Geologic Tags
Tag based links for
The following links have been tagged Geologic by users just like you, because these resources are off-site we cannot guarantee the accuracy or quality of any third-party information.
- Did Vicariance
Mold
Phenotypes of
Western North
American
Fishes?
Evidence from
Gila River
Cyprinids: Evolution,
Vol. 53, No.
1. (1999), pp.
238-246.Pairwi
se, two- and
three-way
Mantel tests
were used to
evaluate a
null
hypothesis of
no significant
covariation
when
morphological
features of
three cyprinid
fish taxa of
the genus Gila
were compared.
Tests involved
ecological
conditions and
past and
present
hydrography in
the Gila River
Basin of
western North
America. A
vicariance
hypothesis was
the only model
statistically
proficient in
explaining
diversity of
fish
phenotypes. Of
paleohydrograp
hic
reconstruction
s compared,
those of the
mid-Miocene
and Pliocene
epochs were
significantly
associated
with
present-day
distributions
of phenotypes.
Of these, the
Pliocene was
paramount.
Source: Evolution, Vol. 53, No. 1. (1999), pp. 238-246. - The Evolution
of Modern
Eukaryotic
Phytoplankton: Science, Vol.
305, No. 5682.
(16 July
2004), pp.
354-360.The
community
structure and
ecological
function of
contemporary
marine
ecosystems are
critically
dependent on
eukaryotic
phytoplankton.
Although
numerically
inferior to
cyanobacteria,
these
organisms are
responsible
for the
majority of
the flux of
organic matter
to higher
trophic levels
and the ocean
interior.
Photosynthetic
eukaryotes
evolved more
than 1.5
billion years
ago in the
Proterozoic
oceans.
However, it
was not until
the Mesozoic
Era (251 to 65
million years
ago) that the
three
principal
phytoplankton
clades that
would come to
dominate the
modern seas
rose to
ecological
prominence. In
contrast to
their
pioneering
predecessors,
the
dinoflagellate
s,
coccolithophor
es, and
diatoms all
contain
plastids
derived from
an ancestral
red alga by
secondary
symbiosis.
Here we
examine the
geological,
geochemical,
and biological
processes that
contributed to
the rise of
these three,
distantly
related,
phytoplankton
groups.
Source: Science, Vol. 305, No. 5682. (16 July 2004), pp. 354-360. - Implications
of shortening
in the
Himalayan
fold-thrust
belt for
uplift of the
Tibetan
Plateau: Tectonics,
Vol. 21
(December
2002), pp.
12-1.Recent
research in
the Himalayan
fold-thrust
belt provides
two new sets
of
observations
that are
crucial to
understanding
the evolution
of the
Himalayan-Tibe
tan orogenic
system. First,
U-Pb zircon
ages and Sm-Nd
isotopic
studies
demonstrate
that (1)
Greater
Himalayan
medium- to
high-grade
metasedimentar
y rocks are
much younger
than true
Indian
cratonic
basement; and
(2) these
rocks were
tectonically
mobilized and
consolidated
with the
northern
margin of
Gondwana
during early
Paleozoic
orogenic
activity.
These
observations
require that
Greater
Himalayan
rocks be
treated as
supracrustal
material in
restorations
of the
Himalayan
fold-thrust
belt, rather
than as Indian
cratonic
basement. In
turn, this
implies the
existence of
Greater
Himalayan
lower crust
that is not
exposed
anywhere in
the
fold-thrust
belt. Second,
a regional
compilation of
shortening
estimates
along the
Himalayan arc
from Pakistan
to Sikkim
reveals that
(1) total
minimum
shortening in
the
fold-thrust
belt is up to
~670 km; (2)
total
shortening is
greatest in
western Nepal
and northern
India, near
the apex of
the Himalayan
salient; and
(3) the amount
of Himalayan
shortening is
equal to the
present width
of the Tibetan
Plateau
measured in an
arc-normal
direction
north of the
Indus-Yalu
suture zone.
This
information
suggests that
a slab of
Greater Indian
lower crust
(composed of
both Indian
cratonic lower
crust and
Greater
Himalayan
lower crust)
with a
north-south
length of ~700
km may have
been inserted
beneath the
Tibetan crust
during the
Cenozoic
orogeny. We
present a
modified
version of the
crustal
underthrusting
model for
Himalayan-Tibe
tan orogenesis
that
integrates
surface
geological
data, recent
results of
mantle
tomographic
studies, and
broadband
seismic
studies of the
crust and
upper mantle
beneath the
Tibetan
Plateau.
Previous
studies have
shown that
incremental
Mesozoic and
early Cenozoic
shortening had
probably
thickened
Tibetan crust
to ~45-55 km
before the
onset of the
main Cenozoic
orogenic
event. Thus,
the insertion
of a slab of
Greater Indian
lower crust
with maximum
thickness of
~20 km
(tapering
northward)
could explain
the Cenozoic
uplift of the
Tibetan
Plateau. The
need for
Tibetan crust
to stretch
laterally as
the Greater
Indian lower
crust was
inserted may
explain the
widespread
east-west
extension in
the southern
half of the
Plateau. Our
reconstruction
of the
Himalayan
fold-thrust
belt suggests
that Indian
cratonic lower
crust, of
presumed mafic
composition
and high
strength,
should extend
approximately
halfway across
the Tibetan
Plateau, to
the Banggong
suture. From
there
northward, we
predict that
the Tibetan
Plateau is
underlain by
more felsic,
and therefore
weaker, lower
crust of
Greater
Himalayan
affinity. Two
slab break-off
events are
predicted by
the model: the
first involved
Neotethyan
oceanic
lithosphere
that foundered
~45-35 Ma, and
the second
consisted of
Greater Indian
lithosphere
(most likely
composed of
Greater
Himalayan
material) that
delaminated
and foundered
~20-10 Ma.
Asthenospheric
upwelling
associated
with the
break-off
events may
explain
patterns of
Cenozoic
volcanism on
the Tibetan
Plateau.
Although the
model predicts
a northward
migrating
topographic
front due
solely to
insertion of
Greater Indian
lower crust,
the actual
uplift history
of the Plateau
was
complicated by
early-middle
Tertiary
shortening of
Tibetan crust.
Source: Tectonics, Vol. 21 (December 2002), pp. 12-1.
If you would like to find additional social bookmark based links on the topic of Geologic we recommend the Open Tag Directory > Geologic. If you would like to find related tags we recommend Tag Patterns > Geologic.
Geologic Tag Pages: 1 | 2 | 3 | Next
Geologic Tag Pages: 1 | 2 | 3 | Next
