Geoscience Reference
In-Depth Information
Figure 9-3.
Surface mining of the Weir-Pittsburg coal
bed (Cherokee Group, middle Pennsylvanian, upper
Carboniferous). This was the most economically
important coal bed mined in southeastern Kansas,
United States (Brady and Dutcher 1974). Coal mining
has now ceased in this vicinity. Photo by J.S. Aber.
Figure 9-2.
Reconstruction of Pangaea during the early
Permian Period about 280 million years ago. The
supercontinent consisted of two main sectors, Laurasia
in the north and Gondwana in the south, which had
joined together through a series of continental
collisions that created the Appalachians, Urals, and
other mountain ranges. Modii ed from original map by
Kieff; obtained from Wikimedia Commons
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commons.wikimedia.org/
different l oristically from coals of Laurasia.
Gondwanan mires were dominated by gymno-
sperms, such as
Gangamopteris
and
Glossop-
teris
. The Gondwanan mires were the i rst
widespread non-tropical peatlands in earth
history, and some at high latitude may have
formed under permafrost conditions similar to
modern palsa mires (Greb, DiMichele and
Gastaldo 2006).
During the Permian, Pangaea's climate began
to dry out, wetlands became increasingly
restricted, and desert zones expanded greatly
(see Color Plates 2-10 and 3-11). These climatic
trends culminated with a massive extinction
event at the end of the Permian, perhaps the
greatest extinction in earth history, which caused
a nearly total collapse of wetland ecosystems
worldwide (Greb, DiMichele and Gastaldo 2006).
The following Triassic Period was dominated by
widespread deserts. Wetlands began to recover
in some places by the middle Triassic, particu-
larly in high southern latitudes of Gondwana
-
thick and extensive coal in modern Antarctica,
and the earliest known salamander, frog, turtle,
and mammal fossils come from this period.
>
.
equatorial and temperate, which were separated
by subtropical deserts. The equatorial coal zone
is mainly upper Carboniferous and stretched
across Laurasia in what are now parts of eastern
North America (Fig. 9-3), western and eastern
Europe, and northern and eastern Asia. These
coal deposits were formed in swamps domi-
nated by lycopods and tree ferns that were the
most widespread tropical mires in earth history
(Greb, DiMichele and Gastaldo 2006). Arthro-
pods, i sh, amphibians and reptiles were abun-
dant in these wetlands.
In the Gondwanan sector of Pangaea, coal
deposits are found in parts of what are now
eastern South America, southern Africa, India,
Australia, and Antarctica. Gondwana was located
in the southern hemisphere spanning climatic
zones from temperate to polar, and ice-sheet
glaciation was centered on the South Pole
(Caputo and Crowell 1985). Gondwanan coals
are mainly Permian in age and are distinctly
9.2.2 Cretaceous-Tertiary coal and lignite
The Cretaceous Period represents the next great
expansion of wetlands in general and peatlands
