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Department of Geology and Geophysics 06520 |
Tim Raub Graduate student in paleomagnetism and geobiology (links under active construction,
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As a paleomagnetist who enjoys field geology and
working in sedimentary successions, I’m always keen to visit or sample
new successions and rock types. If a rock unit anywhere on this website
seems suited for your talents, feel free to drop a line of inquiry. Often
paleomagnetic samples leave enough leftover material for subsequent study.
At least half the fun in science is sharing the
excitement of discovery with enthusiastic and talented colleagues. Over
the last decade, I’ve enjoyed learning and working with David Evans, Joe Kirschvink, Alexei Smirnov, Dolf
Seilacher, Adam
Maloof, Theresa Raub, Bob Kopp, Brian Skinner, Cathy
Skinner, Eben Rose, Dan Peppe, Catherine Izard, Erik Sperling, Clive Calver,
Michael Wingate, Zheng-Xiang Li, Kath
Grey, Maree Corkeron, Michael Higgins,
Ben Weiss, Ryan Petterson, Paul Hoffman,
Francis Macdonald, Tony Prave, Francis Thackeray, Peter
Ward, Jim Haggart,
and many others.
The resulting projects mostly fall into four
categories, listed below with general background and some links to more
detailed pages on specific efforts. My publication list and links are at
bottom, along with “post-publication dialog” pages on each
paper. I’d like those links to record a list of thoughts and
comments, over the years, as the predictions and consequences in my
publications are borne out, elaborated on, or falsified by other folks’
papers and datasets. In the long run, I’d like to add
viewer-comment submission capabilities.
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Earth’s
Precambrian Glaciations Widespread
glacial records, especially in early Paleoproterozoic and mid- to late
Neoproterozoic successions, generally yield low or moderate paleo-latitudes
and appear stratigraphically dramatic, suggesting that Earth’s
Precambrian glacial mode may have been infrequent but long-lasting, and
astonishingly severe (essentially turning Earth into a Snowball whirling
around the Sun) relative to its Phanerozoic state. I
use paleomagnetism to investigate the character and timescales of these
enigmatic glacial intervals. In addition to establishing paleolatitudes
of glaciation, interdisciplinary magnetostratigraphies through pre-, syn-,
and post-glacial siliciclastic and carbonate rocks may help us understand the
pace of glacial advance and retreat; the volume of ice stored in continental
icecaps and glaciers; and the chemistry of Earth’s ocean, strength and
style of its magnetic field, and nature of its climate triggers during the
most ancient of ice ages. Information
and photographs for some ongoing “Snowball Earth” projects:
How long did it take “Marinoan” Snowball Earth to melt?
Magnetostratigraphy of the Nuccaleena cap carbonate.
What makes up the Elatina-Nuccaleena
deglacial “cap sequence” in
South Australia? Siliciclastic
prelude to cap carbonate deposition.
(link under construction)
Can we believe paleolatitudes from Neoproterozoic glacial deposits? A
geodynamo test in Australian “Marinoan” cap carbonates.
Inclination shallowing of Elatina Formation, a
near-equatorial record of
How old are South Australia’s Elatina glacial rocks and
equivalents?
What is the paleolatitude and nature of Gaskiers glaciation? (To further explore the
cutting edge of research into Precambrian glaciation, try http://earth.geology.yale.edu/igcp509; http://earth.geology.yale.edu/~dae22; and www.gps.caltech.edu/~jkirschvink
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True Polar
Wander Try
out a fascinating piece of imagination space: put on your x-ray goggles
and picture the entire silicate Earth – all the mantle and all the
crust – spinning simply in space. A barber’s pole stands
motionless at top and bottom - lined up with Earth’s time-averaged,
daily spin axis, and with Earth’s magnetic field, which is produced by
its spinning, crystallizing, molten Core. This
is how Earth would have looked, on average, to a casual interplanetary
observer at most any point in the last 500 million years. Now imagine,
at the same time the solid silicate Earth is doing its daily Michelle Kwan
impression, it begins to slip – and fast! – about the top surface
of its liquid iron outer core. Earth’s lithospheric plates, which
ordinarily each move in one of a variety of directions at ultra slow speeds
of millimeters per year, suddenly find themselves tumbling en masse in the
same rotational direction, thousands of times faster than normal. In
fact, this phenomenon, called “true polar wander” (or sometimes
“polar wandering”) is effectively what happens every time there is
a massive earthquake. (The length of a day sometimes gets just a tiny
bit longer, or a tiny bit shorter, because the quake jolted enough of
Earth’s lithosphere closer to or farther away from Earth’s poles
to change its shape – just like figure skaters spin faster or slower,
the tighter or looser they hold their arms to their bodies.) And
slightly slower true polar wander has been happening for the last ten
thousand years or so, as the Northern Hemisphere rebounds upward, freed of
the immense weights of the icecaps of Earth’s most recent glaciation. But
earthquake-induced true polar wander happens in seconds; and in a couple
thousand years, glacial rebound-induced true polar wander will probably slow
down, too. Astonishingly, some paleomagnetists think that, more than
500 million years ago, a burst of fast true polar wander lasted more than a
million years, moving
continents that started out near the North Pole to the equator, and continents
that started out near the equator to the South Pole! No one knows
exactly when and why that burst began or ended, or if and how it affected
Earth’s climate and biosphere. Paleomagnetism
can test whether such true polar wander really happened (but that test is
difficult to make complete and unambiguous!), and if so, how long it took,
how many times it happened, and how fast it went. Here are some
photographs and information from individual ongoing projects intended to shed
light on the mystery of Precambrian true polar wander:
Ediacaran-Cambrian true polar wander can independently reconstruct
Gondwanaland: proof of concept that the paleomagnetic signal
is global and coherent.
Paleomagnetism and Geochronology of Sept Iles Mafic Complex.
Paleomagnetism and Geochronology of Callander Alkalic Complex.
Magnetostratigraphy of Brachina and Bunyeroo Formations.
A Methane Fuse for the Cambrian Explosion? Predicted links between
rapid true polar wander and methane clathrate reservoirs. |
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Earth History:
Stratigraphy and Geobiology Here’s
an alluring idea: any question we could think to ask about the surface Earth system
has been answered already in the rock record – any experiment involving
life, climate, and the physical and chemical constituents of both has been
run, and the results presented somewhere in ~4 billion years of strata!
As Earth historians, we’re challenged to reconstruct the
“materials and methods” of those experiments, in order to relate
academic questions in Deep Time to real-world questions today. My
research involves field-based geobiology, laboratory paleomagnetism, and
multidisciplinary collaboration. The Precambrian record is still
a frontier, rife for study at the same intensity as now-famous Phanerozoic
intervals. Newly-recognized critical intervals in Phanerozoic Earth
history merit high-resolution focus with global span. Information and
photographs for some such projects I’m involved with are below:
A sense of place and time: calibrating Ediacaran events of South
Australia’s Adelaidean succession.
A sense of time and place: calibrating Ediacaran events of
Newfoundland’s Avalonian succession.
Biomagnetostratigraphy of the late Cretaceous (Santonian-
Maastrichtian), Tethyan realm of Tunisia.
Biomagnetostratigraphy of the late Cretaceous (Santonian-
Maastrichtian), Pacific realm of North America.
Biomagnetostratigraphy of the Cambrian-Ordovician boundary GSSP.
Petrophysics of a magnetically exceptional Paleocene-Eocene boundary clay. |
Precambrian
Supercontinents: Rodinia By
reconstructing (to reasonable approximation) a global paleogeographic map of
the Paleozoic-Mesozoic supercontinent, Pangea, paleomagnetists quantified the
basic style of plate tectonics over the past 300 million years and helped
diverse geological specialists understand such mysteries as:
Widespread lava hills and plateaus on both sides of the Atlantic
Ocean, from Nova Scotia to Brazil, and from Scotland to
Cameroon.
Unique fossil worms and ferns, common between Australia, Africa,
and South America.
Glacial deposits and smoothed-rock striations at near-tropical
latitudes
of modern Australia The
edges of still more ancient continents are preserved in the surface rock and
internal seismic records, and many equally fascinating questions pepper
Precambrian time. The answers to these questions might also become
evident if we were able to reconstruct paleogeographic maps of the probable
ancient supercontinents Rodinia, Nuna, and Kenorland. Many
paleomagnetists are hard at work trying to make just those sort of maps
– a list of neat websites follows – and I am helping some of
these teams determine new paleomagnetic poles to pin down continent locations
long ago:
Paleomagnetism of Newfoundland’s Long Range Dikes. Paleomagnetism of Norway’s Egersund Dikes. |
Publications:
in press:
Raub, T.D., Evans, D.A.D.,
and Smirnov, A.V. Siliciclastic prelude to Elatina-Nuccaleena
deglaciation: lithostratigraphy and rock magnetism
through the base of the Ediacaran System. Journal of the Geological Society of London.
*post-publication developments and comments* (not yet linked 9/15/06)
2004: Skinner, H.C.W., Nicolescu, S., and Raub, T.D. A tale of two apatites. in Petrescu, I. and Ozunu, A. (eds.), Environment and Progress –
2/2004, EFES Publishing, Cluj. Pp. 283-288.
*post-publication developments and comments* (not yet linked 9/15/06)
2003:
Thackeray,
J.F., Kirschvink, J.L., and Raub, T.D. Paleomagnetic analyses
from Plio-Pleistocene calcified deposits of Kromdraai Cave B, South
Africa. South African Journal of Science, v. 98 pp. 537-540.
*post-publication developments and comments* (not yet linked 9/15/06)
Kirschvink, J.L. and Raub, T.D.
A methane fuse for the Cambrian Explosion? Cambrian carbon cycles and
true polar wander. Comptes
Rendus Geosciences, v. 330 pp. 35-61.
-also see
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*post-publication developments and comments* (not yet linked 9/15/06)
