Geoscience Reference
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of stratigraphy, strata were deposited successively in the course of geological time
and they are often uniquely characterized by fossils such as ammonites that are
strikingly different from age to age. It is remarkable that this fact remained virtually
unknown until approximately 1,800. There are several other examples of geological
concepts that became only gradually accepted more widely, although they were
proposed much earlier in one form or another by individual scientists. The best-
known example is plate tectonics: Alfred Wegener (
1966
) had demonstrated the
concept of continental drift fairly convincingly as early as 1912 but this idea only
became acceptable in the early 1960s. One reason that this theory initially was
rejected by most geoscientists was lack of a plausible mechanism for the movement
of continents.
Along similar lines, Staub (
1928
) had argued that the principal force that
controlled mountain building in the Alps was crustal shortening between Africa
and Eurasia. However, other interpretations including the gravitational concept of
van Bemmelen (
1960
) continued to provide plausible explanations before the
theory of plate tectonics became well established. Figure
1.1
(from Agterberg
1961
, Fig. 107) shows tectonic sketch maps of two areas in the eastern Alps. The
Strigno area in northern Italy shown at the top of Fig.
1.1
is 1600
smaller in area
than the region for the eastern Alps at the bottom. The tectonic structure of these
two regions is similar. Both contain overthrust sheets with older rocks including
crystalline basement overlying much younger rocks. It is now well known that
the main structure of the map at the bottom was created during the Oligocene
(33.9-23.0 Ma) when the African plate moved northward over the Eurasian plate.
On the other hand, the main structure of the relatively small Strigno area was
created much later during the late Miocene (Tortonian, 11.6-7.3 Ma) when the
Eurasian plate moved southward overriding the Adria microplate that originally
was part of the African plate. Incidentally, Fig.
1.1
also provides an example of the
concept of similarity of geological patterns at different scales. As another example
of self-similarity of geological patterns, Fig.
11.1
shows multifractal gold minera-
lization patterns that are strikingly similar in two areas that differ in size by a factor
of 400. Self-similarity or scale-independence will be discussed in later chapters in
the context of fractals and multifractals.
Another geological idea that was conceived early on, but initially rejected as a
figment of the imagination, is what later became known as the Milankovitch
theory. Croll (
1875
) had suggested that the Pleistocene ice ages were caused by
variations in the distance between the Earth and the Sun. Milankovitch com-
menced working on astronomical control of climate in 1913 (Schwarzacher
1993
). His detailed calculations of orbital variations were published nearly
30 years later (Milankovitch
1941
) showing quantitatively that amount of solar
radiation drastically changes our climate. This theory was immediately rejected
by climatologists because the changes in solar radiation due to orbital variations
are miniscule, and by geologists as well because, stratigraphically, their correla-
tion with ice ages apparently was not very good. However, in the mid-1950, new
methods helped to establish the Milankovitch theory beyond any doubt. Subse-
quently, it resulted in the establishment of two new disciplines: cyclostratigraphy
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