Discovery of 260 million year old fossil forest follows stretch of bad weather

Beardmore Remote Camp
Late December 2003

Molly Miller in Antarctica
 
When I last communicated, our lives were controlled by weather, specifically bad weather. Although the sun shone brilliantly all day and all night, the 25 to 30 mph winds combined with the temperatures between 0 and 10 degrees Fahrenheit (F) made it feel really cold. It was difficult to make field observations; your hands hurt with cold when you wrote in your field notebook or fumbled with the metal controls of a camera.

Blowing snow settled around obstructions. Each morning early riser Tim Cully shoveled out the entrance to our cook tent in order to get in. My tent was surrounded on all but the upwind side by a 3-foot-high drift. Each evening I slid on my stomach into the tent and each morning it was harder to crawl out.

 
Sunlight shines through a hole in the clouds on the Prebble Glacier. Weather can change quickly in Antarctica and, when clouds like these move in, we wonder whether the helicopters will be able to return to retrieve us when we are done working.
Even finding food in our storage boxes became a chore. Snow had blown under the covers of the wooden boxes and hardened into something similar to concrete. We could dig into this stuff and, with an effort, could extract an ice-encrusted jar of frozen peanut butter or bag of “Chips Ahoy.” But the extra effort discouraged us a bit from eating, although we still probably packed away about 3,000 calories a day.

People began to feel tired and listless. The loud tent flapping made it hard to sleep at night. During the day there was not enough room in the warm Beardmore camp structures for everyone, so some of our party resorted to playing “Hearts” in our (very) chilly cook tent. We were not getting to the outcrops of rock we needed to work on; we were not making progress toward achieving our science objectives.

Clouds hovering over the top and sides of Mt. Falla.
 
Fortunately we developed a strategy for working under the less-than-ideal conditions. The helicopter pilots determined that they could still fly under the windy conditions. So we decided we would go to outcrops if the wind was bearable and work for three hours with the option of staying longer if we felt we could continue to work effectively. We all knew we could stand working in the wind for three hours, but were reluctant to commit to working for eight to 10 hours in wind chills of -60 degrees F or below. We accepted the risk that, if the weather worsened, we might get stuck staying out a few days with only the Spartan provisions of the survival bags that we always kept with us. It was a bit nerve wracking, however, because some days it seemed unlikely that the helicopters would be able to fly around the encroaching clouds to pick us up.

 
One of the helicopters that took the geologists directly to the sites with the geological strata that they wanted to examine.
The winds remained strong and we were thankful for the shortened workday. In fact, we accomplished a great deal on these short days because we were motivated to make the most of every moment. A few days later the weather gradually improved and before too long we were enjoying long days in near ideal Antarctic working conditions.

Discovery of Permian fossil forest comes as a surprise

Nearly ten years ago, during a field expedition in the Beardmore area, my collaborator, John Isbell from the University of Wisconsin, had discovered petrified stumps that paleobotanists Edie and Tom Taylor of the University of Kansas interpreted as the remains of a fossil forest. The discovery was published in the journal Science in 1992. The woody material in these stumps had been replaced by silica in a process that faithfully recorded the tissue structure of the ancient trees in enough detail to analyze the growth rings. This information allowed Isbell to reconstruct the climate that existed at the time.

An aerial view of Lamping Peak, the site where the fossil forest was discovered. The upper part of the peak consists of sedimentary rocks formed 260 million years ago in the Permian age. The Permian layer, called the Buckley Formation, is underlain by younger igneous rock that was intruded about 150 million years ago
 
This year it was the Vanderbilt team who were the fortunate discoverers. Nichole Knepprath, Tim Cully and I found a much larger, but less well preserved fossil forest at Lamping Ridge , located about 20 miles due south of the Beardmore Camp. The tree stumps – more than 80 in all – occur in three horizons of 260 million-year-old rock, giving an unparalleled glimpse into the structure of an ancient high latitude (Antarctic) forest of that time.

We selected the location because w e were interested in sandstones and siltstones of the Buckley Formation, which dates to the Permian, that are separated from the underlying ice by a thick sill of dolerite – an igneous rock crystallized from magma generated as the super-continent of Gondwana split up about 150 million years ago. The magma squeezed through and between layers of sedimentary rock, heating it and infusing hot fluids, but not deforming its shape. Some of the magma cut through the Buckley Formation. In many places in the Transantarctic Mountains, including Lamping Peak, the dolerite forms near vertical cliffs that block access from the ice to the sedimentary rocks that we want to study. We really appreciate the fact that the helicopter can land directly on the top of the exposure.

 
Paleontologist Chris Sidor from searching for vertebrate fossils in a layer of “coaly” shale with abundant fine-grained plant material.
As soon as we climbed out of the helicopter, we immediately began to see impressions of fossil wood. Some of the fossil logs were more than 20 feet long. In fact, the helicopter skid sat down right on one. It almost seemed disrespectful! Because our goal was to document the distribution of animal tracks and burrows, fossil vertebrate bones and plant material throughout the exposure, we immediately climbed down the hill to the lowest layer in the pile of sedimentary rocks – the one directly above the dolerite. From there we worked our way up, measuring the thickness of the sandstones, shales, and coaly layers. At the same time, we observed the amount of plant material and the degree of disruption caused by the activity of ancient animals.

Disappointingly, the lower layers appeared almost devoid of evidence of past life. Elsewhere in the area, the Buckley Formation teemed with the burrows of animals moving in the ancient river bottoms, but here there were hardly any trace fossils. There were layers of coaly shale, but we saw little plant material and few leaves. Vertebrate paleontologist Chris Sidor from the New York Institute of Technology scoured each bedding plane in search of vertebrate fossils. He found the Swiss army knife that John Isbell had left on a rock ledge in 1985, but there was no sign of fossil bone material.

 
RIGHT: Log preserved on the surface. The ruler is 15 centimeters long. LEFT: Top view of a fossil stump. Because the wood in the trunk was not petrified the center of the stump is a depression. Note the dark roots radiating out from the stump.

Nichole was delighted when we reached the upper layers of sedimentary rocks and found a Permian soil layer littered with plant debris that we had seen when we got off the helicopter. Most exciting were the remains of an upright fossil stump. The wood itself was not preserved so the stump was a depression in the rock, but we could tell it was a stump because of the roots that radiated outward. The stump was darker than the surrounding rock, probably because of chemical reactions between the rock and the hot fluids emanating from the dolerite intrusion millions of years after the tree had died.

Nichole Knepprath measuring a stump that lacks radiating roots. Note the raised margin and dark-colored rock surrounding the stump that contains fossil leaves.
 
As we wandered around the sandstone bed we saw numerous dark depressions that resembled the stumps but lacked the diagnostic radiating roots. Nichole and Pete Flaig, a graduate student at the University of Wisconsin, argued that they were stumps also. But I thought they might be concretions, aggregates of minerals formed long after the rocks were deposited. Fluids associated with dolerite intrusions like those at Lamping Peak are well known to form large concretions, some of which have a concentric structure that would look like the growth rings we thought we were seeing. Nichole's imagination was converting the dozens of “stumps” into a lush Permian forest. I couldn't join the fun until I was convinced that the stumps were not imposters – artifacts of chemical processes unrelated to Permian forests.

Luckily, world experts on fossil forests were members of another science team working out of the Beardmore Camp. Jane Francis from the University of Leeds, U.K. and David Cantrill from the Swedish National Museum both have extensive experience in reconstructing fossil forests. They were working on much younger deposits in the area and were both eager to check out our discovery.
 
A well-preserved leaf from the 260-million-year-old fossil trees found on Lamping Peak. The leaf reveals that the trees were an extinct species called Glossopteris. Brownish rock around the fossil stumps contain leaf litter: layers of compressed Glossopteris leaves and leaf-fragments. Glossopteris leaves have been found in Permian rocks in all the southern continents and provided early evidence that the southern continents had once coalesced into a single large continent called Gondwana.


Jane and David put my reservations to rest by confirming that all of the dark depressions were fossil tree stumps. Some apparently lacked radiating roots because the roots were buried. David and Jane pointed out that the dark areas around the stumps contained impressions of fossil leaves from an extinct species of tree called Glossopteris . Although the imprints were faint and difficult to see, once our eyes were attuned we found them around nearly every stump.

Jane, David, Nichole and I spent an exciting day exploring this Permian forest. Nichole and David mapped the spacing and size of the stumps. Jane and I evaluated the soil on which the trees were growing and assessed both the depth of root penetration and the extent to which soil-forming processes had altered the sediment. The roots were relatively shallow – extending down only a half meter or so and the soil was immature. The surface was littered with logs up to 20 feet long, many of which were oriented in the same direction. Were the trees felled by winds?

The wood was most interesting to me. In some cases branches were preserved, suggesting that the wood had not been transported far by streams. We found an impression of a piece of bark with a knot preserved clearly – not bad for about 250 million years old! The stumps were not replaced by silica, and thus are not “petrified,” but they have been freeze dried in a way that has preserved the growth rings in some cases. On one tree, we counted 26 annual rings, and it was probably older because not all the growth rings were preserved.

 
LEFT: Side view of stump with roots extending downward. The stump in center of the photo is a depression surrounded by raised rock. The darks roots sloping gently to the right indicate a shallow root system. The ruler on the left is 15 centimeter. RIGHT: Branching stem or log on horizontal surface. Preservation of the branches indicates that this fragment was not bounced along a stream bottom for a long distance.

Nichole and I worked more at Lamping Peak, collecting data on the stumps exposed on another level. The forests on these layers are big: we identified more than 80 stumps. They may well be part of the largest Permian forests yet discovered.

Back at Vanderbilt we will begin the process of reconstructing the forests – the height of the trees, the shape, the amount of undergrowth, depth to the water table, etc. These forests have no modern analogues. They thrived at very high latitude during the Permian and there are no lush forests at equivalent latitude today. How could the plants grow so luxuriantly given the long darkness of polar winters? Questions like this make reconstructing the Lamping Peak forest even more compelling.

LEFT: Tree bark that is 250 million years old. Note the preserved knot that marks the location of a prehistoric branch. RIGHT: Close-up of the tree rings preserved in one of the stumps. The wood in these stumps has been altered by a yet-to-be determined mineral during or just after intrusion of igneous rock long after the wood formed. The growth rings are only crudely preserved and the 26 rings we counted on this stump gives a minimum age for the tree.

Since then we've found other neat things and we report on that as well as on our camp move and holiday events in Antarctica in the next installment.

 
 
RETURN TO HOME RETURN TO DISPATCHES rETURN TO tOP