(TC) Sedimentary Logging and Facies Analysis

Question 1

What are the four main features of a graphic sedimentary log?

Answer 1

1. Horizontal scale for grainsize
2. Symbols for sedimentary structures
3. Paleoflow shown as a rose diagram
4. Colour recorded in words

Question 2

What is a fence diagram?

Answer 2

A number of sedimentary logs which have been placed together and their strata correlated

Question 3

What is the main difficulty in analysing a graphical log?

Answer 3

May not show lateral variation very well, e.g. change from channel to overbank

Question 4

What is the typical range of diameters of a core?

Answer 4

100 to 200 mm

Question 5

Oil and gas exploration may rely more on what types of techniques?

Answer 5

Geophysical rather than core cutting

Question 6

What are “facies”? (6)

Answer 6

A sum of characteristics - dimensions, sedimentary structures, grainsize, type, colour, biogenic content
e.g. Cross-bedded fine sandstone

Question 7

What are “lithofacies”?

Answer 7

Description of rock confined to physical and chemical characteristics

Question 8

What are “biofacies”?

Answer 8

Observations which concentrate on flora and fauna

Question 9

What are “ichnofacies”?

Answer 9

Observations concentrate on trace fossils

Question 10

Can one unit of rock have multiple facies descriptions? i.e. have seperate descriptions for lithofacies, biofacies and ichnofacies?

Answer 10

Yes

Question 11

What three main features of facies analysis give the paleoenvironment?

Answer 11

Transport, deposition and paleoecology

Question 12

What factor could complicate the determination of a paleoenvironment?

Answer 12

Multiple deposition settings for a facies

Question 13

Beyond the single rock unit, what other features give an indication of the paleoenvironment?

Answer 13

Sequences in succession

Question 14

What is “Walthers law”?

Answer 14

If one facies is found superimposed on another without a break in stratigraphic succession, those two facies would have been deposited adjacent to each other at any one time

Question 15

What is the name for the law which states: “If one facies is found superimposed on another without a break in stratigraphic succession, those two facies would have been deposited adjacent to each other at any one time”

Answer 15

Walthers law

Question 16

What is “Markov analysis” and how does it work?

Answer 16

A technique which allows the determination of facies sequences and successions: have all of the facies on a grid on the vertical and horizontal axis - make a note of every transition between the two

Question 17

What is the name for the technique by which a grid containing facies is used to determine sequences in the stratigraphic record?

Answer 17

Markov Analysis

Question 18

What does “S xl” mean?

Answer 18

Cross-laminated sandstone

Question 19

What does “Z l” mean?

Answer 19

Laminated silt

Question 20

What are the advantages of associating numbers to facies?

Answer 20

If the numbers are associated with facies commonly found in order then the numbers can be used to show trends. I.e. 1 representing shallow marine, 8 representing deep marine

Question 21

How can we determine the distribution of facies in space?

Answer 21

Rocks at outcrop to assess distribution

Question 22

How can we determine the changes in paleoenvironments with time?

Answer 22

Basin analysis - determine interaction with atmosphere and hydrosphere

Question 23

What is important to remember about paleoenvironments from the past?

Answer 23

May not have a modern counterpart