MFG1904 #07 Geokronologi - 4 Contoh Geokronologi Relatif

Summary

This script discusses the application of relative geological principles, including superposition, original horizontality, and material continuity, through a case study. It explores concepts like angular and disconformities, intrusions, and erosion, emphasizing the importance of data interpretation in geology. The script also touches on faunal succession, using fossils to determine rock ages and illustrating geological time scales.

Takeaways

• 🪨 The discussion centers on applying principles of relative geology, such as superposition and cross-cutting, to geological case studies.
• 🌋 A sequence of rock formations is analyzed, including igneous rocks, sedimentary layers, intrusions, and subsequent lava flows.
• 📏 Superposition and original horizontality are applied to understand how sedimentary layers form from bottom to top.
• 🪓 The concept of cross-cutting is explained, where granite and later intrusions disrupt the existing rock layers.
• 🧗 Deformation and angular unconformities are introduced as a result of tectonic forces, followed by erosion.
• 🌊 Non-conformity and disconformity are highlighted, emphasizing how erosion creates gaps and how sedimentation resumes in marine environments.
• 👷 The final geological layer discussed includes human activity, with man-made structures adding to the geological sequence.
• 🧭 An example of a faulted and deformed geological sequence is explored, where superposition and cross-cutting reveal the relative age of rock layers.
• 🦖 Fossil succession is used to determine the relative ages of rock layers, from trilobites in the Cambrian to later periods like the Ordovician and Silurian.
• ⏳ The discussion concludes with a shift towards absolute dating, moving beyond relative dating principles to more precise geochronological methods.

Q & A

What are the principles of relative geology mentioned in the script?

The script discusses principles such as superposition, original horizontality, material continuity, the principle of cross-cutting relationships, the principle of included fragments, and the principle of faunal succession.

How does the script describe the process of sedimentation in the context of geological study?

The script explains sedimentation as a process where layers of sediments are deposited in a sequence from bottom to top, with the oldest layers at the bottom and the youngest at the top.

What is the significance of the granite intrusion mentioned in the script?

The granite intrusion signifies the principle of cross-cutting relationships, where the granite cuts across the sedimentary layers, indicating that the intrusion event occurred after the sedimentation of those layers.

How does the script explain the concept of angular unconformity?

Angular unconformity is explained as a geological feature where older, tilted rock layers are overlain by younger, horizontal layers, indicating a period of deformation and erosion before new sedimentation occurred.

What does the script imply about the environment during the erosion phase described?

The script suggests that erosion typically occurs on land, as it mentions the formation of a land surface due to erosion, which is then covered by marine sediments.

How does the script relate the presence of fossils to the determination of geological time periods?

The script uses the presence of fossils such as trilobites, corals, and brachiopods to determine the age of the sedimentary layers, as these fossils are indicative of specific geological time periods like the Cambrian, Ordovician, and Silurian.

What is the principle of faunal succession, and how is it applied in the script?

The principle of faunal succession states that different groups of organisms appear and disappear in a definite order in the geological record. The script applies this principle by identifying fossils and correlating them with specific time periods.

How does the script differentiate between disconformity and nonconformity?

The script differentiates between disconformity and nonconformity by describing disconformity as a break in the rock record where both underlying and overlying rocks are parallel, while nonconformity involves a break where the underlying rocks are deformed and the overlying rocks are not.

What does the script suggest about the limitations of geological interpretation?

The script implies that geological interpretation is highly dependent on the available data and that different perspectives or data sets can lead to different interpretations of geological events.

How does the script discuss the impact of human activity on geological processes?

The script mentions human activity as the final process in the geological sequence, indicating that human-made structures and activities such as building and road construction are part of the most recent geological changes.

What is the purpose of the animation mentioned in the script?

The animation is used to illustrate the principles of relative geology, including the sequence of geological events and the relationships between different rock layers and structures.

Outlines

00:00

🪨 Understanding Relative Geology Principles and Case Studies

In this section, the speaker explains the application of relative geological principles, such as original horizontality, superposition, and cross-cutting relationships. They use animations to illustrate the formation and layering of different rock types like granite, lava, and sediment. Various geological processes, including deformation, erosion, and intrusions, are discussed, focusing on how they lead to unconformities and different stratigraphic relationships. The speaker also emphasizes the importance of identifying angular unconformities and nonconformities in geological studies.

05:02

🌋 Cross-Cutting and Intrusive Rock Layers Analysis

This paragraph delves into the analysis of various rock formations and intrusions, such as lava flows and intrusive rocks like R and S. The speaker explains how these layers are cross-cut by other formations, noting the complexities in determining their relative ages due to lack of direct contact. They explore possible interpretations and provide different chronological ordering options, emphasizing the need for careful geological interpretation based on available data. The ambiguity between lava layers R and S is also highlighted as a key issue in this section.

10:02

🦑 Fossil Succession and Geological Dating

In this final section, the focus shifts to the principle of fossil succession and how it aids in determining the relative age of sedimentary layers. The speaker describes different fossils from specific geological periods, such as trilobites from the Cambrian period and corals from the Ordovician and Silurian periods. The use of fossils to establish a chronological sequence of rock layers is highlighted, demonstrating how geologists can date rocks based on the fossils they contain. This leads into a brief introduction to absolute geological dating, setting the stage for future discussions.

Keywords

💡Geologic Relative Principles

These principles are fundamental to understanding the sequence and timing of geological events. In the script, they are used to analyze rock formations and their relationships, such as superposition, original horizontality, and the principle of cross-cutting relationships. The video uses these principles to interpret the chronological order of rock layers and geological features.

💡Superposition

Superposition is a principle stating that in an undisturbed sequence of rocks, the oldest rocks are at the bottom and the youngest are at the top. The script mentions this principle in the context of understanding the order of rock layers, where sedimentation occurs from bottom to top, indicating the relative age of the rocks.

💡Deformation

Deformation in geology refers to the change in shape or size of rocks due to forces acting upon them. The script discusses deformation in the context of rocks being folded or otherwise altered, which can disrupt the original superposition of layers, creating structures like angular unconformities.

💡Erosion

Erosion is the process by which rocks are worn away by natural forces such as wind and water. In the script, erosion is mentioned as a process that can remove rock layers, creating hiatuses or gaps in the geological record, which are important for understanding the timing and sequence of geological events.

💡Intrusion

An intrusion is when magma forces its way into surrounding rock, eventually cooling and solidifying to form igneous rocks like granite. The script uses the example of a granite intrusion cutting through other rock layers, illustrating the principle of cross-cutting relationships, where the intrusion is younger than the rocks it cuts through.

💡Angular Unconformity

An angular unconformity is a structural feature where older, tilted rock layers are overlain by younger, horizontal rock layers. The script describes the formation of an angular unconformity through a sequence of erosion, deposition, and deformation, which provides a record of geological time gaps and changes in the depositional environment.

💡Disconformity

A disconformity is a type of unconformity where there is a break in the geological record with parallel layers above and below. The script mentions disconformity in the context of horizontal layers that are not in direct contact due to erosion or a change in depositional environment.

💡Nonconformity

Nonconformity refers to the contact between sedimentary rocks and underlying igneous or metamorphic rocks with a significant time gap, indicating that there was no deposition during that period. The script describes a nonconformity where sedimentary rocks rest on top of an eroded granite surface, indicating a long period of erosion before new sedimentation occurred.

💡Fossil Succession

Fossil succession is the observation that certain fossils are found in specific rock layers, indicating the relative age of those layers. The script uses the example of trilobites from the Cambrian period to illustrate how the presence of fossils can help determine the age of rock layers, showing the progression of life forms over geological time.

💡Stratigraphy

Stratigraphy is the study of rock layers and their relative positions to understand the geological history of an area. The script discusses various stratigraphic concepts, such as superposition, unconformities, and the use of fossils to determine the age of rock layers, which are crucial for constructing a relative geological timeline.

💡Cross-cutting Relationships

Cross-cutting relationships refer to the principle that any feature, such as a fault or intrusion, that cuts across rock layers must be younger than the layers it cuts. The script uses this principle to determine the relative ages of different rock features, such as when an intrusion cuts through both sedimentary and igneous rocks, indicating its younger age.

Highlights

Introduction to the principles of relative geology and geochronology.

Demonstration of the principles of original horizontality, superposition, and material continuity in sedimentary layers.

Explanation of the principle of cross-cutting, with examples of granite intrusion and lava flow.

Discussion on angular unconformity and how erosion plays a key role in geological formations.

Erosion processes are linked to land formation, with sedimentation resuming in marine environments after submersion.

The significance of human-induced processes, like construction, in the final stages of geological formations.

Step-by-step construction of relative geochronology using cross-cutting relationships and deformation processes.

Erosion results in unconformities, such as disconformity and nonconformity, identified by differences in rock layers.

Importance of deformation and faulting, which occur prior to the erosional hiatus, creating gaps in the geologic record.

Explanation of intrusions that crosscut sedimentary layers and their role in determining the sequence of events.

Differentiating between disconformity and nonconformity based on whether rock layers are horizontal or sedimentary.

Formation of sedimentary layers in superposition, followed by intrusions and fault lines, leading to cross-cutting relationships.

Use of fossil succession to identify the age of rock layers based on the fauna present at different periods.

Introduction to the fauna succession principle, where older fossils are found in lower rock layers and younger fossils in upper layers.

Preview of the transition from relative geochronology to absolute geochronology in upcoming sections.

Transcripts

Hai baik ha kita masuk ke bagian keempat

yaitu bagaimana kita menerapkan prinsip

geologi relatif termasuk prinsip ketidak

selarasan tadi ya di dalam studi kasus

kita kita awali dengan Animasi dulu jadi

di sini ke kita lihat ada beberapa

kondisi ya batuan Jadi kalian lihat di

sini ada batuan beku kemudian batuan

sedimen yang miring kemudian ada intrusi

setelah itu ada batuan yang horizontal

di atas ya nah bagaimana kita menerapkan

prinsip-prinsip tadi geokronologi

relatif ya Jadi pertama kali sedimentasi

superposisi dengan original

horizontality dan material continuity

berlangsung ya dari bawah ke atas

Hai kemudian perhatikan tadi dia

dipotong bagian bawah ini dipotong oleh

batuan beku granit ya Jadi kita

sampaikan ini adalah prinsip proses

cutting

Hai kemudian granit tadi dipotong oleh

intrusi ada Dik disini kemudian ada sel

diatasnya

Hai setelah itu ada intrusi yang kedua

ya memotong baik granit sedimen maupun

yang intrusi presil tadi dan di atas dia

menjadi lava

Hai Nah setelah itu ada sedimen lagi ya

berlanjut disini jadi super terhadap

lava dia bersifat non conformity tapi

setelah itu dia superposisi ya tinggal

Lapisan ini Nah setelah itu kita

deformasi ya Kenapa karena kita akan

membentuk angular unconformity kita

kirimkan ya kemudian kita erosi dan

setelah itu setelah erosi kita mulai

lagi dengan sedimentasi ya di sini

Hai nah kalian lihat tadi kok erosi

harus ada bentuk darat sih ya karena

erosi biasanya terjadi di darat ya Jadi

ini kita bentuk daratan disini Kemudian

untuk sedimentasi ya diasumsikan sedimen

adalah sedimen laut Kenapa Karena Dia

melempar luas ya di sini jadi dia eh

tenggelam lagi oleh air laut dan

mulailah superposisi berikutnya dan

hubungan keduanya ini adalah hubungan

tidak Selaras ya disitu

Nah jadi ini selama manusia sudah datang

ya Jadi ini proses yang terakhir adalah

proses yang dibentuk oleh manusia jadi

ada bangunan ada jalan di sini ya

Nah jadi kalau kita Urutkan ya nomor

satu lapisan paling bawah kemudian ke

superposisi setelah itu ada granit

kemudian intrusi pertama intrusi kedua

setelah itu kemudian sedimen yang di

atas dia mengalami deformasi erosi

kemudian secara superposisi tiga sedimen

paling atas diendapkan sebelum kemudian

manusia datang gitu ya jadi eh menyusun

penanggalan atau geokronologi relatif

kita memang harus menggunakan

prinsip-prinsip tadi berdasarkan data

yang tersedia ini contoh yang lain ya

Jadi kalau kita lihat di sini kita punya

dari asam PT ya perhatikan di sini ada

ada yang miring ada yang horizontal ada

yang memotong ada intrusi ada patahannya

Mari kita larutkan nah ah pertama pasti

superposisi dulu dari a sampai paling

nih kalau kita Urutkan dia pasti sampai

gay jadi ABD

Dede eefg itu adalah superposisi

appalling tua G paling muda ya kemudian

dia harus dideformasi tapi sebelum the

deformasi Dia terkena patahan dulu ya

kemungkinan patah hanya terjadi ketika

batuannya mengalami deformasi termiring

kan ada patahan di sana dan kemudian

kita mengalami erosi ya di sini dan

erosi ini akan membentuk bidang hiatus

yaitu i ya bidang ketidak selarasan

bidang erosi disini ini adalah bidang

ketidak selarasan dan setelah itu ada

sedimentasi tiga lapisan ini jkl ya jadi

jkl Nah setelah itu kelihatannya terjadi

erosi lagi yaitu bidang Erpan amanya

bidang n Tapi sebelum itu perhatikan

disini ada

Hai jkl ini dipotong oleh m jadi setelah

jkl ada intrusi m ya kemudian dia

dipotong ya di erosi Erosi nya di atas l

itu adalah bidang ketidak selarasan n

kemudian di atas m intrusi m tadi itu

bidang tidaklah rasanya Oh kenapa harus

dibedakan karena berbeda ya Jadi kalau

Nini bidang ketidak selarasan perhatikan

sama-sama sedimen dengan di atasnya ya

sama-sama horizontal berarti dia

disconformity sementara kalau itu adalah

nonconformity maka harus dibedakan

Hai setelah itu ada sedimentasi ppo

Hai Esna Nti dulu karena ini batuan beku

lava ya Nah setelah PQ ternyata ada

intrusi er er ini memotong semuanya dari

sampai Oh sampai q ya dia dipotong Semua

Hai nah ini kelihatan biaya ini membakar

sekitar terbakar berarti setelah PQ dia

cross-cutting er ya F datang setelah q&r

lebih mudah karena dia memotong q ya Nah

setelah itu adalah faez nah vs ini Dia

memotong Q tapi tidak memotong

theartinya dia memang lava ya setelah es

baru kemudian ada teh nah ini biasanya

ya kalau kita lihat orang yang jeli akan

melihat apa sih hubungan er dengan es

karena sama-sama batuan beku r&m

sama-sama beton beku hubungannya jelas

ya potong memotong er memotong MPASI er

lebih muda m lebih tua tapi r&s mereka

tidak saling ketemu Nah kenapa

Hai nah ini mesti ada problem di sini

jadi kita sebetulnya bisa saja setelah

pqs dulu baru their itu boleh kenapa

karena r&s tidak bisa ditentukan jadi

kedua jawaban itu bisa dianggap benar ya

jadi pqs er baru Teh atau pqsp er itu

juga boleh ya jadi di ujung itu kalian

punya tiga opsi ya jadi setelah setelah

erosi Enda no ini ya kalian bisa p q s

RT itu opsi pertama opsi kedua pqrst

bisa juga PQ STR ya Jadi terserah karena

er es ini tidak bertemu sehingga

hubungan er dengan teh juga tidak

diketahui yah mana yang duluan ya apakah

teh dulu baru er atau air dulu baru teh

Hai nah Perhatikan ya ini keterbatasan

data di dalam geologi itu sangat

dipengaruhi oleh interpretasi ya geologi

sangat dipengaruhi oleh data Perhatikan

Kalau kalian berada di sebelah Sisi sini

ya yang menghadap kita ini dan

bandingkan kalau kalian berada disisi

sebelah kanan maka apa yang terjadi

Kalian tidak akan punya yg.di Danger OST

II sebagai angular unconformity disini

itu menjadi disconformity

hai kenapa Karena antara g&j itu dia

sama-sama horizontal kita hilang m&r ya

di sini ha patahan juga enggak ada ya

jadi disini kita bisa berurutan saja

efghj erosi i j k l erosi n p q terus

datang es baru Teh jadi lebih simpel ya

tetapi disisi lain semakin banyak Data

semakin rumit apa namanya geokronologi

yang kalian susun diagramnya seperti ini

jadi perhatikan di sini ada sampai G

superposisi kemudian dia default

dideformasi dimiringkan dipatahkan ada

erosi jkl diendapkan ya kemudian ada

intrusi m ya dia mengalami erosi lagi

dan kemudian ada p&q diatasnya kemudian

ya di sini ya Ada intrusi

Hai sementara dia juga erosi Kenapa

karena ada lava lava di darat ya sip di

asumsikan di darat ya jadi Setelah

eslava datang habis dia mengalami genang

laut bagi yang laut menggenangi kemudian

teh dendamkan ya jadi inilah

geokronologi untuk soal kita ini

Hai Yana cukup menarik ya itu memang

perlu latihan Yah nanti kita akan

memberikan beberapa soal untuk latihan

ya kita akan masuk di penanggalan mutlak

dan waktu praktek waktu paruh jadi kita

akan meninggalkan penanggalan relatif

Tapi sebelum ke sini ya di sini Saya

ingin ada Menunjukkan ada satu animasi

terkait dengan prinsip apa namanya fauna

sukses yzmate ya Nah ini contoh yang

jadi kalau kita lihat di sini ada fosil

disini ini adalah fosil prologue

trilobita yang hidup di zaman kambrium

ya kira-kira di 500 juta tahun yang lalu

Nah kalau mereka tertutup sedimen ya

maka sedimen yang ini yang menutup

mereka pasti umurnya juga kambrium ya

Kenapa karena merangkapkan mereka pada

saat hidup Nah setelah itu ya di sini

kita akan melihat ya

di sini ada kerang ya dia sebut sebagai

berhasil voda kemudian di sini ada

rantai Coral ya ini ciri khas kehidupan

pada 450000000 tahun yang lalu atau pada

zaman ordovisium yah disitu nah kalau

mereka ditutup sedimen pasti sedimen

tersebut umurnya juga ordovisium Nah

setelah itu Ya kita memasuki periode

jaman silur disini Dimana ini seperti

ada Coral ya kemudian disini ini Nenek

moyangnya cumi-cumi ya di sini kemudian

mereka juga terkubur oleh sedimen nah

sedimen ini pasti juga berumur silur ya

Nah kalau datang geologis dia sukanya

mempan lupa lu aja gitu ya mencari fosil

maka ketika dia menemukan disini

trilobita dia tahu bahwa batuan di sini

pasti adalah kambrium ya kemudian ketika

dia menggali lagi ya

Hai lapisan atasnya ketemu fosil yang

seperti kerang ini yaitu platys tropia

ini ciri khas kerang pada zaman er

namanya ordovisium ya jadi dia tahu

kemudian Oh ini ordovisium begitu ya Dia

kemudian ketemu juga di sini apa

cumi-cumi tadi ya Endless Eras nah

kemudian di ketemu juga streptelasma ini

Coral ya di sini

Hai Nah kemudian ada jasmok sini

trilobita yang lebih muda dari yang umur

kambrium tadi ya Nah jadi dia

menyimpulkan oase ketemu batuan

450000000 tahun ini Kak ordovisium ah

yang di atas apa ya dia cari lagi Nah

ketemu dia seperti Coral holyshit ya ini

kemudian dia ketemu lagi kerang atripla

di sini ya Nah itu adalah ciri-ciri

silur jadi ini adalah suksesi fauna

superposisi fauna paling tua di bawah

fauna yang lebih muda ada di atas ya oke

dengan demikian kita akhiri bagian

geokronologi relatif kita akan masuk di

geokronologi Absolut atau mutlak ya