Lecture 6: Sedimentary Rocks & Processes

Front 1

Learning Goals

Back 1

1) Describe the ways sedimentary rocks form

2) Compare and contrast the texture and composition of sedimentary rocks

3) List and describe some hazards of designing on or in sedimentary rocks

4) Describe why sedimentary rocks and processes are important to engineering

5) Define facies and describe how they might change in the environment

6) Describe the potential controls on sea level

7) Predict how facies may change with sea level

8) Interpret facies variations from a vertical succession of sediments (stratigraphic

log)

9) Define Walther’s Law

10) Describe the concept of a parasequence and how they react to changing sea level.

11) Describe how sedimentary sequences are

viewed in the subsurface and how they relate to the petroleum industry.

12) Describe how oil is formed and trapped.

Front 2

Sedimentary Rocks

Back 2

Cover 70% of continental surface

Sediments & sedimentary rocks are the most common materials encountered in construction

Contain petroleum & coal deposits

Front 3

Deposition

Back 3

Laying down of material by air, water, ice, gravity, or precipitation from solution

Front 4

Lithifaction

Back 4

Compaction: pressure reduces volume of sediments through reduction of void space

+

Cementation: clastic sediments are converted to rock by precipitation of mineral cement (calcite, quartz, iron oxides) along grains

Front 5

Types of sedimentary rocks

Back 5

1) Clastic (detrital)

2) Chemical (evaporites)

3) Organic (biogenic)

Front 6

Clastic

Back 6

(Detrital) Composed of fragments of eroded rocks

- sandstone, mudstones, shale

Front 7

Poorly sorted = well graded

Back 7

Coarse, angular grains of different sizes

Front 8

Well sorted = poorly graded

Back 8

Fine, rounded grains of relatively uniform size

Front 9

Sorting tells us about transport history of sediment

Back 9

/

Front 10

Chemical

Back 10

(Evaporites) Precipitation of minerals fro solution. Requires restricted basin in warm arid clomate

- halite, gypsum, anhydrite, some limestones

Front 11

Organic

Back 11

(Biogenic) Remains of living things

- most limestones, chalk, coal

Front 12

Sinkholes

Back 12

Dissolution of limestone, dolomite may result in sinkholes and cavities (implications for dams, reservoirs, abutments, mine workings)

Front 13

Facies

Back 13

Environmentally-controlled differences in sediments. Defined by sediment type, type of sedimentary structures, sometimes fossil content

Front 14

Depositional Environments

Back 14

TO BE CONTINUED...