Lecture Covered
Sedimentary Rocks I, Sedimentary Rocks II, Geological Time, Relative Dating, Absolute Dating
Instructions
Below are a series of questions some of which include links to videos, readings, or other
supplemental sources of information. Review each of the questions and answer them below. For
questions requiring a written answer please use complete sentences. Some of these questions are openended and have multiple possible answers. In those cases, you need to present a clear rationale for your
answer. Show work for any calculations you might need to make. These can be done on paper and a
photo of the work uploaded as long as the work is legible.
In order to receive full credit for this assignment you must use the discussion board in at least
one of two way. 1) Interact with your group members about the assignment or 2) ask a geologically
related question to me that is more than a simple yes, no, or other few words answer. You are
encouraged to use the discussion board to bounce ideas off your fellow classmates and discuss the
questions. Especially for those questions with open-ended value-based judgements use of the discussion
boards can make your answers better and more thought out.
1) Look at the two images of sediment samples below (both fields of view are approximately 1cm
across). For each describe the size, sorting, roundness, and composition and explain what type of
environment you might expect to find each sample in today.
Sample A
Sample B
Snail
Shell
2) Sedimentary rocks are produced on the surface of the Earth with the two main groupings by volume
being carbonates (20%) and siliciclastics (75%). The production of each kind is dependent on factors such
as supply of sediment and temperature. Both of these are responsive to climate change over time,
particularly sea level. The blue line in the chart below (figure x) shows sea level through the last 500
million years with the red horizontal line representing current (=1950) sea level. The y-axis is in meters
above or below current sea level. Remember that the edges of continents have the shape shown in
cross-section in figure XX.
When global sea level rises do you expect carbonate production to increase, decrease, or stay the same?
Why?
When global sea level drops do you expect siliciclastic rock production to increase, decrease, or stay the
same? Why?
3) What vertebrate (fishes, birds, reptiles, amphibians, mammals) alive today would be our best tools for
biostratigraphy 50 million years in the future? Give an answer separately for land-based biostratigraphy
and another for ocean-based stratigraphy. Explain your reasoning.
4) With a few exceptions all the stages of the Phanerozoic (the last 541 million years) are defined by the
appearances of individual species (i.e. biostratigraphy) at their respective Global Stratotype Section and
Points (GSSPs). If we could swap out all the biostratigraphic marker with an ash bed dated with isotopic
dating would that be good for building a geological timescale? Explain your reasoning and remember
that the purpose of GSSPs is to provide anchor points for global correlations of rock layers.