PERPETAAN GEOLOGI Sampling, Penomoran & Plotting

8/10/2019 PERPETAAN GEOLOGI Sampling, Penomoran & Plotting

1/19

1

Perpetaan Geologi(Tahap Pemetaan Geologi : Sampling, Penomoran & Plotting)

Oleh :

Irvani

Universitas Bangka Belitung Jurusan Teknik Pertambangan

Referensi :

Sukandarrumidi, 2011. Pemetaan Geolog : Penuntun Praktis Untuk

Geologist Pemula. UGM Press, Yogyakarta.

Coe, A.L., Argles, T.W., Rothery, D.A. And Spicer, R.A., 2010.

Geological Field Techniques, John Wiley & Sons, Inc., UK.

Bates, R.L. and Jackson, J.A., 1987. Glossary Geology. 3th Edition.

American Geological Institute Elexandria, Virginia.

Van Der Pluijm, B. A. and Marshak, S. 2004. Earth Structure. 2nd

Edition. W. W. Norton & Company, Inc., USA.

Dll



2/19

2

Materi (Pokok Bahasan)I Pendahuluan (P.1)

II Pengenalan Kartografi (P.2)

III Jenis Peta (P.3)

Peta situasi, Peta topografi

& Peta tematik

IV Peralatan Pemetaan Geologi (P.4)

a. Macam dan jenis alat/bahan

b. Teknik pemakaian alat

V Metode Pemetaan Geologi (P.5)

a. Orientasi lapangan

b. Lintasan kompas

c. Lintasan kompas dan pita ukur

VI Tahap Pemetaan Geologi (P.6-13)

a. Persiapan (P.6)

b. Pengambilan data lapangan (P.7-9)

- Petrologi dan mineralogi (P.7)

- Stratigrafi batuan

- Struktur geologi (P.8)

- Sampling dan penomoran (P.9)

- Plotting data

c. Analisis laboratorium (P.10)

d. Penyajian peta (P.11-13)

- Rekonstruksi struktur geologi

- Satuan batuan- Kolom stratigrafi dan korelasi

- Sayatan geologi

- Penyajian peta & pelaporan

VII Keselamatan Kerja dan Etika Geologi/Etika Lapangan (P.14)


I Sampling & Penomoran/Labelling



3/19

3

What are the objectives and therefore how much and what

type of sample is required?

Is the sample representative?

What does the sampling resolution need to be?

Is the sample fresh and unweathered? (Unless of course the

study is about weathering.)

Does the sample need to be orientated?

Do I have the appropriate tools for the job?

Have I recorded exactly where the sample is from?

Is there a record of how the samples were collected, forinstance the tools used (to eliminate possible contamination)

and stratigraphic precision?

What are the conservation issues? Am I taking only what is

necessary, have I got the necessary permission and have I

considered the visual impact on the environment?

The key points to consider when taking samples

Selecting and labelling samples

1. Samples for thin - sections

A sample of about 10 cm thick 5 cm 5 cm is

usually sufficient for producing one or more thin -

sections provided the rock is not too coarse -

grained.

In deformed rocks it is useful to cut two or even three

thin - sections at right angles to each other, so a

slightly larger sample may be required.


4/19

4

2. Orientated samples

Younging direction and approximately orientated

samples

For sedimentary rocks the younging direction is often required

and is usually recorded on the face perpendicular to bedding

with an arrow. If the bedding orientation is not clear this may

also need to be recorded so that the section can be cut

perpendicular to the bedding. For igneous rocks the younging

direction may need to be recorded for cumulates, pyroclastic

rocks, and igneous rocks containing flow features and

vesicles. For samples from metamorphic rocks it is also often

necessary to record the top surface because of the need to

obtain thin - sections in a particular orientation relative to the

structural fabric(s).

Precisely orientated samples

This includes samples for palaeomagnetism studies and

some samples for more precise metamorphic and structural

analysis.

Using a compass -clinometer mark the rock exactly with theline of strike, direction of dip and either the way up or the top.

Take note of the dip and strike.

Orientated samples can also be obtained with a drill used for

palaeomagnetic studies.


5/19

5

3. Samples for geochemical analysis

A 200 g sample is usually sufficient for a range of

major and minor element, trace element and isotopic

analyses, except for very coarse - grained or

heterogeneous rocks, where about 1 kg may berequired.

Particular care needs to be taken to ensure that the

sample is fresh.

Some caution may also need to be exercised if the

sample is being analysed for metal isotopes in order

to avoid contamination from metal chisels and

hammers.


6/19

6

4. Samples for mineral extraction

The amount of sample that needs to be collected for

mineral analysis depends on the minerals to be

extracted and the composition of the rock. For

heavy minerals such as zircon that are present only

in low abundance, 1 2 kg of rock may be required.

For volcanic glass and feldspars for 40 Ar 39 Ar

and K Ar dating, generally at least 1 kg of rock is

required. For pyroclastic and sedimentary rocks it is

particularly important to collect from the base of the

bed as the coarser grained minerals that are more

easily picked out will be most abundant there.

5. Samples for fossils

Samples for megafossil analysis

Megafossil samples and their supporting rock

material tend to be large. They are best wrapped in

paper. If they are fragile or the rock needs to dry outslowly, wrap them in cling fi lm/plastic food wrap and

then paper. They commonly have commercial value

and therefore special permission may be needed to

remove and/ or ship them out of the locality or

country where they were collected.


7/19

7

Samples for microfossil analysis

The size of samples for microfossil analysis depends on the

likely abundance of fossils within the sample. For an average

abundance of foraminifers 200 g should be suffi cient; for

nanofossils anddiatoms a small 10 g sample is ample. For

palynology samples of 0.5 1 kg are required.

Samples for molecular fossilsVery small samples are required for molecular fossils but the

sample needs to be large enough (2 5 g) to avoidcontamination. The samples should be packaged in metal foil

or glass or polythene bags of known composition. In addition

care needs to be taken not to cross - contaminate samples bycarefully cleaning the sampling instruments between each

sample.

6. Sampling for regional studies

Regional and low - resolution studies require samples

that are representative of the whole area. In addition

samples should be collected from units that need

laboratory analysis because their composition is

enigmatic.

Collecting a sample from each of the mainlithostratigraphic units is probably a good place to start.

Other samples that are worth considering are a set to test

for compositional variation across an igneous body,

representative fossils, tectonic contacts, representative

samples from metamorphic zones and representative

samples from a set of dykes.


8/19

8

7. High - resolution sample sets

High - resolution sampling requires great care and

patience. A logical means of labelling the samples/sample

positions will need to be devised. In any situation where

closely spaced samples are required it is best to mark the

exposure clearly first with a scale (Figure 13.2 ) and, if

irregularly spaced samples are required, mark where the

samples will be taken from. The exposure can then be

photographed as a permanent record before extracting

the samples.


9/19

9

Labelling samples and their packaging

For regional studies the locality number or an

abbreviation of the name and then sample number at

that locality is often used, but an alternative way is to

use the national grid square and then a sample

number

On the sample bag or outside of the packing

material itself it is useful to record the following as

appropriate:

sample number;

cross reference to fi eld notebook page and/or datecollected;

location;

whether or not the sample is orientated;

rock type;

associated samples.


10/19

10

Practical advice

1. Packing and marking materials

Cling film/shrink wrap: This is very useful for fragile

specimens such as fossils and mudstones. As well as the

obvious advantage of helping to hold the specimen together

the fi lm also retains the moisture in the sample, allowing it to

be dried out under controlled conditions.

Paper: This is useful to help protect delicate specimens and

for packing. It should not be used in direct contact with the

rocks if the samples are also to be used for geochemicalanalysis, particularly organic carbon analyses.

Polythene sample bags: It is good practice to put each

sample into a new bag to avoid cross - contamination. Most

Polythene sample bags: It is good practice to put each

sample into a new bag to avoid cross - contamination. Most

bags come with write - on labels available from a variety of

suppliers. Check for rocks with sharp edges because they tend

to split the bag. If the rock has sharp edges either round them

by gently tapping them using the square end of your hammer orcarefully place the rock in a bag and wrap over this with paper.

Aluminium foil: This is useful for holding together very fragile

specimens such as mudstones. Wrap the foil around the

specimen immediately after extraction in a systematic manner

so that you are able to remove it sequentially in the laboratory.

Aluminium foil is best avoided if the samples will be stored for

any length of time as salts from the rock tend to corrode the

foil.


11/19

11

Glue:A strong glue suitable for metal or wood can be used

for sticking samples together. If you need to protect fragile

specimens such as shelly material within mudstone or

vertebrate teeth before shipping or transporting them back,

soak the sample for several hours in a 50:50 mixture of PVA

glue and water. Then allow the specimen to dry.

Marker pens: Permanent marker pens provide a distinct

label. Note that wet, dusty or fi ne - grained dark coloured

rocks can be diffi cult to mark. It is worth carrying several

markers into the fi eld because they tend to wear out quickly.

2. Extraction of samples

Different rocks break in different ways, but skill and

experience

enable the geologist to obtain the best samples.

Look for somewhere that is safe and easy to access and

where there is a piece jutting out that might easily be

removed.

You should also consider the impact of extraction on the

environment and preferably choose a location that will not

be obvious.


12/19

12

II Plotting

Information to record on field maps


13/19

13

Mapping techniques

Traverse mapping

(a) A linear traverse mapped in the Alaknanda

valley, northwest India. In this complex orogenic

zone, the focus of this project was on gathering

structural data and collecting samples for

metamorphic and geochemical analysis. (b)

Correcting a closed compass traverse for minor

bearing errors. When the traverse was plotted

using the bearings and distances in the notebook

(red lines), the last leg (e to a) did not join up

exactly to the origin (Point A), by a closure error

of 43 m. The traverse was corrected by adjusting

each plotted point (a to e) parallel to the closure

error (green lines) by an amount proportional to

the cumulative distance travelled to reach that

point. So, for point d, correction = 43

(780/1435) = 23.4 m. The result is the corrected

closed traverse ABCDE (dashed blue lines).

Foto 1. Kenampakan lipatan antiklin dan sinklin pada litologibatulempung berseling batugamping pada daerah Salo Mapela,

difoto ke arah barat daya N210E disekitar stasiun 56


14/19

14

http://dearthurjr.blogspot.com/2014/04/struktur-geologi-daerah-tompo-kecamatan_20.html

PETA STASIUN PENGAMATAN

PETA STRUKTUR GEOLOGI DAERAH PENELITIAN


15/19

15

Gambar 4 Mekanisme pembentukan struktur geologi pada daerah penelitian

Gambar 2. Kenampakan foto udara yang memperlihatkan sesar geser (merah)daerah penelitian. Citra Google earth akuisisi 2013


16/19

16

Foto 4. Kenampakan sesar minor pada litologi batugampingberseling batulempung pada daerah Salo Mapela, disekitar stasiun 64

Foto 2 Bentuk kekar tak sistematik pada litologi batulempung karbonatpada stasiun 30 di foto relatif ke arah barat laut


17/19

17

Foto 5. Kenampakan bidang sesar pada litologi tufa halus disekitar stasiun 63

Tabel 1. Hasil pengukuran

kekar pada batulempung

stasiun 30


18/19

18

Tabel 2 Data frekuensi pengukuran kekar pada litologi batugamping

pada desa Kalompie stasiun 30.

Gambar 1 Hasil pengukuran data kekar pada litologi batulempungstasiun 30 menggunakan diagram roset


19/19

Terima Kasih


PERPETAAN GEOLOGI Sampling, Penomoran & Plotting

Documents