Lab 5 Terms/ Definitions

Crinoids (skeletal allochem)

-"stalked" filter feeding organisms -Upon death they become broken apart -Columnals (plates or ossicles) of the stalk can be a few mm to several cm in diameter, and appear individually or stacked in a group (red arrows) -"doughnut" or "cheerio" shaped -An axial canal (can be circular or star shaped, green arrows), runs through center of stalk -Each columnal secreted by the animal as a single crystal of calcite (or aragonite) -Still around today but more common in Paleozoic

Grain aggregates

-(also known as 'grapestones') -are clumps of peloids, ooids, or other micritizied grains adhering to one another and forming highly irregular clusters similar in shape to bunches of grapes (hence 'grapestones'). -The origin of these grains is unclear. They may be bound together by micrite, microbes, encrusting organisms or cement. -They could also be the result of abrasion of partially lithified particles to form a type of intraclast.

Allochems

-Allochems are rarely found in sandstones and sandy limestones of the sandstone member -Any calcite or aragonite particles that are formed and transported as clasts (analogous to grains in siliciclastic rock) -Two main types: --Skeletal grains (bioclasts) --non-skeletal grains

Carbonate Textural Features

-CAN be clastic (clasts/grains that have been transported from elsewhere then glued together by matrix or cement) -Transport distance tends to be short -contain equivalents of framework clasts, matrix and cement

Orthochems

-Calcite and hematite cement are the orthochemical constituents -Components form in place and experience no-little transport -Two types: --micrite(~equivalent to matrix) --spar(clear interlocking crystals of CaCO3 that is analogous to cement)

Corals (skeletal allochem)

-Coelenterates, invertebrates that exhibit radial symmitry -They can be colonial or solitary in terms of life habbit -Colonial varieties include growth forms such as branching, fans, encrusting, chain, plates and massive spherical heads that can be 1 m in diameter or more. -Solitary varieties include rugose or horn corals (arrow) -Each corallite or "cell" would have contained a single animal (or 'polyp') and can be a few mm to several cm in diameter -Tabulate ad rugose corals were commin

Bryozoans (skeletal allochem)

-Colonial, filter-feeding microorganisms known as ZOOIDS -Skeletons that they secrete exist in two forms --branching (blue arrows) --fan-shaped (orange arrow) -Both forms exhibit a "cellular" structure, in which each "cell" or zooid living chamber is <1mm diameter -Were important sediment procedures in paleozoic & more recently have significantly increased in diversity

Micrite2

-Micrite is carbonate mud (clay and silt sized particles) -each mud particle is usually less than 4 micrometers in diameter (i.e. cryptocrystalline). -Micrite is equivalent to the matrix in sandstones, and can sometimes be almost the sole component of a carbonate rock. -In hand sample it can be light or dark, is often brown or tan, can appear smooth, opaque, and solid or massive. -Micrite often appears brown and opaque to semi-translucent in thin section. Micrite may be recrystallized during diagenesis, so in some rocks it may appear to be coarser grained (i.e. microcrystalline). The origin of micrite is polygenetic - there are many ways it can form. It may result from the disintegration or disaggregation of larger coated, non-coated, and skeletal grains, or it can be formed by abrasion and bioerosion. Micrite may also directly precipitate out of the water column. Some carbonate sedimentologists also suggest bacterial or microbial activity can contribute significantly to the formation of micrite.

Micrite

-Type of orthochem component -Micrite is a limestone constituent formed of calcareous particles ranging in diameter up to 4 μm formed by the recrystallization of lime mud. -Micrite can be generated by chemical precipitation, from disaggregation of peloids, or by micritization.

2 main COMPONENTS of carbonate rocks

-allochems (allochemical components) -orthochems (orthochemical components)

Spar/Sparry Calcite

-clear interlocking crystals of CacO3 that is anogous to cement -Sparry calcite is crystalline mosaic of calcite crystals in which individual crystals are easily discernable with an optical microscope (>5 microns). Sparry calcites are often polygonal, anhedral crystals but may also be prismatic. In carbonate rocks sparry calcite forms as a cement during diagenesis within primary porosity or by neomorphism of aragonite

Peloids

-lumps of microcrystalline carbonate material (or micrite). ---They range in size from 1 - 5 mm in diameter lack internal structure (i.e. they lack concentric laminae and a nucleus). -They are spherical to elongate and irregular, and rounded to subrounded. -Many peloids in shallow marine environments are actually fecal pellets. -some form as a result of micritization of other grains. Micritization is the conversion of coated grains, shells, fossils, or indistinct lumps of carbonate into micrite through chemical or biological (bacterial) processes.

Limestone intraclasts

-ripped up and transported fragments of preexisting carbonate. -Internally, you can see the texture of the pre-existing carbonate sediment or rock. -Most are intrabasinal (or intraformational - from the same stratal unit or bed). -Tides, waves, and storms are often responsible for entraining and transporting these clasts.

Bivalves (skeletal allochem)

-shelled invertebrates in which the shell consists of two symmetrical valves -ie. clams, mussles, oysters -most bivalve shells are thin and smooth with a laminated (regular, thin parallel lines) internal structure -oyster shells are thick, with a foliated (wavy or deformed) internal structure -envolved in paleozoic -common constituents of mesozoic rocks

Brachiopods (skeletal allochem)

-similar to bivalves (shelled organism with 2 valves) -each valve displays bilateral symmetry -some also have spines ("s" in image) which look like rings or discs in cross section -punctate (depression/holes/punctures and tubes/canals within shell) and foliated internal structure; orientated perpindicular to the shell surface -common in Paleozoic rocks -Very few survived the Permian extinction event

Gastropods (skeletal allochem)

-snails, secret spiral shells -in cross section, the spiral contains chambers stacked on one another in a conical shape or laterally adjacent to one another similar to a bunch of grapes -generally laminated internal structure similar to bivalves -common constituents of mesozoic rocks

How much of the earths crust is composed of carbonate rocks?

10%

Spar2

=Spar can be calcite or aragonite in origin (although aragonite usually reverts to calcite over time). -Spar is carbonate cement and is found surrounding grains or skeletal fragments in carbonate rocks and is coarser than micrite (> 4 micrometers in diameter). -It can usually be seen with a hand lens or even with the naked eye in hand samples. Spar consists of clear or translucent to slightly cloudy interlocking crystals of calcite, which take various shapes and forms when viewed in thin section. In general, spar forms in two fashions: 1) precipitation out from water as simple, pore-filling cement, or 2) recrystallization of micrite or other carbonate grains susceptible to alteration under the right chemical conditions. -Some carbonate rocks may be completely recrystallized and consist entirely of spar.

Bafflestones

Bafflestones are made of organisms that impede or "baffle" water flow, such as branching corals, platy algae, finger stromatoporoids, or sponges

Bindstones

Bindstones are made of organisms that encrust and "bind", such as stromatolites and some stromatoporoids and corals

What minerals are carbonate mainly composed of?

Calcite Aragonite Dolomite

How do carbonate rocks form?

Calcite, aragonite and/or dolomite (main carbonate rock forming materials) will percipitate out of solution. However many carbonate rock components are formed biochemically. Organisms such as coral, clams, shrimp and starfish extract dissolved ions such as calcium, magnesium, and bicarbonate from water to make shells or skeletons. Upon the death of the organism, these skeletal components are incorporated into the sediment, which is eventually cemented to together to form carbonate rock.

Carbonate rock classification

Carbonate rocks are classified based on the types of allochems present, their relative amounts, and whether micrite and/or spar is present. There are two main classification schemes in use.

How can carbonate rocks form?

Chemically or biochemically

What do the fossils within the rocks tell us?

Earths origin, evolution and paleontology. They also have economic importance

Dunham's Classification Scheme for Carbonate Rocks

Embry and Klovan's modified version of Dunham's classification scheme is slightly more complex, but effectively categorizes almost all carbonate rocks. It considers grain packing (or texture), relative abundance of grains, and nature of grain deposition (transported versus bound in situ). This scheme works more like a flow chart, following four steps. First, the texture of the rock is defined as clastic or crystalline. Second, one must determine whether the components were transported or originally bound during deposition. Third, for rocks that contain transported clasts (often disarticulated allochems), one must determine the amount of mud and size and amount of allochems (no matter what those allochems may be). The final step is to determine whether the rock is micrite or matrix-supported versus grain-supported.

framestone

Framestones are composed of organisms that build rigid, solid structures, such as reef- building corals and stromatoporoids that are usually massive and bulbous

Well known carbonate production site

Great Barrier Reef - Australia

Conditions were carbonate production is highest

Hot, humid, tropical to subtropical settings within 20-30 degrees of equator. However, there are also significant areas of cold water carbonate production in earth's oceans

Uses of carbonate rocks

Important aquifers and hosts for ore deposits Produce cement and building materials Agriculture - neutralize soil acidity Regulating Earth's climate (deposition of limestone indirectly results in the removal of CO2 from atmosphere

What are the two main rock types?

Limestones -mainly biochemical in origin -composed predominately of calcite and/or aragonite Dolostones -composed predominately of dolomite -diagenetically altered post burial through interation with fluids, increased heat, increased preassure

Dolomitic Limestone/Calcareous Dolostones

Mix of limestone and dolostone depends on relative amount of calcite/aragonite and dolomite

ooids (non skeletal)

Ooids are spherical and < 2 mm in diameter (equivalent to sand) and consist of some sort of nucleus (usually a shell, skeletal fragment or grain) surrounded by concentric layers of calcite and/or micrite. Rock composed almost entirely of ooids is known as oolite. Modern ooids form in shallow marine conditions, usually in less than 5 m water depth on shoals or bars.

pisoids (non skeletal)

Pisoids are similar to ooids in that they contain a nucleus surrounded by concentric layers of calcite/micrite; however, they are bigger than ooids - > 2 mm in diameter. Rock composed almost entirely of pisoids is known as pisolite. Pisoids can form in either marine or non-marine conditions. In the marine realm, their origin is similar to that of ooids, while in non-marine settings they are found in cave pools and streams, and in calcareous soils or calcretes.

Brachiopod Floatstone

Step 1 - Does this rock exhibit a clastic or crystalline texture? The dark material is micrite, and all the light-coloured objects are allochems, so this specimen is clastic. Step 2 - Are the components in situ? Do they exhibit original depositional binding? The components are scattered, so they are not in situ. Step 3 - Is this rock mud/matrix-supported or grain-supported? Most of the allochems do not appear to touch one another; they are mainly surrounded by or floating in the matrix, so it is matrix-supported.. Step 4 - What is the average size of the allochems, and how many allochems are there, relatively? There are more than 10% grains, and of those grains, more than 10% of them are greater than 2 mm (along their long axis). This results in the classification of this rock as a floatstone. To complete the name, add the dominant allochem type as a prefix. The lens and crescent-shaped allochems are most common. They are either bivalves or brachiopods. Note that the shell that the white arrow is pointing to is not quite symmetrical. Also note that the large cresent-shaped shell appears to have a punctate internal structure. These are brachiopods. So the name of this rock would be: Brachiopod Floatstone.

Coral Bafflestone

Step 1 - Does this rock exhibit a clastic or crystalline texture? The dark material is once again micrite, and all the brown objects are corallites (you can just make out the radial symmetry in some of them). So, this rock is clastic. Step 2 - Are the components in situ? Do they exhibit original depositional binding? All of the corallites are parallel to each other - some are obviously attached or cemented together. And, they appear to still be in an upright position. So, they do exhibit original binding. This is a boundstone! Considering that the corallites are vertically oriented and that there is micrite between them, this is likely a bafflestone. You can imagine that water currents would be able to flow around and through the corallites, they would slow or baffle the current, and micrite would be deposited in between them (in framestone, water currents are not be able to flow through the more massive and solid structure - any micrite present would settle down into the structure from the top). Considering all this, the rock would be named a coral bafflestone (or colonial rugose coral bafflestone).

oolitic grainstone

Step 1 - Does this rock exhibit a clastic or crystalline texture? The rock appears to consist of grains. Taking a closer look, in thin section, the grains are well rounded, small (0.5-1 mm in diameter) and have a nucleus surrounded by concentric rings of opaque, micritic material. These are ooids! So, this rock has a clastic texture. Step 2 - Are the components in situ? Do they exhibit original depositional binding? No - from what we know about ooids, they are reworked by waves to form shoals and bars. Step 3 - Is this rock mud or matrix-supported or grain-supported? In the hand specimen, the allochems appear to touch one another; in thin section, there is less than 0.1 mm of space in between the grains. All that separates them is a very thin rind of a clear, crystalline material - spar! This rock is grain-supported. Also, there is no (or very, very little) matrix or micrite surrounding the grains. Step 4 - What is the average size of the allochems, and how many allochems are there, relatively? By volume, the rock is predominantly ooids, which are < 2 mm in diameter. So this rock is not a rudstone, it's a grainstone - an oolitic grainstone

Carbonate Rock General Features

Tend to dissolve easy often porous & permeable 80% of all hydrocarbon reservoirs found within carbonate units

Carbonate Rock Example (Texture)

The carbonate rock pictured above consists of a mixture of skeletal allochems (red objects) and micrite (tan-coloured material). Spar is also likely present, however as with most carbonate rocks, a thin section and microscope is required to actually see it.

stromatoporoids

They are quite similar to corals and thus are believed to bridge the evolutionary gap between sponges and corals. These organisms secreted a calcareous skeleton that exhibits a vessicular structure in which the vessicles or "cells" are aligned in layers around a central axial canal. Each vessicle is usually <1 mm in diameter. There are two varieties of stromatoporoid that are most common in the rock record. The first group includes tabular, encrusting, bulbous, or massive hemispherical heads (red arrows) that exhibit a layered texture. The second common type is cylindrical or branching varieties that look similar to modern sponges (green arrows). Most common is Amphipora

Common types of skeletal grains

bivalves gastropods brachiopods crinoids bryozoans corals stromatopoids some may be completely composed of skeletons of organisms that have experience very little transport

Extrabasinal clasts (or lithoclasts)

differ in composition and overall texture, like clasts in orthoconglomerates, and are rare in carbonate sedimentary environments.

boundstones

e components were bound to one another during deposition are known as boundstones, in which the fossils are usually in situ and articulated (unbroken)

Non-skeletal grains

formed chemically or mechanically and include clasts such as: coated grains peloids grain aggregates intraclasts

three types of non coated grains

peloids, aggregates, intraclasts