(TC) Sedimentary Logging and Facies Analysis Flashcards
What are the four main features of a graphic sedimentary log?
- Horizontal scale for grainsize
- Symbols for sedimentary structures
- Paleoflow shown as a rose diagram
- Colour recorded in words
What is a fence diagram?
A number of sedimentary logs which have been placed together and their strata correlated
What is the main difficulty in analysing a graphical log?
May not show lateral variation very well, e.g. change from channel to overbank
What is the typical range of diameters of a core?
100 to 200 mm
Oil and gas exploration may rely more on what types of techniques?
Geophysical rather than core cutting
What are “facies”? (6)
A sum of characteristics - dimensions, sedimentary structures, grainsize, type, colour, biogenic content
e.g. Cross-bedded fine sandstone
What are “lithofacies”?
Description of rock confined to physical and chemical characteristics
What are “biofacies”?
Observations which concentrate on flora and fauna
What are “ichnofacies”?
Observations concentrate on trace fossils
Can one unit of rock have multiple facies descriptions? i.e. have seperate descriptions for lithofacies, biofacies and ichnofacies?
Yes
What three main features of facies analysis give the paleoenvironment?
Transport, deposition and paleoecology
What factor could complicate the determination of a paleoenvironment?
Multiple deposition settings for a facies
Beyond the single rock unit, what other features give an indication of the paleoenvironment?
Sequences in succession
What is “Walthers law”?
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
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”
Walthers law
What is “Markov analysis” and how does it work?
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
What is the name for the technique by which a grid containing facies is used to determine sequences in the stratigraphic record?
Markov Analysis
What does “S xl” mean?
Cross-laminated sandstone
What does “Z l” mean?
Laminated silt
What are the advantages of associating numbers to facies?
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
How can we determine the distribution of facies in space?
Rocks at outcrop to assess distribution
How can we determine the changes in paleoenvironments with time?
Basin analysis - determine interaction with atmosphere and hydrosphere
What is important to remember about paleoenvironments from the past?
May not have a modern counterpart
