Chapter 15. History of the Earth
Recommended Article : 【Earth Science】 Table of Contents for Earth Science
3. Geological Structure of the Korean Peninsula
1. Record of Earth’s History
⑴ Study Subjects of Geology
⑵ Geological Structures and Features
① Information Obtained from the Properties and Distribution of Rocks
② Information Obtained from the Structural Relationships of Rocks
③ Others
○ Trace Fossils : Traces formed by sand shaking in water currents
○ Raindrop Impressions : Marks left by raindrops falling into mud
○ Desiccation Cracks : Patterns formed when mud in wetlands dries and cracks
⑶ Depositional Processes and Features
① Law of Superposition : Investigating the positions of layers in different regions
② Principle of Superposition : The principle that upper layers are younger than lower layers
○ Proposed by N. Steno (1638 ~ 1687)
⑷ Fossils and Depositional Features
① Irreversibility of Evolution
② Index Fossils : Fossils representing certain geological eras
○ Criteria : Wide distribution, short species survival period, abundant fossils
③ Indicator Fossils : Fossils indicating the depositional environment of rock layers
○ Criteria : Narrow distribution, long species survival period, abundant fossils
○ Coral Fossils : Indicate shallow and warm seas
○ Fern Fossils : Indicate warm and humid regions
⑸ Earth’s Age
① Geological Clock : Method to calculate Earth’s time
② Radiometric Clock : Using decay of radioactive isotopes
○ Carbon Dating Method
○ Estimates age by measuring relative ratio of 12C to 14C
○ Half-life of 14C is 5730 years, decaying to 14N through beta decay
○ Applications
Figure. 1. Oxygen Isotope Ratio (18O/16O) and Atmospheric CO2 Concentration Analyzed from Antarctic Ice Cores
○ Principle 1. High CO2 concentration correlates with high temperature : B has higher temperature than A
○ Principle 2. Oxygen isotope ratio in ice cores is higher at higher temperatures
○ Principle 3. Oxygen isotope ratio in marine organisms is higher at lower temperatures
2. Geological Eras
⑴ Criteria for Dividing Geological Eras
① Rapid Changes in the Biosphere
② Major Geological Transformations
⑵ Names of Geological Eras
① “Da” : Names based on biological changes
② “Gi” : Names derived from ancient geographical names, ethnic groups, etc.
⑶ Cambrian Era (Precambrian Era)
① Cryogenian Period
⑷ Paleozoic Era : 580 million years ago ~ 225 million years ago
① Characteristics of the Paleozoic Era
○ Standard Index Fossils : Trilobites, Brachiopods, Arthropods, Foraminifera (Radiolarians)
○ Terrestrial Plants First Appear in the Paleozoic Era
○ Mnemonic : Kam where it’s only desolate , Seoktan Peace
② Cambrian Period : First appearance of Brachiopods and Trilobites
○ Trilobites : Flourished throughout the Paleozoic Era
③ Ordovician Period : First appearance of Arthropods
④ Silurian Period : First appearance of Ammonites and Goniatites
○ Ammonites abundant during the Mesozoic Era, a standard index fossil
⑤ Devonian Period
⑥ Carboniferous Period : First appearance of Foraminifera
⑦ Permian Period (Cisuralian Epoch) : Also known as the “Permian”
○ Age of Amphibians, related to the formation of Pangaea
○ Permian-Triassic Extinction Event : Largest mass extinction in Earth’s history
○ Money Shale : Represents the end of the Paleozoic Era, but representative of the Mesozoic Era
⑸ Mesozoic Era : Age of Reptiles, also known as the Age of Dinosaurs. 225 million years ago ~ 65 million years ago
① Characteristics of the Mesozoic Era
○ Standard Index Fossils : Ammonites, Belemnites, Dinosaurs, Archaeopteryx
○ Generally warmer than the Paleozoic or Cenozoic Eras
② Triassic Period
③ Jurassic Period : Age of small reptiles. Fossil of Archaeopteryx
④ Cretaceous Period
⑹ Cenozoic Era : 65 million years ago ~ Present
① Characteristics of the Cenozoic Era
○ Standard Index Fossils : Money Shale, Mammals
○ Divided into Eocene and Oligocene within the Cenozoic Era
○ Angiosperms flourished during the Cenozoic Era
② Eocene Epoch (65 million years ago ~ 2 million years ago)
○ Paleocene Epoch
○ Eocene Epoch
○ 2 million years ago, massive extinction of marine organisms due to the explosion of a supernova Supernova hypothesized as the cause
③ Oligocene Epoch (2 million years ago ~ Present) : Expansion of glaciers, emergence of humans
○ Experienced four glaciations
⑺ Emergence of Humans
3. Geology of Korea
⑴ Geological Structure of the Korean Peninsula
① Comprised of around 10 uplifts, sedimentary basins, and folded mountain ranges
② Uplifts : Areas with non
-directional distribution of rocks
○ Mainly composed of metamorphic rocks formed during the Cambrian Era
○ Exposed due to past orogenic movements
③ Sedimentary Basins : Depositional rock formations between uplifts
○ Pyeongan Basin : Composed of Paleozoic sedimentary rocks
○ Gyeongsang Basin : Composed of Mesozoic Cretaceous sedimentary rocks and volcanic rocks
○ Taebaek Mountain Basin : Composed of Paleozoic and Mesozoic sedimentary rocks without metamorphism
④ Complex Folds : Areas where rocks have been complexly deformed by folds or faults
⑵ Geological Distribution of Korea
① Distribution by Rock Types
○ Metamorphic Rocks : About 40% of the area
○ Mostly formed during the Cambrian Era
○ (Note) Most old rocks are metamorphic since igneous and sedimentary rocks can ultimately become metamorphic
○ (Reference) Most rocks formed in the Paleozoic Era are metamorphic
○ Igneous Rocks : About 35% of the area
○ Mostly intruded during the Mesozoic Era
○ Sedimentary Rocks : About 25% of the area
○ Mostly formed in Paleozoic seas and Mesozoic lands
○ (Reference) Most rocks formed in the Paleozoic Era are metamorphic
② Distribution by Geological Era : Cambrian Era ＞ Mesozoic Era ＞ Paleozoic Era ＞ Cenozoic Era
○ Cambrian Era Rocks : About 43%. Distributed in Gyeonggi Province, northern Gangwon Province. Metamorphic rocks
○ Paleozoic Era Rocks : About 11%. Distributed in Chungcheong Province, Jeollabuk Province, and Gyeongsangbuk Province. Sedimentary rocks (Haseong Formation)
○ Mesozoic Era Rocks : About 40%. Distributed in Jeollanam Province, Gyeongsangnam Province. Sedimentary rocks (Land Formation) + Igneous rocks (Intrusive)
○ Cenozoic Era Rocks : About 6%. Distributed in Jeju Island, Ulleung Island, Dokdo, Baekdusan. Sedimentary rocks (Land and Sea) + Igneous rocks (Volcanic)
○ Mesozoic Intrusion : From Gangwon Province diagonally downward
⑶ Geological Lineage of Korea
Figure. 1. Geological Lineage of Korea
① Geological Features of the Cambrian Era
○ Geological Structure : Fossils are rarely found
○ Upper Formation : Contains fossils such as Colonies
② Geological Features of the Paleozoic Era
Figure. 2. Geological Structure of the Paleozoic Era[Note:2]
A represents Joseon Group, B represents Pyeongan Group
○ Joseon Group : Thick marine formations consisting of limestone, sandstone, shale
○ Fossils of Trilobites, Ostracods, Brachiopods, Conodonts
○ Cambrian Period ~ Early Ordovician Period
○ Unconformity
○ Late Ordovician Period ~ Early Carboniferous Period. Few rock layers of mid-Paleozoic
○ Recently discovered Hoe-dong-ri Formation from the Silurian Period : Silurian rock layers found in Jeongseon-gun, Gangwon Province
○ Pyeongan Group : Mostly distributed in areas where Joseon Group is found
○ Presence of Non-Coal Seams. Contains both marine and terrestrial rock layers
○ Fern fossils found
○ Feature 1. Trilobites are representative fossils
○ Feature 2. Mostly marine rocks : Eventually transitioned to terrestrial rocks in the Late Paleozoic
○ Age of Marine Rocks : Early Paleozoic ~ Early Pyeongan Group
○ Age of Terrestrial Rocks : Late Pyeongan Group ~
○ Feature 3. Gangwon Province’s rock layers are mostly Paleozoic
③ Geological Features of the Mesozoic Era
○ Songrim Movement
○ Daedong Group : Early Mesozoic terrestrial rock layers. Contains Ginkgoales, Non-Coal Seams
○ Late Triassic Period ~ Early Jurassic Period
○ Dabosan Orogeny : Geological movement in the Late Jurassic Period
○ Korea experienced significant tectonic movements during the Dabosan Orogeny
○ This movement caused intense deformation in earlier rocks during the Jurassic Period
○ Resulted in the east-west orientation of geological structures
○ Dabosan Orogeny deformed the Daedong Group
○ Dabosan Orogeny did not deform the Gyeongsang Group
○ Gyeongsang Group : Sedimentary rocks formed in river and lake environments in the Gyeongsang Basin during the Late Cretaceous
○ Fossils of dinosaur footprints, bird footprints, freshwater clams
○ (Note) Named Gyeongsang Group due to its presence in Gyeongsangnam Province
○ Bulguksa Orogeny
○ Tectonic movement related to the Late Cretaceous dinosaur extinction
○ Feature 1. Dinosaurs are representative fossils
○ Feature 2. High intrusion : Mainly during the Late Jurassic
○ Dominated by viscous igneous rocks, mainly granite
○ The Mesozoic Era was a period of significant tectonic activity in the Korean Peninsula (e.g., Daedong Orogeny, Bulguksa Movement)
○ Most of Korea’s coal was formed during the Mesozoic Era
○ Feature 3. Mostly terrestrial rock layers
○ Rock layers formed in rivers or lakes
○ Late Pyeongan Group ~ Late Cretaceous
○ Feature 4. Gyeongsang Province’s rock layers are mostly Mesozoic
④ Geological Features of the Cenozoic Era
○ Feature 1. Volcanic Activity is active
○ Distributed along the East Coast of Korea, creating small formations : Baekdusan, Jeju Island, Dokdo
○ Dominated by low-viscosity volcanic rocks, mainly basalt
○ Around 25 million years ago : The Pacific Plate began subducting beneath the Japanese archipelago, leading to the expansion of the East Sea
○ Late Cenozoic 3rd Era : Baekdusan volcanic field
○ Late Cenozoic 3rd Era (Neogene) : Active deposition
○ Late Cenozoic 4th Era : Formation of Dokdo, Jeju Island
○ Formation of Dokdo : Primary eruption → Secondary eruption → Weathering → Rise in sea level
○ Jeju Island’s main peak ridges : Composed of Late Cenozoic basalt
○ Jeju Island’s Manjanggul Cave : Formed when highly mobile lava flowed, leaving behind a hollow structure
○ At the end of the last glacial period : The Yellow Sea formed
Input : 2019.04.07 01:43