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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: The Influence of High-Frequency Climate Variability
on Paleoclimate Interpretation
Chevron Energy Technology Company
Houston, TX
Understanding past long-term climate states and their higher
frequency variability can play an
important role in helping to forecast
future climate changes. The insolation
cycles which drive high-frequency
climate variability and their interference
patterns have been mathematically
resolved for the last 50 Ma. Inferences
can be drawn on these patterns back
through at leas t the Paleozoic.
However, different regions of the
Earth have different climatic responses
to the same insolation cycles and
record the changes differently. In some locations, the stratigraphic
record of climate cycles is easily recognized and measured. In
other areas, it’s more difficult because
the climate does not change much or
perhaps stratigraphers who interpret
climate ignore changes to sedimentary
delivery systems
and environments
of deposition caused by the specific
climate response. They don’t
recognize preservation bias caused by
climate cycles so they fail to include
the
phase
relationship of sediment
supply and
sea
- or lake-
level
cycles.
These issues can cause paleoclimatologists
to misinterpret the actual temporal scales of climate change
because they are looking
for similar stratigraphic
responses to the same
climate
cycle
in areas
that just don’t preserve
them the same way.
Presently, most paleoclima te analyse sand interpretations ar e resolved only for mean annual conditions for time intervals ranging from 0.1 to 1 my. However, the greatest insolation chang s occur seasonally at the scale of precession (~20 kyrs) during periods of high eccentricity. Similar to the conditions that cause summer in one hemisphere and winter in the other at
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Figure 2. Relationship between precession-scale paleoclimate states and glacioeustasy for the E. Permian. High
sea
level
is associated with intervals with warm
southern hemisphere summers. Low
sea
level
is associated with cool southern hemisphere summers. The time between these end member states can
be a short as 10 kyrs. Note that cool northern hemispheres summers occur during times of warm southern hemisphere summers and cool southern
hemisphere summers occur during the times of warm northern hemisphere summers. Figure from Perlmutter and Plotnick, 2003.
End_Page 33---------------
the same time in the earth’s orbit, precession cycles cause
northern and southern hemisphere insolation to be about 10,000
years out of phase
. Hot summers and cold winters in one
hemisphere correspond to mild summers and mild winters in the
other. The pattern reverses itself over a precession
cycle
so that
similar climatic successions in opposite hemisphere, and their
associated sediment yield cycles, will be 10,000 years out of
phase
,
as well. These changes occur regardless of whether the earth is in
a greenhouse or an icehouse state.
Until the Plio-Pleistocene glaciations, when they occurred, were
unipolar. Under this condition, precession-scale eustasy tended to
track the insolation cycle
of the glaciated hemisphere.
Consequently, similar climatic successions in opposite hemispheres
would have had sediment yield cycles with distinctly different
phase
relationships to glacioeustasy. Such differences would not
exist in an ice-free world. The regional and temporal variations in
the
phase
relationships between sedimentary and glacioeustatic
cycles may not be consistent with basic assumptions about
stratigraphy and may impact how we interpret the causes and
frequencies of the stratigraphic cycles themselves. This talk is a
discussion of how these issues affect our understanding and
interpretation of paleoclimate.
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