Geological processes
Assignment 3
Paris hanan
12621886
Excursion group 1 (21.4.2018)
Long reef point-
1) Give the geographical coordinates of Long Reef Point: (2 marks)
33°44'30.9"S 151°19'01.2"E
2) How was Long Reef Point formed? (3 marks)
The point was formed when the surrounding sandstone cliffs were eroded. The hard bedrock of the point meant that as the soft sandstone eroded around it, the point remained.
3) How was the rock platform formed? (3 marks)
The rock platform is made up of Bald hill claystone which is comprised of thin layers that are to erosion. Weathering through wave action at high tide continually erodes the claystone and has exposed a large platform of shale. This can be seen clearly in figure 1.
4) What type of rocks make up the rock platform? (1 mark)
Shale and bald hill claystone
Figure 1. stratification of the rock platform
5) What is an anticline? (1 mark)
An arc shaped upward fold of stratified rock that faces away from the earth
6) What processes produced the anticline/s at Long Reef Point? (2 marks)
Pressure from continental movement caused the upward folding
7) Describe some of the cliff faces that you observed: what stratigraphic layers could you determine from the facies? (2 marks)
The cliff faces showed layers of purple, bald hill and grey claystone, with plant fossils present in the grey claystone. Hawkesbury sandstone could also be seen in an upper layer of the cliff and Narabeen shale was arranged in layers underneath.
8) What do you understand by Hawkesbury Sandstone? (2 marks)
Hawkesbury sandstone is a mid-Triassic sedimentary rock made up of quartz, silicones, feldspar, clays and iron compounds. It forms the bedrock of long reef point and most of the Sydney region.
9) What do you understand by Bald Hill Claystone? (2 marks)
Bald hill claystone is an early Triassic sedimentary rock made up of thin erodible layers. It is formed through the weathering of volcanic materials.
10) What does grain size in the sedimentary rocks tell you about the conditions under which they were formed? (3 marks)
The grain size of the sedimentary rock shows the variable cooling rates of magma and the water flow and activity of the area. For example, small grain size is associated with slow moving waters, where these particles can precipitate.
11) Describe the faults you observed. What likely caused these faults? (2 marks)
As seen in figure 2. the faults were small, around 1m, and almost geometric in pattern. This is likely a form of mechanical weathering however it could also be caused by humans as the area was mined for copper in the past.
Figure 2. Fault lines
12) What fossilized plant materials did you observe in the rocks at the rock fall? (2 mark)
The fossil found was identified as a plant fossil, we believe it was most likely Phyllotheca or seed-fern Dicroidium from the Triassic period.
13) What do these fossils tell you about the geological history of the region and Long Reef? (2 mark)
Fossils show that during the Triassic period this site was covered with vegetation.
14) Describe Tafonis or other forms of rock weathering you observed? (2 marks)
Tafonis are concave or bowl shaped cavities or indentations in the rock face. It is also known as Honeycomb weathering and was most notable on the boulders at the base of the cliff face. These can be seen in figure 3.
15) What type of weathering produced these features? (2 marks)
Honeycomb weathering caused these features in the rock and is due to the mechanical weathering that occurs when salt crystalizes within the pore spaces of the rock.
Figure 3. Tafonis caused by honeycomb weathering
16) What is a kitchen midden? (1 mark)
A midden is a prehistoric mound of refuse material, such as bones and shells.
17) What did you notice about the size and condition of the shell fragments at the kitchen midden? (1 mark)
The shell fragments found in this area were weathered, and were a mix of large and smaller fragments.
18) Describe the dolomite dike you observed. What produced this dike? (2 marks)
This dike was produced when the fissure in the sedimentary rock was filled with volcanic igneous rock known as ‘dolerite’. The dike is opaline, confirming the presence of high, volcanic temperatures.
19) Explain the raised basalt ridged that traverse the rock platform: (2 marks)
The ridge is raised as the basalt is an igneous rock making it very slow to erode, so the material around it has eroded faster than it leaving a raised area where the basalt seam runs through the rock.
20) What do you think has caused the tessellation apparent on the rock platform? (2 marks)
Tessellation is often caused by the heating and cooling of the rock as with the temperature fluctuations the rock expands and contracts causing cracks to form. These cracks are then further eroded by the salt, sand and water to form a more drastic pattern.
21) Describe the honeycomb weathering of the rock face at the south-side of the point: (2 marks)
The honeycomb weathering on the south side is extremely evident with the whole area showing signs of rigidness and in some locations Tafonis.
22) How were the Tuffaceous blocks in the cliff face formed? (2 marks)
Tuffaceous blocks are formed when ash is deposited onto the rock and compressed, mostly due to volcanic activity.
23) Describe the iron-filled fossilized plant materials you have seen? How were these fossils formed? (2 marks)
These fossilized plants were formed when they were covered in organic matter or sediments. The organic matter of the plant decomposes and is replaced with iron and other minerals.
24) Figure 4 in the field guide is a ‘rough’ topographic map of the Long Reef Headland. Construct a topographic profile along the line X indicated in the map. (5 marks)
Topographic profile of long reef headland:
Part 2: DEE WHY LAGOON AND BEACH
1) What three ecological communities occur at Dee Why Wildlife Reserve? (2 marks)
The three ecological communities at Dee Why wildlife reserve are 1) coastal saltmarsh 2) estuarine swamp forest complex and 3) freshwater wetlands
2) What rivers feed the Lagoon? (2 marks)
the lagoon is fed by dee why creek however ocean water and storm water runoff also feed the system.
3) Draw schematic diagrams of the Dee Why Deltas. (2 marks)
4) How do you classify the Dee Why deltas? (2 marks)
The delta is classified as a fluvial-Bayhead delta.
5) What type of sedimentary materials would you expect to find at the opening of the deltas, at the opening of the lagoon to the sea, at the front of the baymouth bar (seaward side) and at the back of the bar (lagoon side)? (4 marks)
At the opening of the delta you would expect to find the larger, more coarse sediments, the finer sediments are found in areas where the water is more stow flowing. The opening of the lagoon you would expect to find debris such as plant matter and finer sediments. At the front of the baymouth bar most of the sediment we’d expect to find would be sand however other debris may also collect here. The back of the baymouth bar or the lagoon side you would expect t to find very fine sediments such as silts.
6) Describe the different components of the beach (berm, swash, etc.) and the different zones of tidal influence you saw at Long Reef or Dee Why beaches? (2 marks)
Berm- occurs parallel to the ocean and is the area where coarse materials are deposited, this forms a barrier between the lagoon and beach.
Swash- occurs in the center of the beach and is the area with the most sediment movement.
7) Design a sampling plan to determine sedimentation patterns along the beach. Where would you collect soil samples and how many would you collect? (2 marks)
To determine the sediment patterns along the beach sediment samples should be taken from the length on the beach, analysed and compared. Samples should be taken from the length on the beach as well as areas within the lagoon and delta. A minimum of three samples should be taken at each site.
8) Using available information on East Australian currents, develop a scenario to explain the geological development of the bar and lagoon. (2 marks)
The East Australian current or EAC runs parallel to Dee Why causing longshore drift. This motion pulls the sand down the beach, this sand builds up along the shore. In this instance the sand the EAC brings down the beach has formed a berm, damming the creek and in turn creating the lagoon.
9) Figure 6 in your field guide is a topographic map of the Sydney coast around Warringah. Create a topographic profile of the catchment around Dee Why Lagoon (represented by the line ‘Y’ in the figure). (5 marks)
Topographic profile of the dee why lagoon catchment:
10) How would you apply digital media to support the Warringah Council in their conservations efforts? (2 marks)
Through a digital ad campaign aimed at locals and other interested peoples that spreads information about the conservation program and how they can help the council in their efforts.