Pemetaan Geologi 2021 | Episode 2 - Ploting, Sampling, dan Deskripsi

Summary

The video demonstrates various geological field techniques, including determining potential sampling sites, using GPS and compass methods for plotting locations, and sampling rock formations. The process involves distinguishing between different rock types, using specific geological hammers for sedimentary, igneous, and metamorphic rocks, and properly handling samples. The video also discusses the importance of accurate rock descriptions, including identifying textures, compositions, and structural features such as laminations and grain size. Furthermore, the video emphasizes fieldwork practices such as handling weathered rock samples and using HCl for testing carbonates.

Takeaways

• 😀 The first step in geomorphology is to identify potential locations to visit, often aided by consulting with locals in the area.
• 😀 GPS devices can be used for plotting positions on a topographic map by matching the GPS display with the map and marking the location.
• 😀 Another method for plotting positions is the 'Resection' technique, which involves using recognizable landmarks like mountains or rivers, and orienting them on a topographic map with a compass.
• 😀 Geologists use specialized hammers for rock sampling: a chisel-point hammer for sedimentary rocks and a pointed hammer (pico) for igneous and metamorphic rocks.
• 😀 Before sampling, geologists must determine the type of rock present, which involves examining the layers and properties of the rock in the field.
• 😀 Fresh rock samples are preferred, as rocks exposed to weathering and oxidation may have altered appearances compared to their true internal characteristics.
• 😀 Describing rock samples involves noting the type, color, texture, structure, and composition, with care taken to differentiate weathered surfaces from fresh ones.
• 😀 The process of measuring grain size is crucial in fieldwork, using tools like a comparator to avoid incorrect measurements due to uneven breakage.
• 😀 Sorting refers to the variation in grain sizes within the sample, and good sorting means the grains are relatively uniform in size.
• 😀 Cementing material, such as silica or carbonate, is also analyzed, and reactions with substances like HCl can help identify carbonate cement in sedimentary rocks.

Q & A

What is the first step after observing geomorphology in the field?

The first step is to identify potential sites for sampling, often by asking local residents for guidance.

How can GPS be used to plot a location in the field?

To use a GPS for plotting, activate the device, display the topographic map, compare your current position to the map, and plot your location on the map.

What is the Resection method for plotting locations using a compass?

The Resection method involves identifying two recognizable landmarks, measuring their direction with a compass, and drawing lines on the map where these lines intersect to determine your location.

Why is it important to ask locals for help when determining potential sampling sites?

Locals can provide valuable insights about easier access to the potential sampling sites and may know the terrain better, helping to save time and effort.

What is the difference between the two types of geological hammers mentioned in the script?

The chisel point hammer has a flat end and is used for sampling sedimentary rocks, while the pick point hammer has a sharp end and is used for igneous and metamorphic rocks.

How do you ensure that rock samples are fresh and suitable for description?

To ensure freshness, take samples from newly exposed surfaces and avoid weathered or oxidized surfaces, as they may have altered the rock's original properties.

What is the purpose of using hydrochloric acid (HCl) in rock sampling?

HCl is used to test the presence of carbonate minerals in the rock. If the rock reacts with HCl, it contains carbonate cement.

What should be considered when describing the texture of a rock sample in the field?

When describing texture, it's important to observe both the exposed surface and the unweathered interior of the rock, as weathering can alter the appearance.

What does grain sorting in a rock sample indicate?

Grain sorting refers to the uniformity of the grain sizes within a rock. Well-sorted rocks have grains of similar size, while poorly sorted rocks have a wide range of grain sizes.

Why is it important to measure grain size on a fresh, unbroken surface rather than a fractured one?

Measuring grain size on an unbroken surface ensures more accurate results, as fractures can create misleading measurements due to uneven areas.