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The Transantarctic Mountains

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Click on questions to see pictures and learn about the Transantarctic Mountains and its past

What do the Transantarctic Mountains look like today?

How were the continents arranged in the Permian and Triassic? Where was Antarctica?

How did the landscapes change from the Early Permian to the Middle Triassic?

What was the environment and life in the Early Permian?

What was the environment and life in the Late Permian?

What was the environment and life in the Early Triassic?

What was the environment and life in the Middle Triassic?

So What?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What do the Transantarctic Mountains look like today?

These pictures show different areas of the Transantarctic Mountains, but all the rocks were deposited in lakes or streams during the Permian and Triassic. There are people in each picture for scale.

Geoscientists love working in these mountains because the rocks are not covered with plants and trees so they can easily see the features and fossils in the rocks.

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How were the continents arranged in the Permian and Triassic? Where was Antarctica?

If you were looking up at the South Pole 250 million years ago, you would have seen the continents arranged like this in a supercontinent called Pangea. From left (west) to right (east) there is southern South America, Africa, Antarctica (green, but without the Antarctic Peninsula) and Australia (pale orange).

 

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Big point: During the Permian and Triassic, Antarctica was at southern polar latitude. Its location was similar to its location today.

Links to other maps showing geography of the Permian, Triassic, and time just before the Permian (Carboniferous)
Late Carboniferous (Dr. Chris Scotese)
Late Permian (Dr. Chris Scotese)
Triassic (early) (Dr. Chris Scotese)
Dr. Ron Blakey

 

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How did the landscapes change from the Early Permian to the Middle Triassic?

(The Permian period is the last time period in the Paleozoic era. It is followed by the Triassic period which is the first period in the Mesozoic era. The Permian and Triassic periods are further subdivided into Early, Middle, and Late Permian, Triassic. For more about the geologic time scale: Click Here)

The table below summarizes the changes in environment in which rocks were deposited, climate, and plant and animal life that occurred from the earliest Permian to Middle Triassic. The painting below the table by Mary Parrish depicts these changes in landscape, climate, and vegetation these slices of time.

 

Years ago
(My-million years ag)

Environment
Rocks deposited in:

Climate

Plant life

Animal life

Mid Triassic

~240 My

stream systems

Wetter than Early Triassic

Dicroidium
thin coals

Reptiles and amphibians; Thrinaxodon

Early Triassic

~250 My

streams
(braided)

Drier;
low water table;
warmer(?)

Few plant fossils; abundant roots

Reptiles and amphibians; Lystrosaurus, Procolophon

Late Permian

~255 My

Streams, ponds (anastomosing)
high water table

Cool temperate; wet

Glossopteris
Large trees, forests, coals preserved

Insects, other shallow burrowers on lake bottom

Early Permian

~280 My

Lake, streams

Cold; glaciers retreated

No record of any

Insects on lake bottom
(trace fossils)

Permian start

~300 My

Glacial
(wet-based); glaciofluvial, lacustrine

Cold (not polar frigid)

No record of any

Few shallow burrowers on lake bottom

Below is Smithsonian artist Mary Parrish’s rendition of changes in landscape from the Early Permian to Middle Triassic.

 

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What was the environment and life in the Early Permian?

What it looked like: Glaciers flowing into lakes and lagoons, scraping the bedrock in the process. Rather than being frigidly cold like Antarctica today, it probably was more like southern Iceland, where today an ice sheet terminates in the Jokulsarlon Glacial Lagoon, shown in the photos below.   Note the large amount of sediment carried by the iceberg. When the ice melts, the sediment will be deposited in the lagoon.

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Evidence in the rock record for what it looked like: In the Transantarctic Mountains rocks deposited in the earliest Permian are diamictites (see example below). Diamictite is a sedimentary rock with particles of diverse sizes, from grains of silt to large boulders. Pebbles within the diamictite have striations, formed when the ice scraped them across the bedrock.   These striations indicate that the diamictite was deposited from glacier activity, not by its other possible mode of formation, by deposition by landslide or debris flow.   

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Picture above: This lowermost Permian diamictite from Mt. Richie in the Transantarctic Mountains is composed of grains of all sizes, whereas the overlying sandstone with uniform sized grains was deposited from flowing water. (Photo by J.L. Isbell)

Life of the time: There are few fossils in these glacial rocks. In some areas there are burrows made by animals that lived in lakes adjacent to the glaciers, but these occurrences are rare. There are no plant fossils, although pollen has been recovered, indicating that the presence of vegetation, if sparse.

 

Relation to the rest of the world: At this time the continents were together in the supercontinent of Pangea and many southern continents were affected by glaciers. The diagram below shows a single giant ice sheet emanating outward from Antarctica. More recent authors have suggested that the ice sheets were smaller and not necessarily contemporaneous. 

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Earliest Permian continents and ice sheets (in white); Antarctica is shown as mainly covered by ice. Squares and triangles show occurrences of particular types of conodonts, small internal “teeth” of early fish-like vertebrates. (Figure from ASRG, Department of Geology and Geophysics, University of Calgary.)

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What was the environment and life in the Late Permian?

What it looked like: By the Late Permian plants had become very common and there were forests. There were many many small lakes – it must have been swampy landscape as shown in Mary Parrish’s reconstruction below.

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Evidence in the rock record for what it looked like: The sandstone and shale laid down at this time were deposited in braided streams and on the adjacent sandbars and floodplains dotted with swamps and shallow lakes. Trees fell into these areas. The bottoms of these lakes/swamps were stagnant and lacked oxygen. Without oxygen, bacteria could not decay the plant material, so it was preserved and gradually was transformed into coal. Below is a picture of the black coal layers.

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Life of the time: In the central Transantarctic Mountains, the rocks of this age (Buckley Formation) contain many fossils of the plants and animals that lived at this time. The most common plant was a tree (Glossopteris) that grew up to ~60 feet high. It was related to the gingko tree that lives today. Glossopteris dropped its leaves and stopped growing during the long polar winters.

Below are pictures of leaves and a piece of tree bark. Notice the knots on the tree bark – they are 250 million years old!

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In one area in the Transantarctic Mountains there are > 70 tree stumps that show the size and density of the trees living at the time. Nichole Knepprath, Molly Miller, and co-workers John Isbell and Pete Flaig of University of Wisconsin, Milwaukee found this preserved ancient forest. From the preserved stumps they reconstructed the size and spacing of the trees. Many Parrish has illustrated what the forest looked like based on their reconstruction.

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Relation to the rest of the world: The continents were still together and the central Transantarctic Mountains then, like now, were near the (see world map in FAQ #2). A forest like the one in the Transantarctic Mountains as illustrated above?? Today, no forest could thrive in Antarctica!! This fossil forest demonstrates the magnitude of earth change over the last 280 million years. It also raises questions about how trees can adapt to a light regime of 6 months of dark and 6 months of light!

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What was the environment and life in the Early Triassic?

What it looked like: Climate of the Early Triassic differed from that of the Late Permian. It clearly was drier, and probably was warmer as well. The lakes and swamps that preserved fossil plants and allowed transformation of the organic matter dried up. There is a poor fossil record of plants from the Early Triassic in the Transantarctic Mountains; root structures are the most abundant.

In her reconstruction of the Early Traissic landscape below, Mary Parrish shows the reduction in vegetation inferred to have been caused by lower (or more seasonal) precipitation. Note that most of the sedimentary rocks ( Fremouw Formation) were deposited in and adjacent to braided river channels.

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Evidence in the rock record for what it looked like: Triassic rocks of the Fremouw Foramtion include sandstones with large-scale crossbedding indicating unidirectional flow of the water (e.g., down a river). There are also finer-grained siltstones deposited on the margins of and adjacent to the river channels; these contain mudcracks that indicate the rivers dried up at times. Some of the sandstones contain long burrows. Modern stream-dwelling animals do not dig that deep into river channels. However, deep burrows are made by insects that dig into dry soils and sediments. This suggests that the long burrows might have been made by air-breathing insects during periods when the rivers dried up.

Below: (L)Sandstone deposited in a braided stream that probably nearly dried up during the dry season. (R)Burrows made by arthropods, perhaps air-breathing (vs. aquatic) arthropods.

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Life of the time: Four legged terrestrial animals (tetrapods) were present in the Early Triassic in Antarctica for the first time during the Early Triassic. These include some “mammal-like reptiles” that also occur in South Africa, other reptiles, and large amphibians. These animals and their burrows give the clearest information about the climate conditions. Below at right is the skull of a reptile (Lystrosaurus) and also a burrow of an animal made by a tetrapod of some kind.

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Why were tetrapods able to adapt to life at very high latitude during the Triassic but not during the Permian? We do not know, but it may have been warmer. Alternatively, maybe the groundwater table was lower so that they could spend the long winters in burrows without drowning.

Mary Parrish reconstructs the animals of the Early Triassic as follows:

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What was the environment and life in the Middle Triassic?

What it looked like: During the Middle Triassic, the climate is inferred to have been wetter than in the Early Triassic, with more vegetation and more varied types of plants than existed either in the (cooler) Permian or in the drier Early Triassic. Below is Mary Parrish’s reconstruction.

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Evidence in the rock record for what it looked like: The rocks recording this time are mainly sandstones and siltstones. Like the older rocks in the Transantarctic Mountains, they were deposited in and adjacent to river channels and floodplains. A wetter climate is suggested by the limited occurrence of thin coals (formed from accumulation and transformation of plant material in the absence of oxygen).

Life of the time: By this time there were more tetrapods of various types – reptiles and amphibians. One of the types present was Thrinaxodon – a reptile that also is thought to have lived in a burrow. The reconstruction below is from the Society of Vertebrate Paleontology.

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Relation to the rest of the world: The Transantarctic Mountains were still at polar southern latitudes. In a few million years, in the latest Triassic, the large continent containing today’s southern hemisphere continents (e.g., Antarctica, Australia, South America,and Africa) and India would break apart.

 

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So What?

Three reasons why reconstructing Antarctica’s ancient past is worthwhile!

1. The record in the rocks of the Transantarctic Mountains shows how very different the climate was 240- 280 million years ago from what it is today. This is because then, like now, Antarctica was at the South Pole. However, 260 – 240 million years ago forests and reptiles flourished. This shows how very different the climate was – it shows the magnitude of earth change that is possible.

2. Antarctica’s ancient climate change provides a long-term context for understanding modern climate change.

3. It is fun and exciting to figure out how life and environments have changed through geologic time. In figuring out the past and its life, we as humans see ourselves in the perspective of time. We are the only animals that can do this – so in reconstructing and appreciating the past, we are also celebrating out uniqueness.

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