Biogenic Sediments Composed of the remains of plants

Biogenic Sediments Composed of the remains of plants and animals. Bioclastic sediments consist of broken clasts of remains. Coquina - shells and shell fragments (Fig. 8. 8, p. 225) N. Lindsley-Griffin, 1999.

Biogenic Sediments Coral reefs, where most limestones form, require certain conditions: Shallow water where light penetrates Warm water - tropical or temperate Little land-derived detritus N. Lindsley-Griffin, 1999.

Biogenic Sediments Coral reefs support a complex ecosystem that develops around the coral framework. Algae form a symbiotic relationship with corals N. Lindsley-Griffin, 1999.

Biogenic Sediments Sediment in the lagoon (quiet water behind reef) is biogenic calcareous mud which will form limestone N. Lindsley-Griffin, 1999.

Biogenic Sediments Deep ocean biogenic sediments are mostly microscopic fossil shells: Calcareous (foraminifers, nannofossils) - CHALK Siliceous (radiolarians, diatoms, sponges) - CHERT N. Lindsley-Griffin, 1999.

Sedimentary Rock Names Clastic sediments clastic rocks = siliciclastic rocks conglomerate, breccia, sandstone, siltstone, mudstone, shale, claystone Chemical sediments chemical sedimentary rocks gypsum, rock salt, banded iron formation (a few limestones) Biogenic sediments biogenic rocks limestone ( organic), dolostone = carbonate rocks chert peat, coal, phosphate and chalk N. Lindsley-Griffin, 2000.

Biogenic Sediments –Chalk: which is made up of foraminefera is very fine grained Non-Clastic Sedimentary Particles I Broken fragments of calcite, mostly from algae. Shallow sub tidal sediments from the Yucatan, Holocene. Chalk Largest fragments are about 1 mm in length.

Biogenic Sediments Non-Clastic Sedimentary Particles Broken shell fragments of calcite from bivalve molluscs. These shell fragments accumulated on a beach and are cemented together. This rock is almost 100 percent shell fragments, and is therefore called a coquina. Largest fragments about 2 cm in length.

CARBONATE ROCKS • Limestone: It is a non-clastic rock formed either chemically or due to precipitation of calcite (Ca. CO 3) from organisms usually (shell). These remains will result in formation of a limestone. • Limestones formed by chemical precipitation are usually fine grained, whereas, in case of organic limestone the grain size vary depending upon the type of organism responsible for the formation –Fossiliferous Limestone: which medium to coarse grained, as it is formed out of cementation of Shells.

… and finally. • Organic sedimentary rocks: – Formed from the remains of once-living (now dead) things. These include remains of clams, mussels, coral, and snails. – The shells of these animals contain calcite, a major component of rocks. – Examples include: limestone, coquina, and chalk, phosphate, coal

Phosphorite, phosphate rock or rock phosphate is a nondetrital sedimentary rock which contains high amounts of phosphate bearing minerals. The phosphate content of phosphorite is at least 15 to 20%, which is a large enrichment over the typical sedimentary rock content of less than 0. 2%. [1] The phosphate is present as fluorapatite Ca 5(PO 4)3 F (CFA) typically in cryptocrystalline masses (grain sizes < 1 μm) referred to as collophane. [1] It is also present as hydroxyapatite Ca 5(PO 4)3 OH, which is often dissolved from vertebrate bones and teeth, whereas fluorapatite can originate from hydrothermal veins. Other sources also include chemically dissolved phosphate mineralsfrom igneous and metamorphic rocks. Phosphorite deposits often occur in extensive layers, which cumulatively cover tens of thousands of square kilometres of the Earth's crust

Types of phosphorite deposition (1) Nodular phosphorites: These are spherical concentrations that are randomly distributed along the floor of continental shelves. Most phosphorite grains are sand size although particles greater than 2 mm may be present. These larger grains, referred to as nodules, can range up to several tens of centimeters in size. (2) Bioclastic phosphates or bone beds: Bone beds are bedded phosphate deposits that contain concentrations of small skeletal particles and coprolites. Some also contain invertebrate fossils like brachiopods and become more enriched in P 2 O 5 after diagentic processes have occurred. Bioclastic phosphates can also be cemented by phosphate minerals. (3) Phosphatization: Phosphatization is a type of rare diagenetic processes. It occurs when fluids that are rich in phosphate are leached from guano. These are then concentrated and reprecipitated in limestone. Phosphatized fossils or fragments of original phosphatic shells are important components within some these deposits.

Deposits which contain phosphate in quantity and concentration which are economic to mine as ore for their phosphate content are not particularly common. The two main sources for phosphate are guano, formed from bird droppings, and rocks containing concentrations of the calcium phosphate mineral, apatite

• Coal – Different from other rocks because it is composed of organic material – Stages in coal formation (in order) » 1. Plant material » 2. Peat » 3. Lignite » 4. Bituminous

Stages of coal formation

Stages of coal formation Figure 7. 15

COALS: Organic Remains Coals are carbon-rich rocks that are composed of the altered remains of woody plant debris. The two principal types of coals are: • lignite (brown coal): composed • of loosely bound (friable) organic • detritus, including some clearly • recognizable plant remains • bituminous coal: highly compacted • black coal composed of • recrystallized carbon

• Delta, continental environments • Carbonized Woody Material • Often fossilized trees, leaves present Coal Formation

Coal • Common organic sedimentary rocks • Different from other rocks because it is composed of organic material • Stages in coal formation (in order) • Plant material • Peat • Lignite • Bituminous

Coal Formation Stages

Plant Fragments Are Often Visible in Coal

Coal