SEDIMENTARY SEDIMENTAR Y ROCK CLASSIFICATION SEDIMENTOLOGI SEDIMENTOLOGI & STRATIGRAFI STRATIGRAFI - GL-3053
SEDIMENTOLOGI SEDIMENTOL OGI & STRATIGRAFI - GL GL--3053 •
INTRODUCTION
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SEDIMENTARY ROCKS CLASSIFICATION
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TEXTURES OF SEDIMENTAR SEDIMENTARY Y ROCKS SEDIMENTARY SEDIMENTAR Y PROCESSES (SILICICLASTIC (SIL ICICLASTIC ROCKS) BOTTOM BOTT OM TRACTION AND SUSPENSION (GRAVITY) MASS FLOW DEPOSITIONAL ENVIRONMENT (SILICICLASTIC ROCKS) CARBONATE CARBONA TE ROCKS (SYSTEM, PROCESSES AND EOD) FACIES AND SEDIMENTARY CYCLE –
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Sedimentary Rock Classification o
Sedimentary rock classification (genetic classification ) : Detr Detrit ital al (siliciclastic) sediments – sediment transported as solid o
particles was once in solution Chemical sediments – sediment that was o Biogenic , Biochemical, Biochemical, and and Organic Organic sediments sediments o Volcaniclastic sediments o
Problems (with this classification) :
We Do have
Carbonate Clastic rocks
Sedimentary Rock Classification Sedimentary rock classification ( mixed [descriptive and genetic] classification) :
Volcanic deposits
Detrital sedimentary rocks •
The chief “constituents of detrital rocks” (grain) include •
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Quartz Feldspars Micas Clay minerals Lithic (rocks) fragments
Grain size is used to distinguish among the various
types of detrital rocks
Basic of Detrital Sed. Rocks Classification
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The phi scale is a numerical representation of the Wentworth Scale. The Greek letter ‘f’ (phi) is often used as the unit for this scale. Using the logarithm base two, the grain size can be denoted on the phi scale as : f = -log2 (grain diameter in mm)
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The negative is used because it is conventional to represent grain sizes on a graph as decreasing from left to right
gravel
mud
Breccia & Conglomerate
Breksi & Konglomerat
Sandstone
Batupasir
Basic of Sandstone classification
Mudrock : Siltstone & Claystone
Mudrock : Siltstone & Claystone •
The general term mudrock is applied to any detrital sediment composed by silt and/or clay. If most of the particles (over 2/3) are clay-sized the rock may then be called claystone and if silt is the dominant size, a siltstone. Mixtures of more than one-third of each component are referred to as mudstone (Folk, 1974; Blatt et al., 1980).
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The term shale is applied to any mudrock (e.g. by drilling engineers) but it is best to use this term only for mudrocks that show a fissility, that tends to break parallel to the bedding plane. (Note: the distinction between shale and slate, which is a term used for fine-grained metamorphic rocks which have cleavage planes.)
Mudrock : Siltstone & Claystone •
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Silt is defined as the grain size of material that is 4 - 62 microns in diameter. The coarser grains of silt are just visible (naked eye or with a hand lens). Finer silt is commonly distinguished from clay by touch, as it feels ‘gritty’ while clay feels smooth. Clay is a textural term to define the finest grade of clastic sedimentary particles, those : – – –
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less than 4 microns (Nichols, 2009), or 2 microns (Hopkins,1899; Burgess, 2006), or 1 microns (Atterberg,1903; Simonson,1999) in diameter.
Individual particles are not visible to the naked eye and can only be decided with a high power optical microscope. Clay minerals are a group of phyllosilicate minerals that are the main constituents of clay-sized particles.
Basic of Claystone Classification •
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Even all authors agreed that the definition of Claystone is size bases, the upper size limit of clay is difficulty oppressed due to its tricky nature. Hopkins (1899) defined the clay/silt boundary at 1 micron, a value which is commonly used today by colloid chemists as determining claysized materials (Burgess, 2006). According to Simonson (1999) it was Atterberg in 1903 who decided that the upper size limit for clay should be 2 microns, a value that is widely accepted today in Europe and currently being applied by engineering geologists and civil engineers that have to follow to the European Standard EN ISO 14689-1(ISO, 2003).
Basic of Claystone Classification Clay minerals commonly form as breakdown products of feldspars and other silicate minerals. They are phyllosilicates with a layered crystal structure similar to that of micas and compositionally they are aluminosilicates. The crystal layers are made up of silica with aluminium and magnesium ions, with oxygen atoms linking the sheets
Basic of Claystone Classification
Basic of Claystone classification •
There are, at least, two principal techniques to distinguish and observe clay minerals (Tucker 1988): –
Scanning Electron Microscopy (SEM) is generated from secondary electrons produced by a fine electron beam that scans the surface of the sample. It produces microns across image with much higher resolution than image under an optical microscope
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X-ray diffraction pattern analysis An X-ray diffractometer (XRD) operates by firing a beam of Xrays at a powder of a mineral or disaggregated clay and determining the angles at which the radiation is diffracted by the crystal lattice. The pattern of intensity of diffracted X-rays at different angles is characteristic of particular minerals and can be used to identify the mineral(s) present.
Basic of Claystone classification SID
DC BIO Kelompok butiran tersusun atas
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kuarsa, KF, glaukonit, bioklastik (foraminifera planktonik dan bentonik, serta fragmen moluska).
KF DC
BIO
Mineralogi Lempung:
Magnitude 175 X
@276 Ft TA-44C
@289,68 Ft TA-44C
-kaolinit (28.0-49.5%), -ilit dan mika (34.6-48.7%), -ilit/smektit (17.4-23.1%), -klorit (nil-5.1%).
BIO
SID
I/S Magnitude 2 00 K X
@289,68 Ft TA-44C
Legenda:
I/S SID Magnitude 1 02 X X
@338,20 Ft TA-44C
I/S
Dol : Dolomit Bio : Bioklastik I/S : mixed layer Ilit/Smektit DC : Detrital clay Q : Kuarsa KF : K-Feldspar
Basic of Claystone classification
Basic of Claystone classification
TA129B
TA-94A
TA-83A
Tabel 2. Data XRD daerah penelitian.
Mixed Layer Ilit/Smektit Butiran & Lempung
“Shale” •
Clay + silt + other
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Clays –
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Absorbed Water Sodium Ion
Plate-like form Large surface area Contain Al+3 and Si+4
Water Clay Crystal
Hydration Water
Substitution by Mg+2 Negative charge results Attraction by water and cations
xH
Schematic Outer Water HelmholtzMolecule Plane
Shaly sand (with dispersed clay) 1/R0
Archie
Sw = 100%
Fresh
1/Rw
Salty
“Shale”
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Porosity shaly sand calculation formula to show that we should calculate porosity shale
Shale •
Dispersed Clay Forms –
Kaolinite: moderate perm effects may dislodge, block throats •
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Chlorite: •
significant perm loss
traps water Illite: •
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chokes pores and throats significantly reduce the porosity
SPECTRAL GAMMA RAY LOG EXAMPLE
Carbonate Clastic (Carbonate Breccia/Calcirudite & Calcarenite or Rudstone & Grainstone or others)
Chemical sedimentary rocks
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Consist of precipitated material that was once in solution Precipitation of material occurs in two ways •
Inorganic processes
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Organic processes (biochemical origin)
Chemical sedimentary rocks •
Inorganic processes •
Chert –
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Made of microcrystalline quartz Varieties include flint and jasper (banded form is called agate)
Evaporites –
Evaporation triggers deposition of chemical precipitates
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Examples include rock salt and rock gypsum
Chemical sedimentary rocks •
Common chemical sedimentary rocks •
Limestone –
Most abundant chemical rock
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Composed chiefly of the mineral calcite
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Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms) Inorganic limestones include travertine and oolitic limestone
Dunham classification of sedimentary carbonates, e.g. limestone
Biogenic sedimentary rocks
coral boundstone
20 mm
skeletal grainstone
coral floatstone
*1
*1 *2 *3 *1
*4
*2
*3 *4 *5 *6
1mm
*5 *2 *6
2cm
*3
*6
*4
2cm
1mm
1mm
1mm
1mm
