Geology Reference
In-Depth Information
Geo-Focus
A Miocene Catastrophe in Nebraska
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Figure 1
This mural shows a restoration of some of the fossils recovered at Ashfall Fossil Beds
Historical Park near Orchard, Nebraska:
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one-toed horses,
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small camels,
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turtles,
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rhinoceroses,
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cranes,
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giraffe-like camels, and
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three-toed horses. In the distance,
you can see some carnivores and mastodons.
Twelve million years ago, in what
is now northeastern Nebraska, vast
grasslands were inhabited by short-
legged, aquatic rhinoceroses, horses,
camels, saber-toothed deer, birds,
land turtles, and many other animals
(
animals died when a huge cloud of
volcanic ash rolled in, probably from a
volcano in Idaho. The animals did not
die immediately, but as they breathed
in the abrasive particles of glass, their
Figure 1). This was a temperate
savannah habitat with life as varied
and abundant as it is now on the sa-
vannahs of East Africa. Many of these
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The Cenozoic marine ecosystem was populated by those
plants, animals, and single-celled organisms that survived
the Mesozoic extinctions. Especially prolifi c Cenozoic inver-
tebrate groups were foraminifera, radiolarians, corals, bryo-
zoans, mollusks, and echinoids. The marine invertebrate
community in general became more provincial during the
Cenozoic because of changing ocean currents and tempera-
ture differences with latitude.
Only a few species in each major group of phyto-
plankton survived into the Cenozoic. The coccolitho-
phores, diatoms, and dinoflagellates all recovered from
their Late Cretaceous reduction in numbers. The dia-
toms were particularly abundant during the Miocene
(
the sand and gravel in the United States and Canada is used
in construction and as roadbase and fi ll for highway and rail-
way construction.
The periodic evaporation of pluvial lakes in the Death
Valley region of California during the Pleistocene led to the
concentration of many evaporite minerals such as borax.
During the 1880s, borax was transported from Death Valley
by the famous 20-mule-team wagon trains.
Another Neogene resource is peat, a vast potential energy
resource that has been developed in Canada and Ireland. Peat-
lands formed from plant assemblages as the result of particu-
lar climate conditions.
LIFE HISTORY
Earth's fl ora and fauna continued to evolve during the Ceno-
zoic Era as more and more familiar kinds of plants and ani-
mals made their appearance (see Geo-Focus on pages 654 and
655). We emphasize the evolution of mammals in this chapter,
but you should be aware of other important life events.
Figure 23.17a), probably because of increased volca-
nism during this time. Volcanic ash provided increased
dissolved silica in seawater and was used by the diatoms
to construct their skeletons.
The foraminifera were a major component of the Ce-
nozoic marine invertebrate community. Though dominated
by relatively small forms (Figure 23.17b, c), it included
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