1000 level geology graphic assignment (Earth History-Atlantic Canada Perspective)

Alfred Wegener's idea of continental drift was based upon several types of evidence, including types of rocks and the presence of certain fossil species. In this assignment we are going to look at some of this evidence and try to answer some questions about an early supercontinent called Gondwana. Gondwana was the name given to the large southern landmass that existed from around 500 to 180 Ma (Gondwana collided with Laurasia to form Pangaea, and then later broke away).

We are going to look at some of the rocks from regions thought to have been portions of the Gondwana. We will correlate these rock columns and see what we can discover about the environments of these, now widely separated regions, during the Paleozoic and Mesozoic.

Index Fossils Certain fossils species are always the same age wherever they may occur; these "index fossils" are usually common, widely distributed species with a short (in geological terms) span of time. Rocks containing these fossils, no matter where they are found, can be assume to have been deposited in the same short time period and under somewhat similar conditions. Index fossils can he used to match rocks of the same age, this is called correlation.

Stratigraphic Columns A stratigraphic column is a visual representation of the relative age relationship of the rocks in a particular location - with the oldest on the bottom and youngest at the top.

You are given four stratigraphic columns (Figure 1) from four different areas: Antarctica, India, Brazil and South Africa. The location of these columns are marked on the map of the world (Figure 2). Notice that the columns are filled with different patterns, each pattern represents a different type of rock (see legend).

Let's look at the column for Brazil.

At the base is a pattern that the legend tells us represents a marine sandstone. This is separated from the overlaying (younger) tillite by a wavy line, which represents an unconformity (a period where some rocks are missing). Above the tillite are some coal and shale layers, then another unconformity, fluvial sandstone, another unconformity, and finally a layer of basaltic lava.

Notice that to the right of the column are some strange symbols. These indicate the type of index fossil found in the that particular type of rock at that location (see the legend again). For example, the marine sandstone at the base contains brachiopods.

Make sure you understand how to read the columns and legend.

To the left of the stratigraphic columns is a time scale with some boundaries drawn on it. Notice that the boundaries in the column do not always match the period divisions sa you have learned them. That is because this column reflects how well we are able to constrain the ages of the rocks. For example, the Early Triassic and then the Middle - Late Triassic. There is also a large division that covers the Late Carboniferous and Permian.

Geology 1203 Earth history

Assignment - Gondwana

What to do

Because a stratigraphic column by itself just indicates the relative ages of the rocks you are going to use some index fossils to determine the age of some of the sedimentary rocks. All rocks containing the same fossils are of the same age even if they are located on different areas (even different continents).

Step 1: Look at stratigraphic columns in Figure 1. To the left of the columns is a time scale with some boundaries drawn on it. Shade each of these divisions with a different colour (you should have 6 colours in total) - you can ignore the Pre-Devonian.

Step 2: Early in the twentieth century Robert Scott made a surprising discovery while exploring the continent of Antarctica. His team discovered beautifully preserved fossil plants in coal. Coal, that forms in tropical or temperate regions, buried beneath glacial ice. These fossils have been identified as Glossopteris, a Permian age plant found in coal seams.

Use the same colour you used for the Permian period to shade the beds in the columns in which Glossopteris fossils have been found (as indicated by the symbol for Glossopteris).

Label the locations on the map (Figure 2) where Glossopteris has been found with the letter G.

Step 3: Fossilized pollen found in tillites indicates that they are either Late Carboniferous or Early Permian in age. This overlaps the age of the Glossopteris fossils and so they are lumped together. Use the same colour that you used for Glossopteris to shade the tillites in the stratigraphic columns.

Tillites are formed from sediment deposited by a glacier and so indicate that an area has been buried beneath ice.

Label the locations on the map (Figure 2) where tillites has been found with the letter T.

Step 4: In 1967 a jaw fragment belonging to an ancient amphibian was found not far from where Scott's party found the Glossopteris fossils. Later in 1969 bones and teeth were found in an ancient stream channel . A paleontologist identified the fossils as belonging to Lystrosaurus, a reptile that existed during the Early Triassic. Fossils of this land reptile had been found previously in India and South Africa. Lystrosaurus was not adapted for swimming long distances.

Shade those sediments in the stratigraphic columns that contain Lystrosaurus fossils with the same colour you used for the Triassic period on the time column

Label the locations on the map (Figure 2) where Lystrosuarus has been found with the letter L.

Lystrosaurus Ÿ its name means “shovel lizard” Ÿ1 metre long plant eater Ÿ instead of teeth it had two tusk-like fangs Ÿ it lived in herds near lakes and swamps

Glossopteris Ÿan extinct seed fern Ÿ it grew about 4 metres tall

Pollen Ÿpowder of seed plants Ÿhave a protective coat

Step 5: Shells of Devonian age, such as brachipods, have been found in marine sandstones of Brazil, South Africa, and Antarctica. Shade the sections of the stratigraphic columns in which shells have been found with the colour you used for the Devonian period of the time column

Label the locations on the map (Figure 2) where shells have been found with the letter B.

Step 6: Dicrodium is a plant fossil that is restricted to the Late Triassic. Shade those sections of the stratigraphic columns indicated by the Dicrodium symbol with the colour you used for the Triassic in the time column.

Label the locations on the map (Figure 2) where Dicrodium have been found with the letter D.

Step 7: Basaltic rocks found in Brazil and India are of Cretaceous age. Those in South Africa and Antarctica are Jurassic age. Shade the basalts with the colour you used for the Cretaceous and Jurassic periods in the time column.

Label the locations on the map (Figure 2) where basaltic rocks are found with the letter R.

Step 8: Now having filled in the stratigraphic columns correlate the different rocks between them. Draw lines joining the rocks of different ages (based upon your colours) between the columns and extend the line to the time column on the left. The line dividing the basement rocks (pre-Devonian age) has already been done for you. The boundary between the Permian and Early Triassic layers has also been done.

Use your correlated stratigraphic columns in Figure 1, and the annotated map in Figure 2 to answer the following questions. You will have to refer to the information provided in the preamble and other areas of the assignment text to help you.

What to submit?

Submit the answers to the questions, your correlated stratigraphic column sheet and the annotated map sheet. Put some effort into the correlation - if it is too messy and I cannot read it I will give you a zero for that portion of the assignment.

Remember it must be your sheet - if I get two identical submissions I will give a zero to both people.

Brachiopod Ÿa type of bivalve with shells made of calcite Ÿ lived on the ocean floor

Dicroidium Ÿextinct seed fern Ÿmay have reached 10 metres in height

Questions

1. Look at the stratigraphic column for South Africa. a) Which rock layer is the oldest? b) Which rock layer is the youngest (most recent)?

2. During what age were glaciers present in all four areas?

3. Three areas, as indicated by the columns were once covered by an ocean. a) which three areas? b) when (what age) were they covered?

4. During what age did all four areas have extensive swamps?

5. Based upon the plant and animal fossils what is the most recent time that Gondwana could have been a single continent?

6. When did extensive volcanic activity first occur on Gondwana?

Lystrosaurus

brachipod

Dicrodium

Glossopteris

Legend for Stratigraphic Columns (Figure 1)

Use the patterns below to identify the types of rocks in the columns. The symbols indicate the type of fossil present in specific age rocks and regions.

Basaltic Lava -formed from molten rocks that erupted from volcanoes or rifts in the crust. It is dark, fine-grained and may have round holes formed from trapped gases.

Marine sandstone - formed from sediments deposited in an ocean. It is predominatley quartz with grains about the same size (well sorted). Any fossils will usually be of marine plants or animals.

Fluvial sandstone - formed form sediments deposited in a stream or river. It may have minerals other than quartz and vary in size (poorly sorted). Any fossils will be of plants or animals from on land or fresh water.

Shale - a fine-grained rock of clay or mud with layers.

Tillite - a rock formed from sediment deposited by a glacier. These rocks of angular grains of varying sizes and minerals

Coal - formed form the remains of plants that grew in swamps. It may have fossilized leaves and plants stems

unconformity

Devonian

Pre-Devonian

Late Carboniferous

Pemian

Early Triassic

Middle -Late Triassic

Jurassic

Cretaceous

TIME SCALE

India

Antarctica

South Africa

Brazil

Figure 1 Stratigraphic Columns NAME:

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