, what is the long-term prognosis for an estuary, and what kind of vertical sequence will be generated in the geologic record?  If sea level falls, what is the long-term prognosis for an estuary, and what kind of vertical sequence will be generated in the geologic record?  And thirdly, if  sea level rises, what is the long-term prognosis for an estuary, and what kind of vertical sequence will be generated in the geologic record?

6c)  What controls the total thickness of tide-influenced deposits generated in an estuary setting?

7c)  Why are double mud drapes associated with a subtidal setting rather than an intertidal setting?  What controls the thickness of the sediment deposited between the double mud drapes?  How long does it take to deposit a double mud drape? Could you draw a diagram to explain how and why double mud drapes develop?

8c)  In what other environment(s) might flow fluctuations produce double mud drapes, but rarely?

9c) What are the distinctive features of tidal sand ridges that develop on the continental shelf?   Could you sketch a diagram of them including a scale of their dimensions?  If ancient ridges are beyond the scale of individual outcrops, how can they be recognized?

Continental Slope Sedimentation

1d) In general, how much steeper is the continental slope compared to continental shelves or the abyssal plains?  If you were standing on the continental slope could you actually see the inclination of the slope?  What are the leading candidates for "The Flattest Place on Earth"?

2d) What drives mass flows down the submarine canyons and the continental slope?  

3d)  If a turbidity current loses energy due to friction with the bed and shear with the overlying water column, why don't they slow down and cease motion over short distances?   What allows turbidity currents to travel 102-103 kms?

4d)  How might the deposits of marine turbidity current differ from those generated in lakes?

5d)  What are the characteristics of a Bouma sequence and how are they arranged vertically?  How does the Bouma sequence relate to the continuity equation?

6d)  If you were given a diagram of the stability fields of bedform with axes of flow velocity versus grain size, could you plot a trajectory for a typical turbidity current on that diagram?

7d) What are the relative scales of fining/thinning-upward and coarsening/thickening upward sequences generated by a prograding turbidite fan?  Where and how is each type of vertical sequence produced?

8d)  How might one distinguish the deposits of a fluvial meandering channel from those of a submarine meandering channel?


Deep-Sea Sedimentation

1e) What type of lithosphere underlies the abyssal plains?  What is the long-term prognosis for sediments deposited on the abyssal plain?

2e)  If clay minerals deposited on the abyssal plains are not derived from land, from where do they come and how does the detritus get transported to the deep ocean?

3e)  What observations might you make to distinguish thin, fine-grained levee deposits from a river system from thin, fine-grained deposits generated in the deep sea?

4e)  We discussed a map of the global distribution of sediments on the abyssal plains.  Even though a region may be mapped as a region of, for example, deep-sea clay, the sediment will likely contain some biogenic components albeit in small concentrations.  What controls the ratio of biogenic fraction versus the clay fraction?

5e) If you were to join a deep-sea drilling cruise that was drilling core samples from the modern equatorial abyssal plains, what is the most likely sediment that you would sample?  If the sediment is a calcareous ooze, what is the most likely fossil component in that ooze?  If the sediment is a siliceous ooze, what is the most likely fossil component in that ooze?   What is that siliceous ooze called once it becomes lithified rock?

6e) Once a calcareous ooze is deposited, in what diagenetic setting is it likely to become lithified?  At what range of depths below the sediment-water interface would you expect to encounter lithified rock?   

7e)  What criterion could one use to distinguish between deep-sea limestones versus limestones generated in a shallow carbonate-shelf setting?


Tectonics and Basin Subsidence

1f) How does one differentiate between autocyclic processes and allocyclic processes?  What are typical allocyclic controls on basin evolution?

2f)  List causes of basin subsidence.  Which driving mechanisms are capable of producing several kilometers of subsidence? Which driving mechanisms are capable of producing only modest subsidence?

3f) On what basis are sedimentary basins classified?

4f)  If you were given a cross-sectional diagram of lithospheric plates and their different types of plate boundaries, could you locate,  draw and name sedimentary basins associated with each plate-tectonic setting?

5f) For each type of sedimentary basin, can you locate and list the sedimentary facies that would typify each type of basin?

6f) Can you name and locate a modern example of each basin type?  Can you do the same for an ancient example of each basin type?

7f)  Why do rift basins record a two-phase subsidence history?  In what ways are failed rifts similar or dissimilar to rifts that evolve into passive continental margins?

8f)   How does the age and rheology of the continental lithosphere affect the geometry of a flexural foreland basin?

9f)  Actual observed sedimentary sequences often record several phases of basin subsidence stacked vertically, but suggest different plate-tectonic driving forces for each phase.  How could such a sequence be generated?

10f)  What are typical rates for tectonically-generated basin subsidence? Could you draw graphs of typical subsidence histories (tectonic-subsidence curves) for basins in different plate-tectonic settings?    Which basin types record the fastest subsidence rates?  Which basin types subside the slowest?

11f) What is the relationship between subsidence history of a basin and its thermal history and associated diagenesis?

12f)  If subsidence and basin filling result in a stratigraphic sequence that is 15-20 km thick, what is the nature of the "sediments" at the base of that sequence?