Sedimentary Rocks & diagenesis

Sedimentary Rocks their composition & diagenetic changes. :

Sedimentary Rocks their composition & diagenetic changes. Prepared By Group # B

Group Members Are::

Group Members Are: Muhammad Iftikhar 2K8/GLG/88 Badshah Hussain 2K8/GLG/33 Miandad Hassan 2K8/GLG/77 Khaleq ahmed Zaur 2K8/GLG/67 Noor saeed Khan 2K8/GLG/102

Presentation comprised on THREE related Topics :

Presentation comprised on THREE related Topics 1. Introduction to sedimentary rocks 2. Diagenetic process: Compaction , Cementataion & Recrystalization 3. Compositin of sedimentry rocks Chemical & Mineralogical

Introduction to Sedimentary Rocks :

Introduction to Sedimentary Rocks Sedimentary rocks formed by the sedimentation & consolidation of sediments deposited under water & on the earth surface. Sedimentary Rocks are also formed by the accumulation of chemically precipitated or organically derived material Sedimentary rocks cover 16 Km of earth crust which is estimated to be 5% These rocks are formed in layers. They contain fossils.

Rocks formed in layers:

Rocks formed in layers These rocks contain fossils

Bivalve & Gastropodes presents in Tiyon formation fossiliferous limestone:

Bivalve & Gastropodes presents in Tiyon formation fossiliferous limestone Near laki & tiyon contact

Formation Of sedimentary Rocks They are formed in 3 different stages.:

Formation Of sedimentary Rocks They are formed in 3 different stages. Erosion Sedimentation Lithification & diagenesis

1. Erosion:

1. Erosion Erosion ( weathering & transportation) Pre-existing rocks & thier constituent minerals broken down, the material Produced which is known as “Sediments” Then transported through defferent agencies wind water glacier & so, deposited. Roughly sorted deposited according to size pebble cobble sand clay & dissolved material travel by solution

2. Sedimentation:

2. Sedimentation “ Procees of accumulation of sediments at a site of deposition “ Material carried in a solution precipitates & accumulates is a intermediat stage i the formation of sedimentary rocks

3. Lithification & Diagenesis:

3. Lithification & Diagenesis “ Process by which soft & loose sediments are converted into hard firm rocks “ Such process also known as “ consolidation ” During this process many physical biological changes take place within the sediments That changes known as “ Diagenetic changes process known as “ Diagenesis”

Generally classified As: There are 3 types of sedimentary rocks:

Generally classified As: There are 3 types of sedimentary rocks Mechinaically formed (Through Erosion & weathering) Chemically formed (Through Precipitation) Biologically formed (involve activity of organisms)

Diagenetic process By :

Diagenetic process By Badshah Hussian & Miandad Hassan

Diagenesis process in sedimentary rocks:

Diagenesis process in sedimentary rocks All physical, Chemical & biological Changes undergone by a sediment after it’s initial deposition, and during and after the sediment is changed into rock ( Bates & Jackson 1987) Diagenesis: The process of modification of newly deposited sediments into sedimentary rocks is diagenesis or lithification

Four main process in Diagenesis:

Four main process in Diagenesis Compaction Cementation recrystallization

Compaction :

Compaction When the wieght of overlaying layers copmresess the sediments below the process is called compaction. As the grains of sediments are pressed closer & closer togather, there is a considerable reduction in pore space & volume. Fine grained sediments such as clay consolidated more effectively by compaction. compaction = volume loss (mechanical squeezing) and is accompanied by dewatering (= water loss) (by chemical or physical means)

Cementation:

Cementation A process by which sediments joint togather/cemented. When water circulates throgh the pore of coarse grain sediments, dissolved mineral matter is precipitatedm the grain cause cementation. The most common material are calcite

Chromite cement:

Chromite cement Quartz overgrowth followed by calcite cement

Cementing material in sedimentary rocks:

Cementing material in sedimentary rocks Silica (quartz, opal, or chalcedony) is hardest cementing material Carbonates (calcite, dolomite, or siderite) calcite will effervese with diolute HCl Iron oxides (hematite) gives characteristics red, orange or yellow colour to the rocks.

Recrystallization:

Recrystallization By Miandad Hassan

Recrystalization :

Recrystalization Although sedimentary rocks are lithified by compaction, cementation or combination of both, some are consolidated chiefly by the ecrystallization of their constituents. Cemically formed rocks such as limestone,dolostone, salt & gypsum are consolidated by recrystallization.

Mineral Recrystallization:

Mineral Recrystallization 1. Existing mineral retains original chemistry but increases in size 2. Volume change 3. Amorphous silica to coarse crystalline quartz; fine lime mud into coarse sparry calcite

Composition Of sedimentary Rocks:

Composition Of sedimentary Rocks Khaleq Ahmed & Noor Saed Khan

Composition of sedimentary rocks:

Composition of sedimentary rocks There are two types of composition of sedimentary rocks Chemical Composition Mineralogical Composition

Chemical copmosition: :

Chemical copmosition: The range of chemical composition is quite large and in this respecct they are differ from igneous rocks. ie; sandstone may contian 99% silica in bended iron formation the iron oxides content may be as high as 58% In pure limestone the cao content may reach 55%

Mineralogical Composition:

Mineralogical Composition By Noor Sed Kahn

Mineralogical composition:

Mineralogical composition The most common minerals in sedimentary rocks are: Quartz Clay minerals Feldspars Carbonates (calcite and dolomite) Rock fragments Small amounts of amphibole, pyroxene, and mica.

Mineralogical composition :

Mineralogical composition Most sedimentary rocks contain either quartz (especially siliciclastic rocks) or calcite (especially carbonate rocks ). Sedimentary rocks usually contains very few different major minerals. Carbonate rocks dominantly consist of carbonate minerals like calcite , aragonite or dolomite . In most sedimentary rocks, mica, feldspar and less stable minerals have reacted to clay minerals like kaolinite , illite or smectite .

The end :

The end Thanks for your attention