Lab 5-1: Sequence of Events
Rules for determining the proper
sequence of events for the
reconstruction of a period of geologic
history
Relative age….
• Geologic event sequences are often
ordered using relative time.
• Relative time simply refers to whether
some event is older or more recent than
another event with little concern for the
actual chronological age (actual age in
years)
Unconformity….
• An unconformity is a break in the sequence
of the relative time scale…
• Part of the record in the rock has been
removed by erosion.
5
3
2
1
Erosion Surface...
• The surface which is the boundary
between 2 non-sequential layers where a
layer is missing is most often an erosion
surface.
5
3
2
1
Subsidence...
• Refers to the sinking of land, often below
sea level.
Subsidence...
• Refers to the sinking of land, often below
sea level.
Uplift...
• Is the rising of the land above sea level
Emergence and Submergence
• Emergence refers to the land coming
from below the sea to above sea level due
to a lowering of sea level
• Submergence refers to the sinking of the
land below sea level due to a rise in sea
level
Uniformitarianism...
• “The present is the key to
the past”
Superposition...
Original Horizontality..
• When first deposited, rocks are laid
down in flat horizontal layers. If
they are tilted, folded, broken
(faulted) or intruded into, those
events took place after the rocks
were laid down in their horizontal
position.