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Geology
Plate Tectonics
- Earth made up of: o Crust o Mantle o Core
- Upper part of mantle and overlying curst= lithosphere - Boundaries on Earth
o Transform boundaries
Occurs when plates slide(or grind). Causes faults and earthquakes. o Divergent boundaries
Two plates slide apart from each other
New crustal material emerges o Convergent boundaries
Two plates slide toward each other
Forms
subduction zone (if one plate moves underneath the other)
orogenic belt (if two simply collide or compress)
Geologic Time & Columns
Units: Eon, Era, Period, Epoch
- Only period Cenzoic divided into Epochs
- Oldest rock formed at the bottom of the chart while the youngest one on top
- Formation: basic unit of rock body; distinctive series of strata that originated through same formative processes
- Facies: Implies some environment-related lateral/vertical changes in rock body
Rocks and Minerals
Terms:
Mineral : natural occurring inorganic substance with definite chemical composition and atomic structure Rock : Aggregate of minerals in solid state
Types of rocks:
Igneous rocks Solidified from molten mineral matter (magma) inside Earth
Sedimentary rocks
formed by accumulation of sediments on Earth’s surface
Metamorphic rocks
formed by alteration of existing rocks that are heated &/or under increased pressure
- Three rock types above can be converted to each other respectively by biophysical processes in a rock cycle - Rock cycle: endless pathway along which rocks of various
kinds change into other rock kinds - Lithology: physical character of rock
2 - Sedimentary rocks can be divided into:
o Clastic type (Fragment of other rocks and minerals)
o Chemical type (Precipitated from after dissolving in solution) o Organic type (Dead remains of organisms)
Geology of Singapore
Sajahat Formation Subduction zone between two plates with sedimentary rocks metamorphosed to form the oldest rocks
Gombak Norite Intrusion of igneous rock after the subducting material migrated EASTWARD Bukit Timah Granite Larger intrusion during mountain building stage of Malay Penisula
Jurong Formation Deposition of rocks representing different environmental conditions Old Alluvium Younger deposits when sea level changes
Sajahat Formation
- Variably metamorphosed sedimentary rocks - Mainly quartz sandstones, quartzites & mudstones - Pulau Tekong, Pulau Sajahat & Puggol Point
Gombak Norite
- Basic rocks of noritic and gabbroic rocks
- Plagioclase-rich with varying amount of pyroxene materials - Western edge of Bukit Timah Granite
Bukit Timah Granite
- Acid rocks including assimilation of basic rock - Light grey, medium grain size (3-5mm)
- Mainly consist of Feldspar(60-65%), Quartz(30%) and ferromagnesium minerals
Pulau Ubin Granite
- Richer in minerals than Bukit Timah Granite - Pulau Ubin & Changi
- Vary from 1 cm to tens of metres
Jurong Formation
- Sedimentary rocks with 6 lithological facies associated with different environments o Queenstown Facies
Distinctive purple red mudstone and sandstone o Jong Facies
Beds of roundstone conglomerate & sandstone o Ayer Chawan Facies
Well bedded marine muddy sandstone and mudstone, often black in color o Rimau Facies
Quarziles and conglomerate o St. John Facies
Pale grey mudstone & muddy sandstone
3 o Tengah Facies
Muddy marine sandstone with occasional grit beds and conglomerate - Boulder clay: boulders of sandstone
- General temporal and spatial distribution but relationships to one another is unclear - Involves fold and low grade metamorphism
Sunda Shelf
- Glacial periods
- Channels filled with fine grained marine sediments, intercalated with layers of coarser fluvial or deltaic sediments
Old Alluvium
- Sandy deposit consisting of terrestrial to deltaic loose coarse quartz-feldspar sand & gravel and light cemented sandstone-conglomerate
- Top 8m usually deeply weathered
- Clayey coarse angular sand with stringers of subrounded pebbles up to 4 cm. - Rockbeds are often cross-bedded with some fine-grained beds
- They are interpreted to have fluvial origin but they are NOT related to high sea level - Exists over large area of Sundaland
- Deposited from rapid incision erosion of area far from sea
Local Deposits
Huat Choe Formation
- White lacustarine kaolin clay
- Derived from completely weathered JURONG FORMATION - Used for pottery
Tekong Formation
- Unconsolidated marine & littoral well sorted sand with peat & wood fragments, occasional quartz pebbles
- Possible related to higher sea level stand at about 6m Kallang Formation
- 5 members
o Marine Member
Oldest & lies within valleys cut in Bukit Timah Granite , Jurong Formation, Old Alluvium
Does not appear on surface o Alluvial member
Pebble beds through sand, muddy sand and clay to peat
Found throughout the island o Littoral Member
Beach deposits, immediate offshore deposits and tidal sea banks o Transitional Member
Deposited in low energy environments, black to blue-grey mud o Reef Member
Sand-size coral & detrital fragments
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Geomorphology
Relief
- Difference in elevation between high & low points of land surface - Ridges, Hills, valleys
- Can be represented by contour map, topography,etc
Landforms
- Various features which produced by various agencies (rivers, waves, wind, glaciers,etc.) that make up the surface of the earth
- Geomorphology- study of landforms, more emphasis on processes - Singapore has no large scale of landforms due to the small size
o Relief:
Highest Elevation – Bukit Timah (163m)
Average elevation=15 m; Median elevation=12 m
Percentage
Above 60 m (<1%)
>30m (10%)
<15m (>70%) – Low land dominates o Slopes
Based on conversion of tangent to degrees
Mainly consists of gentle slopes
Dissection: important factor for Old Alluvium
Percentage
<3o (53%)
<6o (56%)
>11o (4%)
>25o (.12%)
- Morphology: Shape of ground with reference to slope
- Morphological unit: assembly of slope elements with have more or less common character - In SG:
o Hills
o HVs1, HVs2,HVg1 o RVs1, RVs2 o P, Pf o Valley - Composition of rocks
o Igneous rocks – Highest elevation & distinct hills o Sedimentary rocks – Ridges
o Old Alluvium – Relatively uniform relief
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Hills
- Bukit Mandai, Bukit Panjang, Bukit Batok, Bukit Timah, etc - Highest relief, all land above 105 m.
- Median slope=8.2o
- Geologically forms Gombak Norite and are along western edge of Bukit Timah Granite
Hills and Valley
HVs1 (Steep, High relief)
- >30 m steep hills and steep valleys - Granite dominated general batholiths
o Average elevation: 27 m o .6o (59%)
- Old Alluvium (Tampines)
o Average elevation: 24 m - Dissected landscape
HVs2 (Steep, low relief) …+HVg2(Gentle, low relief) - HVs2: Hills <30 m. Variable valleys.
- HVg2: Rounded landscape (15-24 m)
- Granite: Elevation decreases SE to give HVs2; decreases NE to give HVs2 & HVg2 - Old Alluvium: Core Unit of HVs1 surrounded by HVs2
o Easily eroded to give rugged terrain
- Sedimentary rocks: less characteristics , juxtaposed with steep ridges
Ridge and Valley
- RVs1: >46 m ridges. Narrow steep valleys - RVs2: <30 m ridges. Variable valleys.
- RVs1 are all associated with SEDIMENTARY ROCKS
o Distinct ridges with steep slopes, sometimes rising from mangroves - RVs2 haved mixed lithology is on the southern edge of central batholiths
Plains (P & Pf) & Valleys (V)
- P : <3 m. Recent deposit materials identifiable with large estuaries o Changi, Bedok, Kallang-Geylang, Jurong-Pandan, Sembawang
- Pf : Fringing lowlands main valleys and along coasts. Widely distributed - V : Distinct round of flat-bottomed valley associated with major streams
o Kallang, Bukit Timah, Bedok, Kranji, Pandan
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Weathering
- Definition: Group of processes causing rock to break up, decay & crumbled into soil - Physical: mechanical action of temperature changes
- Chemical: Water, plants, etc
Soil Erosion
- When covering of vegetation removed, soil will start to erode. - Rapid removal of soil & subsequent dissection of surface - Sedimentary rocks: gullying along Clementi Road
- Old Alluvium: Exposure by sand washing activities; derelict rubber estates
Slope Failure
- Definition: Rocks and weathered materials on slopes moved downslope under influence of gravity - Catalyze by moisture, water,etc
Quarrying
- 3 major groups of rocks of economics importance to Singapore
o Granite: Series of quarries concentrated along western flank of Bukit Timah & Pulau Ubin o Clays from Jurong Formation: Brickworks
o Old Alluvium: Sand for construction
Human Action
- Bring changes to topography: cut & fill
- Often do so to obtain suitable platforms for constructions
- Being viewed as the geomorphological agent in changing surface configuration
