Travel Reference
In-Depth Information
not moved since they were deposited long ago in the Cretaceous, many pre-
vious investigators had concluded. Such was not the case for the Vancouver
Island region. During the 1980s it was proposed that the Nanaimo Group
may have originated far to the south of its present position and moved up the
coast by plate tectonics, the mechanism that causes large blocks of the
earth's crust to travel vast geographic distances over time. The best way to
accept or refute this—the best time machine to use—was again paleomag-
netics. Now I had two reasons to succeed in my drilling plans for the Van-
couver Island region. I still wanted to know about time. But now I wanted to
know about
place
as well.
The story of the paleomagnetic analysis of the California Cretaceous-
aged strata is but one example of how this routinely used method unfolds.
Most such studies proceed in fits and starts, just as ours did. Only slowly
does information accumulate, but it yields some of the best ways in our ar-
senal of time machines to find the age of rocks. Magnetostratigraphy, as this
method is called, is now used on virtually every time interval of the geologic
record.
The solution
Twenty years after beginning a seemingly simple quest, I could finally pro-
pose an age for the Sucia Island fossils. The Sucia strata bear the ammonites
Baculites and, more important, a heavily ornamented ammonite called
Hopluoplacenticeras.
These tell us that Sucia Island is Campanian in age and
therefore is of the same age as the rocks in western France where the world's
finest Champagne is created. The species of Baculites is B.
inornatus,
which
is also found in California. In a few creeks, this ammonite is found at the top
of magnetozone 33R, the first reversal after the Cretaceous long normal. In
the Western Interior Seaway, this same reversal has been discovered in what
is known as the Middle Campanian. Its upper parts are filled with bentonites
that have been dated between 81 and 79 million years in age. This, then, is
the age of Sucia Island.
