Download - Catalyst

Molnar & England, 1990; Egholm, 2009
Austin Rains
 Was late Cenozoic uplift responsible for climate change, or was climate change
responsible for late Cenozoic uplift?
 Uplift is the vector opposite of
gravity and must have a reference
frame as well as an object that
moves.
 In this case, the reference frame is
the geoid (Sea level) and the
object that moves is the Earth’s
surface (rocks, batholiths,
anything apart of the Earth’s
crust).
 Examples: Himalayas, Alps,
Appalachians, Southern Alps
(New Zealand)
 Increased elevations at
temperate latitudes could
increase the duration of winter,
therefore, increasing the albedo
due to increased duration of
snow cover.
 An increase in
elevation of large
regions (Himalayas)
affects circulation in
the atmosphere as
predicted by both
modeling and
observation.
 Increased exposure of minerals due to rapid erosion of sediment. Minerals are
transported from high elevations that are cold, down to warm, humid elevations.
This absorbs more CO2 from the atmosphere, reducing the greenhouse effect.
• Uplift due to isostasy.
• Erosion of sediment creates
an isostatic response,
uplifting the Earth’s surface.
• Climate change increases
erosion rate, therefore,
increasing the uplift rates.
 Glaciers are the
primary agent for
erosion.
 They play a much
bigger role in
denudation than
fluvial processes.
Geomorphology
 The sharp incisions of rivers into gentle surfaces of late Cenozoic sediment.
 The uplift of a surface with respect to the base level of a river increases potential
energy and steeper gradients, which leads to more rapid erosion.
 Ranges such as the Alps are tens of millions years old, but still experienced erosion
that whole time. However, they underwent more rapid erosion more recently due to
climate change.
Sedimentation
 Accelerated denudation revealed by sediment
accumulation far from mountain ranges.
 Accumulation rates of sediment in the Pacific,
Atlantic, and Indian oceans in the late Cenozoic
are four to fivefold in the last 5 million years.
 Sediment around the Southern Alps is younger
than 2.5 million years, which correlates well with
the Pleistocene glaciation.
 If tectonic processes stopped, five-sixths of uplift
would still occur.
Mass of Cenozoic sediment in the
northwestern Gulf of Mexico
Paleobotany
 Using taxonomic analyses to
determine what elevation a plant
fossil grew at.
 One can infer the paleoclimate of
the environment that the fossil
was found at.
 Many studies have ignored global
climate change. Given that the
Earth cooled during the late
Cenozoic, this makes it seem as
though mountain ranges have
uplifted recently.
Based on Paleobatnical data from the Himalayas
 Most arguments of late Cenozoic uplift are exaggerated.
 Climate change can be very different in different places.
 Physical mechanisms linking climate change to uplift should apply most strongly to
regions where mean elevation has increased.
 Could also operate where the crests of mountain ranges have risen, but less so.
 Assigning the cause of late Cenozoic climate change to late Cenozoic uplift is
hypothesis rejected.
 Instead, the phenomena used to infer recent uplift are a consequence of climate
change.
 Gradual cooling over the past 50 million years may still be due to the tectonic uplift
of the Himalayas.
 Mean elevation, climate change, and the phenomena used to infer uplift are all
coupled to one another.
 Possible positive feedback loop: Increased weathering/erosion  negative
greenhouse effect  cooler climate  Uplift  increased weathering/erosion
 It’s still hard to confirm that uplift is a result of climate change.
 Both climate change and uplift may have occurred at the same time.
 Its safer to say that uplift due to climate change varies from region to region.