1. PETROLOGY OF SEDIMENTARY ROCKS
Dr. Sugeng S Surjono
Lab. Sedimentografi
Jurusan Teknik Geologi, Fakultas Teknik
Universitas Gadjah Mada

3. INTRODUCTION Three Rock Types: Igneous, Sedimentary, Metamorphic rocks
Sedimentary rocks : rocks formed at the surface of the earth under low-temperature and low-pressure, result from the accumulation and solidification of sediments, material transported in water, air or ice (Raymond, 1995).
Origin of sedimentary rocks:
- Formation of source rocks/sediment source :
intrusion, metamorphism, volcanism, tectonic uplift
- Weathering :
physical and chemical breakdown of source rocks
- Erosion and Transportation
agent of transportation : water, wind, ice
- Deposition
material is deposited within depositional basins
- Diagenesis
sediment is covered by successive layer of younger sediment; increased temperature and pressure leading to consolidation and lithification of the sediment into sedimentary rocks

4. INTRODUCTION Types of Sedimentary Rocks: (Tucker, 1991)
Sedimentary rocks are characterized by :
Presence of layers
Presence of transported grains
Sedimentary structures
Fossils
Types of Sedimentary Rocks: (Tucker, 1991)
Siliciclastic (fragmental) : - Conglomerates & breccias
- Sandstones
- Mudrocks
Biogenic, biochemical and organic :
- limestones & dolomites
- cherts
- phosphates
- coal
- oil shale
Chemical : - evaporites
- ironstones
Volcaniclastic : (e.g.) ignimbrites, tuffs, hyaloclastites

6. Sedimentary rocks
Clastic (siliciclastic) rocks (80-85% of the stratigraphic record)
Carbonate sediments and rocks (10-15% of the stratigraphic record)
Volcaniclastic sediments and rocks
Others (< 5% of the stratigraphic record) :
Organic (carbonaceous) sediments and rocks
Evaporites

7. SILICICLASTIC SEDIMENTARY ROCKS
Clast (from the Greek klastos, meaning ‘broken’) is the technical term for broken fragment within sedimentary rocks. It is also called as terrigenous grains
Because most terrigenous grains are composed in part of silica, they are often referred to as siliciclastic grains.
Siliciclastic sedimentary rocks are composed by clasts that originated from transportation and deposition of pre-existing rocks within depositional environments. Mechanism involved in the transportation include the wind, glaciers, river currents, waves, tidal currents, debris flow and turbidity currents (Tucker, 1991).
Two important features of siliciclastic sediments related to depositional processes and diagenesis are sedimentary textures and structures.
DESCRIPTION OF SEDIMENTARY ROCKS (Prothero & Schwab, 2005):
Color
Sedimentary textures
Sedimentary structures
Composition
Fossil contents
Geometry of sedimentary rocks

8. Color Basic components of siliciclastic sedimentary rock are :
-clasts or fragments
-matrix
-cements
Color
Color usually reflects some aspect of the rock’s composition (bulk color can reflect the color of major mineralogical components)
Color of rock controlled by color of clast, matrix and cement
Color is not treated as an independent property, however, but as an aspect of sedimentary rock composition

9. Sedimentary textures Grain size
Textures refers to the size, morphology, and arrangement (fabric) of siliciclastic grains that make up a sedimentary rock.
Grain size
Grain or siliciclastic particles range in size from clay to boulder
The grade scale most widely used by sedimentologist is the Udden-Wenthworth scale
The Udden-Wentworth grain-size scale is based on factors of two:  = -log2 d ; where d is grain size in mm
- It extends from <1/256 mm (0.0039) to >256 mm and is divided into four major size categories (clay, silt, sand, and gravel) that can be further subdivided

10. Udden-Wenthworth grain-size scale for sediments and the equivalent phi scale
Mud

11. Grain size parameters : mean, sorting, skewness, kurtosis
Grain-size (particle-size, granulometric) analysis
The old-fashioned way: direct measurement (gravel) and sieve/pipette analysis (sand and mud)
The modern technology: laser particle sizing (sand and mud)

12. Graphical method Graphic Mean Standard deviation Skewness Kurtosis
Grain size parameters
Graphical method
Graphic Mean
Standard deviation
Skewness
Kurtosis
(Mz) =
(σ1) = +
(SK1) = +
(KG) =

13. σø = ( = standard deviation)
Grain size parameters
Moment measures (mathematic method)
First moment: mean (cf. median, mode)
Premier measure of the grain size
x ø =
Second moment: variance (cf. standard deviation)
Measure of the degree of sorting
σø = ( = standard deviation)
Third moment : Skewness
- Measure of the symmetry of the grain-size distribution
Skø =
Fourth moment : Kurtosis
- Measure of the sharpness or peakedness of a grain-size frequency curve
Kø =

15. SK1 class :
+1,0 - +0,3 very fine-skewed
+0,3 - +0,1 fine-skewed
+0,1 - -0,1 near-symmetrical
-0,1 - -0, coarse-skewed
-0,3 - -1, very coarse-skewed
KG class:
<0, very platykutic
0,67 – 0,90 platykurtic
0,90 – 1,11 mesokurtic
1,11 – 1,50 leptokurtic
1,50 – 3,00 very leptokurtic
>3, extremely leptokurtic

20. Grain Morphology
Three aspects of grain morphology are the shape, sphericity and roundness.
The shape or form of grain is measured by various ratios of the long, intermediate and short axes.
Sphericity is a measure of how closely the grain shape approaches that of a sphere.
Roundness is concerned with the curvature of the corners of a grain and six classes from very angular to well rounded.

21. Grain shape classification
Roundness and Sphericity

23. Grain Fabric
Fabric for grain in sedimentary rock refers to their orientation and packing and to the nature of contacts between them.
Grain Packing is a function of the size and shape of grains and postdepositional physical and chemical processes that bring about compaction of sediment.
Grain orientation is mainly a function of the physical processes and condition operating at the time of deposition

25. Sedimentary structures
Sedimentary structures occur at very different scales, from less than a mm (thin section) to 100s–1000s of meters (large outcrops); most attention is traditionally focused on the bedform-scale : Microforms (e.g., ripples) ;Mesoforms (e.g., dunes); Macroforms (e.g., bars)
The majority of structures form by physical processes, before, during and after sedimentation. Other result from organic and chemical processes

27. Laminae and beds are the basic sedimentary units that produce stratification; the transition between the two is arbitrarily set at 10 mm
Normal grading is an upward decreasing grain size within a single lamina or bed (associated with a decrease in flow velocity), as opposed to reverse grading
Fining-upward successions and coarsening-upward successions are the products of vertically stacked individual beds

28. Cross stratification
Cross lamination (small-scale cross stratification) is produced by ripples
Cross bedding (large-scale cross stratification) is produced by dunes
Cross-stratified deposits can only be preserved when a bedform is not entirely eroded by the subsequent bedform (i.e., sediment input > sediment output)
Straight-crested bedforms lead to planar cross stratification; sinuous or linguoid bedforms produce trough cross stratification

30. Low angle planar cross-bedding, Kali Ngalang-Gunung Kidul, YK

32. Planar stratification
Cross stratification
The angle of climb of cross-stratified deposits increases with deposition rate, resulting in ‘climbing ripple cross lamination’
Antidunes form cross strata that dip upstream, but these are not commonly preserved
A single unit of cross-stratified material is known as a set; a succession of sets forms a co-set
Planar stratification
Planar lamination (or planar bedding) is formed under both lower-stage and upper-stage flow conditions
Planar stratification can easily be confused with planar cross stratification, depending on the orientation of a section (strike sections!)

34. Cross stratification produced by wave ripples can be distinguished from current ripples by their symmetry and by laminae dipping in two directions
Hummocky cross stratification (HCS) forms during storm events with combined wave and current activity in shallow seas (below the fair-weather wave base), and is the result of aggradation of mounds and swales
Heterolithic stratification is characterized by alternating sand and mud laminae or beds
Flaser bedding is dominated by sand with isolated, thin mud drapes
Lenticular bedding is mud-dominated with isolated ripples

36. Gravity-flow deposits
Debris-flow deposits are typically poorly sorted, matrix-supported sediments with random clast orientation and no sedimentary structures; thickness and grain size commonly remain unchanged in a proximal to distal direction
Turbidites, the deposits formed by turbidity currents, are typically normally graded, ideally composed of five units (Bouma-sequence with divisions ‘a’-‘e’), reflecting decreasing flow velocities and associated bedforms

40. Imbrication commonly occurs in water-lain gravels and conglomerates, and is characterized by discoid (flat) clasts consistently dipping upstream
Sole marks are erosional sedimentary structures on a bed surface that have been preserved by subsequent burial
Scour marks (caused by erosive turbulence)
Tool marks (caused by imprints of objects)
Paleocurrent measurements can be based on any sedimentary structure indicating a current direction (e.g., cross stratification, imbrication, flute casts)

42. Trace fossils (ichnofossils) are the tracks, trails or burrows left behind in sediments by organisms (e.g., feeding traces, locomotion traces, escape burrows)
Disturbance of sediments by organisms is known as bioturbation, which can lead to the total destruction of primary sedimentary structures
Since numerous trace fossils are connected to specific depositional environments, they can be very useful in sedimentologic interpretations
Soft-sediment deformation structures are sometimes considered to be part of the initial diagenetic changes of a sediment, and include:
Slump structures (on slopes)
Dewatering structures (upward escape of water, commonly due to loading)
Load structures (density contrasts between sand and underlying wet mud; can in extreme cases cause mud diapirs)

47. Clastic (siliciclastic) rocks
Sandstones (20-25% of the stratigraphic record) can be subdivided according to the Pettijohn classification, based on texture and composition (relative proportions of quartz, feldspar, and lithic fragments)
Quartz arenite: quartz-dominated
Arkosic arenite: feldspar-dominated
Lithic arenite: dominance of lithic fragments
Wacke: significantly matrix-supported (>15% mud)
Quartz wacke
Greywacke (feldspathic or lithic wacke)

48. Classification of Sandstone (Pettijohn, 1975)

49. Clastic (siliciclastic) rocks
Mudstones (60% of the stratigraphic record) are also known as mudrocks or shales and commonly exhibit a distinct fissility
Claystone
Siltstone
Conglomerates are consolidated gravels; breccias are conglomerates with dominantly angular clasts
Clast-supported conglomerates
Matrix-supported conglomerates

50. Halang Formation, Panujah, Slawi, Central Jawa

51. Alternating of siltstone and claystone, Sambipitu Formation-Wonogiri

52. Black shale (upper part) overlying above thickly bedded fine sandstone
Sambipitu Formation-Wonogiri

53. Normal grading sandstone, from coarse sst to fine sst, ambipitu Formation-Wonogiri

54. Conglomerate in Kali Ngalang, Gunung Kidul. Nglanggran Formation

55. Breccia, in Kali Ngalang, Gunung Kidul. Nglanggran Formation

56. Siliciclastic rocks classification (Pettijohn, 1975)

57. CARBONATE SEDIMENT AND ROCKS
Principal minerals: calcite, aragonite (unstable), and dolomite (diagenetic)
Principal rocks: limestone (>50% CaCO3) and dolomite (dolostone) (CaMg(CO3)2)
Formation of carbonate sediments and rocks occurs by means of two main processes:
Biomineralization of CaCO3 by organisms
Direct chemical precipitation
Biogenic carbonate formation occurs by a wide range of organisms (e.g., molluscs, corals, forams, algae, bacteria, and many others)
Most organisms initially form unconsolidated carbonate sediments
Coral reefs and microbial mats (e.g., stromatolites) are examples of more solid carbonate structures
Chemical precipitation produces non-skeletal carbonate grains of various sizes (e.g., ooids, pisoids, micrite)

64. CARBONATE SEDIMENT AND ROCKS
Biogenic carbonate formation occurs by a wide range of organisms (e.g., molluscs, corals, forams, algae, bacteria, and many others)
Most organisms initially form unconsolidated carbonate sediments
Coral reefs and microbial mats (e.g., stromatolites) are examples of more solid carbonate structures
Chemical precipitation produces non-skeletal carbonate grains of various sizes (e.g., ooids, pisoids, micrite)

65. After Scholle, 2003

66. CARBONATE SEDIMENT AND ROCKS
Carbonate sand usually consists either of (fragmented) skeletal remains or non-skeletal grains
Carbonate mud (micrite) is commonly the product either of chemical precipitation or algal/bacterial activity
Dunham classification of carbonate rocks:
Texturally-based subdivision (cf. clastics): mudstone, wackestone, packstone, grainstone, rudstone
Organically bound framework during formation: boundstone

71. Modified of Dunham Classification

72. ORGANIC (CARBONACEOUS) SEDIMENTS AND ROCKS
Peat and organic-rich clastic sediments form in relatively anaerobic (reducing) environments (e.g., mires, lakes, oceans)
Minerotrophic peat: mostly nutrient-rich, groundwater-fed mires (e.g., floodplains, delta plains, coastal plains)
Ombrotrophic peat: mostly nutrient-poor, rainwater-fed mires (e.g., relatively high, flat terrains)
Gyttja: organic-rich lake sediment
Sapropel: organic-rich marine sediment
Coal consists primarily of solid organic matter; the remainder is known as ‘ash’
Carbonaceous shales have a lower proportion of solid organic matter
Oil shales (may be formed in anaerobic lake and marine environments) contain organic matter that can be driven off as liquid or gas by heating

73. Thickly bedded coal, in between shale – siltstone (Bontang, East Kalimantan)

76. EVAPORITES
Dissolved salts precipitate out of sea water due to concentration (brine formation) during evaporation (1 km of sea water --> 12 m of evaporites)
Evaporites commonly lithify into consolidated rocks upon formation
Least soluble compounds precipitate first:
CaCO3 (calcium carbonate)
CaSO4 (calcium sulphate: gypsum or anhydrite)
NaCl (halite: rock salt)
Other, less stable (highly soluble) chlorides
Dissolved salts precipitate out of sea water due to concentration (brine formation) during evaporation (1 km of sea water --> 12 m of evaporites)
Evaporites commonly lithify into consolidated rocks upon formation
Least soluble compounds precipitate first:
CaCO3 (calcium carbonate)
CaSO4 (calcium sulphate: gypsum or anhydrite)
NaCl (halite: rock salt)
Other, less stable (highly soluble) chlorides

78. VOLCANICLASTIC SEDIMENTS AND ROCKS
Lava (cooled magma flows) produces volcaniclastic sediment upon weathering
Pyroclastic material or tephra (ejected particulate material) can be subdivided into different compositional categories:
Mineral grains
Lithic fragments
Vitric material (volcanic glass or pumice)

79. Pillow lava, Watuadeg-Bantul, DIY

80. Kekar tiang, lava. Kali Grindulu, Pacitan

81. Tephra of Merapi pyroclastic flow mechanism, Kaliadem, Sleman

83. terima kasih..