Good weather allows the geologists
to wrap up their field studies and head home
Nashville Tennessee
January 15, 2004
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| Molly Miller in Antarctica |
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Given how the month started, it is hard to imagine but good weather
and smooth helicopter operations made for productive work and pleasant,
uneventful life at the Beardmore Camp during the last half of December.
The daily routine became almost as comfortable as that in Nashville.
I'd wake up, get clean (not quite as effective as a shower, but
lots less water-consumptive!), put on well dried and well aired
layers of fleece, retrieve the digital camera from my sleeping
bag and hang it around my neck to position it close to my skin,
make sure that my backpack contained extra socks, gloves, warm
pants, etc., and crawl out of the tent, hoping no one was watching
the strikingly ungraceful process.
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| Researchers gathering in the
cook tent |
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The morning air always felt cold because, except for the floor,
it was quite warm in the mountain tent, which trapped the heat
from the 24 hours of sunlight. It was a treat to unzip the cook
tent and take in the smell of Tim's dynamite coffee, and even more
of a treat to sip it while contemplating what the day would bring
and what needed to be done. That including thinking about what
we should have for dinner – steak, pork tenderloin, chicken stir
fry – and hanging up the frozen stuff so it will be thawed upon
return.
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| Chris Sidor, Miller and Nichole Knepprath,
left to right, searching for vertebrate fossils and burrows. |
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Breakfast of Quaker granola and maybe a toasted English muffin,
hot Tang, then herbal tea. Make a lunch of a Cadbury bar, peanut
butter on crackers, gorp, Slim Jims, and pour hot water into the
Thermos with Tang and then it's off to the helicopter. It was a
bit of a walk from our camp to the Beardmore “town.” Once there,
we'd huddle with the transportation manager and the helo pilot
to pick the location and elevation of the site for the day and
agree on a pick up time. Then we would carry our packs and survival
bags to the helicopter. The feeling as the helicopter rises a bit,
then tilts its nose down and flies off never ceased to be exciting.
After the helicopter dropped us (if it was warm enough) we would
take off the required “Big Red” bulky fur-trimmed down jackets,
secure them under heavy rocks, and get to work looking for fossils,
observing features in the rocks, taking pictures. It was similar
to doing field work in Tennessee, except it was wonderful to have
so much rock and so little soil and vegetation. Especially since
we were finding answers to our questions.
Where are (were) the vertebrates?
In 1995, I found some very large burrows in this area – some over
six inches in diameter and five feet long – in floodplain deposits
of Triassic age (208 million to 245 million years ago). They were
produced by a four-legged animal, probably a mammal-like reptile.
Mammals evolved from mammal-like reptiles later in the Triassic.
I hypothesized this evolution occurred in Antarctica which was
at a very high latitude at the time – far away from the mammal-like
reptiles' fleet-footed and carnivorous contemporaries: theropods
and dinosaurs. If earliest mammals did live at high latitudes,
living in a burrow would have buffered them from weather extremes
over the long, dark winter. I was hoping to find fossils of small
mammals huddled in their burrows. The burrows would be easy to
see and, if my reasoning was correct, would lead us to complete
skeletons of vertebrates, hopefully mammals.
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| Outcrops of dark siltstone overlain by light-colored
sandstone are normally good places to find burrow casts of
mammal-like reptiles. Burrow casts are ancient burrows that
the animals dug in floodplains that were filled in with sand.
Over geologic time, the silt and sand is turned to stone.
Unfortunately, we didn't find any sandstone in the siltstone,
and no vertebrate burrows, in this particular formation. |
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We knew the animal burrows would be most visible if they were
filled with sandstone. The animals dug the burrows in mud along
the edge of the river. During floods the burrows were filled with
sand. With luck, the animal might have drowned in its burrow and
its skeleton preserved intact in the sand-filled burrow. It would
have been a bad ending for the animal – yes, we did think about
that - but perhaps no worse than any other. The light color of
the sandstone would contrast with the enclosing dark mudstone.
I was hopeful that these burrows would be abundant, complete with
bones of their inhabitants.
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| The ruler is just below one of the few large
burrows we found in the Beardmore area. It probably was made
by a vertebrate living on a floodplain. |
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It didn't happen. We looked at almost every available rock of
Triassic age. Other than the large burrow that vertebrate paleontologist
Chris Sidor found earlier, we didn't find any. My hope flagged,
but it was renewed at the last exposure with Triassic rocks where
there were many ledges of light colored sandstone overlying dark
floodplain siltstone. If the burrows were present we would see
them easily.
We found a few of the large burrows, but only in a zone a few
meters thick. The burrows were too small for adults; maybe they
provided shelter for juvenile mammal-like reptiles. The hypothesis
that large burrows would be abundant and contain fossils of early
mammals had been tested, and shown to be lacking. We found enough
to prove that the burrows were very rare and that we were not overlooking
them. Disproving hypotheses is what science is all about, but it
was still disappointing.
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| LEFT: Ribs
and other bones of a dog-sized mammal-like reptile. RIGHT: Jaw
of an ancient amphibian. Its bones bounced along
the stream bottom, as did the well-rounded pebbles
with which the bones occur. |
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While we were looking for large burrows, Chris Sidor was scouring
the Triassic rocks for pieces of fossil bone. He had better luck
than we, finding bones in both river floodplain and river channel
deposits. Many bones of a mammal-like reptile were clustered together
in the floodplain siltstone. Chris also found an isolated amphibian
jaw in river channel deposits. The jaw is in remarkably well preserved
considering that it bounced down the river with the associated
pebbles. Chris will be working to identify and reconstruct the
amphibian.
Under what conditions did invertebrate animals live in Permian
and Triassic lakes and streams?
Channels of rivers that had periods of low water flow: Big,
robust burrows are abundant in some Triassic (less than 245 million
years old) river channel deposits. At times the rivers really flowed
fast, as indicated by the large particles that they carried. However,
for the burrowing animals to swim through the water column to reach
the sand at the bottom, the river must have been flowing slowly,
otherwise they would have been carried downstream. (I determined
in the 1990's that these large burrows were made by insects. Modern
insects almost all have adult reproductive stages in air, not water,
so the burrowers must have entered the water as larvae.) We found
no burrows in older Permian river channel deposits, although the
same type of burrower as present in the Triassic lived on river
margins in the Permian (see dispatch #3) .
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| LEFT: Burrows
made by an insect burrowing in ancient river
channel. Its presence indicates a seasonal period
of very low flow in the river. RIGHT: River
channel sandstone with no burrows that has been
sculpted by winds. |
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This distribution of burrows indicates that river flow in the
Triassic was very low for a significant part of the year. However,
in the Permian, the water flow was too great all year for the burrowers
to colonize the river bottom. Both the presence and absence of
the burrows gives information about the constancy of river flow
that could not otherwise be deduced. Perhaps this is typical of
how we reconstruct the history of the earth – a detective game,
piecing together seemingly unrelated bits of information.
Not where sediment was deposited rapidly: Another of
our tasks was to assess the extent of bioturbation (disruption
by animals) in rocks of the Mackellar Formation that were deposited
in a large lake about 290 million
years ago, soon after an extended period of glaciation. At two
locations with beautiful rock exposure we found no burrows and
no evidence of ancient life. We determined that mud poured into
the lake so fast that bottom dwelling animals were overwhelmed
and unable to survive.
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| LEFT: Light
sandstone and dark shale of the Mackellar Formation. RIGHT: Abundant
burrows can be seen in sandstone deposited shallow
water along margin of the large lake. The undulations
are ripple marks that were made by waves and
reflect shallow water conditions. |
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One area of the Makellar Formation, however, tells a different
story, one dominated by animals crawling on the lake bottom. The
diverse and abundant traces of biological activity indicate that
this shallow part of the lake was teeming with animals. The nature
of the ripple marks left by wave action prove that it was very
shallow. Here the rate of sediment influx was sufficiently slow
for the animals to survive.
Were there vertebrate animals in Antarctica during the
Permian?
It has been known since the 1960's that amphibians and reptiles
inhabited high latitude Antarctica during the Triassic. However,
no one has found vertebrate fossils in the older Permian rocks.
During the Permian, Antarctica was located closer to the south
pole than it was during the Triassic (See
continental drift simulation), and there are glacial deposits in the early part of the Permian.
Was it too cold in Permian Antarctica for vertebrates to live?
To answer this question we searched the “highest and driest” Permian
deposits that we could find. We knew that it was wetter in Antarctica
during the Permian than during the Triassic. Our interpretation
of the constant river flow of the Permian vs. periods of low flow
during the Triassic was consistent with a wetter Permian. Besides,
the shallowness of the roots of the Permian-aged trees at Lamping
Peak versus the long, vertical roots that we had found in Triassic
deposits indicated a higher water table during the Permian. A high
water table would keep vertebrate animals from burrowing – they
would drown in burrows. But burrowing was the best strategy for
surviving long, dark, and cold winters. We figured that the highest
areas, with the lowest water table, were the habitats most likely
to have been inhabited by vertebrates in the Permian.
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| Tracks that may have been left
by a Permian reptile. If this is the case, then it would
be the earliest evidence of vertebrates in Antarctica. |
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Lamping Peak, with its fossil forest, recorded the driest Permian
habitat. However, our search there, as at other Permian outcrops,
for large vertebrate burrows and for bones yielded nothing (See
dispatch #4) . Maybe
it was too cold and too wet for amphibians and reptiles; mammals
and birds did not appear until tens of millions of years later.
Our last day of field work, Nichole, Tim and I went to an exposure
of Mackellar Formation deposited near the shoreline of the early
Permian lake. We found “tracks” that are reminiscent of vertebrate
tracks because they appear to record the marks of digits. These
are accompanied by swish marks that could record a dragging tail.
These tracks might have been produced by fish, but a much more
exciting possibility is Mesosaurus , a Permian reptile
that inhabited lakes in South America and South Africa. ( Click
for background on Mesosaurus)
If these tracks were made by a reptile, it will be the first evidence
of vertebrate life in Permian Antarctica and will demonstrate that
the climate was not so cold as to exclude all vertebrates.
Logistics – camp move and coming home
The Beardmore Camp provided helicopter and logistical support
for six science parties. Each group was self sufficient, living
in tents, cooking independently. Tanya Zastrow, the talented camp
cook. provided delicious meals and freshly baked bread and cookies
for the camp staff of five and helicopter and airplane pilots and
mechanics, but the science parties ate what they cooked on a Coleman
stove. It was fun getting together with the camp staff, and the
quality and diversity of food in our occasional “Beardmore pot
lucks” rivaled those of the best Nashville pot lucks.
The other science groups left in time to get home for Christmas.
The Beardmore camp moved about 100 miles to the north to a location
better suited for the geophysical survey that would be conducted
during January. The temporary buildings were removed in a matter
of days by carpenters from McMurdo Station and were erected even
more quickly at the new Moody Nunatak location.
Our team of six moved to the new camp as well. It took about a
day of work to pack up our equipment and wrap it securely on a
pallet. One of the big jobs was digging out the tents from the
several feet of drifted snow in which they were buried. It was
satisfying to watch the pallet of our stuff be dragged onto C-130
transport plane, but sobering that it would need to be unpacked
that afternoon!
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| LEFT: Removing
drifted snow from around cook tent so it can
be taken down. RIGHT: Gear
being loaded onto a C-130 Hercules airplane. |
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We worked from the Moody Camp for several days and realized that
we were approaching completion of our work. Because the helicopters
would not be operating for about five days over Christmas, we decided
to return to McMurdo Station and prepare for return the States..
In celebration of our leaving and of the winter solstice, Tanya
produced a feast of barbequed ribs and lobster tails, with pies
that Nichole, team member Zelenda Koch and I baked in Tanya's oven
for dessert. It felt like a celebration of a successful field season,
a celebration of the rich experience of working in Antarctica.
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| Scientists dozing during the
eight hour flight from McMurdo to Christchurch, New Zealand. |
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McMurdo Station is big and bustling – overwhelmingly so when you've
spent days in the quiet and have become accustomed to the voices
and habits of your five or six co-workers. We unpacked the equipment
that had taken us days to organize in record time of a few hours
and headed to our dorms to take showers.. It felt terrific after
five weeks, although a shower a day no longer seemed imperative.
Eight hours on a C-130 flying to New Zealand, watching as the
ice of Antarctica is replaced gradually by open ocean allows plenty
of time for reflection, for making the transition from the intense
but simple life in Antarctica to the complexities we deal with
at home . . . and for sleeping. What a relief to shed our cold
weather gear in Christchurch, especially the “Big Red” parka that
had been such a life during the periods of strong winds.
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| LEFT: The
New Zealand rainforest may closely resemble
Antarctica's Permian forests. RIGHT: Rivers
flowing down from the mountains in New Zealand
are choked with sediment and develop a braided
form, probably similar to the ancient rivers
of Antarctica. |
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New Zealand is intensely green and there is water all over – something
you don't find in Antarctica! New Zealand forests and rivers provide
modern analogues for what we saw in the Permian and Triassic rocks
of Antarctica. Its temperate lush rainforests have trees with shallow
roots that must resemble the Permian forest we discovered at Lamping
Peak. And the sediment-choked rivers flowing off the Southern Alps
probably are dead ringers for the Triassic rivers that were home
to insect burrowers.
I'm awed by the change that has occurred in Antarctica over time.
Perhaps the only constant in the earth is change, change that is
so slow as to be imperceptible on a human time scale. I'm unbelievably
lucky to work in Antarctica, which has made it impossible for me
to either miss or deny the reality of this change.
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