Three types of rocks exist in the Earth’s crust and at its surface :

1. Igneous rocks

2. Metamorphic rocks

3. Sedimentary rocks

Rocks are naturally occurring combinations of one or more minerals, with each mineral retaining its own discrete characteristics within the rock.

Minerals are the naturally occurring elements or chemical compounds that comprise the soil and rock materials.

Most rocks are aggregates composed of two or more minerals.

Rocks that solidified from molten rock material (magma) are called igneous rocks (from the Latin ignis, or fire).

As magma cools, the ions that compose it arrange themselves into orderly patterns during a process called crystallization.

Igneous rocks are the most abundant rocks on the earth’s crust, making up about 64.7% of the Earth’s crust.

Two groups of igneous rocks: a) Igneous rocks that form

when molten rock solidifies at the surface are classified as extrusive, or volcanic rocks.

b) Igneous rocks that form at depth (deep-seated) are termed intrusive, or plutonic rocks.

Igneous rocks are most often classified by their texture and mineral composition.

The term texture is a measure of the overall size, shape, and arrangement of its interlocking crystals.

The most important factor affecting texture is the rate at which magma cools.

Metamorphic rocks form from preexisting rocks (either igneous, sedimentary, or other metamorphic rocks) that have been altered by the agents of metamorphism, which include heat, pressure, and chemical active fluids.

Metamorphism (change form) is a process that leads to change in mineralogy, texture, and often the chemical composition of rocks.

The changes that occur in metamorphosed rocks are textural as well as mineralogical.

Making up 27.4% of the Earth’s crust.

Metamorphism most often occurs in one of three settings:

1. Contact or thermal metamorphism, which occurs where rocks are heated by direct or close contact with magma.

Most contact metamorphic rocks are fine-grained, dense tough rocks of various chemical compositions.

2. Hydrothermal metamorphism results from the interaction of a rock with high-temperature fluids, producting metamorphic and metasomatic reactions that depend upon temperature and compositional differences between the country rock and the invading fluid.

3. Regional metamorphism, which occurs over extensive areas of rock are subjected to directed pressures and high temperatures associated with large-scale deformation, generally in an area of plate convergence.

Metamorphic Rock Classification: 1. Foliated rocks SHALE SLATE

PHYLLITE (sedimentary rock)

SCHIST GNEIS

2. Nonfoliated rocks: Marble is a coarse, crystalline

metamorphic rock whose parent was limestone or dolostone.

Quartzite is a very hard metamorphic rock formed from quartz sandstone.

Hornfels is a metamorphic rock formed next to intrusions.

Sedimentary rock consists of sediment that has been lithified into solid rock.

Sediment from the Latin sedimentum, meaning settling. Sediment consists of fragments of solid material derived from pre-existing rock, the remains of organisms, or the direct precipitation of dissolved minerals from solution in water.

Although sedimentary rocks account for about 7.9% by volume of the Earth’s crust, however, 75% of all rocks exposed are sedimentary.

Sedimentology encompasses the study of sedimentary processes and sedimentary rocks [included modern sediments such as sand, mud (silt), and clay].

Sedimentary Process: 1. Erosion and Transportation

All rocks including igneous, metamorphic and sedimentary that are exposed to the elements of wind, rain, heat and cold eventually give way to wear and tear and are eroded.

Some are simply broken up into small pieces by running water and frost while others are dissolved slowly as weak acids in ground water react with the minerals contained within the rocks.

In either case, the debris or sediment, is gradually carried downhill by the forces of gravity and running water.

As the sediment is washed further and further "downstream", it is broken into smaller and smaller pieces.

Eventually, these rock fragments are deposited in sediment traps such as ponds or lakes.

A large depressed area in which a lot of sediment has been or is being deposited is called a sedimentary basin.

During transport, the sedimentary particles become sorted by size and density. This means that the larger and heavier fragments will settle faster than the lighter ones.

The very smallest particles (fine sand and mud particles) can be carried hundreds of kilometres out to sea before settling to the bottom in the quiet deeper waters.

The larger pieces (sand, gravel and boulders) will be deposited closer to the shore such as along beaches.

Sedimentary rocks that are formed primarily from fragments of other rocks are called clastics.

Clastic sedimentary rock -

conglomerate

The flowing waters also contain dissolved minerals such as calcium and salt. These minerals will eventually come out of solution and form precipitates (solids) when the conditions are right.

• 2. Deposition/ Sedimentation

As sediment is continuously dumped into the ocean, it gradually sinks to the bottom and starts to form layers.

Coarser, heavier material (gravel) is deposited close to the shore and finer grained sediment (fine sand and clay particles) is deposited further out, in the deeper water.

Varying the water depth and environmental conditions of an area results in different types of sedimentary layers being deposited in the area at different times.

The result is that in any given area there can be many different layers, containing different kinds of sedimentary rock.

Turning sediment into sedimentary rock:

A great deal of change can occur to sediment from the time it is deposited until it becomes a sedimentary rock.

Diagenesis refers to all of the physical, chemical, and biological changes that occur after sediments are deposited and during and after lithification.

Diagenesis includes lithification, the processes by which unconsolidated sediments are transformed into solid sedimentary rock.

Most sedimentary rocks are lithified by means of compaction and/or cementation.

Compaction occurs when the weight of overlying materials compresses the deeper sediment.

Cementation, the most important process by which sediments are converted to sedimentary rock, occurs when soluble cementing materials, such as calcite, silica, and iron oxide, are precipitated onto sediment grains, fill open spaces, and join the particles.

Sediment Texture: The vast majority of sediments are detrital.

They are composed of transported solids fragments, or detritus, produced by mechanical weathering or released by erosion from preexisting rocks.

Detrital particles are deposited when the transporting medium loses its capacity to carry the sediment farther.

Sediment texture depends on the source rocks of the sediment particles, the energy of the medium that transported them, and their environment of deposition.

During transport, sediment grains undergo sorting, a process by which they are carried or deposited selectively, based on the energy of their transport medium and the grain’s size, density, and shape.

A well-sorted deposit consists of particles of one size; a poorly sorted deposit contains particles of widely varying sizes.

Rounding – Relative sphericity. Sediment grains start out as angular grains. With transport, sediments become more

spherical. Well-rounded – long transport distances Angular – negligible transport

Concept of maturity:

1. Physically mature

All grains well rounded/ spherical

All grains same size

No matrix

2. Chemically mature

All grains are quartz.

– Unstable minerals (feldsfars, micas) are removed with transport and by chemical weathering.

Classification of Sedimentary Rocks Can be divided into two major groups:

detrital/ clastic and chemical. Detrital (clastic) sedimentary rocks: All detrital rocks have a clastic texture, which

consists of discrete fragments and particles that are cemented or compacted together.

Classification depends on their particle sizes rather than the composition of their particles.

Common detrital rocks include conglomerate/ breccia, sandstone, and shale.

Conglomerate

Breccia

Sandstone

Shale

Classification of Sedimentary Rocks

Classification of clastic rocks according to texture

Grain Size Composition Shape/Description ROCK NAME

Gravel size >2mm Fragments or any

rock type - quartz,

quartzite, and chert

dominant

Rounded

Conglomerate

Angular Breccia

Sand size 2mm -

0.0625 mm

Mostly quartz Relatively uniform

grain size

Quartz

Sandstone

Mostly feldspar Pink K-Feldspar

present

Arkosic

Sandstone

Silt size 00039 to

0.0625 mm

Quartz grains,

feldspar grains, clay

minerals

Siltstone

Clay size <0.0039 mm Clay minerals Fissile Shale

Clay minerals Non-fissile Claystone

Chemical sedimentary rocks:

The primary basis in the chemical group is their mineral composition.

There are two kinds of chemical sediments: inorganic, and biogenic.

Inorganic chemical-sedimentary rocks precipitate directly from water, usually when the water evaporates or undergoes a significant temperature change.

They include inorganic limestone, evaporites, chert, and dolostone.

Inorganic limestones include travertine and oolitic limestone.

Evaporites include halite (rock salt) and gypsum (rock gypsum).

Oolitic limestone

Grain Size Composition Shape/Description ROCK NAME

<2mm Mostly calcium carbonate (CaCO3) Fizzes with cold dilute HCl

Spherical grains like tiny beads with concentric laminations

Oolitic Limestone

Coarse crystalline

Banded Travertine

Cryptocrystalline

Variety of Quartz (SiO2)

Scratches glass Chert

Fine to coarse crystalline

Gypsum (CaSO42H2O)

Can be scratched with fingernail

Rock Gypsum

Fine to coarse crystalline

Halite (NaCl) Salty taste Rock Salt

Biogenic chemical-sedimentary rocks form when organisms extract dissolved compounds from water, convert them into biological hard parts (such as shells and skeletons), and subsequently deposit them as sediment when they die.

They include biogenic limestone, biogenic chert, coquina and coal.

Grain Size Composition Shape/Description ROCK NAME

Mostly calcium

carbonate

(CaCO3)

Fizzes with cold

dilute HCl

Muddy matrix with

fossils

Fossiliferous Limestone

(Wackstone)

>2mm Shells or shell

fragments poorly

cemented to form

porous, earthy rock)

Coquina

<0.0625 mm Chalk

<0.0039 mm Shells or shell

fragments well

cemented to form dense

rock

Micrite

(Calcareous

Mudstone)

Dull brown and plant-

like

Porous and easy to

break apart in plant

fragments

Peat

Woody appearance,

light weight

Lignite

Highly altered plant

remains (Carbon)

Black, dense and brittle

or porous and sooty

Bituminous

Coal

Depositional Environments: Sedimentary environments are

those places where sediment accumulates (or deposited).

They are grouped into continental, marine, and transitional (coastal) environments.

Continental environments are those environments which are present in continents (alluvial fan, fluvial, lacustrine, desserts and swamps).

Transitional environments are those environments at or near the transition between the land and the sea (deltas, beaches and barrier islands, lagoons tidal flats).

Marine environments are those environments in the seas or oceans (reefs, continental shelf, continental slop and continental rise).

Each is characterized by certain physical, chemical, and biological conditions.

A sedimentary facies is the set of unique properties that distinguish a rock in a given layer from surrounding rocks formed in different depositional settings at the same time.

Sedimentary Structures: Sedimentary rocks form as layer upon layer of

sediment accumulates in various depositional environments.

This layers, called strata, or beds, are the single most characteristic feature of sedimentary rocks.

Separating the strata are bedding plane. Changes in the grain size or in the composition of the sediment can create bedding plane.

The thickness of beds ranges from microscopically thin to tens of meters thick.

Cross-bedding refers to sediment layers that are oriented at an angle to the underlying sets of beds. It is most characteristic of sand dunes, river delta, and certain stream channel deposits.

Graded bedding when the particles within a single sedimentary layer gradually change from coarse at the bottom to the fine at the top.

Graded beds are most characteristic of rapid deposition from water containing sediment of varying sizes.

The deposition of graded bed is most often associated with a turbidity current, a mass of sediment-choke water that is denser than clear water and that moves downslope.

Ripple marks are small waves of sand that develop on the surface of a sedimentary layer by the action of moving water or air.

Mud cracks occurs at the top of a sediment layer when muddy sediment dries and contracts.

Stratigraphy is the study that deals with the formation, composition, sequence, and correlation of stratified rocks.

Rock layers were studied since the time of Avicenna (Ibn Sina, 1027). He was the first to outline the law of superposition of strata.

“Sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top”.

Grand Canyon Rock Layers

Thus the goal of any stratigraphic analysis is to establish the temporal sequence of sedimentary rocks in the area under investigation.

Petroleum exploration without stratigraphic analysis degrades to simply drilling the largest structures seen on seismic—without attempting to determine whether the source, reservoir, and seal exist.

Stratigraphy includes two related subfields: lithostratigraphy and biostratigraphy.

Lithostratigraphy, or lithologic stratigraphy, is deals with the physical lithologic, or rock type, change both vertically in layering or bedding of varying rock type and laterally reflecting changing environments of deposition, known as facies (a body of rock with specified characteristics) change.

Lithostratigraphic correlation should only be applied with great care, and only within a well-defined biostratigraphic and/or sequence stratigraphic framework.

Biostratigraphy or paleontologic stratigraphy is based on fossil evidence in the rock layers.

Strata from widespread locations containing the same fossil fauna and flora are correlatable in time.

Fossils are the preserved remains or traces of animals, plants, and other organisms from the remote past.

Biologic stratigraphy was based on William Smith's principle of faunal succession.

Principle of faunal succession states that “fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances”.

Correlation: Matching rocks or to fit together sedimentary strata of similar age found in different areas.

Correlation involves comparing the rocks and fossils in separate rock exposures.

Sequent Stratigraphy was developed from seismic stratigraphy in the 1970s by Exxon.

Examines sedimentary packages over a large area (entire sedimentary basin).

Sequence stratigraphy focuses on the relationships between sequences of conformable layers and the unconformities that bound them. The strata patterns were as distinctive as the biostratigraphic correlations.

It can provide a predictive tool for determining the likely presence of source rocks, and the distribution of reservoirs and seals.

The basic unit in sequence stratigraphy is the sequence (succession of strata bounded by unconformities). Unconformities: represent a gap in the rock record.

Smaller units of subdivision are beds and laminae.

A marine

transgression is a

geologic event during

which sea level rises

relative to the land

and the shoreline

moves toward higher

ground, resulting in

flooding.

The opposite of

transgression is

regression, in which

the sea level falls

relative to the land

and exposes former

sea bottom.

Generalized Stratigraphy of Malay Basin

Stratigraphy of Zagros Foreland Sediment Iran