batu sedimen biokimia

8/18/2019 Batu Sedimen Biokimia

1/24

Kamal roslan mohamed Geologi UKMKamal roslan mohamed Geologi UKM

STAG2003Sedimentologi

Batu sedimen

Batuan sedimenKimia / biokimia


Batuan sedimen kimia / biokimia terbentuk daripada proses kimia, iaitudaripada bahan kimia yang larut dalam air (terutamanya air laut). Bahankimia ini termendap hasil daripada proses kimia (contohnya prosesperwapan membentuk hablur garam), atau dengan bantuan proses biologi(seperti pembesaran cangkang oleh hidupan yang mengambil bahan kimiayang ada dalam air).

PENDAHULUAN


2/24


3/24


Batuan atau sedimen evaporit terbentukhasil proses perwapan (evaporation) air(selalunya air laut).

Perwapan yang berlaku menyebabkanterbentuknya wap air yang naik ke udara,

dan yang tinggal ialah bahan kimia yangakhirnya menghablur apabila hampir

kesemua kandungan air manjadi wap.

Proses pembentukan garam dilakukan

dengan cara ini. Proses perwapan inimemerlukan iklim panas yangmemanjang, dan selalunya berlaku dikawasan gersang.

Antara persekitaran yang selalu berlaku

pemendapan evaporit ialah;

•Barred basin

•Intertidal flat

•Salt lake

EVAPORIT


Batuan gipsum (Rock gypsum )Terdiri daripada gypsum (CaSO4.2H20)

Composition CaSO4 . H2O; Hardness 1.5-2; Cleavage perfect one direction, distinct in other two (when visible); white, colorless, gray,yellow, red, brown; Luster pearly on cleavages.Description Laminated alabaster gypsum. Gypsum takes on many forms, such as alabaster, selenite, satin spar, and rose gypsum.Formation & Environments

Sedimentary gypsum forms under high evaporative conditions in sedimentary rocks, both clastic and carbonate. It usuallyrequires desert conditions in shallow marine basins, or along coastal tidal flats. Gypsum commonly forms in association withhalite and dolomite in evaporation basins. Sometimes the gypsum appears simply as gypsum roses in the sediment; othertimes it can form beds tens of feet thick.


4/24


TravertineTerdiri daripada calcium carbonate (CaCO3), jadi secara teknikalnya, ianyamerupakan batuan karbonat. Bahan ini terbentuk dalam gua batu kapur dan jugakawasan air panas (hot springs).


Sedimen dan batuan sedimen karbonat terdiri daripada CaCO3 danMgCO3. Bahan ini merangkumi sekurang-kurangnya 20 - 30% daripadakeseluruhan batuan yang ada.

Batuan sedimen karbonat merupakan salah satu daripada batuantakungan utama untuk bahan hidrokarbon (minyak dan gas).

BATUAN KARBONAT

Kebanyakkanpemendapan sedimenkarbonat berlaku dilautan. Pemendapansedimen ini boleh secarapelarutan kimia(inorganik) atau melaluiaktiviti haiwan yangmenyerap bahan kimiadaripada ait alut (secaraorganik).


5/24


Kalsit (Calcite ) CaCO3Sistem hablur RhombohedralBanyak ditemui dalam batuan sedimen tuadaripada Tertier

Low magnesium calcite (4%) still maintaincalcite crystal structure

Dolomit (Dolomite ) CaMg(CO3)2Sistem hablur RhombohedralBerasosiasi (associated) dengan mineral kalsitdan evaporit

Aragonit (Aragonite ) CaCO3Sistem hablur OrthorhombicBanyak ditemui dalam batuan sedimen karbonatrecent (Cenozoic)

Mineral utama


Butiran karbonat (allokem) - kerangka (framework)

Kalsit mikrokristalin - matrik atau mikrit

Kalsit spar - simen

Pengelasan batuan karbonat dibuat berdasarkan kepada kehadiran ketiga-tiga tekstur di atas.

Tekstur batuan karbonat

Butiran karbonatKalsitmikrokristalin

Kalsit spar


6/24


Butiran karbonat juga dikenalisebagai allokem. Ianyabersamaan dengan butirankerangka atau klas untuk batuanklastik.

Butiran karbonat ini mempunyaisaiz daripada saiz lodakhinggalah kepada saiz yangsangat besar. Terdapat empat jenis butiran karbonat yangutama;

BUTIRAN KARBONAT

Pecahan cangkang

Ooid

Peloid

Butiran karbonat atau litoklas


Pecahan cangkang (Skeletal fragments )

•Boleh terdiri daripada keseluruhan cangkang

•Merupakan antara allokem yang paling banyak ditemui

•Boleh ditemui di kesemua sekitaran karbonat


7/24


Ooid

Merupakan butiran berbentuk bulat, dan mempunyai lingkaran kalsit (internalconcentric layers of calcite) mengelilingi nukleus (samada pecahan cangkang,pellet, butiran kuarza dan lain-lain)

Mempunyai saiz pasir halus hingga kasar

Oncoids - merupakam ooid yang mempunyai garispusat 1-2 cm

Oolit – batu kapur yang mempunyai ooid

Selalunya ditemui di sekitaran karbonat yang

mempunyai air / gelombang yang berkocak secaraberterusan (constantly reworked by waves).

Ooid yang terdapat di persekitaran karbonat sekarang.


Peloid

Allokem yang berbentuk bulat ataumembujur, tetapi terdiri daripada kalsitmikrokristallin atau kriptokristallin

(microcrystalline or cryptocrystallinecalcite) atau aragonit.

Dalam peloid tiada apa-apa struktur,

biasanya bersaiz lodak atau pasirhalus. Kebanyakannya terdiri daripadafecal pellets . Pecahan cangkang yangbulat dan ooid yang tidak mempunyaiapa-apa struktur juga dikenali sebagaipeloid.

Boleh ditemui di kebanyakkansekitaran pengendapan


8/24


Butiran karbonat atau litoklas (Carbonate clasts (lithoclasts )

Merupakan sedimen atau klas yang berasal daripada batuan karbonat sedia ada(setelah dihakis), mempunyai saiz pasir atau lebih besar dan selalunya berbentukbulat.

Litoklas ini tidak sebanyak ooids, peloids or pecahan cangkang (jarang ditemui).Biasanya ditemui dalam endapan akibat ribut (storms deposits ), alur, dan juga

endapan turbidit

Ekstraklas (Extraclasts ) – klas

berasal daripada luar lembangan

Intraklas (Intraclasts ) – klas berasal

daripada lembangan yang sama


Kalsit mikrostallin merupakan butirankarbonat (hablur kalsit atau aragonit)yang bersaiz halus (lumpur), danianya juga dikenali sebagai mikrit.Secara umumnya, mikrit inimembentuk matrik dalam batuankarbonat.

Dalam sekitaran moden, mikrit terdiridaripada mineral aragonit, dan ianyaberasal daripada algae berkalka.Secara ummnya, kehadiran mikrityang banyak mencadangkansekitaran bertenaga rendah. Walaubagaimanapun, keadaan ini tidaksentiasa benar.

KALSIT MIKROKRISTALIN (Microcrystalline calcite )


9/24


KALSIT SPAR (Sparry calcite )

Kalsit spar merupakan hablur kalsit yangbersaiz besar. Hablur ini membentuksimen, dan boleh ditemui di ruang antarabutiran karbonat.

Simen ini terbentuk hasil daripada prosesdiagenesis, iaitu terbentuk selepas sedimendiendapkan.

Kehadiran kalsit spar, dan ketiadaan kalsitmikrokristallin mencadangkan persekitaranair yang tertenaga tinggi, sehinggakanbutiran halus dibawa keluar ke kawasanlain.



10/24


Penamaan batuan karbonat tergantungkepada jenis allokem yang ada, dan

masada allokem tadi sisimen oleh kalsitspar atau terkandung dalam matrik(mikrit).

Pengelasan umum batuan karbonatboleh dibuat berdasarkan kepadakehadiran kalsit, dolomit dan bahanimpuriti (bukan karbonat). Pengelasanterperinci untuk batuan karbonat telah

dibuat oleh;•Dunham

•Folk

PENGELASAN BATUAN SEDIMEN KARBONAT

Batuan sedimen karbonat terbentuk hasil daripada proses kimia, dan jugaproses biokimia. Antara batuan yang termasuk dalam kumpulan ini ialahbatu kapur dan dolomit.


Pengelasan oleh Dunham dibuat berdasarkan kepada kehadiran mikritatau tidak, dan jenis sokongan allokem. Pengelasan ini juga mengambilkita samada butiran/bahan karbonat yang ada telah terbebat (bounded)semasa pengendapannya.

PENGELASAN DUNHAM

Pengelasan ini lebih mudah, dansesuai digunakan di lapangan.

Nama-nama yang ada berdasarkankepada pengelasan Dunham ialah;

•Batu lumpur karbonat (mudstone)

•Batu wak (wackestone)

•Batu padat (packstone)

•Batu butir (Grainstone)

•Batu bebat (boundstone)

•crystalline carbonate


11/24


"Is depositional texture still recognizable?"This is the first question a student should ask when classifying carbonate rocks, regardless of

the classification schemes used. In this course, we will use the Dunham classificationscheme; the names used are straightforward, and the approach is similar to that ofsiliciclastic rock classification. Step by step instructions for classifying a carbonate rock arebelow, as is the classification scheme as devised by Dunham. Spend some time becoming

familiar with the classification scheme!

STEPS:Is depositional texture still recognizable?

Yes: Go to (2)After making the initial determination of presence or absence of primary depositional texture, the Dunham scheme differentiates

rock types in a similar manner to siliciclastic sediments, except that many of the "grains" are fossil fragments!

No: Crystalline carbonate: (subdivide on crystal size)

Determine if rocks originally bound together during deposition

Yes: BoundstoneNo: Go to (3)

Components deposited as discrete grains or crystals

Contain lime mud, < 10% grains: (Lime) MudstoneContain lime mud, (matrix supported) >10% grains: Wackestone

Contains lime mud, grain supported: Packstone

No lime mud, grain supported: Grainstone

THE 'HOW-TO' OF CLASSIFICATION


BATU LUMPUR BERKAPUR (LIME MUDSTONE )

Lime mudstones are composed of clay sized carbonate particles. These particlescan be derived from the disaggregation of relatively complex organisms such asHalimeda , or they can be tests of organisms such as coccolithophorids orforaminifers. These rocks can be of any colour, and, like siliclastic mudrocks the

colour is primarily determined by the redox conditions at the time of deposition.


12/24


BATU WAK (WACKSTONE )

Wackestones are carbonate rocks which are matrix-supported; i.e., there are morethan 10% grains, but the fine grain clay size matrix essentially surrounds the grains.


BATU PADAT (PACKSTONE )

Packstones are grain-supported carbonate rocks; i.e., there is less clay size matrixthan allochems. Sometimes it is difficult to differentiate between a packstone and awackestone, depending on the surface you are examining. Try and look at all sidesof the rock! The two pictures below show a cut and a weathered surface. Notice the

weathered surface allows a better view of the relationship between the grains andthe matrix!


13/24


BATU BUTIR (GRAINSTONE )

Grainstones are grain-supported carbonate rocks with NO mud. Often theinterstices of these rocks are filled with a sparry cement. The photo below is a bit ofa stretch for a carbonate because the original carbonate has been replaced byquartz. However, the concentrically laminated texture of the oolites has beenpreserved, making it a good photo for showing texture!


BATU BEBAT (BOUNDSTONE )

Boundstones are carbonate rocks which are bound together in the originaldepositional environment by framework building organisms such as coral,encrusting organisms such as bryozoans or sediment trapping mechanisms such asthose of the cyanobacteria. They can have complex structures which show cellular

detail, or appear laminated. The two photos below illustrate two of these types.

Algal boundstone Coral boundstone


14/24


Pengelasan batuan karbonat oleh Folk berdasarkan kepada kehadiran danperatusan komponan allokem, mikrit dan kalsit spar. Antara nama-namabatuan karbonat yang ada dalam pengelasan Folk ini ialah;

Pengelasan Folk ini memerlukan kajian petrigrafi di makmal, jadipengelasan ini tidak sesuai digunakan di lapangan.

•mikrit

•biomikrit dan biosparit

•oosparit dan oomikrit

•pelsparit dan pelmikrit

•intrasparit atau intramikrit

•biopelsparit dan lain-lain

PENGELASAN FOLK



15/24


Penamaan yang diberikan berdasarkan allokem yang paling dominan, dandiikuti oleh allokem yang ke-dua dominan dan seterusnya, dan di bahagianakhir diletak samada sparit atau mikrit, bergantung kepada jenis simen ataukandungan mikrit yang ada. Contoh menamaannya ialah;

Oolites + Fossils + Spar matrix = Oo bio sparite (Oobiosparite)Pellets + Oolites + Fossils + Micrite matrix = pel oo bio micrite (Peloobiomicrite)Fossils + Spar matrix + Micrite matrix = bio spar micrite (Biosparite)

PENGELASAN FOLK



16/24


Composition Micrite = lime mud; CaCO3, the mineral calcite. Micrite is the equivalent of clay (rock = shale) in clastics. Originally depositedas microscopic aragonite needles, but now converted to calcite and then calcite cemented to form the rock.Description Dense, uniform, fine grained rock with conchoidal fracture. Faint, weak laminations running parallel to top of picture (see nextto penny). The laminations are probably algal laminates, produced on tidal flats by colonies of blue-green algae.Formation & Environments Micrite is one of the most common carbonate rocks. Most of what people call " limestone" is largely or exclusively micrite. Aswith clay (shale) it is deposited in generally quiet water, and appears in any environment where those conditions exist. Oftenwe associate quiet water with deep water, where waves and currents do not touch bottom. But with carbonates that may notalways be a good rule. Micrites (especially algal laminated micrites, as is this specimen) form readily in the upper regions oftidal flats (upper intertidal and supertidal), where periodic exposure to air is common.

Mikrit (Micrite ) (microcrystalline limestone )Berbutir sangat halus, mempunyai warna kelabu cerah hingga gelap. Ianya terdiridaripada lumpur karbonat (lime mud ) yang juga dikenali sebagai calcilutite.


Composition Calcite - CaCO3, formed into small pearl-like spheres, constructed as concentric layers. This is a chemical rocks, precipitatedfrom warm, supersaturated marine water.Description A pure oolitic limestone with spar cement. The oolites are white, rounded, and concentrically layered, in the sand sized range.In some of the broken oolites we can see the seed in the middle which began the oolite, and the concentric layers by whichthe oolite was built. In the unbroken examples the oolite just looks like a tiny pearl. The spar cement is clear calcite precipitated between the oolites by ground water after deposition. It looks transparent or slightly gray, almost like a clear gluebinding the oolites together.Formation & Environments Oolites form today in warm, supersaturated, shallow, highly aggitated marine water. They are commonly associated withzones of high tidal activity in a subtidal or lower intertidal environment. The mechanism of formation is to begin with a seed of

some sort, perhaps a shell fragment. The strong currents wash this seed around on the bottom where it accumulates a layerof chemically precipitated calcite from the supersaturated water. Only this process is going on with uncounted trillions ofoolites. The oolites are commonly found in large dunes (megaripples); if you could be there you could scoop up the oolites inyour arms and hands. The concentric layers is formed as the oolites are alternately exposed to pick up a concentric layer, andthen buried to set the layer. The next exposure then adds another layer.

Batu kapur oolitik (Oolitic limestone )Batu kapur yang komponen utamanya terdiri daripada bahan atau allokem oolit

yang berbentuk bulat


17/24


Composition Micrite = lime mud; CaCO3, the mineral calcite surrounding and supporting skeletons, mostly of crinoids (white fragments)and brachiopods (black, curved fragments), although bryozoans and other organisms are present. Micrite is the equivalent ofclay (rock = shale) in clastics.Description Saw cut slab of limestone, wet with water before being photographed. Black and white objects are cut sections of fossils. Thewhite pieces are mostly crinoid stem fragments. Crinoids stems are cylindrical columns made up of discs strung together likea stack of poker chips. Sometimes they appear round when the stem has been cut across the axis, while longitudinal cuts arerectangular. The curved black fossils are cross sections through brachiopods or trilobites. The light gray areas are theunform, dense micrite.Formation & Environments This outcrop is either a reef, or is closely associated with a reef. It was a high energy environment as indicated by the lack offine grained sediment (micrite), and the presence of spar cement. Spar is crystalline calcite crystals precipitated by groundwater in the spaces between the fossils after deposition. Before this became a rock we can imagine it as a rubble pile ofskeletons lying on the bottom with no other sediment intermixed with them.

Batu kapur berfosil (Fossiliferous limestone )Merupakan batuan karbonat hasil daripada proses biokimia. Fosil yang terdiridaripada bahan / mineral kalsit atau dolomit merupakan bahan utama yangmembentuk batuan ini.


Composition Shell debris, sometimes whole; typically broken and wave washed.Description

Badly broken, current washed, relatively well sorted, poorly cemented bivalve shell debris.Formation & Environments Coquina is a limestone consisting almost completely of mechanically transported fossil debris with little or no matrix, looselycemented together so that the rock looks very porous. Such rocks form in zones of high energy where finer material iswinnowed away. Typically the shells are clams and snails.

Kokina (Coquina )Cangkang fosil yang tersimen.


18/24


Composition A biochemical rock composed of the microscopic tests (skeletons) of single celled organisms belonging to the phylumHaptophyta; common name coccoliths or coccolithophorids. Although we provide a close-up of this rock there is nothing moreto see than in the larger image. Haptophyte skeletal elements can only be seen with a scanning electron microscope.Description Soft, white, powdery, gritty rock that easily rubs off on you fingers. Reacts with dilute HCl producing large, foaming bubbles.May be confused with kaolinite or alabaster gypsum. Neither of these, however, react with acid.Formation & Environments The Haptophyte organisms that produce the coccolith skeletons that become chalk are pelagic organisms living in the surfacewaters of the world's oceans. The skeletons eventually settle to the bottom and accumulate to become chalk - if conditions arefavorable. Coccolith skeletons are settling most everywhere out of today's oceans, and should be accumulating everywhere inthe oceans. But, if the water is too deep it becomes too cold, and the skeletons dissolve. Therefore, chalk accumulates only at shallower depths, and today that is along the oceanic rift systems (divergent plate boundaries). We might also expect chalk toaccumulate in shallow waters next to continents, such as on the continental shelves, but here there is too much clastic sediment, and whatever skeletons get to the bottom are typically lost in the clays, silts, and sands.

Chalk Terdiri daripada organisma microscopic planktonic seperti coccolithophores; fizzesreadily in acid.


Composition Dolomite/dolostone = CaMg(CO3)2. Rock probably began as a calcitic rock (CaCO3) (an algal laminated micrite), but wasconverted to dolomite after formation.Description Dense, uniform, fine grained rock with conchoidal fracture. Faint, weak laminations running parallel to bedding. Thelaminations are probably algal laminates, produced on tidal flats by colonies of blue-green algae.

Formation & Environments There is a lot of controversy about the origin of dolomite. Most of it is probably of secondary origin from the recrystallization oflimestone by the substitution of magnesium atoms for calcium atoms in the crystal structure. This rock is likely a recrystallized algal laminated micrite. See Origin of Dolomite for more information. One way or another, dolomitic rocks are formed in manyof the environments limestones form in - just depending on the limestone. This particular exposure is algal laminated, andfound with other evidence of tidal flat feature. It most likely formed in the upper intertidal to supertidal region

DolomitSecara umumnya, batuan dolomit atau dolostone adalah terbentuk secaradiagenesis daripada batu kapur. Dolomit ditemui dalam batuan tua, dan jarangterbentuk sebagai sedimen baru.


19/24



Batuan bersilika terdiri daripada silika (SiO2) yang dominan. Batuan initerhasil daripada proses kimia dan / atau biokimia, iaitu boleh terbentukhasil himpunan organisma bersilika seperti diatom, radiolaria dan sponges.

Kadang-kadang batuan karbonat boleh menjadi batuan bersilika apabilaberlaku tindak balas kimia silika mengganti kalsium karbonat.

BATUAN BERSILIKA


20/24


Diatomite

Kelihatan seperti chalk , tetapi tidak berbuih bila dikenakan tindakan asid. Ianyaterdiri daripada organisma mikro plantonik yang dikenali sebagai diatoms . Ianya juga kelihatan seperti kaolinit, tetapi mempunyai ketumpatan yang rendah, danporositi yang tinggi.


Composition Silica Description Extremely hard (H=7), tough, dense, silica rock with conchoidal fracture. Color varies extremely from opaque black, to gray,white, yellow, brown, red. Chert is resistent to weathering and so tends to stand out of the ourcrop. At first it would be veryeasy to confuse this specimen with some micrites. This chert and micrite #2 look superficially almost identical. Two testseparate them clearly, however. First, hardness; micrite is softer than a knife blade, while the blade just slips across thissurface. Second, micrite reacts with acid, chert does not.Formation & Environments Many kinds of chert form from recrystallization of siliceous skeletons (glass sponges, diatoms, radiolarians). Some chert may

be produced chemically. Two broad types of chert form, nodular and bedded, with abundant variations in between. Beddedchert typically forms in clastic starved basins (i.e. those with little sediment influx), along the edge of continents (such asdivergent continental margins) where strong upwelling occurs. Deep water upwellings bring nutrient rich waters to the surfaceresulting in algal blooms, population explosions of microscopic organisms, many of whom produce silicious skeletons whichsettle to the bottom and recrystallize to form form thick bedded chert. Nodular chert is more associated with shallow waterenvironments, especially in carbonates. Here the silica chemcially replaces the carbonate, often times including fossils.

Rijang (Chert )Merupakan batuan yang sangat keras dan tahan terhadap proses luluhawa. Ianya

boleh masif atau berlapis, terdiri daripada mineral kuarza mikrokristalin, berwarnacerah hingga gelap. Rijang boleh terbentuk hasil daripada proses biologi (himpunanorganisma bersilika, atau boleh juga daripada proses diagenesis batuan karbonat.


21/24


Endapan organik terdiri daripada himpunan bahan berorganik yangakhirnya mengeras menjadi batu - batu arang.

Serpihan daun dan batang tumbuhan yang tebal dalam suatu lembangan(biasanya dikaitkan dengan sekitaran daratan), apabila mengalami tekananyang tinggi akan termampat, dan akhirnya boleh menjadi bahan

hidrokarbon batu arang.

ENDAPAN ORGANIK



22/24


Composition Partially decayed organic matter Description Porous, very light weight mass of matted, partially decayed organic fibers.Formation & Environments Peat forms when plant material accumulates in an anoxic environment where decay is inhibited. Typically this is in marshesand bogs associated with deltas, flood plains, tidal marshes, etc. If it becomes progressively buried and heated it caneventually turn into bituminous coal, then anthracite coal, and finally graphite.

Peat (gambut)


Composition Partially decayed organic matter Description Black, well jointed, often layered, sometimes conchoidal fracture, smudges off on fingers.Formation & Environments Bituminous coal (all coal) forms from the destructive distillation of plant remains under anaerobic conditions. It results from burial and compression, and the driving off of hydrogen and other volatiles leaving behind fixed carbon, with varying amountsof sulfur, and other elements. If it is buried and heated enough it will turn into anthracite coal, and finally graphite.

Batu arang berbitumin (SOFT COAL Bituminous coal)


23/24


Composition Partially decayed organic matter Description Black, shiny, homogeneous, breaking with a conchoidal fracture.Formation & Environments Anthracite coal forms when bituminous coal undergoes very low grade metamorphism, accompanied by structuraldeformation. The fixed carbon content under these conditions reaches 85-95%. If anthracite is metamorphosed further itturns into graphite.

Batu arang (HARD COAL Anthracite coal)



24/24


Sekian…

batu sedimen biokimia

Documents