Geoscience Reference
In-Depth Information
Figure 9-7.
Specimens of Cretaceous amber from Kansas, known as jelinite. Dollar coin is 1 inch (25 mm) in
diameter. Photo by S.W. Aber.
Polymerization is a chemical fossilization that
may be relatively rapid when the resin is exposed
to sunlight and air (Langenheim 2003). These
criteria explain why it is believed amber was
created from copious resin-producing trees in
moist tropical or subtropical environments; these
conditions favor photosynthesis throughout the
year and provide abundant carbon in spite of
low-nutrient tropical and wetland soils. When the
hardened, polymerized resin is buried with veg-
etation, soil and sediment, it undergoes addi-
tional change over geologic time. The maturation
from polymerized resin to amber is a continuum
wherein modern resin progresses to ancient
resin, and this in turn changes to subfossil resin
or copal, and then to amber. Hardened resins
such as copal have not yet completed polymeri-
zation and preserve extant species of l ora and
fauna, whereas amber preserves extinct species.
The oldest known amber is from the Carbon-
iferous, 320 million years old, found in U.S. coal
deposits in Illinois (Bray and Anderson 2009).
Amber is known also from the Triassic (Grimaldi
et al. 1998) and Jurassic (Philippe et al. 2005;
Azar et al. 2010). Relatively abundant Creta-
ceous amber is found in Canada (McAlpine and
Martin 1969; McKellar et al. 2008; McKellar and
Wolfe 2010; Zobel 1999), the United States,
the Middle East, and Asia (Zherikhin and Ekov
1999). Some of the oldest reported wetland
insects come from early Cretaceous amber in
Lebanon (Azar, Prokop and Nel 2010; Poinar
and Milki 2001). Cretaceous amber in the United
States is located in Wyoming (Grimaldi et al.
2000; Kosmowska-Ceranowicz, Giertych and
Miller 2001), Kansas (Fig. 9-7; Aber and
Kosmowska-Ceranowicz 2001a, b), and North
Carolina (Fig. 9-8).
Cretaceous amber from New Jersey is some
of the best known in North America and most
signii cant in the world because of the abundant
and diverse l ora and fauna (Grimaldi 1996).
This amber contains more than 250 species of
plants and animals with some of the oldest
primitive fossil ants (Engel and Grimaldi 2005),
mushrooms, potter wasp, bee, and l ower. New
Jersey amber was likely derived from the conifer
Pityoxylon
in the Pinaceae family (Grimaldi,
Shedrinsky and Wampler 2000). This amber tree
grew in coastal swamps and resembled modern
Pinus, Picea
or
Larix
(Greb, DiMichele and
Gastaldo 2006). In addition to preserving life,
amber contains fossil air bubbles that have been
analyzed to show that Earth's atmosphere some
67 million years ago (end of the Cretaceous)
contained 35 percent oxygen compared to
present levels of approximately 21 percent
(Landis 2009). The consequence of this elevated
oxygen level is unclear, but is another example
of how amber reveals the past.
