non clastic sedimentary rocks

NOBORA, JAMES

PRESENTEROF

TOPIC

THENON-CLASTIC (First Half)

THE CARBONATE

ROCKSEDIMENTARY

1

LIMESTONE

Limestone

Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO3) in the form of the mineral calcite. It most commonly forms in clear, warm, shallow marine waters. It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal and fecal debris. It can also be a chemical sedimentary rock formed by the precipitation of calcium carbonate from lake or ocean water.

Limestone (Origin)

• Limestones may be deposited in seas, lakes, rivers, and on the lands.

• Circulation, and presence of land-derived detritus, such as arenaceous, argillaceous, and ferruginous materials, are factors of importance.

• Certain forms, such as algae, Foraminifera, and corals, are important rock builders, while others are rarely so.

• Limestones may also form through evaporation.

Limestone (Texture)• The texture of limestones are variable and unequalled by any other

group of rocks.-some are clastic (cementation of sand and/or mud by calcite)-others result from processes of organic accretion-others are formed by postdepositional changes-some are coarsely crystalline, and others are fine-grained or even

aphanitic.-oolitic or pisolitic (chemically deposited limestones)-consist of carbonate grains all of uniform size, whereas others are

mottled large crystals scattered through a matrix of finer grains-porous (owing to algal structures)-other carbonate structures are so interlocked

Limestone (Varieties)

Chalk Coquina

Limestone (Varieties)

Fossiliferous limestone Lithographic limestone

Limestone (Varieties)

Oolitic limestoneOolitic limestone (calcium carbonate "oolites“)

Limestone (Varieties)

Travertine Tufa

THE CARBONATE

ROCKSEDIMENTARY

1

EVAPORITES

Evaporites

Formed by precipitation of salts from landlocked bodies of concentrated solutions or brines

are common where lakes form and then evaporate in a desert, or in shallow and warm arms of the ocean adjacent to desert areas

are light in color, and so can be readily recognized, even from a great distance

Varieties of Evaporites

• Rock Gypsum - is formed by the evaporative deposition of gypsum from solution. It is mainly composed of gypsum and can be scratched with your fingernail.

• Rock Salt -is a chemical sedimentary rock formed by the evaporation of seawater and the precipitation of halite. It is mainly composed of Halite. Large enclosed bodies of seawater and desert lakes commonly form rock salt deposits.

Varieties of Evaporites

• Anhydrite – typically occurs as uniformly bedded deposits with mosaics of interlocking anhedral grains, or with large, well-shaped crystals that are set in a mosaic of fine-grained base. Mainly composed of anhydrous calcium sulfate. It represents gypsum without its water of crystallization and it alters readily to gypsum, from which it differs in crystal form (anhydrite is orthorhombic) and in being harder and slight less soluble.

Varieties of Evaporites

• Chemical Limestones– Travertine– Tufa

SILICEOUSSEDIMENTARYROCKS

2

Siliceous Sedimentary Rocks

Siliceous rocks are sedimentary rocks that have silica (SiO2) as the principal constituent. The most common siliceous rock is chert other types include diatomite. They commonly form from silica-secreting organisms such as radiolarians, diatoms, or some types of sponges.

Siliceous Sedimentary Rocks (Origin)

• commonly form from silica-secreting organisms such as diatoms (skeletons are mainly silica, known as siliceous oozes, and when they are formed in the rocks (ex. thru diagenetic process), these rocks are diatomites or diatomaceous earth ) , radiolarians ( accumulates forming a siliceous deposit known as "radiolarian oozes" ), or some types of sponges (Class demospongia - Astylospongia primosia)

Siliceous Sedimentary Rocks (Texture)

• Usually dense• Layered (bedded cherts)• Cryptocrystalline (Novaculite, Flint)• Microcrystalline (Chert)• Texture of unglazed porcelain (Porcellanite)

Siliceous Sedimentary Rocks (Varieties)

Chert Flint

Siliceous Sedimentary Rocks (Varieties)

Jasper Tripoli

Siliceous Sedimentary Rocks (Varieties)

Novaculite Porcellanite

Siliceous Sedimentary Rocks (Varieties)

DiatomiteLooks like chalk, but does not fizz in acid. It is made of microscopic planktonic organisms called diatoms. It may also resemble kaolinite, but is much lower in density and more porous. It is formed when accumulation of diatoms and radiolarian tests develop deposits of siliceous sediments.