Slide 1

1GEO 316P: Sedimentary Rocks (Unique # 26830)Spring 2015Lecture: Meets MWF 10-11 AM, JGB 2.324

Instructors: Dr. William Fisher, wfisher@jsg.utexas.edu Office: JGB 6.130, Office hours: MW 1 3 PMDr. David Mohrig, mohrig@jsg.utexas.edu Office: EPS 3.162, Office hours: T 11 12PM; W 11 12PM Teaching Assistants: Sarah Bateman, sarahbateman@utexas.eduOffice: JGB 6.120, Office hours: T 11 12PM; W 11 12PMMoonsoo Brian Shin, mshin@utexas.eduOffice: JGB 6.134, Office hours: M 11 1PMLaboratory: No labs

2Final Exam: none*Required course materials:- B: Boggs, Principles of Sedimentology and Stratigraphy (4th edition or 5th edition)*Other texts (library reserve): T&W; Tucker, M.E. and Wright, V.P. (1990), Carbonate Sedimentology.S: Wolfgang Schlager, (2005), Carbonate Sedimentology and Sequence StratigraphyLecture notes: Lecture notes and readings from other texts can be found on Canvas (http://canvas.utexas.edu).

3Class policy, procedures and grading: Historically, there is a very strong correlation between exam grades and attendance.There will be 4 lecture exams; each will consist of multiple-choice and/or short answer questions and will be worth 100 points. The four exams together will constitute 80 % of the final class grade. On each exam you will be responsible for all material covered in lectures (lecture notes + materials NOT in lecture notes), as well as materials covered in required reading from textbooks. There are no make-up lecture exams in this class.If you miss an exam, that exam grade becomes 0. Make-ups are permitted only with a physician-certified illness report or an agreed on prearranged absence (e.g., professional trip, religious holy day).There will be four unannounced in-class quizzes. Unannounced in-class quizzes will constitute 20% of the final class grade.There are no make-up quizzes in this class. If you miss a quiz, the quiz grade is a 0. Make-ups are permitted only with a physician-certified illness report or an agreed on prearranged absence (e.g., professional trip, religious holy day).

4Class policy, procedures and grading: continuedCourse grades will be curved, but the boundaries between letter grades are determined by the instructors judgment and are very different every semester. Recently the A/B boundary has been in the high 80 %s and the B/C boundary in the high 70 %s, etc.University Electronic Mail Notification Policy (Use of E-mail for Official Correspondence to Students) In this course e-mail will be used as a means of communication with students. You will be responsible for checking your e-mail regularly for class work and announcements. Note: if you are an employee of the University, your e-mail address in Canvas is your employee address.

5Sedimentology = scientific study of sediments and sedimentary rocks. Includes production of sediment, and the transport, deposition, & lithification of sediment (i.e., loose sediment rock). Stratigraphy = a branch of geology dealing with the classification, correlation, and interpretation of stratified (layered) rock.What is a Sedimentary Rock?Rock that has formed through the deposition and solidification of sediment.Scientific fields that are primarily focused on sedimentary rocks.

6In this classWe are going to learn how to read sedimentary rocks to aid reconstruction of earth history.

We are going to learn what controls distribution of rock properties (strength, porosity, permeability, etc.) in order to predict the character of subsurface deposits.Reasons to be interested in sedimentary deposits and rocks:1. Most people live on top them.

2. Serve as reservoirs for important subsurface fluids, including groundwater and hydrocarbons.

3. Directly linked to most carbon-based energy sources (e.g., coal, gas, gas hydrates, oil).

4. Preserve record of life on Earth.

5. General recorder of earth-surface history.

7Sedimentary rocks only make up 5 % of the Earth's crust, but cover about 70 % of the surface of the earth.

Sedimentary rocks have an average thickness of about 1800 m on the continents.

Global sediment thickness based on the 1o x 1o compilation of Laske and Masters (1997)For example: Canadian Shield 0 m;Louisiana & TexasGulf Coast 20 km.Thickness is quite variable.

8

Older sedimentary rocks are less exposed on Earth surface than younger sedimentary rocks.

Over 40% of the exposed sedimentary rocks are younger than 100 million years in age.

9

Geologic time scale was largely constructed from age dating of distinct packages of sedimentary rock. Most geologic periods were defined by stratigraphic events, including:

1. Paleontological change (e.g., extinctions);

2. Tectonic change (regional unconformities);

3. Geochemical change (change in environment).See page 517 of Boggs

10

11Types of Sedimentary Rocks: A. Clastic (fragmental)- Particles are derived from pre-existing rocks - Source of particles is typically external to the depositional basin

12B. Biochemical: Sedimentary rocks composed of grains produced by organic (biogenic) processes.

Shell fragmentsLimestone reef rockBiochemical particles compose most carbonate rocks, including limestone.

13Biochemical, continued. Particulate organic matter

Common sources of organic matter include plants and microorganisms

CoalParticles are typically produced within the depositional basin.

14

Laminated Castile Formation, west TX. Dark layers are calcite plus organic matter; light layers are gypsum (photo by Peter Scholle)C. Chemical: Sedimentary rocks composed of mineral grains precipitated by inorganic processes. Common chemical rocks are evaporites (including salts)Particles are always produced within the depositional basin.

15Grain Size(nominal grain diameter)

Millimeters Microns (Phi Scale) Wentworth Size ClassParticle Attributes

16Modified after Powers, M . C., 1953, Journal of Sedimentary Petrology, v. 23, p. 118.

2. Roundness:angular vs. subangular vs subrounded vs rounded

3. Grain Shape or Form:Where a, b, and c are the longest, intermediate and shortest axis of the particle (and are mutually perpendicular).

cba

17

Beard, D.C., and Weyl, P.K., 1973, Influence of texture on porosity and permeability of unconsolidated sand: AAPG Bulletin.

Trask Sorting Coefficient =

4. Sorting (range of particle sizes in deposit)Graphical representation of Grain-size Distribution

1st QuartileMedian (D50)3rd Quartile

17.4 - .3 mm = 3 %, .3 - .2 mm = 9 %, .2 -.1 mm = 13 + 25 = 38 %, .1 -.08 mm = 20 %, .08 -.06 mm = 5 + 9 = 14 %, .06 -.04 mm = 10 %, .04 - .02 mm = 5 %

18The original grain size & sorting of a deposit controls:how fluid moves through the deposit; andtotal amount of inter-granular fluid contained in the deposit.

River Bottom

Fine sedimentCoarsesedimentField of view 30 m by 10 m

Vertical sequence of sedimentary deposit(field of view 2 m by 0.5 m)

19

Beard, D.C., and Weyl, P.K., 1973, Influence of texture on porosity and permeability of unconsolidated sand: AAPG Bulletin, v. 57, p. 349-369.Deposit Porosity = (1 volume concentration of sediment) = void space fractionPorosity of a granular deposit is primarily a function of grain sorting.Porosity (%)So = Trask Sorting

20

Beard, D.C., and Weyl, P.K., 1973, Influence of texture on porosity and permeability of unconsolidated sand: AAPG Bulletin, v. 57, p. 349-369.Permeability = measure of a deposit to transmit interstitial fluid (e.g. fluid flow through the pore network)Permeability controlled by grain size & sorting, equally important

21

ODP Leg 180 Site 1115Two important processes associated with burial are:

1. Mechanical compactionthe loss of porosity by rearrangement of the grain framework due to overburden pressure.

2. Lithification processes through which loose sediment becomes solid rock

.Many sedimentary deposits do not remain at Earth surface, they are buried, sometimes to great depth. Depth (meters below sea floor)

Examples ofcementation

22Subsidence ()We all know that in plate tectonics, horizontal motion leads to vertical motion, e.g. uplift of mountain ranges.But for every place where the crust is going up, there must be somewhere else where it is going down this is tectonic subsidenceBasic idea: subsidence induces net depositionWhat causes considerable thicknesses of sedimentary deposits to accumulate?

edimentaterSEA LEVEL(figure from Chris Paola)

23

Velocity Vector Map of Tectonic Plate MotionsTypical rates of horizontal plate motion: ~1-100 mm/yrTypical rates of vertical motion (uplift & subsidence): ~0.1-10 mm/yr

23Average growth rate of fingernails = 0.1 mm/day = 36.5 mm/yr (American Academy of Dermatology)

Questions You Should be Able to Answer1. What does sorting measure in a sample? What factors determine sorting? 2. What determines grain shape? How is it measured? What are the basic grain shapes? 3. What is grain roundness? What factors determine grain roundness? What does grain roundness tell you?4. What is porosity? What is permeability?5. What is the relationship between porosity/permeability and grain size? Why?6. What is the relationship between porosity/permeability and sorting? Why?7. What is the range of depositional (original) porosity in sand? What factors influence depositional porosity? 8. What is the scientific field of Sedimentology?9. What is the scientific field of Stratigraphy?10. Sedimentary rocks make up what fraction of Earths crust? 11. Sedimentary rocks cover what fraction of Earths surface?12. What is the average and maximum vertical thickness of sedimentary rock sections on the continents?

13. 40 % of exposed sedimentary rocks on the continents are younger than what age?14. Periods on the geologic time scale were original defined by what three types of stratigraphic events?15. What are the three fundamental types of sedimentary rocks? Which two rock types are composed of particles that primary form within the depositional basin? Which rock type is primarily composed of particles derived from outside the depositional basin?16. What is the definition of the Trask Sorting Coefficient?17. What are typical rates of horizontal motion for crustal plates?18. What are typical rates of vertical motion for crustal plates?19. What is basin subsidence? How is basin subsidence connected to net sediment deposition?