Lecture 7 - Interpreting Cross Sections and Geological Maps Flashcards
What is a geological map?
A plan view of the distribution of rock types.
What is a cross section?
A vertical section illustrating the changes in rock type with increasing depth.
What are the uses of geological maps?
They are used to understand the sequence of events, structures, chemistry of water, rocks and soils and to locate and estimate resources.
When does folding occur?
After the rock has been deposited.
When do igneous intrusions occur?
After the formation of the surrounding rocks.
When do faults occur?
After the fractured rocks have been formed.
When do unconformities form?
They are gaps which are caused by periods of erosion.
What is an angular unconformity?
A unconformity where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers.
This results in a difference in the angle of dip with the rock above and below the unconformity.
What is a nonconformity?
Where sedimentary rock overlies a metamorphic or igneous rock.
What is a disconformity?
A period of extensive erosion that is a smaller length of time than an angular unconformity.
They are marked by features of subaerial erosion.
What is a paraconformity?
A conformity that represents a very small gap in time. There is little apparent erosion and the unconformity surface resembles a simple bedding plane.
Which igneous intrusions show cross-cut bedding (discordant)?
Dykes
Batholiths
Volcanic Pipes
Which igneous intrusions are parallel to bedding (concordant)?
Lava flows
Pyroclastic flows
Sills.
What are the features of a sill?
It forms parallel to the bedding.
There is a chilled margin at the top and bottom of the sill.
It wasn’t formed by a lava flow otherwise the chilled margin would only be seen at the bottom.
How does the angle of dip affect the apparent surface thickness?
A larger angle of dip gives a more accurate representation of the actual thickness.
